Stalls and Leading edge question

[Petehdgs]

2 hours ago, ArtVandelay said:

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.

I hear what you are saying but if you look at page 19, the minimum drag of the laminar flow bucket is virtually identical in all 4 airfoils presented.  The laminar bucket actually expands as the airfoil is modified.  

[Niko182]

@ilovecornfields @LANCECASPER @aviatoreb are all people that have it. Ilovecornfields installed it on an ovation and said he said no change in cruise.

[Petehdgs]

22 hours ago, takair said:

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.

Yes the stall strips are installed and I found a really interesting article about how the factory tests and installs them during post production testing.  The purpose of the stall strips are to make sure the airplane stalls straight ahead without rolling more than 15 degrees.  They got that dead on on my bird!  But there is no perception of shudder or buffering at all.  

I also watched a video of a Mooney pilot who suggests landing in the flare by pulling back until the horn just blows and keeping the yoke in that position until touchdown.  That will be leaving some low speed performance on the table but I think it is a good starting point for training.  

I am coming down final 1 tick above best angle of climb AOA and that is a sweet spot for good semi-short landings, and managing obstacle clearance.  I can easily slip down and have a really good feel of the aircraft  especially if I reduce flaps by about 1/3 or so at treetop level.  It is much easier to make a good smooth landing that way, but again that means leaving some low speed performance on the table.  I have not done much experimentation with adding power at the bottom of the flair.  I read some good suggestions about that and that is another area I am looking at.

Hope that answers your questions 

 

 

[Larry]

Petehdgs-

Have you researched how much time and cash it will take for the DER and the STC needed to install it on one of our planes? 

Larry

 

 

[takair]

1 hour ago, Petehdgs said:

Yes the stall strips are installed and I found a really interesting article about how the factory tests and installs them during post production testing.  The purpose of the stall strips are to make sure the airplane stalls straight ahead without rolling more than 15 degrees.  They got that dead on on my bird!  But there is no perception of shudder or buffering at all.  

I also watched a video of a Mooney pilot who suggests landing in the flare by pulling back until the horn just blows and keeping the yoke in that position until touchdown.  That will be leaving some low speed performance on the table but I think it is a good starting point for training.  

I am coming down final 1 tick above best angle of climb AOA and that is a sweet spot for good semi-short landings, and managing obstacle clearance.  I can easily slip down and have a really good feel of the aircraft  especially if I reduce flaps by about 1/3 or so at treetop level.  It is much easier to make a good smooth landing that way, but again that means leaving some low speed performance on the table.  I have not done much experimentation with adding power at the bottom of the flair.  I read some good suggestions about that and that is another area I am looking at.

Hope that answers your questions 

 

 

Hi Pete

My experience with my own plane seems to be somewhat different than yours.  Based on other responses I think that others are not experiencing the same thing as you.  I always experience a shudder prior to stall, high speed or low....primary or secondary.  Reading an article by Bob Kremer on stall testing at the factory, he too mentions the shudder prior to stall.  This shudder is likely a secondary benefit of the stall strips when they start to upset the laminar flow.  That said, the shudder is under the stall horn and I never experience that on landing....nor would I want to since it is cutting the margin too close....within a couple knots of stall break.

I came across another one of your threads on another site and you had some additional info there.  You mentioned you are not riding the horn on final, just maybe at level off.  You described the problem as a sudden stall and hard drop in.  I wonder if you might not really be experiencing a stall, but a reduction of lift when getting behind the lift/power curve.  I’ve certainly done this....dropped in hard on the main gear from a foot or two, then a pitch forward with the risk of porpoising.  I do not consider this stalled, even if the horn was blaring.  The stall tends to drop the nose simultaneously where as this is really a drastic increase in sink rate.  With the Mooney gear, this feels like orders of magnitude worse than a Cessna.  To prevent this drop in, I might use a touch of power into the flare, even on a short field landing...sometimes even until touchdown.  This allows you to use power to manage the lift curve.  The laminar flow wing does have a more drastic drop off in lift.....but I feel this is different than the stall that you are looking to correct.  I would worry you might invest a lot of money only to find the problem is not actually solved.  Perhaps try using some power through the flare and work from there....just to see if it is stall or sink rate.  I know you aren’t looking for flying advice, but something just sounds different about your description than typical experience.  
 

One other thing I am curious about, do you have flap gap seals?  I do not, but have been wondering if the seals result in any difference in low speed handling.  Interesting conversation.  Would be interesting to compare notes in air in each other’s planes.

