Need prop for Onex

Discussion for builders, pilots, owners, and those interested in building or owning a Onex.

Need prop for Onex

Postby dfcpac » Sun Sep 17, 2017 6:13 pm

I have a Onex with a Revmaster 2300 I'm ready to test fly but the prop I have is way under pitched
If someone has one around new or used let me know
It's going to take 7 weeks for prince to exchange it.

Thanks
Dan Carley
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Re: Need prop for Onex

Postby gammaxy » Sun Sep 17, 2017 6:40 pm

I noticed from your other post you're looking for a 54X52. What size are you currently using? What method did you use to determine it is under-pitched? I'm using a Prince 54x46 on my 2180 Aerovee and consider it to be slightly over-pitched so I'm kindof surprised you'd need a 52 inch pitch (that's about what the Aerovee turbo uses), but it seems the Jabiru 2200 guys are also using 50+ inch pitches, so not unreasonable.

Sorry I just have questions, I'm always curious about people's propeller experiences. Hopefully someone will see your post and if they don't have exactly what you're looking for, maybe there's a compromise that will work for the near term.
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Re: Need prop for Onex

Postby dfcpac » Sun Sep 17, 2017 6:54 pm

Chris
When I went to full throttle tied down went past red line
This is a Revmaster and has 85 hp. A little more than the aerovee
Prince recommends 54x52 he wil gladly exchange the 54x46
Which i have now. I'm ready to hav e the plane signed off but can't fly it
With this prop
It's going to take 7 weeks to get the new one
Danny
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Re: Need prop for Onex

Postby onex28 » Sun Sep 17, 2017 10:57 pm

I'd like to hear from others who have an R2300 in their Onex. From all the research I've seen a 54 x 44 would be the prop for the Revmaster. Haven't flown mine yet but that is what I have bolted on by Props Inc.

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Re: Need prop for Onex

Postby dfcpac » Mon Sep 18, 2017 2:47 am

You might want it o call Joe from Revmaster about that prop you have. Sounds
Like it might be a problem. Just wondering who recommended
It?

Danny
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Re: Need prop for Onex

Postby Corby202 » Mon Sep 18, 2017 6:37 pm

Don't forget because the aircraft has a 56x48 Prince prop, you cant just put a 56x48 Sensenich prop on or vice versa, the prop companies all have their own way of calculating pitch.
A 48 inch pitch Prince prop would be around 54inch pitch on the Sensenich.
Phil Bird
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Re: Need prop for Onex

Postby gammaxy » Mon Sep 18, 2017 11:33 pm

Danny,
If you don't mind me asking, what RPM is the redline you exceeded static? 3200rpm? If you were closer to me, I'd be interested in swapping my Prince 54x46 with yours since I only get around 2800 static on mine with the Aerovee. I know you've got more power, but man that seems like a lot more power.

I'd expect your extra 6.9% displacement to result in a similar amount of extra torque. The torque required to spin a propeller in static conditions is proportional to rpm^2 (more accurate over small RPM differences like I believe this is), so I'd expect that extra 6.9% torque to yield 3.4% more rpm. If I get 2800 rpm, I'd expect you to get about 2900. My number isn't very exact since I rarely do a static full-power run-up so it could easily be off by 100rpm, but if you're getting well over 3000rpm static, I'd be suspicious of:

  • The difference in torque between my 2180 Aerovee and the 2300 Revmaster is due to more than just displacement. It would be interesting to understand what that difference is.
  • Our two Prince 54x46 propellers are not very similar. Sonex has made a similar claim about Prince propellers when they stopped selling them, but I'm unaware of any evidence.
  • Your tachometer is not correctly counting RPMs. On the Aerovee it's possible to set up the tachometer incorrectly since it counts alternator pulses. I verified mine with a laser tachometer counting the blade directly.

Maybe someone who is flying a Revmaster 2300 will volunteer their propeller dimensions and static rpm.

Corby202 wrote:A 48 inch pitch Prince prop would be around 54inch pitch on the Sensenich.

That's interesting. I know there isn't an exact definition of pitch used by all manufacturers, but I didn't realize it was that different between Prince and Sensenich.
Last edited by gammaxy on Tue Sep 19, 2017 1:48 pm, edited 1 time in total.
Chris Madsen
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Re: Need prop for Onex

Postby dfcpac » Tue Sep 19, 2017 8:17 am

Hi Chris
I'm getting 3700 rpms static withe 54x46 Prince prop could probably go a little
More but I shut it down. I did check my tac with a hand
Held one and they were close. We're are you located?

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Re: Need prop for Onex

Postby gammaxy » Tue Sep 19, 2017 10:24 am

I'm in North Alabama.

For comparison, I get about 3400 rpm in a full throttle descent at 150-160mph. I'd probably be full throttle close to Vne before I got 3700rpm in flight.

Using the RPM^2 rule-of-thumb, this would mean your engine is generating over 75% more torque than mine. Your engine isn't turbocharged is it? That would be funny if I've been giving you a hard time over your propeller and it's been turbocharged all this time.

I suspect either the tachometer is wrong or the propeller is not the dimensions it is labeled. I'm more inclined to believe it is a tachometer problem.

With my laser tachometer, I attached a reflective sticker to the back of one blade to prevent it from counting both blades. Does your airplane's tachometer count alternator pulses like the Aerovee or something on the ignition? I understand it's possible for the tachometer to count correctly at low speed and be incorrect at high speed due to changes to the waveform it's counting, but I'd expect you'd see a jump in RPM when it happens and maybe some jumps back and forth that you don't feel while you smoothly increase throttle.

The easiest propeller geometry to double-check is the diameter. Torque required to turn a propeller is proportional to diameter^5, so I'd expect your diameter to be 90% of mine (48.5") if that's the problem, but that seems extremely unlikely.

If after all this you still feel like listening to a random guy on the internet, you can measure propeller blade angles on the aft surface of the propeller and the chord lengths at the same stations. I could compare it to mine to see if we even have the same propeller. You could probably use one of those digital level cellphone apps. Stand the prop vertical and measure the back edge of the propeller where it's flat near the hub for the 0 degree reference, then rotate the prop horizontal and measure the propeller at a handful of stations. I've been planning on measuring mine this way anyway, so I'll at least have numbers you can compare to. If we were closer, I'd just bring the propeller to you and I'd expect the difference would be obvious to cause the difference we are seeing.
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Re: Need prop for Onex

Postby dfcpac » Tue Sep 19, 2017 11:14 am

If you like to talk
Six three one eight eight 0 two three four three
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