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Mooney Aerodynamics


Blue on Top

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47 minutes ago, Blue on Top said:

@PT20J and @cliffy  This is interesting.  I should think about this more, but off the top of my head the trailing edges should be as small/sharp as possible for minimum drag (at these speeds).  Thicker trailing edges make the surface more stable … at the cost of drag … similar to adding a T-strip.  Both will have a tendency to center the surface when the controls are let go (stick free).  The more centering, the more force would be required to move the surface.  Changing the TE to more pointed will cause the lateral-directional stability to not be as good.  IOW, the aileron will not return to neutral when let go.

Aft camber (of the wing but showing up as a cusp on the aileron) will aft load the airfoil.  An NLF airfoil is typically/already aft loaded.  This will not increase/decrease the aileron forces as the opposing aileron is helping it, and the ailerons act as a loop (yes, the system is push-pull tubes, but …).  Aft loading will cause the ailerons to "float" more, but in a Mooney that just means that all the aileron control system free-play is taken out in that direction.  So … when roll control is input is made, the down-going aileron will move first.  This is totally irrelevant as we typically only care about what is called "total aileron".  IOW (for roll control), a degree of UP travel equals a degree of DOWN travel; we add the two for calculations.  IOW, if the left aileron goes up 10 degrees and the right goes down 5 degrees, we use 15 degrees of aileron travel.

Hope this helps, but I'm guessing I have added confusion.

Blue on Top, Ron 

If you search the NASA Technical Reports Server for old NACA reports on beveled ailerons, you will find a lot of reports of wind tunnel and flight test results. Generally I believe the conclusion was that beveling reduces aileron effectiveness, decreases the section lift curve slope and reduces hinge moments. 

Here’s one example: https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19930093563.pdf

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I have no idea what Al M was thinking about with the undercambered ailerons on the early models aerodynamic wise BUt he must have had some thought to do it. 

I built lots of undercambered airfoil model airplanes looking for slow flight , high lift, low sink, for gliders with aspect ratios waaaay out there compared to real life airplanes. 

I'm sure we'll agree that 10 degrees down on one aileron doesn't mean 10 up on the other side on a Mooney due to linkage slop. 

Most Mooneys I see have quite a "lift" factor when in flight on the ailerons due to slop. Most that I have flown you can see the TE of each one way above the flap TE. You can go hold one in neutral position and pull the other one up 5 degrees or more on most Monneys. I rig them to account for this "lift" factor and have the TEs aligned IN FLIGHT with the flap TEs. Gotta make sure the flap TEs are set correct first.  

Don't know too much about break away force on control surfaces and what controls same. I have seem many airplanes with small bulb trailing edges or small half round devices parallel to the TE of control surfaces which from what I have learned are there to help stop TE wandering in separated airflow at the back edge of the surface, 

BoT- Just a short comment on Mooneys for you :-)  I was at a Nooney gathering years ago where they showed a picture (computer generated) of a Mooney with a smooth surface skin (like  a Cirrus) and I commented that if one had the surface co-ordinates all around it would be a simple matter to make a mold and fill it in with compostite formers and bulkheads.  All I got was a big smile. This was just beofre the 2 door model with the composite cabin shell. I guess I was prophetic!!!!  :-)

One more comment on drag- John Thorpe once commented on using a venturi to drive the gyros in the T-18 homebuilt ( a real well designed machine IMO) and said they lost 5-8 mph by using one.  Something that little has that much drag. I may find one and design a streamlined shell for it and use it to drive a stand by ADI as "if you're flyin' you got a gyro". No battery worries, no vac pump worries. 

Edited by cliffy
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1 hour ago, cliffy said:

1.  I have no idea what Al M was thinking about with the undercambered ailerons on the early models aerodynamic wise BUt he must have had some thought to do it.  

2. I'm sure we'll agree that 10 degrees down on one aileron doesn't mean 10 up on the other side on a Mooney due to linkage slop. 

