Custom Build... Thing. Need Advice

[Fogwalker]

So in preparation for an architecture internship I resolved to learn a few new programs. Instead of practicing modeling houses which is insaely easy, I modeled this thing. I actually discovered Flite test randomly letting YouTube play in the background while I did this. Now that I put in all the work I actually want to build it, however.... I have never flown RC before. So I was thinking I would buy one of the twin engine kits like the guinea or the FT cruiser and learn to fly on something I dont mind crashing whilst I build this. Then I can swap the guts over to my custom build. I'm completely out of my depth gaugeing how much power i need to make this fly. Does anyone think the Power Pack C (twin) will be enough to get in the air or do I need to look at something not sold in the FT store, and if so ...what? I'd like to stay electric because glow looks like a pain.



Wingspan: 65"

Length: about 48"

Wing area: About 380 sq/in

Construction is mostly Balsa (1/8, 3/32, 1/16 and1/32), with some Basswood on the areas that I think would need some extra strenght. I also included a 25mm and a 15mm carbon fiber tube to run 1/2 the length of the wing and support the two proposed engines in a pusher configuration. The wings will be partially sheeted in Balsa but I didn't model that. The internal structure has about 140 cu/in of space for things and activities. The engine pods are currently capped with Firewalls I stole from a FT pdf. (Didnt trust myself to be original) Im going to laser cut the pieces.

Any input or advice would be appreciated.

 

[Jugsy]

This looks really interesting, I've never seen a twin pusher like that!

You're on the right track flying a tried and tested design first, but even the FT Kits can go wrong for someone who hasn't built or flown anything before (making an assumption here, what is your background?). I'd recommend a trainer of some kind first, park size preferably but micro's fine if you're on a budget. Even the FT Tiny Trainer will be way more forgiving than a large(ish) twin.

As far as using a twin Power Pack C on your design, we might need a balsa expert to drop in here, but just looking at it I think you might need something beefier. If you're able to calculate the weight of all those components, compare it to the weight of a Guinea/Cruiser!

 

[Fogwalker]

Thanks for the reply, I agree a "trainer" would be ideal, I was leaning toward a guinea or cruiser just for the fact that components could be transferred to the project plane. ( I should name it) I actually have a fair amount of experience building planes. I love going to the hobby store and buying the balsa kits, I just end up doing something dumb with the finished product like tossing them off of tall building after days of slaving over them. Ive gotten behind the sticks a few times when i was younger (Im 31 now) on my dads old glider. But that was early 90s tech and a completely different type of flying.

As far as weight goes, I dont know. Im currently trying to figure out how to take the rhino model and export it to auto cad so I can use the "nesting function" to lay it out for laser cutting. At that point I should be able to atleast see how many sheets it takes. It's mostly 3/32 balsa. Anyone ever weigh a 4" x 36" piece of balsa?

 

[wilmracer]

Looks really nice! It definitely wouldn't be a trainer so getting some stick time would be critical. Also, have you considered landing gear mount points? With that sleek design I'd be thinking retracts with doors but that is extra complexity. And covering... Sheeted and glassed or film?

One thing you might do is check out FTGroups.com to look for local fliers in your area who can help get you in the air. If you're in the US you might have a local AMA club that offers training. There is a lot of help on these forums but there is no substitute for getting out and flying.

 

[PsyBorg]

Flight sims for the win!!! These are invaluable when learning to fly. The worse the program the better. If you can fly smooth in a bad program you should be able to fly OK IRL.

I do agree that your design will be much heavier then any FT made foam planes. Add to that 65 inch wingspan is a BIG plane. According to spec sheets that motor will produce max 30 ounces of thrust.
http://www.headsuphobby.com/Emax-GT2215-09-1180kv-Outrunner-Brushless-Motor-C-691.htm

Going by the recommended sport weights of 18 -35 ounces you are looking at a max model weight between 3 and 4 pound range for them motors to safely move. I'm thinking you would be heavier then that on 65 inch wings as well as motors and electronics. Also think ahead when calculating your all up weight about any cameras or fpv gear you may wish to use or add.

