Gross Weight Increase STC for J's

[mooniac15u]

5 minutes ago, bluehighwayflyer said:

Seems reasonable to me. Another interesting and perhaps less academic observation about the Missile and Rocket STCs is that they do not require relocating the nose gear farther forward to support the heavier engine on the ground, as the factory did with the long body.  I would  be more concerned about that than I would be about the tube you have identified if I owned a Rocket Engineering conversion, personally. I have read about one that failed. There may or may not have been others. As you said, their universe is small. 

The nose gear definitely has to carry more weight.  How much extra weight does a stock M20K have up front?  According to the Rocket Engineering website the Missile conversion adds 250 lbs. Does the M20K have the same nose gear as the M20J?

[carusoam]

The Missile uses the K's cowling to help cover the extra pair of cylinders.  Battery moved to help with Cg.

Other interesting tidbits of info...

http://www.rocketengineering.com/content/missile-conversion

best regards,

-a-

 

[M016576]

8 hours ago, PTK said:

Perhaps you misunderstood my post. What tubes were changed by Mooney for the 2900# gw?  Certainly no tubes were changed by Rocket Engineering other than the engine mount for the 3200# gw.

I'll take a picture of the missile STC.  It has additional parts that were added/modified in the landing gear.  I'll snap a photo of those today and post- just haven't had a chance to grab my logs yet.

[M016576]

1 hour ago, mooniac15u said:

I suppose that one way to look at it is that because Rocket Engineering got an STC for a 300 lb increase it means that the original thinner tube can handle the weight.  The counter to that viewpoint is that the engineers at Mooney appear to have felt that a stronger structure was needed.  The former is largely regulatory and the latter is hopefully based on in-depth knowledge of the airframe.

Either way I don't think the issue is catastrophic failure from a single flight with an extra 300 lbs.  It seems more likely that the concern was the long term stress on that tube.  What does that mean in terms of the pre 24-1686 M20Js with the Missile conversion?  There probably aren't enough of them to know yet whether the increased load on that tube will lead to failure.

Rather than assuming that the Missile STC validates an increased GW in my early M20J I would personally be more concerned about the long term potential for issues with early M20J Missile conversions.  If I owned one I would make sure my IA looked carefully at that tube and its associated welds at each annual.

Mine is 24-1302.  

the MSC'a and A&P's that have seen my airplane have not run across a single issue structurally with this mod or airplane.  To imply that rocket didn't "do their homework" because of the higher max GW is a bit callous, particularly if you have not actually looked at the missile STC.

first off- the stc DOES INCLUDE changed or modified structural parts.  I believe they are landing gear parts from later K models.

Second- The missiles DID NOT all start out at 3200lbs max gross.  They were limited to 2900lbs based on J serial number.... just like all the other J's.  at some point a new STC was released that allowed for a new envelope and increased max GW.  I believe that was tied to either S/N and/or the incorporation of the new parts.

I think some of this confusion stems from looking at the ROCKET STC and making assumptions on what the MISSILE STC says.... I'll go grab my logs and post pictures today a bit later.

in the meantime- I'll make sure the nose gear hasn't splintered into oblivion and the wings fallen off my missile

[KSMooniac]

Don't discount a couple non-technical factors in this puzzle. Rocket Engineering used a different cert office than Mooney did/does, and very likely might have had different requirements for substantiation of their STC's. They might have been less rigorous, allowing a higher GW with no structural mods to the base airframe.

Mooney could've been VERY reluctant to approve the GWI to the earlier J models while they were still selling J models...an early J with +160 lbs of useful load would put it in the neighborhood of 1150-1200 lbs, which is far more attractive than the later J models at 2900 lbs and 900-1000 useful loads. They intentionally would avoid a scenario that might hurt sales of new planes.

I wish they would extend the approval now that the J is long out of production and not a threat to sales of current models.

Sent from my VS985 4G using Tapatalk

[M016576]

Ok- the moment we've all been waiting for. 

 

Missile STC documents describing the modification requirements for the GW/envelope expansion.  Straight out of my STC packet....

 

 

Edit: if anyone has questions on the Missile STC- let me know- I'll try to provide the DATA... as opposed to the speculation.

this plane I'm flying has been modded since 1996... 20 years, and no structural problems.  But who knows what the future brings.  Judging by the engine mount and gear pieces though- is say Rocket engineering has a propensity to over-engineer if anything...,

 

2nd edit-  I bet there would be a line around the block to modify J's with those gear parts, if it meant another 150lbs useful.  Imagine- early J'a with 1200-1250lbs useful load...

