BlackRV7

BlackRV7

Well Known Member
I posted the original message under RV Photos and URLs but you can't post replies so I moved it over here. While with TeamRV this past weekend I talked with several people at airshow center and autopilots seemed to always come up. With a thread started on another forum, I posted a quick note about my impending install of the Trio EZ Pilot and EZ 2 altutude hold with vertical speed. I got several off list emails of people wanting pictures, so here goes. I am going to do the same as I did when I got one of the first totally prepunched emps, same day coverage. Here goes, I will start at 3PM eastern time and see just how long it takes me to fire it up.

http://rvflying.tripod.com/id33.html
 
Did you decide where to put the ALT hold yet? I'd put it as close as I could to the altimeter. That's where you'll be looking to see if you've hit your target altitude. When you do, just push da button.
 
Did you decide where to put the ALT hold yet? I'd put it as close as I could to the altimeter. That's where you'll be looking to see if you've hit your target altitude. When you do, just push da button.
Click to expand...


The new Trio EZ-3, which will be shipping soon, has altitude preselect so you don't gotta push nuttin', your plane just levels off and holds the selected altitude!

I bet Dana will upgrade to the EZ-3 before he flies his plane. ;)
 
You got that right Sam, as soon as Trio releases it...I'm there!! Yes, I like the idea of placing the altitude near the throttle. See my page and thoughts below. Thanks.

OK gang, 4.5 hours of actual work and see the progress. More to follow tomorrow.

Don't worry about any spelling or gramatical errors...I put them there on purpose:)

As my last sentence says on the site, Trio and Steinair ROCK.

http://rvflying.tripod.com/id33.html
 
Dana, a suggestion; flip your bellcrank-to-pushrod attach bolt. The bolt is cantilevered in single shear. Poor practice to concentrate bending load on the threaded end of the bolt. Push the bolt through the bellcrank from the back side, then stack up two 960's, a 970, the rod end, another 970, then a castle nut with cotter.

While you're back there in the hole, check the upper elevator pushrod bolt. Lotta threads sticking out the back of that nut. Did it bottom on the root thread before fully clamping the rod end ball between the bellcrank ears? Bottomed AN3's show 5 or 6 threads with a 365 nut, AN4's show 4 or 5 threads. As I recall, a Van's elevator bellcrank has more space between the ears than you can fill with the rod end ball alone. A few washers between the ball and the ears may be necessary to clamp the ball properly without bending the ears inward. If the ears are parallel, the ball is clamped and the nut isn't bottomed, you're cool and I'm being a mother hen <g>

DanH
 
DanH, As I understand your post I would merely be positioning the smooth portion of the bolt within the elevator bellcrank as opposed to positioning it within the rod end bearing. I would still need to offset the rod end bearing away from the bellcrank via the washers. Is there a difference between having the threads in the bellcrank verses having them within the rod end bearing? It seems to me the shear (I'm a CPA not an engineer:) factor would still be there. I'm certainly open to suggestions though. Thanks.

I also checked the width of the bearing slot of the elevator bellcrank and found the base and top to be within one thin washer of each other. Valid points but am I seeing something different than others? Now is the time to "fix" it.

The pics should be pretty awesome (my kids word) by days end:)
 
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Dana,
<<Is there a difference between having the threads in the bellcrank verses having them within the rod end bearing?>>

Yes indeed. Consider your bolt as a round section cantilever beam fixed at one end and loaded at the other, which is an accurate representation of the problem. The highest material stress in such a beam is found at the support (fixed) end; the equation is (load x length)/section modulus. Section modulus = moment of inertia/distance from the neutral axis of the beam to the most extreme fiber. The MOI of a solid round beam is 0.049 x d^4.

Our trusty AN3 bolt has a "d" of 0.1875" and thus a radius (distance to extreme fiber) of 0.09375" at the shank end. At the other end the thread root diameter is only about 0.160" and radius is 0.080". Assume a beam length of 1/2" and a servo load of 20 lbs, then run the numbers. You'll find that the material stress is about 15,500 psi if you locate the shank in the bellcrank, but almost 25,000 psi if you locate the threads in the bellcrank. You pick up a 60% safety margin just by installing the bolt the right way.

The above ignores fatigue and stress concentration. Fatigue failure is directly related to the number, amplitude and type of load cycles. In this application you have fully reversing load cycles, which are the worst kind. As for stress concentration, AN bolts have rolled threads to reduce the notch effect, but it is common to have a bolt with a less than perfect root thread. A sharp V root thread (rather than a nice rolled U) is a "break here" sign; the base of the V is exactly where you find the 25,000 psi material stress. This is particularily true if you managed to locate that root thread flush with port side surface of your bellcrank.

Is it safe with the threaded end in the bellcrank? Maybe. AN bolts are 125,000 psi material, but stress concentration, number of load cycles, and the amplitude of the load cycles all conspire to chop the margin by many multiples. Why take chances? Whole lot easier to remember that neither shear nor bending loads should be applied to bolt threads.

Usual caveat: I am not a professional engineer, and even if I were you should check my math <g>

Dan
 
Trio is installed and the panel is back in and fired up across the board. I will cut it short and tell you to read my opinion on Trio Avionics and Steinair on my website, suffice to say, these two companies are, in my opinion, at the top of the totum pole. Thanks guys and all who sent private emails with opinions and questions on the install. It is certainly time to make airplane noises with the Trio and new Dynon fired up since Thursday afternoon.

See the final product at http://rvflying.tripod.com/id35.html

I know, black will be hot............thought I'd save your voice:)
 
Dana,
That sure is a nice looking panel.

<<I know, black will be hot...>>

But it will look good, and maybe you'll fly more in the winter <g>. Gonna use a few polished bits for accent, maybe a spinner?

Dan
 
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