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Old 08-28-2005, 08:00 PM   #1
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YS rpm regulating

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I am just starting to setup my F90 with YS110 after about 4 flights on it. First 2 flights i used a Zinger 15x6 (it's all I had) on 15% pink stuff. I tacked it at 9300 on the ground. Today i flew it with a APC 16x6 on the same fuel and it tacked at 9100. The difference between the 2 props was amazing. With the 15x6, it would hover at 90-95% throttle barrel opening with very very little pullout but with the 16x6 it will hover at about 75% throttle barrel opening and pullout is ok. I guess this leads up to my main question: How is it that the YS engines swing so many different props at the same rpm? From my experience with 2 stroke engines and Saito's, the bigger the prop, you get a fairly significant rpm drop at full throttle. Going from a Zinger 15x6 to an APC 16x6 is a fairly substantial change in engine loading however the YS still spins it at pretty much the same rpm at WOT. Does the YS engine have some sort of built in rpm governer? Or is it a function of the pressurized fuel system/air chamber system?
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Old 08-28-2005, 09:39 PM   #2
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Actually all you are seeing is the engine being loaded down into it's torque band. I've found that YS engines seem to develop there best power around the 9000 rpm area (I think I mentioned that to you the last time we talked). Here is a useful formula D2 x P = PL Where D = diameter of the prop, P = Pitch of the prop and PL = Prop load factor. I don't think formula explains all the forces acting on a prop but it works So if we plug in the numbers.

15(2) x 6 = 1350 9300 rpm
16(2) x 6 = 1536 9100 rpm
15(2) x 8 = 1800 9000 rpm????
14(2) X 10 = 1960 (I have this prop in my truck for you to try)

Looking at the prop load factors my choice would be a 15 x 8 and get the engine down around 9000 rpm.

To answer your questions No YS's aren't governed.

Hope this makes sense.

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Old 08-29-2005, 06:59 AM   #3
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When comparing same size props from different manufacturers, different size being pitch or diameter, a baseline has to be established.

First and the easiest, is the 6.0" pitch actually what it says it is? At what stations along the prop blade does the pitch change. Are the prop airfoils the same. Unless those facts are known then it is impossible to say why one make of prop is better than another. We have to rely on the engine to tell us.

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Old 08-29-2005, 07:15 AM   #4
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Thrust Calculator

I don't know where I came across this little program but is is a prop thrust calculator. I don't know how accurate or usable it is but if anyone wants it send me a PM with your email.

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Old 09-02-2005, 09:26 AM   #5
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Re: Thrust Calculator

Originally Posted by Propworn
I don't know where I came across this little program but is is a prop thrust calculator. I don't know how accurate or usable it is but if anyone wants it send me a PM with your email.


The program is called "Thrust HP". Just do a web search and you will find it quickly. The site is currently under some maintenance tho. The program works very well to give you an idea what to expect for from different props. It allows you to compare the load and Hp requirements of two props at the same time. What you really get when you fire up the engine will not be exactly the same as the program. Ie you will not get exactly xxxx rpm from xyz prop. However, the expected results will be in the ball park and the results from one prop to the next will be mostly true.

I use the program for initial prop choices on a new engine. Pick your target rpm and plug it in. Pick the base pitch you are going for (4" 5" --10" whatever) - do you want speed or do you want tractor thrust. Plug that in. Then start putting in different prop diameters until you achieve a "horsepower" value that is about 85% of what the engine is rated for. (Iterate) Take that prop and one on either side of it to the field and go fly/experiment. It is a good tool. It works for me.


When changing diameter or pitch you should be using props from the same manufacture to achieve the expected results. Some times staying with the same pitch and dia and just changing manufacturer will make a big different. A Master Airscrew performs dif than a APC performs dif than a Zinger performs diff than ....
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