Edited December 8, 2016 by M016576

[aaronk25]

Touched on above mooney wouldn't have sold many new planes as of the older ones were upgraded to 2900lbs no one would have bought newer ones.

2nd, and this is dumb as heck. The newer Js at 2900 lbs had 20 degrees btdc timing where the older 2,740 ones had 25d btdc, worth about 10hp. So a newer heavier one has less power.

The tube upgrade appears to be to help carry a heavier engine. If the FAA didn't suck bad we would have upgrades to older J's with take off limitations based on Density altitude and runway length not gross aircraft weight. What a joke.




Sent from my iPhone using Tapatalk

[ArtVandelay]

So what does it take to create an STC with just the landing gear mods to get the extra 160lbs? Is it a paper exercise or is there real engineering data required?

[aaronk25]

So what does it take to create an STC with just the landing gear mods to get the extra 160lbs? Is it a paper exercise or is there real engineering data required?

Called rocket engineering 3 years and he said the amount of money required to stc the Js up 160 lbs would be cost prohibitive given its only a few years worth of Js.

This is one of these deals where it's just paperwork but given the gov bureaucracy it just isn't going to happen.

I also think (which doesn't mean much) that additions such as powerflow exhaust should raise the gross weight. PF should be worth my best guess of 100-150lbs of trade off, but not a option now.




Sent from my iPhone using Tapatalk

[carusoam]

Time to look up some landing gear parts...

If you guys can do that, we have a couple of known STC writers around here... at least two have supplied things for our aircraft(s)

This could actually be Rocket science.

would it be possible to mount Bravo/Ovation legs on a J?  They were improved after the L ran into weight challenges....  it might be as simple as spar change or as complex as a bolt pattern change....

Funnier things have happened along the way...

Best regards,

-a-

[PTK]

Thank you for posting all that info @M016576.

If I understand it correctly the sn 24-0001 to 24-0763 need those bolts and nuts in the gear (items 1-9 in note 1) but sn 24-0764 and up don't need anything?

And no mention is made unless I missed it on ASI change. Are there Va considerations with higher weights?

I'm even more confused!

 

[mooniac15u]

13 hours ago, M016576 said:

Ok- the moment we've all been waiting for. 

 

Missile STC documents describing the modification requirements for the GW/envelope expansion.  Straight out of my STC packet....

 

 

Edit: if anyone has questions on the Missile STC- let me know- I'll try to provide the DATA... as opposed to the speculation.

this plane I'm flying has been modded since 1996... 20 years, and no structural problems.  But who knows what the future brings.  Judging by the engine mount and gear pieces though- is say Rocket engineering has a propensity to over-engineer if anything...,

 

2nd edit-  I bet there would be a line around the block to modify J's with those gear parts, if it meant another 150lbs useful.  Imagine- early J'a with 1200-1250lbs useful load...

Thanks for sharing these.  I have to agree with @PTK. In these three pages there is no requirement listed to modify the landing gear on serial numbers 24-0764 and up.  Mooney made a change to the gear at 24-0764 per the parts catalog.  There is a separate drawing for 24-0001 - 24-0763.  You said yours is 14-1302.  Was the gear modified on yours? 

[mooniac15u]

13 hours ago, M016576 said:

Ok- the moment we've all been waiting for. 

 

Missile STC documents describing the modification requirements for the GW/envelope expansion.  Straight out of my STC packet....

 

 

Edit: if anyone has questions on the Missile STC- let me know- I'll try to provide the DATA... as opposed to the speculation.

this plane I'm flying has been modded since 1996... 20 years, and no structural problems.  But who knows what the future brings.  Judging by the engine mount and gear pieces though- is say Rocket engineering has a propensity to over-engineer if anything...,

 

2nd edit-  I bet there would be a line around the block to modify J's with those gear parts, if it meant another 150lbs useful.  Imagine- early J'a with 1200-1250lbs useful load...

A couple more takeaways from this:

1) It doesn't address the steel tubing issue that Mooney used as a cutoff for their GW increase.  There is no reference to a difference for serial numbers below 24-1686.  So, it doesn't provide any additional answers to that question.

2) The increase to 3200 lbs is not a straight GW increase across the board.  It is an increase in takeoff weight with a lower landing weight.  I believe the Mooney increase to 2900 lbs did not have limitations.

3) What is the modification to the "right hand lower tubular fuselage longeron"?  It is required through serial number 24-1037.  Is there a drawing that shows this change.

