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Mystery Project - Will it fly - 9/18/2012 2:14 PM   
Chevelle


 

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Status: offline 		I'm working on a fun project with a couple of club members. I know it looks very odd but there are reasons.  (I'll show you in later posts.)  Aside from the missing support structure for the lower wing and other such details, do you think this will fly?  A couple of things to know: Because of the stuff not shown, the balance point is actually right where it needs to be and the engine is at a proper place in relation to the two wings.  The wings are a Clark Y profile.  Total weight will be 5 to 5-1/2 pounds.

There is quite a bit of TLAR (That Looks About Right) in this design.  I'd like to know your thoughts on the size of the rudder, elevons, and wing cord.  It is pretty short coupled but will it fly reasonably by an average experienced pilot?

Thanks.


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RE: Mystery Project - Will it fly - 9/18/2012 3:03 PM   
eagle1945


 

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I  see no support for the trailing edge of lower wing which will cause the lift unreliable. I think I'll get my bottle of wine out. Your building a real nice cork-srew.



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RE: Mystery Project - Will it fly - 9/18/2012 3:52 PM   
Chevelle


 

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Status: offline 		hehe.  You are quite right.  There is plenty of stuff missing from the illustrations.  I don't want to spoil the surprise.  Assume that all the surfaces and other bits are secured where they are shown.  If that were the case, would the thing fly?



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RE: Mystery Project - Will it fly - 9/18/2012 3:56 PM   
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Status: offline 		I'd feed VERY uncomfortable with the thrust-line up that high, consider moving the engine to the lower wing. With that kind of top-heavy moment you will nose-over very easily on any kind of landing, and take-off's will similairly be frightening until the elevator gains authority.

On that note I would suggest much larger control surfaces on the elevator.

A flat airfoil like you have detailed would be quite unstable, I'd add some dihedral, maybe even some sweep if you need to maximize wing chord while minimizing wingspan, as your design suggests.

I presume you have some very interesting design constraints, I'm going to assume it has to have a very short wingspan (fit within a 1-meter box or some such) and probably carry an odd-shaped load. Rather than comment on your soultion, perhaps you could present us with the problem?

-Curt



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RE: Mystery Project - Will it fly - 9/18/2012 4:12 PM   
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Status: offline 		I forsee something afoot. the design is ment to, shall I say, carry some kind of payload perhaps.

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RE: Mystery Project - Will it fly - 9/18/2012 4:20 PM   
Chevelle


 

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Status: offline 		Ok. Ok.  This is what we are dealing with.


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RE: Mystery Project - Will it fly - 9/18/2012 4:25 PM   
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RE: Mystery Project - Will it fly - 9/18/2012 4:40 PM   
Chevelle


 

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Status: offline 		These might help as well.

Flying the dog house with one or more WWI planes is a big hit at our events.  We have/had two versions of the dog house, each with their plusses and minuses.  The original MAN design was OK.  Decent form but pretty squirrelly because of the huge moment caused by all that drag way above the thrust line and much less below.  The FlyingThings version flies nice because the engine is more on the midline of the front profile drag.  The problem with that design is because the wing is more in the middle, the nose gear is very long.  Landing on grass is very problematic.  Any deflection of the nose gear just caused the whole thing to tumble.  The look of the FlyingThing version isn't all that great either.

This design attempts to solve the negatives of both designs yet be a reasonable flier with reasonable looks.

This is a video of our original MAN version.  (This video has been hijacked by lots of others so you may have seen other versions.)






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RE: Mystery Project - Will it fly - 9/18/2012 4:57 PM   
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RE: Mystery Project - Will it fly - 9/18/2012 5:54 PM   
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Status: offline 		I think you may have a problem rotating for takeoff with the aft location of the main gear.

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RE: Mystery Project - Will it fly - 9/18/2012 8:00 PM   
BMatthews



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Status: offline 		I see lots of things wrong with this design unfortunetly.

First off the roof and wall slats will greatly affect the inner "airplane" despite your gaps to let the air fly through it. So much so that I doubt if the inner control surfaces will have much effect at all.

My approach, and that of most of the folks that have done doghouses before you, is to make the floor, walls and roof the actual flight surfaces. The floor can be one wing and the roof panels the other. To counteract the destabilizing force of the anhedral you can keep most of the weight down low and minimize the effect of the anhedral. Besides with that short an aspect ratio I doubt if the anhedral has enough effect to cause much in terms of major troubles anyway.

