Elevator bungees question

[cliffy]

Anyone know the difference between the 2 bungees used in early Mooneys? Seems one p/n allows the use of 19 degrees up elevator at 3 1/2 degrees negative stab and the other allows 10 degrees at the same setting and same basic short body. 

Have been searching and haven't come up with anything yet. 

Why the change?

Stronger compression springs on one?

More speed?

 

[Hank]

Changes were made to the tail in 64-65. Earlier models have short rudders that stop at the horizontal stab. My 70 model has a full-length rudder that goes past the stab, which is how the new planes are still being built. What effect does this have on the bungees? I dunno, but they all involve the tail. [No tales of tail here, those are reserved for over post-flight beer.   ] 

[StinkBug]

My 68C has the rudder that stops at the elevator also. FWIW.

[cliffy]

The bungees have nothing to do with the rudder. They are connected only to the elevators. According to Bill Wheat

(he told me personally last year) they were used by AL Mooney to get the proper amount of elevator force required

while using tail surfaces about 25% or 30% smaller than what would normally have been required, All in an effort to reduce drag and gain speed.

[cliffy]

Forgot to add

I want to understand what the difference is between the 2 P/Ns that allows less elevator up for the same elevator effort in pitch and why it was changed. Still digging.

[Andy95W]

Cliffy- here's my guess. The only different bungee part numbers I could find were from the 1965 and on M20 C,D, E, and F parts manual. (Oddly, the 1961-1964 parts manual I have for our airplanes doesn't even show the bungee. Guess attention to detail wasn't that important before 1965.)

740044-1.........BUNGEE ASSY, ELEVATOR.........CDE

740091-501.....BUNGEE ASSY, ELEVATOR.........F

Based upon what Bill Wheat said, I surmise that when they stretched the fuselage to make the F Long Body, to get the "proper amount of elevator force required" they needed to change up the bungee.

If you are talking about only the short body C, D, E airplanes, I think the same rationale applies- different manufacturer product needed a different set up to provide that somewhat subjective "proper amount of elevator force required."

I love the fact that our pre-1965 airplanes are such a link to the past, where you can tell somebody said, "yeah, that looks about right" and stopped before over-engineering a simple system. But like you, I sure wish the manuals and reasoning were at least a LITTLE easier to fathom.

[cliffy]

 

When one looks at the TCDS sheets for the M20C we find this:

 

S/N up to 690001

With stabilizer set at 3½° negative setting to the thrust line, adjust trim assist unit

(740044) for elevator up angle of 19° ± ½° at the zero spring travel position.

 

S/N above 69001

With stabilizer set at 3½negative setting to the thrust line,adjust trim assist

bungees (740188) for elevator position of 10° ± 1at the zero spring travel position of the bungees.

 

The only difference is the P/N of the bungee. In addition, the elevator travels are different.

For the earlier S/Ns it is 24 up and 10 down, for the later ones it is 22 and 22.

 

I want to find out the aerodynamic reasons for the change. Haven't found it yet and Bill Wheat didn't have an answer either.

Al Mooney is far to under ground to ask him :-)

[jetdriven]

Al left for Mooney for Lockheed in 1955, so he wouldn't likely know about the P/N change.

[Andy95W]

When one looks at the TCDS sheets for the M20C we find this:

 

S/N up to 690001

With stabilizer set at 3½° negative setting to the thrust line, adjust trim assist unit

(740044) for elevator up angle of 19° ± ½° at the zero spring travel position.

 

S/N above 69001

With stabilizer set at 3½negative setting to the thrust line,adjust trim assist

bungees (740188) for elevator position of 10° ± 1at the zero spring travel position of the bungees.

 

The only difference is the P/N of the bungee. In addition, the elevator travels are different.

For the earlier S/Ns it is 24 up and 10 down, for the later ones it is 22 and 22.

 

I want to find out the aerodynamic reasons for the change. Haven't found it yet and Bill Wheat didn't have an answer either.

