I'm planning to put Conversion engines on a big WW1 vintage - Twin Engine Bi-Wing. The airplane specs are as follows:
Wing Span : 163.4 Inches
Length : 104.7 Inches
Weight : 42 Lbs
Wing Surface : 7936.2 Sq. Inches
Wing Load : 12.2 Oz/ Sq. Ft
Would like for the plane to fly realistically, but - with some measure of reserve power. The thing is a huge brute with a very light wing loading - may need a long runway. Plan to have the engines turn in opposite directions. Any suggestions or comments would be appriciated.

Sides7

With that light a wingloading at that size an aircraft, you could just about put a couple of the weakest Weedeater 18cc on there and still fly "scale" for a WWI biplane.

You may want to consider also the shape and size of the "cowl" or engine nacelle to see what engine configuration might work best. If they are long and narrow, RIRE engines like the Ryobi 31 might work best. For short and broad noses, SISE would be better. If you plan on counter-rotating the two engines, you may want to look around for pusher prop availability for the sizes you may need for particular engines, as their selections are typically not very extensive.

Hi sides7

I am almost done my B-25 with twin Ryobi's. You say your plane weighs 42 lbs. Each ryobi weighs 4 lbs, that's 50 lbs. You can expect an average of 12 -13 lbs of thrust from each ryobi depending on how you prop it. To me it would look underpowered. The one advantage of a ryobi though is it is rear induction making it a streamline installation.

Peter[img][/img]

Thanks for responding guys.
The twin Ryobi's may be an acceptable solution as I already have one of these in "flight ready" status and another waiting to be converted. At 50 to 55 Lbs, my initial reaction was to put two Poulan 46cc in & let it rip. I know 50 Lbs sounds like a lot of weight, but with the extremely light wing loading----- Well that 's why I came to the forum because I'm not sure? My guess now is, given a long enough runway, realistic flight can be acheived as stated by Volfy, ie as small a conversion gasser as is available. However, Peter G. points out, flying with two Ryobi's, is flying that much weight with only about 26 lbs of thrust???????
Peter G. - that B25 is sure a good looking ship. How did you do the polished Aluminum looking finish? Did you convert one of the Ryobi's to run in the opposite direction?
If anyone out there has some more input, please pass it on.


Sides7

Thanks sides7, the aluminum comes as is and costed less than $10.00. It is basically the same stuff as flight metal only he sells it at a great mark up. I have them both running counter clockwise, intend to put a gyro in her for the rudder, insurance for a dead stick on one engine.

Peter

Hello sides7,
I just seen your question and something came to mind. You can convert Homelite 33cc bandit chain saw very easily and have much power then a 31cc Ryobi. A neat idea that I had for reverse rotation is to have a hub made for the tail shaft of the engine. This will give reverse rotation with the engine mounted with the flywheel in the rear. No modification of ignition is necessary and you can use the stock flywheel and coil. The engines will mirror each other also, with both carbs inboard etc. My 33 weights exactly four pounds with muffler. Best the saws are $99 each at homedepot brand new.

Regards, Dave

Two Poulan 46s will give you about 36 lbs thrust....
I would think something like two Q52s would be ideal, or some 3.2 Sachs conversions....
Or some Red Max 62cc chainsaw conversions, 50+ lbs thrust...

How about (2) 34cc 4 cycle Briggs & Stratton Fource engines. It would sound so realistic and fly very scale.

I don't think any WWI aircraft has anywhere near 1:1 power-weight ratio. Probably not even 1:5. I don't know which WWI aircraft you're modeling, but 163.4" wingspan is at least 30% of the real thing. At that scale, it will likely have flight characteristics very similar to full scale. I think a couple of Ryobi 31cc will give a good measure of reserve power. At the quoted 26lbs of combined thrust, that'll yield a 1:2 power-weight ratio. Not at all bad for a WWI vintage twin.

sides7,

The airplane sounds exotic.

My experience is that twins have some unique problems. It might be a good idea to build or bash a less complicated prototype twin. The bash could be used as a test bed for the engines and to gain twin experience.

Someday when I run across a beat up, used up airframe I would also like to bash a wing for two Ryobi’s.

Bill

Bills
The airplane is the Vickers Vimy, WW1 Britsh Bomber. It is produced by 3 SeeBees Models in an ARF, ARC and Museum Quality versions. I'm seeking an optium gas conversion engine selection for this model. Right now I'm leaning toward the two Ryobi 31cc engines OR a pair of homelite 33 chain saw engines.
Sides7

The 3 SeeBee kit calls for 90-.120 2stroke (glow I presume). Ryobi 31 would be plenty power, and the RIRE might hide better in those nacelles. Very interesting project.

Sides7,

I believe either engine would fly your project successfully.

A gas engine twin would be a lot of fun. Twins have their own unique flight characteristics especially when it comes to engine out. I simply would not attempt any complex (high time and expense) project without plenty of flight time with the same gas engines on another less expensive airframe. Call me conservative because I also would not attempt a twin until the same engine had been flown in a single.

Bill