[Hank]

It's a bit of an old video now, but this is landing my C on the obstructed 3000' field where I used to live. Mynwife njst held the camera up by the windshield and didn't answer when I asked what she was doing, she said "don't worry about it, jjst land the plane."

 

You'll notice when power is added to level off at 150agl to clear the trees, then pulled to idle to reach the runway. The stall horn is also audible just before touchdown.

My C is the same airframe as your E. I find turning final with Takeoff flaps, and adjusting them as needed to reach the runway [per my Owners Manual] to work very well. 

[PT20J]

The Mooney mission is economical high-speed cruise. It's not designed to be a STOL aircraft. It's not clear to me that the wing change would solve any real-world problem. Landing distance is related to stall speed. Mooney stall speed is similar to other airplanes in it's class, and a 2000' strip should not be a problem. Unless I misunderstand, the proposed wing change seems aimed at producing a less abrupt stall break rather than a reduction in stall speed. That won't help you land shorter unless you reduce approach speed to say 1.1 Vso feeling that you have more margin because the stall is "softer." But, a stall close to the ground -- regardless of airfoil shape -- will still kill you if there is not enough altitude to recover from the high sink rate produced.

There is no doubt that modern CFD design techniques can produce superior airfoils. However, retrofitting already built aircraft is not a minor engineering undertaking, so there has to be a significant benefit. The vortex generators are inexpensive and proven and would probably be a much simpler way to go.

As far as the laminar drag bucket -- I seriously doubt you will find that on a Mooney. The NACA wind tunnel data is for 2D airfoils that were polished very smooth. A 3D wing has manufacturing imperfections in the shape that probably prevent any significant laminar flow. 

As to whether or not vortex generators cause extra drag at cruise, here's a paper on that:

Vgs_cruise_wide_screen.pdf

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[carusoam]

Around here there are a few things that cause some drag... but get accepted for their benefits...

And then you see how they minimize the drag they experience by selecting the altitudes they fly at...

Some people like their FIKI systems... the anti ice hardware is resident on the leading edges... the imperfections of their shape compared to the wings native leading edge cause additional drag...

VGs are engineering art... highly functional and easy to install... in cruise flight in the lower FLs the additional drag is hard to measure... the winds at altitude keeps people from bothering to measure it...

So yes there is some drag added... but not enough to not get them if lowering stall speed is what you want...

We are going to be hard pressed to find any addition to the wings that won’t cause drag in cruise, while it lowers the stall speed...

Going faster on one end... makes the stall speed faster at the other end... find the Lancairs... 

Where we could really see improvements... complex flap designs and trailing link landing gear... we could also increase MGTW... for the longer runways...

To get these nifty add-ons is going to require Mooney to build it... which will be about 700 AMUs... at current costs...

So... how do you feel about some decent modern flaps for your bird?

Keep in mind  I’m trying to get Mooney to build an Ovation with a power plant that has beta.... aka reverse/braking... would that work for you?

Best regards,

-a-

 

[Yetti]

It's not as fun of a discussion but you could just update your skills.   One thing I have found is that flying around at 21 21 (cessna 172 speed) top of the white arc makes my feel of the slow much better.   45 degree bank turns and 59 degree bank turns.   I was making the 2000 foot turn off during my mooney transition training.  It was annoying the instructor because he wanted me on glideslope and on the stripes.   Full flaps the Mooney really will helicopter down you just have to be comfortable with the feel as it is much different that mooney zoom.

[Hank]

Fs do much better landing with Full Flaps.

Short bodies land very well with Takeoff Flaps or anywhere in between . . . . I usually land rjght about the Takeoff mark, with trim right around the Takeoff mark, too.

[N201MKTurbo]

Back in 86, I was 29 yo. Had owned a Mooney for 2 years and was flying over 500 hours a year doing service calls for Raytheon Data Systems. One day, the wind was blowing real hard and I had a DME, so I decided to see how low a number I could get on the DME. The holy grail would be to get a backwards number on it. This was out of 01V the long gone Aurora (Columbine) Airport outside of Denver. I went up to 9500 feet and flew directly into the wind pointed towards the DEN VOR. I slowed as slow as I could get, if I recall I could only get the DME down to 7 KTS. Anyway, I stalled the plane and instead of aggressively recovering it, I gently eased the power up until I got control back. The plane was perfectly controllable, except I was descending at 4000 FPM. I did 20 degree turns in both directions with no problem. I didn’t have much time because of the ground and the descent rate. I increased the power to arrest the descent, but the airspeed never was above 1/2 a needle above stall. Even after leveling out, the plane was amazingly controllable. I flew around like this for a few minuets and then decided to try a landing. In retrospect, this was amazingly stupid, but I flew a complete pattern and landed a knot or two above stall. I could have landed on a 100 foot runway! Remember there was a 50 KTS wind going on.

