Apr 11th

Night Engine Failure: #1 Rule

By Dave Schultz
Featuring Bob Martens

MAINTAIN AIRCRAFT CONTROL; AVOID STALLING

Pilots are not killed when they fly the airplane to the ground under control.

Pilots are killed when they stall an airplane into the ground

Bob Martens:

"You need to have a plan. You need to think about what you're going to do ahead of time so that it doesn't create so much panic that you're unable to safely fly the airplane.

You absolutely have to be sure that you don't stall the airplane. I've been to many aircraft accident scenes, I've evaluated hundreds and hundreds of accidents and pilots are not killed when they fly their airplane to the ground under control. They are killed when they stall an airplane into the ground. So maintaining airspeed safely above stall speed right on down to the ground is so very, very important."

http://www.pilotworkshop.com/tips/pilot_emergency_training.htm


Mar 19th

Virga: Clouds To Avoid?

By Dave Schultz
Featuring Scott Dennstaedt

Virga
is a common weather condition that can be hazardous to pilots. Do you know what Virga is and when it should be avoided?

Scott:

"Most pilots have been taught to stay away from virga. However, not all virga is dangerous.

Virga is produced when snow or rain is falling from the base of the cloud, but evaporates in dry air before reaching the surface. The key here is the dry air below the clouds.

Evaporation is a cooling process. As the rain or snow evaporates, it cools the air, and the air becomes denser than the surrounding air. The heavier air tends to accelerate toward the earth producing a downdraft. Why is this a hazard? A large enough downdraft could cause the airplane to sink.

Virga looks a lot like a rain shaft that isn't reaching the surface or can look a lot like the extension of the cloud base itself with a tattered or shredded appearance as shown in this picture. It will often have silk-like filaments that can have a wavy texture, often falling from very high-base clouds. In most cases you can see through the virga.

When should you avoid virga?

If the temperatures aloft are at or below freezing, virga can contain supercooled liquid water, and flying through it is an icing hazard.

If there are thunderstorms in the immediate area or virga appears to be falling from towering cumulus, virga might be a sign that a downdraft or microburst is active in that region.

It is best to avoid all virga and rain shafts in regions of convective activity or virga that is solid enough that you can't see light filtering through."


See the article, pictures, and comments at:  http://www.pilotworkshop.com/tips/aviation_weather_clouds.htm

Jan 26th

Mandatory Alert Service Bulletin: Checking Oil Pump Attachment Bolts 912 and 914 Series

By Dave Schultz

Rotax has released a Mandatory Alert Service Bulletin which covers checking of the oil pump attachment bolts on certain Rotax 912 and 914 series aircraft engines. This ASB affects only a limited number of engines and is serial number specific. Engines affected were produced after August, 2011.

To check whether your engine or crankshaft is affected by this bulletin, see section 1 of the bulletin for a list of engine serial numbers affected.

Serial numbers for Certified and Non-Certified engines are listed in separate bulletins. Be sure to check the corresponding bulletin for your engine type. Serial numbers for Certified engines are listed in Alert Service Bulletin ASB-912-060/914-043. Serial numbers for Non-Certified engines are listed in Alert Service Bulletin ASB-912-060UL/914-043UL. The "UL" designates Non-Certified engines. Certified engines are identifiable by a RED colored serial number tag (located on the ignition housing). Non-Certified engines have a BLACK serial number tag.

Engines found to be within the affected serial number ranges as listed in the ASB, must be checked before further flight is permitted, but at the latest before August 1st 2012.

On affected engines, an initial inspection is required to determine if your oil pump is leaking. If no leaks are found, the oil pump attachment screws need to be check tightened to correct torque value of 90 inlb. If NO LEAKS have been found, and bolts have been check torqued, NO FURTHER action is required.

If OIL LEAKS ARE FOUND, the oil pump must be removed and o-rings replaced with new. A valve train inspection also has to be performed to rule out any potential damage that may have occured due to the loose oil pump bolts causing air ingestion into the oil system. Once the oil pump has been replaced and the valve train inspection completed, the engine must have it's lubrication system purged.

To better assist Owners and Operators in determining if their engines are affected by this Critical to Safety ASB, and if so what steps need to be followed to take corrective action, Rotax-Owner has released a FREE video covering the specific details of the ASB itself. This FREE Video will help Owners and Operators better understand the best way to review the ASB and take any required corrective action.

http://www.rotax-owner.com/index.php?option=com_content&view=article&id=307

Jan 18th

Has your Mechanic just cost you $10K and the Sale of your Aircraft?

By Dave Schultz

Has your Mechanic just cost you $10K and the Sale of your Aircraft?

Written by  Rotax Owner

Over the last several years I have seen many logbook entries from mechanics, some good, some bad and some just downright ugly. In the last several weeks I have been involved with a buyer looking for a used Flight Design CT ($70K - $90K). This has given me a unique opportunity to really look at logbook entries and documentation (or the lack of it) and see just how that might affect the ultimate selling price of the aircraft itself. Surprisingly, many poor entries have also come from A&P’s and not only RLSM-A’s from the logbook entries I have seen. These poor logbook entries and lack of documentation will cost the owner dearly when it comes time to sell. From what I have seen lately, it’s not hard to lose $5K-$10K in value due to lack of documentation. These are legal records and need to be treated as such. This is one of the only legal ways you can show either someone did something to your plane or did not. As important, log books showing compliance to not only the aircraft manufactures Service Bulletins for the airframe but also for its Rotax engine greatly increases the Aircrafts total value!

 One of the first tasks I perform when doing a pre-buy inspection on behalf of a customer is to check the aircrafts Rotax Engine against all published factory Service Bulletins by using the Document Retrieval Service provided on this web site by www.Rotax-Owner.com under the information button on the main page(click here http://www.rotax-owner.com/information/service-bulletins ). This is a FREE Service and worth its weight in gold when cross checking SB compliance of any Rotax engine by serial number. I then cross reference this list to those shown as complied with in the aircraft log books. No records mean no compliance which means extra cost for the buyer if he still wants the plane or a lower selling price for the seller or more often than not no sale at all!

