Motor Glider Design

[oldcrow]

Hello, All

 

I am in the process of designing a wooden motor glider and would like some help. I am using Autodesk and like to draw to keep my mind sharp. I probably would not ever be able to build this aircraft but I would like to have the plans out there for any one else. There aren't to many motor glider plans out there that are inexpensive and most of them are composite aircraft which construction is costly to build.

 

So here are the parameters of the motor glider ( name to be determined):

 

1. wood and fabric construction with the fuse being built mostly with white pine and aircraft ply construction is of spruce

 

2. parasol cantilever wing

 

3. low hp (28-40)

 

4. narrow fuse (11 inches wide) to straddle like the "Air Bike"

 

5. folding wings for trailer storage

 

6. 3 axis control

 

I would like to use WB-135/35 as the airfoil loos kinda like a clark y with a little under camber.

 

My thinking was the fuse to be around 16ft with around 35-40 wingspan.

 

If any one is interested please chime in.

 

Thanks, Ken

 

 

[kasper]

Well two of your parameters appear to be at conflict with low cost construction.

 

Any cantilever wing is going to weigh and cost a lot more to manufacture than a strut braced wing.

 

Given its a motor glider with the person sitting at least semi outside the performance as a glider is not your design point so the loss of glide performance from the struts is probably very minimal after you take away the weight saved on the wing spars/structure ... you are at the low end of weight so every lb/kg/newton saved is very useful

 

On wooden build (having been there done that a coupl of times) the only way to do it simply and cheaply is to have constant chord wings - its a real killer to homebuilders from plans having to make SO MANY rib jigs and cut up SO MANY different rib components ... when you only have 2 of any rib :-(

 

The second area is 'folding wings' ... I hope you mean detachable wings not folding because the fittings to fold a wing are a bugger to make from plans accurately and again they are more weight that adds nothing to the flight performance but detracts.

 

Good luck with the design exercise but its a really good thing to think always on your design exercise - how to NOT add the weight means you don't have to redesign it out after you discover the prototype is not as light as you thought and again look for either off-the-shelf options (bit more cost but less time to build) and design elements that are repeating ... build 1 wing rib build another 45 exactly the same ... much more attractive than build 2 and now start again on another 2.

 

 

[facthunter]

There was a period back a while where this concept was popular. There were some about in the 80's. As stated your design will not be that clean so you will be using the motor frequently on low lift days. Wood won't give you the dimensional accuracy you might wish for. It will have to be well crafted. Nev

 

 

[Deskpilot]

Not quite what you're thinking about but a 'wooden motor glider could look the 'bee's knees'

 

 

 

 

 

 

[kasper]

Yes the Bowlus Baby Albatross is a lovely looking little glider ... but I prefer the Backstrom Plank for simplicity and there was 1 powered plank development ... less to build if you leave off 10 ft of fuselage and all the tail group :-P

 

Sorry to derail the thread - back you your design for a powered motor glider ...

 

 

[facthunter]

Using the engine for take off poses some limitations. Look Up Hoinville Fred. Goulburn Airodrome. Nev

 

 

[Methusala]

Mitchell Wing B-10 or U-2 for more streamlining. Don

 

 

[oldcrow]

interesting thoughts, thank you. constant chord is what I was going for because it is easier to construct. I know that hanging out in the wind will cost me glide performance but I am not looking at a completion glider. 20:1 would be outstanding. Here is a quick sketch of about what I am looking for;

 

 

good point about the folding wing detachable wood be better. more input please

 

Ken

 

 

 

[bexrbetter]

........ kinda like a Clark y with a little under camber.

NACA 4412?

 

 

[diesel]

look up airchair. They have come a long way. Very active yahoo group. Yor drawing is way too boxy for me. Constant cord can be tidied up quite simply. ie tailwind or jodel. Chas