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  #21  
Old 08-07-2013, 11:20 AM
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Toobuilder Toobuilder is offline
 
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Quote:
Originally Posted by F1Boss View Post
It's not the engine - it's the PSRU...
Sort of... When stuff "breaks", it’s often the TV issue. And TV is an issue for the entire system from one end of the crank to spinner. Change the mass of one part in the system and you alter the TV signature of the whole thing. So finding a robust gearbox or a coupler that "fixes" the issue on one combination may be a disaster on another. Without instrumentation on each combination, it's little more than blind luck when something works.

TV is a very complex issue for aircraft because we don't have the luxury of a heavy drivetrain rolling along rubber tires to dampen the whole mess out. We often have a large metal tuning fork (the prop) singing away undampened along with the crankshaft constantly winding up and springing back – find the right condition where those two elements line up and you get a rapid force amplification that can snap a crank like a dry twig. Throw a reduction gearbox in there and you have just compounded your problem exponentially.

There is a very good dissertation about TV and how it plagued the early BD-5 development. Also, the now ubiquitous P&W R2800 engine almost didn't make it out of development because of seemingly insurmountable TV issues.
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WARNING! Incorrect design and/or fabrication of aircraft and/or components may result in injury or death. Information presented in this post is based on my own experience - Reader has sole responsibility for determining accuracy or suitability for use.

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Last edited by Toobuilder : 08-07-2013 at 12:04 PM.
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  #22  
Old 08-07-2013, 11:35 AM
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John Clark John Clark is offline
 
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Quote:
Originally Posted by Mike S View Post
Remember the "Hog Air"???
Yeah, but I really liked the one that went the other way.

[/url]

I wonder how far it goes between oil stops?

John Clark ATP, CFI
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  #23  
Old 08-07-2013, 11:41 AM
Aryana Aryana is offline
 
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Now that is AWESOME!
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  #24  
Old 08-07-2013, 12:20 PM
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Madredr1 Madredr1 is offline
 
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Default Poking around online found this...

I guess it's a Zenith with a Yamaha engine!

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  #25  
Old 08-07-2013, 12:26 PM
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Quote:
Originally Posted by F1Boss View Post
It's not the engine - it's the PSRU. Start there, and then look for an engine that will provide the power/torque required.

Seems that Geared Drives had broken the code in terms of vibration by simply adding the clutch springs back into the drive system. The accident stopped all that R&D....as far as I know, the engine/drive system was not at fault?

Carry on!
Mark
The Geared Drives design is under new ownership and they are working on some fixes to retain oil seals properly and beef up the clutch mechanism having had failures on both with rather serious results. The basic gearbox design seems pretty sound to date on V8 applications but once again, change one thing and the track record goes out the window. The 200Z box as applied to a six cylinder Subaru had a possible TV failure in very short order for one early customer. The clutch springs actually do very little in this system.

Four and 8 cylinder TV signatures and problems are vastly different. The V8 is quite benign by comparison because there are no torque reversals and generally, the common gearbox designs have F1 well below typical idle speeds. The well regarded Geschwender chain drives usually had the death rattle (probable F1) around 300-400 rpm so they would hit this only on startup and shutdown. On the V8 apps, the Geared Drive clutch effectively gets rid of F1 problems by decoupling the engine and prop, on 4 and 6 cylinder engines it may do nothing. No engineering, testing or calculation was used in this design to my knowledge so only a few thousand collective flight hours on a certain combination will validate the design

Changing propeller and flywheel inertias can result in pretty major TV changes. While the gearbox manufacturer can probably supply the recommended flywheel, it is harder to confine users to a certain range of propeller inertias because of different airframe requirements but this is really what should be done as Rotax does. Ideally, the PSRU maker should perform a complete TV and prop vibration study for each approved combination. These days, the cost of the equipment to perform these tests would only add maybe 5-10% to the gearbox price on a run of say 50-100 gearboxes. It would give everyone a lot more peace of mind.
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Last edited by rv6ejguy : 08-07-2013 at 04:37 PM.
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  #26  
Old 08-07-2013, 01:53 PM
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http://www.youtube.com/watch?v=LSTRlAx_YSc
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  #27  
Old 08-07-2013, 01:55 PM
rv9aviator rv9aviator is offline
 
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I remember at least one of the Dawn Patrol guys having a Biplane with a Yamaha Virago Vtwin engine on it. You might google that for some information.
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  #28  
Old 08-07-2013, 03:24 PM
David-aviator David-aviator is offline
 
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Quote:
Originally Posted by F1Boss View Post
It's not the engine - it's the PSRU. Start there, and then look for an engine that will provide the power/torque required.

Seems that Geared Drives had broken the code in terms of vibration by simply adding the clutch springs back into the drive system. The accident stopped all that R&D....as far as I know, the engine/drive system was not at fault?

Carry on!
Mark
And I hear from a friend in Minnesota with a Geared Drive psru, the company is alive and well.

Here's the link with more info.

http://www.eaa.org/news/2012/2012-12...-auto-PSRU.asp
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  #29  
Old 08-07-2013, 03:47 PM
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Default Steve Wittman

The August 2013 issue of "Sport Aviation" has a great article by Lane Wallace called "Travels in Space-Time." I think it is probably her best one ever.

At one point Lane describes flying with Steve Wittman in Steve's Oldsmobile powered Tailwind when Steve was about 90 years old. I don't know the details of that particular conversion but thanks to Lane I now know how excited Steve was about it and the airplane.

In general I would say I don't want to fly in a home designed, home made airplane with an automobile engine flown by a decrepit 90 year old pilot. In this case, if I had had the opportunity, I would have been nuts to pass it up.
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  #30  
Old 08-07-2013, 05:03 PM
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There are quite a few Yamaha 3 and 4 cylinder powered gyros and Kolbs flying. The engines seem to work fine for this type of flying.

Rotax C gearboxes appear to be popular on them so they must be easy to adapt. I follow along occasionally on the Rotary Wing Forum as these guys are pretty creative and always looking for economical powerplants.

While loosely on the subject of PSRUs, I saw last month that Tracy Crook of RWS will no longer be producing aviation products including his drives of which many were fitted to Wankel powered aircraft for over 10 years. One less choice in the gearbox market.
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Ross Farnham, Calgary, Alberta
Turbo Subaru EJ22, SDS EFI, Marcotte M-300, IVO, Shorai- RV6A C-GVZX flying from CYBW since 2003- 441.0 hrs. on the Hobbs,
RV10 95% built- Sold 2016
http://www.sdsefi.com/aircraft.html
http://sdsefi.com/cpi2.htm



Last edited by rv6ejguy : 08-07-2013 at 05:58 PM.
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