I also use the video section of the Rotax-Owner site (click here http://www.rotax-owner.com/all-videos ) to show both buyer and seller exactly what’s involved in complying with certain SB’s and other tasks I deem required to not only check the condition of the engine(see related videos following this article below) but to also bring the engine up to a serviceable standard. The better the aircraft is maintained and the better the record keeping to show it, the easier it sells and the higher the price it gets! When I was on the Fire Department as a Captain & Medic and doing reports it was essential that everything done be included in that report. I have been to court many times over the years and if it wasn’t in writing it wasn’t done and there is little you can do to save yourself. Cry all you want that it was done, but the jury and judge don’t care. I’ve seen three to four people lose plane sales in the last several weeks due strictly to poor logbook keeping andbad documentation even though the aircraft themselves didn’t look that bad. In the end their aircraft values fell because of it. Paper work documenting the work done is as important as the work itself. How do you know a service bulletin was done, a compression test or a simple carb balance was done? How does the next mechanic know what the other did or didn’t do? How do you know the mechanic found anything wrong or gave additional attention to anything or fixed a problem? If he didn’t log it you may still be flying and it still may be broken and you don’t know it because he didn’t follow the inspection sheets or enter it in the logbook. Not only parts in good condition like hoses etc. may be entered as acceptable but also every deficiency should be entered.

My Mantra;
There is something wrong with every single plane brought in for a 100 hour or the Annual Condition Inspection and it is up to the mechanic to find it.

Show me a logbook entry from a mechanic that says he didn’t find anything and I’ll show you a poor inspection and a very poor logbook entry. I just heard from one A&P and he said he doesn’t log compression test results unless they are under 70 psi residual pressure. WOW! Where is the log that shows any decline or trend when it totally fails the compression test next time? How do you go back and ask him what the numbers were last year. How does he defend a problem that arose in court? You are supposed to use the aircraft Mfg’s and Rotax’s check list. That’s why they went to the trouble to make one up and it is supposed to be part of the legal documentation of that inspection. If you don’t have one for your plane then use the FAA sample or make one up yourself and have the mechanic follow it. You should demand that these check list be followed and signed for your own protection and your pocketbook. You should then keep them with your logbook entries in a safe place and not in your plane. It is your only recourse in case you need legal help because the mechanic did something wrong or didn’t do something he was supposed to do. It will be your legal help with the court system, the FAA and the Insurance Company. When it comes time to sell would you want to buy something that had such poor records thatyou can’t tell what was really done or not done or do you want the plane that has had a serial record of each inspection, oil change, plug change and SB, ext….

 

You may be getting what you pay for with some mechanics, so if the price is too good to be true maybe you should walk away or at the least ask a lot more question or for references. Like any profession there are good mechanics and bad. Some of the good mechanics have gone through Rotax school and some have gone through the RLSM school. Each one of my clients from day one gets his logbook documented in detail, an original aircraft Mfg’s and a Rotax inspection sheet signed, a separate discrepancy list and all given to the owner/pilot, hole punched for a 3 ring binder. I make notes on the inspection sheets and sign each entry so myself and the owner know I have done the work and I didn’t forget something. If a 100 hour or Annual Condition inspection was done in 4-6 hours you better look for another mechanic. It can’t be done. Those who have hung around while I work know it takes days to complete a proper inspection and the more things you find or the owner has you do the more time you need to add to that. I would say a mechanic that knows his way around a specific aircraft and the Rotax engine and doesn’t have but a couple of minor things to fix may take 2 days for an easy one and maybe more if more problems exist. You are paying good money for your inspection you should get it the way you want it and it should be done.

 


You should demand that the aircraft Mfg and Rotax inspection check list be followed and signed. The logbook needs to have a lot more than “I found this aircraft to be in a Safe Condition”. Protect yourself and have your mechanic perform to the level of competency you require and deserve.

 


Here are a couple of examples of what I see on a too regular basis:
This is an entry in the logbook for an Annual Condition inspection minus the A&P’s signature;

 

1

 

Here is the Annual Condition inspection for a Rotax engine minus the A&P’s signature:

 

2

 


Some short logbook entries might be barley legal, but they aren’t doing you any good and it’s just lazy not to fill out a proper logbook entry. Paperwork usually takes me 2-3 hours per plane. Just as important have them make entries legible if hand written so anyone can read them. If they can’t, printing them on a computer with a sticky label works wonders.

 


Here are a couple of examples (and only examples) that are better and your own A&P or RLSM-A may word it differently, many mechanics will list each item on its own separate line, that’s great and makes it easier to follow through, either way this will give you an idea of what a better logbook entry may look like. You need to list all discrepancies and items of importance or any continual ongoing SB’s. By the way the Light Sport Repairman is supposed to sign his title RLSM-A and not any other way for airplanes.


 

12-12-2011 740.2 hrs. TTSN Maintenance performed on N???? Engine #??????? Aircraft serial # ??????

In accordance with the High Flyer 12 and Rotax maintenance manuals this aircraft had its required Rotax 5 year rubber replacement program, 100 hr. and Annual Condition inspection performed. The engine was removed and re-installed. The engine mounting bolts were torqued to 200 in/lbs as per the High Flyer maint manual. The top right engine mount bolt was bent and it was replaced. Both carb sockets and carb diaphragms replaced. All coolant, fuel and oil hoses were replaced inside the engine compartment and behind the instrument panel. Fire sleeve was placed on all oil and fuel hoses and Oetiker and Band-It band clamps used. The coolant was replaced with Prestone 50/50. An oil purge procedure was performed as per the Rotax maint. manual. Start up oil pressure was 75 psi that settled at 55 psi after the engine operating temp was reached. The carb air intake 3” CEET tubing replaced. The 1 ¾” CEET cabin heat hose on top of the muffler was replaced. Carb throttle and choke Bowden cables were safety wired. The 16 rubber engine isolators were replaced and the bolts torqued to 200 in/lbs per the High Flyer maint manual. Carbs mechanically and pneumatically synced. The magnetic oil plug was checked, it was clean and safety wired. The gearbox friction torque is 424 in/lbs. The plugs were re-gapped at .023 for cold weather and thermal paste applied. Engine run and idle set at 1750 +/- rpm. Both wheels were removed and inspected and both wheel bearings were greased. The front steering pulls right. Lengthened the right steering rod end to push the front wheel slightly left. The ELT test was performed and the batteries are due March 2017. The right center and outer flap bearings were loose. Re-glued with Loctite 480 as per the High Flyer maint. manual. The left lower and the right lower engine ring mount bolts were loose. re-torqued to 29.5 ft/lbs as per the Rotax Heavy maint manual. Compression test results #1 87/86 , #2 87/86 , #3 87/86 , #4 87/86. Gascolator was clean and fuel flow within High Flyer maint. manual specs. Throttle lever friction was too loose. Tightened the friction on the throttle lever to keep it from creeping forward. All engine operating parameters were normal on start up on this aircraft and it was checked for leaks and fluid levels. No abnormalities noted. I certify that this aircraft has been inspected in accordance with the scope and detail of the High Flyer and Rotax maint. manuals and was found to be in a condition for safe operation. This aircraft’s next inspection is due at 840 hours TTSN or by Dec. 31, 2012.

