My 13B engine configuration (tentative)

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PMD

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My memory is of Tracy saying that those bearings only saw load in the car when the clutch pedal was depressed. Was a long time ago; could be defective memory. Certainly much less load than that imparted by the helical cut sun gear.
Don't be so sure about that. When you consider the approximate mechanical advantage between clutch pedal travel and release bearing travel is way over 10:1 it isn't hard to appreciate the axial load on the crank from clutch operation can be in the hundredS of pounds. The helix angle of a gear x the radius of rolling contact point x engine torque just can't produce any force of that magnitude. The reason cars with tiny thrust faces can get away with it is that the duration of the loading is fairly brief whereas a gear thrust or propeller thrust in nearly constant.
 

rv7charlie

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[sigh]
I guess I was too general in my comment. Clutch pressure plate loads are (relatively) smooth in buildup and release, and extremely rare, compared to the twice-per-rev hammer blows from combustion events for the entire time the engine is driving the prop. See Finn's comment about the input shaft spline pattern hammered into the end of the E-shaft.
 

dwalker

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[sigh]
I guess I was too general in my comment. Clutch pressure plate loads are (relatively) smooth in buildup and release, and extremely rare, compared to the twice-per-rev hammer blows from combustion events for the entire time the engine is driving the prop. See Finn's comment about the input shaft spline pattern hammered into the end of the E-shaft.
The input shaft cannot hammer the spline pattern into the end of the e-shaft, it just does not work that way.
I have had MASSIVE clutch force- capable of holding 1,000hp and not had a single thrust issue in the 13B.
In fact, I have had an automatic torque converter balloon to the point that in a piston engine it would have destroyed the thrust bearing and in fact machined the face of the converter on the flexplate counterweight bolts, but I have never seen any issues with the thrust in a rotary.

Now that said, I can see that in the PSRU itself there could be a thrust issue without a proper thrust bearing, because of the prop load on the prop-shaft. See the drawings below. The planetary gear is not designed to handle any thrust loading in its usual home inside a auto transmission, but has no choice when bolted to a prop shaft.
 

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PMD

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[sigh]
I guess I was too general in my comment. Clutch pressure plate loads are (relatively) smooth in buildup and release, and extremely rare, compared to the twice-per-rev hammer blows from combustion events for the entire time the engine is driving the prop. See Finn's comment about the input shaft spline pattern hammered into the end of the E-shaft.
I would hate to have to calculate those numbers, but I was not thinking (clearly) about #1 the variable angular velocity of the engine output, #2 the total slop in the gear train, #3, the inertia of the rotary side and #4 the potential size of the harmonic TVs coming back from the giant ringing flywheel stuck on the other end of the drive.

Do you suppose that might be why amateurs seldom design workable PSRUs?
 

dwalker

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the potential size of the harmonic TVs coming back from the giant ringing flywheel stuck on the other end of the drive.
I believe there is a reason that Tracy and others have moved to elastomer or similar discs and aluminum flexplate/flywheels when building a planetary or other gear driven PSRU.

It will be a few weeks before I pull the PSRU off the engine and tear both down, maybe even a month or more, but I will document when I do.
 

PMD

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I believe there is a reason that Tracy and others have moved to elastomer or similar discs and aluminum flexplate/flywheels when building a planetary or other gear driven PSRU.

It will be a few weeks before I pull the PSRU off the engine and tear both down, maybe even a month or more, but I will document when I do.
Will be watching with great interest.

IMHO: one of the most important things that genav overall can learn to do is build better PSRUs. First of all, it allows higher RPM thus potentially lighter prime movers and lastly it allows for far more propeller efficiency - not that I need to tell most of the people on this site, but IMHO one of the fundamental failings of genav over the past half century. When people mention Rotax, I have to point out that I have been around them and watching their involvement (and buying a LOT of engines - for airboats ans some for airplanes) and I genuinely believe their main accomplishment was to make reliable drives. The engines anyone could build, but they did an outstanding job of the re-drives (courtesy of a LOT of influence from Ron Shettler).

I have in the past also watched a century old automotive engineering company attempt to dabble in aircraft conversion of one of their engine designs. Things went really well until they went from dynos and test clubs to bolting an aluminum prop onto the gearbox. They had to find a genuine TV guy to fix the problem (obviously not me, I was a casual observer). Now, that being said: ALMOST anyone with enough money can hire the TV guys to solve the applied problems, but it seems very few people have ever learned to do so on 180 degree or fewer power pulses without hanging an ugly boat anchor on the end of what could have been a nice, light and potentially economical engine.
 

Cardmarc

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What happened to the Defiant these engines came from? And has anyone broken down and examined the internals of the successful Mistral PSRU?
 

dwalker

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What happened to the Defiant these engines came from?
My understanding is the fellow that built it passed and his family donated it to a museum. The museum got it to run and taxi, then decided to remove the rotaries and installed some sort of Lycoming. Now, I am very fuzzy on those details, so it could just as well be it was donated to a museum, the museum traded or sold it and the new owner converted it, but that is the best of my knowledge.
I can say I would not want to fly a Defiant on these normally aspirated rotaries. Even if we are generous and say they are 180hp each the performance during taking off and climb would be.. lackluster at best. Now turbocharged... changes that game, but these were not and in fact the exhaust is of such poor design I cannot see how the engine I have would have made 130hp at best.
 

FinnFlyer

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Perhaps the clue is RPMs. I assume it's unusual to have the engine running at 6,000+ RPM when activating the clutch.
Tracy had to change input shaft thust bearing design after failures. Apparently continuous high RPM loads on roller bearings shorten their lifetime.

