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tomklop
12-03-2006, 07:02 AM
I'm about to start building a BTE Venture 60. It has a 72" wing with 876sq.in. I hope to build it to less than seven pounds. I will be changing the aft formers to balsa. I will be changing the fuse from lite ply to balsa. I will change the sheet balsa tail to built-up. I will enclose the front end with a vacuum formed plastic cowl. I intend to power it with an AXI 2826/12 with a 13x10E APC electric prop. It will be powered by a 4S pack of A123Racing cells. I expect it to pull max 36amps and produce 480 watts. I'm considering cutting the wing down to 66".

Any thoughts or comments you'd like to share?

Thanks
Tom

B.L.E.
12-03-2006, 03:06 PM
I think you are going to want more than 480 watts on a 7 pound plane. That's like putting a .40 glow engine on a plane that is designed for a .60.

I just did a maiden flight on a scratch built Stephen's Akro, 66 inch wingspan, 7.25 pound all up weight and my power combo is a e-flite power 60 with a APC 14x10E prop and 6-s 4500 mAh lipo. About 950 watts. This combo flies the way a .60 glow powered plane should fly.

ray foley
12-03-2006, 03:51 PM
An Axi 413016 with 6s lipo of 4000mah or so, a CC phx 80, an APC 15x10 or 16x8 eprop, an rf choke if required, will meet your needs handsomely. Some may say a bit overpowered but it is better to be amazed than disappointed.

ciao -rjf

tomklop
12-04-2006, 12:21 PM
Thanks for the opinions, guys. I figured that this set up would be a bit low on power, but I think it will fly, though not with a lot of acrobatic possibilities.:(

I have thought of breaking up one of my four cell packs and making a 6S, but I'm not sure I really want to do that. But, if I do I should get around 710 watts without going overvoltage on the motor. Because of the way that A123Racing packs are wired this is not too difficult. Maybe I should.

I live in Nairobi, and don't have easy access to a larger motor or more cells. Since I love building I'm willing to settle for less power until I can get back to the US. Then I'll bring a 4130, some larger props and some more cells back with me.:D

balsadust
12-05-2006, 01:27 AM
Tomklop,
Don't worry about the motor being able to handle the weight, if your mods work out you will probably be down to 6 or 6 1/2 pounds. I fly a Great Planes Trainer 40 with a 2826/12 with 12 nimh 3300mah batteries and it flies great on a 12x8 prop (wont clear anything larger), its current weight with standard servos, reciver and reciever battery is 6lbs 12oz. I am sure I could save some weight with lipos but it flies fine the way it is.

cooper998

tomklop
12-05-2006, 03:21 AM
Cooper,
In secret I'm hoping to have it weigh less than the 7 pounds I quoted. But, I figured that I'd ask about the worst case. I'm glad to hear that your GP Trainer flies fine. I think that what I'm planning will be marginal, but easily upgradeable when I get the chance.

Tom

B.L.E.
12-05-2006, 12:38 PM
The term "enough power" is something that's open to interpretation. Like ray said " it is better to be amazed than disappointed". I like to amaze the glow engine flyers at my club.:D

I'm not sure if shortening the wingspan is a good idea, I don't think it will save much weight and will probably increase the wing loading meaning you will need more power. The watts per pound rule of thumb is really an over simplification that assumes a "normal" airplane. A more complete formula would take into consideration parasitic drag, wing area loading, and wing span loading. In other words, the more your plane resembles a sailplane, the less power you need per pound, the more it resembles a delta wing jet, the more power it needs per pound.

Dereck
12-10-2006, 06:53 PM
The term "enough power" is something that's open to interpretation. Like ray said " it is better to be amazed than disappointed". I like to amaze the glow engine flyers at my club.:D

I'm not sure if shortening the wingspan is a good idea, I don't think it will save much weight and will probably increase the wing loading meaning you will need more power. The watts per pound rule of thumb is really an over simplification that assumes a "normal" airplane. A more complete formula would take into consideration parasitic drag, wing area loading, and wing span loading. In other words, the more your plane resembles a sailplane, the less power you need per pound, the more it resembles a delta wing jet, the more power it needs per pound.

Two small credit card slips worth...

The clipwing V60 got done by so many folk who were happy with it that Bruce Tharpe pretty much endorsed it on his website at one point. Assuming the mod behaves much like the ditto Four Star 40 - which I flew for three years on mine - it doesn't degrade the low speed handling, improves the roll rate (okay, mine has slightly wider ailerons too) and actually makes it easer to land - the model doesn't float like it can in 'standard' form. Mine has spent its life operating from a tight, short tarmac slab and is far easier to land decently than with its standard wing.

The ideal power loading was figured out after I found the best prop it flew with! That's a 15 x 10 APC-E at a shade under 7,000 RPM BTW. Behind it is a Hacker B50 13S on 6.7:1 sucked some 40-A from 16 x 3300 mA NiMh if you want to get technical.

I can't even recall her last flying weight unfortunately! The model's been so chopped and changed, I gave up keeping up on trivia. But no sceptic has ever seen her fly and been quite the same about what electrics can and cannot do afterwards. Bruce Tharpe is, IMO, one of the top sports aerobatic designers going, on the strength of the 4* / Venture designs alone!

Deltas only take a lot of power if you fly high alfa, low speed. Keep the AOA low, they'll go fast on relatively low power - but, IMO, are way more fun on the back of the drag curve, engine howling and going slower than the local OT fleet. Not a good way to fly with electrics though...

Regards

Dereck
(who has to leave Florida tomorrow and fly back down to the Disaster of Columbia - bummer)