I have never tried this again. I want to the library and looked it up. NASA wrote a bit about this. They called it a Deep Stall. They actually built a modified Switzer glider to research it. If they only had a Mooney.

[Petehdgs]

I missed that Riblett put a performance curve for the GA cuff on the next page.  I think I got it confused with the evolution of GA airfoils, which looks similar.  See attached. 

1.  There is an improvement in climb performance and extension of the laminar bucket. 

2.  The stall is softened considerably and extended. 

3.  There is indeed a drag penalty at high speed cruise of about 2% drag, or about 2 at 200. 

4. There is no drag penalty at economy cruise. 

5.  The estimated weight addition is only 6 lbs based on .050" skin over 2lb density foam.  

I still think this bears further investigation, even if I am the only one. 

Mooney 64 wing cuff performance .pdf

[carusoam]

Pete,

Any idea if there a pics of this device mounted on a wing somewhere?

Mounted on a Mooney wing would be extra credit!

 

There are a few devices that have gained popularity around here...

Early discussions start slowly and painfully...

 

Some MSers are early adopters on things...

Some are waiting to not be first...

Some have to answer to a higher power to get funding...

Some know this technical stuff like an aero-engineer...

Others are really bright experts in their field, but like there Mooney the way it left the factory...

 

And in some cases... the Mooney factory buys the rights and includes the item in new production...

 

So...

If it makes sense to one MSer... it probably makes sense to a lot more...

MSers with forever-planes are often interested in adding to their aviation tool box...

 

Keep digging up the research, and posting it...

PP thoughts only, not an aero engineer...

Best regards,

-a-

[Blue on Top]

On 12/6/2020 at 6:13 PM, takair said:

Would be curious to get @Blue on Top thoughts?

OMG!  Thanks,@takair, for the ping.

Of course I have thoughts  .  For those on this thread that haven't read my 7 articles in "The Mooney Flyer", you need to.  They only touch the tip of the iceberg on these topics, but I'm here to further expand on any of them.  I'll learn from you, too.

1) Laminar flow is for wind tunnels and CFD.  There is very little of it in the real world.  Sailplanes are a good exception, but they scrape bugs off the leading edge that got there during the takeoff and tow to 1-2K feet.  Laminar flow has little to do with stall speeds except possibly increasing stall speeds.  Ask Dick Rutan about that.  

2) @PetehdgsPlease do not confuse C_l with C_L.  Section lift coefficient (C_l) has little to nothing to do with wing lift coefficient (C_L) and the associated stall characteristics.  Most certificated airplanes have 2D C_l versus alpha (aoa) curves that show an abrupt stall break ... including Mooney ... and Cessna aircraft, but that is not relevant for a 3D wing design.  Planform, twist, etc. are used to control stall progression.  Your mention of an abrupt stall break (nose down pitching moment) is good, a goal of designers.  The other (like you mentioned) is that the wings have to be kept +/- 15 degrees in roll.  The last requirement can't be accomplished analytically because there are so many other factors that influence it (inertia being the largest item).

3) VGs add drag.  Those that say that they don't don't have instrumentation accurate enough to measure it.

4) Yes, VGs can lower stall speeds (I have not personally tested an M20 ... except for tufting and airplane ... which are little VGs).  Certification testing alone (if done with an FAA ACO that actually makes the applicant meet the regulations) will cost more than one can ever think about making on selling them ... and VGs are really, really inexpensive.

5) The Mooney TKS installation is a scab on over the base airfoil.  It modifies the airfoil significantly.  Airfoil designers look at 0.010" as significant; TKS is closer to 0.250".

6) Do I personally think that a modified airfoil (drooped leading edge, larger leading edge radius, etc.) would be a good idea?  If your sole purpose is to lower stall speed.  Yes.  Plan on losing top end speed.  Plan on a very, very expensive certification program ... if done properly, probably including a spin program.  Is that $3M recoverable in sales? 

