Extreme Speed Prop Planes Discuss the need for speed with fast prop planes (Screamin Demon, Diamond Dust, Shrikes or any REAL sound breakin'''' plane)

15 cc Heli engine faster ?

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Old 09-29-2012, 12:44 AM
  #1
ger56
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Default 15 cc Heli engine faster ?

Hi ,

Question : Why not using heli engine like :91HZ-R 3D Speed Competition Heli Engine
instead of Jett 90 or webra 91 etc ....

Seems performance are better ?

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Old 09-29-2012, 02:31 AM
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Default RE: 15 cc Heli engine faster ?

It really helps to have the engines that you are comparing in your hands so that you can physically examine them for their potential air handling capabilities. Assuming that the engines are equal in quality of materials and finish, you are left with only one last way to compare the engines and that is with a speed prop that would be feasable to use on that size engine.
The high performance engine designers / builders who cater to the speedplane market most likely do these comparisons on their own with engines that are in the popular sizes for racing and speed.
Your helicopter engine might be a great discovery..?
I'll bet the true speed freak fraternity over in Europe have had very few commercially available engines of any type get past their watchfull eyes un-noticed.
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Old 09-29-2012, 03:58 PM
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Default RE: 15 cc Heli engine faster ?

It's been done before on 46 size war bird, except it was powered by YS 91SR-3DS two stroke heli engine with a Mac tuned pipe running an APC 11x11 15.500 rpm on the ground. and it unloads in the air!
That's some serious power, about 3.8hp. It does not seem to have the poor mid range that's exhibited by some other heli-on-prop conversion I've seen. Heli's work hard at part throttle(hover), prop engines do not. hence the carbs are set rich in mid range and some just have problems leaning when proped.
You would need to contact Tru Turn to select a "short shaft adapter" in order to run a prop on SOME heli engines. There is no free lunch for power, expect to consume about 6 oz. a minute of 30% fuel at continuous full throttle.

If your wallet is deep, you could substitute the OS 91HZ-R 3D for OS 105HZ-R. Same weight and bit more power at a lower RPM, both desirable for a big efficient prop. More HP=friend, more RPM=bad.
Same thing said for YS 91SR-3DS to a YS 120SR. I do not know how the mid range mixture will respond on the OS and the YS120SR engines, that may need some tweaking. The bigger engines may be happier with less nitro TOO!
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Old 09-29-2012, 04:12 PM
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Default RE: 15 cc Heli engine faster ?

That YS 91 was on Marcelo's Spitfire that was quite draggy and heavy. Somewhere around 9 lbs I think. I think that the use of any 2 stroke requires a clean, light airframe. I have been reasonably successful going this route. My Rossi .45 powered Macchi held it's own against Marcelo's Spitfire. I have a Rossi .61 powered version that is just not quite fast enough to run in gold. Spins the same 11X11 at 13,500 on the ground. If I was able to have gotten it down to 5.5 lbs it would have had a chance. I am slowly coming to the conclusion that the 4 strokes are going to give better top end speed with the drag coeffecints we are dealing with.
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Old 09-29-2012, 04:19 PM
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Default RE: 15 cc Heli engine faster ?

Speed, your planes have the frontal area and drag of a friggen dart! LOL
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Old 09-29-2012, 07:07 PM
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Default RE: 15 cc Heli engine faster ?

LOL Thanks. Wait until you see the next generation. All composite with YS 115 power. Working on the fuse plug now.
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Old 09-29-2012, 08:00 PM
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Default RE: 15 cc Heli engine faster ?

I'm envious [&o] I wish I had the time to scratch build.
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Old 10-01-2012, 03:08 AM
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Default RE: 15 cc Heli engine faster ?

Freakingfast

Do you want to say the 4 strokes may give better top end speed with the same propeller in case of bigger airframe ?
What 4 strokes are you thinking about except Ys ( need Nitro I do noi use ) Vs Webra P5 or Novarossi R91 we have strongly tested .

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Old 10-01-2012, 10:47 AM
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Default RE: 15 cc Heli engine faster ?

the newer carbs on the 60-90 size OS heli engines are as good as it gets, i have been running a os-sx-wc with nelson minipipe, with the three needle carb..the midrange needle makes it very easy to deal with peaky pipes and small props....i have use 11x6 thru 11x12 and 12x8 12x10 props apc , so far zero issues i did run out of pipe resonance with the nelson ultrathrust at 16,500 rpm . carbs come in 10.5 MM throat diameter and work just fine with pipe pressure.
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Old 10-01-2012, 12:14 PM
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Default RE: 15 cc Heli engine faster ?

lfinney :

16500 rpm with what prop
What Rpm did you get with a 12X8 and 11X12 ?
Nitromethane ?

Best result with a R91 plane engine was 14600 rpm with an 11X9 APC on the ground sea level 15°C

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Old 10-01-2012, 01:20 PM
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Default RE: 15 cc Heli engine faster ?

16,500 rpm with 11x6 on wildcat premium 15% with three ounces of sig castor merlin 2003 and k&b1l 13800 on 12x8 apc same fuel and plug, my next runs will be with nelson AAC sleeve and piston with exhaust timing of 172 degree duration, piston and ring seem fine with this 6 gallons thru engine so far, i did run several tanks of 30 percent heli fuel with 23 percent oil ran fine original plug still

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