Replacement parts sources

[Robert Lees]

Re: Replacement parts sources

The wing struts are designed to be put under a tensional load not compression

You are quite right, of course, Mike. But the primary failure mode of all strut-braced (and pin-jointed) monoplanes is the compression [buckling] failure of the struts. That's why, by design, long struts have a jury strut somewhere along the length. It's not anything to do with tension...it's to reduce the effective buckling length.

Take a look at an aerobatic Taylorcraft or Cub...the struts are super-sized to cope with the compression (buckling) loads under negative "g".

Typically, a strut is four-times stronger in tension than in compression.

Which is one reason why any corrosion (except extremely severe and probably externally-visible) in the lower 12" of the strut is not going to affect a failure in tension: because the wall thickness is typically four times thicker than necessary. So buckling strength of pin-jointed struts (like the Taylorcraft) is a lot less affected by corrosion in what is already an over-engineered wall thickness.

In conclusion, the AD-mandated limits of permissible corrosion have not been adequately researched in terms of the failure in either tension or buckling.

(As an aside the Cub, by design, does not have a pin-joint (in the correct axis) at the lower strut end, which is why "No Step" signs are mandatory, and corrosion at the strut lower end is more significant than on a Taylorcraft.)

Incidentally 1: The weight increase (on average) of the three Taylorcraft I have re-strutted with Airframes struts is 9lbs in total.

Incidentally 2: Mike, your recent (but much later than promised...I guess that's between you and the purchaser) strut delivery to Leicester arrived this week and bolted up OK.

[Guest]

Re: Replacement parts sources

You are quite right, of course, Mike. But the primary failure mode of all strut-braced (and pin-jointed) monoplanes is the compression [buckling] failure of the struts. That's why, by design, long struts have a jury strut somewhere along the length. It's not anything to do with tension...it's to reduce the effective buckling length.

Take a look at an aerobatic Taylorcraft or Cub...the struts are super-sized to cope with the compression (buckling) loads under negative "g".

Typically, a strut is four-times stronger in tension than in compression.

Which is one reason why any corrosion (except extremely severe and probably externally-visible) in the lower 12" of the strut is not going to affect a failure in tension: because the wall thickness is typically four times thicker than necessary. So buckling strength of pin-jointed struts (like the Taylorcraft) is a lot less affected by corrosion in what is already an over-engineered wall thickness.

In conclusion, the AD-mandated limits of permissible corrosion have not been adequately researched in terms of the failure in either tension or buckling.

(As an aside the Cub, by design, does not have a pin-joint (in the correct axis) at the lower strut end, which is why "No Step" signs are mandatory, and corrosion at the strut lower end is more significant than on a Taylorcraft.)
Incidentally 1: The weight increase (on average) of the three Taylorcraft I have re-strutted with Airframes struts is 9lbs in total.

Incidentally 2: Mike, your recent (but much later than promised...I guess that's between you and the purchaser) strut delivery to Leicester arrived this week and bolted up OK.

Hey Rob,

You got me thinking.

If the end had been modeled as a pinned joint (ie no bending moment) then we aught to be carefull not to tighten the attach bolts so much that they bind the strut in the fitting and prevent rotation, thereby no longer matching the model.

For that matter we should lube them too.

I suspect the only end that is really at "risk" of this is the lower end.

I have some 7AC struts that where damaged in an accident and it is obvious that the lower attach fitting bound tight and behaved as a fixed end, the strut end bent (curled) around the rusted in place bolt & fitting. Obviously wasn't free to rotate

Ironically though I think the Pcr is about 2x if one end becomes fixed thru tightening or rust so its all good.

So then one might find it advantageous to tighten up the lower fitting for increased Pcr if doing negative G's assuming the fuselage fittings can handle the bending moment applied.

Yet overtightening on our planes might perhaps contribute to cracks in the fitting inside corners.

Also makes me wonder about that Aeronca compression crack in the spar AD, how likely is it that the cracks are related to upper strut ends that get bound and carry bending moment to the spar. The cracks are often (but not only) near the plywood reinforcements at the strut attach and alleged to be on airplanes doing aerobatics by some folks.

Enough thinking for now. I practice Elec. engr now, have ME and EE but haven't actively practiced Mech. engr in a while. Liked your post made me remember things(hopefully correctly)! Think I'd like to work with something I can see and touch again!

Feel free to correct as needed, no offense will be taken.

Thanks. Dave

[Forrest Barber]

Re: Replacement parts sources

Ah the old engineering talents emerge. Then we have the famous move by Taylorcraft , frowned upon by C.G. in alter years where they moved the stab attach bolts to a vertical position from the horizonial to ease installation but ignored the bending moment. Yes I use lube and light torque on strut end bolts and wing bolts too.... Just like C.G. meant it to be.

