Need sprag clutch

skyguynca

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I am building a single place helicopter. Two stroke powered to keep the weight down. Now looking for a sprag clutch, was thinking about the Morse MG300A but the darn things new are now $1700.00.

Are there any guys out there using a different clutch on their two stroke heli?

Thanks
David
 

bryancobb

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Most automotive automatic transmissions have a Formsprag that is appropriate. Brantlys sprag clutch was purported to have came out of a 1950's Ford automatic. Gary Goldsberry may have an older one that has reached it's life limit and cannot be on a FAA certificated ship any more. No one is legally allowed to rebuild them and get them yellow-tagged. Rebuilding them for an experimental is 100% OK though. It's strong and never gives any problems on 180 Horsepower Brantlys.
 
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Los Angeles
I am building a single place helicopter. Two stroke powered to keep the weight down. Now looking for a sprag clutch, was thinking about the Morse MG300A but the darn things new are now $1700.00.

Are there any guys out there using a different clutch on their two stroke heli?

Thanks
David
1990 Model Nissans as well as the Mid 70s Ford Granada use essentially the same Morse Sprag Clutch. I've autopsied many of them. They're vert good, also very close to the Hughes spag clutch and only cost $55...that's the path I'd take. Save the $1500...
 

skyguynca

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Thanks for the heads up, I will definitely take a look at it. What is it called in the automatic transmission?

Thanks
David
 
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NoWingsAttached

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Arrow gearboxes used GM transmission sprags circa late 1950's through late 1960's. Like your idea, these were used on 2-stroke engines. You really need to understand a few things here.

1. The closer to the engine in the gearing arrangment, the smaller your sprag can be. Sprags are torque-limited critters. When you install it next to the prop you need a much larger sprag.

2. Life of a sprag is severely cut by vibration. When coupled to a piston engine the life is 1/4 or even much worse than when used on a smooth electric or turbine motor. Notice that sprags are quite common on hydraulic automatic car/truck transmissions. They are so successful in these types of installations due to the vibration damping characteristics of that type of drive.

3. Using a sprag on a gear reduction unit that itself creates harmonics reduces life

4. Using a sprag on any fan - props and rotors included - reduces life greatly.

5. The worst thing you can do is install a sprag on a 2-cycle engine. 4-stroke engines are far smoother.

6. Cog belt reduction units are terribly hard on sprags.
 

GyroCFI

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Yeah, I used to have an Arrow engine on my two place. seemed like at least once a season one of the dogbones in the spraue clutch would flip and lock the clutch up. Wasn't a problem really because it never kept the prop from turning, but was a real chore to get the clutch out with that one bone flipped.
 

NoWingsAttached

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Yeah, I used to have an Arrow engine on my two place. seemed like at least once a season one of the dogbones in the spraue clutch would flip and lock the clutch up. Wasn't a problem really because it never kept the prop from turning, but was a real chore to get the clutch out with that one bone flipped.
What typically happens - especially in a case like yours where it continues to occur multiple times - is vibration from engine, gearbox and prop all come together to form the perfect wave - literally. Constructive wave formation wears out the sprag dogs and/or the races. The tolerances are just thousandths of an inch, and in due time the dogs roll over. In your case the race becomes dimpled so that the dogs grab that same spot wearing it out faster and they roll over in it.

The early Arrows did not have adequate lubrication and wore sprags out very quickly during shut down. The later Arrows lasted quite a while, especially for those who changed the Dexron II cherry juice often. I spoke with several gyro pilots getting 800-1200 hrs on an Arrow sprag.

A guy is now making, selling, and shipping a completely new, sprag-loaded PSRU - before they have been completely tested.

This is a 3-gear design to place the prop shaft as high up as possible on the upright 4 Yamaha, which is great for most FW tractor installations but is strictly verboten on a pusher gyroplane - but the units have been marketed to gyro builders! WTF?

Every gyro builder worth his salt knows that raising the seats and/or engine raises the COG of the gyro, while lowering it lowers the COG and thus creates a greater HTL. In most cases, gyro designers have determined the limits of HTL for a particular airframe and built within that, so that if one were to lower a 165 lbs engine by 3 inches such as in this case then the COG will go down by 1/2 that, and the HTL thus increases 1-1/2", putting the prop thrust line above the acceptable design limits of HTL for safe climb out and push-over, and zero G events.

Said PSRU builder/seller was properly warned of this danger and chose to ignore it, instead pushing his new gearbox for sale to gyro builders w/o warning that his product increases HTL and thus reduces safety on gyroplane installations. This is not the first time for this fellow to do things that are not on the up-and-up.

The same guy withheld information and personal experience concerning Rotax rubber donut failures, as well as other Rotax C box problems and RK400 clutch failures he knew of in the past on his modified installations, while he continued to promote and sell them for years until someone finally blew the whistle on the laundry list of failures and concerns.

The basic problem with sprags in any new, unknown installation is that often when sprag clutches fail they do so without warning, and completely let go so that all power is uncoupled all at once. The new sprag PSRUs mentioned above have three gears, which increase harmonics dramatically over two-gear PSRU's, with no known precedent except to say that sprag failure at some point in time due to prop and gear vibration is inevitable. But when? You may think that automatic car & truck tranny sprags last forever, but those are soft, fluid-coupled applications, not hard-coupled to a very strongly vibrating prop pushing 650 lbs thrust and a set of three very noisy gears grinding out 150 hp at 300 lb-ft torque.

After 20 hours of running and two hundred starts the builder declared his PSRU ready to fly test. After a very short while he found that it created way too much heat - engine power lost to heat in the gears - and pulled it off for a redesign to hold more oil. That set the test clock back to zero hours.

Units were shipped to customers shortly after very little test time.

They have just been recalled for problems.

A few folks in the gyrocopter community know that Arrow sprag gearboxes could be relied on to last 800 hrs before rebuild. Based on that history, until this builder has reached a minimum 800 Hrs on a single PSRU from start to finish, without a single change being made to the test unit other than oil changes, the consumer is advised that the unit is completely experimental and may fail catastrophically at any time up to the known test duration currently completed.

Gyroplane and gyrocopter builders are advised to use PSRU's which keep the prop thrust line as close as possible to COG, and to stay away from increasing HTL unnecessarily for any reason.

I have never seen a single gyrocopter in my entire life built with an unnecessarily tall PSRU which increases HTL for no reason whatsoever.
 
Joined
May 11, 2005
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149
Location
Burlington Wi
Hi All

I think in my collection of parts I may have a R22 pulley, shaft and sprag clutch assy if someone still needs a clutch I can take a look and see if I still have it.

Doug
 
Joined
May 11, 2005
Messages
149
Location
Burlington Wi
Hi All
took a look in my collection I have an R22 upper pulley and shaft with the sprag clutch assy $700.00 plus shipping if someone still needs one. Less than half the price of an MO300A
Doug
 
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