Hi Robert,

That prop would work, but your plane will go slower, albeit cruising with much better fuel efficiency. The bigger problem is that your static RPM will be much lower than it really should be, which means that your takeoff performance will be severely reduced.

If it was a case where you were asking about a prop somewhere between 68 and 72 pitch, I wouldn’t even mention it, but 80 is pretty far out there.

If you look at page 24 of “part 2” of my paper on Q200 aero performance modeling ( http://n8wq.scheevel.com/documents/All_Text_and_figures_Part2.pdf ), you will see how much horsepower is needed (to overcome induced and airframe drag) for level flight at different airspeeds. My model is matched to the performance of the factory demonstrator N81QA(chart shown below).

If you were using a prop with a pitch of 80, and you were able to turn 2900 RPM (prop efficiency of 87%) it would get you to 191 mph. However, flying straight and level at 191 mph CAS in the conventional Q200 configuration, the amount of drag would require more than 150 HP (unless you have really pared down all of the drag elements, like Sam Hoskins has done over the years).

In your case (standard O-200), you will generate  104 HP at 2900 (at sea level), then you would burn all your power up in drag at around 168 mph. An 80 in pitch prop at 87% efficiency, would be turning only 2550 RPM at 168 mph. But…. at that RPM, you would only be making about 92 HP, so the speed would be further reduced, and the RPM would also be reduced, so realistically that 80 in. pitch prop will probably be turning just north of 2300 RPM before you reach a dynamic equilibrium and no matter what you do, you cannot turn the engine/prop any faster with that prop pitch, even at full throttle. The result will be much better fuel economy, and a slower airplane

…..But I return to my previous point, you will not like the takeoff performance at all. It could even be dangerous!

Cheers,

Jay

Wow that was a terrible spell error on my part ... I meant to say Prince recommends a 58/70 prop. So back to my original question ... the 60/80 prop won't work for the 100hp, correct?
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Robert "TheFrisco" Schmid
(408) 805-5450

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Love building planes almost as much as flying. Latest completed build is "Loki", a Chinook Plus 2 bush plane.