ETLB Squawk Forums — Archive

Guys,
I have posted here before on a few subjects regarding my Minimax 1600R (Type designation 91 in UK). It's G-NADS, which I know causes some hilarity  

Well I finally got around to digging deep to find the cause(s) of what I call my 'Wet Dog Shake'. I removed the wings because I could move the left wing tip, front to back by around one and a half inches. David urged me to stop flying until I found the cause and I listened!

So, background first. Airframe 258hrs. One fairly severe landing accident prior to my ownership and fully repaired under the UK LAA permit scheme. In other words an approved repair scheme overseen by an inspector.

So, I found that the left wing had undergone some repairs, comprising the rear wing attach brackets replaced. Repairs to the Strut attach brackets as well. There are repair patches in both areas on the underside of the wing; I haven't looked inside because the repairs have been signed off.

OK, the front attach brackets are sound but the alloy carry through holes are worn oversize - the front wing pins can be moved a fair bit.

Question 1. Can I go up one size on wing pin/holes in carry through and wing attach bracket?

The rear carry though spar holes are fine (they have metal tubes through of course). But, the rear wing attach brackets have worn holes.

Question 2. I don't really want to disturb the rear carry though as it's fine - Can I ream and bush the Rear Wing Attach Brackets?

I also found when removing the motor, that all 4 vibration mounts were perished. I've replaced them all. Before I replace the prop, I'm going to check balance complete with spinner and crush plates/bolts, just in case.

The Motor - 447. Crank around half life by measurement, needs new rings however. I have a 503 in good condition but could do with rings to finish the job. It's a twin plug/twin carb DCDI. I've listened to all the arguments but I'm sorely tempted to install it. On the one hand I'm adding 10lbs to the nose.... As for fuel consumption I've looked at power and fuel graphs for both engines. I actually don't agree with the figures from my own experience (on the 447) but based on comparisons, it looks like the cruise sector of the power/torque band would leave far less difference in consumption than people say?

I'm carrying 20 + 13ltrs at max. I have a wing tank to fit (and now would be the time with the wings off) but it would put me over 590lbs at MAUW.

I've also had the thoughts about CofG.

Question 3. I know some of you have fitted 503s so how has it effected your a/c?

Question 4. Do I stick the 503 in or not?

Have fun!

My 503 1600R / 91 can climb like a Bast'd.

Low level   Fun.

What if anything did you do about CofG Antoni? And do you find consumption at cruise rpm is reasonable?

Quoted from Max SSDR Guys,

OK, the front attach brackets are sound but the alloy carry through holes are worn oversize - the front wing pins can be moved a fair bit.

Question 1. Can I go up one size on wing pin/holes in carry through and wing attach bracket?

The rear carry though spar holes are fine (they have metal tubes through of course). But, the rear wing attach brackets have worn holes.

Question 2. I don't really want to disturb the rear carry though as it's fine - Can I ream and bush the Rear Wing Attach Brackets?

While I suspect that reaming to the next size is OK I would ask the question of Dave at TEAM and get at least an educated answer.  The answer comes down to edge distance on the metal parts.   Edge distance is the distance from the center of the fastener to the edge of the material. The edge distance should not be less than twice the diameter of the fastener.

I had a similar issue on my old Sonex.  When I bought the plane I soon noticed that the tip of the left wing would move up/down about an inch.  I flew it that way for a couple of years before making the fix.  I reamed the spar holes to the next size bolt successfully and solved the problem.

Quoted from Max SSDR What if anything did you do about CofG Antoni? And do you find consumption at cruise rpm is reasonable?

I didn't build the plane. The CoG flies noticeably forward when compared to the last Minimax I had - a 447. In that one I liked to land tail-wheel first, not so easy to do that in the 503 CBIN but 3-pointers no problem at all. Did some this evening.

9 litres per hour, or 2.4 US gallons per hour at 55 knots, approx 1000 ft per minute climb

[Lowered engine, aerofoil struts and axle, penny washers under the rear engine mounts, penny washers under the leading edge of the tail-plane mounts, using -5 degrees flapperon reflex, aerodynamic trim tab]

My LL 1623 391083.

This is what I would do.
Bush the carry through,There seems to be enough edge distance.
Make new attach brackets,all of them. Just clamp old ones to 2024 T4 plate and drill on a press for AN4  or drill 6mm and ream 1/4.

Use a proper size 1/4 clevis pin at front if you think the bush could fall out,I doubt if it would be more difficult to install than the traditional

L shaped thing.

And Can you please tell me what the term ( 447 crank half life by measurement means ? )


KK

Edge distance is specified for adequate tear-out strength.  Going to 3/8" bolts or pins would still allow enough tear-out strength and tensile strength.  I would be concerned that the drag/anti-drag truss in the wing is compromised.  The lift, drag and torsion reactions of the wing require the spars, struts and drag braces work as a system.

I still think that the engine is bouncing up and down.

KK - http://www.skydrive.co.uk/products.asp?cat=12  We use this tool (you can make your own) to measure bearing play. You can keep a graph and this will give you an indicator of how your big end bearings are wearing. There are permissible limits, so you can get a good idea of how things are shaping.

Tom Shep, whilst I'd lay SOME blame on the engine mounts, there's little doubt that the wingtip aileron bracket wear coupled with the combination of carry through/attachment wear would play a big part. Vibration is entirely speed related. If it were the engine mounts then the airframe would shudder at full throttle, during take-off for example. This ONLY occurs as ASI hits around 70mph (statute).

Dave Cooper has suggested a repair scheme and I'm going to follow that for obvious reasons.

Antoni - I generally 3 point as a matter of pride! I think that moving the starter battery back will help too. What revs are you using for 55mph? (What prop?)

Thanks for the suggestions.