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Chucker's Sonerai II (minus)

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Chucker

Well-Known Member
Supporting Member
Joined
Nov 1, 2013
Messages
894
Location
Prescott Valley
All right gentlemen(Do we have any ladies in the group?), well, ladies and gentlemen,

If I don't start posting something about my own project, there will likely be no record whatsoever of my build. For starters, let me describe the project I purchased, and then, where I plan to go with it. As you all know well, where I will end up is another story entirely.

The project was purchased from Bob Jenkins in Phoenix. Bob was not the first builder...nor the second. The fuselage was welded and on its gear with elevator and rudder controls mostly complete. It is currently fitted with a mid-wing carry through. The project also included a low-wing carry through. The rear spar support is yet to be fabricated. It came with Plexiglas but no canopy frame. The turtle deck had been modified to accommodate a fighter style canopy (rear hinge). Bob had already started removing that apparatus due to the impossibility of getting in and out of the back seat and encroachment in the head and shoulder area. The wings were complete. In fact, Bob had stripped the skins and incorporated the modification. It still has 9 ribs each. One wingtip is on. The ailerons needs tips, balancing, and installation. The engine is a Revmaster 2100D with the blue dual Bendix magneto. It appears, and I was told, that the engine is zero-time.

What I am planning:

I plan on removing everything that has to do with the front seat. I am going to modify the canopy by drawing a straight line from the spinner to the trailing edge of the canopy. I considered bringing the skirt from the cowl all the way back to above the spar and then a small canopy like the Sonerai I. However, sitting in the cockpit, I can see that any extension of the cowl line that is not transparent will greatly reduce forward visibility and obscure the runway (more) on landing. Two inches of skirt fore and aft will allow me to make a canopy with a 4x4 sheet of acrylic. I will also need to stretch the nose of the cowl enough to fair with the spinner because of the long Revmaster prop flange.

Forward of the firewall there will be no electricity not generated by the magnetos...and subsequent enlargement of my left arm. I have spoken of it before, but I plan on using an updraft cooling system. I have offroad VW cylinder covers and the only way for air to leave the cowling (except for leaks) is through the cylinders and heads or through the oil cooler. I like the idea of dumping the hot air overboard immediately rather than have it linger under the cowl. The oil cooler will be top-mounted. I am still wavering on the oil filter question. However, I plan to run the engine on the ground for a few hours with the filter installed either way. To make this work on the Revmaster, I am drilling a hole through a pressure relief piston and installing it in the normal position. This is where the Revmaster full flow system re-enters the engine case. The drilled piston will direct all the oil through the upper gallery and oil cooler. If I remove the filter and port the oil through the stock passages, the drilled piston will do the same thing....no pressure relief and no bypass of cold oil....but that is how external oil coolers work anyway.

Enough for now. Pictures in my gallery.

Chucker
 

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With that flat-wrap canopy design that you have sketched, you may want to consider a very small 'skull-cap' made of fiberglass, to smooth the transition from the canopy glass to the angle of the headrest. Look at a stock cassutt cap for an idea…Just a thought. Going from positive inflow pressure instantly to negative pressure just aft of the seam may cause some burbled flow…
Anyway, it does look a lot cleaner than a big bubble…..
 
I like the skull-cap idea!

I considered a two-step transition using skirting, but then you have two hard angles instead of one. I thought it better to "rip the band-aid off" all at once!

With your suggestion, I get a smooth transition where the change is greatest (on top) and I also get back an inch of headroom without giving up lateral visibility.

Thanks
 
Destructive testing of horizontal stabilizer jack screw:

I welcome advise from any engineers among us. I have a degree....which was not structural or materials related (systems engineering) and which I received 36 years ago... Having been a pilot for 36 of those years and an engineer for...none, I remember very little.

Stress Analysis:

750 lb. aerobatic max weight * 9.0 ultimate g's = 6,750# maximum force on wing spar

Forward most cg is 8" fwd of spar
Horizontal stab post is 132" aft of spar
Maximum force at horizontal stab post is 6,750*8/132 = 409#

Assuming center of lift on spar is no further forward than 40% of distance from post to jackscrew:
Maximum force on jackscrew is 40% of 409# or, 164#

Therefore, at maximum forward cg, maximum aerobatic weight, and ultimate g-force, the jackscrew must withstand a pull force of 164#

I then performed destructive testing on a portion of the stock used to make the jackscrew by torquing one lubricated nut against a washer stopped by a second nut. The part failed at 130 inch-pounds of torque. Thanks to the internet, I used a clamping force calculator to determine the axial load on the part at failure. Based on a 5/16" major diameter of threads, lubrication, and 130 inch-pounds of torque, the axial load at failure was 2,512#.

If my calculations are correct, the jackscrew has 15.3 times the required tensile strength to withstand the ultimate design load of this airframe.

I wouldn't ask anyone to take responsibility for my design decisions...but am certainly inviting criticism and the identification of any errors in my assumptions or logic.

Thanks,
John

I'll post some photos....but I first need to shrink them to a file size acceptable to Sonerai.net.
 

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Another issue was that I unloaded the nut every 5 inch-pounds and reset the torque in a continuous motion. Although this ensured that the torque reading was accurate, the multiple cycles beyond the yield limit of the material undoubtable weakened the part. That is another reason for me to believe that the assumed ultimate axial load of 2,500# is a conservative number. However, without a pure pull test, there is no way of establishing the true maximum.
 
Okay, last post...but this is interesting.

The material cross section of the 4130 chromoly (after the threads were cut) was .028 sq.-inches.

Divide that into the failure load of 2,500# and you get an ultimate tensile strength of.... drum roll please... 89,286 psi.

According to the website I have up (onlinemetals.com), normalized 4130 has a minimum tensile strength of 97,200 psi. Annealed 4130 has an advertised minimum tensile strength of 81,200 psi.

I think that I am in the ballpark. :)
 
I took the plunge today and cut out everything to do with the front seat....almost. I am leaving the mounting points for the controls so she can be converted back to a two-seater without any welding. I also left stubs from the front seat for my luggage rack. 8)
 
Without a front seat, Sonerai 2 'minus' is starting to look more like a racer……I Like the color scheme on your avatar.
 
Thanks, Ed. I am collecting the cuttings in a box to see just how much weight I am saving. We'll see. It may not be as much as I want to imagine...but the ounces grow up to become pounds and the pounds add up over time.
 
Built my seat yesterday....not the frame, but the bottom and back support.

Total weight without lacing is .655 pounds. One square foot of 1/4 plywood (not enough for even the bottom seat) would have weighed .71 pounds. Every ounce counts!
 

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About to get my parts back from the machine shop. Need to concentrate on the engine build. The cases already received bronze sleeves for the lifters. Today I mated the cases with my HAPI accessory case and removed everything that did not appear useful.

I left the front tin mounts in case I switch to an electronic ignition and need them to mount the crank position sensors. I also left the TDC lug....but I'm not sure why. Perhaps it goes in the scrap heap tomorrow.

Chucker
 

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Okay. I think it is time for an intervention. Someone needs to hide my grinding tools and wire brush.

Chucker
 

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