Strut angle conundrum

[PA1195]

Re: Strut angle conundrum

Some more of today's pics. The trailing edge of two T's. Note the straight line across the fuselage tip to tip. The dog pic is for her fun in the snow.

Gary

[Guest]

Re: Strut angle conundrum

I think I figured it out.

Gary's picture of the black strut, comment about the trailing edges and info about the few number of 8 degree struts sold realigned my thinking.

My initial guesses were;

1) Strut damaged by bowing back near middle causing the end to deform in the direction we see on the 8 degree struts, that is not likely because when strut is fixed or replaced there would no longer be an angled end.

2) Wing and spar swept back due to accident, by swept back I mean pivoted at the spar butt fitting and spar axis is not perpendicular to the flight direction. It would cause the strut end to deform in the direction we see on the 8 degree struts. This scenario requires a near miracle to get both wings at the same sweep by accident damage. Also Gary saw no sweep.

3) Wing spar attach fitting to strut has been moved back by .050" to .100". I thought that this would cause the strut end to deform in the direction we see on the 8 degree struts but that is wrong. When I was thinking about the separator tube being short, tight or un-shimed I was thinking this scenario. However I now believe that this scenario is not one that will cause a need for the end to be bent like the 8 degree struts but will create a need for a lower angle of bend not a higher angle. That's because while saying the spar fitting was was moving back (translation backwards, but still mostly parallel to the original spar axis) I was really thinking about sweeping it back (pivot) and that leads to wrong conclusion.

4) Gary's pictures and observations bring to mind that the when the wing spar attach fitting to strut has been moved forward by .050" to .100" that will generate a need for the strut end to have a greater backward angle as we see it in the Alaska Airframes pictures.

Again when I say move forward I mean move ahead in a direction perpendicular to the spar axis and moved forward only at the location of the attach fitting. In this scenario the wing axis is not swept. The strut attach fitting can move ahead if the spar is slightly bowed forward near it. The flexibility of the spars and stiffness of the wing truss when assembled makes this possible. The spars still attach at the correct location on the fuselage and the tip end is still in the correct location thus no swept back wing. The spar has just a slight forward wave or bump at the strut attach point.

When this happens the strut end will not slide into the wing fitting unless you bend the strut end backwards a little bit because a) the strut end has to arc forward a little bit to follow the wing fitting, b) then the inside rear edge of the wing fitting will strike the rear side of the strut end and the front side of the strut end will be unable to fit inside the wing fitting.

Another way to say it is that the wing fitting slides forward and the strut then has to arc forward to attempt to slide into it it, but it cant slide in because the fitting surfaces are no longer parallel.

I will make some pictures tomorrow using some spars, fittings and struts to try to demonstrate #4.

So how can #4 occur? It can by putting one of the long compression struts between the wing strut attach fittings instead of the short one that is supposed to be there. How does the strut end get bent to 8 degrees? A mechanic heated it and bent it to fit.

I think this is the simplest explanation of the two angles. Anyhow that's my story and I am sticking to it! (for now)

Dave R

[Robert Lees]

Re: Strut angle conundrum

Some more of today's pics. The trailing edge of two T's. Note the straight line across the fuselage tip to tip. The dog pic is for her fun in the snow.

Gary

I laughed out loud, and perhaps a small amount of coffee was spilled on the keyboard!

Rob

[Robert Lees]

Re: Strut angle conundrum

Some more of today's pics. The trailing edge of two T's. Note the straight line across the fuselage tip to tip. The dog pic is for her fun in the snow.

Gary

But how can you bear to leave a fabric aircraft parked outside? It is pretty much unheard of here in the UK (or even in Europe). We have hangars to keep rain, snow, hail and UV off fabric-covered aeroplanes. But you in the USA (particularly AK) have more acres of land than we do, so it must be cheap to have land for construction of hangars.

Confused of Britain:

Rob

[Guest]

Re: Strut angle conundrum

But how can you bear to leave a fabric aircraft parked outside? It is pretty much unheard of here in the UK (or even in Europe). We have hangars to keep rain, snow, hail and UV off fabric-covered aeroplanes. But you in the USA (particularly AK) have more acres of land than we do, so it must be cheap to have land for construction of hangars.

Confused of Britain:

Rob

When I was in New York it was $48/month for tiedown outside and $360 to $400 a month for hangar.

The $300 to $350 a month difference will pay for a recover job over 20 years.

Dave R

[M Towsley]

Re: Strut angle conundrum

Rob,

I almost spilled my tea after reading your inquiry, lol. There may be a lot of land but some folks think that land is priceless. Though I am lucky my two hangars are very reasonable at my airport, which happens to be a very nice airport in the Capitol of Illinois, (no it is not Chicago), there are some hangars where the rent is more than my former mortgage on my home. Some airports do not have the room to build anymore, usually larger cities. Some, (most?), cities barely have enough budget to keep an airport open, let alone build new hangars. My former hangar in Taylorville, IL had so much space under the doors I had to shovel more snow from inside out than that which was outside. There were issues with taxiways and runways that the FAA had to be involved due to cracks being big enough to swallow a tailwheel. So money is a big reason, and some folks wonder why they have to pay for hangars for the 'rich' folks with airplanes. Some local governments feel the same way.

I am sure there are so many other reasons I am sure others will share.

