BMatthews

Here's a twin project that I started working on recently. It's a cargo model that's intended to carry about 5 or 6 lbs of payload (video mini cam.... ) and perform a lot of functions using a replaceable mission pack and nose section. The nose is removable as is the lower fuselage. Options for new pods are a one peice flying boat nose and hull lower with plug in wing tip floats, a bomb drop belly pod that has a latch to allow dropping up to 10 bombs one at a time or all at once, the camera belly with numerous windows, a plug in rack that lets me piggyback gliders up to 2 meter wingspan and the coup de resistance....... a belly launcher system for the radio controlled rocket plane powered by two F class Estes motors........

Span for this puppy sits at 100 inches. I'll be using all my free flight building experience to keep the basic model weight down to about 6 lbs and power is planned to come from 2 OS 25FP engines. The wing is going to use the Selig S4026 airfoil and flaps will be used for landings and takeoffs. The attached drawing shows flaps and aileron but I'm seriously thinking of using spoilers for roll control and 80% span flaps instead. The fuselage will be a hollow composite of inner and outer fiberglass skins with localized carbon with a 3/8 core of blue styrofoam. Inner structure will be kept to a minimum to allow maximum room for different payloads.

I've had the concept for some years now and originally ran the numbers in the David Fraser sailplane performance software. At it's empty weight it shows as being quite capable of thermal soaring but with the Dumbo fuselage the sink rate went up for higher speeds...... Ya right.....

At least no one can acuse me of small thinking...... I've been thinking of this one a lot recently so it's just possible that this might be the winter. I'm going to get the plans done at least and see how my time goes from there.

Edwin

My Feedback: (2)

BMATHEWS,
Except for the wing tips and number of engines, I've been thinking along the same lines. I have 4 matched engines I want to put on a cargo type of plane, then drop things out of it. Just about have the rear door mechanism thought out. Its still a distant project, but will be drawing up plans in cad soon enough. This would be a proof of concept for a latter C-130 project. I got in my mind to do a low on the deck unload proceedure with a drogh chute. Drop out about 5 paratroopers. Would spice up a fun fly or our airshow flight demo.
Edwin

BMatthews

Edwin, what size engines?

The idea of the size for this one came from the Quickie 500 with a 25FP I had. It was 3 1/2 lbs and flew like a rocket. So when I was trying to figure out what I could get away with on the twin I sorta used the DeHavilland Mosquito school of design and just figured double the wing area and double the weight. Simple but it should work. For the gross weight max I felt like the Quickie would have flown "adequitely" at 2 lbs over with no problem. That means it would climb at a reasonable pace and land at a reasonable speed. So the 11 to 12 lbs gross takeoff weight came up. The empty weight projection came from my one foray into large models. I've got an 84 inch Roger Hammer Flamingo old timer. This is one big pully of a model. The ready to fly weight was only 5 lbs on this one but I had to add 1/2 lbs of lead in the tail to balance the engine. The engine for this one is a OS 35 loop scavange model from years ago and it still climbs way faster than I need.

So all in all I'm pretty confident that I can build the twin here to an empty weight of 5 to 6 lbs. This is with all the engines and radio gear.

The redline speed won't be too high though. No heavy maneuvering for this one.

Edwin

My Feedback: (2)

I have four .40's. Will probably be in the 90" to 100" range. I'm starting with the TwinStar moments and basically almost doubling the size. Then move the wing to shoulder mount.
Edwin

BMatthews

I think that would be a little small. Let it fly on the wing instead of the props. I admit I'm going a little too far in the other direction but for me it's a personal challenge to build it down to the target weight. In your case the structure required to brace the wing for the engines that far outboard would require a fair bit of extra structure and at 100 inches you might be going for too heavy a model. With 4 40's I'd say go for 120 inches and about 1400 to 1600 sq in's. If you were to build it using advanced sturctures I think you could easily go for 150 and 1600 to 1800 sq inches and still have a great flying model. It would be easy to build it to about 10lbs assuming you use any structural finess at all. With 4 40's it would be a rocket and it would carry 4 or 5 lbs like it wasn't even on board.

And with that much power a flying boat lower or floats would make a float flyer option easy.

I think a lot of our thinking as a group these days is based around very high power to weight ratios and we've forgotten how to fly on the wing. Certainly speed management becomes more an issue with a larger model with a lighter power loading but this just brings us into the realm of the fulll size cargo carrier pilot's shoes. That 35 on my old timer is hauling around the 1000 sq inches and 5/1/2 lbs with no problem. In a 45 second contest climb I'm getting about 300 to 350 feet high. There's NO need for a cargo model to climb that fast when fully loaded. Come to think of it your 4 40's would have a 25 lb load limit and would STILL climb as well as my old timer..... provided you give them the wing area to fly. If you use my quickie 500 example you should still be using 2000 sq inches of area and 6 lbs per engine. That would be 24 lbs gross. So a 14 lb model would give you a 10 lb payload.

Am I helping? Anyone else? Multi's of this stature are so rare compared to overpowered aero machines that I think we are in a new realm that needs some study and rationalisation. Great fun this.....

Edwin

My Feedback: (2)

Those deminsions were basically off the cuff. I still have 2 or 3 more twins to build and fly to become more proficient. And familiar with what is necessary when designing a cargo carrying model. The last .40 powered B-17 I saw was 120" wescraft that flew at one of our airshows. It did allright. No overpowered at all. I was figuring a little smaller and more power, but may re-examine based on your thinking. We'll see.
But, I do like over powering from time to time for the thrill and speed.
Edwin