3. Most Mooneys I see have quite a "lift" factor when in flight on the ailerons due to slop. Most that I have flown you can see the TE of each one way above the flap TE. You can go hold one in neutral position and pull the other one up 5 degrees or more on most Monneys. I rig them to account for this "lift" factor and have the TEs aligned IN FLIGHT with the flap TEs. Gotta make sure the flap TEs are set correct first.  

4. Don't know too much about break away force on control surfaces and what controls same. I have seem many airplanes with small bulb trailing edges or small half round devices parallel to the TE of control surfaces which from what I have learned are there to help stop TE wandering in separated airflow at the back edge of the surface, 

5. BoT- Just a short comment on Mooneys for you :-)  I was at a Nooney gathering years ago where they showed a picture (computer generated) of a Mooney with a smooth surface skin (like  a Cirrus) and I commented that if one had the surface co-ordinates all around it would be a simple matter to make a mold and fill it in with compostite formers and bulkheads.  All I got was a big smile. This was just beofre the 2 door model with the composite cabin shell. I guess I was prophetic!!!!  :-)

6. One more comment on drag- John Thorpe once commented on using a venturi to drive the gyros in the T-18 homebuilt ( a real well designed machine IMO) and said they lost 5-8 mph by using one.  Something that little has that much drag. I may find one and design a streamlined shell for it and use it to drive a stand by ADI as "if you're flyin' you got a gyro". No battery worries, no vac pump worries. 

@PT20J  Thanks!  I'll read the NASA report … tomorrow (when I am more coherent).

@cliffy 1. He used the NLF airfoil of his choice.  The under-cambered ailerons are a fallout.

2. Yes, that's why I said 10 UP and 5 down.  Mooney ailerons are VERY differential to reduce adverse yaw.  TCDS travels show this clearly.

3. Agree with you, but I don't know how much.  That seems high to me, but you would know more.  Does an UP aileron put the long, wing, aileron push-pull tube in compression?  That would explain the high amount of float.

4.  Small bulbs are for strength (aka Cessna).  Vertical dimension (and shape) will determine centering/control "stiffness"

5. Ummmmm … don't want to burst your bubble, but the composite shell is more expensive, more labor intensive and heavier.  As far as drag goes, well … it isn't less.  Sorry.  We can talk in person about why all is as it is.

6. You might be surprised on which little things cause drag (and which big ones don't :) ).  Low wings are inherently more draggy because of the wing fuselage interference drag and reducing fuselage width before the trailing edge of the wing .. without a really big fairing.

I really love all y'all's comments.  I learn so much from all of you.  Thanks! Ron

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4 hours ago, Blue on Top said:

Low wings are inherently more draggy because of the wing fuselage interference drag and reducing fuselage width before the trailing edge of the wing .. without a really big fairing.

Are you saying the M20-NG should be a high wing? ;-)  But joking aside, thank you all for a discussion that while going way over my head is at the same time extremely interesting to try and follow.

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1 hour ago, tmo said:

Are you saying the M20-NG should be a high wing? ;-)  But joking aside, thank you all for a discussion that while going way over my head is at the same time extremely interesting to try and follow.

@tmo  First and foremost, thank you.  Secondly, I think you're following along very well.  So … on that high wing Mooney (you've just started a good rumor :) ) ...

We will start thinking in 2D (2 dimensions) with a "typical" wing (an airfoil), the type all pilots are taught about.  As angle of attack is increased, airflow starts to separate at the trailing edge.  The point of separation moves forward as AOA increases further  At stall AOA, lift drops off some, and drag goes up significantly.  Now comes the part we need to think a little more about.  It's not hard, but we'll add the fuselage into the equation.

Looking from the top, the fuselage is shaped similarly to a symmetrical airfoil (it's not truly symmetrical, but we will say it is).  Now we simply put the fuselage down on top of the wing.  If the fuselage is getting smaller (suction) while over the top of the wing (suction side), airflow will want to separate earlier … causing more drag.  Both the wing (locally) and the side of the fuselage (locally) will separate, causing lots more drag.  A high wing doesn't have that issue because the fuselage is on the pressure side of the wing.

