Speed range in Strut wings vs Cable braced wing

Published by: Rizwan Bukhari on 21st Oct 2017 | View all blogs by Rizwan Bukhari

 

Hi all,

 

Most strut wing manufacturers always highlight the wide speed range in their wing advertising.

 

I am trying to figure out that what makes a Strut wing have a wide speed range. Would a strut wings offer a wider speed range than a similar sized and shaped cable braced wing?

 

And if that is the case then what makes a Strut wing have the wider speed range.

 

Any help in understanding this concept would be greatly appreciated.

 

Regards,

 

Rizzy

Comments

23 Comments

  • Paul Hamilton
    by Paul Hamilton 1 month ago
    Strutted wings have less drag. Simple.
  • Bill Chance
    by Bill Chance 1 month ago
    Struts have less drag over wires is certainly true but aren't you a Aeros dealer? This is a question for your wing manufacturer Aeros as they are one of the few wing builders that still build both topless and king post designs. I would say beside the reduced drag it would also be improved design.
  • Larry  Mednick
    by Larry Mednick 1 month ago
    Other countries tend to use small cars with small trailers. Here in the US. we easily pull enclosed trailers with our trucks and transport the trikes with the wings on. For those that want to put a Wing into the bag for transport the cable braced Wing is easier to bag. Yet it is impossible to fold. The approach for transport by itself favors each type based on how you will transport.

    We also tend to keep our trikes hangared and leave the Wing on. In that case the aerodynamics favor the superior aerodynamic strut braced design.
  • Abid Farooqui
    by Abid Farooqui 1 month ago
    Riz:
    I question iif a quarter inch thick cable in good tension has more drag than a strut of airfoil shape with a frontal width of 1 inch. If a spherical cable was 1 inch and airfoil shaped strut's frontal area was also 1 inch then yes for sure the strut would have a much lower Cd and drag but the round cable is only at most 0.25 inches in diameter .

    But its completely different when the cable is not in good tension and can vibrate due to wind blowing by it. That is the case on all the cables on top on a cable braced wing. There is a lot more drag due to cables that are not taut and there are 6 to 8 of them on cable braced wings. That is why a strut braced wing with nothing on top is a much cleaner design. Also, the drag being on top actually is less efficient than drag being lower where the thrust line is.

    However, if your carriage is draggier than you can't just look at the wing. You have to look at the whole system. Some of the efficiency of the strut braced wing is cancelled by it being a bit heavier than cable braced wing. Say cable braced wing is 100 pounds and strut braced wing is 112 pounds. That is extra 12 pounds of lift that needs to be created to maintain level flight.

    Hope that helps.
  • Abid Farooqui
    by Abid Farooqui 1 month ago
    I would also suggest that strutted wings are not just about less drag r better speed range. They are also about being able to fit in most T-hanger across the US. Some king post wings are tricky to get in hangers and some really can't.
  • Bill Chance
    by Bill Chance 1 month ago
    Riz, sometime back Abid posted a link to an old video that proved there is a big difference between the drag of a small cable and a larger airfoil shape. Back when planes still had 2 wings and you can see them on newer/older biplanes today that they ditched wires for metal strips for wing bracing.

    Here is my real world experiment. I fly an open carriage Maverick with a slow single surface wing that has round struts and down tubes. I installed strut and downtube covers with an airfoil shape. I flew it on a calm morning without the covers. Wrote speed and RPMs numbers. Landed and installed the covers and went back up. Didn't pick up but maybe 1-2mph in speed on the GPS but the biggest eye opener was that hands off trim speed engine RPM reduced by over 400 RPMs. A really big deal when flying with a weasly, measly, 5 gallon tank.
  • Andy Hughes
    by Andy Hughes 1 month ago
    Paul it is not that simple. Compare the size of a soft ball and a hard ball which flies fastest through the air?
  • Andy Hughes
    by Andy Hughes 1 month ago
    https://en.wikipedia.org/wiki/Bracing_(aeronautics)
  • Lindsay Mannix
    by Lindsay Mannix 1 month ago
    Drag increases to the square of the increase in speed ...
    A faster wing will benefit from drag reduction more than a slower wing but less drag is less drag on both.
    cables are easy to inspect but struts have huge hangar advantages
    The real questions are.
    Why do we want to go fast?
    And why do we want to go slow ?
    Sports car in the sky?
    Or off road motorcycle?
    When/If the fan stops ....I know what I prefer
  • Larry  Mednick
    by Larry Mednick 1 month ago
    From a design stand point, it is much harder to get a strut braced Wing to handle as good as a cable braced Wing. It can be done. But take Airborne’s new wings which are available in both cable and strut braced. The struts have better performance and the cables have better handling. That is of course with all things being equal.
  • Lindsay Mannix
    by Lindsay Mannix 1 month ago
    Yes Larry ,
    I wonder if being able to twist the struts might evolve to a form of aerodynamic control.

