Tailwheel design.

Quoted from toliver66

Has anyone tried DURAPLEX HIGH-IMPACT ACRYLIC instead of lexan?

A few negative thoughts related to acrylic:

• Cracked acrylic is sharp like broken glass, not something I'd want close to my face.
  
• Tends to crack easily around holes drilled in it, especially when drilling the holes.
  
• Harder to cut into complex shapes
  

The lexan I used on my bird seems impossible to crack. I've folded it in half and it did not crack. It was easy to cut with standard sheet metal shears. Easy to drill holes into.

The only negative to polycarbonate is that it scratches easy and cost more money.

Your build is looking great!

DURAPLEX HIGH-IMPACT ACRYLIC is supposed to be an economical alternative to lexan. It's very flexible almost rubbery like. And is the only thing Home Depot  or Lowes had instock short of buying a full 4x8 sheet of Lexan which cost $200 and I would have more than half of it left over. But it doesn't matter as the largest sheet of "DURAPLEX HIGH-IMPACT ACRYLIC" they carry is 6 inches to short any way. so I ordered a piece big enough through Amazon Prime (free shipping     ).

But your points are valid. Although this new stuff supposedly doesn't have the issues you pointed out.

I don't mind spending the money, I just didn't want to wait or have a 1/2 sheet of Lexan laying around for no telling how long.

Thanks. She will look a lot better once I get her cleaned up and varnished.

Since work on the fuselage has been delayed, I've shifted my attention to the wings. Working on removing the supporting structure for the 2 wing tanks. I also have some broken ribs from hanger rash to fix and then I have to figure out the best way to remove 20 years of dirt and dust so I can varnish them.

The supporting structure for the wing tanks weighed 3 lbs + 10 lbs for the one fuel tank removed for a total of 13 lbs shaved off the total weight. that should leave me about 27 lbs for varnish, fabric, paint, and instruments. It's gonna be close. May have to get the light weight plastic main wheels.

Instruments are exempt from the 254 lb.

SWEET! I did not know that. That will save me a few pounds. Thanks for the info.

What part of Part 103 says instruments are exempt?

FAR 103 explicitly says instruments count toward the weight:
"Other devices, such as seatbelts, roll cages, instruments, or wheel brakes, are considered part of the airframe and are included in the empty weight"

However, if instruments are not part of the airframe and not needed for flight then maybe you could argue that they do not need counted.
They would need to be easily removable, like an add-on accessory rather than fastened into a dashboard. In my opinion the safe way to think about this, if it is bolted/screwed on it counts towards the weight. If attached with Velcro or some sort of quick release mechanism and is not essential to flight then maybe you can exclude it from the weight.

You are correct. FAR 103 reads "(1) Weighs less than 254 pounds empty weight, excluding floats and safety devices which are intended for deployment in a potentially catastrophic situation."

So the only things excluded are floats and a BRS system. Oh well, I wasn't planing on going overboard on the instrumentation any way.

If I were picking instruments for my MiniMax today I would look for something like the Skylab Flybox, likely be the lightest weight and cheapest solution too.
https://www.aircraftinstruments.eu/

Other options I would consider:
http://www.beliteaircraft.com/electronics/
http://www.mglavionics.com/html/blaze_color_singles.html

I've not had any experience with any of the above, they are just things I'm aware of and would consider using myself.

Another option is DIY instruments, I am considering doing this as my next project now that my MiniMax is flying:
https://experimentalavionics.com/

Started varnishing the left wing.

My bad! I stand corrected.

Greg: how is your rebuild coming?

Puff, The airplane is fine. I've flown a little in the last two months. Unfortunately I've had about 5 dead stick landings. Three at the strip, and two off site. The engine runs fabulous wide open, but quits when brought to a mid range to idle. It's now back home in my garage for the winter.

Have you done the troubleshooting to see what's going on?

Puff, Yes, I've done a ton of trouble shooting. As a refresher, I had an event back on March 20th. I repaired my Max, and went through months of
trying to find out why my engine had a bad miss, and ending up quitting on takeoff. Several times I was convinced I had pin pointed the problem
only to be disappointed. Among other things I (1) double checked the points, and timing, (2) replaced the fuel pump, and filter, (3) cleaned the
air cleaner, (4) changed the carburetor. Plus all the normal things like a new spark plug, fuel lines, pulse pump lines etc. Each time I thought I had
it fixed after 10 to 15 minutes of running it would stumble, and sometimes just quit. All this testing was done on the ground, and not flying. Finally I changed
the spark coil, and that fixed it. I haven't done it yet, but it's my intentions to check the resistance on the bad coil cold, and then put it in the oven,
and see if it "breaks down". Next I flew it with a first generation 3 bladed Ultra Prop, and it lacked performance, but it ran. Unfortunately when I
pulled it back on final, it acted like a air brake, and it dropped out of the sky creating some damage. I had it fixed in 10 days, and got a brand new
Tennessee propeller. Wide open the engine runs great. It's just that now when I pull the throttle to just above idle, it shuts down. The first 4 times
it seems to have been rich (flooded). The last couple of times I think it was lean. So at this point with all the things I had tried, I thing I got both
of my carburetors way out of adjustment. That's what I will focus on next spring. And by the way both of my carburetors have the correct needles
and seats for a Rotax 277. One of the carburetors is brand new with maybe 60 hours of running. I hope 2020 will be a better year for Max flying for me.

