New engine for Sonex.

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tdpilot

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Feb 20, 2011
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The gearing at say 3.2 would produce a prop rpm of 2500 and that multiplies the torque to 275!
Your computations reflect my thinking. With this kind of torque, I would be able to turn my very coarse prop at the power to give me good takeoff performance, and with shifting gears, I would also be able to utilize that coarse pitch for high speeds. All my work, WHICH IS MINIMAL since the only thing I am doing is adapting a strong prop shaft support to the engine, is empirical. I really don't care about "numbers" yet, because I have yet to prove the concepts. The engine is ready to mount into the plane right now with its prop adapter already on. I just have to mount the cog belt drive, and connect things. But, I do have other projects with much higher priorities. The engine conversion is a labor of love, because that is where my real interests lie. And, if it doesn't work, then I will remount the VW that came with the plane, and sell the whole thing. Very little cash out, and a nice idea at least that satisfies my curiosity as to whether I could revolutionize aviation. Or not.
 

danman

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Will you have a support bearing outside of the output pulley to take side loads from the belt?
 

Aviacs

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Elmira, NY
The ratios of engine to output shaft are "interesting".
As an aging Britbike guy, i'm not sure i accurately understand the Honda engine's architecture; but it seems that into the gearbox, the ratio is pretty close to .550. 1st gear is 1.90, so x another .526, = .290 at the output shaft (5000 rpm engine, 1450 rpm output shaft)
5th gear is .697, so .550 x 1.435= .790 at the output shaft (5,000 rpm = 3950rpm output shaft) (Online reference sources were used for gear ratios for VTX1300 engine. I carried the operations on my calculator, but some answers above are rounded within less than 1%. )

It's probably going to only be practical (useful) to use 2 or 3 adjacent gears (out of 5) in the box. Again, my familiarity is ancient Britbikes so this may or may not apply: Top gear & bearings arranged to take full power 100% of the time. Lower gears & bearings were not expected to be used for constant running. If this applies, then your ratio between the final drive and the propshaft should probably be based on the top 3 gears; and dependent on the diameter prop you hope to drive.

There's a lot of weight, heat, wear, & lost power in the 3 steps of ratios (Primary & secondary drive in the engine, drive ratio between transmission output shaft and propshaft) not including the loss in the tranny itself. Seems like chopping off the gearbox and using a cheap electric controllable prop would be more efficient.
But i already said that in a previous post.

moving along, any chance you'll at least try the set up on a sled/test stand for a few hours with the intended prop and check all systems before moving it onto your airplane?

smt

Edited:
PS: In digging deeper i see that once again, i got confused by which Honda 1300 is to be used. Numbers above are in reference to the V-twin, not the V4. Without adding further confusion, my intended points are:
1.) because of primary reduction between engine and gearbox in a motorcycle powertrain, the output shaft in 5th gear may be close to the final drive ratio of a given propeller, at high cruise speed. Verify.
2.) the ratios in a bike box are fairly wide; in terms of efficient propeller driven rpms - probably only 2 or 3 will be useful - choose them biased toward high gear as that is probably the one the manufacturer made most durable for steady high output.
3.)Is it really a good idea to keep all the stages of rpm manipulation up and down, for an airplane engine?

Good luck, many of us are interested in your success.
 
Last edited:

tdpilot

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Feb 20, 2011
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Will you have a support bearing outside of the output pulley to take side loads from the belt?
Not planning on it, Danman, tho I might possibly. That would be a rather heavy addition. The forces that the shaft will be subjected to by the belt are rotational and torsional. torsional is what the shaft is designed for, of course, and the rotational forces are also of a sideload type that is evenly spread across the shaft in all directions as it turns. Sideloads are generally assumed to be critical in the type of bending forces encountered with a prop strike, or extreme gyroscopic forces such as in an Acro plane such as my Christen Eagle. The Eagle, by the way, is shaft-limited in some planes--It requires a solid shaft to be legal in competition. That is a somewhat unusual shaft in most planes with an IO-360. Some lighter shafts in that engine have parted company with the plane. And it hasn't been the shaft that failed, but the flange. You have to remember tho that the acro shaft flange suffers extreme gyroscopic loads, repeatedly every single flight. Either one of those forces are far outside of what the Honda shaft will be subjected to in driving a simple belt gear--it doesn't have the leverage of a propeller. I don't foresee it being a problem, but that is again one of the things that will only be proven when I actually fly the plane. --- After about 1,000 hours of "proofing", which of course I will never reach. And, I guess I am a little jaundiced about the chances of the shaft breaking. If it did, it would only result in a precautionary, thrustless landing. It won't cause anything drastic like losing a prop would.
 

danman

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Ok, I just figure most shaft drive engines are not designed for a side load. Good luck 👍
 

tdpilot

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Feb 20, 2011
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Ok, I just figure most shaft drive engines are not designed for a side load. Good luck 👍
Actually, they are in the bearings. It is the strength of the shaft that might be affected, which is why the VW engine is really a kinda skeptical engine for aircraft. If you get a hard prop strike, even with a wood prop, you have the probability of bending the shaft. That will lead to potential, even probable failure if uncorrected. Your comment has been well received by this pilot/engine developer.
 

danman

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Actually, they are in the bearings. It is the strength of the shaft that might be affected, which is why the VW engine is really a kinda skeptical engine for aircraft. If you get a hard prop strike, even with a wood prop, you have the probability of bending the shaft. That will lead to potential, even probable failure if uncorrected. Your comment has been well received by this pilot/engine developer.
Its called experimental for a reason. :) I asked because my son and I used that technique in his go kart when we mounted a v-twin MC shaft drive engine on it. The short splined shaft didn't look too solid with a sprocket for 50 hp. Hopefully yours is longer with more area to mount a pulley. I can't wait to see this on a plane.
 

Aviacs

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Elmira, NY
What is your intended cruise rpm on the engine?

From torque curves published on the web, it looks like the Honda at aprox 5500rpm could be competitive with a 2180 VW at 3300 rpm. (Would have aproximately the same HP & torque (with reduction to 3300 rpm propshaft) at 5500, as the VW does at 3300 direct drive. (At least without the gearbox drag on the Honda :^) ) The Honda's torque and HP fall off faster with lower revs, than does the VW, though. Above 6,000rpm, the Honda appears to win, but can it be used for more than TO & occasional rapid climb?

5500rpm looks like about the same as 103mph in the bike? Thoughts on TBO? For instance, if it is cheap and easy to overhaul, even 500 hrs might be acceptable. ( crudely, same as 51,500 miles @ 103MPH on the bike) Of course I have no idea what is actually a reasonable guess.

So if you can make it work with no loss in aerodynamic efficiency, it's down to whichever is lighter and more durable, and then which is more cost effective.

Really wish you'd get done "sandbagging" (your storm surge barriers :) ) & get on with trying the engine.

smt
 


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