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Yamaha 160 lb engine. 130 hp

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cblink.007

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Unless I'm sadly mistaken, a sprag clutch is an 'over-run' clutch. My understanding is that it disengages as soon as the driving force is removed, which will allow the prop to freely windmill. If you're flying a high-drag airframe, the extra drag from the freewheeling prop may get lost in the noise of airframe drag, but it would have a significant effect on a low drag airframe's glide performance.

Or I could be wrong about the sprag...

Charlie
You are correct. I was not saying drag from the windmilling prop was negligible. I was stating that the effects of said propeller windmilling are not expected to kill glide range unless at altitude with my design (a pusher) given the best glide airspeed... this being said, I am looking forward to testing the point when the time comes. Perhaps a better non-sprag clutch design will be developed by that time. I am being led to believe such a solution is under development
 

cblink.007

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I'm itching to buy a Velocity SE and turn it into a mini-V-twin with a pair of 200hp Epex engines. Hmmm.....

View attachment 101488
That might be an interesting idea. Perhaps two Epex motors feeding into a combining gearbox? We have the basic outer dimensions (supplied to us via Mohawk Aero) of the Apex installed (with angle but without PSRU installed), created a box-shaped dummy for fitting against our 25% scale test model. As it stands, we will not need to reshape our cowling, pending virtual fitting on CAD. Fun times!!
 

rbarnes

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That might be an interesting idea. Perhaps two Epex motors feeding into a combining gearbox?
No gear box. Mount one each out on the wings, put a real vertical tail in the middle and ditch the winglet rudders altogether. Velocity has already figured out how to make it work on the XL body and wing, just need to scale it down to fit the SE body and wing. That much thrust on that light a body should equal some insane climb and single engine performance. Combined with Airmaster electric prop with the controller with the "feather" feature. Not mention it would probably be a 200+knt plane on 12-15 gph total.
 

cblink.007

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No gear box. Mount one each out on the wings, put a real vertical tail in the middle and ditch the winglet rudders altogether. Velocity has already figured out how to make it work on the XL body and wing, just need to scale it down to fit the SE body and wing. That much thrust on that light a body should equal some insane climb and single engine performance. Combined with Airmaster electric prop with the controller with the "feather" feature. Not mention it would probably be a 200+knt plane on 12-15 gph total.
Ah ok.. Mini V-Twin. Got it. Was thinking you were considering co-locating 2 Epexs and combining them to a single drive. My abstract thinking in action!

Speaking of fuel burn, I saw this on the Fakebook group:

Apex Fuel Burn TEST-Actual & Calculated

I finally got around to checking ACTUAL fuel burn in the Kitfox-4 / Apex today. I did a small XC that totaled 132 nm that included 3 take-offs & 3 landings. I completely topped tanks before, and measured fuel back in tanks to full when completed via cans. I only climbed roughly 1000-1500 AGL typically. Airports were at 4000' (Susanville, CA) & 5000' (Stead/Reno) elevation and made 1 stop at Dead Cow Lake Bed.
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Conclusion:
I think my calculated fuel burn based on injector duty cycle is pretty accurate. I might be a bit high but always better to land with extra fuel right!
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Actual Fuel Burn, In Flight Average: 3.8 gph
Actual Fuel Burn, Total (startup, taxi, run-up, etc): 4.6 gph
Calculated (AEM EFI) Fuel Burn, Cruise: 4.8-5.1 gph
Safe Range, Time: 5-6 hours
Safe Range, Miles: 400+ miles
Note: Range decreases with increased take-off's, landings, and climbs obviously!
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Here is the data if you want to dissect it some other way:
Airplane: Kitfox 4/1200
Engine: 2006 Yamaha Apex, AEM EFI
Total Engine Run Time: 2.12 hours
Total Flight Time: 1.75 hours
Total Fuel Used: 8.0 gallons
Distance: 132 nm
Altitude: 1000-1500 AGL (4000-6500 MSL)
DA: Approximately 6500'
Wind: Variable direction, less than 5 knots typically
Route: 1/2 North, 1/2 South
Cruise Engine RPM: 7700-8000
Cruise Prop RPM: 2000-2100
Cruise Speed: 85-90 mph Ground
Prop: NR SR118, 81" 2 Blade
 

Vigilant1

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Speaking of fuel burn, I saw this on the Fakebook group:
. . . .

