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Thread: A faster bush plane...

  1. #31
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    Re: A faster bush plane...

    Georden

    A higher cruise speed in a STOL aircraft has also been on my list for some time. After doing over 50+ engine packages for the STOL Zenair 701 by Chris Heintz, I would say that the only complaint voiced by our engine customers is the slow cruise speed. So far in this post, however, no one has mentioned the PegasSTOL wing option for the Zenair. It basically adds the proven automatically retractable slats, fowler flaps, and a much higher cruise speed favorable airfoil of the Helio Courier to the Zenair 701 airframe with tail-dragger option. In the Ultralight area at Oshkosh this year, there was one, and he has flown it in cross country from Los Alamos, NM more than once. It has a great cruise speed (but with more than 100HP). I will try to post a photo of it.

    Trimming drag off the gear and fuselage of a 701, though useful up to a point, would probably not be as beneficial as a better STOL wing design. I spent some time this year in the museum at Oshkosh taking a look at the wing on the Buttercup. When you look at what Whitman was doing in his era, its more than just a little impressive. Remember, he had integrated decent STOL performance/ VERY high cruise speed/ AND was doing this on LOW HP. This guy knew what he was doing in the arena of aircraft design.

    Anyone know what airfoil he was using on this application and what the camber was when the leading edge flap was fully extended?

    Jeron Smith
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  2. #32
    Registered User Jan Carlsson's Avatar
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    Re: A faster bush plane...

    The Buttercup have a 2412 basic airfoil, with the LE extended I don't know the camber.

    see LuceAir ~ Replica Wittman Buttercup
    Jan.

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  3. #33
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    Re: A faster bush plane...

    From the friends at yahoo groups airfoil :
    Mike Shuck
    http://xa.yimg.com/kq/groups/3854470...309update2.pdf
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  4. #34
    Registered User snaildrake's Avatar
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    Re: A faster bush plane...

    Quote Originally Posted by raven-rotor View Post
    .

    Anyone know what airfoil he was using on this application and what the camber was when the leading edge flap was fully extended?
    .
    Hi-
    My guess is that the people who could answer those questions would be a) Earl Luce, who created the Buttercup replica plans (and who knew Steve W. personally) and the staff at the museum in Oshkosh where the original B'cup lives. Earl's email address is listed on the Luce Air web site.

    I would note the obvious about Mike Shuck's brilliant analysis of the W10 wing airfoil, that the W10's wing has nothing in common with the Buttercup. But man, is it a cool window into just how sophisticated Wittman's thinking was, after many years as a top air racer. I bow in the general direction of Wisconsin in awe....

    -Dan

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    Re: A faster bush plane...

    Nice words Dan, here are some photos I took a few weeks ago.
    Attached Thumbnails Attached Thumbnails A faster bush plane...-dsc00504.jpg   A faster bush plane...-dsc00507.jpg   A faster bush plane...-dsc00503.jpg  

    A faster bush plane...-dsc00505.jpg   A faster bush plane...-dsc00506.jpg  
    Rock and Roll ain't noise pollution, Rap is !

  6. #36
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    Re: A faster bush plane...

    Seems like the Buttercup would fly pretty good with a VW engine. 132 sq. ft. of wing area.

    You'd sacrafice some STOL capability, but stil....
    If you want to put ice in the lava river,
    First you must climb,
    Then you must stand and shiver. -N.Young

  7. #37
    Super Moderator orion's Avatar
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    Re: A faster bush plane...

    One thing that folks did not mention yet - under 200 mph there is little justification for retracting the main gear. It is actually possible that the extra weight of the retraction system and structure may actually end up costing you more performance than the gear as is. And this is especially true if your retracted gear sits on the outside of the plane behind some form of integrated fairing.

    A well designed gear strut and fairing, coupled with a good wheel fairing (several possibilities here, some even functional in the bush) will actually hurt you overall performance very little, although there would be some sacrifice (obviously) if you go to Tundra type tires.
    "To live is to learn; to learn is to live" (author unknown)

  8. #38
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    Re: A faster bush plane...

