May 23rd

Airspeed Calibration - Acceptable method

By Abid Farooqui
Although there are various acceptable methods for airspeed calibration chart development like boom with low flying aircraft, chase plane etc., now-a-days GPS methods are becoming extremely popular. I have been involved in certifying some airplanes in recent years and that of course entails developing and executing a full flight test program. 
After some initial flights to test for rigging, engine function and reliability, one of the very first test flights is done for airspeed calibration because almost all the rest of the performance testing depends on getting to know your airspeed .. more specifically your calibrated airspeed (CAS) which can vary from your indicated airspeed (IAS). This variation is due to instrument error as well as static port position error. Any time our static port opening senses static pressure from wind blowing past it at a "different speed than aircraft true airspeed" it sees a different pressure and all instruments relying on static port produce unreliable results. These include primarily airspeed indicators, altimeters, and vertical speed indicator. One can see why airspeed calibration to get within a reasonable range is so important for the rest of the performance testing.

ASTM standard require that calibration show that throughout the range the error is no greater than 5 knots or 5%, whichever is greater. So how does one check this. Its actually quite easy technically with todays GPS technology.

FAA has an Advisory Circular (AC 23-8C) for testing means for Part 23 certified aircraft. This AC should be consulted among some other well written articles and books on flight testing. This AC can be downloaded from:
http://www.faa.gov/documentLibrary/media/Advisory_Circular/AC%2023-8C.pdf

One of the methods described in this AC for airspeed calibration is the 3 track GPS method as recommended to FAA by National Test Pilot School (NTPS). This is described in Appendix 9, sub-section 3.

The method requires 3 ground tracks at the same airspeed and altitude. They can be almost any ground track. It is however advised that they be between 60 to 120 degrees off from each other, example,  40, 160, 280.

So for instance, you want to calibrate your airspeed. You put your trusty old handheld GPS or any GPS on your trike. Make sure it shows ground track heading. Make sure it shows ground speed in the same units as your airspeed indicator (knots, MPH, etc.) and to get enough data points you want may want to select 7 to 10 airspeeds. I for example selected, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90 knots for CHEVAL 12 wing, I would select something different for say CHEVAL 14 wing which is expected to be slower.

You make yourself a data card which looks something like this for each data point (indicated airspeed) you want or you may even want to fill in the indicated airspeed (data point) in the air to what you can hold as long as its a bit different than your other data points. Your track can be dynamically selected as well as long as track 1, 2 and 3 for a single data point are flown at the same indicated airspeed and similar altitude. For next airspeed they don't even have to be exactly the same tracks. This makes aviating really easy and calculations longer but it can give us better accuracy.

ASI-CAS-Data-Card.JPG

Note that this data point is for one speed of 45 knots indicated (or as seen on my air speed indicator). Pressure altitude is gotten by setting the Kollsman window to 29.92 inches of Mercury, ground trach heading from GPS is recorded and outside air temperature (OAT) is recorded. You can use a cheap temp sensor from Walgreens as long as it reads the temp right.

It is completely unimportant what GPS ground tracks you do. Being further apart reduces chances of error so just do 3 approximately 90 degree turns and let things stabilize for 10 seconds at the desired airspeed and altitude and record gps ground track, ground speed, pressure altitude, OAT. Turn and do it again at the same airspeed and same altitude, turn again and do it for the third track. If the altitude remains within 50 feet, you will be ok. However if the airspeed varies even a couple of miles, you will get a big error. That is why early morning or late evening when thermal activity is low and at higher altitude like 3000+, you will get a good data point.

Now simply repeat this at 50, 55, 60 and so on airspeed data points also. You will notice that OAT does not change much if you stay at the same altitude or within 300 - 500 feet. So usually no need to change that once you get it.

Now you need to get what is referred to as True Airspeed (TAS) from this raw data and then adjust that true airspeed to standard sea level conditions to get your Calibrated Airspeed (CAS). 

How do you get TAS from this raw data?
Well fortunately, there is something called Microsoft Excel Worksheets where we can plug in formulas etc. This 3 track in any direction gps method was first described by Doug Gray (Australia) but really is a special case of the 3 track method used and described by NACA in the 1920's. It was adopted by National Test Pilot School in Mojave, Ca where they developed some complex Excel worksheets because they are dealing with aircraft where Equivalent Airspeed (EAS) and other things have to be taken into account. Since most trikes are not cruising at above 100 knots compressibility errors etc., can be ignored and I simplified the worksheet so we can just plug our numbers in and get Calibrated airspeeds out as seen below from one of my initial test runs. ( 1 knot = 1.15 mph = 1.852 km/h)

TAS-CAS.JPG




One can then also do some more handy work in Excel and get it to draw a calibration chart with a calibration equation, like an example shown below for an airplane I worked on and this calibration chart can be put into a pilot operating handbook for use by pilots.