________________________________________________
John Doe RLSM-A LSA Cert. XXXXX issued 5-28-08

----------------------------------------------------------------------------------------------------------------------


Here is a second sample;

10-19-2011 193.4 hrs. TTSN Maintenance performed on N???? Engine serial #??????? Aircraft serial #???????

In accordance with the High Flyer and Rotax maintenance manuals this aircraft was inspected for its 200 hr. and Annual Condition inspection. Gascolator cleaned and fuel flow test conducted / passed. Both carbs removed and inspected per the Rotax maint. manual. Lubed all bell cranks and bearings. ELT test performed and batteries expire March 2016. All hoses in engine compartment are in good condition. The K&N air filter was removed, cleaned and re-oiled. Rotax gearbox friction torque is 428 in/lbs. Carbs pneumatically synced. Engine run and idle set at 1750 +/- rpm. Compression test done for differential: #1- 87/86, #2- 87/86, #3- 87/86, #4- 87/86 psi. New NGK DCPR8E spark plugs were installed, gapped at .025 and heat conducting paste applied. The 4 Rotax engine ring mount bolts were slightly loose. Re-torqued the engine ring mount bolts to 29.5 ft/lbs as per the Rotax Heavy maint. manual. The oil was not due to be changed, but the magnetic plug was inspected and it was clean and safety wired. The muffler joints have a lot of exhaust blow by. Adjusted the muffler to the right 1” to better help align the muffler sockets and lubed with copper anti seize. The underfin rear light was not working and a broken wire was found. Re-soldered the wire and remounted the underfin. The light is now functional. The old factory coolant was drained from the engine and coolant reservoir and Prestone 50-50 was installed. All SB’s are current. I certify that this aircraft has been inspected in accordance with the scope and detail of the High Flyer and Rotax maint. manuals and was found to be in a condition for safe operation. This aircraft’s next inspection is due at 293 hours TTSN or by Oct. 31, 2012.

__________________________________________________
John Doe RLSM-A LSA Cert. # XXXXXXX issued 5-28-08

----------------------------------------------------------------------------------------------


Which planes would be more comfortable with, one with the first two log entries or one with the last twoincluding all respective airframe and Rotax checklists in hand? These were only examples and your mechanics wording may be very different, either way there’s no substitute for accurate detaileddocumentation!

I hope this personal reflection on “buyer beware” shows how accurate logbook entries can affect youwhether you’re buying or selling an aircraft .

I hope this article will prove useful to all my flying friends out there!



Full article at:  http://www.rotax-owner.com/rotax-blog/item/18-has-your-mechanic-just-cost-you-$10k-and-the-sale-of-your-aircraft?&utm_source=Has+your+Mechanics+2012-01-17&utm_medium=email&utm_campaign=Has+your+Mechanic+2012-01-17
Jan 5th

Go Around Procedure

By Dave Schultz
Last week, Bob Martens explained the importance of practicing go-arounds on a regular basis.  This week, he provides a simple procedure for performing safe go-arounds.

"Remember, doing a go around is a positive maneuver, not a negative one!"


Mark:

"Is there a standard go around procedure that works in every aircraft?"

Bob:

"Absolutely. As we stated previously, the go around is not an inherently difficult procedure. Pilots should always refer to the Pilot’s Operating Handbook for specific details, but power, pitch, and configuration are the big three. In that order!

Smoothly advancing the power to full is the first step. Jamming it forward may produce a very uncomfortable sound and very negative results.

Establishing a positive pitch attitude will provide separation from the ground, but over rotating at low airspeed could produce a stall, and under rotating could create collision issues. We’ll elaborate further about problems on the go around in just a moment.

Clearing the runway to avoid whatever was there is a good idea - choosing the appropriate side to keep the conflicting object in sight as necessary.

Radio calls are the least important item on the go around not the most important. There is no rush to get the call in. Aircraft control is paramount!

Obviously, every pilot should master the procedures called for in their airplane, but power, pitch and configuration works in all situations."

Mark:

"You referred to problem areas on go arounds, Bob. What are the common mistakes?"

Bob:

"Well Mark, we’ve already made reference to several, but the biggest problem is waiting too late. Be proactive. Good judgment calls for us to recognize when we are falling behind and take positive action. Remember, doing a go around is a positive maneuver, not a negative one!

Many pilots are reluctant to pitch the aircraft to a positive climb attitude. Remember, we really want to put some separation between us and the ground. Fly the airplane safely away from the ground as airspeed permits."

Full article at:  http://www.pilotworkshop.com/tips/pilot_safety_go-around.htm

Jan 2nd

Panel Labeling

By Dave Schultz
The FAA requires that everything in the cockpit be labeled as to it's function. Dick Koehler shows how he uses a standard label maker to satisfy this requirement.

http://www.eaavideo.org/video.aspx?v=1316990171001

Another great video brought to you by the EAA!
Dec 29th

Practice Go-Arounds!

By Dave Schultz

Practice Go-Arounds!

Featuring Bob Martens

Mark: "We’re going to discuss the topic of go arounds. And this is a topic so basic, so fundamental. Why should we focus additional attention on the subject of go arounds?"

Bob: "Mark, I’ve always been a big advocate of the go around. I refer to it the most under utilized maneuver in aviation! Think about it. When was the last time you did an intentional go around without being required to? I’ll bet it’s been a while!

Now, think about how many of our awful landings might have been avoided had we exercised the good judgment to do a go around.

When I queried the NTSB data base to check out go-around accidents, there were over 1300 go-around accidents in the data base! That’s a lot of accidents. Clearly we have some work to do in this area."

Mark: "Why do we have so many go-around accidents, Bob?"

Bob: "While the go around is certainly not an inherently difficult maneuver, the fact that it is most often accomplished in close proximity to the ground cuts into our margin of error. Add to that the fact that the pilot is probably experiencing at least some degree of stress associated with the reason for the go around, and we start to understand the problem.

Now, factor in that the pilot has probably not done this maneuver in months, and we are now looking at a very serious problem. How can you expect to be good a something that you don’t practice regularly? Simply stated, you can’t!

The challenge of go arounds is that they must be performed instinctively, without hesitation, with precision. Far too many pilots are just not up to that challenge!"

Mark: "Bob, why is it that pilots fail to integrate go arounds into their training regimen?"