    Quote Originally Posted by steveair2 View Post
    I saw this 701 at Oshkosh. I don't know what the cruise speed is. Cool though.
    That's Scott Ehni's, and I talked with him at some length about his ideas and methods. It is serious cool. There's a lot there to inspire people to reach a little further (and he will graciously help any serious student of this art, it seems) but cruise speed isn't one of its strong points, it's still a 701. Even with extensive aerodynamic cleanup (all flush driven rivets, fairings, etc.) and a 13 gph turbine engine it still goes about 85 kt. He wanted to make everything as light and slick as possible so he could get a reasonable amount of fuel onboard.

    If you don't care so much about climb angle, you can build a 701 without slats and gain about 5 kt. The lift/drag curve just doesn't ever get so steep as it does on a 701. You can pick an intermediate point with VGs but there is still no free lunch.

    Get Chris Heintz' book and read up on his design ideas for high lift and you'll see why. I am still asking these same questions myself and keep coming back to the same answers. If you want to analyze it in some more depth, get John Lowry's "Performance of Light Aircraft" and the foundations for all of these lift/drag tradeoffs become clear. (The book is out of print but available from AIAA as print-on-demand.) You don't have to get too deep into the math to begin to realize how power and drag and weight and lift all balance in a design. The sexy new designs differ mostly in one area: where the centers of lift of the various airfoils are.

    The only way you can bend these results is when you can reconfigure the wing (retractable slats, double slotted flaps etc.) which directly eats into your useful load. You could probably implement Helio-style retractable slats on a 701 for about 50 pounds, is it worth it for 5-6 kt? Wheel pants will cost 20-30 lb and give you another 2-3 kt. Going along that line brings you to the Pegastol approach, which is fine if you don't need a steep initial climb angle. All else being equal, you can lose enough drag to pick up 6-8 kt by making the frontal area smaller, this means tandem rather than side-by-side. You can certainly study Scott's plane and see where to add fairings that will allow you to pick up 1 or 2 kt. He says closing off the ends of the slats yields maybe 1 kt. Experiment, but don't be expecting anything drastic.
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  9. #39
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    Re: A faster bush plane...

    I've always liked the Dyn'Aero designs. Their high-lift wings do very well. Composite obviously and deep double-slotted flaps that are hinged below the wing. Very low cruise drag, but still very high lift. It might be possible to achieve the same with a metal wing, covered in a single layer of glass for extensive laminar flow.
    Aude somniare

  10. #40
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    Re: A faster bush plane...

    The stated 'specifications' - 150 mph cruise, 30 mph stall 100hp 1100lbs AUW are certainly acheivable just not by copying aircraft that don't.

    The additional criteria hold the clue to why you can't seem to get the result you want -- eg 'highest aspect ratio without excessive span " --what is meant by excessive span ? --by constricting span you will impose a high induced drag and induced power and place the aircraft in the dangerous backside of the power curve region at low speeds and also require a higher nose up attitude adding to gear landing gear drag and weight problem.

    Incidentally, it is only the WING that needs a high angle and an assumption that this means a tall and heavy undercarriage --the Rogallo wing is the classic case of de coupling the wing angle of attack and the body angle (--also incidentally the actual inventor of the modern hang glider _Australian John Dickenson, is recognized and honoured this week by the FAI for this fact ) several other aircraft have variable incidence wings . And when it comes to big fat tyres for rough surfaces you can use a pivotting bogey of two much smaller tyres which are a lot less drag (especially when very close together ) -- I've built recumbent bicycles with bogey wheels and prefer them to a big single wheel although for different reasons to a balloon type tyre which might be better on mud or really lose scree and sand . A centreline type landing gear and balancing outriggers is at least worth consideration for the real maximum rough surface case --a really large but buried main tyre could be used --

    Leading edge slats or hinged flaps will be hard to do without destroying any laminar flow making the cruise speed more difficult -- but overall you need a highly variable geometry wing --MUCH greater area span and camber for low speed and get rid of them for cruise .nothing magic about it. (Henryk's Kasperwing is another approach )

