Duncan's got a Flea

Discussion in 'Aircraft Design / Aerodynamics / New Technology' started by rtfm, Aug 3, 2017.

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  1. Sep 28, 2017 #481

    cluttonfred

    cluttonfred

    cluttonfred

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    Henri Mignet's dream was not just "piloting for the uncoordinated," though it is certainly true that he found conventional three-axis controls challenging. Keep in mind, too, that he would have received his limited training in 1920s aircraft that most modem pilots would find challenging, too.

    Mignet's dream was an airplane cheaper and easier to build and fly than ever before in order to bring the joy of flying within reach of people of modest means. The name Pou-du-Ciel is a riff off a nickname for the Ford Model T (pou-de-la-route) that brought the automobile within reach of ordinary people. That France's EAA, la Fédération RSA (le Réseau du Sport de l'Air), takes its name from the title of Mignet's book about the HM.14 (le Sport de l'Air) is a testament to his lasting impact.

    The basic Mignet formula *is* simpler and cheaper and faster to build and easier to fly than any other rigid wing aircraft I know, all other things being equal. Three surfaces, two of which move, and one flight control. Stray far from that and you may well have a perfectly good airplane, but you have lost the simplicity. As I have said before in various ways, it's not about orthodoxy, it's about minimalism.
     
    Last edited: Sep 28, 2017
  2. Sep 28, 2017 #482

    BBerson

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    My friend has a rudder control Kadet RC Model. The rudder is instant. I can sometimes do a full sloppy roll with it. The rudder control is too quick actually for my preference, with about 40° of rudder travel. I also had an I.F.O. from Dan Kreigh that I built with rudder only instead of ailerons. It could turn on dime also. Seems a rudder could be made more effective if desired.
    "Don't overcomplicate"
     
  3. Sep 28, 2017 #483

    TFF

    TFF

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    I do rudder rolls with my son's old Kadet II. Enough throw and enough dihedral, it will roll. I built it old style no ailerons on purpose. Unless you live in a very windy place, i would not build ailerons into a Pou. Especially my first one. You could build in provisions, if you just had to. it will never be a crisp to fly aircraft. It is a wallow around and be approximately where you want to go plane.
     
  4. Sep 28, 2017 #484

    BBerson

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    I think upturning the wing tips a bit more should provide more aggressive rudder roll. The Flea doesn't have dihedral, just the up turned tips. Might need a bit more. My Grob has quite a bit of dihedral but the rudder only is almost ineffective for roll. My friend had a scale Grob with rudder only. He gave it to me because the rudder was ineffective. If it had polyhedral it would roll with rudder.
     
  5. Sep 28, 2017 #485

    TFF

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    I consider the upturned tips as the dihedral;its just not the whole wing. I can see the Grob with the long wing resisting, needing LOTS of dihedral or polyhedral, if you did not have to deal with linkages, to have the effect. It just comes to a point where it gets silly chasing a trait 100%.
     
  6. Sep 28, 2017 #486

    Victor Bravo

    Victor Bravo

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    The Grob motorglider wing panels may weigh 180 pounds each, and that weight is a long ways away from the center of the airplane. So it is probably not a good comparison for a Flea. The Grob was designed with ailerons,a nd only enough dihedral to have the amount of roll stability appropriate for a 3 axis controlled aircraft. If Grob for some reason had designed the airplane for 2 axis controls, as BBerson says the outer wingtips would be cranked up two feet above the T-tail.

    Myself, BBerson, and many many others of us have flown rudder-only or rudder-elevator models, and they work just fine the way model airplanes are flown. But extrapolating this out to a full size aircraft reveals two problems that you would never have with your ancient Live-Wire Champ or Top Flite Schoolgirl model.

    First, the quick and powerful yaw-roll coupling that makes 1 or 2 channel R/C models fly just fine would make a pilot hopelessly airsick within the first 20 seconds during the type of flying we do with the models. You would have to be muchmore gentle with a full size aircraft.

    Second, the typical small 2 channel R/C model is not required to make long rolling crosswind landings. Most of these models land and groundloop as a matter of course, probably because the early R/C models had the main wheels much further forward than would be appropriate with a full size model. They were designed that way to minimize propeller damage.
     
