What's new
Van's Air Force

Don't miss anything! Register now for full access to the definitive RV support community.

Belted or Geared?

T

TXFlyGuy

Well Known Member
I'm new to this, but have made a few phone calls plus a bit of reading on the subject. There seems to be arguments for both sides here. However, a story by a former PSRU manufacturer told of a belt that had lost all (or most of) it's cogs and the plane was able to land at an airport, make some adjustments, and fly home for the needed repairs. A gear driven unit may not have done as well.
Also, Rotorway Helicopter (remember the Scorpion?) switched from belted to geared, and then had many issues with torsional vibration. They soon switched back to belts. I was told also that the U.S. Army uses belts in all of it's helicopters.

I'm looking at a Chevy engine, perhaps the V6, maybe V8. Two schools of thought are from Belted Air Drives (Jess Meyers), and Firewall Forward Aero of Canada (Archie Dobbins).

If anyone has researched this issue and has empirical evidence to support an argument, please feel free to expound on your data!
 
Welcome to VAF!!!!

Myron, welcome to VAF:D

I suspect you are going to get a lot of opinion on your question, and much of it will be -----Lycoming.

Hopefully Ross Farnham will chime in, he is one of the more knowledgeable folks out in RV land currently flying with an auto engine conversion.

I have a couple buddies who have done auto conversions, and both were belt drive-----the lack of needing a lubrication system, and the adjustability of a belt were factors in their choice.

Good luck with the question, what are you planning on building ?
 
Mike S said:
Myron, welcome to VAF:D

I suspect you are going to get a lot of opinion on your question, and much of it will be -----Lycoming.

Hopefully Ross Farnham will chime in, he is one of the more knowledgeable folks out in RV land currently flying with an auto engine conversion.

I have a couple buddies who have done auto conversions, and both were belt drive-----the lack of needing a lubrication system, and the adjustability of a belt were factors in their choice.

Good luck with the question, what are you planning on building ?
Click to expand...

Not sure yet...but doing all of my homework now so that an intelligent decision will be made in the end. This will be a big project and I'm hoping to get another individual involved.

Thanks for the welcome!

p.s. Yes, Lycoming is OK. Flew behind one in my C-172 for 11 years...ran like a top after switching to auto-gas! But for my purposes a V6 / V8 is more desirable now.
 
Last edited:
The Belted Air Drives, Firewall Forward, RAF and Raven drives have all accumulated a lot of reliable flight hours over many years. Just beware that you should only fit these PSRUs on the recommended engine/ prop combinations. Don't just put any old drive on any old engine/ prop combo- make sure your exact combination has been well flight proven. Belted have been used on a lot more V6s than V8s so ask questions about flight hours on V8 examples from the vendors and talk to some customers before you buy. Out of these mentioned, only Belted and FF are offering V8 drives.

Contrary to some opinions, belts do not get rid of TV issues- for the most part, people have just been lucky with the designs.

With gearboxes, the Autoflight from NZ is the most proven, with tens of thousands of flight hours and a proper TV absorber, the Real World Solutions gearboxes also have a lot of flight hours but primarily on Wankel engines, Marcotte boxes also have a long track record but service is slow. Marcotte is the only one here which has been doing V8 applications for a long time but there may not be many hours on those big boxes. EPI offers some high end boxes with TV absorbers (Quill shaft), Geared Drives offers boxes for V8s but again, they have not accumulated very many flight hours to date and the their future is in question after the death of the owner and designer recently.

Some engines, V engines in particular, require crankshaft to prop shaft offset to fit under the cowling so planetary boxes like the RWS ones may not be suitable in some cases.

A few hundred hours is not sufficient proof of a sound design IMO.

Be aware that many of these drives will require an electric prop and that auto engines generally don't perform well with fixed pitch props on most aircraft.

Carefully consider all factors before going down the alternate engine path. It has not worked out for many people in the past.
 
Last edited:
On the engine / PSRU combination question, have been trying to find good data on V8's. Strangely, the few people that I know of that have (had) them, put very few flight hours on them. One example is an owner that in a little over 6 months has 10 hours flight time on his V8. Another tale was related where an owner was literally afraid to fly his V8 powered plane...even after investing mega-bucks in it. Finally sold it. Most of the examples I'm finding are in the 3/4 scale warbird community.

Did find one C-172 flying behind a marine version V6 for over 20 years with no issues...the PSRU is belted in this example.
 
TXFlyGuy said:
On the engine / PSRU combination question, have been trying to find good data on V8's. Strangely, the few people that I know of that have (had) them, put very few flight hours on them. One example is an owner that in a little over 6 months has 10 hours flight time on his V8. Another tale was related where an owner was literally afraid to fly his V8 powered plane...even after investing mega-bucks in it. Finally sold it. Most of the examples I'm finding are in the 3/4 scale warbird community.

Did find one C-172 flying behind a marine version V6 for over 20 years with no issues...the PSRU is belted in this example.
Click to expand...