[N601RX]

For certification purposes the tube would have to withstand 3.8g's of loading as a minimum. It's possible that mooney had an internal requirement that is higher than that (perhaps 4.5 or higher) Rocket eng could have then decided that they didn't wish to keep the extra margins and that 3.8 was good enough for them. There is pretty good evidence mooney did add extra margins, look at the one that flew into the storm.  Rocket could have simply decided to cut into these margined a small amount and may very well still be well above 3.8g's.

Its also possible that that their engine mount distributes the loads in the airframe in a slightly different manner that the original factory one. It does have asditional attach points. 

[mooniac15u]

3 minutes ago, bluehighwayflyer said:

Does the marketing department ever drive engineering changes?  It could be that Mooney just needed an inexpensive structural change to justify not applying the 2900 pound gross weight increase to the vintage J fleet for the reasons we have already discussed.  We will likely never know, but the Missile fleet's successful service history would seem to suggest that the original tube diameter is more than sufficient for the 2900 pound gross weight increase to have been more broadly applied. 

The change was made with the introduction of the 205 in 1987.  At the time they were still making 201s with the thinner tubing.  They continued to make both in 1987 and 1988.  The GW upgrade was applied to new M20Js starting in 1991 and the retroactive increase was announced in 1992.  That seems like a long time to be running a marketing ploy.  Maybe it took them that long to get the increase approved

[M016576]

18 hours ago, PTK said:

Thank you for posting all that info @M016576.

If I understand it correctly the sn 24-0001 to 24-0763 need those bolts and nuts in the gear (items 1-9 in note 1) but sn 24-0764 and up don't need anything?

And no mention is made unless I missed it on ASI change. Are there Va considerations with higher weights?

I'm even more confused!

 

More pictures- IRT the airspeed indicator and maneuver speed.  The STC paperwork is over 30 pages long, so I didn't post everything- just what I thought you guys were interested in.

LSS- Manuever speed is 123 at max gross.  The airspeed indicator isn't swapped out... but does require additional placards near by (most likely due to the fact that there is no airspeed dial face that shows the speeds per the rocket STC.  I believe Mooney could have chosen this option instead to requiring a new indicator... but they sell those indicators with the STC... so why not.)

[M016576]

14 hours ago, N601RX said:

For certification purposes the tube would have to withstand 3.8g's of loading as a minimum. It's possible that mooney had an internal requirement that is higher than that (perhaps 4.5 or higher) Rocket eng could have then decided that they didn't wish to keep the extra margins and that 3.8 was good enough for them. There is pretty good evidence mooney did add extra margins, look at the one that flew into the storm.  Rocket could have simply decided to cut into these margined a small amount and may very well still be well above 3.8g's.

Its also possible that that their engine mount distributes the loads in the airframe in a slightly different manner that the original factory one. It does have asditional attach points. 

Correct- the engine mount is much larger than the stock J engine mount, and has 8 (eight) attach points to the fuselage, instead of four.  But the motor is also much heavier.

[M016576]

15 hours ago, mooniac15u said:

A couple more takeaways from this:

1) It doesn't address the steel tubing issue that Mooney used as a cutoff for their GW increase.  There is no reference to a difference for serial numbers below 24-1686.  So, it doesn't provide any additional answers to that question.

2) The increase to 3200 lbs is not a straight GW increase across the board.  It is an increase in takeoff weight with a lower landing weight.  I believe the Mooney increase to 2900 lbs did not have limitations.

3) What is the modification to the "right hand lower tubular fuselage longeron"?  It is required through serial number 24-1037.  Is there a drawing that shows this change.

I'll look in my airframe log to see about that mod.  There are no pictures of it, as the packet is for the pilot, not the installer.  Willmar did the conversion on this airframe... not sure if that's relevant data, but from what I understand, they deal (dealt with?) lots of mooney's.  

And yes- that's also a huge point- my max gross weight of 3200lbs is take-off weight.  Max landing weight is less.  But the max landing weight is still over the 2900lb max gross on the "stock" weight increased J's.

[M016576]

16 hours ago, mooniac15u said:

Thanks for sharing these.  I have to agree with @PTK. In these three pages there is no requirement listed to modify the landing gear on serial numbers 24-0764 and up.  Mooney made a change to the gear at 24-0764 per the parts catalog.  There is a separate drawing for 24-0001 - 24-0763.  You said yours is 14-1302.  Was the gear modified on yours? 

I don't think so, but I'll check the airframe log and see.  You're correct- from what I can tell, it's just the serial numbers before 0764 that require the gear mod- but there is some sort of other structural mod and a different engine mount required for all the Missiles.  Maybe some of the weight is increase piece is attributed to that?