Check Gear!

[PT20J]

9 minutes ago, jaylw314 said:

Doesn't that mean the force required to deflect the aileron is INCREASED?

That's a good point. I was trying to simplify the explanation by relating to commonly understood wing aerodynamics and that was a mistake. Let's try again with a more correct, though more complex, description:

Consider the aileron that is deflected UP. (The effect happens in both directions, but it is easier to visualize with the up aileron). As air flows "up" the deflected aileron, it slows until it reaches the sharp trailing edge where it accelerates "around the corner." This flow pattern creates an adverse pressure gradient along the top surface of the aileron and, at some deflection, flow separation begins to occur. As the flow separates, the force on the aileron, and thus the hinge moment, increases. The effect is not linear and tends to cause the aileron deflection to be limited at some point depending on the mechanics of the control system. The effect increases as TAS². Beveling the trailing edge reduces the acceleration of the air flowing over the trailing edge by increasing the radius of curvature and thus reduces the adverse pressure gradient which in turn reduces the hinge moment.

Skip

[Andy95W]

5 hours ago, jaylw314 said:

Somebody mentioned this before--how does the beveled trailing edge reduce aileron forces?

Thanks, Skip, for the explanation.  I always wondered why that was the case.

The Mooney's ailerons weren't always beveled (see picture, below).  They were changed in 1965 when the PC system was added to the airplane.  The original ailerons, like mine in the picture, required higher forces to move them and weren't acceptable for the PC servos.

I had this conversation with Russell Stallings of SWTA about a year before he died.  He noted that because of the aileron design, STEC servos were the only ones that were strong enough to effectively move the ailerons at speed under an air load.  I wonder if or how this will be addressed by TruTrak.

[carusoam]

Expect that electric servo motors can be selected to deliver the punch that is needed... to deliver more force, there are choices of voltage and size...

For the vacuum servos there is quite a size limitation... and vacuum can’t get stronger than 1atm...

The design guys have a job to do, but it won’t be as hard with the modern technology.  They will have to cover all the bases from early Mooney to later Mooney... the STCGroup guys didn’t explain how they were going to cover all the bases... that will require knowing these types of details... for a one size fits all... STC... There may be some parts that are over spec’d for some Mooneys...

Lots of speed differences between the models that will affect forces too...

PP thoughts only, not a mechanical design engineer...

Best regards,

-a-

[PT20J]

23 minutes ago, Andy95W said:

The Mooney's ailerons weren't always beveled (see picture, below).  They were changed in 1965 when the PC system was added to the airplane.  The original ailerons, like mine in the picture, required higher forces to move them and weren't acceptable for the PC servos.

I didn't know that. The earliest one I've flown was a '67 M20C. Thanks :-)

[jaylw314]

4 hours ago, PT20J said:

That's a good point. I was trying to simplify the explanation by relating to commonly understood wing aerodynamics and that was a mistake. Let's try again with a more correct, though more complex, description:

Consider the aileron that is deflected UP. (The effect happens in both directions, but it is easier to visualize with the up aileron). As air flows "up" the deflected aileron, it slows until it reaches the sharp trailing edge where it accelerates "around the corner." This flow pattern creates an adverse pressure gradient along the top surface of the aileron and, at some deflection, flow separation begins to occur. As the flow separates, the force on the aileron, and thus the hinge moment, increases. The effect is not linear and tends to cause the aileron deflection to be limited at some point depending on the mechanics of the control system. The effect increases as TAS². Beveling the trailing edge reduces the acceleration of the air flowing over the trailing edge by increasing the radius of curvature and thus reduces the adverse pressure gradient which in turn reduces the hinge moment.

Skip

Ooooooooh, I think I get it now!  

[HRM]

66' M20E Super 21 w/PC

[PT20J]

11 hours ago, Andy95W said:

The Mooney's ailerons weren't always beveled (see picture, below).  They were changed in 1965 when the PC system was added to the airplane.  The original ailerons, like mine in the picture, required higher forces to move them and weren't acceptable for the PC servos.

I'm curious if your airplane has the aileron-rudder interconnect springs. The usual reason for such an interconnect is to alleviate some adverse yaw. If the aileron change made the yaw worse, the springs might have been added to help with that. If the yaw is due primarily to the wide chord of the ailerons, then I would think the springs would be part of the original design.