  7. Sep 28, 2017 #487

    rotax618

    rotax618

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    I have built and flown a flea, and probably unfortunately for me my long experience flying conventional 3 axis aircraft made for an uncomfortable experience. I'm sure if I had perservered I could have overcome the feeling that I wasn't in total control.
    Takeoff was ok if the wind was straight down the strip otherwise it felt dangerous. In the air was fine, landing didn't feel safe almost ground looping every time because of the short coupling and inability to keep the wings level.
    I'm an average pilot with lots of hours. Roll control would make the flea into a really great machine, at least for me.
    As I said in a previous post, the 2 axis advocates who havnt flown a Flea, on the next flight don't use the ailerons and get a feel for the "simplicity".
     
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  8. Sep 28, 2017 #488

    BBerson

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    How much rollout does a Flea need? Looked like 50 feet on the one that stalled. I always takeoff at an angle across the runway with the Grob, it needs 700 feet. For a Flea landing on grass an intentional groundloop might be possible in a crosswind. Takeoffs are optional for a sport plane or ultralight so just wait for calmer wind.

    I never had much interest in the Flea because of the history and poor L/D. But I can see they might be fun. Perhaps a bit larger.
     
  9. Sep 29, 2017 #489

    cluttonfred

    cluttonfred

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    It's too bad that Gilbert Landray never sold plans. His planes used higher aspect-ratio wings and he and his son were both big guys 100+ kg each so the designs might have had broad appeal.

    gl4-c1.jpg

    gl4-b1.jpg

    http://pouguide.org/avions-de-gilbert-landray

     
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  10. Sep 30, 2017 #490

    rtfm

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    Hi,
    Well, funds have run out, so I'm reduced to making templates out of MDF again. It is engrossing work, and at least it doesn't cost anything, since I have quite a lot of 3mm MDF sheets in the workshop.

    Over the past few days I have made the template for the floor. Quite a tricky operation. I had to use a number of small pieces of MDF, and then join them together. But I've done it, including the cutout for the seat. That part had to be done three times before I got it right.

    I am not posting this "progress" in the build thread, because making templates isn't really part of the build itself.

    And talking about templates - I have a template for a seat. What I did was to spray foam into a comfortable chair (covered with plastic) and then cover the foam with another sheet of plastic. And then I sat in it till it set. Problem was, it took over 2 hours for the foam to harden sufficiently. It was a long sit. So I used the time to page through back copies of old flying magazines. It was quite a fun morning, truth be told.

    I then had to wait till the foam did its final irregular rising, and then sand it smooth. I discovered that I sat lopsided - the right leg is about an inch higher than the left. So more sanding to get both sides balanced. I now have a mold for the seat. And the seat will hinge in the front, so that one has access to the quite generous space underneath - for baggage.

    Next step: make the seat. That'll take a day or two - because I don't expect the first seat to be servicable, to be realistic...

    Duncan
     
  11. Sep 30, 2017 #491

    nestofdragons

    nestofdragons

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    A guy who flew a Butterfly, the lightest motorized Flying Flea, told me he never had a problem with crosswind. If the wind was cross, he simply landed sideways.
     
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  12. Sep 30, 2017 #492

    Twodeaddogs

    Twodeaddogs

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    A friend of mine made a seat for his VP-1 using a similar technique; he sat on a plastic bag that had just had builder's foam squirted in and it molded to his shape and he was able to trim off the excess later. very good idea.
     
  13. Oct 1, 2017 #493

    Thunderchook

    Thunderchook

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    Question for anyone who has actually flown a flea:

    (This may be a silly question, so I do apologise.)

    How does turning work?

    So, given that if you have a three-axis aircraft, you use the stick, coordinated with rudder, to achieve desired angle of bank. Then, you return the stick to the centre and, depending on aircraft type, leave varying degrees of rudder throughout the turn. Then, when you wish to cease your turn, you apply stick and rudder in the opposite direction, and centre the stick and rudder when you are straight and level.
    The degree of deflection only controls the rate at which you bank.
    If you hold the stick into the turn you will continue rolling around the axis and either enter some kind of aileron roll and/or reach a maximum angle of attack, thus entering a stall and spin.

    So, if the Flea is turned by applying stick in the direction of the turn, and holding it there, then returning stick to centre to end the turn, what happens when you hit the stops of the rudder?
    Does the flea then only have a maximum bank angle, and so angle of bank can roughly corresponds with degree of stick deflection?
    Controlled by maximum rudder deflection?
    The considerations go on.

