Rozandshu

Hi All,

If a mate of mine changes the variable two blade prop on his Cessna 182 for a variable 3 blade where can I find out about the improvement in takeoff roll etc?

Cheers Rozandshu

Longbow55

You will have to ask other folks, for the best answer. Those that I have seen have it done, there is an increase in climb, but top cruise speed drops by 2-3 knots. Haven't been told of takoff roll.

PAPI-74

Increaseing the number of blades will reduce the load on the prop. This is done to allow a smaller diameter of prop and therefore a lower RPM for the same performance. A lower RPM means less noise as the tips have a lower velicity and are more efficient (less turbulence from sonic tips and a nice ride from the cockpit).
This will also increase the take off performance as SOLIDITY (aspect ratio of the blade disc) is increased. The other way to do this is to increase the blade chord, but this will effect the gravitational forces on the prop and as it produces more lift, the CTM force will twist the prop to fine with massive stress, obviously reducing efficiency.
If solidity is increased, so is drag at idle power......it will drop like a brick on the threshold so land with a squirt of power and once over the TH, reduce it at the same rate as you want to sink when in ground effect.
SOLIDITY=number of blades x chord/2PYEr (if it helps)
JD

PAPI-74

mind you, with the best will in the world, I don't think a C182 can drop like a brick......can it?
But a low wing a/c would. Try it and see.

Mark 1

Most people seem to go for 3-bladers because they think that they look better.

In most cases there is only about a 1 inch diameter reduction.

Going to smaller diameter and higher solidity will give less noise, reduced static thrust and improved cruise thrust, all else being equal.

The noise reduction is due to a lower tip mach number for a given RPM and an increase in the blade passing frequency; and the thrust reduction is due to the propeller having to move a smaller amount of air at a higher velocity to achieve that thrust. This requires more work input to produce the same momentum reaction (propulsive efficiency).

It will also cost about £1000 more, be heavier, and almost impossible to hand swing.

drauk

Plenty of scientific answers already, which is great. I doubt you'll find solid figures, so people's impressions will be your likely best answer -- alas, a notoriously poor way of evaluating anything in my opinion.

I used to fly a 3-blade 182 and now a 2-blade 182. I think the 3-blades looks better, take-off performance seemed slightly better and ground clearance is a good few inches more. All the differences seem fairly minor to me. Certainly I wouldn't change one for the other unless it was time for a new prop anyway.

Cusco

We replaced the 2 blade c/s prop on our Arrow 2 with a 3 blade c/s prop several years ago:
The main reason was that FOD from landing at another airfield had written off our prop and surprisingly we got a far better deal on the 3 blade than a 2 blade.
The change of prop has made absolutely no difference to the performance: the only difference discernible is an increase in vibration which persists despite dynamic prop balancing.

Safe flying

Cusco

microlight AV8R

The EV-97 Eurostar is now available with a 3-blade for an extra £300 or so. As a retrofit I understand it would cost circa £1800. The improvement is a gain of about 15mph cruise for the same rpm which equates to 10litres per hr at 100mph airspeed. Technical justification aside, the 3-blade does look very good.

Human Factor

Which equates to it paying for itself in fairly few hours.