Cog belt


There are 3 cog belt designs out in the market as far as we are aware of.

1     The Pro Drive system from John Spurling which came out about 98
2     Homebuilt Performance Products Inc, AKA Eric Cymbaliuk which came out in 99
3     Al Behuncik in Canada which seems to have come out in 2002


 # 1     The Pro Drive system

This year to date as of December 04 there have been 2 reports
of Pro Drive Cog belts breaking

The 1st one to break

John said had 85 hours on it and that it showed no signs of belt ratcheting like it’s being implied to have.

John says the 2nd one

was a belt system that was purchesed second hand by a fellow.

  According to the owner of the ship it was installed on, he had it set to Pro Drive’s specs and he further stated that it hadn’t jumped any teeth while it was in operation.

In a conversation with John on the belt he stated that if it was in fact set up correctly there isn’t anyway in the world it could jump teeth.

It also showed no signs of belt ratcheting and it was installed on a Scorpion ship with a 145 engine.  I don’t know anything about a scorpion other than it has less horse power than the newer 162’s so with all the ships out there running higher horse power engines in the past and present years this one purely makes no sense.

John has stated to me that he has over 600 units out
there at this moment (Dec 04) and there are in fact two belts that have broke.

These belts have been being used over 5 years now in two different versions and these are the only ones to date that have failed.  No one can say there won’t be more but if it’s as bad as a few people are making it out to be they all should have failed

especially the 1st generation (Blue) belts.

I say that because from what I got out of EPI’s site the blue belts John first used carried 30% less load capability then the second generation gray belts do so if I wanted to change my mind and believe in the, It’s gonna break theory this sure doesn't help justify it?

Another thing to bring up here is that by the time the tail rotor, alternator, water pump, and mostly the cooling fan rob the horse power they need from the engine there is only, according to John Spurling,
about 60 to 65 horse power running through the cog belt to the main blades
not 130 to 150 like people are assuming there is.

I don't know about every else
but this was something I'd never thought about before and it sure makes sense.

This is sniped off Epi's site

2.  BROKEN BELTS:    Recently, there have been two cases of the ProDrive belt fracturing across a single tooth root, as shown in this picture of Mike Morgan's belt, which broke after slightly more than 3 hours of operation. Ardie Greenameyer's broken belt looked very similar to this one.


EPI sent Mike Morgan's broken belt to Gates Engineering for analysis. Their opinion (a consensus of several knowledgeable Gates engineers) is that the belt almost certainly fractured because of being operated in an undertensioned drive system. They said there was clear evidence of the belt having skipped teeth, which severely overstresses the belt cords AND the shafts AND the bearings.

A copy of that report from Gates is shown below. (It has been edited to remove names and phone numbers. REMEMBER, Gates doesn't want their stuff on aircraft.)

This may be the real deal but then again
with the names andnumbers edited off who knows

#  2    Cog Belt Drive by Eric Cymbaliuk back in 1999

The Drive in this ship was from a fellow named Eric Cymbaliuk in Canada.

The Owner of this ship said it worked great and that he was very happy with the drive.

This is an article by John Spurling
in the October 1999 Homebuilt Rotorcraft Magazine
reguarding Eric and his drive system

Homebuilt Performance Products Inc.

Phone/ Fax (780) 586-2012
Box 103 Norris beach
RR 1 Westerose Alberta


You now are being introduced to one of the worlds finest Synchronous drives to this day.

This system is designed and engineered by the best as an after market Synchronous drive system kit meeting the requirements of the Rotorway helicopter. This kit includes complete set of HP charts and graphs also including installation manual with certificates and documents Fine design and engineering was accomplished from the raw metal to the manufacturing and including a custom designed carton meant for worldwide shipping. You’re drive system includes all certificates and documents that start at the foundry then heat treated for temper and artificially aged to T6 standards all with certificates. You also receive engineering manufacturing drawings. Every system has an engineering manufacture stamped to the large sprocket including the serial numbers. Most important as a finished product it includes an individual dynamic balancing certificate of proof with matching serial numbers and date Finally it includes a none-restricted 14MM synchronous belt rated 2500HR, which should last the life of helicopter. There are enough documents & certificates to certify this system. Actually if a customer wants we will have it certified for him for additional $21,300.00 USD. The only prerequisite is you must sign a waiver agreement unless you purchase a certified system. It is impossible to install this system without an electronic level you may purchase or rent one from us. To this date FEB 02/2000 our price for this system complete is $3118.40 USD. We do offer a quantity discounts. Our Company to date has already manufactured two runs of ten spoken for with deposits or sold. Our next run of ten we are offering as a one time special on a first comes offer of $2711.00 USD. This offer ends FEB 28/2000 or as the ten units are sold.

There is shipping and handling charge

FEB 04/2000update.

It was discussed with our engineers because Rotorway is experiencing secondary shaft failures so now our manufactures have made changes to our system.

The design change in attaching sprockets to the shafts will help prevent and maybe stop secondary shaft failures.

It was a long and detailed engineers report. All systems that were sold including ones that were spoken for with deposits are being recalled at our expense to make this new attachment change with no cost whatsoever to the customer.

APPROVED by Eric Cymbaliuk President.

Eric posted several nasty posts on various Sites attacking Pro Drive.  Shortly afterwords he posted that his helicopter was a victim of Rotorways bad exhaust gaskets, caught fire and burned to the ground.  To my knowledge that was the last anyone ever heard of him.  There are several rumors that Al Behuncik copyed Eric designs or vice versa on his drive along with many other things for the Rotorway.  Personely we have never had any dealings with either of them so we have no idea because everything we know came 2nd hand from the internet.

# 3       Al Behuncik's Drive system

From what little information we can gather on Al's System it has the very same type of belt as the Pro Drive unit,

its just longer in length but the sprockets themselves are different in a couple of ways

Al's system uses an idler pully on the cog belt to maintain the belt tension which is fed from the ships engine oil pressure which goes though a pressure regulator. Looking at it from my prospective, it adds alot of bells n whistles not to mention more weight.  Al says it maintains a constant tension on the belt under any condition of flight and in any tempreture.  The system also uses larger diameter sprokets which is supposed to put less load on the secondary shaft which if the shafts are indeed breaking from load is a good thing.  The large Sproket from pictures I've seen has large fan blades built into its center acting as spokes.  I've no idea but it would seem it would take more engine horse power to turn it plus in an autorotation it may take more to drive it which may possibly use up a very valuable asset called Rotor Inertia which we don't have any to spar of in a Rotorway, like I said I've no idea what thats about.

From what I get from Al and his customers
its their belief that its loading issues that are breaking shafts and not fretting corrosion.

Nothing is impossible and it's very easy to buy into this theory, but every one of the broken shafts we have encountered so far (even ours) doesn't show a load break according to engineers we have encountered because of the size of the plastic zones.  They say if it was from loading (to much pressure on the shaft) the plastic zones on the broken shafts would be much much larger, well except Jack Kane at Epi, and he just seems to be all over the place.

In December of 2004 I spoke with Al on the phone and he stated that he has 46 drive systems out there around the world all sold from January through December 2004 and there has never been a shaft break or problem with any one of them but then again no one other then al himself seems to have any time on the system.

Al seems to be the only person that has any time on his system which If im not mistaken he reported 200 hours on his personel ship in January 2005.

I'd like to have more information here for you but there isn't any, other then he says it works and he gives no rhyme or reason other then it puts less load on the Secondary shafts.


If by chance we run across any data or Al's consumers ever send us any real time data on the drive well post it here.
So far it appears that they are all keeping it secret

There is more information in the secondary drive section that may pertain to some of these units