Skip

[Andy95W]

Yes, it has the interconnect springs.  The interconnect mechanism is identical to later models, such as the '67 M20C that I used to own.  Below is an old picture before I cleaned it up.  In the photo, the springs are disconnected from the rudder pushrod.  I was in the process of removing it and figured I should take a picture first.

[PT20J]

35 minutes ago, Andy95W said:

Yes, it has the interconnect springs.

Thanks, Andy,

One more mystery solved. Way back in the early '90s, I was working on a flight simulator project and since I owned a '78 M20J at the time, contacted with Mooney engineering. Rob McDonnell was VP of engineering at the time and we had a deal that if he sent me engineering data I needed, I would send him estimates of stability derivatives. He sent me some stuff but he freely admitted that Mooney had been through so many ownership, management and personnel changes that many reasons why things were done the way they were were lost. I can't imagine that it's gotten better over the intervening years. It's interesting to piece all this stuff together.

Skip

[steingar]

1 hour ago, PT20J said:

Thanks, Andy,

One more mystery solved. Way back in the early '90s, I was working on a flight simulator project and since I owned a '78 M20J at the time, contacted with Mooney engineering. Rob McDonnell was VP of engineering at the time and we had a deal that if he sent me engineering data I needed, I would send him estimates of stability derivatives. He sent me some stuff but he freely admitted that Mooney had been through so many ownership, management and personnel changes that many reasons why things were done the way they were were lost. I can't imagine that it's gotten better over the intervening years. It's interesting to piece all this stuff together.

Skip

At one of the Oshkosh Mooney forums a guy from Mooney said when they most recently stared back up no one knew how to build the airplane.  They had all the blue prints, but how they turned that into an airplane, with all the engineering and whatnot was lost.  Sort've the same thing as why NASA couldn't build a Saturn V today if they wanted to.  They're all the drawings, but the engineering on how to put the things together is long gone.

Mooney apparently hired back some of the old workers who were able to show them how to assemble the aircraft.  Seems to have been a success.  I hope Mooney can keep going, better for all of us.

[mike_elliott]

A Mooney is an aluminum skinned airframe airplane. There really isn't any "tribal knowledge" that has been long lost in putting these together. Sure, tips and tricks on how to do it effectively pass out the door as a craftsman leaves if doesnt share the knowledge, but this is just an airplane. Pounding rivets together on a jig is what sheet metal craftsmen do. Perhaps this is why production time/unit  is waaaay longer than it should be, but I would look elsewhere for the answer to this problem. 

[bradp]

Speaking of the Saturn V rocket ... my boss’ father was a NASA engineer.  He’s got a bunch of original blueprints he found in a box for one of the old Cold War rockets.  He’s going to donate them to the smithsonian.  I sent a pic of the rocket garden from our visit  at the Kennedy space center and he pointed out five rockets that his dad had engineered  (Viking, Titan, Gemini)  

 

I also wonder if these difference in control surface design and control force differences have much to do with the lack of GFC 500 STC for the C/D/E models or whether it’s just the shorter airframes? 

[jaylw314]

8 minutes ago, mike_elliott said:

A Mooney is an aluminum skinned airframe airplane. There really isn't any "tribal knowledge" that has been long lost in putting these together. Sure, tips and tricks on how to do it effectively pass out the door as a craftsman leaves if doesnt share the knowledge, but this is just an airplane. Pounding rivets together on a jig is what sheet metal craftsmen do. Perhaps this is why production time/unit  is waaaay longer than it should be, but I would look elsewhere for the answer to this problem. 

The saying among homebuilders is that once you're done with the airframe, you're almost halfway done.  All the systems like the motor, prop, hydraulics, electrical, controls, landing gear, etc have their own standard work as well as work that is unique to the interaction with the specific airframe.  So while anyone could probably build a Mooney airframe given sufficient plans and materials, and put together a landing gear assembly, figuring out how to integrate the two is not going to be straightforward or standard

[mike_elliott]

3 minutes ago, jaylw314 said:

The saying among homebuilders is that once you're done with the airframe, you're almost halfway done.  All the systems like the motor, prop, hydraulics, electrical, controls, landing gear, etc have their own standard work as well as work that is unique to the interaction with the specific airframe.  So while anyone could probably build a Mooney airframe given sufficient plans and materials, and put together a landing gear assembly, figuring out how to integrate the two is not going to be straightforward or standard

Yea, true for those that have not tested systems, have jigs, or are having how to hold a bucking bar. 