    Lock the machine in roll (a frame corners to trike base tube )and perhaps better in turbulence ?

    tip rudders ... rc servos on trailing edge ?

    It is where faster trikes are headed ..you might be the guy to nail this ?
  • Rizwan Bukhari
    by Rizwan Bukhari 27 days ago
    Thanks everyone for your input. This is helpful.
  • Tony  Castillo
    by Tony Castillo 24 days ago
    Riz, although the king post and wires may indeed add more drag, the max speed of the wing and speed range is not just because of struts or cable braced ... many other design, size and tuning factors come into play for both. The cable brace QUIK wing is faster than many strutted wings and with a wide range usable speeds ... but that is because of size, wing loading, design, tuning, etc. So do not assume that a strutted wing is faster because struts..
  • Joe Hockman
    by Joe Hockman 23 days ago
    Tony, it is true that many flex wing design characteristics determine the performance envelope that is possible including max speed. However, Rizzy's original question was related to speed range, not max speed. Yes, the QUIK wing is faster than many strutted wings and I am sure it is related to design but mostly to its size 10.6M. Just using the information posted on your web site at pmaviationusa.com there is a slick little table at (http://pmaviationusa.com/images/p-m%20ac%20comparison-quik%20gtr.png?crc=3848056404) which offers a very nice side by side comparison of the various wings offered (both KP and strutted). My interpretation is that the QUIK wing has the narrowest speed range of all wings listed. It mentions that Trim Speed Range (@ min TOW) is 55 to 82mph, which is only a spread of 27mph. Indeed that is the narrowest range of all wings listed. The 13M wing for the QUIK GT450 (also KP) is 47 to 80mph with range of 33mph. All the others listed (for PulsR, Quik GTR, and QuikR) are all strutted and those have a listed speed range of 35mph (GTR), 40mph PulsR, or 45mph QuikR. These all have a wider speed range than the listed KP wings.

    So the upshot from my perspective is that even with the P&M Aviation offerings, it appears the root cause of reduced drag on strutted wings may be the primary reason for the larger speed range. Abid did a good job above describing how the loss of the large parasitic drag associated with the top rigging, absent on strutted wings, is likely responsible for the net lower drag on strutted wings. Lindsay above correctly pointed out that drag goes up by the square of the speed increase. So at the top end of the speed range on KP wings, that parasitic drag component is magnified. Bill Chance gave some data on a nice little experiment he conducted flying with and without fairings on struts and DTs. He saw a >400rpm decrease for hands off trim speed. That, of course, is not a direct comparison of KP vs struts since side cable diameter would be no more than 1/4" vs ~1" for round struts but it does speak to the benefit of streamlined fairings on structural members like DTs and struts. So in my mind, the larger speed range of strutted wings still comes down to drag, which Paul mentioned at the beginning.
  • Bryan Tuffnell
    by Bryan Tuffnell 23 days ago
    ...and the extent to which the design allows the pilot to pitch the wing without needing a steady diet of protein bars, or having the wing start porpoising in phugoid oscillations, comes into it. Pitch stability of the wing and the geometry of the carriage and A frame also affect the speed range.
  • Larry  Mednick
    by Larry Mednick 22 days ago
    Good point Bryan. It is in fact pitch stability tha generally limits top speed in a flex Wing. The more washout the Wing has the more it will try and nose up when excessive speed is induced. The secret to going really fast is to remove billow and get the tips flat while still maintaining positive pitch stability. That formula works ok for handling at high speed but caused problems with low speed handling which had to be addressed by new technology. In any case people often think you can pick up speed with aerodynamics and HP which is true in a fixed wing, but mainly the pitch stability of the Wing will allow the top speed to be what it is going to be.
  • Joe Hockman
    by Joe Hockman 21 days ago
    Very good point Bryan and Larry. Pitch stability has to be critical for higher speed range. I am trying to remember the details but doesn't the STARS system on some of the newer P&M wings actually vary the amount of washout, perhaps through washout sprog adjustment. More washout or twist added for slower flight at higher AoA and less twist for higher speed flight at lower AoA. I recall Tony giving me an overview at SnF and I thought that was what the STARS system was doing in addition to varying sprog settings on each side in a bank. If my interpretation above is incorrect, let me know.
  • Andy Hughes
    by Andy Hughes 21 days ago
    Reading and rereading our trike forums I think WTF? Myself, has/have come to the conclusion that our sport is looking for the last few MPH. Wasn't our sport about low and slow? Why have we sacrificed that for a trike that goes 110mph and is a nightmare below 45mph? If I want to go faster than 80 mph with a 912 I would be in a different aircraft, a fixed wing RV-4 will do 200mph. Lots of us are going to get bit by excessive speed bug in a flying in a flex wing trike. What is the limit? The limit is switching to another style of fun/aircraft/design. That is my thoughts. I am from a powered paraglider family. Our speeds were 30 mph, guys were trying for 60 mph and dying every month so I moved to these wings and engines. One aircraft can't do it all. Be careful my bro's! Best regards, Andy.
  • Paul Hamilton
    by Paul Hamilton 20 days ago
    Andy,
    Low and Slow is only one corner of the choices in trikes. There is a huge selection for each taste, dreams, and lifestyle.

