8.8X9.75 @ 19,300+ !

8.8X9.75 @ 19,300+ !
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8.8X9.75 @ 19,300+ ! - 4/23/2008 2:19:43 AM

freakingfast

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From: mather, CA, USA
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Just for giggles I mounted a OS 46 VX DF engine on a test stand and mounted a new
APC 8.8 X 9.75 prop that just came in. This is the same header length and pipe that I ran an APC 7.4 X 8.25 carbon at 24,500. I expected the engine to lug because the header is too short for this working range. It was fired it up and the engine jumps hard to 19,300, it even liked the same needle setting. I was surprised, but I was wondering if the prop was simply stalled because it’s over square. The test stand was put on rollers (don’t ask) and a scale was attached and the thrust measured just over 8 lbs. Not bad. So it’s slightly stalled but remember some of the thrust is lost/deflected against the test stand too.

I will take it to the field to run more tests with different pipes and header lengths soon. I had to stop, it started to rain and I wanted to give my neighbors a break as well.

I’ve ran this engine on a Diamond Dust before with the carbon prop and tell the truth it seemed slower than my dust with a YS 45 RE and 9X9 prop but the OS sure made a wicked high pitch sound. I think the Dust just needed more disc area than 7.4”.
I’m building another dust for the DF engine, the other sustained some damage from a fuel leak and it’s just easier to build another. I think there may be a lot of potential with the larger prop.

The formula for the safe speed for the pylon prop is 225,000/8.8 = 25,568 rpm, so I think I'm safe there.

The OS 46 VX DF engine is not just an insanely high RPM motor but seems to be strong and well mannered all the way down to a slow idle.

The weight is not as bad as first I thought:
OS 46 VX DF 16.6 oz.
YS 45 RE 14.2 oz.
OS 55 AX 14.3
Jett 60 LX (FIRE) 12.oz

< Message edited by freakingfast -- 4/23/2008 3:06:46 AM >

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RE: 8.8X9.75 @ 19,300+ ! - 4/23/2008 4:37:24 AM

Razor-RCU

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Wow! Great performance....that is quite a load there-

I have also realized that you are in a separate engine category than myself...

I cannot even get my K&B 7.5 to run properly on the pump

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RE: 8.8X9.75 @ 19,300+ ! - 4/23/2008 4:49:42 AM

freakingfast

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Hi Razor!
Is that a K&B Ducted Fan engine. Pump?

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RE: 8.8X9.75 @ 19,300+ ! - 4/23/2008 5:12:27 AM

combatpigg

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Don't waste any more time running it that hard on the ground, it's pointless. Get it in the air!

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RE: 8.8X9.75 @ 19,300+ ! - 4/23/2008 5:41:18 AM

freakingfast

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That will happen soon combatpigg. Curiosity and I think I have an even better pipe makes me want to test a few things, plus I've got a few of these engines. I'm looking into moving the main spar tube to the rear or box frame the center section so the I can install a bubbleless tank. Not sure if I'm going that route. Need at least 8oz. tank, that thing is thirsty LOL.

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RE: 8.8X9.75 @ 19,300+ ! - 4/23/2008 6:16:49 AM

combatpigg

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Moving the spar to the rear sounds good. A strong tie in with the wing tip framing and L.E. and T.E. should work.

Is the engine eating plugs? If not, I agree that there is still power to be found......[)]

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RE: 8.8X9.75 @ 19,300+ ! - 4/23/2008 6:28:10 AM

Razor-RCU

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K&B 7.5CC DF with Pump and Perry carb. Funky pipe though....

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< Message edited by Razor-RCU -- 4/23/2008 6:31:03 AM >

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RE: 8.8X9.75 @ 19,300+ ! - 4/23/2008 7:06:54 AM

combatpigg

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It would be great to be able to gas weld aluminum that well. I've seen it done, the weldor has just a split second to react to the puddle getting shiny. I think it is still taught within the EAA. I asked Macs once what their batting average was on finished pieces and the reply was "not very good in the beginning".

