Hey i love ww2 planes and saw a German plane that had one pusher and one puller prop. counter rotating to counter act the spin. this made the plane extremely fast. I'm wondering if you could design a plane that uses that same Technic to achieve extreme speed.
The plane you're talking about is the Dornier Do335 "Pfeil". Someone on the forums is already working on one, so you might want to check their thread out.
As a speed model, there's probably easier ways to achieve high speeds, since the second prop working in the wash of the first one will be less effective. The reason the 335 was designed the way it was would provably be that they couldn't squeeze more power from a single engine but wanted to keep drag to a minimum. With a brushless motor your limiting factor is not the motor, but how to feed it enough electrical energy so it can achieve maximum powrr output.
An interesting note is that in spite of all that power, the Do-335 was not the fastest piston aircraft deployed in WWII (474 mph), being outpaced by the P-51H (487 mph). I think it may have been the fastest to see combat, though, by the narrowest of margins (P-47M at 473 mph). It's worth noting that the current piston speed record lies with the single-prop, direct drive Rare Bear, at roughly 523 mph. (I've seen quotes that it could do 550 at altitude.
What this means for us is that the best speed is going to come from a direct drive, high speed, high pitched propeller on a single motor airplane. The only exception for this item would be in regards to aircraft which are sensitive to torque, which is why the propeller driven seaplane record set by the double-engine, contra-rotating prop Macchi MC.72 has stood for nearly 80 years and is unlikely to ever be broken.
Hey I built that! It's done, just waiting for a Maiden. I'm thinking about sending it to josh to maiden. To make it scale I had to make it quite large. If you want the rough plans I have some sheets of paper I made for it I could scan and email you.