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Thanks for the info Bill. Sounds like it was the input shaft thrust bearing that went out. That is without question the most highly stressed bearing in the drive. All the others have easy jobs by comparison. That bearing requires the cooling of the oil flow via a very small passage through the input shaft. That’s why full oil pressure to the drive is important. Now that you mention it I do recall Dave asking about the effects of ‘T’ing the turbo oil supply on the same line as the drive. That could potentially drop the pressure too much, especially on -4 lines which the drive calls for. Tracy Sent from Mail for Windows 10 IFRC the gearbox oil feed was shared with the turbo and had been operated that way for several hundred hours prior to Reno. I think Dave posted the information but I don’t see it in the archives. Hopefully Dave will chime in. Bobby From: Rotary motors in aircraft [mailto:flyrotary@lancaironline.net]
Sent: Thursday, March 23, 2017 11:47 AM
To: Rotary motors in aircraft
Subject: [FlyRotary] Re: redrive options Tracy, Paul had the photos on the newsletter. I don't think there was anything wrong with the drive. He was just way outside normal HP and load. Turbo 13B in his RV-6. The bearing at the rear of the output shaft, not sure if it was a thrust bearing or support, looked siezed. There was considerable amounts of swarf and the outer ring was bright blue from what looked like over heat. There is also the possibility that there was an oiling problem completely unrelated to the gearbox that caused the failure. Since the planes are at high revs and pulling some g-load on the course all the time oiling could be a problem. I would love to be able to examine the gearbox to be sure of what happened. Since you evidently DIDN'T my guess is they felt what they were doing was abusive and caused the failure. They got another redrive from someone else and changed it out that night. Dave never got to race it as that was the year the Mustang broke and went into the crowd. Dave was a military doctor and was quite heroic doing lifesaving work on many of the survivors of the accident. I have made clear when ever mentioning the incident that this was racing and the loads and forces are very unusual doing so. Having built many cars for racing I can state things fail in places you wouldn't believe. (Ask me about the battery cable failure I had on a formula C SCCA car sometime.) Also the causes of failures may be unrelated to the soundness of design on the parts involved, and can be caused by other outside problems. The point of the discussion was not a critique of the parts involved, rather a cautionary tale to keep new rotary engine converting owners to be aware of the need to do careful assembly to prevent problems. Check with P.L. to see if he has the pictures of Dave's redrive stored somewhere. On Mar 23, 2017 4:16 AM, "rwstracy" <flyrotary@lancaironline.net> wrote: Hi Bill, This is the first I’ve heard of Dave’s gear drive having a burned bearing. If Dave is around I’d like to know which bearing and any other relevant information, operating RPM, turbo boost on the engine, etc. If you have any details Bill, let me know. Tracy Sent from Mail for Windows 10 Charlie, No they build a complete gearbox using planetary gears first. (spur only so no end thrust) They found as you ran the engine through various speed ranges it was possible to incur damage due to second order vibrations that could be just as damaging. Sorry Charlie, but if you think their work was an unnecessary rabbit hole I won't be flying in your plane. That isn't intended to be insulting. I just have seen the results of not handling these forces. Dave Lenard flew his RV-6 behind Tracy's gearbox at Reno qualifying and totally torched the internal bearings. Regarding the transmission locked in gear, I wouldn't stand near the plane that was using the gearbox regardless of the time he had on it. It was a disaster waiting to happen. Everyone thinks this is easy. You can get away with it for a while but if you want to use your engine at a significant HP level, for a cross country flight that you intend to return from in the same plane, you MUST account for torsional vibration. The math isn't terribly tough nor are the parts a lot heavier, but the close meshing gears and stiff model never had a problem. They had to properly support the pinion gear, and after that the thing was bullet proof. That can't be said about any of the other reduction boxes I have seen that are even close to the same weight. The guys built a beautiful torsional dampener into a rotary e-shaft that worked perfectly with a planetary, it just required too much expensive machining. Your comment about in resonance problems being regardless of power level is true. Fortunately you can usually transition the specific rpm without a lot of damage, but if you spend any time there even at idle you are going to break parts. I am tired of people thinking an auto conversion is too easy and then dead sticking their plane in a field somewhere. (As a best case) The base engines are rarely the problem. Automotive engines are built pretty well today, but a broken gearbox, or drive belt, or torque converter, or flex plate, or clutch disk can still spoil your whole day. On Tue, Mar 21, 2017 at 2:15 PM, Charlie England <flyrotary@lancaironline.net> wrote: Uh, that wasn't me. :-)
But I've heard the case made that exactly what you describe is what happened (dyno designed for V-8s at 4per-rev; twice the excitation frequency). I didn't stay in a Holiday Inn last night, but those who did tell me that *in resonance*, power level doesn't really matter much; stuff is going to break. I'd love to see that same driveshaft & dyno hooked to something like a big 4cyl engine (2per-rev) capable of the same HP & rpm where their failure occurred. Doesn't it make you wonder if the results would have been the same?
