Ace Aviation Redrive: New model

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Vigilant1

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So, the GK 976cc engine weighs 42kg (92.6 lbs), John's redrive might(?) weigh another 5 kg (11 lbs), then maybe a gallon of water/coolant (8 lbs), some oil (2 lbs) and we'd have about 114 lbs. Extras would be the exhaust system and engine mount, prop, maybe the radiator isn't in that weight, etc.
It could be an attractive alternative for planes now using the VW Type 1, at least by weight and HP--the PSRU would get the prop up high so maybe it would even work with stock VW cowlings. The standard Ace 1:1.8 PSRU ratio would turn the prop at 3611 RPM at the engine's 6500 RPM top speed, so even a stock VW prop designed for 75 HP at 3600 RPM wouldn't be a bad starting point, though we might find we need a bit more blade to absorb slightly more HP.
Initial unknowns are cost, total system reliability (at high output, for hours at a time), and availability of parts.
 
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103

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So, the GK 976cc engine weighs 42kg (92.6 lbs), John's redrive might(?) weigh another 5 kg (11 lbs), then maybe a gallon of water/coolant (8 lbs), some oil (2 lbs) and we'd have about 114 lbs. Extras would be the exhaust system and engine mount, prop, maybe the radiator isn't in that weight, etc.
It could be an attractive alternative for planes now using the VW Type 1, at least by weight and HP--the PSRU would get the prop up high so maybe it would even work with stock VW cowlings. The standard Ace 1:1.8 PSRU ratio would turn the prop at 3611 RPM at the engine's 6500 RPM top speed, so even a stock VW prop designed for 75 HP at 3600 RPM wouldn't be a bad starting point, though we might find we need a bit more blade to absorb slightly more HP.
Initial unknowns are cost, total system reliability (at high output, for hours at a time), and availability of parts.

The Gk1000 drive John made for Kevin Armstong 800cc variant is 2.32:1 the ideal for these would be 2.6:1.

Look Kevin up in youtube he was under proped but just installed a new prop. 160kgf static on the 800cc

This has high potential for all type 1 applications to loose some weight and pickup a larger diameter prop for better climb. Don't know if I am ready for fuel injection inam sure it could be switched to carburation with carb heat....
 
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John Penry-Evans

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Not bad. Were you able to purchase it without the gearbox? Did it come with the engine controller, throttle body, injectors, etc? Is this the engine John mentioned earlier? He mentioned 80 HP. This is the 1st one I found in a search, but it says 60 HP.
Thanks,
Charlie
This is the GK engine.
They now make three V-Twins. 61 hp, 66 hp and 83hp versions.
We have developed redrives for these engines.
GK redrive for 83 hp - Copy.JPG
 

John Penry-Evans

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So, the GK 976cc engine weighs 42kg (92.6 lbs), John's redrive might(?) weigh another 5 kg (11 lbs), then maybe a gallon of water/coolant (8 lbs), some oil (2 lbs) and we'd have about 114 lbs. Extras would be the exhaust system and engine mount, prop, maybe the radiator isn't in that weight, etc.
It could be an attractive alternative for planes now using the VW Type 1, at least by weight and HP--the PSRU would get the prop up high so maybe it would even work with stock VW cowlings. The standard Ace 1:1.8 PSRU ratio would turn the prop at 3611 RPM at the engine's 6500 RPM top speed, so even a stock VW prop designed for 75 HP at 3600 RPM wouldn't be a bad starting point, though we might find we need a bit more blade to absorb slightly more HP.
Initial unknowns are cost, total system reliability (at high output, for hours at a time), and availability of parts.
------- > Our standard Ace Aviation redrives for the GK engines are 2.32 ratio
Engine RPM is 6,250 on all engines. So max prop speed is 2,693 rpm

GK redrives.jpg
 

Vigilant1

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------- > Our standard Ace Aviation redrives for the GK engines are 2.32 ratio
Engine RPM is 6,250 on all engines. So max prop speed is 2,693 rpm
The Gk1000 drive John made for Kevin Armstong 800cc variant is 2.32:1 the ideal for these would be 2.6:1.
The best PSRU ratio may differ based on geometry factors that can limit prop length. A Sonerai or Sonex will typically be limited to a 54" prop, and that works pretty well at their typical climb and cruise speed. If we're limited to a 54" prop, a 2.32 reduction ratio may be not be so good. At this prop diameter, an approx 1.8 ratio allows use of a (less expensive) 2 blade prop, will provide considerably better climb, and will give cruise thrust that is close to the same.
For a 54" dia prop, 6250 engine RPM, Jan's program gives:
Prop blades....PSRU ratio.....Prop RPM....80 MPH design speed...........100 MPH design speed..........120 MPH design speed
....2....................2.32.................2693....................unk......................................50% eff................................77% eff
....3....................2.32.................2693....................29%.....................................76% eff................................80% eff
....2....................1.8..................3470....................64%......................................72% eff................................77% eff
....3....................1.8..................3470....................64%......................................72% eff................................77% eff

For comparison: VW at 3600 RPM, 75 HP:
...2.....................Direct................3600....................64%......................................72% eff............................... 77% eff
 
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cluttonfred

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Vigilant1, is there a software tool you are using for those estimates or...? Also, is the 29% efficiency n the second row a typo?

