M20C crack found during annual. Worried.

[Mooneymite]

 

I just happened to have part of the belly of my electric flap Mooney off today.  It's easy to see that the electric flaps were a complete re-design from the earlier hydraulic flaps.  There are four sturdy mounting brackets and the drive motor is mounted on a fuselage bulkhead.

[flyer338]

When I bought my 1965 M20C in 1992, the pre-buy revealed vertical cracks where the flap brackets attached to the spar. The cracks has been stop drilled. Over 20 years and 2000 hours, the cracks did not grow. The plane is still flying out of New Jersey. I suspect the repair might have been done before Mooney issued the SB.

I was careful to avoid flaps down at speeds in excess of Vfe. I think I only did it once or twice.

[flyer338]

Another thought, why wasn’t this discovered and addressed during the pre-buy?

[MCDsiena]

Parts are ordered and the repair will soon be underway. 
 

Thabk you everyone for the help 

[DJE22]

On 1/15/2021 at 2:49 PM, Hank said:

This happens by forgetting to raise the flaps after takeoff . . . A situation usually found while wondering why cruise speed is so low.

Ha!  Never happened to me....nope never ever ;)

[Hank]

On 1/15/2021 at 2:49 PM, Hank said:

This happens by forgetting to raise the flaps after takeoff . . . A situation usually found while wondering why cruise speed is so low.

 

46 minutes ago, DJE22 said:

Ha!  Never happened to me....nope never ever

Me neither!    I  heard about it from a friend . . . . . 

[MikeOH]

14 minutes ago, Hank said:

 

Me neither!    I  heard about it from a friend . . . . . 

I must have the same friend

[Mooneymite]

On 1/15/2021 at 3:49 PM, Hank said:

This happens by forgetting to raise the flaps after takeoff . . . A situation usually found while wondering why cruise speed is so low.

On the C, the published max airspeed is for full flap deployment.  Since the takeoff flap position is less, I would suspect that no damage, or adverse flight characteristics would occur until a higher airspeed.  Perhaps a significantly higher airspeed.

I wonder if the Mooney engineers ever tested the real world max airspeed for the takeoff setting and what that real world airspeed is.

Do any of the Mooney models publish a max airspeed for takeoff/approach flaps?

[PT20J]

5 hours ago, Mooneymite said:

On the C, the published max airspeed is for full flap deployment.  Since the takeoff flap position is less, I would suspect that no damage, or adverse flight characteristics would occur until a higher airspeed.  Perhaps a significantly higher airspeed.

I wonder if the Mooney engineers ever tested the real world max airspeed for the takeoff setting and what that real world airspeed is.

Do any of the Mooney models publish a max airspeed for takeoff/approach flaps?

Your point is well taken. I doubt that forgetting TO flaps causes the cracks unless done repeatedly since the cracks are probably fatigue induced.

Mooney did list a higher TO flap speed for the 205 and then deleted it for later serial numbers. I have no idea why. Perhaps they decided it was a bad idea. The flap mechanism is not the most robust part of the Mooney design.

 

[Mooneymite]

4 hours ago, PT20J said:

Your point is well taken. I doubt that forgetting TO flaps causes the cracks unless done repeatedly since the cracks are probably fatigue induced.

Mooney did list a higher TO flap speed for the 205 and then deleted it for later serial numbers. I have no idea why. Perhaps they decided it was a bad idea. The flap mechanism is not the most robust part of the Mooney design.

 

Very interesting.  Thank you for posting that.

I have an electric flap C model.  I suspect that the 205's flap installation is very similar to mine....so, probably a 16 knot buffer?

Virtually all the heavy iron airplanes have different airspeeds for each flap setting, which really makes sense.  Having one speed for all flap settings may be simple (KISS), but not very realistic.

[carusoam]

In C152 training... the first flap set point didn’t have a limit...  (old memory)

The non-linear relationship of force, flap angle, and speed...

It wouldn’t be too hard to instrument the flaps to see how much force is applied using a chart of the different variables...

It would be too hard to guess...

 

Also...

The ASI white arc had steps to represent different flap settings and stall speeds...

PP thoughts only, not a CFI...

Best regards,

-a-

[Hank]

The 172s I trained in had 110 knot limit for 10° flaps, so they could be lowered pretty much anytime. There was a much lower speed (85 knots? 90 knots?) to put the flaps any lower. They moved in 10° increments only.

My C just says "no flaps above 125 mph." My electric flaps are infinitely variable.

[generalaviationguru]

This issue came up on a Mooney we’re looking at purchasing.

What would the cost for doing the SB M20-217 be?  Seems like it would be at least $2000 given all the labor time….

[Ragsf15e]

50 minutes ago, generalaviationguru said:

This issue came up on a Mooney we’re looking at purchasing.

What would the cost for doing the SB M20-217 be?  Seems like it would be at least $2000 given all the labor time….

Yes, i had to have that done a few years back and it was around that.  The airplane was already opened up for annual at an msc.  I wouldn’t let that stop me from buying the airplane, but have a good plan for how much it will cost and who will do it.  The repair itself is relatively straightforward but access is tough.

[A64Pilot]

On 2/5/2021 at 7:34 AM, Mooneymite said:

On the C, the published max airspeed is for full flap deployment.  Since the takeoff flap position is less, I would suspect that no damage, or adverse flight characteristics would occur until a higher airspeed.  Perhaps a significantly higher airspeed.