    The Bronco OV 10 mentioned earlier was in fact homebuilt by K.P.Rice to convince the military that it was the right idea --the slispstream blown wing is a feature of the Zimmerman 'flying flapjacks' that also get an incredible speed range by never flying at slow AIRspeed within the propwash --even to VTOL if enough power . (I correspondence with Mr Rice some time back -his website on the Volante flying car is well worth a look ) The criteria described are those for a viable ATOL URBAN use flying car --where long landing runs are not available simply because they all got built out years ago. Sailplanes have investigated large speed range and efficiency at both ends --the Europa rundflug competitions and the Lympne light aircraft trials are still worth studying because of the emphasis on exactly the criteria set here -- grass field and docile bottom end plus efficient fast cruise on low power.
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  11. #41
    Registered User BBerson's Avatar
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    Re: A faster bush plane...

    Fred Keller , from Alaska, designed a low drag bush plane. It won EAA award and was on the cover of Sport Aviation.

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    Re: A faster bush plane...

    Air Car

    Thanks for the tip on the Bronco OV10 and Mr. Rice's initial design with the 21 ft. wing span. Reading his report on the bureaucratic process was interesting. Would like to have seen his original smaller prototype actually built. Short span seemed like a problem for a STOL application until I realized the type of horsepower he was packing into his design.

    IMO one thing that is often not stressed enough in the STOL aircraft design parameters is the positive effect of 'excess' engine power. If a substantial increase in take-off power can be added to a STOL aircraft design with a minimal weight penalty, the result will definitely increase the STOL performance of the aircraft in take-off and climb out. Two of my talks at Oshkosh this year detailed our latest engine conversion targeting what we are calling the 'Super-STOL' engine market. Using the Honda Jazz/Fit 110HP stock base auto engine, we are adding our own turbo upgrade to bring the horsepower up to 140+ and almost double the torque for takeoff. At cruise, the boost drops back and we are shooting for max fuel economy with this engines VVT technology. Turbo's the best 12-15 lbs. of weight you can add to an aircraft. The power is then optimized for the ground roll and climb out phase of flight. Hope the moderators can go with someone's earlier request to add a Honda section to the engine category part of this great site.

    Jeron Smith
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  13. #43
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    Re: A faster bush plane...

    Quote Originally Posted by BBerson View Post
    Fred Keller , from Alaska, designed a low drag bush plane. It won EAA award and was on the cover of Sport Aviation.
    That would be the Keller FK-1 STOL Prospector. Here's the article, which might provide some inspiration and practical numbers. Cheers, Matthew
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    Re: A faster bush plane...

    Quote Originally Posted by BBerson View Post
    Fred Keller , from Alaska, designed a low drag bush plane. It won EAA award and was on the cover of Sport Aviation.
    Quote Originally Posted by Matthew View Post
    That would be the Keller FK-1 STOL Prospector. Here's the article, which might provide some inspiration and practical numbers. Cheers, Matthew
    Guys, Thanks for that. I've been looking for any example of a successful conventional (i.e. non-canard) design with a hot-wired wing core, and this is the best example I've seen. Now if I could only find some design and construction details and how Keller figured out his layup schedule. Well, that's for another thread . . .

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    Re: A faster bush plane...

    MATTHEW- I lost track of your address and still have the stack of photocopy on the tandem Lysander gathering dust on my desk -please PM your current address and I will send it off ..

    Raven - yes it is EXCESS power that matters with getting airborne and climbing and only a few extra available horses can easily double the rate of climb --the first thousand horses under the bonnet on Moller's Skycar for example just get it to dangle in mid air --any more make it move and climb ,that is the extreme example.

    But that simple fact cuts both ways --if you don't NEED so many ponys to just get moving (inertia -weight) and then waste so many on pushing air down too fast (short span -high induced power) then you will also get the same effect as more power in the baseline aircraft but without the fuel bill for a bigger engine . (Again I ask what 'excessive span' is defined as and why ..)

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