Yep, the V8 auto engine concept in most experimental aircraft over the last 20 years has not been very successful for the most part. There are some examples which have been very successful long term and these have generally been built by engineer/ gearhead types. Here are a couple links: http://www.pursuitofflight.com/longezv8.html
http://www.airventure.org/news/2011/110728_seabee.html

Robinson has done some really nice LS conversions on Seabees and there are a number of Pawnee glider tugs in Australia with high time V6 and V8 conversions. Can be done, but you need the right people to be working on the project.

There have been lots of engine/ PSRU failures in the replica fighter and fast glass world so beware. This is not as easy as it might seem.
 
Ross is the man, for sure.

Also, if you aren't too far away you may want to go talk to the scale Spitfire outfit in Cisco, Texas. They use a belted V-8 and I believe they also have their own aircraft ECU for it. Their spits have been around a while and may have some history to share. The ECU is very important as well.

It is sad what happened to Geared Drives founder. His clutch PSRU with provision for std hydraulic prop seemed to have a lot of promis.
 
Last edited:
TXFlyGuy said:
I was told also that the U.S. Army uses belts in all of it's helicopters.
Click to expand...
Don't believe everything that you are told. Every significant military helicopter that I am aware of uses very large transmissions with gears to drive the main and tail rotors.
 
Kevin Horton said:
Don't believe everything that you are told. Every significant military helicopter that I am aware of uses very large transmissions with gears to drive the main and tail rotors.
Click to expand...

The info was given from a manufacturer of belted drives. Oh well...
 
helicopter belts

OK just what i know. When i was in mechanic school I worked on a Hughes 269 (often called a Schwiezer 300) and its main drive was multi V belts from the lycoming to the transmission. But I think this might have been done to allow the transmission to disconnect from the engine during start; not sure exactly the reason its been a long time ago.
 
RV8RIVETER said:
Ross is the man, for sure.

Also, if you aren't too far away you may want to go talk to the scale Spitfire outfit in Cisco, Texas. They use a belted V-8 and I believe they also have their own aircraft ECU for it. Their spits have been around a while and may have some history to share. The ECU is very important as well.

It is sad what happened to Geared Drives founder. His clutch PSRU with provision for std hydraulic prop seemed to have a lot of promise.
Click to expand...

Just checked out their website. Looks very interesting, indeed! Thanks for the heads up on these guys.
 
I've done certification analysis for the static and dynamic loads on helicopter accessories which were belt-driven.

The dynamic environment and the modal behavior of the entire system, not merely the belt but including it, were absolutely necessary. It's not something that can be guessed at. It has to be right and either expensive analysis or more expensive testing needs to be done to verify it.

Dave
P.S. Retired, not taking new work....
 
Suzuki "mini Merlin with belt drive.

Hi folks, Lou here. I am amidst a Titan t-51 project, and I could use some advice regarding my Zero time Suzuki mini merlin. It is fitted with a belt drive that is matched to the engine (in 2006) by Dan Hawken, of Canada.

Some tell me that I should switch to a gear drive. I am told that belt and crankshaft failure have occurred.

I am here because I am told that you guys have an all knowing, international man of mystery type, who is the guru of belt driven pro-pellors.

Does anyone know or this Ross Farhnam person ? Is he really all that and a bag of potato chips ? Is he taller than Yoda ?

Lou, Tulsa
 
What they said....

Speaking for myself, I'd never try to do any reduction drive without the assistance of a knowledgeable & experienced mechanical engineer, meaning the purchase of their proven product for my engine.

What others haven't said, is to ask which airframe & which engine? Most of the common choices of V-6/V-8 engines (Ford & GM) will be very heavy if you're looking at a 2 seat RV (except *maybe* the -14). If you're building a -10, you'll have a lot more options in the weight department. It's just really difficult to find a small V-6/8 that's light enough to do well on a small airframe designed for a LYC. When power needs get closer to 300 HP, the picture changes quite a bit, & aluminum automotive V engines can sometimes be very competitive with 6cyl a/c engines in the weight department.

And do it for fun & education. It's not likely to be much if any cheaper, & it's a LOT more work.

Charlie
(Mazda Renesis rotary on RV-7, in progress)
 
Welcome to VAF!

Lou, welcome to VAF :)

Yes, Ross is taller than Yoda------and pretty savvy about flying behind auto conversions.

Another wealth of wisdom here when it comes to Torsional Vibration is Dan Horton, also taller than Yoda:D
 
I feel the force left me long ago...;)

I actually have never flown behind a belt drive but know many who have hundreds and even thousands of hours behind them. Properly built and tested, they can be very reliable. Improperly built... well you get the idea.

A lot of it also boils down to using a drive with a specific engine/ flywheel and prop combination. Change one part and all experiences and flight time can go out the window and you are into unknown territory again.

I do know a guy with a belted V6 Suzuki powered T51 at my airport. He and the previous owner had no problems as far as I recall. The second owner is still flying it. I'll see if I can dig up his contact info for you. People flying the exact same thing are the best people to talk to, not people flying a different drive/ engine/ prop as this has no bearing on it.

The original T51 belt drive had no formal TV testing involved in the design but that is the case with 95% of all aftermarket PSRUs out there today. If other people are getting 500+ hours with no failures, that somewhat validates that you should have similar experiences.

Skyhawk, check your PM for contact info.
 
Last edited:
You must log in or register to reply here.
Back
Top