What metal is the (British?) designation T26?

see spun part of tubular rivet assembly in diagram.




The only references i can find on the web are about welding rod substitution options that also seem to indicate it could be magnesium based? Any links to better spec or description of the actual material?

thanks!
smt

stephen thomas said:

see spun part of tubular rivet assembly in diagram.

View attachment 336342


The only references i can find on the web are about welding rod substitution options that also seem to indicate it could be magnesium based? Any links to better spec or description of the actual material?

thanks!
smt

Click to expand...

I would be surprised if the tubular rivet was really Mg based, as mag alloys are typically more brittle than Al alloys:

A rare-earth free magnesium alloy with improved intrinsic ductility

Not to mention weaker, more corrosion prone, etc. Especially not bearing directly against a stainless steel element.

I did a little searching out of curiosity, didn't find anything. Maybe one of our British members can provide a lead.

It appears to be just mild steel tube, according to this

British T26 Spec tubing - Aircraft engineering - Eng-Tips

Milland -

Yes, based on the rest of the rivet assembly i had started out expecting T26 to be some sort of ductile stainless steel. So the hints i was findin online did not make sense. Let alone brittle and low tensile strength, putting a 3rd metallic element that is prone to instant corrosion in the sandwich just seemed fiendish.

Peter- That is perfect! Thanks for the effective sleuthing.
That link makes much better sense for the application.
Even the low tensile strength, upon reflection, should be in keeping with the rest of the assembly - the stainless "close fitting ferules" take all the shear loads, the aluminum distance tube is probably somewhat limited in crushing resistance, and the hollow rivet merely holds it all together.

I'm in a "discussion" about how easily the components could be made, should someone determine specs for modern materials & confirm the engineering. Apparently most restorers are not familiar with screw machines or "turret" lathes & believe the manufacturing (as opposed to materials) issues are insurmountable.

The joint was used at tubing clusters in 1920's/30's by Hawker for Hart/Demon/Fury, including apparently through at least the early Hurricanes. Although much more complex that welding, perhaps it was faster to batch mating tube components and brackets? (No fitting, so long as the parts were manufactured in jigs?) Or maybe to avoid having to straighten fuselages and anneal clusters as tends to be necessary with welding? I doubt it was an original concern, but if the correct materials are available it should make repairs easier than cutting out and refitting tubes, as well.

Replicating a Hawker spun rivet joint | Homebuilt Aircraft & Kit Plane Forum




smt

Before pop rivets got invented?
Bill D

each connection requires the spacer tube to prevent crushing, and high shear strength between the strut and the brackets (the "ferules"). Hawker must have decided that the design was more reliable & lighter weight than solid steel headed rivets in crush tubes. I don't know when Cherry N or Q rivets became available.

smt

Stephen, got a question about a note in the original drawing. "Holes in tube and plate reamed in situ" How on Earth did they keep the washer/plate and crush tube from simply spinning driven by the reamer?

Interesting question.
I wonder if the "tool"? (if such there was?) that positioned the tube had provision for gripping?

The whole system is new to me.
And not really one i'm likely to be involved with.
Fascinating, though.

smt

stephen thomas said:

Although much more complex that welding, perhaps it was faster to batch mating tube components and brackets?

Click to expand...

People did not use to like welding. Even as recently as the late sixties, early seventies the Brits would go to great lengths to avoid a welded motorcycle frame.

Stephen, got a question about a note in the original drawing. "Holes in tube and plate reamed in situ" How on Earth did they keep the washer/plate and crush tube from simply spinning driven by the reamer?

Click to expand...

I had some of the same questions. And also wondered if the note was a shorthand for "everybody knows how this is done" just to distinguish it from another instance that required nothing special. In the video I think I caught something about Hawker positioning the crush tube with wires which wouldn't have held if from spinning. (you gotta get that stinking little part down inside the larger tube somehow - then get your positioning tool back out) With multiple parts I wondered if a clamp over the whole assembly before reaming might have kept everything in place.

I never heard of it and to my shame worked for hawker siddly but in defence the alloy plate sheet and extrusion bit
Mark

And also wondered if the note was a shorthand for "everybody knows how this is done" just to distinguish it from another instance that required nothing special.

Click to expand...

I'll bet you are correct.
The tubes probably arrived already reamed. Afterall, there is no advantage to ream those in place.
The other pieces must have been for the "ferules" to properly do their job. Perhpas the (pre-reamed) tube might have helped guide the reamer to the "offside" hole a little, as well.

Mark, that's pretty cool.
My perception, though, is that those joints were last used during WW2 or thereabouts.

smt

stephen thomas said:

I'll bet you are correct.
The tubes probably arrived already reamed. Afterall, there is no advantage to ream those in place.
The other pieces must have been for the "ferules" to properly do their job. Perhpas the (pre-reamed) tube might have helped guide the reamer to the "offside" hole a little, as well.

Click to expand...

My guess would be that the structural tube was the only thing that needed reaming (for the OD of the ferules). Spacers and washers could be made with an OD or ID (as required) to match the known T26 steel tube OD and the ferule OD.

If the T26 steel tubes tended to have varying OD's from a nominal diameter, perhaps then there would need to be a sandwich clamp that allowed the final match-reaming.