I seem to recall seeing the input spline pattern on the end of the e-shaft after about 250-300 hours with the Ross drive, and I did not run it particularly hard.

Finn
 

dwalker

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Perhaps the clue is RPMs. I assume it's unusual to have the engine running at 6,000+ RPM when activating the clutch.
Tracy had to change input shaft thust bearing design after failures. Apparently continuous high RPM loads on roller bearings shorten their lifetime.

I seem to recall seeing the input spline pattern on the end of the e-shaft after about 250-300 hours with the Ross drive, and I did not run it particularly hard.

Finn
Yes, we normally expect the drivers to shift between 9800 and 10,000rpm.

Perhaps the issue was in the PSRU and not the engine?

I really need to understand how you are seeing an input shaft spline pattern on a tapered/keyed shaft.
 

FinnFlyer

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Have you taken the Ross PSRU apart?
Have you looked at the end of the PSRU input shaft that goes into the hollow end of the e-shaft? The splines go into the clutch (dampener) plate, but also continues and rests against the end of the e-shaft. Each combustion event turns the input shaft which has helical cut gears, which pushes the input shaft against the e-shaft. If you had straight cut gears it would not be an issue.

Finn
 

Lendo

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I remember someone saying that Ross's Son didn't do the quality work that his father did, but to my mind any Ross drive is suspect for the reasons mentioned. I haven't heard bad reports about Tracy's drive. Someone mentioned Paul Lamar's time to climb PSRU suffered badly blued Thrust Bearing.
George
 

dwalker

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Have you taken the Ross PSRU apart?
Have you looked at the end of the PSRU input shaft that goes into the hollow end of the e-shaft? The splines go into the clutch (dampener) plate, but also continues and rests against the end of the e-shaft. Each combustion event turns the input shaft which has helical cut gears, which pushes the input shaft against the e-shaft. If you had straight cut gears it would not be an issue.

Finn
Are you not using the pilot bearing? There is a reason the eshaft has a needle bearing pilot bearing. I'm going to look into this as I see no reason for the gears to have that much movement in the gears.
I can't wait to get it apart. At some point it will go to Colorado to be cryoed and if a thrust bearing or shim stack needs to be added that will be no issue.
 

Vigilant1

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I can say I would not want to fly a Defiant on these normally aspirated rotaries. Even if we are generous and say they are 180hp each the performance during taking off and climb would be.. lackluster at best.
The original Defiant, with two 160hp NA O-320s and fixed pitch props, climbed at 1,600 fpm. ( And it climbed safely on one engine, too.) Maybe not a rocket ship, but it is as good as many light twins (Twin Comanche, Cessna 310, Cessna 340, etc). If the 13Bs could make 160hp each, I'd think the Defiant would climb well. But, yeah, with turbocharging the climb (and cruise up high) would have been better still.
The Defiant has very impressive cruise speeds and single engine performance considering it used fixed pitch props.
 
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dwalker

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The original Defiant, with two 160hp NA O-320s and fixed pitch props, climbed at 1,600 fpm. ( And it climbed safely on one engine, too.) Maybe not a rocket ship, but it is as good as many light twins (Twin Comanche, Cessna 310, Cessna 340, etc). If the 13Bs could make 160hp each, I'd think the Defiant would climb well. But, yeah, with turbocharging the climb (and cruise up high) would have been better still.
The Defiant has very impressive cruise speeds and single engine performance considering it used fixed pitch props.
The 13B I have sitting in the warehouse is simply not capable of producing 160hp. The biggest problem is the exhaust they installed. The engine in OEM form made 146hp if you believe the manual. Put the must more restrictive exhaust on it and I would expect this motor to struggle to make 120, if not closer to 100hp.

Which honestly is neither here nor there, as I have no plans to run an NA motor at all.
 

FinnFlyer

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Are you not using the pilot bearing? There is a reason the eshaft has a needle bearing pilot bearing. I'm going to look into this as I see no reason for the gears to have that much movement in the gears.
I can't wait to get it apart. At some point it will go to Colorado to be cryoed and if a thrust bearing or shim stack needs to be added that will be no issue.
Sorry that I can't explain it better to you. Helical (slanted) cut gears will always introduce longitudinal forces on the gear shaft and gear holders. With the Ross PSRU those forces on the input shaft are transferred to the e-shaft and handled by the roller bearings at the other end of the e-shaft. The e-shaft pilot needle bearing is for radial forces (keeping input shaft centered) and not relevant in this discussion.

So, yes, if your Ross PSRU does not have an added input shaft thrust bearing you need to add it. No a big deal, other than choosing one that can handle the forces at high RPMs.

Finn
 

Cardmarc

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Use a planetary redrive a la Tracy Crook, Mistral, Ross, et all. Don't use anything else. Unfortunately, currently I don't know who even makes these anymore, but the planetary design is superior to all others. Why have turboprops and helicopter used them for ages? Just need a bulletproof tested design like Mistral had perfected!
 

rv6ejguy

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Several viable gearbox designs besides planetary. Hundreds of thousands of WW2 inline engines used spur gears for instance, the Marcotte internal pinion gear is also well proven.
 

dwalker

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If there was a reasonably stable demand for a psru for the rotary I would think of making them, but near as I can tell the Marcotte works and is available if someone wants new. There are several RWS and ROSS PSRUs out there in the used market. The cost to tool up and develop/test a PSRU at this point is simply too high for the return.

I am quite sorry I have not moved forward faster on this, I have been spending all my time lately divided between flying, working on my Dragonfly, and some other lingering projects. With any luck I should move forward much more rapidly towards the first of the year.
 
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