Ultralight questions

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Nichoxx

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Jul 6, 2020
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Hi,
I am fairly new to the world of ultralights and I have a few questions I was hoping you could answer about an ultralight I would be hoping to base my own project off. (Some of them are probably very stupid)
All of my questions refer to the Quicksilver MX Sport: http://www.quicksilveraircraft.com/images/MX SPORT/scan0003-1.pdf

I would be after the same propeller which is a 66x34, however what else do I need to know? Do I need to ask for it to be a pusher propeller? Is that a thing? Etc
The engine used in this is 40hp which seems awfully low for a propeller of this size? I was expecting to use a 100hp converted engine, for this propeller will I need that much power?
Also the RPMs shown would put that propeller over speed of sound which I thought was bad?
 

Dana

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The propeller isn't spinning at 6500 rpm, there's a reduction drive, I think 2.58:1, so the prop is only turning around 2500.

100HP is way too much for a Quicksilver.

A propeller doesn't care whether it's a puller or pusher, what does matter is the direction of rotation, RH or LH.
 

radfordc

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Hi,
I am fairly new to the world of ultralights and I have a few questions I was hoping you could answer about an ultralight I would be hoping to base my own project off. (Some of them are probably very stupid)
Maybe not stupid, but certainly shows that you lack a great deal of knowledge of the subject. What sort of project are you considering? And, why not just get a nice used Quicksilver and have some fun.
 

Nichoxx

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The propeller isn't spinning at 6500 rpm, there's a reduction drive, I think 2.58:1, so the prop is only turning around 2500.

100HP is way too much for a Quicksilver.

A propeller doesn't care whether it's a puller or pusher, what does matter is the direction of rotation, RH or LH.
I couldn't find if they used one but I guess they do. What happens with 'too much' HP
 

TFF

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In general the traditional ULs are physically not strong enough for a heavier engine or the extra 60 hp push. There is no extra fat on something like that to cover big changes.
 

Dana

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Also, with that much power the plane would be too fast to qualify as an ultralight.
 

Tiger Tim

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I am fairly new to the world of ultralights
Hi Nichoxx,

Perhaps before we get too into it, it would help to let us know what country you’re in and why you want to design your own airplane. The answers to both could be a big help in getting advice due to regional regulations and whatnot.
 
Last edited:

Nichoxx

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But surely more power does not equate to more RPM, an engine has an RPM and surely once its got enough power to turn it at a certain RPM no matter how much more powerful the engine gets, the propeller is the same (eg 50hp at 1000rpm vs 100hp at 1000rpm)
 

TFF

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A 100 horsepower engine turning a 50 hp prop at your 1000 rpm is only using 50 hp of its 100. There is still 50 to spare, and the little 50 hp prop will not be able to restrain the 100 hp engine if the user throttled it to 100 hp. Power will have to go somewhere if you use the excess; rpm is unrestrained unless you don’t make enough power. A 50 hp engine at 1000 rpm and a 100 hp engine at 1000 rpm will be completely different in design as the requirements were different.
 

WonderousMountain

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I am going to go ahead and say sure,
you can use your 100HP, 150 pound
engine, or you can use the 50 pound
30 Horse. Aircraft designers usually
chose as light an engine as will make
sufficient power for their airframe.

Also, it is true, excess power in
small craft will add a failure mode,
Engines are controlled, propellers
will usually just fly faster with throttle open.

LuPii
 

Dana

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But surely more power does not equate to more RPM, an engine has an RPM and surely once its got enough power to turn it at a certain RPM no matter how much more powerful the engine gets, the propeller is the same (eg 50hp at 1000rpm vs 100hp at 1000rpm)
No, if you take propeller designed for a 50hp engine and put it on a 100hp engine, the engine will overspeed.

Regardless, 100hp is too much power for a Quick, and almost certainly too heavy. What kind of "100hp converted engine" did you have in mind?
 

radfordc

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An internet friend of mine built a TEAM Minimax some years back and powered it with a 95 hp converted snowmobile engine of some sort. He tried flying the plane and it was an absolute dog and scared him to death. He finally took some good advice and reengined the plane with a Rotax 503 and now he loves it.
 

Lendo

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Most props are sized to the power the engine produces (all other things being equal).
George
 
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