Design structural limits for the b series taylorcraft

[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

[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).

[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

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.)

[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

[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?

[Jim Hartley]

Re: Design structural limits for the b series taylorcraft

Shouting gets attention and emphasizes important points...

[jstall]

Re: Design structural limits for the b series taylorcraft

I'm really bad about the "SHOUTING THING" as Forrest once said and I think he actually was offended, said "STOP SHOUTING" well I didn't mean anything at all about it, this comes from a business practice I used where a ball oratator was used on a typewriter years ago, and I got use to using it and not having to capitalize, like that quick point so got in the habit of doing it on line, then found out that was a no no to some folks.

I still have a tendency to do it, if I do please don't be offended

JS
Alva, Ok
N95083

[Joe cooper]

Re: Design structural limits for the b series taylorcraft

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

I remember in the 70's three of us owned a BC12 D which we flew a lot. I landed once and a good friend CFI with many hours, , an aero commander demo pilot asked if he could take it up. He did and promptly stalled it at around 2000 feet, spun it a little, then did 17 consecutive loops right over the field. I would think a good rebuilt would be safe to loop and a stall spin would not put much stress on it at all. If rebuilt correctly, it should be as good as new or better. Originally, they were inexpensive trainers and were stalled -spun a lot and probably looped a lot. (Eric minns should be up on this subject.) When I learned, spin training was mandatory. The first two made me very nervous but when he explained that it was stalled, no longer flying hence very slow speed, the light bulb came on. Recovery was gentle and easy. ( aeronca champ)

[Joe cooper]

Re: Design structural limits for the b series taylorcraft

In the Air Force the teletype we had was ALL CAPITAL letters. No one considered it shouting. It was easier to read which was why it was THAT WAY.

[jstall]

Re: Design structural limits for the b series taylorcraft

In the Air Force the teletype we had was ALL CAPITAL letters. No one considered it shouting. It was easier to read which was why it was THAT WAY.

Yes that is true and, most all of the old teletype and telex messages
were also done in caps, anyway, it is quick easy to read and you don't have to do the capitalization on first line and nouns

I like it cause in a email chain and can easily see where I respond vs the
other person, kinda a identification deal, anyway, many don't like it
as I was repremanded once big time for it, so I have tried to slow it down


JS
N95083

[Bird]

Re: Design structural limits for the b series taylorcraft

As a side note most of you know I am a tower crane operator ( the guy that sits on top of the high rise buildings). On the Linden tower cranes there is 1 spot that the load line terminates right beside the crane and there is a pin about 3/8" that holds the line and the crane is certified in a 2 part line for 13,000lbs. I have often looked at this pin and wondered about it, I know I did 1 lift that maxed the crane out at 26,000 lbs in a 4 part line but still only had the 1 pin at the end, all I can say is I have had a 8,000 lb load break free and what happened would make most people stay away from under the tower cranes, took me damn near 10 minutes to find my dentures

[Hank Jarrett]

Re: Design structural limits for the b series taylorcraft

Hey Bird, you weren't up there yesterday when the roof caught fire on the hospital were you? We were a little worried when the TV pictures looked like the smoke plume engulfed over the crane control cab. They give you a O2 mask up there for that?
Hank

[Bird]

Re: Design structural limits for the b series taylorcraft

Sorry Hank, I'm not on that job any more-nor will ever work on a project that has anything to do with the Navy. I am not gonna have some puke that knows natta about tower cranes tell me (28 years experience in tower cranes alone) how to run a tower crane.
Stupid jerk said I was turning the crane to fast, both cranes turned at the same rate but mine had 130' more jib so it looked like it was but really wasn't.
The best part was the guy that replaced me in less than a week had caused more than $50k damage to the crane. I was jumping through hoops for the Navy and just said ta hell with them, the employer had never used tower cranes before and did not support the operators, the other crane operator is leaving also.
Bird

[Hank Jarrett]

Re: Design structural limits for the b series taylorcraft

Looks like they not only didn't know how to run the cranes, they set the building on fire too! I was always worried about your safety on that project.

Hank