Calibration-Chart-AS.JPG

 
I will try and upload the simplified excel sheet so people can do this gps test in good calm conditions and take 5 to 10 data points and plug the results in to see how close their airspeed indicators are reading to reality. Errors here may also suggest  errors in altimeter reading, and also in VSI reading which may mean that takeoff distance to clear 50 foot obstacles may be off as well.

ASTM standard for trikes does not require manufacturer to give airspeeds in calibrated, but instead only in indicated airspeeds which makes sense because that is what the pilot sees but when doing testing calibrated and adjusted to sea level speeds are used for standard performance metrics to be gathered correctly. Many of our trikes have open static ports at the back and depending on the design, they may be off or not. 

Anyway, if anyone wants to do some fun gps flying and collect some data at a few speeds and wants to plug it in, feel free to contact me at abid@silverlightaviation.com to see where your airspeeds may fall.

May 18th

FAA selects Sport Aviation Center - Paul Hamilton to train their new safety inspector to fly trikes.

By Paul Hamilton

FAA Light Sport Branch in Oklahoma City who manages Sport/Private Pilot Weight-Shift Control implementation has selected Sport Aviation Center  - Paul Hamilton to train their new safety inspector to fly trikes.

Paul Hamilton comments on his WSC trike flight school:

“We have two full time private pilot trike CFI’s, we specialize in full time trike training 24/7/365, we wrote the FAA WSC Flying Handbook and we developed the only comprehensive trike flight/ground  training system for FAA WSC pilot certification. We have great weather for flying 300 out of 360 days per year and fly modern state of the art equipment”.

Sport Aviation Center now trains in the top of the line Evolution Revo which has the easiest to handle with a reliable 912S 100 HP Rotax engine for maximum power and reliability.

May 18th

The story about FAA Light Sport Branch AFS 610

By Paul Hamilton

I have been working with the AFS Light Sport Branch for over 10 years now from the beginning to current. Do I like government regulation? NO. Do I agree with all the rules? NO. Do I wish we could have less government control for aviation? YES. Do I wish we could have less government control for all aspects of the government? YES (But look at the people of the US, they are voting for bigger government - WTX).

 

I have learned to deal with this because IT IS WHAT IT IS. I decided about 15 years ago to quite my high paying career as a professional engineer to pursue what I loved, flying trikes. I have done what ever I needed to do to pursue this. WHAT EVER IT TAKES.

 

Never imagined I would be an FAA DPE. This was farthest from my mind but……

 

If I were running things from the top level things would be allot different.

 

 

OK back to the topic. The Light Sport Aviation Branch manages and provides oversight of the sport pilot examiner and the light sport aircraft repairman-training programs. The branch also provides subject matter experts for FAA and the aviation industry concerning the sport pilot/light sport aircraft safety initiatives.

They perform

Acceptance of Light Sport Aircraft Repairman Training Providers

National Examiner Board

Oversight of Designated Pilot Examiners (Sport Pilot)

Designated Pilot Examiner Initial Training Seminar

Designated Pilot Examiner Recurrent Training Seminar

 

 

 

It must be understood that this AFS 610 branch are a group of LSA enthusiasts. Yes there have been some people in AFS 610 that were not helpful to us but generally these are good people,. They are just like any other profession (engineers, bankers, scientists, police, fast food server, cashier, construction worker, etc…), they do what they are told by their bosses/upper management. These AFS 610 FAA inspectors are the same. They enact policy passed down by their superiors. As I tell everyone, if you want to change things for the better, you must go to the top. The policy makers who created Sport pilot/LSA AFS 800 in Washington DC. If you try and blame the low level 610 branch for your problems, you are shooting at the wrong target, barking up the wrong tree. This is a waste of time and a detriment to the industry overall. Thanks for Part 103

 

I have had my disagreements with policy, procedures, and especially with many of the current SP/LSA laws, but IT IS WHAT IT IS and just like I do as an engineer on a project, I do WHAT EVER IT TAKES TO DO THE JOB/COMPLETE THE MISSION. Do I always like this? NO

 

Right NOW I know AFS 610 is transitioning management and I think there will be a number of improvements coming such as my three favorites.

Commercial WSC trike license.

Sport Pilot CFI time can count towards Private pilot.

Easier LODAs for training in E-LSA

Any other suggestions that we should put in the pipeline?

May 18th

Tips and tricks of setting up a wing

By Rizwan Bukhari

Today as I attempted on setting up my new wing, I found it very challenging to secure the last 4 or 5 battons with the cord (bungee). Is there a tip to make it easier. I thought of disconnecting the strut where it attaches the cross bar so the wing has a bit more play but I was not sure if that would be a good idea. Do you have any tips.

My Manta wing just like the Northwing I use to have does NOT have a bungee to secure the battons but it is a little cord or rope. Bungee would have made it easier.

Regards,

Rizzy

 

May 9th

Apollo Delta Jet II (SilverLight Aviation version)

By Abid Farooqui
As some of you may know, SilverLight Aviation is bringing a US version Delta Jet II to market. There has been many hours of deliberate scripted test flying going on at Zephyrhills between Apollo AG-1 gyroplane test program that recently finished and Delta Jet II 912S trike whose test flights continue.

