Design structural limits for the b series taylorcraft

[Jim Hartley]

Re: Design structural limits for the b series taylorcraft

Shouting gets attention and emphasizes important points...

[Hank Jarrett]

Re: Design structural limits for the b series taylorcraft

Sorry for the YELL! ;-) The method Tim used has several assumptions that added up to a huge safety margin in the calculations. All of them seemed to be more conservative (which is a good thing) than needed.
When I did an analysis what I found was that if the plane didn't have any flaws, the wing would fail at the outboard strut attach through the wing spars if you just kept pulling up on it (maybe beyond what the airfoil could generate). I don't remember what G loading it was, but it was more than I would ever want to pull (remember that was for a new plane with no hidden flaws, not one of our 70 year old planes). If there is a flaw, like a crack or spar split, the failure point would change, and I made some assumptions that I can't prove are any good either, but it made me feel more comfortable with the design safety margins.
As far as I know, no Taylorcraft has ever suffered an in flight breakup that was traced back to a design flaw and not an unknown crack or damage. That does not include things like massive overloads from something like a mid-air or hitting objects (birds, trees, buildings, towers.....).
You could optimize the design and remove a LOT of weight if you were doing a clean sheet build.

Hank

Didn't think I could do a whole message without at least one all cap word did you?

[otrcman]

Re: Design structural limits for the b series taylorcraft

My takeaway was that the safety factor is appropriate, but by no means huge. (Or HUGE as Hank would say.)

Agree 100%, Tim.

In my case, I had actual Taylorcraft calculations to work from, although they were for the L-2. As you probably know, working backwards through somebody else's calculations is labor intensive because they often use different symbols, skip steps (where the heck did they get that number ?), etc. So I only did a few cases. But I kept getting the same bottom line -- about 4.1 G limit.

Over the years I've heard all the same stories about how Taylorcrafts, Cubs & Champs were overbuilt and could pull lots of G's. In every case when I inquired as to the source of this knowledge it turned out to be rumor based. Of the engineers who have bothered to check the numbers, nobody that I know has claimed the planes to be anything more than nicely adequate for ordinary flying around.

Dick Fischer

[TimHicks]

Re: Design structural limits for the b series taylorcraft

Naw, my quick n dirty calculation was more like (remember I was making general assumtions to make the math easy):
Assume that the plane weighs 1200#. Each wing takes half that, or 600#.
Assume all the lift force goes through the main strut (it doesn't, the root attach can take some, the rear strut can take some)
Assume 20 degrees angle of the strut (I don't know what it really is).
So the steady-state tension in the strut would be about 600#/sin20 = 1750# (just flying along, no accelerations)
A 5/16" bolt either end of the strut has a cross section of about 3.14 *5/16"^2 / 4 = 0.077in^2
So the shear stress on that bolt calculates to about 23,000 psi. Since it's in double shear, its really half that, say 11,000 psi
That was all I did. I think that Hardware store bolts allow about 44,000psi so at 4G, they would be at their limit. AN bolts are a lot stronger, but I don't know how much
My takeaway was that the safety factor is appropriate, but by no means huge. (Or HUGE as Hank would say.)

[Hank Jarrett]

Re: Design structural limits for the b series taylorcraft

Yea, but the critical load model is for long column buckling in the struts, not tension. The tube is sized for a bending load in the center causing the strut to buckle and is also why there is a jury strut (effectively reducing the span of the column). When you design something like a wing strut you have to analyze multiple cases and size the part for the worst case. If tension was all you had to design for you could use a couple of cables (not too good in compression though!)
For a strut you do a case for tension, buckling, torsion, compression, foot load end bending, tie down end load bending, slipped down rope tie down near end loading in bending, and probably a few I have forgotten. I do remember that long column bending was critical when I did a strut analysis and there was a HUGE safety margin in tension to be able to sustain the buckle load. I think the second most critical load case was either a foot on top of the strut out away from the fuselage attach or a rope tied to teh the strut that had slipped down the strut towards the jury strut (both of which are really special cases of long column buckling).

Hank

NEVER lift your wing by pushing up on the strut except at the VERY END!

[TimHicks]

Re: Design structural limits for the b series taylorcraft

I remember that, years ago when I first got my TCraft, someone was telling me how strong it was and that there was a generous safety factor on the lift struts. Well, being a mechanical engineer, I did a quick "napkin sketch" calculation on the lift strut stresses. I was thinking that I would just confirm what the old guy was telling me, that there was generous safety factor. Instead, after my calcs, I remember thinking that "wow, these airplane designers really do their homework and don't make these things any stronger (heavier) than they need to be"

It cured me of any desire to start doing silly things in the airplane (although I'm comfortable stalling and spinning).