7) Flying below 1.3 on approach will shorten the landing distance (both in air and ground roll), but it is relying on your engine to continue running and will make go-arounds significantly more difficult.  BTW, that is the scenario that is the #1 fatal accident cause for the last several decades.

8) Most certificated GA airplanes do not stall at forward CGs.  They will develop a significant sink rate, though.

Okay, way more than my 2 cents worth.  But I hope we all learn a little from this thread.  Knowledgeable and proficient pilots are typically safer pilots.

Blue on Top, Ron

PS. Fire away.

[BlueDun]

14 minutes ago, Blue on Top said:

7) Flying below 1.3 on approach will shorten the landing distance (both in air and ground roll), but it is relying on your engine to continue running and will make go-arounds significantly more difficult.  BTW, that is the scenario that is the #1 fatal accident cause for the last several decades.

Could you expand on the mechanics of this point? The MAPA PPP has an emphasis on go-arounds which is good. How does the below 1.3 make go-arounds "significantly" more difficult? What happens? Is it due to being behind the power curve or greater pitch up due to trim for that speed or both?

[Blue on Top]

15 minutes ago, BlueDun said:

Could you expand on the mechanics of this point? The MAPA PPP has an emphasis on go-arounds which is good. How does the below 1.3 make go-arounds "significantly" more difficult? What happens? Is it due to being behind the power curve or greater pitch up due to trim for that speed or both?

@BlueDunBoth ... and more.  

I am happy to know that MAPA PPP is concentrating on this maneuver.  The slower the airplane is traveling, the higher the thrust will be when full power is added for the go-around (note: I am not sure how all the POHs over the decades say to preform a go-around).  With the higher thrust comes higher torque, higher P-factor and higher out of trim forces ... especially if the airplane was trimmed to the lower airspeeds.  If all of those items are planned for in advance, all works out very well and easily.  If not ...

Hope this helps.

[midlifeflyer]

1 minute ago, Blue on Top said:

@BlueDunBoth ... and more.  

I am happy to know that MAPA PPP is concentrating on this maneuver.  The slower the airplane is traveling, the higher the thrust will be when full power is added for the go-around (note: I am not sure how all the POHs over the decades say to preform a go-around).  With the higher thrust comes higher torque, higher P-factor and higher out of trim forces ... especially if the airplane was trimmed to the lower airspeeds.  If all of those items are planned for in advance, all works out very well and easily.  If not ...

Hope this helps.

I agree. In addition, a sudden increase in power results in a pitch up which can, if not anticipated, result in a "temporary" increase in AoA.

[BlueDun]

Yes, @Blue on Top. Pretty much confirmed my thoughts and then some. I was impressed by MAPA's focus, since other aspects of flight safety usually receive more training/media attention, despite the stats on go-arounds. Thanks.

[Blue on Top]

The 3 main areas we are trying to attack are: takeoff, go-around and moose turns (low altitude maneuvering/showing off).  These areas are far and away where the vast majority (more than 75%) of fatal accidents occur.  Base to final turns account for roughly only 5% of loss of control fatalities.

Although I am a fan of spin training, it will not help at pattern altitudes and below.  It will help after demonstrating/practicing the first one, when the pilot realizes that although the nose is very low (60-70 degrees nose down), they still need to push to lower the angle of attack.  Our research is showing that inadvertent stalls in the pattern (which have a large startle factor) are followed by full aft elevator control all the way to the ground, spin, spiral or straight ahead.

We need to get to the pilot BEFORE the departure.

[201Steve]

2 hours ago, Blue on Top said:

Our research is showing that inadvertent stalls in the pattern (which have a large startle factor) are followed by full aft elevator control all the way to the ground, spin, spiral or straight ahead.

That’s what Dan Gryder talks about, specifically on takeoff. It *sounds* ridiculous that so many people would pull rather than push in a low altitude stall, but, at least according to him, the predominant reaction is pull. 

[PT20J]

I used to climb at Vx and then Vy thinking that quickly gaining altitude on takeoff was the safest thing to do. Then I got a job flying seaplanes in Ketchikan and the chief pilot emphasized staying in ground effect and building up speed. He pointed out how quickly the speed would bleed off if the engine quit right after takeoff with the nose high. His favorite saying was, "Always remember the speed of life." I was completely cured of slow climb outs after reading John Deakin's  analysis. https://www.advancedpilot.com/articles.php?action=article&articleid=1842

Skip

 

 

[MikeOH]

11 minutes ago, 201Steve said:

That’s what Dan Gryder talks about, specifically on takeoff. It *sounds* ridiculous that so many people would pull rather than push in a low altitude stall, but, at least according to him, the predominant reaction is pull. 