[PA1195]

Re: Strut angle conundrum

Where do I start and finish regarding parking? I pay $540/year to park along the Fairbanks Intl floatpond with access to wheel/ski designated runways. No electricity available. That's what happens when the State of Alaska owns and maintains an airport. There is land available for lease and some have built business and private hangars for hundreds of thousands of dollars. There's a few open T-hangars for hundreds a month. See typical lease rates for hangar space near Anchorage-Kenai/Soldotna Alaska here: http://alaskaslist.com/?cityid=1&lan...catid=59&area=

Suffice to say I can't afford it nor can most plane owners. There are several private airstrips nearby where one could buy or build a hangar on cheaper land...but the cost of building in Alaska is high due to imported materials and high labor rates.

I assume elsewhere private, municipal, and corporate equity investment supports hangars. Not so here.

If I were in my '20's again and could afford the outlay I'd build a hangar and live in it. Too late now, and that's unfortunate because for several months in the winter flying is....well...not pleasant and indoor aviation activities would be a good way to pass the time.

So the dog gets a happy daily walk by the plane when in town and I get to watch the grass grow, snow fall, and fabric fade away.

Gary

[Scott]

Re: Strut angle conundrum

At least in the north we're "freeze-dried" for half the year so the airframe should last twice as long...

[Guest]

Re: Strut angle conundrum

I set up crude system to test my item #4 above.

#4 does result in a bend in the proper direction but the magnitude of the bend is small in fact the clearances in the fitting would allow for the required angular mis-alignment. It may be because I don't have the inboard end of the strut clamped in position. Will work on that tomorrow.

So I think number 4 is a proper scenaro to result in a bend as seen by AA but there is not way it will produce a 6 degree offset in my setup. My setup may be the problem here. I had to move the spar 1" forward to get the small change seen in the pictures.

Middle picture is normal situation, rightmost picture is with spar moved 1" forward

[PA1195]

Re: Strut angle conundrum

Let's pretend the fuselage end of the strut's tang is further forward relative to the strut centerline and outboard end fitting on some than others. When attached to the fuselage fitting that might move the front strut slightly rearward, and that might require the outboard end to be bent rearward as well to fit the spar fitting's ears. Just a thought. I need to take some pics tomorrow of the four planes I posted above.

Edit 11/16: I looked at all four T's I photographed that I photo'd the upper struts of earlier. All struts had the same front strut face to lower tang distance, even #3 that appears to have an 8* bend to the upper fitting. So I'll forget the above theory as there is only about 1/8" between front and rear struts at the bottom so lateral lower tang placement on the strut isn't much of a manufacturing option.

Edit: Airframes strut pics. The lower tang and outboard end fitting's bend relative to centerline on the front strut is what I'm discussing http://www.airframesalaska.com/produ...-tcraftset.htm

Edit: Univair struts: http://www.univair.com/taylorcraft/v...nt-lift-strut/

I also guess if the landing gear attach fittings on the fuselage were offset rearward relative to the wing spar fittings (due to an atypical airframe jig) it would require a sharper bend in the front strut outer fitting. But then wouldn't that also require a change to the rear strut angle? Maybe the rear outboard fitting adjustment screw has more slop tolerance than the front.

Merely all speculation.

Gary

[jstall]

Re: Strut angle conundrum

Since my struts are do after the first of the year, I've spent the last six months bouncing back and forth on what I was going to do. I noticed a week ago that AA has 10% off until the end of the year so I decided to just go with their struts. After reading up on their site on how to measure the angle, I measured mine a couple days ago and came up with 10* on both sides!?? I'm heading into town this morning and might even go up for a little bit so I'm going to measure again. I noticed on the order page there was 2*, 8* and (call me) options.

Wing sweep make a difference?

I'm not thinking there is any wing sweep, leading edge is straight with the longitudinal
axis. The angle sets the sweep back of the strut from wing attach point to the fuselage
attach point, forming that vee look at the fuselage attach point. I'm wonderning
if the rear strut which also sweeps forward is any issue??

JS

[PA1195]

Re: Strut angle conundrum

I helped a mechanic a couple of times trammel some wings for two different planes. Had no idea at the start what was up with all that but did get a good lesson in alignment and squareness. That was with metal spars. I wonder if wood bends enough to offset the attached strut fitting causing the need for different struts? I have no experience so just asking.

Gary

[astjp2]

Re: Strut angle conundrum

Has anyone thought of if the attach fitting lower hole is off by a smidge then it would cause the same problem where the strut bolt wont go through? Once its clamped up, it will flex enough to be plenty tight...

[Hank Jarrett]

Re: Strut angle conundrum

The bolt is NOT supposed to clamp up the fitting on the strut. The standard for pinned joints is that the bolt should be able to rotate (yea, it doesn't say how much torque you may need). Squeezing the lugs together is NOT a good idea. They were designed for a bolt bearing load, not a bending load plus bolt bearing load.

You also would have to put a bending load on the strut itself which would significantly reduce the long column buckling load capacity. Under a snow load or negative "G" the strut would fail much sooner. Not a huge risk for how our planes are flown, but not a good idea.

[Guest]

Re: Strut angle conundrum

Has anyone thought of if the attach fitting lower hole is off by a smidge then it would cause the same problem where the strut bolt wont go through? Once its clamped up, it will flex enough to be plenty tight...

Hi Tim,

No I hadn't but that is a good idea.

If the angle or position of that fitting, hole, assembly is of by a small amount it could shift the upper end a lot.

I have to think thru the geometry, good thought.

Dave