Al Mooney is far to under ground to ask him :-)

Wasn't it in 1969 that Butler put the goofy stinger on the tail? That thing probably threw it so far out of whack they had to monkey with the bungees.

I thought there was a guy from the factory in the 70's who is now writing for either the MAPA Log or Mooney Flyer magazine. I believe he worked in engineering/flight testing. Maybe ask him?

[Hank]

I think the Butler stinger was 72-73 or so. My 70 doesn't have it, nor a friend's 69.

The elevator travel was changed. Was this the same time the rudder was lengthened to reach below the horizontal stab? Did trim positions change any too, I wonder?

Maybe Stacy can comment. Not sure how long he's been at the factory.

[Andy95W]

Changing the rigging due to a different bungee part number makes some sense to me (different spring K factors, if nothing else) but basically DOUBLING the down limit is very strange.

I'm definitely curious. Not as curious as Cliffy, perhaps, but still looking forward to the answer, if we get one.

[cliffy]

I am REALLY curious and somehow hope to find out the history of all this.

I really want to understand the aerodynamics of the entire situation.  WHY??

[Hank]

I'll try to remember to bring "Those Remarkable Mooneys" back from the hangar tomorrow, see if it says anything.

[carusoam]

Thoughts on elevator use...

My 65C would run out of up trim. But never run out of elevator in either direction.

Extreme up elevator for

-Slow flight

-Stalls

Full up elevator for

-Aero braking on ground for short landings

Have I missed anything?

Best regards,

-a-

[cliffy]

Just thinking out loud-

I don't think any airplane will run out of up or down trim if it is within prescribed CG limits for loading AND

ALL other trim settings are correcrt.

 

There have been several comments here about running out of trim both ways and its my contention that something other is going on.

 

Maybe the bungees have been replaced with the wrong P/Ns.

Maybe the zero spring setting on the bungees is set wrong.

Maybe the elevator throws are incorrect.

Maybe the Stabilizer settings are wrong.

There have been Mooneys that have run right off the end of the runway on take off with the trim set wrong.

 

Just one short story on bad trim settings.

I was departing KTOA in the LAX area early one morning in a Navajo with 6 paxs and me (well with in CG limits and weight limits). Wx was 100' over and 3 miles (usuall June conditions). Just as I went IMC at @150' agl the airplane made a snap in pitch to about 30+ degrees above the horizon. It took almost full down elevator to regain control. At about 600' I went VMC on top. I found that when I could get full down elevator trim cranked in I could remain in control only to about 140 kts indicated. Any faster and I was climbing. WhenI got to my landing spot not too far away a partial flap landing was made.

In looking to see what happened, I found that the elevator down force spring (similar to the "extention spring" in some Mooneys) had failed and caused the pitch up. The point being that I ran out of down trim but it was caused by a failure. It could also be caused by a miss rigged trim in a Mooney.

 

There are many "tricks" used to comply with regulations on required pitch force and ultimate stick force. Bob weights on some Mooneys and Pipers, Servo tabs on others and our spring bungees. A full understanding of our beloved vintage Mooneys pitch system may well be worthwhile when it can be full explained. We might learn something and a few may find the issues they are facing resolved.

 

I would very much like to know how to contact the person mentioned in an earlier posting here that supposedly was a test/engineer for Mooney and now has something to do with MAPA (?) - can anyone give me a lead?  Thanks.

[cliffy]

For got to add- I use the elevator to go from floor 1 to floor 15 also :-)

[DonMuncy]

You are probably asking about Bob Kromer. He was with Mooney and then top dog at MAPA for some years. He has since worked for Piper or Cessna. The Mooney Flyer has quoted him a few times. I don't know how to get in touch with him now.

[cliffy]

Thanks I'll follow that lead.

[JaredDavis]

Link for Bob:  http://www.avweb.com/press-releases/635.html