    This might be helpful to many to help decide which aircraft to choose. It is a choice of dreams and the lifestyle you want to choose.

    http://lsapilot.sportaviationcenter.com/learn-to-fly/light-sport-flying/

    Be thankful we have such a variety of choices in trikes.
  • Gregg Ludwig
    by Gregg Ludwig 20 days ago
    I’m with a Paul, however, ideally one would own more than a single trike to match the mission of the day.
  • Joe Hockman
    by Joe Hockman 20 days ago
    I agree with Paul and Gregg's comments above. We can be thankful that we have a number of choices. Low and slow is not for every trike pilot and conversely there are many that would prefer to not fly the fastest trikes. One of the real attractive aspects about flying trikes that most trike pilots do not take advantage of is that simply by changing the wing you can have an aircraft with a significantly different performance envelope. I count my self fortunate to have that arrangement on my Maverick trike.

    However, getting back to the original focus of this blog, it is extremely nice to have a trike / wing combination that has a wide speed range. A wide speed range presents a wider performance envelope to exploit and it does have safety implications. Personally, if I could only own one trike / wing combination with a speed range of 40 (or 45) mph I think I would rather have one with a usable speed range from 35 to 80 than one with a range from 50 to 95. That is simply a personal preference as I have a lot of value for slower stall and slow flight speeds. BTW, my observation is that most trike / wing combinations do not have a speed range of >40mph but I'm guessing that those pilots that do have it really do appreciate it.
  • Tony  Castillo
    by Tony Castillo 20 days ago
    Joe, a better comparison will be GT450 (King Post) vs GTR (Strutted) .. the speed range is about the same, the size is identical at 13 SQM. Speed range 33mph for the Gt450 (king post) and 35mph for the GTR (Strutted).

    Note: King Post GT450 can be tuned to actually have a greater speed range that the strutted GTR or vice-versa. I can actually tune either to fly hands of faster than the other ... design and tuning is key not just struts - for top speed and speed range. I have had GT450 tune to fly hands-off at 92 mph which gave me a speed range of 92-47 = 45mph

    Typically a similar wing but strutted instead of king post will be a little heavier than its kingpost counter part. That may upset to some minor degree the gain in less drag... but only in some cases.

    Kingpost does add a bit of drag so may be harder to tune to go as fast as its strutted counterpart.. but be close. The tuning will be key to the performance and in my opinion more than struts or kingpost.

    I will venture to say the value of a well designed strutted weight-shift wing in mostly on its ease of folding, setup, storage (less height), etc - ALWAYS ... .. and THEN perhaps some performance gain in some cases.
  • Tom Currier
    by Tom Currier 19 days ago
    My Cygnet is a compromise. With a stall speed of 37 and cruise at just over 50 I'm happy but in the bumps and in windy conditions the large sail is difficult to manage and requires muscle. I've tailored my workouts so I'm working on the muscle groups required to move the wing around :)

    Having an amphib is definitely a compromise and though owning two trikes might work, I prefer that they're combined. Now if I could get a REVOLT with amphib capability and still maintain it's touted characteristics.....that's a whole 'nuther story.

    My goal is not speed but rather mid day flying; something I avoid in the Cygnet unless over large bodies of water or at the coast.
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