Stalls and Leading edge question

[Petehdgs]

I have been using my '64 Mooney Super 21 to travel between Culpeper VA CJR and Dexter MI 2E8 several times last summer.  Because 2E8 is 2100 ft grass with displaced thresholds and has a down slope on RWY 6 in the center third of the runway, it has me working on my short field technique quite a lot.  I added a lift indicator and train with it to get better at slow flight and stay safe.  This training has helped me to identify a glitch that merits further investigation and I decided to ask you all for some advice.

 

During slow flight practice at safe altitudes I noticed the wings fly well right up to the stall then break quickly and recover quickly causing the airplane to porpoise.  At altitude this is not a big deal except the break occurs without warning.  When this happens near the ground the results are a hard drop and perhaps a bounce.  I would like the stall to be softer with some feel to it, if that is possible without too much difficulty, and without loss of cruise performance and fuel economy.

 

I reread Harry Ribletts book about GA airfoils and he suggests a leading edge modification (page 42) to the 64-212 (and similar 6x series airfoils) to correct errors in the initial NACA file.  The main advantage would be a softening of the approach to the stall, allowing you to fly closer to it safely, and a slower release of the air at the stall, aiding in smoother and slower landings.  Because of these two things you would be able to land slower and shorter, but this would not be a true STOL mod and would not affect cruise at all.  

 

If a leading edge cuff were made available, adding about 15 pounds total weight, for a parts cost of about $2500 and a labor cost about the same, how many mooney owners would be interested in it?  I guessing less than 1% of short body Mooney owners.  I need to know if there is enough interest to pursue this any further.   

 

I have attached my research in this area. It is a compilation of about 15 pages.  The meat is in page 12 paragraph 7, page 19 figure 2, page 42 and the few pages that follow.  There is a full explanation in all the pages, but those give you the scope of it.  

 

One Miracle at a time.  

Riblett explanation NACA Flaws.pdf

[carusoam]

it’s possible that I am misunderstanding what the OP wrote... 

Wouldn’t be the first time...

 

Choices...

1) re-invent the wheel... requiring an STC...

2) Add those things on the top of wing... vortex generator devices... ask @aviatoreb he has them...

3) Realize there is no change to soften the stall... it can be lowered...  but, not softened... that requires changes to the wing, so parts of it stall earlier than other parts...

That would be re-inventing the wheel...  STC, new wing, or a different airplane...

4) realistically, people operate Mooneys on 2k’ of runway as their home drome...

5) What you are asking for is not particularly a change in the machinery... but, a change somewhere else...

6) You may want to be a bit more specific with your challenges... to improve the responses you are getting...

I’m only a PP with no special background in aviation ... and used 5B6 with a 2.3k’ long runway...

Somewhere along the way.... multi tasking gets really challenging... and short field performance goes away... 

7) stalling above the runway, is not a landing technique... soft or not... 

8) The act of landing transfers the weight from the wings to the wheels... control does the same...

9) the act of stalling, is losing control over the aircraft...

10) During landing videos, you will often hear the stall horn trigger as the wheels are screeching... the stall horn comes on about 10kias before the stall actually occurs.

Let us know if you would like recommendations...

PM, if preferred...

Best regards,

-a-

[takair]

I am surprised it would not affect cruise performance.  TKS, which barely changes the airfoil, has at least a 5 it penalty, as does the twisted wing in some F models.  I would personally look at another plane if I needed to routinely fly into a short grass field rather than modifying my current plane....might do VGs, but not much more.  Even if the stall break was modified, I would still be worried about sink rates and the stiff Mooney gear.  That said, 2100ft seems reasonable for a stock Mooney, unless there are obstacles. You had another thread going, a couple of us asked about your stall strips, can’t quite zoom in on the picture, but are they installed?  My experience with the same model is that there is a notable build up of shuddering to the point of stall.  Have you compared to anotherMooney?  Maybe you are flying the approach different, are you riding the stall horn down on final, do you have tall trees to clear?  Not questioning you, just trying to understand.

[takair]

Would be curious to get @Blue on Top thoughts?

[carusoam]

Keep in mind the Naca document quoted is from 1959...

Not very relevant to a modern conversation... regarding techniques to flying into a grass strip using a well known Mooney...  

But if you need a reason to do something different... that will work.

Best regards,

-a-

[GeeBee]

+1 on vortex generators. Had them on my PA-18. Could not get the airplane to stall. A Mooney airfoil would stall albeit at a much lower speed and your aileron control would be superb all the way to stall. You should check out this option first.

 

[Petehdgs]

23 minutes ago, carusoam said:

Keep in mind the Naca document quoted is from 1959...

Not very relevant to a modern conversation... regarding techniques to flying into a grass strip using a well known Mooney...  

But if you need a reason to do something different... that will work.