Bob: "Well Mark, first, and foremost, not enough pilots have a training regimen. I challenge all pilots to look into their log books and validate just how little time we spend on training. We all need to get back to basics, working hard on take offs and landings, heading to the practice area for stalls, steep turns and slow flight drills, and practicing emergency procedures. Integrated into this training must be go-around practice.

Any time we find ourselves out of sync with our airplane, go around and catch up! Far too often we find ourselves frantically chasing our airplane, hoping to catch up and make all the corrections before the airplane lands. That’s a dumb way to fly. Flying is like playing chess. We should be always looking several moves ahead, not playing from behind.

The go around is our tool to do just that. Far too many pilots perceive the go around as a negative procedure after a mistake. That is wrong! The go around demonstrates excellent judgment and has no down side! By practicing it and integrating it into our flying, we will be real good at go arounds and not hesitate to perform one at any time."

Full article at:  http://www.pilotworkshop.com/tips/aviation_safety_go-around.htm

Dec 25th

AIRCRAFT HARDWARE: What You Need To Know

By Dave Schultz

AIRCRAFT HARDWARE
What You Need To Know

By Ron Alexander

The quality of our workmanship in building an airplane is very important. We all take the needed time and spend the necessary money to ensure we have a high quality airplane. We want it to not only look attractive, but also to be safe. But what about the materials that hold the airplane together the aircraft hardware? Do we try to cut expenses by using questionable bolts or used nuts? Is it really necessary to spend money on high quality aircraft hardware? Absolutely! The hardware used to assemble your airplane should be nothing but the best. Why take the time to build a perfect wing only to attach it to the fuselage with used hardware. It makes no sense. To quote the Airframe and Powerplant Mechanics General Handbook . . . "The importance of aircraft hardware is often overlooked because of its small size; however, the safe and efficient operation of any aircraft is greatly dependent upon the correct selection and use of aircraft hardware." Very well stated. The same book also provides us with a very good definition of aircraft hardware. "Aircraft hardware is the term used to describe the various types of fasteners and miscellaneous small items used in the manufacture and repair of aircraft."

The subject of aircraft hardware can certainly be confusing. Thousands upon thousands of small items are used on a typical airplane. What does the custom aircraft builder really need to know about hardware? Where do you find the information? What reference is really the end authority on proper installation? What do all of those AN numbers mean and do I have to know them? What types of hardware should I really learn more about in order to build my own airplane?

These questions will be answered in this series of articles on aircraft hardware. I hope to eliminate some confusion over what type of hardware to use and how to properly install it. To begin our discussion, it is absolutely imperative that you use nothing but aircraft grade hardware. Commercial grade hardware found in hardware or automotive stores is legal to use on an experimental airplane but should not be considered for even a moment. Why? Let's look at bolts as an example. Common steel bolts purchased from a hardware store are made of low carbon steel that has a low tensile strength usually in the neighborhood of 50,000 to 60,000 psi. They also bend easily and have little corrosion protection. In contrast, aircraft bolts are made from corrosion resistant steel and are heat treated to a strength in excess of 125,000 psi. The same comparison applies to most hardware items. So, use only aircraft quality hardware on your airplane. Save the other hardware for your tractor.

If aircraft hardware is special, then there must be a standard against which it should be measured and manufactured. That standard was actually developed prior to World War 11, but became more definitive during that war. Each branch of the military originally had its own standard for hardware. As time went on these standards were consolidated and thus the term AN which means Air Force-Navy (some prefer the older term Army-Navy). Later the standards were termed MS which means Military Standard and NAS which means National Aerospace Standards. Thus, the common terms AN, MS and NAS. Together they present a universally accepted method of identification and standards for aircraft hardware. All fasteners are identified with a specification number and a series of letters and dashes identifying their size, type of material, etc. This system presents a relatively simple method of identifying and cataloging the thousands and thousands of pieces of hardware. Several pieces of hardware will have both an AN number and an MS number that are used interchangeably to identify the exact same piece. A cross reference exists that compares these two numbers. So in the end, you are able to read your plans or assembly manual and identify, by number and letter, each piece of hardware on your airplane. You can then obtain that piece and properly install it in the right place. Imagine trying to do that without a system of numbers. The specifications for each piece of hardware also define the strength, tolerance, dimensions, and finish that is applied. If you would like further information on this numbering system, you can contact the National Standards Association in Washington, DC.

Out of all the thousands of hardware pieces manufactured, which ones are important to the custom aircraft builder? The following types and categories of hardware will be discussed:

  • Bolts
  • Nuts
  • Washers
  • Screws
  • Cotter pins and safety wire
  • Rivets
  • Turnlock fasteners
  • Miscellaneous items such as 0-rings, crush washers, etc.
  • Control cable hardware
  • Fluid lines and fittings
  • Electrical wiring and connectors

Where do you find information concerning aircraft hardware? Your aircraft plans or assembly manual should provide you with a general overview of hardware used on your project. Use the hardware the aircraft designer or kit manufacturer recommends. Do not substitute with your own ideas. This can be dangerous. The manufacturer has tested the design and its safety is dependent upon the proper pieces of hardware. FAA Advisory Circular 43-13-IA is an excellent reference source. The Airframe Mechanics General Handbook also has a very good section on the selection and use of hardware. These two books are considered the primary authority on the proper use of hardware. In addition, I would recommend two other small reference books: the Standard Aircraft Handbook and the Aviation Mechanic Handbook. Both of these provide a good reference source. The Aircraft Spruce & Specialty catalog also contains good reference material on hardware. If you have any doubts about the quality of the aircraft hardware you are purchasing, request a copy of the manufacturer's specifications. These specifications along with a specific manufacturer's lot number should be available.

BOLTS

Bolts are used in aircraft construction in areas where high strength is needed. Where this strength is not necessary screws are substituted. Aircraft quality bolts are made from alloy steel, stainless or corrosion resistant steel, aluminum alloys and titanium. Within our industry the first two are the most common. Aircraft bolts will always have a marking on their head. If you see no markings at all on the head of a bolt, do not use it. It is probably a commercial grade bolt. The markings on bolts vary according to the manufacturer. You should see an "X" or an asterisk along with a name, etc. If you purchase a corrosion resistant (stainless steel) bolt, the head of that bolt should have one raised dash. An aluminum bolt will have two raised dashes on its head. Aluminum bolts have limited use. They should not be used in tension applications or where they will be continuously removed for maintenance or inspection. A chart of typical bolt heads is presented in Figure 1. NAS bolts have a higher tensile strength (usually about 160,000 psi) and can be identified by a cupped out head. Close tolerance bolts are machined more accurately than general purpose bolts and they are used in applications requiring a very tight fit. Close tolerance bolts can be either AN or NAS and typically have a head marking consisting of a raised or recessed triangle.

