Early Mooney Stab Trim Indicator

[cliffy]

Anyone have a reference to how to set the trim indicator on early Mooney? 

Can't find any SBs, Sis, Maint manual reference or anything else.

The question is where to set the stabilizer to set the take off range on the indicator

 

Any good ideas out there? 

[N201MKTurbo]

Why do you ask? What did you take apart?

Did you disconnect the trim jack screw? Did you take apart the trim wheel? Did you remove the indicator cable? Did you change the stops on the trim wheel assembly?

Does your plane have a Dorsal fin?

[N201MKTurbo]

The easy answer is to just do a few takeoffs and find the trim setting you like for takeoff. Remember where it was and set it there on the ground. Now readjust the cable to put the indicator at the takeoff position.

[cliffy]

Well for one you have to remove it to remove the Johnson bar which I did and found the roller bearings frozen with dried grease. 

Number 2 I took the jack screw out to replace the bushing and shackle and bolts to eliminate some play. 

Number 3 this is the only plane I've ever worked on that didn't have a reference in the MM on how to set the trim indicator for the take off position. 

Obviously there is one setting (or span of setting for CG span) that equates to the correct position for the stabilizer for take off. If set wrong it could be dangerous. 

Number 4 I've called 4 MSCs and no one knows how to set the indicator.

That's why I posted here to see if anyone else had an idea on how to do it correctly.

I can understand your suggestion of flying it and setting it to some convenient position but that is not any "approved" way of doing it, if there is one. I wouldn't set a King Air or Lear Jet that way, would you? 

Number 5 I am doing research on the Mooney elevator system and the history seems lost in space. I have been trying to work with the factory but so far they have not responded.

One question that has come about is why the elevator deflection angles were changed from the early to later models according to the TCDS sheets. Early one have a 24 up/10 down setting and later have 22 each way. Why did it change? What changed on the airplane? 

Another question is what is the difference between the two spring assist bungees? Anyone know?

[carusoam]

Sounds like evolution...

Best regards,

-a-

[Andy95W]

Call the folks at Dugosh. Bill Wheat still works there occasionally as a consultant. His days at the Mooney factory go back to the 50's. if he doesn't have any historical knowledge, it probably doesn't exist. The last time I saw him was at the factory around 1997, and I've heard he is just as on the ball now as he was then.

I appreciate your comparison of Mooneys to Lear Jets and King Airs, but I think my 64 M20C has a lot more in common with 64 Bonanzas and Comanches than a Lear Jet.

And yes, I would rig the trim indicator on an old Bonanza by doing what N201MKTurbo said.

And no, I don't think that dangerous if done with some common sense.

BTW, Bill probably test flew your Mooney at the factory. Check your first airframe logbook. It will be one of the first entries.

[N201MKTurbo]

I asked all that stuff, because depending on what you took apart you can get it back to its original position pretty easy. The long answer is to rig it so the stops on the trim wheel are at the specified angles, then set the indicator so the limit marks match when the trim is at the stops.

I set the spring bungees for the most efficient cruise trim. When you are in cruise flight trim nose down and use the elevator to fly level and see if the plane goes faster. Then trim nose up and do the same thing. It will tell you which way to adjust the bungees. They are almost perfect from the factory.

[cliffy]

Now this is some real good info. I appreciate it. I didn't think of Dugosh in my calling around but I will try them. All I can say of is-

Why didn't I think of that? Crap. Brain fart time.

 

I think I remember that he did do the test flight on my 64 D but I'll look it up to make sure.

 

I agree that it might be set by using the outer limits as a start point and do a fly off to reset for best spot but I'm concerned many are not as capable as you and some others are on this board. I just had a C model in here with gear troubles and they have been flying it for a year with the gear not going up all the way. They didn't feel there was any problem. BTW, the owner had had 3, yes 3, gear ups in this airplane.

 

I mentioned the Lears as I used to fly and fix them in a life far behind now.

 

Spring bungees! My favorite subject right now. My manual and all the TCDS sheets say for the Cs to set them at 19 degrees up at 3 1/2 degrees a/c nose up on the stab. My manual also has a hand written note (its a copy of someone elses that I bought when I bought the airplane) that says 9 degrees for Cs and 10 degrees for Fs. In checking mine I found it at 12 degrees, I suspect because it is a D model converted and no one ever reset the bungee after the conversion in 1965! D models are set at 12 degrees. I reset mine to 9 degrees (like the manual notes) and then test flew and gained 5 to 6 kts true A/S. I have previously set my flaps and ailerons for a perfect fit in flight, everything lines up perfect with no roll to speak of.

 

Has anyone ever tried to set 19 degrees on the bungees? I tried but couldn't get more than 1 1/2 threads into the rod end. I'm going to try again just to verify.

 

As far as the stab trim goes, I am anal about such things I admit, It comes from many years in the 121 and 135 field and the fact that I know of 2 Mooneys that have "driven" off the end of the runway in Stockton, never having gotten airborne, because the trim was set wrong. It does happen.

 

I guess the older I get (50+ yrs flying) the more anal I get as I see more and more stupid mistakes and just I don't want to see others make stupid ones if I can help it.   

 

Again, thanks for the info. I honestly do appreciate it.  

[cliffy]

BTW didn't Bill Wheat pass away a while back?

[Marauder]

BTW didn't Bill Wheat pass away a while back?

He had some health issues a few months back, but I believe he is still tapping the rudder.

[jetdriven]

from the J manual, yours will be similar if not the same:

 

Stabilizer Trim Indicator Rigging. The indicator is geared to the trim control wheel and indicates stabilizer position relative to the aircraft thrust line. Set horizontal stabilizer to an angle of incidence of minus 2 degrees 00 minutes to minus 2 degrees 30 minutes. Adjust trim

indicator cable at (F) (Figure 27-10) to set indicator in the cabin to the center of the takeoff range mark.

 

(the figure, 27-10 shows the end of the bicycle cable at the stab trim wheel. Loosen and adjust there.)

[cliffy]

Thanks jetdriven!

I haven't seen that manual yet. I've seen 3 older ones. As  a J it "should" be similar setting. I'll give it a try and see how it works when I get off the jacks, 

[cliffy]

Bill Wheat isn't doing anything at Dugosh anymore. I have rigged the stab for full travel either end on indicator and marked with tape the 2 degree point on the indicator (does not line up with the T/O marking).  Will do a test flight over the weekend. 

[Andy95W]

Good luck, Cliffy.

The more I dig into the old Service Manuals, the more I'm convinced they did things back then to the TLAR method... That Looks About Right.

[Andy95W]

And thanks for the note about Bill Wheat. Hope he's doing okay.

[DonMuncy]

I saw Bill last Friday and he seems just like always.

[cliffy]

Dugosh told me that he wasn't working in the office any more  Glad to hear he's still doing OK

 

Does anyone know if he would accept a letter with a couple of historical questions to be answered?

[DonMuncy]

Knowing Bill, I am certain would accommodate you.