Best regards,

-a-

The all metal mooney wing was designed in 1960.  I'd say the information presented is relevant.   

[M20F-1968]

2 hours ago, takair said:

...at least a 5 it penalty, as does the twisted wing in some F models.  

I have a 68 F which is highly modified and has a twisted wing.  At 10,000 ft, wide open it is a 168 kt airplane, at 10,000 ft at 75% power it is a 160 kt airplane, and at 17,000 ft it is a 170-175 kt airplane.  I have heard other say the twisted wing is slower but in my experience, I would say not.  Where do you get your information.

John Breda

[carusoam]

1 hour ago, Petehdgs said:

The all metal mooney wing was designed in 1960.  I'd say the information presented is relevant.   

Pete,

Let me see if I can say this in a friendlier manner... 

I think you may be missing my point...

Go ahead and read the document...

You will see it is all numbers... and a few graphs...

The wood wing came first, it isn’t much different than the metal one...

I used to fly a 65C, kind of original...

I now fly a 94O, has fancy wing tips...

The P51 came decades earlier... strikingly similar wing design...

very little has changed in regards to those wings.... 

Very few people go and change the design of the wing... where there are plenty of opportunities to train to fly that wing better...

There are a few ways to lower the stall speed...  (covered above...)

 

Really direct from here....

don’t stall the plane above the runway... 

Good training and practice is really helpful to achieve this goal...

You will find the training includes a lot of numbers (like the document you showed us) to achieve the precision you are asking for...

Some people memorize the numbers and do the math... others use an AOAi

And yes some people trade the Mooney in to get a more outback suited machine...

it really helps to do some slow flight to identify a few things... from stall speeds to the speed where the stall horn sounds...

When your load changes, so do these numbers...

 

So the first paragraph says... The NACA wings aren’t designed for GA or GA pilots... do you buy into that?  
Which of the designs is the Mooney wing?

That would be a 1950s statement that didn’t include modern training techniques, GPS position sensors, color portable screens, with Apps that draw a line on Google maps representing your exact flight...

You are much better than you believe...

You have more skill than the document believes you have...

Have you seen a Mooney specific CFII fly your plane at your airport yet?

 

I think your plane can handle that fancy grass strip, better than you believe...

Want to meet my favorite CFII in your neighborhood?

PP thoughts only, not a CFI...

Best regards,

-a-

[takair]

6 minutes ago, M20F-1968 said:

I have a 68 F which is highly modified and has a twisted wing.  At 10,000 ft, wide open it is a 168 kt airplane, at 10,000 ft at 75% power it is a 160 kt airplane, and at 17,000 ft it is a 170-175 kt airplane.  I have heard other say the twisted wing is slower but in my experience, I would say not.  Where do you get your information.

John Breda

Hearsay and a one time formation drag race with twisted wing F model..  I thought I read they went back to the straight wing because of this as well?  Don’t recall where.  Admittedly there could have been a dozen other factors.  That said, perhaps yours could be even faster with the straight wing?  I know they call it the twisted wing, but to me the leading edge also appears to be different as well.  

[takair]

11 minutes ago, M20F-1968 said:

I have a 68 F which is highly modified and has a twisted wing.  At 10,000 ft, wide open it is a 168 kt airplane, at 10,000 ft at 75% power it is a 160 kt airplane, and at 17,000 ft it is a 170-175 kt airplane.  I have heard other say the twisted wing is slower but in my experience, I would say not.  Where do you get your information.

John Breda

By the way...I did not mean to imply that the twist wing was 5kts slower.....I intended that for the TKS, but it certainly reads poorly.  I don’t know what the value is, just thought it was slower....

[M20F-1968]

The leading edge is the same, the only difference is the outboard lap joint is riveted son the the outboard leading edge tip is about 1 1/2" lower than usual.  

It is not really a twisted wing, but rather the outboard wing section has a slightly lower angle of attack.  

John Breda

[carusoam]

The twisted wing was a nice way to change the AOA for part of the wing... thus changing the speed of which one part of the wing stalled...

1) it adds to the difficulty of building the wing...

2) Didn’t significantly change the stall characteristics...

3) Compare to a cirrus where there is a step change in the wing design to stall characteristics...  even I can see it.

4) Walk by John’s plane... unless you know it’s his... you will be extra challenged to see the twist...

 

It was a nice idea, but didn’t really achieve very much... and cost some drag...

we kind of get saddled with choosing speed and efficiency, over slow flight and soft stall characteristics...

I kind of like speed and efficiency...

And I really love the 800’ T/O run of the 310HP IO550... on those short runways...

Deciding at the halfway point... is go or stop... with enough room to execute...

-a-

[Niko182]

The mooney lands fine on short fields. Piper painter has proven that it is more pilot skill than the aircrafts ability to land in short distance. VGs will be cheaper, will not impact the useful load, and will not affect the cruise. IMO you are trying to solve a problem with a complex solution, while the simple solution has already been created.

