Prerotator Bendix Assembly Mounting

[Xorandor]

Here's the deal. I finaly got enough cash saved up to buy the upper bendix unit for my Gyro. I had a bit of a time mounting it. I had to do a bit of fabrication. (I had to make an additional 1/8' spacer). Any how I have two concerns. the 1st The rotor heads range of motion has been limited. It can no longer tilt back as far as it once did. The amount of loss is very minimal, but for all I know this might be enough to adverly affect its performance.

My 2nd is that the flex spring inside the cable seems to be too long. I can't get it to seat in all the way. I think that its just not inserting into the wheel end completly. It only goes in about 1/2 and inch, yet when I probed with a screwdriver its at least an inch deep. I'll post a link with pictures as soon as I get it set up. The 150K limit, limits the resolution required to see what I'm talking about.

[Xorandor]

Okay here is a link to the pictures.

ftp://ftp-www.earthlink.net/Gyro%20Head%20Prerotator/

[Rotor-Head]

requires a user name and password!!!

[Xorandor]

http://home.earthlink.net/~rkirchhof/Gyro%20Head%20Prerotator/

[WindRyder06]

You are missing a cotter pin in one of your castle nuts!!!!

Fly Safe,
Chris

[Xorandor]

I have pins, but I may have to disasemble it again. I think I need to move the upper bendix unit back just a bit. 1/8' or so. Is it okay to oval out the mounting holes in the main arm.

[rehler]

This is common. The bendix setup you have is made for a gyro with less offset cheek plates (rotor head closer to the mast). Your cheek plate offset is for a heavy pilot and light engine, requiring the rotor head to be far forward from the mast.

The cure is to replace the bendix with one that is made for this setup, located farther back (behind the cross arm). It has two in-line gears to transfer the drive force from the bendix to gear one, then to gear two, then to the large ring gear. Dick Wunderlich sells these just for this situation.

It is a shame to have to spend more money to get the correct bendix drive unit, but what you now have will not work properly. I had to do the same thing several years ago and hated to spend the money but was glad I did when I was finally flying.

However, first make sure your rotor head has to be positioned so far forward (hang test). If it can (or should) be closer to the mast then new cheek plates might solve your problem.

[Friendly]

"I have pins, but I may have to disasemble it again. I think I need to move the upper bendix unit back just a bit. 1/8' or so. Is it okay to oval out the mounting holes in the main arm."



I think (just my opinion) you would do better to get a new torque bar from Brock and drill your holes where they are supposed to be. There is a certain peace of mind that comes with parts fitting precisely. When you are flying you don't want to be wondering should I have replaced that piece. Also there is a thread called pictures 101 by Mike Gaspard that is very helpful for posting pictures to your threads. Good luck on your project.

[Xorandor]

"Your cheek plate offset is for a heavy pilot and light engine."

I'm 6ft Tall and around 215 Lbs. Does that make me a heavy pilot?

I assume a Mac 4318 is considered a light engine.

BTW when it's suspended how shoud it hang?

[rehler]

The heavy-light pilot and engine is different with every gyro. For example, if a heavy Subaru engine is put on an Air Command which was designed for a lighter Rotax 503 engine then the cheek plates would need to be remade to move the rotor head back to balance the gyro properly. Or, if a single place gyro is changed to a two place, then the rotor head will need to move towards the front, again to balance the gyro properly.

The location of the rotor head and the required cheek plates to put it there is determined by the "hang test". As a simple description, the gyro is hung by the teeter bolt with the gyro in typical flying loading (fuel tank half full, pilot with helmet in the seat sitting in the normal flying position). The keel should be tilted down in front about 9 degrees. Or, since the mast on many kit gyros is built at a 9 degree angle, the gyro can hang nose down so the mast is vertical (straight up and down). However there are recommended limits by most gyro kit sellers, which usually allow 1 degree less nose down to 3 degrees more nose down from this 9 degree angle - from 8 to 12 degrees.

I personally set my gyro up with a 11 degree nose down angle, which I believe is best.

[Xorandor]

Wow good info, thanks very much. Okay so before I go any where else, I'll find a way to hang it and check out it's angle.

[Xorandor]

Well, I talked to Dick Wunderlich. He said that it's okay to oval out the holes. He went on to say there have been many cases where they have done it that way intentionally in order to provide some adjustability. The flex cable is too long as well but, it can be shortened to my specifications for $25.00. I still may need to change the cheek plates but, that's nether here nor there. The 3 gear solution will not work with my configuration due to the direction of its rotation. Another option he mentioned would be to mount it off to one side and use springs to trim it out. this I feel would be the worst alternitive.