I do like the design of your aircraft. It reminds me of the high altitude spy planes of the 70's and 80's Looks like it should have a nice glide ratio so once its up it shouldn't be a power hog for cruising speeds.

 

[Craftydan]

Beautiful lines.

Lots of ribs. Lots and lots of ribs

No leading edge spar?!?

Twin pushers will give you good propwash over the tail-surfaces, but none over the wings. You'll have good Rudder and Elevator authority while the motors are running, but you'll stall at lower airspeeds than a twin tractor of the same lines. Not killer by any stretch of the imagination, but do be aware of the form/function tradeoff you're making.

Twin pack C should be fine. 65" span is leaning on the big side for those motors, but there are two -- if you build her light she should be happy with it.

Have you designed in any way to break-down the wings? (65"x50" is a HEAUGE footprint to transport to the flying field)

Planned a launch/landing strategy? 65" span can still be hand launched, but pushers aft of the CG will make the poor sap . . . um . . . I mean "good buddy" at the flying field nervous as they toss it. You've got plenty of space for retracts to ROG, and while cool, they add a lot of weight (which may push you up to a larger motor). Catapult launch is a good balance between the two, but you'll have to design in the hard-point for the hook now.

. . . and a final note . . . Carbon fiber isn't all that expensive or hard to work with, in either rod/strip or tow form (carbon tow is raw fiber bundles you'll need to epoxy into place). Judical use of it can give you both an increase in strength and a drop in weight (from the removal of structure you no longer need). It is not a silver-bullet solution for added strength, but it's an incredibly useful material.

 

[Montiey]

65"x50" is a HEAUGE footprint to transport to the flying field

Well said.
:applause:

 

[Fogwalker]

Responses

I finally worked out some weight estimates. Unless I did something horrible with the math, there should be between 218 and 380 grams of balsa in this airframe depending on exact density, and about another 170 grams worth of carbon fiber in the wings. No idea what kind of glue weight i will add to it or how much the skin will weigh. As far as launching I was thinking a light toss from the wingtip or some fixed tricycle (cant get the ground clearance with a tail dragger)

As far as transport, currently the wing is one piece but the whole center section of closely spaced front to back ribs you see will lift out giving you easy access almost the whole length of the "activities bay", and making it fit in the trunk of most cars if you put the rear seats down. Also forgot to mention, there is 6 degree dihedral in it.

 

[Fogwalker]

If I used two seperate servos for ailerons and programmed in some "flap-eron" action do you think that could compensate for stall speed? If the consensus is that I need bigger motors, do you think the guinea or cruiser could take the added power?

 

[Fogwalker]

No, no leading edge spar, I figured if I was sheeting the leading edge it would be sufficient. I tried thou, but the complex wing shape which has a slight break about 1/3 of the way down the wing length combined with the shrinking thickness of the wing towards the tips made it really hard to model and i figure with the break I'd negate any strength. Thats why I included the carbon fiber tubes.

 

[Fogwalker]

Thank You!

I'd like to thank everyone for their input in this thread. It has been invaluable and has prompted me to think about design choices that I never would have considered. I've settled on the name WoW flyer because learning the programs and designing the plane has consumed my life like I havn't experienced since I played that game back in college. Im going to try to power it with a C twin pack and Ill try learning on the new Sea Duck because when I saw the video the described its flying characteristics as almost like a trainer (and I absolutely loved Tail Spin as a kid....and as an adult.) Its an ironic first plane for someone learning to fly in Las Vegas. Worst case scenario, The C pack doesnt have enough power for my plane and I'm stuck flying the sea duck until I buy bigger motors, (Oh darn). Ill also include some static trike landing gear to give me adequate ground clearance for the props and if I decide I have plenty of power Ill install some retracts to make it pretty again. Or Ill just include that on my next build. Im sure there will be design problems mbecause Ive never done this but Im already looking forward to making the next design. I go all zen.

Unfortuneatly I just found out that the two laser cutters I have access to are miniscule. 18x24 being the larger one. So I have to do the sensible thing before I start this. Build my own 4ft long 90w cutter. As soon as I can get this project restarted Ill post progress pics.