[takair]

41 minutes ago, M20F-1968 said:

The leading edge is the same, the only difference is the outboard lap joint is riveted son the the outboard leading edge tip is about 1 1/2" lower than usual.  

It is not really a twisted wing, but rather the outboard wing section has a slightly lower angle of attack.  

John Breda

A quick look at the 68 vs 75 F model POH and it seems to show that there was no penalty in 68.  In other words, seems to support no speed difference as you suggested.  A search of Mooneyspace shows where I got the thought from....some folks felt that their aircraft were slightly slower due to washout...but that too could be a dozen other things.   I also compared F model to E model manuals and see that there is a difference there....so side by side flight test of and E vs an F with or without washout is not a valid test.  It is probably fair to say, as old as these aircraft are, maintenance, rigging and mods likely are a bigger factor than these subtle design changes.

[Petehdgs]

52 minutes ago, carusoam said:

Pete,

Let me see if I can say this in a friendlier manner... 

I think you may be missing my point...

Go ahead and read the document...

You will see it is all numbers... and a few graphs...

The wood wing came first, it isn’t much different than the metal one...

I used to fly a 65C, kind of original...

I now fly a 94O, has fancy wing tips...

The P51 came decades earlier... strikingly similar wing design...

very little has changed in regards to those wings.... 

Very few people go and change the design of the wing... where there are plenty of opportunities to train to fly that wing better...

There are a few ways to lower the stall speed...  (covered above...)

 

Really direct from here....

don’t stall the plane above the runway... 

Good training and practice is really helpful to achieve this goal...

You will find the training includes a lot of numbers (like the document you showed us) to achieve the precision you are asking for...

Some people memorize the numbers and do the math... others use an AOAi

And yes some people trade the Mooney in to get a more outback suited machine...

it really helps to do some slow flight to identify a few things... from stall speeds to the speed where the stall horn sounds...

When your load changes, so do these numbers...

 

So the first paragraph says... The NACA wings aren’t designed for GA or GA pilots... do you buy into that?  
Which of the designs is the Mooney wing?

That would be a 1950s statement that didn’t include modern training techniques, GPS position sensors, color portable screens, with Apps that draw a line on Google maps representing your exact flight...

You are much better than you believe...

You have more skill than the document believes you have...

Have you seen a Mooney specific CFII fly your plane at your airport yet?

 

I think your plane can handle that fancy grass strip, better than you believe...

Want to meet my favorite CFII in your neighborhood?

PP thoughts only, not a CFI...

Best regards,

-a-

 

"So the first paragraph says... The NACA wings aren’t designed for GA or GA pilots... do you buy into that?  "

I do.  There is more detail on pages that weren't included.  NACA basically had a test program to determine what does what to an airfoil.  Some of those forms make good wings for all around use in aircraft, some are ok, and some are not well suited at all.  Others are fantastic at some things and so-so at other things.  NACA never designed airfoils for use in specific aircraft but expected designers to roll their own for the exact aircraft they were designing.  That is a lot to ask of a airplane designer.  That is why most designers pick an airfoil from the  NACA list and take the good with the bad.  

"Which of the designs is the Mooney wing?"

In Mooney's case they actually did combine 2 different airfoils into the one wing.  The root is 63-215 and it becomes 64-415 at the tip.  The middle of the wing is an interpolation between them.  There are many things the Mooney wing does exceptionally well, even slow flight... to a point.  If you look at the next to the last 2 pages of the pdf reference, Lift Cl vs AOA graph on the 63-215 and 64-415 wings with flaps, the stall breaks away sharply at the top of the lift curve.  Without flaps it is similar, but not near as sharp.  I can feel that difference in my bird when practicing.  The discrepancy is there, plain as day if you look for it.  

Harry Riblett has Identified that discrepancy as a fixable flaw in the airfoil design and shows an evolution of correction on page 19, the 5th page in the pdf.  He does not show it as Lift vs AOA, but instead as Lift vs Drag, but just look at the changes to the top of the lift curve between the 64-212, 212c, 212a=0.5c, and the GA-37-212.  Each change softens the stall and extends the lift slightly, making the airplane more forgiving and docile at the slow end of the envelope.  On page 42, the 19th page of the document, he shows exactly how to fix the airfoil with a leading edge modification, bringing the airfoil to the third modification, 212a=0.5c.  I'm no expert but that looks like a good sized improvement to me.  Besides, leading edge mods are out there for other aircraft and they work.  

I know that I can simply back off the envelope a little bit and fly just fine.  I am currently doing just that.  But that means leaving some performance behind on the table.  Now most pilots are not going to want to use that performance anyway, but some will.  I know I do.

What I want to know is how many Mooney owners would be interested?  It is a simple question.  