The walls up front would need to be made as hinged vertical blinds for the first 3/4's of the length from leading edge and back. You want them to hinge and float in the air so that they don't produce any "fin effect". Then the rear 1/3 of the vertical walls is fixed with movable rudders along the trailing edge to actually satisfy the need for vertial tail stabilizing and yaw control.

Although.... if you put the elevators and rudders mixed as inverted "ruddervators" on the upper roof wings then you could put ailerons on the lower side. And in fact thinking further "ruddervators" on an inverted V tends to have a PROverse rolling effect. So it's quite possible that you could have only the upper wing with controls on it and fly it as though it was a rudder-elevator model without much trouble. In this case you'd still want the forward 2/3's of the "walls" to be free floating vertical blinds with the hinge line at or near their leading edges so they don't act like fins. You just would not require any rear rudders.

For the same reason Snoopy hisself should be mounted up top so that he's well to the rear instead of being perched so that his side area is in the middle.

The airfoil choice for what would effectively be a flying wing would be best if it was a simple symetrical section. The lower one should be thick enough to contain all the radio gear and to provide the support required for the engine on the pylon. You want the engine to be on a pylon in order to get it up somewhere close to the center of drag of all the structure. Otherwise a low mounted or high mounted engine will produce a lot of pitching moment due to being too far from the center of drag.

For something like this you don't need anything all that scientific either. Well other than being either symetrical or a reflexed sort of airfoil. A decent enough option would be to take a NACA 0015, scale it up to about 1.5 inches thick and then "cut" it at the point of maximum thickness and stretch the ends out far enough with simple flat lines in between to be long enough for the chord. For what you're doing with it this will work just fine and give you enough thickness to be structurally strong yet light if built with all the wood on the outside of the surfaces. The walls can be simple sheet stock or something of the like. For the free floating slats some of the card stock clad foamcore board would be excellent since they are light but stiff.

The engine would be located on a pylon mount off the lower "floor" wing so that it's got the thrust line centered just a little below the center of the opening. No inner fuselage, wings or other stuff would be needed or desired on the inside of the "doghouse" as it would simply disturb the airflow through the core and likely have minimal effect anyway.

If you have the stuff to do so then a simple concept proof small scale electic model out of depron or fan fold foam would be strongly advisable regardless of what you believe in terms of going with your concept, my concept or some other options.

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RE: Mystery Project - Will it fly - 9/18/2012 8:14 PM   
Chevelle


 

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Status: offline 		Very interesting points.  I've gone back and fourth on the side vanes issue.  The MAN design had them, the FlyingThingz version does not.  The latter flies pretty well without them so I figured I could get away with not having them on my version.  No?

As to the roof, I would think that one lower wing would provide enough lift so it might be possible to have the roof one piece but without a lifting profile.  It would just be to provide stable airflow across the ruddervators (ruddevons? eleruddevons?)



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RE: Mystery Project - Will it fly - 9/19/2012 12:34 PM   
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Status: online 		I would suggest a canard at the front of the dog house to support the nose gear.  Or mount a tail gear to the bottem rear of the dog house structure.  It is going to nose over with the nose gear so close to the center of gravity and all of that top weight.

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RE: Mystery Project - Will it fly - 9/19/2012 5:23 PM   
eagle1945


 

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Status: offline 		Maybe  an inflatable wing like a para-sail would work on this.

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RE: Mystery Project - Will it fly - 9/19/2012 9:15 PM   
BMatthews



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Status: offline 		The issue is that there is simply no way to avoid all that wall and roof area adding a lot of lift and drag. Even with the slots to let the air leak through the effect of them is very high.

The MAN version you have in your video works well because the big floor wing has enough pitching authourity courtesy of the full length chord to "manhandle" the drag from the roof and walls. But even then it still causes a lot of wobbles in flight from the looks of things. Wobbles that the pilot has to react to on a more or less constant basis?

The full floor size wing also mandates that the balance point be well forward at around 17 to 20% of the floor's chord. Which, happily, is more or less where the sides and roof would also demand it be. But with the airplane within the shell style this isn't the case.

Anyhow, my ramblings are all WAG's (Wild Assed Guess's ) Ideally you'd want to try it at a reduced size with something cheap like fan fold foam or the like at half size before looking at the idea of all the work of a full size version.

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RE: Mystery Project - Will it fly - 9/20/2012 7:54 AM   
turbo.gst


 

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Status: offline 		If you get the power to weight right it will fly. As much as it pains me to say, this is true. Of course, you still have to find the right balance point. This has been proven over and over by those electric foamies. They don't even have airfoils, and they have incredible power to weight ratios.



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