evrytngelswstkn

Hey, I originally posted this somewehre in beginner, but somebody referred me to this forum instead. I'm just looking for basic information, here's my story:

I'm an ARO (aerospace engineering) majoring freshman at Cal Poly Pomona and on a whim decided to join a Design-Build-Fly club at my school where we :ahem: design, then build, and then fly a plane in a competition hosted by the AAIA. Since it turned out that I had the most experience with electric motors (from my experience with ground-hugging vehicles) the whole matter of propulsion for our plane has dropped into my lap. This includes what electric motor to use, which batteries and yes, prop choice.

This year's competition requires a huge, heavy plane to be powered by a max of 3lbs of batteries and by a motor that is limited by a 40amp fuse. :O

The most difficult mission we're going to fly requires us to load two 4.4lb water bottles, fly around a short 2000ft course, land, load another water bottle, fly a lap. land, load another bottle and so on to 5 water bottles for max points. That’s 22 lbs of water. We figure our design (a high-wing dual boom looking thing, looks exactly like the plane from Flight of the Phoenix) is going to weight about 8 lbs. Add water to that and you get 30lbs max. The design currently has a 9.5 ft wingspan.

We can't use LiPoly's either.

I'm seriously not sure what motor, batteries or prop i should go with. Since were not caring at all about speed, I guess a huge propeller would be good, The fuselage’s diameter is going to be about a foot n a half. With landing gear figured in, we should have clearance for one monster of a prop.

With something that large, using an electric motor would probably require gear reduction? Maybe? Is it possible to create about 7lbs of thrust (what the seniors say we'll need) with a 40 amp limit and around a 26 volt limit? (I get 26 volts from being limited to 3lbs of batteries, which means a max of 24-26 Sc cells).

I'm sorry I don't have an actual straight foreword question, I'm just digging for any information. Any ideas and or suggestions would be greatly appreciated. Basically, I'm looking for somewhere to start at, to start experimenting with.

The same guy suggested that I document our plane as we build it, if it sounds like something ppl woudl be interested in I definetly will once we start fabricaiton.

Thanks a lot!

SoCal GliderGuider

Try this part of this web site: http://www.rcuniverse.com/forum/default.asp?forumid=227

More along the lines of electrics.

Do you have a teacher named Edberg?

BMatthews

For the electric part of this I strongly suggest you ask again in the electric motor forums both here and over at rcgroups.com . If you need help with the aircraft structural design then come back and ask here. For airfoil and planform choices the Aerodynamics forum is the place to be.

Campy

My Feedback: (1)

If you don't have MotoCalc http://www.motocalc.com/ I suggest D/L the program. It is free to use for 30 days (about $35 to register ).

You can do a lot of "what ifs" and see what is going to provide the best performance for you - prop, gearing, motor, airfoil, etc.

As far as a plane goes, I suggest looking at the work of Gusippe Bellanca. His Airbus could carry it's own weight. EVERY surface was a lifting surface. A remarkable feat for the early 30's.

cyclops2

The current USAF --A-10 Warthog has a manufactured empty weight of 20,246#-- maximum takeoff weight of 47,400#. And the design is brutaly simple as you can modify the bottom body air dams for even more lifting by the entire bottom of the plane.

Forget the twin engines in the back. The plane is designed to LIFT.-- TO fly easily.-- To take off by it self.-- It has standard, a very arched wing, to fly slow with a huge load in it.

A call to the USAF public relations group, may even get some help setting up the plane for the contest, if you tell them they can put their logo on it.

Lifting is all about, in simple terms, the total weight to be lifted, by the maximum wing area that can be built inside of the rules.

cyclops2

Did a quick check of known heavy weight bombers. True, they lift with engines far more powerfull.

But ability in a job has commons.

plane type-----------------------empty------------------------max.
A-10--------------------------20,246----------------------------47,400
B-1---------------------------192,000----------------------------447,000
B-2-------------------------100,000------------------------------400,000 &&& NO WAY!!
B-52---------------------------236,000-------------------------------480,000

better than 2. 2 to 1 ratios

I will check the B2 somewhere else.