[jstall]

Re: Design structural limits for the b series taylorcraft

just curious. Anyone have a accurate airspeed number that they got coming out the bottom of a loop properly performed? (in a 12d say).
Dc

100 to 120, but beeeee careful, these are old airplanes and each has its thing so to speak, when was it recovered or restored, what was the wood like?? They are not new. Duane Cole did alot in them, Piche also does but he told me that nothing about that a/c was stock except the airfoil and that is why they use it, very good inverted

a well executed loop or a spin is a no brainer, recovery from a spin will be about 2.5 to 3.0 g's for about 4 or 5 sec and about 100 to 120, loop 100 to 120 in the start 3.0 past vertical, relax it let if flot thru and then come on back and recover, back out at about 100 to 120

[flyguy]

Re: Design structural limits for the b series taylorcraft

Just curious. Anyone have a accurate airspeed number that they got coming out the bottom of a loop properly performed? (in a 12D say).
DC

[otrcman]

Re: Design structural limits for the b series taylorcraft

There are some old design books with "guidelines" but if anyone has actual numbers for the Taylorcraft I would REALLY be interested. It would make engineering any modifications MUCH easier!

Hank

I don't have data for the B, but do have some of the original stress analysis work for the L-2. There doesn't seem to be anything that comes right out and says, "This many G's". But I did back out some load numbers from their calculations and was very surprised at the results.

Contrary to urban legend, it appears that the L-2 design limit was only around 4.1 positive. I didn't work on any negative stuff because it's pretty labor intensive to do this kind of work. But 4.1 ? That's not even Utility category by today's standards.

Y'all be careful out there.

Dick

[Bigdog]

Re: Design structural limits for the b series taylorcraft

My 41 was certified under "Standard Normal" which in 1941 allowed loops, rolls and many other maneuvers. I like steep turns (old sailplane flyer) but somehow I don't really want to loop a 1941 Taylorcraft. Kind of like taking my grandmother out on a race track. I treat my baby with respect, and someday if I really NEED those G's, I hope she will still be able to give them to me.

Hank

Besides, I really DON'T LIKE negative G!

The 46 BC-12D I owned in the 70's was also Standard. I flew acro in it - loops, rolls and spins. I even flew it in an IAC Sportsman contest in 1976. I did not do the snap roll that was in the program. I rented a Decathalon to do serious acro but I found myself enjoying inverted gliding in the Tcraft too much and decided that pushing the limits of a 33 year old (at that time) airplane wasn't really smart and stopped cold. I haven't done acro in a non-Acro rated plane since.

I'm leaving the inverted systems out of the RV I'm building because my days of hanging from the belts is long gone.

[Hank Jarrett]

Re: Design structural limits for the b series taylorcraft

My 41 was certified under "Standard Normal" which in 1941 allowed loops, rolls and many other maneuvers. I like steep turns (old sailplane flyer) but somehow I don't really want to loop a 1941 Taylorcraft. Kind of like taking my grandmother out on a race track. I treat my baby with respect, and someday if I really NEED those G's, I hope she will still be able to give them to me.

Hank

Besides, I really DON'T LIKE negative G!

[Bird]

Re: Design structural limits for the b series taylorcraft

Believe it or not, that is my information, there is a taylorcraft owner close to me that was told by another owner of a taylorcraft that he took his plane up and did 26 loops with his finance and she keep saying do it again. I do not know how much time he used to set this or each loop up but have heard it is possible and that the taylorcraft can and is acrobatic to the limits of the engine.
It is possible that people have lied to me but I really do believe I have seen the numbers of +6 and -2 to the best of my knowledge but can not place were I saw them

[Randy]

Re: Design structural limits for the b series taylorcraft

Seem to remember +6 -2 although not sure on the -2 could have been -3

Wow, great, that means I can take my 1940 BL-65 and start doing loops, spins and everything else :joy:

[Bird]

Re: Design structural limits for the b series taylorcraft

Seem to remember +6 -2 although not sure on the -2 could have been -3

[Garry Crookham]

Re: Design structural limits for the b series taylorcraft

The certification basis for the Taylorcraft is CAR04. It's been quite a while since I looked at the data but if I remember correctly the load limits are not presented as absolute G force limits but have to be calculated for the weight of each airplane. Civil Aviation Regulations are here: http://ntl1.specialcollection.net/sc...&site=dot_cars