    Can anyone answer this?

    Thanks.
     
  14. Oct 1, 2017 #494

    TFF

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    With the effect of dihedral, airplane rolls as it yaws. The turn is not a perfect coordinated turn in that way. The yaw accelerates the outboard wing and slows the inboard and it rolls. If you are slipping a plane in for a landing you cancel out the yaw roll with opposing ailerons. An aileron equipped airplane does not need a lot of roll with the yaw but a rudder only needs more. Once you get the plane rolled then pulling on the elevator is the same. If you hold the rudder in the turn it will be slightly slipping around the turn with a slight wallow. It wallows because the dihedral is trying to stabilize the plane and you are upsetting it.
     
  15. Oct 1, 2017 #495

    BBerson

    BBerson

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    I was reading that early Quicksilvers had the stick operate the rudder, same as Flea.
    Then spoilers were added to the Quicksilver wings for more control (instead of ailerons). The spoilers were operated by the foot pedals. So if needed the pilot could apply right foot for more right turn using both rudder and spoiler. Or both feet for glide path control only.
    Might be easier to fit spoilers. Floppy wings designed for no ailerons are not always torsionally stiff enough for ailerons.

    Apparently the Flea was intended for self instruction. Two axis is probably superior for self teaching because of self righting tendency with enough dihedral.
    Early ultralights were often designed and sold as safe for self teaching.
     
  16. Oct 1, 2017 #496

    bmcj

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    But how was his taxi experience when hi had to turn crosswind in the ground?

    (NOTE: this question pertains to an issue for all lightweight planes, not specific to 2-axis aircraft.)
     
  17. Oct 2, 2017 #497

    Tiger Tim

    Tiger Tim

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    I think the answer is to not expect a lightweight slow single seater to be in any way practical. If there's somewhere you absolutely have to be, drive.

    Seems to me we're all guilty at one time or another of expecting too much from machines made to provide simple joy and nothing more. It's kind of like criticizing an aluminum baseball bat for being theoretically prone to lightning strikes; what are you doing playing baseball in a thunderstorm?
     
  18. Oct 2, 2017 #498

    Thunderchook

    Thunderchook

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    Yup.. I get all that.


    Yes, I get that, but what I was trying to get my head around is that, if in a flea, you don't centre the controls during a turn (as in a 3-axis aircraft) what happens if you apply full deflection and hold it there?

    As we know, in a three axis aircraft, if you apply full stick and hold it there, the sum total of effects will result in the plane continuing to roll about the axis until you either perform an aileron roll or the aircraft exceeds maximum angle of attack and so enters a spin.

    What happens in a flea? Do you get to a maximum angle of bank and that's it?

    A question best answered by someone who has actually flown a flea.

    Koen? Rotax? Cluttonfred? Any flea pilots here?
     
  19. Oct 2, 2017 #499

    BBerson

    BBerson

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    From level flight, holding rudder beyond about 45° of bank results in the nose dropping into a spiral dive. At some angle the rudder longer has any roll power so can't do a full roll from level flight.
    No Flea experience, but lots of two axis R/C models.
     
  20. Oct 2, 2017 #500

    rtfm

    rtfm

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    Bit of a rainy day here, so I spent the morning writing some build notes - and planning how to proceed. The most time consuming issue I have at the moment, is figuring out in what sequence to do stuff. And making mistakes. For example, I have worked out how to mount the main gear legs, and then I built the mounts. Only to discover that once bonded together, I can't drill the required bolt holes. Bugger. So I have to start again - this time drilling the holes in the drill press first. Little things, but time consuming.

    I will pick up another sheet of 5mm Hoop Pine ply tomorrow, as well as order the 4mm 6061-T6 for the various engine/wing mounts. I already have the templates for the floor, and have measured and cut the side X-bracing. Fortunately during the MDF template-making operation, I realised that I wouldn't be able to get the floor in if the X-braces were already in place. Saved just in time.

    So, next week:
    • Make and fit the main gear mounts
    • Seal the airframe with very low viscosity epoxy
    • Fit the engine/wing mounts using my MDF templates to check fit and positioning

    Duncan
     
    Last edited: Oct 2, 2017

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