Now, before y'all run off and say, "Ron said Mooney airplanes should have high wings."  … if life were that easy … EVERYTHING in design is a tradeoff/compromise.  Where is the landing gear going to go now?  How do I get mechanical flaps to operate?  Etc.

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9 hours ago, Blue on Top said:

@PT20J  Thanks!  I'll read the NASA report … tomorrow (when I am more coherent).

@cliffy 1. He used the NLF airfoil of his choice.  The under-cambered ailerons are a fallout.

2. Yes, that's why I said 10 UP and 5 down.  Mooney ailerons are VERY differential to reduce adverse yaw.  TCDS travels show this clearly.

3. Agree with you, but I don't know how much.  That seems high to me, but you would know more.  Does an UP aileron put the long, wing, aileron push-pull tube in compression?  That would explain the high amount of float.

4.  Small bulbs are for strength (aka Cessna).  Vertical dimension (and shape) will determine centering/control "stiffness"

5. Ummmmm … don't want to burst your bubble, but the composite shell is more expensive, more labor intensive and heavier.  As far as drag goes, well … it isn't less.  Sorry.  We can talk in person about why all is as it is.

6. You might be surprised on which little things cause drag (and which big ones don't :) ).  Low wings are inherently more draggy because of the wing fuselage interference drag and reducing fuselage width before the trailing edge of the wing .. without a really big fairing.

I really love all y'all's comments.  I learn so much from all of you.  Thanks! Ron

2.  Agree that most if not all ailerons have differential throws for adverse yaw issues. My comment was more to the slop in most systems I see where the differential is somewhat lost due to wear. Measuring the throws in a static environment without air loads does not take into account real world positions of the surfaces flying.

There is some study available that shows no adverse yaw (in fact , yaw in the proper direction for the turn) in a pure flying wing plan form if the tips of the wing are drooped about 17 degrees. A couple of test models were flown to at least prove the theory.  Draggy tip rudders were not needed. Maybe Northrup didn't go far enough with his early wing design that tested wing tip droop before he abandoned the idea. He never went down that far. 

3. Yes 5 degrees of "lift" is not uncommon when a force is applied upward when the other aileron is clamped in place

4. Agreed 

5. No bubble to burst. My commentary (at the time)  wasn't so much advocating for a composite outer shell as it was on the observation of what appeared to be a study in wetted area definition (smooth vs formed riveted metal) because at that time much was being talked about on how Mooney could/should compete with Cirrus. 

6, Agreed. Wing/fuselage interface has always been a bugaboo for a/c design. Lockheed Vega used a high wing, the Spatan Executive used it by making it a low wing with big fairings. This evolution has been going on since the days of Lilienthal  Century fighters used a mid-wing placement before the days of the F-104 and the "coke bottle " design to reduce drag at this juncture. When the first "Pregnant Guppy" flew at KVNY for Aerospace  Lines  (modified KC-97 Boeing airframe) (I was there ) it was found by the test pilot (Clay Lacy ) that more work needed to be done on the wing root faring due to vibrations from turbulence in that area. With the HUGE top fuselage added to the original one   drag I'm sure was a big issue.  EVERYTHING is a compromise in aircraft design. EVERYTHING affects everything else when changes are made. Again I'm just a layman but with empirical experience after so many years of study. I, too, am learning a lot by this thread. 

 

 

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I find it fascinating to look at various designs and try to figure out what was in the mind of the designer when various design choices were made. And, Mooney's have a lot of interesting choices. The nemeses of control systems from a handling qualities standpoint are stick forces/gradients, friction and lost motion (slop, play, etc). High stick forces cause obvious issues. Stick force gradients affect perceived stability. Friction causes high breakout forces and poor centering (the control doesn't return to the original position when released) and any slop makes precision flying difficult.

The Mooney aileron system has a lot of rod ends and a little wear over the years leads to lost motion. (Keep your rod ends lubed with Triflow -- it forms a dry teflon film that doesn't attract wear-causing grime like oil-based lubricants).

