Quote:
Originally Posted by Piotrsko
Other huge advantages: no exhaust in your face, ditto for prop blast. Having friends that designed these, correct engine placement seems to be not that difficult.
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Surely having the engine in a the right place helps balance the vehicle. But I'm talking about propeller placement which is a totally different animal.
When the aircraft takes off the rear is going to have to go down and the front go up in order to lift off. With a propeller in the front this allows for a bigger propeller that still sits in line with the center of gravity. But a propeller in the rear means you either have to install a smaller propeller, or make the air craft sit higher off the ground on it's wheels, or position the propeller up above the center of gravity. All of these have a disadvantage. A smaller propeller, for an example, wouldnt' be able to deliver as much thrust. Therefore the most popular "solution" is to just move the propeller up above the center of gravity of the aircraft.
Look at this picture and see how the center of the propeller is very high compared to the center of gravity. This setup means that under power you're pushing the nose down. So you have to use the cyclic (rotor) pitch control to push the nose back up. This makes for a situation that certain changes could cause the vehicle to suddenly nose dive or nose up and go backwards. Lose power and you could suddenly nose up. Lose air speed (try to climb a little too quickly) and you could suddenly nose dive.
This is especially problematic in a vehicle that can have as little as 0 (or even negative) forward speed. If you're going very slow or even "floating" straight down and then suddenly hit the throttle, perhaps with the intention to start climbing again, you could suddenly nose dive.
With the engine in the front it can be placed in line with the center of gravity without making the propeller super small. That way it pulls the vehicle in a straight line making it just as safe (if not safer) than a fixed wing aircraft since there'd be no need to compensate for the properller being off the center of gravity. That's because thrust won't affect pitch so you don't have to compensate. Hit the throttle, let off the throttle, speed up, slow down, it won't affect pitch. The nose stays the same.
Quote:
Originally Posted by Piotrsko
If it won't yaw without power, then it doesn't have enough rudder.
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Remember were talking about a vehicle that can have as little as zero forward speed. Normally under zero speed you don't have yaw because you have no air going over the rudder. Going very close to 0 speed also makes you have very little controlabilty.
But with the propeller right in front of the rudder the vehicle will yaw under power even if it was previously "floating" straight down. This is because thrust from the propeller blows right over the rudder.
But with the propeller in front then yaw is much more vehicle-speed dependent. If you're "floating" straight down in a front-propeller autogyro and then suddenly want to yaw you can't just hit the throttle and a rudder pedal and turn. You have wait for the vehicle to get back up to speed in order to get enough air moving over the rudder in order to turn.