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Thread: Penrose Gremlin

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    Re: Penrose Gremlin

    Quote Originally Posted by cluttonfred View Post
    Different strokes.... I already think the Penrose Gremlin is really cute! Here it is in color. ;-)

    Attachment 78308
    Ah someone has beaten you to it.

    And of course my own vision of a tandem seaplane.
    A short drive shaft would move the prop aft of the wing to prevent interference and shield the prop from spray.

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    Re: Penrose Gremlin

    The Briffaud G.B. 10 Pou-Push and the Landray GL3 Pouss-Pou pictured below are both two-axis Mignet types with a variable incidence front wing for pitch control and rudders but no ailerons. As far as I know, the Delanne designs and the Delanne-inspired Westland P.12 and Penrose Gremlin were all conventional three-axis types. So similar but not quite the same....

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  5. #33
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    Re: Penrose Gremlin

    Quote Originally Posted by cluttonfred View Post
    Old thread, new thought....

    Per Harald Penrose, the Gremlin was never built because of the "lamentable failure of the special Wren engine to materialize" because other available options were too heavy given the engine's position and therefore moved the CG too far aft.

    If you were to take the Gremlin configuration but make it a pod-and-boom design, whether that boom were a tube or a truss, then you could move the engine forward closer the main wing. You'd still have clearance for a prop of reasonable diameter and it would be a perfect application for the larger modern paramotor engines.

    Hmmm....

    Attachment 78305
    One very big problem with the Gremlin layout is access to the engine. It could hardly be worse, and any dropped items or drips wind up on the rear wing. Your pod and boom idea would improve this.

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    Re: Penrose Gremlin

    Sorry, I am not sure that I follow your point. At this scale the engine is still not very high, why would access be an issue? Looking at the Briffaud and Landray examples, I don’t see a problem.
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    Re: Penrose Gremlin

    Quote Originally Posted by cluttonfred View Post
    Sorry, I am not sure that I follow your point. At this scale the engine is still not very high, why would access be an issue? Looking at the Briffaud and Landray examples, I don’t see a problem.

    I'm just going by the line drawing of the Gremlin, but my back hurts just looking at it. Unless there's some sort of prop shaft or extension, the aft 50% of the engine is over the rear wing and the rear wing projects well beyond the prop disk. When it comes time to remove the cowl and do work, unless I can step/crawl on that wing (!!?!!!), I can't really see/get to the aft part of the engine or the prop. I'd probably wind up building a platform/gantry to provide a catwalk around the engine compartment. I guess as a taildragger it wouldn't be as terrible, but as a trigear--uggh.

    Also, any leaks and dropped items aren't going to hit an easily cleaned lower cowling, they are going right down into the empennage/tailcone, unless we build a drip apron to take them somewhere else.

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    Re: Penrose Gremlin

    That issue would be solved with a short drive shaft of perhaps two feet coming off the rear of the crank. The engine can be mounted centrally, and a shaft that short is unlikely to produce enough torque vibration to be a problem.

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    Re: Penrose Gremlin

    OK, I see the issue now. For a two-stroke powered single-seater, I think we have so many very light paramotor engines to choose from that it ought to be possible to put the firewall at the trailing edge of the rear wing and/or sweep the rear wing back to make engine access convenient, basically the Gremlin with a rear fuselage more like the Briffaud GB.10. A straight section and then swept outer sections like the Miles M.35 Libellula might be a good idea.

    Click image for larger version. 

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    If necessary, the pilot's seat could be adjustable fore-and-aft, though the wide CG range of the tandem may make that unnecessary. Assuming the fuel is carried on the CG and not a factor, you could balance the aircraft just forward of the rear CG limit with the lightest allowable pilot, say 40 kg/88 lb so that heavier pilots would just move the CG forward from the limit. I suspect you could get up to quite a heavy pilot without busting the forward limit and therefore needing an adjustable seat, but that would have to be checked.

    For side-by-side two-seater and heavier four-stroke engines, you'd probably need to move the engine forward for more of a pod-and-boom layout like the Thunder Gull or Kolb designs, thought it might be possible to keep the tail mounted engine with tandem or staggered seating.
    Last edited by cluttonfred; February 17th, 2019 at 07:14 AM.
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    Re: Penrose Gremlin

    Inspiration has struck.

    Using a delta for the rear wing makes the rear wing stall-proof. As the front wing carries more weight-per-area, it's less draggy to have that one carry most of the weight and be a higher aspect ratio.
    The extreme sweep gives effective dihedral and yaw stability.
    Could you get away with having no rudder and using the ailerons as forward elevons for two-axis control?

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    Re: Penrose Gremlin

    1. M. Payen would have approved.

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    2. I don't know of any designs without vertical tail surfaces that worked except pure flying wings and most of them had marginal directional stability at best.

    3. Ewwww...and this from the guy that thinks Volksplanes and Flying Fleas are cute.

    4. Still with one central or two tip rudders you might be on to something.
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    Re: Penrose Gremlin

    Quote Originally Posted by cluttonfred View Post
    1. M. Payen would have approved.

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    2. I don't know of any designs without vertical tail surfaces that worked except pure flying wings and most of them had marginal directional stability at best.

    3. Ewwww...and this from the guy that thinks Volksplanes and Flying Fleas are cute.

    4. Still with one central or two tip rudders you might be on to something.
    Heh, yeah it's fugly. Should have mounted the engine further back but I didn't feel like going back and making the changes.
    I think it has potential for being just as good, or at least easier to build, than the Sea-era. A low delta makes a pretty good seaplane hull as it's wide enough not to need outriggers, and the tandem pou-like configuration means you don't need positive AOA on the fuselage to take off.


    It's an offshoot of a couple other ideas I had. One was for something Pou-like with a tractor engine.
    The delta would be the "fuselage" with the engine at the nose of the delta and the straight wing mounted on top of the engine with the pilot straddling the narrow nose of the delta just behind the engine.

    The other idea was a variant on the hemipetere configuration, only with the rear wing being a high-mounted delta rather than straight wing. That way the wider straight lower front wing could be all one piece and be removable for trailering.

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    Re: Penrose Gremlin

    Quote Originally Posted by Sockmonkey View Post
    Inspiration has struck.
    Close enough?

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    Re: Penrose Gremlin

    Quote Originally Posted by Tiger Tim View Post
    Close enough?
    What is THAT? Is it really asymmetrical?
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    Re: Penrose Gremlin

    Quote Originally Posted by Topaz View Post
    What is THAT?
    I knew I'd get some eyebrows up with that one. It's a model of Eut Tileston's Tern, a homebuilt amphibian that was never completed. The shape is pretty weird (though not asymmetrical) but it's essentially a little bit of Spratt, a little Mignet, and a little Thurston as far as I can tell.


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    Re: Penrose Gremlin

    I have to agree that the configuration of that Lysander variant is a good candidate for the ultimate bush plane.

    You get the STOL, the safety, the utility, all the things you want.

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    Re: Penrose Gremlin

    Throwing another render out there because it's what I do.

    Imagine it as a refit of the Dehavilland Beaver.
    Big rear cargo hatch for easy loading.

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