Axle material

[Brian Jackson]

In perusing Ralph's GyroBee documentation, I am uncertain from what material the axles are made. I had thought they were steel, and may very well be. If so, can aluminum be substituted? Thanks.

 

[Rick Martin]

Hey Brian,
I don't believe I ever saw anyone use aluminum for the axle stubs. I believe my documentation specified steel. Err on the safe side and use steel.

 

[gyrojake]

I would use 4130, 3/4" x .090 tube, or 4130 solid 5/8" round bar.
I use the 5/8"

 

[Doug Riley]

Steel, for sure. In fact, with brakes added, the stub axle needed to be longer and the cantilever effect became worrisome when using 5/8" dia. I had those longer stub axles heat-treated at a shop that serves the Vermont rock-quarrying industry. I used 4130 for both models.

Ken Brock's axles (the ones Ralph mentions in his narrative) were aluminum, but they were more than 5/8" dia. -- IIR, the bearing journals on these axles was turned to 3/4" while the portion that fit inside the 1.25" axle tube was 1" dia.

I like steel in this situation for its tendency to bend and flow rather than crack and snap.

 

[Brian Jackson]

Thank you, Gentlemen, very much.

4130 it is. My concern was weight, as Doug mentioned the 1" I.D. of the strut tube. I'm always hesitant to add any more weight below the CG than absolutely necessary, and willing to explore all options. Since I will more than likely be lathing/fabricating these items I would like to submit a detailed drawing later in this thread for review by the resident experts here.

Lastly, has there been any problem with galvanic corrosion of dissimilar metals at the axle / strut union?

 

[gyrojake]

Lastly, has there been any problem with galvanic corrosion of dissimilar metals at the axle / strut union?

The workforce difference in aluminum and 4130 is not as bad as Stainless alloys.
You will have more of an iron oxide problem than corrosion.
I have always painted my axil root with a light coat of clear lacquer then grease the Poo out of it before installation.
I also grease everything outside of the axial socket before assembly to slow down oxidation..

 

[Brian Jackson]

The workforce difference in aluminum and 4130 is not as bad as Stainless alloys.
You will have more of an iron oxide problem than corrosion.
I have always painted my axil root with a light coat of clear lacquer then grease the Poo out of it before installation.
I also grease everything outside of the axial socket before assembly to slow down oxidation..

These are the practical tips I live for! Thank you Jake

 

[Doug Riley]

What Jake said. Stainless and aluminum go at each other viciously in the presence of salty or acid moisture. Plain steel and aluminum less so, tho' it still happens.

Brian, are you aware of the 6061-T6 axle-holder sleeves that I used sell through AEROTEC? The internal (5/8") bore accepted plain old 4130 rod, of course, but the bore was non-parallel to the exterior. It had a 3-degree offset, so the main axle tube could slope "uphill" toward the center of the aircraft with the wheel vertical. The OD obviously was 1", to match the internal diameter of the axle tube. I stuck the 5/8" axle rod into the sleeve with epoxy, which should keep the water out.

 

[Brian Jackson]

Doug,

I do recall the insert you're speaking of. Brilliant idea. ( spend my spare time reading the RF archives... true nerd.) I may end up using this method. A quick sketch reveals max. rod insertion of ~5" before the thinnest point on the ends approaches 1/16". Does that sound about right?

 

[Doug Riley]

Sheesh, it's been awhile. I don't recall letting the wall of the sleeve get that thin. IIR we limited the angle of the stub to the axle tube to 3-ish deg. I'll pull the shop drawing and post it in 1-2 days.

 

[Doug Riley]

No Title

Here ya go.

The red squiggle is a setscrew that locks the steel axle against rotating while you're drilling-on-assembly. The vertical 1/4" bolt that passes through the everything to secure the U-bracket for the shock strut should be held well inboard of the end of the axle tube (2" or more). This keeps the weak spot created by this hole away from the natural breaking point at the outer end of the axle tube. This is a departure from the plans, IIR.

I also expoxied the stub axle into this holder. This eliminates any small motion resulting from clearance between the stub axle and the holder.

 

[Brian Jackson]

Thank you for posting this, Doug. It really is a cleverly simple approach. In my profession, engineering simplicity is the hardest thing to do.