The standard bolts used in aircraft construction are AN3 through AN20. Each bolt typically has a hexagon shaped head and a shank that fits into the hole. The shank is threaded on the end and the unthreaded portion of the bolt is termed the grip. The diameter of a bolt is the width of the grip. The shank of a bolt will be either drilled to accept a cotter pin or undrilled. Another option is to purchase a bolt that has the head drilled for the purpose of accepting safety wire. Clevis bolts are manufactured with a slotted head and are used for control cable applications. The size, material, etc. of a bolt is identified by an AN number. A breakdown of a typical bolt AN number follows:

AN4-8A

  • AN means the bolt is manufactured according to Air Force-Navy specs.
  • 4 identifies the diameter of the bolt shank in 1/16" increments
  • 8 identifies the length of the shank in 1/8" increments
  • A means the shank of the bolt is undrilled (no letter here means a drilled shank)

So, this particular bolt is a 1/4 inch diameter AN bolt that is 1/2 inch long measured from just under the head to the tip of the shank. The bolt also has an undrilled shank which means it cannot accept a cotter pin. Also, bolt length may vary by +1/32" to -1/64". If the letter "C" follows the AN designation (ANC) that identifies a stainless steel bolt. The letter "H" after AN (ANH) identifies a drilled head bolt.

FIGURE 2: AN Aircraft Bolt Dimensions

In constructing you airplane, you will not encounter many bolts larger than an AN8 (1/2 inch diameter). To add a bit more confusion, if the dash number defining the length of the bolt has two digits, the first digit is the length in whole inches and the second number the length in additional 1/8" increments. In other words, an AN514 bolt would be I- 1/2 inches long.

Now that you are totally confused let me recommend a hand tool to simplify bolt selection and sizing. An AN bolt gauge is available that will assist you in identifying a bolt (click on the above link to Figure 2).

If you need to determine the proper size of a bolt, the length must be sufficient to ensure no more than one thread will be inside the bolt hole. This is the grip length of the bolt and it is measured from the underneath portion of the head to the beginning of the threads (see Figure 3 below). The grip length should be equal to the material thickness that is being held by the bolt or slightly longer. A washer may be used if the bolt is slightly longer. A piece of welding rod or safety wire can be used to measure the length of the hole. In his book titled Sportplane Construction Techniques, Tony Bingelis shows a simple tool that can be made for this purpose.

It is important that you do not "over tighten" or "under tighten" a bolt or the nut attached to a bolt. Under torque or under tightening results in excessive wear of the hardware as well as the parts being held. Over tightening may cause too much stress on the bolt or nut. The best way to avoid this is to use a torque wrench. AC43-13 presents a table of torque values for nuts and bolts. It shows fine thread and coarse thread series with a minimum and maximum torque limit in inch pounds. I recommend using a torque wrench whenever possible, at least until you get an idea as to the amount of force required. Of course, critical installations should definitely be torqued to proper values. A torque wrench is not that expensive and will be a worthwhile investment for a custom builder.

Basics of Bolt Installation

Certain accepted practices prevail concerning the installation of hardware. A few of these regarding bolt installation follow:

  1. In determining proper bolt length - no more than one thread should be hidden inside the bolt hole.
  2. Whenever possible, bolts should be installed pointing aft and to the center of an airplane.
  3. Use a torque wrench whenever possible and determine torque values based on the size of bolt.
  4. Be sure bolt and nut threads are clean and dry.
  5. Use smooth, even pulls when tightening.
  6. Tighten the nut first - whenever possible.
  7. A typical installation includes a bolt, one washer and a nut.
  8. If the bolt is too long, a maximum of three washers may be used.
  9. If more than three threads are protruding from the nut, the bolt may be too long and could be bottoming out on the shank.
  10. Use undrilled bolts with fiber lock nuts. If you use a drilled bolt and fiber nut combination, be sure no burrs exist on the drilled hole that will cut the fiber.
  11. If the bolt does not fit snugly consider the use of a close tolerance bolt.
  12. Don't make a practice of cutting off a bolt that is too long to fit a hole. That can often weaken the bolt and allow corrosion in the area that is cut.

AIRCRAFT NUTS

Aircraft nuts usually have no identification on them but they are made from the same material as bolts. Due to the vibration of aircraft, nuts must have some form of a locking device to keep them in place. The most common ways of locking are cotter pins used in castle nuts, fiber inserts, lockwashers, and safety wire. The aircraft nuts you will most likely encounter are castle nuts, self-locking nuts, and plain nuts. Wing nuts and anchor nuts are also used.

Castle Nuts

AN310 and AN320 castle nuts are the most commonly used (see Figure 4). Castle nuts are fabricated from steel and are cadmium plated. Corrosion resistant castle nuts are also manufactured (AN310C and AC320C - remember, when you encounter a "C" it will designate stainless). Castle nuts are used with drilled shank bolts, clevis bolts and eye bolts. The slots in the nut accommodate a cotter pin for safetying purposes. The thinner AN320 castellated shear nut has half the tensile strength of the AN310 and is used with clevis bolts which are subject to shear stress only. The dash number following the AN310 or AN320 indicates the size bolt that the nut fits. In other words, an AN310-4 would fit a 1/4 inch bolt.


Self-Locking Nuts

Self-locking nuts, as the name implies, do not need a locking device. The most common method of locking is derived from a fiber insert. This insert has a smaller diameter than the nut itself so that when a bolt enters the nut it taps into the fiber insert producing a locking action. This fiber insert is temperature limited to 250-deg. F. The designation of these nuts is AN365 and AN364. This brings us to an example of a cross-reference MS number. An AN365 is also termed MS20365 with the AN364 being MS20364. Both of these nuts are available in stainless. The AN364 is a shear nut not to be used in tension.

An all metal locking nut is used forward of the firewall and in other high temperature areas. In place of a fiber insert, the threads of a metal locking nut narrow slightly at one end to provide more friction. An AN363 is an example of this type of nut. It is capable of withstanding temperatures to 550-deg. F.

The dash number following self-locking nut defines the thread size. Self-locking nuts are very popular and easy to use. They should be used on undrilled bolts. They may be used on drilled bolts if you check the hole for burrs that would damage the fiber. One disadvantage, self-locking nuts should not be used on a bolt that is connecting a moving part. Am example might be a clevis bolt used in a control cable application.