AG-1 can reach and hold 106 knots at 5500 RPM (Rotax 914 UL). Climbs at 1350 FPM one up and 900 FPM at gross weight (515 pounds of payload) in standard conditions. Its smooth and can cruise at 87 to 90 knots comfortably and slow down below 30 and do what most gyros can do. The control forces are small.

Delta Jet II recorded consistent 1450 FPM climb rate one up in standard conditions with Cheval 12 wing. The wing has been getting its icing and changes. It started out not being able to go any faster than 75 mph. After certain changes and tweaking, I am able to get it to cruise via electric trim at 90 MPH hands off with 2-up at 5000 RPM with Rotax 912ULS. There are still some small changes and tweaks to come. I like good tracking and smooth handling so one of the changes was addition of small winglets that kept its light center handling and a linear increase in roll resistance for steeper banks. A slight unloading to start the roll gives a nice carving through the sky (J maneuver).

I installed a static port on one side on the composite body after flying with a bunch of yarn stuck to the body to get a more accurate indicated airspeed and more accurate climb rate and altimeter reading.

Today I was able to fly it in gust factor of 15 mph (indicated airspeed was jumping up and down by 15 mph 6 to 8 times a minute) and got to see its etiquitte in frontal conditions. I think those can be improved a little. But then again, you take the AG-1 gyroplane in that and you wonder where it all went away to? I had not much issue (besides saying, its gusty darnit) landing the trike either but a new pilot would have gotten spooked. That's where I think a gyroplane has an edge over trikes when the pilot experience level is lower and they want to fly in gusty conditions etc.

Look for this beast getting its S-LSA in coming weeks.
May 5th

How do you short pack a wing?

By Rizwan Bukhari
Hi everyone,

I bought a new wing and my 19 meter strut wing has to go. I wanted to know how do you short pack a wing.

Has anyone short packed a 19 meter wing, how long of a crate do you need for that. The wing crate I have is about 18 feet by 1 foot by 1 foot. Would that be a big enough crate for a 19 meter wing? If you have pictures that show how to short pack the wing, I would really appreciate that.

Regards,

Rizzy
Apr 27th

P&M Aviation LTD - 2014 Spring Newsletter

By Tony Castillo
P&M Aviation LTD
2014 Spring Newsletter
(.pdf format)

http://www.pmaviationusa.com/Newsletters/Spring%20Newsletter%202014%20LR.pdf

 
Apr 25th

About the Weight-Shift Control Aircraft Flying Handbook. Who, what when and where.

By Paul Hamilton

Since there have been allot of questions about the FAA WSC Flying Handbook expressed through the years, I thought I would share with you the development of the book.

How The Book Got Started

With the new weight-shift control (WSC) category, the FAA had to write a book to set standards used to train pilots and provide information for the FAA Knowledge exam. Safety Research Corporation of America (SRCA) was contracted to write it. Typically SRCA hires different industry experts in the appropriate field or subject to write different chapters. And typically, SRCA obtains the pictures and copyrights for a project.

A trike pilot was contracted by SRCA to write for the project but not much was produced. The project got behind schedule and SRCA was running out of time fast to complete the project on time. I got a call from SRCA asking if I could help with the project in 2007. I agreed to help and I took on one chapter and banged it out it out with pictures and provided copyrights to the pictures, because I was the photographer. They were amazed.

We did another chapter and they were again very happy with the results. After I proved that I could accomplish the task, they asked and I agreed to do the complete book, beginning to end with text, photos, diagrams and drawings. It took about a year to complete.

The Process

The process was that I would write a chapter and send it out to a handful of industry experts and SRCA. SRCA would comment on the content and send it on to the FAA for their comments. For each page I submitted to SRCA and the FAA, I would receive back, on average, 2 pages of questions and comments. Half of the comments were useless and questions ridicules. But, the other half were very useful and a big help overall.

I’m an engineer and entertainer…Not a graphic artist. So, one of my greatest joys on this project was submitting a rough engineering diagram and getting it back the next morning in beautiful artwork. It was incredible. The SRCA artist was amazing.

As far as the Acknowledgments in the book, yes, the FAA was allowed to only acknowledge image contributors. But, I listed both image contributors (of which there were not many) and the industry experts who reviewed and contributed to the content. I have since revised this list of contributors in the print and downloadable eBook editions I publish to:

Paul Hamilton of Adventure Productions

AirBorne Australia

Matt Liknaitzky of MGL Avionics

Jon P. Thornburgh

Abid Farooqui of SilverLight Aviation

Gerry Charlebois of Birds in Paradise

Wills Wing, Inc.

Larry Mednick of Evolution Trikes

I will explain the development process of each chapter in upcoming posts. Each chapter had unique challenges, beginning with the history section of Chapter 1, which the FAA slashed from 12 pages to its current 6 pages.