Discussion: Conceptual Design of an "Inexpensive" Single-Seat Motorglider

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Hole in the Ground

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If your centre sections had some anhedral and therefore extended slightly below the fuselage could you use that for impact resistance? Wheel safely crushes up and then the wings spring up too?
 

RPM314

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I think that if the center went down far enough, it would make the wingtips drive through the ground.
 
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Hole in the Ground

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only anhedral on the centre section. So a w-wing a-la stuka/corsair.
 

RPM314

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Ah, an inverted gull wing. I think sailplanes used to do that for a short time in the 80s or something.
 

Jan Carlsson

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What about the AH 93-K-130 to 132/15 series? and what is different between them except the 1/10 percent thickness and camber? are they used in any good(er) gliders?
 

Topaz

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I am talking about external crash structure. The Piper Cherokee series has external skids on the belly for crash day.
An option for low wing designs where the pilot seats on the spar.
Ah, I understand now. I think the drag penalty would be too high, but I'll consider it. Thanks.
 

Topaz

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Ah, an inverted gull wing. I think sailplanes used to do that for a short time in the 80s or something.
And there's a reason they're not used currently - weight and drag increase. A gull wing will have a higher induced drag than a planar wing or one with elliptical dihedral. While that might be a small penalty on a typical sportplane (because of all the other drag penalties going on), it will be a noticeable penalty for a glider.

Some really creative ideas coming, though. That's cool.
 

Topaz

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What about the AH 93-K-130 to 132/15 series? and what is different between them except the 1/10 percent thickness and camber? are they used in any good(er) gliders?
Is this stepping back to airfoils? I don't have the coordinates for those sections. What's their current usage?
 

autoreply

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What about the AH 93-K-130 to 132/15 series? and what is different between them except the 1/10 percent thickness and camber? are they used in any good(er) gliders?
There's been considerable controversy about it, whether it's the actual airfoil of the ASH26/ASW27. Haven't found anything definitive so far and forgot to ask when I should have.
 

Himat

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Ah, I understand now. I think the drag penalty would be too high, but I'll consider it. Thanks.
The drag penalty of a skid might be negotiated by making it two and double as wing fairings. If the wing fairings where turned vertical they would also act like underbelly protection in a wheel up landing. The downside is again how it look, but you can probably do better than I me.
ds54_side_1.jpg

Next option does have a higher weight penalty. Move the outrigger wheel inboard and attach them to the two sturdy beams. The trouble is that the weight here probably is as large as a landing gear. With some detail change you could probably dismiss the retractable wheel, but then the retractable gear idea went out the window. And the lower drag benefit of a retractable gear.
ds54_side2.jpg
 

Topaz

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The drag penalty of a skid might be negotiated by making it two and double as wing fairings. If the wing fairings where turned vertical they would also act like underbelly protection in a wheel up landing. The downside is again how it look, but you can probably do better than I me.
If they project at all below the belly of the aircraft, as they'd have to in order to act as impact attenuators, then that's at least two, and as many as four, more near-90° intersections added to the aircraft. The drag increase would be considerable.

I'm not trying to play "yes, but..." with you guys. But you really do need to understand the sensitivity to drag we're talking about here. I'm already significantly compromising the airplane with my "ease of build" conic-sections fuselage. Adding even more drag is something I'm very strongly trying to avoid.
 

Radicaldude1234

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Thinking aloud here: would it be an option to partially, instead of fully, retract that center main wheel so you can use the tire as a shock absorber/skid? Drag penalty would be similar to having a separate skid and it would have the advantage of using to existing structure to serve a dual purpose...
 

Himat

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The analogy to the vertical wing root fairing is the P51 Mustang compared to the Spitfire. The Spitfire did have quite large wing root fairings, the Mustang did have the radiator scoop performing some of the same function.

I do not find this “yes, but …” at all, rather a washing of ideas between engineers to find possible good solutions. Progress is best when both the pro and con of different solutions are found.
 

Jan Carlsson

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Is this stepping back to airfoils? I don't have the coordinates for those sections. What's their current usage?
Sorry, I am late to the party, I was just thinking loud.

About drag, I think you made the best out of it, you know the rules what made AR5 and 6 so fast, highest part of canopy over the TE, straight fuselage sides from wing highest point to or close to TE, canopy starting at wing highest point, and engine cowling fairing into the same point.

Did you look into the B&S Vanguard engines?
you seems to get it right, 30 or so HP, one liter of fuel for every HP is a good number. Calculate with 0.5 - 0.55 lb per HP, if can't lean the carb.

And remember that most imperial engines is SAE rated, so use 85% of that for performance or size calculation. so to get 30 hp at the prop you need 35 SAE gross hp, or BHP
 
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Swampyankee

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The least drag penalty and weight penalties would, obviously, be to follow traditions of light aircraft attention to crash safety, and do nothing. Otherwise, the least drag penalty would be to increase the fuselage height to accommodate the needed energy absorbing structure.
 

BJC

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Many years ago, a friend and a true craftsman, and builder of five or six scratch-built airplanes, observed that engineers take forever to complete an airplane because they get distracted thinking about too many insignificant design details.


BJC
 

BBerson

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The drag penalty of a skid might be negotiated by making it two and double as wing fairings. If the wing fairings where turned vertical they would also act like underbelly protection in a wheel up landing. The downside is again how it look, but you can probably do better than I me.
View attachment 49550

Next option does have a higher weight penalty. Move the outrigger wheel inboard and attach them to the two sturdy beams. The trouble is that the weight here probably is as large as a landing gear. With some detail change you could probably dismiss the retractable wheel, but then the retractable gear idea went out the window. And the lower drag benefit of a retractable gear.
View attachment 49551
I would use one " external skid" perhaps 1" wide. Call it a " crash keel" or crash fin.
The Rutan Defiant had a belly rudder called "rhino rudder", but not for crash crush.
The skid in your drawing is what I suggested.
 

Jan Carlsson

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I would use one " external skid" perhaps 1" wide. Call it a " crash keel" or crash fin.
The Rutan Defiant had a belly rudder called "rhino rudder", but not for crash crush.
The skid in your drawing is what I suggested.
you don't want a center keel, but two one on each side.
 

BBerson

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you don't want a center keel, but two one on each side.
One center keel would streamline the center wheel.
I don't recall if retractable or not. But leaving 4" wheel stick out while retracted is common. So my keel fairing would be less drag than nothing.
The wheel really can't absorb crash like a purpose made crash keel.
 

Topaz

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Sorry, I am late to the party, I was just thinking loud.
No worries at all. Great to have you back.

Did you look into the B&S Vanguard engines?...
I haven't. I haven't found a turn-key conversion for them, and coming up with my own is out-of-scope for this project. If you know of one, I'll consider it. Right now, I'm baselined on the 32 hp Hummel 1/2 VW.
 
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