Actual Fuel Burn, In Flight Average: 3.8 gph
Actual Fuel Burn, Total (startup, taxi, run-up, etc): 4.6 gph
Must be some aggressive run-ups and very fast taxi time there!
 

rv7charlie

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I suspect he meant cruise only, and total including all phases of the flight.
Numbers aren't really worth much though, without MAP values at cruise power settings. At that DA, and that rpm, the engine is likely making way under 75% power.
 

cblink.007

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I suspect he meant cruise only, and total including all phases of the flight.
Numbers aren't really worth much though, without MAP values at cruise power settings. At that DA, and that rpm, the engine is likely making way under 75% power.
Agreed. With that post, all I really got out of it was his observed burn rate at cruise...at the conditions he flew at. What the guy wrote about start/taxi/runup (ie the 4.6 gph) didn't make sense to me.

So, with respect to our test plan, when we build our Apex, our scheme of maneuver is to get a couple good dyno pulls to see what power we have at sea level (where our shop will be), along with vibration spectrum data. Taking other known data out there, we will interpolate some kind of performance envelope (with the assistance of an SME, of course). Then, we test against it, properly, and post our findings. Our bird is designed for a 10000 msl cruise, but will run tests at different altitude blocks as well for the sake of data collection and any tweaking of Engine Management software that may be needed.
 

rbarnes

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I suspect he meant cruise only, and total including all phases of the flight.
Numbers aren't really worth much though, without MAP values at cruise power settings. At that DA, and that rpm, the engine is likely making way under 75% power.
And that jives pretty close to what an O-320 lycoming will do. He's saying it's burning 5gph at 75%. The O-320 is also a 160hp engine and it burns about 6gph at 75%. The difference is the Yamaha weighs about 60lbs less. Dyno graphs show the Apex engine makes peak power from 7,500 to 8,000 rpm and flat lines at 160hp all the way up to 10,000 rpm. So he's cruising in the sweet spot
 

vhhjr

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You are correct about the Sprague. I have seen one on these installations in a STOL competition aircraft and the prop just free wheels when the engine is cut. I would think this could be a big problem on a Velocity Twin as they don't have as much rudder authority as a normal tractor aircraft configuration. I have flown in a Velocity with 180 hp and can see the excitement of 400 hp. They take a long time to get off the ground and the extra hp would help with the initial acceleration.

Vince Homer
 

rbarnes

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You are correct about the Sprague. I have seen one on these installations in a STOL competition aircraft and the prop just free wheels when the engine is cut. I would think this could be a big problem on a Velocity Twin as they don't have as much rudder authority as a normal tractor aircraft configuration.

Vince Homer
That's why you use the Airmaster CS prop with "feather" feature. The STOL installs are using fixed pitch props, so they're going to do whatever they're going to do based on windspeed through the prop.... but put a CS prop that you can feather on the engine and now we've got something that should work on a twin.
 

Victor Bravo

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And that jives pretty close to what an O-320 lycoming will do. He's saying it's burning 5gph at 75%. The O-320 is also a 160hp engine and it burns about 6gph at 75%. The difference is the Yamaha weighs about 60lbs less. Dyno graphs show the Apex engine makes peak power from 7,500 to 8,000 rpm and flat lines at 160hp all the way up to 10,000 rpm. So he's cruising in the sweet spot
That doesn't make sense to me. The O-200 in the Cessna 150 uses 6 gallons an hour at cruise. The O-290 I had once burned about 7. The larger Lyc engine has to be burning a little more than that, and I have a distant recollection that most of the stock 320 powered RV airplanes were using about 8 gallons an hour. It is certainly possible to pull the O-320 back to 6 gallons an hour, but I will bet that it's not a real 75% cruise.
 

cblink.007

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That's why you use the Airmaster CS prop with "feather" feature. The STOL installs are using fixed pitch props, so they're going to do whatever they're going to do based on windspeed through the prop.... but put a CS prop that you can feather on the engine and now we've got something that should work on a twin.
I think I need to take a look at the Airmaster prop you mention!
 

rv7charlie

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And that jives pretty close to what an O-320 lycoming will do. He's saying it's burning 5gph at 75%. The O-320 is also a 160hp engine and it burns about 6gph at 75%. The difference is the Yamaha weighs about 60lbs less. Dyno graphs show the Apex engine makes peak power from 7,500 to 8,000 rpm and flat lines at 160hp all the way up to 10,000 rpm. So he's cruising in the sweet spot
Nope; not even close. Just because you're running a Cessna 172 or Cherokee 140 at 'cruise', doesn't mean that you are running at 75%. Any fuel spent on dragging a brick through the air faster than a certain point is just pouring it out the window, so no one runs them at more than about 55-60% power.

