One question that I hope someone can answer. Why do most of the real warbirds have a 3 blade prob but the RC versions use 2?

from what i know rc airplanes don't fly well with 3 blade props. correct me if i'm wrong

The war birds of old needed the ground clearence. The F4U Corsair for example went from a three blade to a four blade as horse power increased. The gull wing gave some rough duty ground clearance but a more efficient two bladed prop would have to be nearly twice as long. The more blades the less effective. A one bladed prop would actually be better than a two. It might be a bear to balance though.


David

Ok, it makes a little more sense. Could I run a three blade prop on a .60 stuka with a saito 100 4 stroke?

what size three blade?

The drop in efficiency is caused by the blade moving through the turbulence created by the blade in front of it.

The more blades the more the turbulence (since the blades are closer)

Three and four blade props look cool though!


Terry

Eeeerrr ... does anyone see if its a 3 or 4 or 2 bladed prop when the plane is flying?

Because multi-bladed props are less efficient in the RC versions. Full size warbirds fly at speeds over 350 mph with their engine turning under 4000 rpm. By the time the same prop blade comes around, the plane is way ahead of its original location and the prop blade is biting into fresh air. On the other hand, the RC version is flying between 60 mph and 120 mph, with the engine turning above 9000 rpm. Thus, the plane didn't move forward a whole lot by the time the same prop blade comes around. As a result, that blade is constantly bitting into turbulent air created by the blade ahead of it.

If you want to swing a large multi-blade prop, then use an RCV "SP" engine since it swings the prop at only around 5000 rpm, which gives you back some efficiency.

You could run either a 13x8 or 13x7 three bladed prop on the Saito 100. The Stuka is not designed to be a fast plane, so losing some speed won't matter.

Richard, thank you very much for the info. I makes a lot more sense now. One last question for you. For the 60 size plane, should I use the Saito 100 or 120?

The Saito 100 would be plenty for the 60 size plane. Even the Saito .91 would be more than enough.

NO WAY would I run a 2 bladed prop on my P-40'S..just doesn't look right..I just put big 4 strokes in little planes.[sm=lol.gif]

Gray 3-bladed prop doesn't look right either Curtiss Electrics are black with yellow tips.

The 1150 HP Allison engine stripped the black paint off the prop![sm=lol.gif]

Another thing to consider is engine load vs. thrust, both on model engines and full size. If you want a scale prop , an engine at the upper end of the range for your model is much better. A three or four blade prop will provide more thrust at a given rpm than a two blade of the same diameter(and pitch), even given the reduction in efficiency, allowing lower engine speeds for a specific airspeed. In a glow engine the danger is overloading the engine, causing overheating and/or detonation. A four-stroke is more desireable for lg. diameter or multi blade props because it develops its max torque at lower rpms than 2-strokes. Turning larger diameter props at high speed is noisier, too, because the prop tips are running closer to sonic speed, and they lose efficiency that way, also.