Plain Aircraft Nuts

Plain nuts require a locking device such as a check nut or lockwasher. They are not widely used in most aircraft. AN315 is the designation used for a plain hex nut. These nuts are also manufactured with a right hand thread and a left hand thread. The check nut used to hold a plain nut in place is an AN316. If a lockwasher is used a plain washer must be under the lockwasher to prevent damage to the surface.

Other Aircraft Nuts

There are a number of other aircraft nuts available. Wing nuts (AN350) are commonly used on battery connections or hose clamps where proper tightness can be obtained by hand. Anchor nuts are widely used in areas where it is difficult to access a nut. Tinnerman nuts, instrument mounting nuts, pal nuts, cap nuts, etc. are all examples of other types that are used.

Basics of Aircraft Nut Installation

  1. When using a castle nut, the cotter pin hole may not line up with the slots on the nut. The Mechanics General Handbook states "except in cases of highly stressed engine parts, the nut may be over tightened to permit lining up the next slot with the cotter pin hole." Common sense should prevail. Do not over tighten to an extreme, instead, remove the nut and use a different washer and then try to line the holes again.
  2. A fiber nut may be reused if you are unable to tighten by hand.
  3. At least one thread should be projecting past the fiber on a fiber nut installation.
  4. No self-locking nuts on moving part installations.
  5. Do not use AN364 or AN365 fiber nuts in areas of high temperature - above 250' F.
  6. Shear nuts are to be used only in shear loads (not tension).
  7. Plain nuts require a locking device such as a lockwasher or a check nut.
  8. When using a lockwasher, place a plain washer between the surface of the airplane part and the lockwasher.
  9. Shear nuts and standard nuts have different torque values.
  10. Use wing nuts only where hand tightness is adequate.

WASHERS

Finally, a hardware item that is simple. You are likely to encounter only a couple of different types of washers AN960 and AN970. The main purposes of a washer in aircraft installation are to provide a shim when needed, act as a smooth load bearing surface, and to adjust the position of castle nuts in relation to the drilled hole in a bolt. Also, remember that plain washers are used under a lockwasher to prevent damage to a surface.

AN960 washers are the most common. They are manufactured in a regular thickness and a thinner thickness (one half the thickness of regular). The dash number following the AN960 indicates the size bolt for which they are used. The system is different from others we have encountered. As an example, an AN960-616 is used with a 3/8" bolt. Yet another numbering system. If you see "L" after the dash number, that means it is a thin or "light" washer. An AN960C would be - yes, a stainless washer. I can tell you are getting more familiar with the system so I will throw another wrench into the equation - an AN970 washer has a totally different dash number system. I am not even going to tell you what it is. I will tell you that an AN970 is a larger area flat washer used mainly for wood applications. The wider surface area protects the wood.

There are other types of washers. I mentioned lockwashers that are made several different ways. They are often split ring, they are sometimes internal tooth and even external tooth (see Figure 5). You will also find nylon washers and finishing washers that usually have a countersunk head. So, as you can see, washers are not quite as confusing as other hardware even though we can make ft difficult if we wish.

COTTER PINS AND SAFETY WIRE

The cotter pins mostly used on custom aircraft are AN380 and AN381. Cadmium plated cotter pins are AN380 and stainless are AN381. Cotter pins are used for safetying bolts, screws, nuts and other pins. You will normally use them with castle nuts. The MS number you may see is MS24665. The dash numbers indicate diameter and length of the pin. As an example, AN380-2-2 would be a cadmium plated pin 1/16" in diameter and 1/2" long. All supply companies will have charts showing the various sizes versus the reference number.

Safety wire is also widely used. The most used sizes in diameter are .020, .032 and .041 or small variations thereof. The material is usually stainless steel or brass. The easiest method of installation is acquired by using safety wire pliers (see Figure 6). The pliers are used to twist the wire. The wire is installed so that if the nut or bolt begins to loosen it will increase the tension on the wire. Be sure you do not overtwist the wire - doing so will weaken the safety wire. Leave about 36 twists and then cut off the excess wire and bend its end so you do not snag it with your hand at a later time.


I want to emphasize the major point of this article. USE ONLY AIRCRAFT QUALITY HARDWARE.

Do not assume the engineer role by using hardware types or sizes that are contrary to your plans or assembly manual. In future articles I will discuss the other hardware items including control cable installation, screws, rivets, turnlock fasteners, etc.

Full article and diagrams at: 
http://exp-aircraft.com/library/alexande/hardware.html

About the Author, Ron Alexander

This article was written by Ron Alexander of Alexander SportAir Workshops.

Ron has been flying since the age of 16; he flew for the Air Force for five years (including one year in Vietnam) and started flying for Delta Airlines in 1969, where he now pilots the Boeing 767. He currently owns a J-3 Cub, C-3B Stearman, and a Beech 18. Ron started restoring antique airplanes in the early 1970's and could not find parts so he founded the Alexander Aeroplane Company which he operated for 17 years. He sold the company to Aircraft Spruce and Specialty in 1995 so that he could focus his efforts on providing education within the sport aviation industry.

Ron is currently president of Alexander SportAir Workshops, a series of "hands-on" workshops on building airplanes is presented throughout the country for education. For a schedule of locations and dates of upcoming workshops and information (prices, curriculum, etc.), call 800-967-5746 or visit their web site at www.sportair.com

This article was first published in EAA's Sport Aviation magazine.

Dec 17th

Evaluating a competent mechanic, and how do I recognize whether or not if I already have one?

By Dave Schultz

Written by  Rotax Owner

This can be a dynamic topic, but there are certainly some markers to look for in finding yourself a good mechanic that you can really trust to keep you in the air, safe and happy. You probably already have a mechanic, but the important thing is in recognizing if he has more than just the basic skills, but that certain something that gives you the confidence to trust life and limb to him. Let’s examine what the traits are that define “a good mechanic” and steps you can take to find one.


Let’s talk about looking for a good mechanic first. As in any profession, you’ll find varied degrees of competency. Just as in choosing a surgeon, you’ll want to avoid marginal competency and shoot for the elite, or as close to it as possible. Here are a few questions in the determination if whether a prospective mechanic is right for you. 

(In the interest of simplification and unencumbered continuity of thought, we will use the pronoun “he” as being asexual.)