The Mooney aileron design leads to fairly heavy aileron forces, especially before the beveled ailerons were incorporated. (Not much you can do about that-- it's part of the price you pay for the very effective wide-span flaps)

The push-pull tubes run through greased guide blocks that add friction. In some Mooneys, you can hear a "groan" within the wing during preflight when you move the ailerons full up or down. The sound is the tubes rubbing the guide blocks and it happens near the extreme range of motion due to a slight eccentric motion of the outboard bellcrank. (Keep the blocks lubed).

There is low pressure on the top relative to the bottom of the ailerons and this tends to make them want to float up in flight and put the control tubes in compression. The tubes are long and thin and will flex slightly in flight increasing the friction especially as the airspeed increases (remember, dynamic pressure increases with the square of TAS). Back in the early 1990's, Mooney cobbled together a M20-based entry for the JPATS competition (Beech finally won the contract). An engineer told me that at high speeds the flex was enough to bind the ailerons so that the stick would stay pretty much wherever you put it. (This isn't a problem in normal Mooney flight since you are not flying that fast or doing aerobatics at cruise speeds, but it does point out that all designs have limitations).

So, the push-pull tubes are great when everything is lubed, and new, and if you don't fly too fast. :)

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39 minutes ago, cliffy said:

2.  Agree that most if not all ailerons have differential throws for adverse yaw issues. My comment was more to the slop in most systems I see where the differential is somewhat lost due to wear. Measuring the throws in a static environment without air loads does not take into account real world positions of the surfaces flying.

There is some study available that shows no adverse yaw (in fact , yaw in the proper direction for the turn) in a pure flying wing plan form if the tips of the wing are drooped about 17 degrees. A couple of test models were flown to at least prove the theory.  Draggy tip rudders were not needed. Maybe Northrup didn't go far enough with his early wing design that tested wing tip droop before he abandoned the idea. He never went down that far. 

3. Yes 5 degrees of "lift" is not uncommon when a force is applied upward when the other aileron is clamped in place

4. Agreed 

5. No bubble to burst. My commentary (at the time)  wasn't so much advocating for a composite outer shell as it was on the observation of what appeared to be a study in wetted area definition (smooth vs formed riveted metal) because at that time much was being talked about on how Mooney could/should compete with Cirrus. 

6, Agreed. Wing/fuselage interface has always been a bugaboo for a/c design. Lockheed Vega used a high wing, the Spatan Executive used it by making it a low wing with big fairings. This evolution has been going on since the days of Lilienthal  Century fighters used a mid-wing placement before the days of the F-104 and the "coke bottle " design to reduce drag at this juncture. When the first "Pregnant Guppy" flew at KVNY for Aerospace  Lines  (modified KC-97 Boeing airframe) (I was there ) it was found by the test pilot (Clay Lacy ) that more work needed to be done on the wing root faring due to vibrations from turbulence in that area. With the HUGE top fuselage added to the original one   drag I'm sure was a big issue.  EVERYTHING is a compromise in aircraft design. EVERYTHING affects everything else when changes are made. Again I'm just a layman but with empirical experience after so many years of study. I, too, am learning a lot by this thread. 

@cliffy  2. That is interesting; I'm learning.  As one moves up the totem pole, yaw dampers are included and spoilers for roll control … and differential ailerons go away.  Part 25 airplanes must have 2 systems to handle a jammed surface.  Plus at higher speeds, ailerons become ineffective or with a lot of sweep, twist the wing the wrong way.  On the other hand, spoilers aren't real effective at low deflections.

3.  Wow!  I am amazed, but now I know.

5. Depends on boundary layer thickness at that location.  If the rivet is well within the boundary layer, a protruding head won't matter … hence the flush rivets on the forward section of the wing and protruding on the aft section. 

6.  BAM!!! Out of the park homerun!

7 (PS) I know all y'all are PhD Aerodynamicists just playin' with me.

