Replies to This Discussion

Permalink Reply by Wyatt Ciomperlik on July 18, 2012 at 10:26pm

Note:

I designed this model to be scalable, but currently I am aiming for a 9 ft wingspan and about 4.75ft long.

The bombs on the bottom are just for show...  but I could make them real and use them as exterior fuel pods.

If anyone has a prop size/pitch/thrust cheat sheet, I lost mine.

Permalink Reply by Wyatt Ciomperlik on July 19, 2012 at 1:30am

I was studying NASA's X48-C and I got inspired when I managed to find more details...

I have updated my design, and I would still like opinions on both.   At this point, I have lowered my expectations as to how much fuel/weight I need to carry.   I am expecting 12-15LB from the engines, and 1-2LB from the electronics.  Once I know what I have to play with, I will add fuel.

Tomorrow I will start working on more calculations and pay a visit to my CNC and make a mini model of it.

Here is a picture of V2.  

Note - the blue things at the back of the plane are where I expect to have the props.

Permalink Reply by Martin on July 19, 2012 at 2:45am

Firstly, it's hard to say anything just by looking at the CAD model.

Anyway, wing loading will probably be quite high. That means that the lift-off and landing speeds will be high.

What's the wing area?

For long endurance I would try to achieve low wing loading.

Permalink Reply by Wyatt Ciomperlik on July 19, 2012 at 2:49am

I dont have the exacts on wing area yet. The models shown in the image were made in OpenVSP and it doesnt play well with me. Just exported to autodesk and I am bringing everything to size.

I should have exacts soon.

Permalink Reply by Wyatt Ciomperlik on July 19, 2012 at 3:15am

Autodesk and OpenVSP do not want to work together.  When I wake up tomorow, I will have to remake it from scratch in autodesk...   Good night (morning for me) everyone.

Permalink Reply by Wyatt Ciomperlik on July 19, 2012 at 1:28pm

I am doing more math on the updated model and I have gotten exact details on the airframe.

19.373 FT^2 (1799810.593 mm^2) surface area.  This includes control surfaces.  Triple checked.

8.939 FT (2724.61 mm) wingspan.

4.526 FT (1379.524 mm) from the nose of the plane, to the rear of the airfoil along the X axis (for total length).

3.198 FT (974.750 mm) from the nose of the plane, to the rear of the fuselage (down the center)

Airframe designed as a Flying Wing.  Follows NACA 6 standards.

I have decided to use the Honda GX35.  A bud of mine has a gx50 and I was allowed to look at it...  Does not fair well when faced with free fall or dramatic turns...

I have abandoned the idea of dual engines, so now I am working with 1KW of power total.

I haven't made up my mind between a 20x8 or a 20x6.  Its been a long time since I have done static thrust...

Ideas, comments and suggestions please.

Permalink Reply by Jake Stew on July 20, 2012 at 12:14am

The stock GX35 weighs 7.6 pounds dry.  You should be able to strip the GX35 down to about 5.5 pounds or less.  You should remove the flywheel/magneto and replace it with a CDI ignition system.  Maybe also put a stack on the carb.  Probably can ditch the pull starter, clutch, and the compression let off system.

People seem to be running 20x8 props, and 20x10 props on slightly souped up models.

Permalink Reply by Wyatt Ciomperlik on July 20, 2012 at 12:20am

Thanks for the suggestion, and I will defiantly be ditching those items.

The think that is concerning me is that a 20x8 on a GX35 in optimal conditions produces 148.85OZ of thrust.   It has been quite a long time since I have played with static thrust and airplanes...   Is it enough thrust?

EDIT: Its actually 203.88OZ of thrust...

EDIT2: Its also been a long time since I have cared about calculations... but im on a serious budget for this build.

Permalink Reply by Zachary Eldridge on July 20, 2012 at 5:35am

As a avation expert how heavy is the aircraft.

Permalink Reply by Wyatt Ciomperlik on July 20, 2012 at 9:27am

Here is a run down on weight.  These are not exacts, but what I am expecting...

5.5LB - Engine

~4LB - body

1.5LB - flight electronics

~0.5LB - PTZ camera and transmitter

As much fuel as I can hold

The beauty of this design I am working on, is that it is not your basic "tube with wings" design, so it is low drag.   I will be improving my design some more in an attempt to lower drag at a 0 degree angle of attack, but the total wing area should stay roughly the same.

What I am wondering is, does anyone have any math charts I could have.  

I would like to figure out max payload.

Permalink Reply by Martin on July 20, 2012 at 10:39am

Ok, let's take the lift equation. As I'm from Europe I'll use the metric system.

L=CL*(rho*V^2)/2*A

As I don't know all the right figures I'll just make some up.

Maximum coefficient of lift CL=1,2

Density of air rho=1,225 kg/m^3

Speed V=30 m/s (about 60 mph)

Wing area A=0,9 m^2

Maximum lift Lmax=1,2*(1,225*30^2)/2*0,9=600 N

That is about 60 kg or 132 lbs.

That would also mean that your take off and landing speed would need to be 30 m/s or more. You would have to use a catapult for take off and a parachute or a net for landing.

In the case of a more reasonable take off/landing speed V=10 m/s Lmax=66 N. Which is about 6,7 kg or 14 lbs.

Permalink Reply by Wyatt Ciomperlik on July 20, 2012 at 10:44am

Thanks for the info, will be looking into the calculations more...

When it comes to take off and landing, I tend to use the farming access road/rifle range.  if I cant take off in 500 yards (457.2 meters), something is wrong.

If I am in need of some serious take off and landing power, I could just mimic the flight deck of a carrier.   One nice big catapult and a few catching wires.

EDIT: I may have to do this...  I like to launch and recover via my boat in my off season.  The beaches that are abandoned out here are beautiful.

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