One of our former members (since deceased due to natural causes) flew successfully for years using a Mazda transmission as a reduction drive. Worked great until one day when the engine started on only one rotor (1per-rev) & *at idle power* it destroyed the gearbox.
I can't help but wonder if that dyno incident took them down an unnecessary rabbit hole of expensive zero-clearance gears & extra weight.
Charlie
On 3/21/2017 3:51 PM, William Jepson wrote:
Charlie, In terms of simple vibration caused by out of balance you are correct. It terms of torsional vibration though the rotary is a tough customer. Part of the problem is that the e-shaft on the rotary is so stiff. I have been working with Steve Beckham from the original PowerSport. Steve told me about how a 200 HP rotary just blew up the input shaft on a dyno that was regularly used to test 600+ HP V8 piston engines. This is the torque pulses of the engine, not out-of-balance. It is likely that in that case the rotary hit a amplifying couple or harmonic frequency with the dyno causing the failure. That said Steve and Everett Hatch did a LOT of work to be sure their "stiff" model reduction drive placed all the frequencies above the normal operating range. If you hit one of those frequencies with one of the rubber couplings or the bushing-around-bolt dampers it will fail period. Most of those systems try to push the first order frequency below the operating range. That is why you will often hear the engine shut down rattle with a planetary. Typically the energy in the system is low enough to pass through that RPM without damage. Usually. But if not planned for those pulses can be a disaster. On Tue, Mar 21, 2017 at 10:40 AM, cozygirrrl <flyrotary@lancaironline.net> wrote: Rotary torque pulses can be very destructive before buying anything specifically mention the rotary. If they know anything they will be worried.
Somebody please correct me if I am wrong but I have understood the opposite, the rotary engine does not have the 4 bangs per prop revolution of a traditional 4 cylinder aircraft engine which shows as a spiky positive and negative graph when plotted.
The output of the rotary is always positive torque in nature and overlapping sinusoidal due to the two rotors when the output wave forms are plotted, hence the smoothness of the rotary. When peak output is plotted it shows an always positive gentle wave. -----Original Message-----
From: William Jepson <flyrotary@lancaironline.net>
To: Rotary motors in aircraft <flyrotary@lancaironline.net>
Sent: Mon, Mar 20, 2017 7:02 pm
Subject: [FlyRotary] Re: redrive options Rotary torque pulses can be very destructive before buying anything specifically mention the rotary. If they know anything they will be worried. On Mar 20, 2017 3:48 PM, "drhyed" <flyrotary@lancaironline.net> wrote: I had brief conversation with them last fall and they designed the gearbox with the intention of offering higher horsepower options: "We do have plans for a higher horsepower engine. When we designed our gearbox we intended to do engines to about 225 hp from the start.
Our intent is to do a 155 hp normally aspirated 2 liter and a 200 hp turbo version"
I did not mention a rotary engine specifically though. Jay These guys have been advertising on ebay for a while. I have no idea about whether they are legit, or whether the drive is suitable for a rotary. The web page claims 'good up to 225HP', but their target installations are closer to half that, so....
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