flyrotary@lancaironline.net Mailing List Archive

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.

Bill Jepson

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.

Bill Jepson

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.

Bill Jepson

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.

Chrissi
CG Products

www.CozyGirrrl.com

-----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.

Bill Jepson

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

On Mar 20, 2017, at 5:31 PM, Charlie England <flyrotary@lancaironline.net> wrote:

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....

http://www.aeromomentum.com/partslist.html

Charlie