[Len Petterson]

Re: Replacement parts sources

Thanks for GOOD hints about the strut bolts.
Here in Canada we last a Challanger ultralight and the pilot for the same reason last year.
I did not realise the importance of this on the Taylorcraft and I have not reed anything in the Taylorcraft manual about it, I will read it again.
So lubricate the strutbolts and leave them lightly torqued!
Would light torque equal 15 to 20 inchlbs?
I am about to have mine removed for testing shortly.
Thanks again Len

[VictorBravo]

Re: Replacement parts sources

You are quite right, of course, Mike. But the primary failure mode of all strut-braced (and pin-jointed) monoplanes is the compression [buckling] failure of the struts.

Rob, perhaps you can allow me to borrow a small spoonful of brain cells for just a moment, mine are somewhat insufficient in true engineering.

If the strut loads in a positive G maneuver are tension, then how can the failure mode be in compression? What happens at the point of failure to switch the loads from tension to compression?

[Richard Boyer]

Re: Replacement parts sources

so what torque *should* be used?

[Guest]

Re: Replacement parts sources

Rob, perhaps you can allow me to borrow a small spoonful of brain cells for just a moment, mine are somewhat insufficient in true engineering.

If the strut loads in a positive G maneuver are tension, then how can the failure mode be in compression? What happens at the point of failure to switch the loads from tension to compression?

Think about it the other way around; assuming no other parts fails what generates a strut failure with the smaller load, a wing in neg load or a wing in positive load?

most common answer: negative load, because struts fail with a smaller load in compression than they do in tension.

Hope that helps

[Robert Lees]

Re: Replacement parts sources

Rob, perhaps you can allow me to borrow a small spoonful of brain cells for just a moment, mine are somewhat insufficient in true engineering.

If the strut loads in a positive G maneuver are tension, then how can the failure mode be in compression? What happens at the point of failure to switch the loads from tension to compression?

Bill, the loads don't switch...it's just that thin structural members are inherently weaker in compression (in that they can buckle), and designers must cater for the fact that struts do see compressive loads as well.

I guess a simple analogy would be to imagine cables being used instead of struts. The cable will be strong enough in tension, but the slightest compression load (gust, landing loads, etc) will buckle the cable.

So put a thicker cable on, to resist the buckling load. Now the cable is much stronger in tension than it needs to be, but probably still not "stiff" enough in compression, so we'll make it a bit thicker still.

Now we have a weight problem, so let's exchange the cable for a hollow tube...

[Mark Julicher]

Re: Replacement parts sources

Love this stuff!
So one way to save weight on a biplane would be to install only the flying wires and leave off the landing wires -- and always touch down very, very carefully.

[VictorBravo]

Re: Replacement parts sources

Love this stuff!
So one way to save weight on a biplane would be to install only the flying wires and leave off the landing wires -- and always touch down very, very carefully.

If you put the landing gear struts halfway out on the wings, you wouldn't even need to be that careful landing

[UNIVAIR]

Re: Replacement parts sources

Taylorcraft Owners,

In an effort to serve you better, I am doing a little market research to try to find out what parts are in the greatest demand among you. I know that there are dozens of things that you all would like us to make, but like most small companies we have to pick wisely where we choose to put our money when investing in new projects. What I would like you to do is to send me your suggestions of what it is you need. We can then take your suggestions, find out where there is the most demand on particular parts, assess their difficulty in making and cost to product and hopefully start bringing some of these items back into production.

If you have some items that you would like to suggest, you may contact me directly at my email here at Univair, [email protected].

Mike Sellers
Marketing and Sales Manager
Univair Aircraft Corp.

[Len Petterson]

Re: Replacement parts sources

Now that is what I call a good bussiness response!
Maybe it is the reason they been in the bussiness for LONG time.
Len Petterson

[astjp2]

Re: Replacement parts sources

I have corresponded with Mike, he seems willing to at least look at the demand of parts needed and maybe we can get alternate producers of some of the high usage items. tim

[Forrest Barber]

Re: Replacement parts sources

maybe I should resend the list that we made up 4 years ago!! How about strut clamps for the struts.....

[Ragwing nut]

Re: Replacement parts sources

Taylorcraft Owners,

In an effort to serve you better, I am doing a little market research to try to find out what parts are in the greatest demand among you. I know that there are dozens of things that you all would like us to make, but like most small companies we have to pick wisely where we choose to put our money when investing in new projects. What I would like you to do is to send me your suggestions of what it is you need. We can then take your suggestions, find out where there is the most demand on particular parts, assess their difficulty in making and cost to product and hopefully start bringing some of these items back into production.

If you have some items that you would like to suggest, you may contact me directly at my email here at Univair, [email protected].

Mike Sellers
Marketing and Sales Manager
Univair Aircraft Corp.

Instrument panel blanks
rudder steering arms (correct steel ones)
just to get started