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RE: 8.8X9.75 @ 19,300+ ! - 4/23/2008 7:35:40 AM

idigrc2

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I've gotten my Y.S 45 up to 18,880 with a 8.75x8nn on 40% with a nitro pipe.

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RE: 8.8X9.75 @ 19,300+ ! - 4/23/2008 11:07:25 AM

freakingfast

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quote:

ORIGINAL: combatpigg

Moving the spar to the rear sounds good. A strong tie in with the wing tip framing and L.E. and T.E. should work.

Is the engine eating plugs? If not, I agree that there is still power to be found......[)]

I was thinking the same thing about the spar, the only bummer is it wount build in my fixture

You're right.
I only ran it long enough to warm and tach two quick tests and the only adjustment was to start rich and lean out, so the plug life is not yet known.
A too short header may blow them. I will try 1/2" spacer if needed(the pipe was slipping back and it was gaining speed). A bit more ground test and some air time (barring any foaming) will give me plug life info. Plug are a major issue with the price of rare metals going up and harm to the engine.

< Message edited by freakingfast -- 4/23/2008 1:45:31 PM >

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RE: 8.8X9.75 @ 19,300+ ! - 4/23/2008 11:19:37 AM

freakingfast

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quote:

ORIGINAL: Razor-RCU

K&B 7.5CC DF with Pump and Perry carb. Funky pipe though....

Razor, that carb looks like a Perry non-pump carb (gold anodized wheel). The midrange would be too fat to run right. Perry pump carbs have a blue anodized wheel.
I would like to see it run with a more known/traditional pipe to get some baseline numbers, than try that pipe. I like wierd.

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RE: 8.8X9.75 @ 19,300+ ! - 4/23/2008 11:54:01 AM

freakingfast

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quote:

ORIGINAL: idigrc2

I've gotten my Y.S 45 up to 18,880 with a 8.75x8nn on 40% with a nitro pipe.

Nice plane. I like the retracts.
19k, Dang thats haulin. Good and loud too with no muffler and 40% LOL!

40%....good to know. Some YS's wont take 30% nitro, the compression is too high on some (add head a gasket). Luv those YS 45's

I have not had great luck with nn blades up to now. To me they seem to slip too much/ low thrust. I will try what you did on my 45.

Some time ago, I-Like-Jets posted that the 46 vx df will tach 20k with a 8.75X9.5nn. But I think Im staying with the 9.75 pitch on the DF.

< Message edited by freakingfast -- 4/23/2008 1:42:17 PM >

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RE: 8.8X9.75 @ 19,300+ ! - 4/23/2008 12:25:47 PM

daven

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That is very impressive rpm, in comparison, the Nelson .40 Q500 motor might hit 19k with that prop, but no more.

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RE: 8.8X9.75 @ 19,300+ ! - 4/23/2008 3:09:10 PM

bob27s

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You probably do not have to touch a thing......... it is likely running at a pipe harmonic.

As long as the needle is easy to adjust and set, leave it alone.... fly it. If the needle is over-sensitive or the engine gets hot, then yeah, the pipe is short. Sounds to me like it runs well....... so leave it there.

On the right plane, that prop will unload a ton in the air.

Don't read anything into the over-square stuff too much, and static thrust does not mean squat unless its for take-off acceleration or hovering. Props are designed for flight - dyanamics.

Bob

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RE: 8.8X9.75 @ 19,300+ ! - 4/23/2008 3:11:03 PM

proptop

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FF I will haveta tell Nitro Junky about this, the next time I see him...

FWIW Razor...that's the right pump carb if the throttle bore is .375 and straight through (no venturi, it acts like throttle body fuel injection...sorta

)
The early pump carbs (1970's ) had the natural alum. disc and the old style needle valve (with the spring ) and the later ones (1980's ) the brass like yours...the newest ones are blue.

< Message edited by proptop -- 4/23/2008 3:14:05 PM >

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RE: 8.8X9.75 @ 19,300+ ! - 4/23/2008 3:16:14 PM