8.8X9.75 @ 19,300+ !
04-22-2008, 08:19 PM
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8.8X9.75 @ 19,300+ !
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.[X(]
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
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.[X(]
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
04-22-2008, 10:37 PM
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RE: 8.8X9.75 @ 19,300+ !
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 
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
04-22-2008, 11:41 PM
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RE: 8.8X9.75 @ 19,300+ !
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.
04-23-2008, 01:06 AM
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RE: 8.8X9.75 @ 19,300+ !
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".
04-23-2008, 05:07 AM
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RE: 8.8X9.75 @ 19,300+ !
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......[)]
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......[)]
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.
04-23-2008, 05:19 AM
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RE: 8.8X9.75 @ 19,300+ !
ORIGINAL: Razor-RCU
K&B 7.5CC DF with Pump and Perry carb. Funky pipe though....
K&B 7.5CC DF with Pump and Perry carb. Funky pipe though....
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.
04-23-2008, 05:54 AM
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RE: 8.8X9.75 @ 19,300+ !
ORIGINAL: idigrc2
I've gotten my Y.S 45 up to 18,880 with a 8.75x8nn on 40% with a nitro pipe.
I've gotten my Y.S 45 up to 18,880 with a 8.75x8nn on 40% with a nitro pipe.
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.
04-23-2008, 09:09 AM
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RE: 8.8X9.75 @ 19,300+ !
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
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
04-23-2008, 09:11 AM
#15
RE: 8.8X9.75 @ 19,300+ !
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.
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.
04-23-2008, 09:16 AM
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RE: 8.8X9.75 @ 19,300+ !
ORIGINAL: freakingfast
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.
ORIGINAL: Razor-RCU
K&B 7.5CC DF with Pump and Perry carb. Funky pipe though....
K&B 7.5CC DF with Pump and Perry carb. Funky pipe though....
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.
04-24-2008, 11:13 PM
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RE: 8.8X9.75 @ 19,300+ !
The ground testing is over.
Here is the setup so anyone can emulate the results:
Engine: Well used but excellent condition, OS 46 VX-DF (purple head).
Pipes are pressure taped at the apex.
Prop is an APC #LP88975 Pylon 8.8X9.75 (hole reamed out to .375”)
Short shaft adapter (Tru Turn part number TT-0141-A)
Glow plug OS #8.
Fuel: Wildcat 30% nitro 23% synthetic (Curtis Youngblood label),
I forgot to bring the Power Master 30% heli.( I like some caster)
These are stable peak readings, not the needle setting for flight.
And here are the two best pipe results:
First up was the Macs quiet tuned pipe #1050 and it’s best RPM was just over 20,000.
The tuned length measurement was 9 7/8” cylinder centerline to apex or 10 7/8” to first inside baffle. This ended up only 5/8” longer than the first test.
High speed needle open 1 1/8 turn.
The best for last. Macs muffled pipe #1250 with a top speed of 20,400 rpm.
The tuned length measurement was 9 7/8” cylinder centerline to apex, the same length as above !!!??
High speed needle open 1 ½” turn.
You realy need hearing protection with this one! And I did remember to bring it.
The engine would maintain a very reliable Idle of 3000 rpm on both pipes.
Two different tachs were used to confirm all readings. Air temp was 67*
I brought a nitro pipe but it did not have a pressure tap so I setup an i.v feed 20” (gravity).
I used a filter as a line coupler and the feed proved too restrictive and I could not see a rich setting so this test was aborted. This pipe was barrowed so I didn’t want to modify it.
The testing consumed 24oz. of fuel and the glow plug still looks fine.
Looking through the exhaust port, the piston looks great.
The best air speed may be found with a shorter tuned length setting so it peaks in the air as it unloads. So what combatpigg and bob27s said is probably correct.
I may shorten back later. At first I didn’t think it could unload in the air past the props safe speed of 25,568 but now I’m not so sure anymore. I may have to tone it down with less nitro??? LOL.
One Thing left to do…Fly it on the Diamond Dust.
Here is the setup so anyone can emulate the results:
Engine: Well used but excellent condition, OS 46 VX-DF (purple head).
Pipes are pressure taped at the apex.
Prop is an APC #LP88975 Pylon 8.8X9.75 (hole reamed out to .375”)
Short shaft adapter (Tru Turn part number TT-0141-A)
Glow plug OS #8.
Fuel: Wildcat 30% nitro 23% synthetic (Curtis Youngblood label),
I forgot to bring the Power Master 30% heli.( I like some caster)
These are stable peak readings, not the needle setting for flight.