  1. Does he come recommended by other aircraft owners?
  2. Do you hear from others that he does a satisfactory job?
  3. Does he have experience in your type aircraft and is he qualified to work on your Rotax engine with the proper iRMT ratings?
  4. Do you hear the prospects name brought up favorably in conversations?
  5. When you talk to the prospect, is he friendly, helpful and patient before the subject of fees is discussed?
  6. Ask the prospect if he has the service bulletins (SB’s) and all the manuals for your engine and fuselage on site?
  7. Is your prospect familiar with the tips, tricks and technical procedures for your Rotax Engine as shown on the Rotax Owner Videos.
  8. How many aircraft like yours has he worked on or inspected?
  9. Does he keep you abreast of issues he found and answer your questions knowledgably?
  10. What’s his philosophy regarding regular and preventive maintenance?
  11. Is he a self absorbed mechanic, or open-minded to your ideas, suggestions, concerns and will he research problems including Rotax Owner videos and forum?
  12. Does he use an inspection check list, discrepancy list and do accurate, detailed logbook label entries? (Possibly ask to see a couple of his labels and check lists)
  13. Does he document well? It’s for your benefit as well as his legal protection.
  14. Does he give you copies of the maintenance check list, or other documents for your personal file? This should be an absolute in case you need it for the FAA, insurance and the re-sale of your plane. You’re paying for the work, get it the way you want it not him.
  15. Does he seem to have the proper tools and education for your particular plane?
  16. Last, but not least and this item is not a real marker of the mechanic’s professionalism, but should be kept in the back of your mind. What is the charge? If the price sounds too good to be true then there may be a reason for it and you might get exactly what you paid for. Caveat emptor. Now I know this is not necessarily always true that’s why this is last consideration while looking for a mechanic that you have compatibility with and do the job that you expect and deserve.
  17. Ask the prospect if he has access to the Service Bulletins
 Your life might be in the hands of the mechanic. Strive for one who displays all or most of the attributes shown above.

  The mechanic’s motto should be: If there is a problem with your aircraft, major or minor, I’m going to find it. Your safety is priority one. 
Due to a plane’s wear and tear, loosening of attachment items or just sitting for extended periods things change and it’s your mechanics job to find these. He needs to be a skilled hunter of problems and an organized repairman for these items.

  You’re probably already use or have used, a mechanic. Use these questions, and your own, to determine if he is right for you. If there are some areas about which you wish your mechanic would do better then sit down with him and explain your issues and concerns. You’re the boss. The right mechanic needs to live up to your expectations.

Life is full of choices. We chose doctors, lawyers expecting them to be honest; to work in our best interests; to be receptive to our needs. You fully expect understanding and consideration of your input. Chose your mechanic in the same way.

Full article at:  http://www.rotax-owner.com/rotax-blog/item/5-evaluating-a-competent-mechanic

Dec 8th

The Anatomy of a Carb Sync

By Dave Schultz
Written by  Rotax Owner :

The carburetor sync on a 2 stroke or 4 stroke ROTAX Engine is one of the most important functions to keep up with for the health of your engine.

Let’s take a look at performing a carb sync on a 912 series engine. The carb sync is nothing to be afraid of and with a few times at bat, performing this function will become fairly easy. First, why is it so important? The carb sync should be done anytime the carbs or throttle cables are removed or adjusted and at the 100 hour or Annual Condition Inspections. The reason for this is cables stretch, cable hysteresis (cable stickiness), pulley system wear, cables slip and because parts wear and end up with more tolerances. The carbs are almost always out of sync at each 100 hours or the Annual. If you did a carb sync back at the last inspection then they may not be out of sync much, but they will in most cases be out at least a bit. The sync instrument should also be used to set the idle sync if you change idle settings. Let’s start off with thinking of the engine as two engines, a left side and a right side. Two carbs controlling different sides of the engine. You don’t want one side trying to operate at 5000 rpm while the other side is trying to operate at 5100 rpm. These opposing rpms will cause excessive stress and wear on your engine over time and possible damage. You say there is a balance tube in between to help balance them out. The operative word in that sentence is “help”. The balance tube can correct and help with small differences between the two carbs, but it is not a cure all and it is there to help make the system run a little smoother than if there was no connection or correlation between the two carbs...

 

 

So which sync instrument to use? Well that is up to you, but here are a few considerations. You might use an electronic sync instrument like a CarbMate, Syncromate or a set of gauges. Here are a few pros and cons of each sync instrument. The electronic instrument may have the capability to split hairs and give you a very fine adjustment, but they are harder to interpret as far as knowing which carb you want to adjust to achieve a specific goal to bring the two carb vacuums together. It takes more time and going back and forth to get this accuracy. You also need a power supply like your battery to attach electrical leads to operate the instrument. There is nothing wrong with this, it’s just different. The standard type dial gauges (liquid filled are better for dampening with needle valves in line to assist for dampening needle pulsation) allow the user to see immediately which carb he needs to adjust and how much he may need to make this adjustment. This writers’ one thought here is; does the accuracy of an electronic device to split hairs that fine over a gauge really make a difference and can the carbs and engine really tell the difference? If you pay attention to detail and use good gauges you can be very accurate. The drawback to standard gauges is they may not be as accurate as the electronic tools are. Picking one of these sync instruments is strictly up to the end user and their personal preference, both systems are acceptable.

Let’s move on to the actual anatomy of the sync and what to look for. I would like this discussion to be on the use of the gauges because it will offer some visual numbers to work with and helps in the understanding of this article. First the engine should be up to operating temperature. Safety first so put in place wheel chocks, hearing protection, eye protection and a person at the controls for safety. Now you need to separate both carbs. You can use hose pinch pliers to clamp off the rubber hose used to connect the balance tube between the intake manifolds or just remove one side rubber hose off the air intake and plug your gauge into the rubber hose end and the other over the metal nipple it was attached to. Later model engines have two small screws, one on top of each air intake manifold you can attach your sync instruments into also, but you still need to address isolating the carbs by either clamping off or plugging the cross over tube we discussed earlier. This writer prefers to slide the cross over tube rubber hose back off one intake manifold since it makes sure the carbs are fully isolated while preventing any hose pinching damage from using pliers to squeeze the rubber hose instead. This is only what I prefer, it’s up to you to choose your method.
 

 

There are two syncs to perform, the mechanical sync and the pneumatic sync. The mechanical sync is really well explained in the Rotax Owners video (http://www.rotax-owner.com/information-reg/elearning-videos-reg/43-exp-si-912-018) and I recommend anyone wanting to perform this task to watch this e-learning video! As well the procedure is also described (although not in quite the same detail) in the Rotax Line Maintenance manual, either way with proper knowledge it’s quick and easy to perform. So now you’re all set in your safety gear so have your safety cockpit operator start the engine. (Don’t forget to advise them that if they see you spin more than three times in the prop to turn the engine off!) 