Any air cooled internal combustion engine running a carb and fixed timing ignition (mags) is going to burn fuel at a BSFC (brake specific fuel consumption) of about 0.45 pounds of fuel per horsepower, per hour, *best case, properly leaned*. If you do the math, 75% of 160 HP is 120 HP. 120 HP * 0.45 = 54 lbs. 54 lbs / 6 (pounds per gallon) = 9 gallons per hour. Don't believe it? Download a Lycoming operator's manual and see for yourself; it's documented in great detail.

Some people are running a/c engines using electronic ignition with automotive style electronic fuel injection and claiming BSFC numbers down in the 0.35-0.38 range, but I won't believe those numbers without seeing them on a calibrated dyno. I assign about as much confidence to them as I do the C172/Cherokee numbers. 0.42? Probably, but I seriously doubt that they're getting any closer to 0.40 than that.

I can fly my Bendix injected, 1 mag/1 electronic ignition 180 HP Lyc powered RV6 around all day at about 5.8 GPH & 120 kts. Doesn't mean I'm running 75% power, though.

A significant data point about '75%', that seems to be rarely understood, is what it takes to make that 75% power *at altitude*. At around 7500-8500 feet density altitude (depending on pumping efficiency of the engine), an IC engine will make 75% power. BUT...To do that, it must be turning *at its rated rpm to make maximum sea level power*, AND, be operating with the throttle wide open, AND, be leaned to 'best power'. Again, the data is right there in the engine mfgr's operating manual. So for that Apex to be making 75% power at 6500' density altitude, he'd need some combination of being very close to 7500 rpm, and very close to wide open throttle. If you can get him to answer, I'll bet his throttle was at about the 60-70% range, at most. (See the 'brick' reference, above.) If he's running the stock engine controller, he likely has no way to effectively lean to optimum at altitude, and I wouldn't expect the controller to do it perfectly; it wasn't designed for that kind of operation.

Charlie
 

JetProvost

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I have used large German sprag clutches For twin Step up drives on 3ton Centrifuges. If power is switched off the Centrifuge will coast for a very long time. Unless a brake is used the propeller will windmill.
 

rv7charlie

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I have used large German sprag clutches For twin Step up drives on 3ton Centrifuges. If power is switched off the Centrifuge will coast for a very long time. Unless a brake is used the propeller will windmill.
And, the extra drag will greatly affect glide ratio, unless you're flying a 'box kite' that won't stay in the air without power anyway.
 

Pops

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That doesn't make sense to me. The O-200 in the Cessna 150 uses 6 gallons an hour at cruise. The O-290 I had once burned about 7. The larger Lyc engine has to be burning a little more than that, and I have a distant recollection that most of the stock 320 powered RV airplanes were using about 8 gallons an hour. It is certainly possible to pull the O-320 back to 6 gallons an hour, but I will bet that it's not a real 75% cruise.
True-- Lyc -320, 150 hp will burn about 8 gph, 160 hp about 9 gph and the Lyc-360 at 180 hp at about 10.5 gph all at 75% power.
 

cblink.007

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I have used large German sprag clutches For twin Step up drives on 3ton Centrifuges. If power is switched off the Centrifuge will coast for a very long time. Unless a brake is used the propeller will windmill.
This fact has long since been established, repeatedly, and yes, once again, glide ratio will be affected by the subsequent drag of the windmilling propeller!

It is my understanding that this engine/PSRU setup is a consequence of PSRU wear issues due to torsional vibrations and or a consequence of PSRU adaptation and fitting..........and, a better non-free rotating solution is being engineered as we speak.

So, now that we all know for absolutely sure, the theory of operation of a sprag clutch, as well as the aerodynamics of a rotating propeller, I need to ask the other readers here...

This whole category for the Yamaha engines was made by the moderators by popular demand, ostensibly to discuss the powerplant, lessons learned, latest news and such, right? So, why are people insisting on repeatedly bringing up the sprag clutch and windmilling prop issue time, and time............and time again? Yeap, got it; this is a major point of concern. But, this particular issue and its related questions are being asked and have been answered. Repeatedly. We are traveling around in circles!

Not trying to be the bad guy here, but @Dana, looks like some moderation is in order.
 
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