 

[Hank]

Yes, @Petehdgs, as mentioned by @Niko182 above, search youtube for piperpainter's videos flying the red M20-C into back country strips with his tundra-tire & tail wheel friends. He eventually sold the Mooney and bought one of those . . . .

I was based my first seven years at an obstructed 3000' field and never had a problem. I would sometimes visit a nearby 2000' grass strip, but due to the uneven and curved runway, I never went there heavy; my limit was 2 people and half tanks.

On the other hand, I visit a 3500' grass strip at the beach, generally mowed well only ~2000', that's obstructed by pine trees and power lines landing toward the ocean, and go there loaded to the gills, call it gross less a couple or three hours fuel. Never had any trouble there, except landing once after lots of rain and almost bogged down, had to release brakes and almost straighten the rudder and gjve it full power to keep crawling . . .

[Hank]

P.S. @Petehdgs, I used to fly to KSJS, Prestonsburg-Paintsville, KY. Sure, it's 5000' long, in the hilly E. KY coalfields, and approaching from the north takes you right over a good sized prison. My first landing on 21 was quite a surprise, the first 4000+' were in a 3° downpipe, just like me! But with only light braking, I made the turnoff well before the end, and affer a couple of times it was old hat and no challenge.

The secret is getting comfortable in the airplane. Fly often, go new places. As a new pilot and new Mooney owner, that was most of my flights. Keep working, it will come. 

[carusoam]

Pete,

I’m pretty happy to share things with the Mooney factory, mechanics, STC writers, and pilots... around here...

It is an interesting question...

But it surely isn’t an easy one for everyone to understand...

Some of the people you are trying to reach won’t have all the time and/or inclination to go through all the documentation like we are tonight...

So if the question was something like...

Would you like a bolt on wing modification that would lower the stall speed of your Mooney from 58kias to 48kias... without altering the top speed at all... (or some minor amount...)

Here’s a pic of an example... how it is made, how it is installed...

Even a guess at its cost to manufacture...

By the time you get to STC costs... the idea has to be really good, and the costs be really low...

 

Have a look at the VGs and the AOAis... two really good ideas that have gone all the way through the wringer...

You can get a really good idea how large the market is for your next step...

 

Some people are comfortable with experimental planes... some people don’t want to be first to find out how ice affects the new device...

 

If you can...

Simplify your question as much as you can... keep all the tech detail as support...

Kind of a method of selling the idea... 

Then find PiperPainter’s / Bryan’s Outback videos... with his red M20C... purely magical...

Bryan didn’t mind using his Mooney on un-improved strips... Dad’s ranch... complete with big critters in fields...

Best regards,

-a-

[BDPetersen]

Curious about VG’s on the Mooney. On the C310 they mellowed out landings considerably, but the Mooneys ( at least the short ones) don’t seem to need help in that regard. The 310 benefitted from some performance improvements (weight, Vmc).

[N201MKTurbo]

When I bought my J it was quite a bit out of rig. I did my BFR in it at night and when we stalled it, it snap lolled almost inverted. 

After I fixed the rigging, it stalls nice and straight. I was surprised how much rigging adversely affected the stall behavior.

So, If the stall isn't quite right, you might want to take a look at the rigging.

[Marcopolo]

12 hours ago, Petehdgs said:

What I want to know is how many Mooney owners would be interested?  It is a simple question. 

So far=0, including myself!

 

But don't give up, if you build it, they will surely come.

 

Ron

[ArtVandelay]

...and will not affect the cruise.

Im not buying that, you can’t put something into the air stream that affects the flow, change a laminar flow wing to non laminar flow, and not get additional drag. Maybe it’s not significant, but energy you’re adding to the flow has to come from somewhere...laws of physics being what they are.

[jaylw314]

I should point out that all the study stuff about the NACA airfoils seems to be related to stall performance in open air, not in ground effect.  if @Petehdgs is interested in short-field landing stall characteristics, I suspect that would be more important to know about than open air stall characteristics.  Anyone know if there's been more recent computer modelling work in that area?

[Petehdgs]

19 hours ago, Niko182 said:

The mooney lands fine on short fields. Piper painter has proven that it is more pilot skill than the aircrafts ability to land in short distance. VGs will be cheaper, will not impact the useful load, and will not affect the cruise. IMO you are trying to solve a problem with a complex solution, while the simple solution has already been created.

I disagree that VGs don't impact top speed or cruise speed fuel economy.  I admit I don't have direct experience with them.  The people that I have talked to that have them say there is a drag penalty, but the improved low speed performance is worth it to them.  I'd like to hear from a Mooney owner that has them installed.  To me VGs are a band-aid and are unclean to the airflow, but they do have a proven track record of effectiveness.  To me the slight modification to the leading edge is a lot cleaner to the airflow, but it is too bad it is more time consuming to get built and installed.