 

Now we have the engine running and we take a look at our gauge set. If the needles are pulsating then close the needle valves slightly until they stop and become smooth. Set the RPM to slightly more than idle (off-idle as Rotax calls it). Idle and low RPM is the most critical RPM for smoothness as the power pulses are very pronounced and the gearbox will be working hard as it must settle this argument between the piston power pulses and the huge inertia of the prop. At RPMs over 3000 the engine becomes smoother and the shaking is less pronounced. Let’s mention here that to change the RPMs you adjust the Bowden cable screw either in or out which will add or subtract some rpm. You use the carb idle adjustment stop screw to affect the engine idle only. You do sometimes need to adjust the Bowden cable length to get the idle screw to have enough affect, but we can cross that bridge later.
 

 

Okay back to our running engine. Have your cockpit operator advance the throttle up to at least 2000 RPM and check to assure your still in sync, if so continue to advance the throttle all the way up to at least 3500 RPM minimum to assure your high speed sync remains matched. Assuming that’s still working continue to even higher RPM’s just to make sure the carbs remain balanced to the higher power settings respecting the fact you need to assure you are out of the prop blast and the aircraft remains secure. If at the higher RPM’s you don’t remain balanced one of two things might be happening. Because an engine well synced at 2000 RPM should hold that sync all the way to full throttle, if it doesn’t you either have binding in the cables or there is something hanging up in your throttle system not allowing the throttle arms on the carbs to move uniformly with one another. If so; check and correct. The second and much more remote possibility is you have a cylinder that is falling off line due to a hanging up valve or other issue. This is very unlikely on a Rotax but I mention it because even though it rarely happens it might save someone from scratching their heads after verifying the throttle actuation of the cables and throttle levers is all working properly yet an out of sync condition remains. So, backing up to the first off idle sync check at 2000 RPM, let’s say you look at the gauges and see that the left side is at 5” of vacuum (more fuel) and the right side is at 6” of vacuum (less fuel). (Vacuum is expressed in inches of water “H2O or inches of mercury “Hg) The higher the vacuum in our case (6”), the harder the carb is trying to draw in air and fuel, leaner , less fuel. The lower the vacuum (5”) the more fuel it is receiving (richer). Keep this in your head about vacuum, the higher number is less fuel (leaner)and the lower the vacuum number, more fuel (richer). Now let’s go to the left side and loosen the Bowden adjustment nuts and screw it back out toward the cable and shorten the cable which pulls the throttle arm and reduces the rpm and fuel flow. Adjust it back until its 5” moves to 6” like the 6” on the right side. Now they should both be equal at 6” of vacuum at 2000RPM allowing you to proceed to the higher RPM checks. If you went to adjust this left side and the adjustment was already way back and you didn’t have enough adjustment there to pull it back any farther then you have two choices. Go to the other side and adjust that Bowden cable adjuster forward to lengthen it and lower the vacuum towards the left side. The other thing you may need to do is shut down the engine, screw the Bowden cable adjustment in towards the half way position and then loosen the cable at the throttle arm screw and shorten it by 1/16” to give you more room to adjust the Bowden cable adjuster farther back on that left side. Sometimes because of how these are setup you may need to adjust one side back a tad and adjust the other side forwards a tad to make them equal and not run out of adjustment on either side.

 

Now pull the throttle back to idle and see where it is. If you have a 912ULS a good idle is around 1750-1850 rpm to stay above the low RPM vibration and hammering the higher compression of this engine has(it doesn’t like really low idle settings so they should be avoided). Now if your idle is too high after you pulled the throttle back then look at the gauge and see which gauge has the lower vacuum number. Remember the lower the number the more fuel it is receiving. Let’s say the idle rpm is 1900 rpm and you want 1800 rpm. The right carb gauge is at 12” and the left carb is at 11”. The carb on the left side is getting more fuel and the rpm is too high. So that is the carb we want to reduce the rpm on and raise the vacuum to get to 12” like the right side. So you back out the idle stop screw and the 11” of vacuum raises to 12” of vacuum like the right side. If that made your idle rpm 1800 and you are happy then you’re done. If your idle rpms were still too high then back the idle stop screws out on both sides a little more until the idle rpm is where you want it and the vacuum on both sides is equal. Always double check your work. Run the engine back up to 3500+ rpm and see if the needles are still equal and if not then you may have hysteresis, a broken strand or some other factor causing unequal cable movement that needs attention(or as discussed earlier, that lazy cylinder, another topic for another time). Then back to idle to check that vacuum setting and the idle rpm. If you idle for a long time making an adjustment then run the engine up for a few seconds now and then to help keep it cleared out and from loading up at those low rpms. If your idle rpm was too low (1600 rpm) then screw the idle stop screw in more on the carb with the higher vacuum 12” down to 11” until the vacuum number lowers to match the other side of 11”and the idle comes up where you want it.
 

 

After you have doubled checked your work then shut down the engine and make sure all the jam nuts to the Bowden cable adjuster are snug. Remove the gauge set and connect the carb balance tube setup. Even after a sync the engine may be slightly rougher with the carbs balance tube separated, but should be a little smoother when it is reconnected.

Two last parting comments. The throttle control system in your cockpit at idle should have an idle stop on it and when you pull it back to its stop at idle then the idle stop screw on the carb should just make contact at the same time. If you do not have a throttle stop for idle in the cockpit then you will most likely bend the idle stop levers on the carbs due to the leverage advantage you gain from the cockpit throttle control. This over powering of the idle stops on the carbs will result in the idle ending up too low. This continuous bending towards lower idle could also lead to a much bigger chance of stalling your engine from low rpm in flight and it won’t be when you want it to quit. Pay attention to how your aircraft design addresses this issue and adjust accordingly!
 

 

Second; You should check the balance of the carbs at both high rpm and at idle. I have seen some back off the idle stop screw until it no longer functions and that means the carbs can only be synced at the higher rpms and not at idle. That means the engine is operating at idle at opposing rpms. If you thought it was important to sync your carbs at the higher rpms to keep them from opposing each other, reduce vibration and from hammering the engine why on earth would anyone not sync them at idle? This is a poor practice to get into. You spend a lot of time idling. Remember what our Dad’s told us; “If it’s worth doing, it’s worth doing right”.
 

 

I know this was a long article, but I thought it may be worth covering for some Rotax owners. If you fell asleep half way through, print it out and take it to the airfield.
 

 

FLY SAFE AND FAR AND ABOVE ALL, HAVE FUN LIVING YOUR DREAM OF FLIGHT!

Find the full article at:  http://www.rotax-owner.com/rotax-blog/item/16-the-anatomy-of-a-carb-sync