Thinking this reaction sounds ridiculous is, I think, EXACTLY the insidious reasoning that is responsible for why it IS the predominant reaction!  Low altitude, unexpected stall, ground rushing up,....

[201Steve]

45 minutes ago, MikeOH said:

Thinking this reaction sounds ridiculous is, I think, EXACTLY the insidious reasoning that is responsible for why it IS the predominant reaction!  Low altitude, unexpected stall, ground rushing up,....

Well, yeah. That’s the point I’m making as well

[carusoam]

1) Slow, near stall, with either Vx or Vy.

2) Four seconds to realize the engine out and next steps, not the usual two we usually use or discuss...

3) keep flying because stalling around... won’t work.

4) We are storing the same amount of energy whether we are increasing speed or altitude...

5) sure there is more loss due to friction at high speeds, but how often is frictional loss mentioned in the traffic pattern?  Mostly when changing configurations...

6) Seems like safety is the biggest focus...

• Do not stall
• Landing in front of trees is better...
• Landing in the tree tops makes the list of better options...
• A strong push on the yoke, to get light in the seat will assure you keep flying for another moment...
• Efficient gliding occurs near Vy...
• accidentally exceeding Vy is not much of a penalty...
• accidentally not exceeding stall speed has a huge penalty...
• Landing straight ahead... the stall speed is easy to avoid...
• Maneuvering... the stall speed increases with bank... eyes are required to be on a couple of instruments to make this work... or on the AOAi if you have one... and outside too...
• Steeper banks, are best with the nose lowered to reduce wing loading... got a g meter for that?
• We can always convert speed back into altitude once the maneuvering is done...

7) The reaction you get may be hard to notice... you probably haven’t had the stall horn sound in the traffic pattern...?

Subconscious thinking does some good things for us... keeps us flying while conversing with ATC and friends... 

It can also give you insight to how your subconscious thinking skips a few things...

Trimmed for level slow flight in the traffic pattern... requires no back pressure on the yoke to maintain the descent when the power is reduced...

While scanning for traffic and executing the turns... watch your arm tense up slowly trying to level things out... if you don’t have much feeling in your arms and fingers it can be more of a challenge to sense...

Now, if you have ever had the stall warning go off in the traffic pattern... loosen up! Your subconscious thoughts are trying to kill you... 

PP thoughts only, not a CFI...

-a-

[Blue on Top]

1 hour ago, PT20J said:

https://www.advancedpilot.com/articles.php?action=article&articleid=1842

I would NOT recommend this procedure, but I am also the idiot (I forget the word he used) that makes the AFM/POHs that are there to guaranty (or state the way we got those performance numbers).  But, I also don't agree with Dr. Rogers all the time either (gasp!).

@PT20JThere are sooooooo many factors that determine V_R and the "best" way to climb out.  V_X is the number to fly to clear an obstacle in your path (at the exact end of the runway surface.   V_Y is the number to fly to get to altitude in the quickest amount of time.  The engine will remain below redline temperatures during a V_X climb to maximum altitude; it's required by regulation.  In Alaska, airplanes are allowed to fly 15% over gross weight, which is not allowed in the Lower 48.  There are so many places to land in Alaska, which changes the equations a lot.

Funny side note.  When the Citation X was only a new prototype, we brought in a private T-38 for chase.  We quickly learned that the climb schedules were significantly different (climb rates are actually close).  The problem was that at Citation X climb speeds, the T-38 had to fly S-curves behind it.  Then we got the brilliant idea (sarcasm is gushing out of me) to fly the formation climb at T-38 speeds.  We BARELY cleared the Wal-Mart a mile off the end of the runway.  I would much rather be 2,000 feet above the runway at V2 than 300 knots and 30' above Wal-Mart.  But then, we both had two engines  

As for what to do after an engine failure on takeoff (or anywhere for that matter), plan the flight; fly the plan.  Airplane or sailplane, every airport, all environmental conditions, my capabilities, etc., I plan my decision altitudes as to where I am going to put the airplane/sailplane if X happens when ... before I push the throttle up or give the take up slack signal.

Bottom Line: and as @carusoam stated, DON'T STALL.  Odds of survivability go up significantly.