And here are the two best pipe results:
First up was the Macs quiet tuned pipe #1050 and it’s best RPM was just over 20,000.
The tuned length measurement was 9 7/8” cylinder centerline to apex or 10 7/8” to first inside baffle. This ended up only 5/8” longer than the first test.
High speed needle open 1 1/8 turn.
The best for last. Macs muffled pipe #1250 with a top speed of 20,400 rpm.
The tuned length measurement was 9 7/8” cylinder centerline to apex, the same length as above !!!??
High speed needle open 1 ½” turn.
You realy need hearing protection with this one! And I did remember to bring it.
The engine would maintain a very reliable Idle of 3000 rpm on both pipes.
Two different tachs were used to confirm all readings. Air temp was 67*
I brought a nitro pipe but it did not have a pressure tap so I setup an i.v feed 20” (gravity).
I used a filter as a line coupler and the feed proved too restrictive and I could not see a rich setting so this test was aborted. This pipe was barrowed so I didn’t want to modify it.
The testing consumed 24oz. of fuel and the glow plug still looks fine.
Looking through the exhaust port, the piston looks great.
The best air speed may be found with a shorter tuned length setting so it peaks in the air as it unloads. So what combatpigg and bob27s said is probably correct.
I may shorten back later. At first I didn’t think it could unload in the air past the props safe speed of 25,568 but now I’m not so sure anymore. I may have to tone it down with less nitro??? LOL.
One Thing left to do…Fly it on the Diamond Dust.
04-25-2008, 12:42 AM
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RE: 8.8X9.75 @ 19,300+ !
Should work ok. You need to move the firewall back some for CG reasons and put the fuel tank under the wing in the main compartment. The engine and new mount will make the plane a tad nose heavy if you dont. The main task is in making the engine mount. Use a riser header (you may have to cut both header and pipe so that you dont need a cut at the bend) and mount it over the wing than the exhaust will shoot right between the V tail. I was looking in to it too
04-25-2008, 12:45 AM
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RE: 8.8X9.75 @ 19,300+ !
freakinfast- Awesome info. man I have got to keep my eyes open for one of those....[)] That is pretty insane for an engine that will idle at 3K. [)]
Anybody have a header or pipe or both for a K&B 7.5cc?
Anybody have a header or pipe or both for a K&B 7.5cc?
04-25-2008, 09:40 AM
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RE: 8.8X9.75 @ 19,300+ !
great summary ........ and well prepared data.
Good to see the engine performace well and runs consistante.
The quite pipes usually do run a few rpm below the old type muffled pipe or the nitro pipe..... so that shift is about right.
Id probably leave the pipe length alone and just fly it like that
Needs a good home. I bet it would fit great into that Streaga 45 Look is building in the other thread [&:]
Good to see the engine performace well and runs consistante.
The quite pipes usually do run a few rpm below the old type muffled pipe or the nitro pipe..... so that shift is about right.
Id probably leave the pipe length alone and just fly it like that
Needs a good home. I bet it would fit great into that Streaga 45 Look is building in the other thread [&:]
04-25-2008, 10:15 AM
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RE: 8.8X9.75 @ 19,300+ !
ORIGINAL: freakingfast
At first I didn’t think it could unload in the air past the props safe speed of 25,568 but now I’m not so sure anymore. I may have to tone it down with less nitro??? LOL.
One Thing left to do…Fly it on the Diamond Dust.
At first I didn’t think it could unload in the air past the props safe speed of 25,568 but now I’m not so sure anymore. I may have to tone it down with less nitro??? LOL.
One Thing left to do…Fly it on the Diamond Dust.
04-27-2008, 10:52 PM
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RE: 8.8X9.75 @ 19,300+ !
I decided to try and reuse the Dust that had fuel damage and it’s not as bad as I first thought.
I used some “Stick it” where some fuel got on the wood and test covered that spot. The covering was destroyed trying to remove it again, so the test was a success. A Sullivan SS8 (8oz.) tank will be used. Foam used under and sides will keep it isolated and an OS bubbleless clunk will be used. If the fuel foams, I will look into a bladder in the tank, but it didn't need it when I ran the high RPM carbon prop, hope my luck holds.
I’m framing up another one too.
I used some “Stick it” where some fuel got on the wood and test covered that spot. The covering was destroyed trying to remove it again, so the test was a success. A Sullivan SS8 (8oz.) tank will be used. Foam used under and sides will keep it isolated and an OS bubbleless clunk will be used. If the fuel foams, I will look into a bladder in the tank, but it didn't need it when I ran the high RPM carbon prop, hope my luck holds.
I’m framing up another one too.