Lazair.com

try a industrial pulley bearing belt supplier he may have something off the shelf and if he has it will be cheaper than machining a shaft up. ozzie

Well I finally got my shafts made out of 4140. That wasn't very easy stuff to machine. I machine 4130 all the time and it machines nice compared to 4140. I don't think I have to worry about the props coming off. I want to thank everyone for their input, it always helps one way or another. I might have this Lazair back up in the air in about a month or so, hopefully. (A471)
I am looking for some new lord mounts for the nacelles now. I sent an e-mail to lordmpd.com but have no reply so far. I have found other mounts very similar at a refridgeration supply store but found them to be a bit to stiff compared to the Lord mounts. I would like to stay with the original.
Daffy

If I ever design and build another set of reduction drives, they will not use the original type Lord mounts! The reason for that is that this type of mount is NOT designed for torsional loads - only shear and compression! Lord, and every other mount manufacturer that I am aware of, are very clear about that. In my opinion, the improper use of this style mount on the Lazair's engines is the reason they fail so often, not the oil and gas that they are subjected to that is so often blamed.

When I designed my re-drives almost twenty five years ago, I chose a much larger diameter Barry mount for additional strength in tension, and the softest one available to help keep the system from being too awfully stiff. (You can't see them in the above photo of my old drives.) It worked out fine, and I have never had a mount failure, but I still keep a close eye on them...

Chappy

PS. Ultraflight originally used this style mount because they had a ready supply - they held the handles on the Pioneer chainsaws, and seemed to work and hold up OK. Personally, I think it was a terrible idea to continue using them when they went with the heavier, more powerful Rotax engines. A redesign to utilize a proper style mount was in order.

Hi Chappy,
These Barry mounts you talk about, will they replace the existing lord mounts?

Daffy,

No, they won't. They are much larger and "stiffer" than the small Lord mounts Ultraflight used. I was able to use them on my design because they basically only had to isolate the rocking motion of the engine/redrive assembly from the nacelle mounts. They have held up to the tension loads, because even though they are not rated for tension, they only have to deal with a much smaller amount - in relation to the mounts other ratings. Most of the little Pioneer's vibration is absorbed right into the engine mounted front and rear aluminum mounting plates. I originally made them out of 1/8" 6061-T6, but they developed cracks in only about 15-20 hours running time. I remade them with 3/16" 2024 T3 (might have been T4), which just seemed ridiculously thick, but have held up fine. Four Barry Controls mounts are used in each assembly.

Maybe I can include a picture below to help illustrate the above description.

Chappy

PS. My original starter assembly mounting was made from all aluminum, but couldn't stand the vibration either. The nylon standoffs replaced aluminum plates and angle. The bolts attach to rubber "well mounts", and never loosen up even though they are not safetied. The well mounts (like a rubber grommet with a nut imbedded in it) also help absorb vibration.

The solid prop shafts are loctited and pinned into the aluminum eccentrics that rotate to allow belt tension adjustment. A bolt threaded into the end of the solid shaft keeps the pully bearings from pulling off. One belt would easily handle the power of this engine, but by using two, I could run the belts with much less tension. This allows a little belt slipping which helps to absorb some engine vibration. It's not as efficient as it could be, and they slip in the rain, but it has worked out fine - not a bad tradeoff.

Hi, Chappy,
I basically finished the mounts and don't really want to redesign the nacelles. I would like to find something that would replace the lord mounts with minimal of change to the existing design if that is possible. You have any ideas?
Your design looks good.
Daffy

Daffy,

Nice looking job! That's a mess of mounts you've got there! Probably will be as reliable as the Ultraflight setup.

I think you will find that the rivits in the portion of the mount that gets the full engine vibration will probably loosen up pretty quickly. If so, just replace them with AN3 bolts and nylocs. Keep an eye on the plates for cracks. Expect problems. Maybe you'll get lucky and not have any!

Chappy

PS. You probably noticed that I extended the front plate up, and added a second top structure to my nacelles. Doing so made the nacelles very ridged. This reduces the bending loads on the wing spar mount area that's imposed on it when the nacelles twist , especially when the engines sometime shake at idle.

Chappy,
Your 5.5 hp Pioneer redrive set-up, would you say it would perform as well/better as the 9.5 hp Rotax with direct drive set-up? I am very curious about this. You must have a lot of hours on your Lazair, can you give me a figure?
I am sending a front view of my redrive and from the picture you will probably figure out how I tighten my belt. The bolts aren't in the picture yet but the pencil shows how it pivots. This design I think would have less stress on the engine- without the propeller forces acting on it.
Daffy

hi guys, i am looking at using this set up for an alternate engine for mine ,trying to move away from those lord mounts and use a setup i used on the Thruster. the rubber mounts are car type ones from shock absorbers they worked well on 50hp engines. maybe it will give you some ideas to get away from those load mounts
ozzie

if you don't mind the shaft being made from steel you may find something suitable at your local trailer maker look at some stub axles. the skycraft scout used this set up