M20J maximum take off weight

[carusoam]

Fill us in on the UL while you are reading the docs.

Look for any gussets that were added to strengthen tube joints.

Best regards,

-a-

[Oldguy]

On 1/18/2020 at 3:14 PM, Hyett6420 said:

Bump, did anyone see the stc parts upgrades?  Im intrigued by this.

What is AL's s/n?

You can look here for Missile info. It has some description of parts replaced/rebuilt, but not specific part numbers.

http://web.archive.org/web/20070218094522/http://www.rocketengineering.com/missile.html

 

[carusoam]

The two routes of raising the MGTOW for an M20J...

1) Check the S/N... after a particular number there was a frame tube change that initiated the GW increase... any airframe after the key number has the heavier tubes and was eligible for the increase...

2) If below the key S/N... the fine folks at Rocket engineering generated the Missile STC and covered a much wider range of airframe numbers... and improved the MGTOW for all of those covered by their STC...

If able... fly a Missile... then contact Rocket Engineering... be ready to discuss why they should generate an STC to cover your needs... they stopped the production on new Missile projects years ago...

I didn’t explain this very well... hope you get enough of the basic idea to go forwards...

Best regards,

-a-

[Oldguy]

1 hour ago, Hyett6420 said:

interesting, does not mention ANY thing about airframe parts, only engine mountings.  So by hanging all that weight out the front, they have shown that the airframe is strong enough to take it, so the tube size increase by Mooney later is for "what" exactly because i cant see a reason for it.

24-1601

Missed it by 85 planes.

Mooney SL 92-1-1 details out serial numbers available for the 2,900 GW increase and how to go about doing it. Text snippets taken from the Service Letter shown below:

 

S/N 24-1686 thru 24-3200, 24-3202 thru 24-3217

The gross weight of 1991 and later M20J aircraft has been increased from 2740 pounds ts 2900 pounds. This increase in useful load is retrofitable to some earlier M20J aircraft. See S/N'S listed above.

[Oldguy]

17 minutes ago, Hyett6420 said:

ok, so now what would be interesting would be to understand EXACTLY what hanged form 1685 to 1686

A

And here is your answer...

 

[PT20J]

27 minutes ago, Hyett6420 said:

But this says there are two different weights, well if im reading the text correctly.  So what was tube 26 in weight before this?  Anyone know?

aorry for the delay in replying, JF Andrew has the norovirus so im looking after a "sick, literally" hubby.

I think WT refers to wall thickness. Thicker wall tube used for higher gross weight. 

[PT20J]

Well according to the IPC snippet that @Oldguy posted it was .035 for 2740 lb gross and increased to .049 for 2900 lb gross.

Skip

[Hank]

55 minutes ago, PT20J said:

Well according to the IPC snippet that @Oldguy posted it was .035 for 2740 lb gross and increased to .049 for 2900 lb gross.

Skip

And for our friendly Brit, those are Imperial measurements as promulgated around the world by the British Empire, not those funny "metric" things pushed so hard for so long by the French. So it's 0.049" wall thickness tubing, likely the same outside diameter as the thinner 0.035" wall tubing.

[carusoam]

Seems like...

An industrious owner with a tube cutter and a welding torch and other skills like an A&P/IA and a law degree... could swap out said thin tubes and replace with the thickerer ones...   hence making it eligible for the higher MGTOW.... if the aviation lawyer can make sense out of it...
 

No STC required when following standard procedures and using standard or Mooney supplied parts...

Keep in mind... just accessing the tubes to do the work is major surgery...

This surgery is not unprecedented... the lower tubes are the ones that collect rust most often... when they rot, they get replaced...

So... you get the mechanic to swap the tubes...the plane will fly like all the others with the thicker tubes... but does that allow the plane to legally fly at the higher MGTOW...?

Run this idea past the AOPA Legal board for the few dollar entry fee they require... could be interesting... 

Good luck to the other Andrew...

PP thoughts only, not a mechanic...or legal expert...

Best regards,

-a-

[Andy95W]

I think that's probably the case, Andrew.  That would also explain why one modification (the Missile, IIRC) is allowed the higher weight, by STC, without having the thicker tube.

[bradp]

But it’s Hanging on a SN. It seems like the increase was done for purposes of marketing needing to do something for increasingly bloated airframes over engineering reasons. 

[PT20J]

Well, the increased weight goes in the cabin and the load must be carried by the wing which is attached to the fuselage in the vicinity of the tube in question. Since we seem to have some amateur engineers here, perhaps you could calculate the limit load on this tube as a function of gross weight for us and settle the matter. If you are not capable of performing that calculation, perhaps it might be best to trust that the Mooney engineers did it correctly.

Skip

Edited January 22, 2020 by PT20J

[Hank]

2 hours ago, PT20J said:

Well, the increased weight goes in the cabin and the load must be carried by the wing which is attached to the fuselage in the vicinity of the tube in question. Since we seem to have some amateur engineers here, perhaps you could calculate the limit load on this tube as a function of gross weight for us and settle the matter. If you are not capable of performing that calculation, perhaps it might be best to trust that the Mooney engineers did it correctly.

Skip

I think he is questioning Mooney's calculations showing the exisitng, thin-wall tube won't support 2900 GW, versus Rocket Engineering's calculations showing that the existing thin-wall tube will support more than 2900 when a J is turned into a Missile with a much larger, heavier engine . . .