That's all well and good and I'm sorry to hear about your troubles, but what does that have to do with my "1500R to 1030H conversion" thread?

Weather finally allowed me to Finnish varnishing the left wing.

The canopy latch finally came in.

Toliver, Sorry that Puff and I communicated on this thread. Puff knew I had trouble earlier this year, and he just wanted an update.

Toliver66


78486144            Isnt the diagonal member supposed to be attached to the top of the spar flange(inside) ?



Greg doe              Glad you recovered from concussion after the max overturned on a forced landing.

Glad your OK and all is well  Greg Doe. Hope you get it sorted out soon.

mullacharjak - I originally built the wings for wing tanks, which according to the plans for wing tank installation the drag strut is notched and lowered to make room for the wing tank. But as I pointed out a few post ago I removed the wing tanks and supporting structure from the wings to meet the 5 gallon fuel capacity limit and shaved off a few pounds in the process. But I obviously don't want to remove the drag strut. I don't see where the difference will make any structural compromise, if anything its a stronger glue joint due to increased surface area.

I'm no engineer but I agree with your assessment and think it is plenty strong.

  Just want to understand the situation.I dont think this area is clear in the plans.

   The strut in question is called an Anti-Drag diagonal. I think it will be loaded in tension when the wing is pulling forward.It would be pulling the glue joint in tension.

   While if it is attached to the inside then the glue joint will be in shear.

   Cant say if a glue joint should be in tension or shear or if that makes any difference.

It will never be in tension, it is in compression. The drag on the wings created as your airplane flies through the air tries to fold your wings back against the fuselage.  The "anti-drag strut" braces the wing against this force keeping this from happening.

Quoted from mullacharjak

  Just want to understand the situation.I dont think this area is clear in the plans.
   The strut in question is called an Anti-Drag diagonal. I think it will be loaded in tension when the wing is pulling forward.It would be pulling the glue joint in tension.
   While if it is attached to the inside then the glue joint will be in shear.
   Cant say if a glue joint should be in tension or shear or if that makes any difference.

Right.  The drag/anti-drag truss in the wing with its geometry and loading, is a Pratt truss.  A feature of the Pratt truss is that the diagonal members are loaded in tension.  The TEAM stress report says the root diagonal has a tensile force of 831lbs in the design case and a safety factor of 1.99 so the fixtures of the diagonal should be able to resist 1654lbs.  System3 quotes a tensile strength for T88 of 7000psi and a lap-shear strength of 1800psi. The TEAM report states the shear strength of western white pine is 920psi so the glue is stronger.  In the original Minimax wing, the diagonal attachment is a lap joint at both ends and the aft connection has a slightly smaller area, 1.8 in², so it is the weak link. Then we have:

1.8in² x 920 psi = 1656lbs.

With the wing tank mod, the forward joint is still a lap joint so the joint has the same strength plus any extra supplied by the butted joint area. It is stronger than originally designed.  However, the aft attachment is now butted to the spar cap and the joint is dependent on the tensile strength of the spruce spar cap (170 psi, ANC-18 ) plus the shear strength provided by the ply gusset. We have:

2in² x 170 psi + 1.8in² x 990 psi x .5 = 1231 lbs  

Quoted from toliver66

It will never be in tension, it is in compression. The drag on the wings created as your airplane flies through the air tries to fold your wings back against the fuselage.  The "anti-drag strut" braces the wing against this force keeping this from happening.

You're forgetting the contribution of the rear lift strut which is in tension whenever the wing is lifting and pulls the wing forward as well as down.  And in the design case, high alpha + high g, lift greatly overwhelms drag but even at low alpha and 1 g the forward component of lift defeats the rearward drag component.  Pm me an email address and I'll send you a spreadsheet that models the loading.

Awsum, so bottom line is my inner drag strut is fine just the way it is. Thank you Mr Bob for clearing that up. Although I'm not sure I follow you on the rear lift strut. The drag strut is still loaded in compression regardless of the lift strut.

An illustration might help.  Here's the Minimax in level flight at 36 mph at gross wt and 1 g.  The angle of attack is ~14°.  The forces shown are drawn in proportion to their magnitude.  Lift is per wing panel and about 216 lbs, drag is 34 lbs. The wing moment is not represented but is accounted for in the lift strut forces.  As you can see the three larger forces are inclined toward the nose of the plane.  If we resolve all the forces into normal and chordwise forces, the net chordwise force is forward acting.