The International Cessna^® 170 Association

Hey, Tye! Spruce sells streamline tubing! 877-477-7823

gahorn wrote:Hey, Tye! Spruce sells streamline tubing! 877-477-7823

Hi George, they sure do but the smallest commercially available size, in major axis, is 1.012". The jury struts on a 46 120/140 are made of .682". I actually found a mill that could make it and provide cert paperwork for about $3.50 a foot. Check out the price of that 1.012" at Spruce or Univair! $3.50 /ft is a hell of a good deal. Problem is the mill needs a 2500' minimum order and that is enough for about 416 120/140's worth of jury struts. Could make the struts out of 1.012" I suppose but I think that might look funny.

The '47-48 120/140 and 170 jury struts are made out of 1/2" round tube flattened to 3/8" for a streamline affect. Cheaper and easier to make I think.

tye

Tye, I apologize. I was just too brief in my previous msg to get my idea across. I've found that Spruce always is happy to share info regarding their sources of materials. I was thinking that perhaps you might call them, ask who supplies their oval tubing, and then give that mfr. a personal call....and perhaps get lucky.
$3.50/ft is not a great price if you have to buy $8750.00 of the stuff per order. I'd rather pay $20/ft just for the few feet you might need.
Good luck.
(or maybe you could tell the supplier you found that you'd need to inspect their capability and see if they'll send you a 10-foot sample of their product in the size you're interested.)

Univair or Wag Aero probably has the jury struts already made . How much are they asking for them?

blueldr wrote:Univair or Wag Aero probably has the jury struts already made . How much are they asking for them?

Nope. Been there. Nobody makes new jury struts for 120/140's, especially not the '46 type, which is the streamline tubing. The 47-48 type appears to be the same construction as a '48 170, maybe even the same size, and no one makes those struts either.

I'm willing to be proven wrong on this though. If someone finds a place I can get new jury struts from I'll eat a big plate of crow and be happy with the new struts.

Aircraft Spruce gets their streamline from Columbia Summerill, supposedly the only manufacturer of streamline tubing and they don't carry it and so far no one I've talked to at any of these commercial places is willing to get it.

tye

gahorn wrote:Tye, I apologize. I was just too brief in my previous msg to get my idea across. I've found that Spruce always is happy to share info regarding their sources of materials. I was thinking that perhaps you might call them, ask who supplies their oval tubing, and then give that mfr. a personal call....and perhaps get lucky.
$3.50/ft is not a great price if you have to buy $8750.00 of the stuff per order. I'd rather pay $20/ft just for the few feet you might need.
Good luck.
(or maybe you could tell the supplier you found that you'd need to inspect their capability and see if they'll send you a 10-foot sample of their product in the size you're interested.)

Hi George,

According to Spruce's catalog Columbia Summerill is their manufacturer, supposedly the only one in the world but I found someone else. I was unable to locate contact info for Columbia Summerill but I didn't call Spruce for it. Might try that.

I found a machine shop that can make the streamline tubing out of 1/2" round tube but they don't do the inspections and don't certify the material. They would do it for 10.50 a foot for 16 to 18 foot lengths. I might be reduced to trying that and finding someone who can inspect it but that is likely to cost another $10 a foot and it might all be scrap. So I'm leary about trying that route. Could be throwing $500 or more out the window.

i did attempt to talk the mill into a smaller amount for a higher per foot cost but they were not willing to do it. I couldn't get any other owners interested in any kind of group buy either.

tye

My ragwing's jury-strut tubing looked round to my nekked eye-- I didn't believe you about it being oval until I miked it. Very definitely oval! I guess the old eyeballs ain't what they used to be.
In leiu of streamlined or even oval tubing, what if you just used 1/2" round? Probably plenty strong, easier/cheaper, plus probably not noticable except to someone who's too damn close to the airplane anyway.

Eric

zero.one.victor wrote:My ragwing's jury-strut tubing looked round to my nekked eye-- I didn't believe you about it being oval until I miked it. Very definitely oval! I guess the old eyeballs ain't what they used to be.
In leiu of streamlined or even oval tubing, what if you just used 1/2" round? Probably plenty strong, easier/cheaper, plus probably not noticable except to someone who's too damn close to the airplane anyway.

Eric

According to the Cessna print for the 120/140 jury struts they're made of 1/2" round steel tubing that is flattened to 3/8" in one dimension. I suspect that the engineers wanted the tubing flattened to avoid vibrations that can get setup in cyindrical shape. Or maybe just because it looked cooler. Fluid flowing around a cylinder creates "lift", NOTAR (NO TAil Rotor) helos use this force. With my luck the FAA would probably want a DER to say round tube is ok in lieu of the streamlined or flattened tubing.

Tye

Actually Tye NOTARs have ribs or tabs running parallel to the tail and ports releasing air pressure which make the round tail-boom act like an airfoil.

I don't believe a perfectly round cylinder with symmetrical surface drag will create lift as air passing around it will not be accelerated faster on either side creating unequal pressure.

But now we are way of subject and that rarely happens around here.

N9149A wrote:Actually Tye NOTARs have ribs or tabs running parallel to the tail and ports releasing air pressure which make the round tail-boom act like an airfoil.

I don't believe a perfectly round cylinder with symmetrical surface drag will create lift as air passing around it will not be accelerated faster on either side creating unequal pressure.

But now we are way of subject and that rarely happens around here.

Yep. The air ejected is used to take advantage of the Coanda effect, the tendency of a fluid to follow a curved surface provided the angle of incidence is not too sharp. This causes what is essentially "lift" to pull or push, depending on your point of view, the clyinder (tail boom) to one side. I'm a rotor-head too, although my experience is limited to R-22's. I've only read about the fancy stuff.

pictures worth 1000 words http://www.scienceweb.org/movies/speed4.html

You're right, I chose my words poorly attempting to offer a simple explanation. Maybe a better description would be the fluid flow around a cylinder will "break" irregularly, create drag irregularly on the downstream side and can setup vibrations that can cause structural problems. The surface drag is not always equal on all sides. Bridge designers have to take this into account when designing pylons for bridges and even large buildings like the Patronas <sp?> towers in Kuala Lampur. Or so says the engineers, I have to take their word on it since I'm not one.

Anyhow, the streamlining effects offered by squeezing a 1/2" tube to 3/8" would seem to be insignificant for a 100mph airplane. My assumption would be the streamlining would have the most benefit in avoiding vibrations that the cylinders could develop that would lead to fatigue problems.

I'm assuming the engineers had a reason for attempting to streamline the struts otherwise it doesn't make business sense to do so since the material and/or fabrication steps would cost more, make the product more expensive and most likely, reduce profits. I'm thinking cost is why they quit using the streamline tubing for the jury struts after only a single model year (46).

I'm not an engineer, but I would think the cold working
of the material (by squeezing it from a cylindrical shape
to an ellipse) would tend to strengthen the part. Thoughts?

Well, certainly "flattening" the tubing would make it stiffer fore/aft due to the increased axis. I wouldn't know if cold-working figures in the picture at all.

Ovalizing the tubing would make it stiffer on the wide axis, but less stiff on the narrow axis. No? Seems like leaving it round would provide as much strength overall.

Eric