Bendix/Ring Gear Question

[KenSandyEggo]

I still have the original RAF set-up and it's been working O.K. I had to replace the RAF-supplied Bendix with a new one from NAPA a few years ago, but otherwise it has been working fine, even at over 200 rrpm.

When I get up to those higher speeds, the gear-howl is really loud. I have put some grease on the large ring, but I'm sure that it is quickly thrown off. My concern is whether this noise is to be expected ot may be due to a misalignment. My step-son David and a few "Rats" at Fallbrook Airpark were really concerned when they watched me prerotate and take off, as I learned though a later phone-call from David. They thought I was having some metal-to-metal grinding malfunction. I guess they didn't realize that it stopped as soon as I let off the clutch handle.

Any suggestions as to what to look for, any improvement(s) to make, a better Bendix design that's available, or............"if it ain't broke, don't fix it." Does the gear noise relate to something detrimental or is it just noise that dry gears make when spinning furiously?

[gyromike]

Ken,

It is a sound that all spur gears make. Nothing you can do about it. It comes from the way the gear teeth make contact with each other all at once along the face of the teeth.

The reverse gear in a car/truck uses a spur gear. That's why you hear the whirring sound. The forward gears are helical and it is more like a sliding contact between the gear teeth. That's why they're quiet.

More info here:
http://auto.howstuffworks.com/gear.htm

[Harry_S.]

I agree with Mike.

If you were able to spin up to 350 rrpm...the noise would scare even YOU!!


Cheers :)

[Vance]

Hi Ken, no kidding now. In my experance it is the ring gear ringing. The noise that the gears make is bad enough, but is amplified by the hub of the ring gear. Try tapping on the gear with a ball peen hammer and you will see what I mean. You can find out by taping some rubber to the hub of the ring gear, spin up but don't fly. If you find that it helps, a company called Devcon makes a product called flexan for quieting conveyers and chutes. It will form a soft shiney black rubbery cover on your ring gear hub, not the teath, to stop it from ringing. Good luck and congratulations on your progress. I think that your methodoligy is first rate and your persistance is admirble. Thank you, Vance

[KenSandyEggo]

Mike, Harry and Vance, thanks for the input. I thought it was just by-product noise but didn't really know if it related to anything else. I have to have close to 1,000 pre-rotation cycles on the thing and it's held up well over the years. I'll look into that "silencer" option and see if it'll keep the "Rats" from having a heart-attack when they hear me spinning up. The reverse gear in a car analogy really made sense to me and helped me understand it. Now I know which type of gears howl and which don't.

[Jerseywing]

Ken,
I'm not too familiar with the assembly but you may want to check that the ring gear can take that kind of torque/speed load. I don't know how the ring gear is mounted to the hub but it may need to be pinned to keep it secure
Just a thought...

[KenSandyEggo]

I think it's riveted to the hub. It hasn't flown off yet. I think it's probably secure enough, but I'll take a closer look next time I'm standing on the top step of my ladder.

[Vance]

Ken, tap it with your beer can and see if it rings. Thank you, vance

[gyroman]

Can you get the ring gear and bendix from the local auto parts? If so, what are the part numbers?

Ken you said you picked up one at NAPA, what is it out of?

I would really like to rig up some type of test prerotator so I can test several things out. Don't have the cash to buy a full blown system and then rip it apart to run my tests.

Or does anybody have some old parts? Doesn't have to be flight worthy.

[Harry_S.]

Mike:

The RAF ring gear is riveted with, I think 6, 3/16" SS rivets. If one comes apart, I believe I'll get rid of my machine. :eek:


Cheers :)

[Jerseywing]

cool,
Thanks Harry

[KenSandyEggo]

Toby, I have the Bendix number written down in the hangar. I'll try to remember to get it next time I'm there, probably Monday, maybe Sunday a.m. It is a direct replacement in the RAF upper housing. You have to remove the circlip and remove the inner spring without blasting off the tips of your fingers.

I got my tube of red grease today. Doesn't seem much different than my blue marine grease, except it's red. I guess looks don't mean anything. I should be trying it out Monday. I'll see if the grease in itself does anything for the rrpms.