I wonder if the Mooney engineers ever tested the real world max airspeed for the takeoff setting and what that real world airspeed is.

Do any of the Mooney models publish a max airspeed for takeoff/approach flaps?

I’ve heard of someone who did a low pass at J model VNE (196 kts) with T/O flaps, once without any apparent harm.

But just because it didn’t break anything right away doesn’t mean there wasn’t any harm done, there was certainly fatigue, and that’s the issue. Many think that I’ve done X several times, those max airspeeds aren’t real, they are so conservative etc. without understanding the damage is cumulative, the first time you bend a coat hanger it doesn’t break, but keep bending and see what happens.

Here’s another thing, most of the fleet is actually being flown well beyond original design life expectancy, it probably behooves us to add in additional cushion to those max limits if we want to keep these things flying without breaking parts, some that aren’t available anymore. As a maintainer one thing that drives me nuts is the instructors that teach to drop gear at the max gear extension airspeed, sure it’s allowed, but isn’t it logical to think that if anything is done repeatedly at the maximum limit that over time it just might cause more wear and fatigue than if it wasn’t done at max allowable limit?

[skykrawler]

32 minutes ago, A64Pilot said:

I’ve heard of someone who did a low pass at J model VNE (196 kts) with T/O flaps, once without any apparent harm.

But just because it didn’t break anything right away doesn’t mean there wasn’t any harm done, there was certainly fatigue, and that’s the issue. Many think that I’ve done X several times, those max airspeeds aren’t real, they are so conservative etc. without understanding the damage is cumulative, the first time you bend a coat hanger it doesn’t break, but keep bending and see what happens.

Here’s another thing, most of the fleet is actually being flown well beyond original design life expectancy, it probably behooves us to add in additional cushion to those max limits if we want to keep these things flying without breaking parts, some that aren’t available anymore. As a maintainer one thing that drives me nuts is the instructors that teach to drop gear at the max gear extension airspeed, sure it’s allowed, but isn’t it logical to think that if anything is done repeatedly at the maximum limit that over time it just might cause more wear and fatigue than if it wasn’t done at max allowable limit?

I think you would really need the nose pointed (way) down to get the airplane to Vne with TO flaps - so I have trouble believing that.

'Most are beyond original design life expectancy' - Based on what? Airframe hours? Age?  What is the life expectancy?   - for the whole fleet I also have trouble believing that.

I do agree that its better to extend gear and flaps at speeds less than limits.    It takes discipline and patience as a pilot to plan ahead so it can be accomplished. 

Based on the history, those C model flap mechanism were probably under-designed.  I've seen early Bonanza flaps where the bracket attached to the flap cracked the stringer and pealed the flap skin away - it looked like a poor design, too.

 

[Mooneymite]

44 minutes ago, A64Pilot said:

....., but isn’t it logical to think that if anything is done repeatedly at the maximum limit that over time it just might cause more wear and fatigue than if it wasn’t done at max allowable limit?

Same with gear retraction.   Lower airload=lower stress.

[Hank]

4 hours ago, Mooneymite said:

Same with gear retraction.   Lower airload=lower stress.

Positive rate, gear up!

Like this local departure:

When in control, positive rate, gear up. Accelerate to Vx = 80-85 mph to clear obstacle, then pitch for Vy to climb out.

[A64Pilot]

6 hours ago, skykrawler said:

I think you would really need the nose pointed (way) down to get the airplane to Vne with TO flaps - so I have trouble believing that.

'Most are beyond original design life expectancy' - Based on what? Airframe hours? Age?  What is the life expectancy?   - for the whole fleet I also have trouble believing that.

I do agree that its better to extend gear and flaps at speeds less than limits.    It takes discipline and patience as a pilot to plan ahead so it can be accomplished. 

Based on the history, those C model flap mechanism were probably under-designed.  I've seen early Bonanza flaps where the bracket attached to the flap cracked the stringer and pealed the flap skin away - it looked like a poor design, too.

 

Trust me, I didn’t have to point the nose down that much at all, more than normal I’m sure but not as much as you would think, not enough to think something was wrong.

On edit, go out and just push down on your flaps, I don’t mean hard enough to bust anything, but see how much they flex? well the faster you go the higher the air load, the more they come up, at high speed I’d expect they come up quite a bit.

Way back in the day manufacturers usually designed for roughly 20 years, they logically expected on average small aircraft would be replaced about like cars are.

Before far 23 fatigue wasn’t even required to be analyzed, just “considered” Of course even before far 23 it was obvious that GA aircraft were going to be used for far longer than ever considered and that’s why far 23 aircraft have airframe life limits and other major structure limits based on analysis, CAR 3 aircraft have no life limits, not because they were thought that they would last forever, but because it was expected they would be junked like automobiles before fatigue and life limits would be exceeded.

If you have ever worked with the FAA small airplane directorate and or the ACO, there are very concerned about “the aging aircraft problem” their words not mine.

Not read this, just popped up with a quick Google

https://www.faa.gov/aircraft/air_cert/design_approvals/small_airplanes/cos/aging_aircraft/media/roadmapGAAgingAirplane.pdf

There is not a small number of FAA Engineers that want to establish mandatory retirement’s  for GA aircraft, in their opinion it’s the only way to eliminate the “problem”

 

Edited July 1, 2023 by A64Pilot