DKjens

My Feedback: (50)

I had one of these setups before, but with an apc14x10. It didn't sound fast, but was when flying with other planes. I sold it, but now I bought another. This one, with the apc11x12 is faster I think, I just worry about the engine. My YS91AC turns this prop at 11.3K on the ground, so it may get to 12k in the air. I am wondering for how long this engine will stay together, and I should probably get an apc12x12.
DKjens

Cyclic Hardover

My Feedback: (3)

Here is my WM .40 size P-51. I am running a ST G90 and a Pitts underneath. I started with a 12/8 apc. Went to a 12/10. The magic prop turned out to be a 12/9 apc. I get around 100mph with this and it is smoooooooth. A .91 four stroke would also be very awesome too. The 12/12 or maybe 13/10 would be a good area to start. The one area I was using as a judge on my prop selection was my climb out after a high speed pass. The 12/8 was not problem. So I thought I want more prop and went to a 12/10. Speed was good but climb out was very poor. 12/9 brought it all together.

RyanG

My Feedback: (1)

About 10 guys at my field fly 40 size warbirds with ys .91 They are all spinning 13x8 and getting about 12,000 on the ground with ys 20/20 fuel. They clock their planes at about 140 and go up for a split S until you can't see them anymore.

bugsiegel

My Feedback: (2)

can a ys .91 turn 18500 out of a dive

jlong34016

My Feedback: (1)

unless you have clocked or radar gunned a plane these guesses are really meaningless. Everyone thought my DD was really going fast too. Radar gun 115. A trainer was doing 85 at the same time. The smaller the plane the faster it looks.

maverick

My Feedback: (12)

Where do you get the radar gun from? How much are they?

bugsiegel

My Feedback: (2)

stay away from the 99.00 ebay job. to get any kind of reading off that gun you have to be almost directly in line and real close to the passing plane. way too dangerous. we had one at the club. we wound up putting it back on ebay for a 15.00 loss.

jlong34016

My Feedback: (1)

I got mine off the internet. There are many to chose from. I went with an expensive one that reads to 300 mph and has good enough sensitivity so a normal pass down center of runway is easily detected. Mine is from Astro Products. Cost 850.00. But there are several that read to 200 mph for under 200.

jlong34016

My Feedback: (1)

www.astroproducts.net

maverick

My Feedback: (12)

Thanks for the tips on the speed radars guys! It is not something I have ever looked at before so had no idea where to start.

DKjens

My Feedback: (50)

Bought an apc12x12 yesterday, and flew it today. My YS91AC turned the apc12x12 at 9700 on the ground. It didn't seem as fast in the air, but I feel better (engine health wise) with this prop. With the 12x12 it may unload to 10700 - 11k in the air, with the 11x12 it may unload to 12300 - 12500 in the air, or what do you think. When does valve float start taking place in a YS91AC, and how big is the chance of valves hitting piston top, or other internal no nos?
DKjens

AeroD79

My Feedback: (2)

WHere did you get your WM ARF mustang from?
Also do you think Saito 100 would do better than YS91?

Btw im the person who I was flying the BLUE mustang at Whittier Narrows...I decided not to move to hawaii ...so im planning to get back my planes together..

BernieG

You can't evaluate precisely how much an engine "unload" in flight (which is not as much true for a 4 stroke than for a 2 stroke anyway), just as it's very difficult to evaluate how efficient/inefficient a given propeller is. So, for the sake of discussion, let's say both parameters nullify each other. What is interesting, is the comparison. You say your engine reach 11.7 thousands rPm on the ground with a 11*12, and 9.7 thousandd RPM with the 12*12. Let's see: 12 inch per rotation 11300 times a minute => 140400 inches per minute, or 8 424 000 inches per hour, which is 132.95 mph.

Now, the same 12 inches per 9700 => 110.22 mph. Knowing that the wider prop is more efficient than the smaller one, I would bet that a radar reading would read about 100, maybe 105 mph with either prop ! (Airplane drag does not change with the prop...) BTW, this estimation assume an extremely aerodynamically clean airplane....

So I would certainly go for the prop which is the more efficient and is not going to wear your engine too fast.

Bernard

BernieG

What I mean is, just the fact to not have doors to close properly the openings when the gear is up take easily 5 to 8 miles from the top speed ! Those planes ARE NOT aerodynamically clean, all the control horns are exposed to the airflow, etc....

Bernard