[0TreeLemur]

9 minutes ago, bradp said:

Speaking of the Saturn V rocket ... my boss’ father was a NASA engineer.  He’s got a bunch of original blueprints he found in a box for one of the old Cold War rockets.  He’s going to donate them to the smithsonian.  I sent a pic of the rocket garden from our visit  at the Kennedy space center and he pointed out five rockets that his dad had engineered  (Viking, Titan, Gemini)  

 

I also wonder if these difference in control surface design and control force differences have much to do with the lack of GFC 500 STC for the C/D/E models or whether it’s just the shorter airframes? 

The NASA competition this century for a heavy launch vehicle led Rocketdyne to estimate how to re-fabricate the F1 engine using contemporary construction practices.   To do that, they took one out of the freezer and disassembled it.  The originals required several person-years of labor to construct each engine, and today most of the manufacturing would be done using automated techniques.  They did build and test a 'gas generator' which is a huge turbine that runs the fuel land oxidizer pumps.   That worked- see video on Youtube.

Now, according to what I've read on AVWeb, Mooney is way and above the most labor-intensive production certified light single aircraft today.  Something like 40% more person-hours of the next large competitor.   @steingar reported above that when Mooney re-started production, they brought workers out of retirement to show them how to build Mooney's.   Maybe they would have done themselves a favor if instead of bringing back the old way, they went out and hired some recent graduates in engineering and mechatronics. and maybe pilfered a few experienced manufacturing folks from the automotive industry.   I could be a consultant...

[Yetti]

Watching the news last night they were saying the Tesla 3 frame was way heavier and more complex that it should be for current manufacturing methods.   Like 9 parts to do one wheel well where most current cars do it in one.   You would have to believe applying modern manufacturing to the mooney would be a good thing, I thought that is what the china owners were going to do.

[steingar]

What was said at the Mooney forum was a Cirrus takes 1500 hours to build, a Skylane 3000 hours, and a Mooney 7000 hours.

[toto]

12 hours ago, steingar said:

What was said at the Mooney forum was a Cirrus takes 1500 hours to build, a Skylane 3000 hours, and a Mooney 7000 hours.

Sheesh. 3.5 person-years? Is that even possible?

[PT20J]

A Mooney engineer, who had also worked for Cessna, told me years ago that it took 750 hrs. to knock out a Skyhawk and 2000 to build a M20J. Cessna tooled everything. A lot of the Mooney is “hand crafted.”

[bradp]

Re the China investment comment. Remember what happened to the M10...? ... 

If they wanted to increase the production, composites and advanced alloys would be the way to go.  That too would be a lot of investment.  The last 40 years have been lather rinse reapeat .  

[thinwing]

On 12/14/2018 at 7:58 PM, gsxrpilot said:

I'm always expecting Sam Elliott to let me know the gear is good for landing, as I'm turning Final and slowing to the final approach speed.  Passengers always get a kick out of it, and often believe me when I tell them it's Sam.

Know what is worse than a gear up runway landing in an amphib.

[Revelstoke]

8 hours ago, thinwing said:

Know what is worse than a gear up runway landing in an amphib.

Gear down in an amphibious on water is much worse. They flip so fast and violently it almost doesn't seem real. 

This is a great thread! 

Glad it never strayed off topic to. 

And since when are Doctors not perfect?

[thinwing]

Plus you are upside down ,head under water ,belted in wondering what just happened?

[bonal]

44 minutes ago, thinwing said:

Plus you are upside down ,head under water ,belted in wondering what just happened?

That's what happened to this fellow a couple years ago, departed Lampson and is under one minute from the approach to landing on the lake and forgot to put the gear UP, fortunately no one seriously injured. Flying an amphibious could be confusing.

[toto]

Since we've gone pretty far afield from the OT, I'll post this just for viewing pleasure.  This is effectively the "Red Asphalt" clip for seaplane students... proof that you don't need to forget the gear to have a bad day on water