Prop size - bigger vs smaller

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Prop size - bigger vs smaller

Unread post by lampiesJR » Wed Jul 13, 2016 9:04 am

What is the advantages of a bigger prop installed compared to a smaller prop?
Lets take a bigger prop. What I can think of is it will give better climb and make better use of the incoming air but it will put more strain on your engine and engine mounts. Apart from that, how wil the bigger prop affect maneuvers like tumbling, spins, snaps etc. where the prop's gyroscopic force plays a big role?

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Re: Prop size - bigger vs smaller

Unread post by Aerodon » Wed Jan 04, 2017 5:29 am

Oh, I think you could write a book on this subject. It all depends what you are trying to do. There are so many variables I don't know where to start. Fixed pitch climb and cruise props. Constant speed 2,3 and now 4, 5 blade. Aluminum and composite. Even between manufacturers, there can be a huge variance in weight and performance for similar performance props.

In general we rely on the airplane manufacturer to make good selection of 2 or three good props. But this might not be optimum as it may be based on corporate relations (Cessna and McCauley both owned by Textron), price, availability etc.

Then other manufacturers come along and develop STC's and claim some performance improvement. For my Seneca I could go from the factory McCauley 3 blade to a heavier Hartzell 'Top Prop' or a much lighter MT prop. I don't think there is any advantage in changing to Hartzell, I just think they wanted to make their prop available to Seneca owners. The MT is lighter and they do claim a slight increase in climb and cruise. I'm also told they are much smoother. But I know enough about torsional vibration to know that lighter does not mean better. The engine and prop really need to be tested together, and its an expensive process. It gets real expensive to change and each option may have an advantage.

Mooney did a lot of research on the 231 and settled on a wide chord 2 blade prop for best high altitude cruise, because they were chasing speed and economy. A different prop may well have been better for low altitude shorter flights.

The Aerostars with the smaller diameter are faster - so they are converting the same power into more thrust.


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