Im here trying to design a high endurance UAV (24 hour missions) and would like to hear the communities suggestions/comments on my design. Its been a very long time since I have designed an airframe like this one, so please bear with me.
Currently I plan to be using dual weed eater engines. I am debating between using dual Honda GX35, or dual Honda GX50.
The engines (dual GX35 dry) weigh at 15.2LB, the electronics should weigh about 5LB, and I intend to have as much fuel as I can carry. To reach my goal of 24 hours with these engines, I need to carry 6 gallons of fuel (witch weighs 36LB).
Each engine (gx35) produces 1.0 kW @ 7,000 rpm.
I havent done too much calculations, but does anyone here have any ideas?
Does anyone think this is possible? Local aviation thinks im crazy.
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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.
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.
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.
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.
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.
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.
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.
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.
As a avation expert how heavy is the aircraft.
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.
Ok, let's take the lift equation. As I'm from Europe I'll use the metric system.
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.
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.