[KenSandyEggo]

Toby, I finally got the prerotator Bendix number for you. The original, that came from RAF, didn't last long at all before it fell apart...probably around 50-75 hours. My replacement has been working fine since, about 400 hours. I probably do more spin up time than anyone. I often spin up and then am told to hold for landing traffic. I may spin up and spool down 5 times on a busy day. It's hard to gauge if anyone's coming in, because the tower switches the landing traffic from runway to runway (parallel) for spacing. There's a circlip on the unit that you have to remove and take out the inner spring and then put it back together.

It's called a "656-1101 Drive." That should be a NAPA number, but maybe not and maybe that number can get one from any auto parts store. I have no clue what vehicles it's designed for...or rather, what starters. It's a perfect fit replacement for the RAF supplied one.

[gyroman]

Thanks Ken,

I really appreciate it. I still need to know where I can find a ring gear for it. I've asked a few times over the years and noone seems to know where to find the ring gear.

Keep up the work on the prerotator... you keep at it and you'll have the market cornered..

[teiland]

Toby, the number for the bendix that I have used is 400R. This is apparently a common starter drive number familiar to all starter rebuilders, or at least that is what I was told. It worked fine on my RAF unit. I suspect Ken J's number is the NAPA number,as he said.

The only source I know of for the ring gear is Dick Wunderlich.

[gyroplanes]

Dick Wunderlich has the ring gear custom made for him. It used to be an "off the shelf" item, but was rapidly becoming obsolete (except for Dick's purchases)

I heard a rumor recently that Dick may not be able to buy them anymore.

[Harry_S.]

I wonder who supplies RAF and AAI with the ring gear???


Cheers :)

[gyroman]

What about the standard size of the ring gear? Number of teeth? There's a company here in Texas that specializes in gears. Maybe could get one made up...

[gyromike]

What about the standard size of the ring gear? Number of teeth? There's a company here in Texas that specializes in gears. Maybe could get one made up...

108 teeth, if I remember correctly Toby.

[KenSandyEggo]

Just tell them it's for a gyro and they'll understand. :eek:

[Brent_Brown]

My rotorhawk starter and ring gear combination is a 16262 starter and
FRG620 ring gear. Looks like 9 on the starter and 104 on ring. I just made the mounting plate and will wire it up to see how well it works, I am hoping for 100+ RRPM

[automan1223]

Gear clearance is very important. Make the teeth as close as you can noise comes from clearance as well as the profile of the teeth. I would find and use a dry spray graphite lube for your needs. Of course if you make the contact too small it may not engauge or may not release. if your bendix has an overrun feature it should disengauge on its own with the rotor overspeeds the driver.

Jonathan



When I get up to those higher speeds, the gear-howl is really loud. I have put some grease on the large ring, but I'm sure that it is quickly thrown off. My concern is whether this noise is to be expected ot may be due to a misalignment. My step-son David and a few "Rats" at Fallbrook Airpark were really concerned when they watched me prerotate and take off, as I learned though a later phone-call from David. They thought I was having some metal-to-metal grinding malfunction. I guess they didn't realize that it stopped as soon as I let off the clutch handle.

Any suggestions as to what to look for, any improvement(s) to make, a better Bendix design that's available, or............"if it ain't broke, don't fix it." Does the gear noise relate to something detrimental or is it just noise that dry gears make when spinning furiously?[/QUOTE]

[SNelson]

Ken
The noise from the gears on prerotator could be from improper spacing. When the gears are tight they will cause excessive noise. The clearance on automotive starting systems require .015/.030 backlash at starter bendix. This is usually checked with dial indicator at bendix gear but using your micrometer eye should give you a clue.
Sig n San Bernardino

[SNelson]

RE:Ring gear #s

Sorry, I didn’t post this sooner but been under the weather. The FRG620 ring gear is a Pioneer number it fits 68-84 Toyota with stick trans. It also is a “W” popularity which means warehouse stocked. The following information is dimensions and pricing as of 1-04-2004. Most automotive machine shops deal in Pioneer parts and should be able to find this item. I did not stock check this number.

OD ------10.681
ID -------9.325
Pitch -----10
Width ----.355
Chamfer –Front
Teeth ---106
$61.39 List/42.93 Dlr pricing.
I hope this is of some help to somebody - Sig n San Bernardino

[gyroman]

Wow, thanks for the info, that's the most information I've received on the ring gear.