These engines are looking very attractive. If someone with more knowledge than I have were to develop a complete firewall-forward package using an Ace redrive , I think there would be a ready market as an alternative for the many VW-powered aircraft out there.
 

Vigilant1

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I'm using Jan Carlsson's prop design software. The 29% isn't a typo, I can dig in later and see the trends--the program wouldn't even provide an efficiency number for a 2 blade 54" at low airspeeds at this low RPM.
I suspect that with the limited prop length and at this low RPM, it gets difficult to effectively load the blades. There's only so far we can go by increasing blade pitch at low airspeeds before they are effectively stalled and efficiency plummets. Maybe a 4 blade prop would help. But a 2 blade wood prop is a simple, light, inexpensive thing that works well at the typical 120+ MPH cruise speeds of these relatively clean planes. The simple answer in this case would be to reduce the PSRU ratio a bit so those props can also work well at climb speeds.
 
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cluttonfred

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Cool. Just out of curiosity, how does this work out with the standard Ace ratio for a two- or three-bladed 60” prop, which is the design diameter for a VP-2?
 

Vigilant1

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Cool. Just out of curiosity, how does this work out with the standard Ace ratio for a two- or three-bladed 60” prop, which is the design diameter for a VP-2?
Here's how things look at 60" diameter. In all cases, the props are optimized for the shown airspeed.

For a 60" dia prop, 6250 engine RPM, Jan's program gives:
Prop blades....PSRU ratio.....Prop RPM....80 MPH design speed...........100 MPH design speed..........120 MPH design speed
....2....................2.32.................2693....................66%......................................75% eff................................79% eff
....3....................2.32.................2693....................70%.....................................77% eff................................81% eff
 

cluttonfred

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Thanks much! Definitely some food for thought for a VW alternative in a VP-2.... If I understand correctly, this is working backwards from aerodynamic considerations and will tell you the engine power needed at a given speed? It looks like a four-bladed prop might be worth it at VP speeds.
 

Vigilant1

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If I understand correctly, this is working backwards from aerodynamic considerations and will tell you the engine power needed at a given speed?
Not precisely. The user inputs the engine RPM and HP at that RPM, the program assumes you are telling the truth (i.e. that the engine can make that power at that RPM). The program then computes the torque at that RPM and uses the user-supplied prop diameter and cruise airspeed to design the prop and to tell you the efficiency of that prop. We can manually compute thrust if desired using
Pounds thrust = Engine HP x prop efficiency x 375 / airpseed (in MPH)
 

pictsidhe

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Thanks, I haven’t done much with prop efficiency so it sounds like there is a lot I need to learn.
It's pretty simple: Size is everything! 75hp into a 54" prop at 80mph is going to need huge blades...

I use javaprop. I have not been able to compare it to JCs program, as the latter is now unobtainable. But it seems to give sane answers that are in the ballpark.
 

cluttonfred

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Let me put it this way...what percentages are considered excellent/good/fair for efficiency and how does that translate into rough guidelines for power/speed/diameter/number of blades? That’s all. ;-)
 

Vigilant1

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General observations:
1) All fixed pitch props are compromises.
2) Props usually have lower efficiency at low airspeed, and gain efficiency as the speed approaches their design speed.
But (see formula in post 33), even as their efficiency may be increasing with airspeed, the thrust they produce decreases at higher speeds (note the airspeed in the denominator of the thrust formula. That's the culprit).
3) Fixed pitch props still perform fairly well at airspeeds below their design airspeed. Things get bad quickly at airspeeds above their design speed (a 75% efficient prop will be about 40% efficient at airspeeds 30% above it's design speed. I think the blade just runs out of AoA)
4) Roughly-- with wood fixed pitch props I've looked at, of practical lengths and 3000 to 3600 RPM, optimized for cruise, I'm used to seeing 65-70% efficiency in climb and 75-80% efficiency in cruise.

I don't know much about props. There are enough nested interdependencies that it looks like black magic IMO.
 
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pictsidhe

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Let me put it this way...what percentages are considered excellent/good/fair for efficiency and how does that translate into rough guidelines for power/speed/diameter/number of blades? That’s all. ;-)
It's complicated...
Fred Weick wrote a great book. It is available here as a pdf. I had a print on demand copy made.
 
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