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Old 05-08-2014, 12:13 PM   #1
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What props to use?

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I wish to fly a .40 size Ultimate biplane and I put a .46 OSM in the plane turning a 10/7 prop. Now what prop do I use to safely slow it down and still keep it flying with control . Someone who knows pitch x RPM = speed and the stable speed of the Ultimate could answer say an 11/5 or 10/6 or a prop I need to get could reply it would help me as I am getting to lazy to experiment. In fact talking about being lazy my wife is so lazy she quit tying my shoes!
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Old 05-08-2014, 12:51 PM   #2
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Re: What props to use?

I use 11 x 6 props on most of my 46's, seems to be the best compromise between speed and pull and on a biplane I think would be a good choice.

I prefer MAS in this size, seems to work better than APC on my set ups... I think (IMHO!) APC may be better for top end speed and on slick airframes with MAS better for pull.
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Old 05-09-2014, 12:16 AM   #3
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Re: What props to use?

For me an APC 11x5 has found it's way onto all my 46 size engines.
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Old 05-09-2014, 08:07 AM   #4
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Re: What props to use?

Depending on the engine performance(Make, Age, Fuel used), the RPM's desired and prop clearance (ie in the case if a trike), 45's seem to run best on 10x6 to 11x5 props.

If you want to be lazy, throw anything in that range on it and you will be fine. If you are motivated to experiment, try a couple of flights with each prop on your engine to see how it performs with either prop and decide for yourself what is best.
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Old 05-11-2014, 07:36 AM   #5
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Re: What props to use?

Anything in the combination or winds up being in the same resulting number (11x7 = 77) will give a fairly equal power loading for the engine. However, too large or too small will have problems. I probably wouldn't go beyond 12 inches diameter or below 9 inches.

Question that you didn't answer is if you want the plan to go fast (increase the pitch and decrease the diameter), or slow (increase the diameter and decrease the pitch). What you want is comparable volumes of air moving behind the airplane to provide the same amount of thrust so the plane will actually fly and the flight surfaces will have control.

Also, be sure to check the prop clearance for take-offs and landings -- too big a prop and you'll get ground strikes which can ruin the prop and motor or even the airplane (stumble and cartwheel on landing because you came in nose-down).

Do a bit of Googling around and you'll be sure to find the recommended prop ranges for your motor.

Sad to say, you are going to have to go to the LHS and pick up some props, and play around with them to find the prop and needle value setting that works best.

Like the warning label on other products say, results are the results of others experiences and may not be suitable for your own needs.

Personally, I go for the recommended prop settings and throttle back if I'm going too fast. If still going too fast or run out of airspeed, switch to larger prop/lower pitch.
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Old 05-17-2014, 08:11 AM   #6
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Re: What props to use?

Thanks for all the information, it's working great. I went to the 11X5 prop and it made the plane slower for this old has been and now I have time to get scared when I make mistakes. Before I slowed it down I could only fly it after a haircut as my hair would lift my cap and the wind would blow it away. Thanks a bunch again!
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Old 05-17-2014, 08:33 AM   #7
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Re: What props to use?

Too bad Bolly props are no longer available as they came in 1/2 sizes. For example 10.5 x 6 and 11.5 x 5. Very usefully in fine tuning airframe performance! I miss them.

As someone already pointed out Tommy, try pulling back on the left stick. That can slow a plane down too!!
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