[PT20J]

9 minutes ago, Hank said:

I think he is questioning Mooney's calculations showing the exisitng, thin-wall tube won't support 2900 GW, versus Rocket Engineering's calculations showing that the existing thin-wall tube will support more than 2900 when a J is turned into a Missile with a much larger, heavier engine . . .

Redistribution of weight might affect load on individual members. FSDO approving engineering of STC might have approved a lower factor of safety. 

[Hank]

1 minute ago, PT20J said:

Redistribution of weight might affect load on individual members. FSDO approving engineering of STC might have approved a lower factor of safety. 

More weight on the nose should increase the axial compressive force on the lower frame member behind it. Unless I've completely forgotten everything I learned as an undergraduate Mechanical Engineering Student.

          —BSME, MSE

[PT20J]

21 minutes ago, Hank said:

More weight on the nose should increase the axial compressive force on the lower frame member behind it. Unless I've completely forgotten everything I learned as an undergraduate Mechanical Engineering Student.

          —BSME, MSE

Perhaps the limiting case is not a static load issue. Hard to tell without having access to the structures analysis from Mooney and Rocket. 

Skip

[Hank]

7 minutes ago, PT20J said:

Perhaps the limiting case is not a static load issue. Hard to tell without having access to the structures analysis from Mooney and Rocket. 

Skip

True dat. Didn't think about the dynamic load when writing that, either. Bending moment down from weight, which way does thrust run, exactly? 

Still seems that if Rocket can put an IO-5XX on the old tubing, should be able to add 160 lbs inside the cockpit . . .

[PT20J]

7 minutes ago, Hank said:

True dat. Didn't think about the dynamic load when writing that, either. Bending moment down from weight, which way does thrust run, exactly? 

Still seems that if Rocket can put an IO-5XX on the old tubing, should be able to add 160 lbs inside the cockpit . . .

I’m not disagreeing. I just don’t know.

[ArtVandelay]

Does anyone know if they had to redo the drop tests for the Missile,Rocket? Obviously they would have easily passed the climbing tests.


Tom

[Oldguy]

14 minutes ago, Hyett6420 said:

...who flies their J using the 2900 load rather than the 1700 load,

Assuming you meant 2,740 instead of 1,700?

[EricJ]

4 hours ago, Hyett6420 said:

Well this has turned into a very interesting discussion.  As @bradp said above, it does seem to be a marketting thing, or they really did run out of that thinner tube, and then discovered the thicker was cheaper etc and worked out it could take more load.  

So be honest, who flies their J using the 2900 load rather than the 1700 load, if their serial number is for the lower limit. Perhaps i need to do that as a survey, (just dont know how). Anyone know how to add a survey to this thread.

I don't, but I've never worried about accidentally going a little over gross because of it.   

[Blue on Top]

Wow!  I just gotta say that all y'all are good.  I'll a couple comments.

1) Although there is a single set of regulations, ACOs do interpret them differently (or at least used to).  In addition, the thoroughness of an STC is typically less than the TC holder (OEM, Mooney in this case) would look into.  In addition, the OEM will also know all the critical areas to look at.  In this particular case as @Oldguy so beautifully pointed out, the wall thickness of the fuselage tubing changed.  This is a modification for a compressive failure (buckling).  Engine loads will definitely travel through those tubes.

2) It is hard to look at everything without knowing the weakest point(s).  In a Mooney, the wing typically isn't the weakest point.  Landing gear, maybe, but not always.  If the Js have the same gear as the long-bodies, then the gear is not the issue either.  The OEM will follow the entire load path, where an STC applicant may not.

3) If one has an accident and the aircraft is over the certificated gross weight (i.e. considered unairworthy), it is highly like one will be footing their own bills.

4) On a related note, everyone thinks that Va is an airspeed for keeping the wing attached, but that is only at GWmax.  The wing is fine at lower weights to go to higher G-loads (same total lift).  What is NOT covered is going to higher G-loads on the engine/engine mounts, baggage areas/floor, occupants going through the floor, etc.

5) On most typical small GA airplanes there is no GWzero fuel (zero fuel gross weight).  IOW, the wing is designed to take the entire maximum gross weight (minus the weight of the structural wing).  Rarely do we fly with no fuel in the tanks (fuel relieves wing bending moment … but is required for powered flight).

Keep the Blue on Top, -Ron

[ArtVandelay]

The only accident where weight and balance was clearly the fault I am aware of is a E/F model that had 5 overweight persons on board, with the 5th in the luggage compartment.


Tom

[Hank]

5 hours ago, ArtVandelay said:

The only accident where weight and balance was clearly the fault I am aware of is a E/F model that had 5 overweight persons on board, with the 5th in the luggage compartment.


Tom

I thought that was a C and the pilot had been drinking before the flight. Probably everyone had been drinking before the flight . . . couldn't been more than a couple hundred pounds over gross, plus whatever fuel the plane had in it at takeoff. Hit a berm, didn't it?

[ArtVandelay]

I thought that was a C and the pilot had been drinking before the flight. Probably everyone had been drinking before the flight . . . couldn't been more than a couple hundred pounds over gross, plus whatever fuel the plane had in it at takeoff. Hit a berm, didn't it?

You may be right, I just remember the selfie picture with 4 plus the girl sitting in luggage area.


Tom