8 (PS2) "7" above can't be correct because I normally start the conversations off with them as, "I know all of you have PhDs in Aerodynamics, but here is how it works in the real world."  :) 

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4 minutes ago, PT20J said:

I find it fascinating to look at various designs and try to figure out what was in the mind of the designer when various design choices were made. And, Mooney's have a lot of interesting choices.  -Skip

@PT20J  Great analysis, Skip.  And for the line I quoted, not only :lol::lol::lol::DB), but sometimes we're not thinking.

The only item(s) I'll add is that is that aileron forces can be changed with leading edge shape, hinge line location (look at a Cirrus) and gap sealing (or gap seal removal in the Mooney case).  Personally, I love the Mooney designed-in gap seals, but they do make the surfaces more effective and increase the forces. 

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49 minutes ago, Blue on Top said:

@PT20J  Great analysis, Skip.  And for the line I quoted, not only :lol::lol::lol::DB), but sometimes we're not thinking.

The only item(s) I'll add is that is that aileron forces can be changed with leading edge shape, hinge line location (look at a Cirrus) and gap sealing (or gap seal removal in the Mooney case).  Personally, I love the Mooney designed-in gap seals, but they do make the surfaces more effective and increase the forces. 

Hinge line position, leading edge shape, balance weights, span-chord ratio, gap seals, trailing edge thickness/shape. Lots of variables. Makes my head hurt. I wonder how you guys ever arrive at a design.  And of course, sometimes things don't work out during flight test and fixes get added. The engineers probably would like to go back and correct the design with the new knowledge, but the accountants will declare "good enough." 

Here's an example I ran across a while back: https://aviation.stackexchange.com/questions/32960/what-is-the-purpose-of-this-aileron-trailing-edge-strip

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7 hours ago, tmo said:

Are you saying the M20-NG should be a high wing?

Not when the M20-NG is flown upside down (usually a joke about positive/negative camber theory of lift but let's make it about high/low wings theory of drag :lol:)

Edited by Ibra
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Aileron authority has many avenues,  on some Boeings  we have 2 ailerons per side and roll spoilers. The outboard ailerons are physically blocked out of movement at high speeds and only the relatively small inboard ones are used for roll control. 

All of the spoiler boards may or may not actuate at a particular flight regime. They all usually come up on landing for lift dump 

It was said that the 727 wing basically disassembled itself upon touch down  :-)

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3 hours ago, PT20J said:

Hinge line position, leading edge shape, balance weights, span-chord ratio, gap seals, trailing edge thickness/shape. Lots of variables. Makes my head hurt. I wonder how you guys ever arrive at a design.  And of course, sometimes things don't work out during flight test and fixes get added. The engineers probably would like to go back and correct the design with the new knowledge, but the accountants will declare "good enough." 

Here's an example I ran across a while back: https://aviation.stackexchange.com/questions/32960/what-is-the-purpose-of-this-aileron-trailing-edge-strip

Skip

@PT20J Skip:  … and if there is fixed surface on neither, either or both ends of the aileron  … and if there is a winglet (ask Honda)

Your example is great … and real..

There is a Citation that the roll characteristics can be changed from flying like a truck (airliner) to flying like an aerobatic airplane by simply changing the aileron leading edge.  We compromised in between those two :) 

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11 hours ago, tmo said:

Are you saying the M20-NG should be a high wing? ;-)  But joking aside, thank you all for a discussion that while going way over my head is at the same time extremely interesting to try and follow.

Making a small cross-section fuselage with a high wing is possible only if the pilot's head protrudes through the upper wing surface into a blister (greenhouse).   Data suggest that the interference drag created by the low wing configuration is significantly less than the additional drag of a larger x-section fuse due to pilot visibility requirements (M vs C) with equivalent O360.  :)

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12 minutes ago, 0TreeLemur said:

Making a small cross-section fuselage with a high wing is possible only if the pilot's head protrudes through the upper wing surface into a blister (greenhouse).   Data suggest that the interference drag created by the low wing configuration is significantly less than the additional drag of a larger x-section fuse due to pilot visibility requirements (M vs C) with equivalent O360.  :)

@0TreeLemur :lol::D:D  I am not bias (it would hurt my company).  Compare all the numbers.  The C has a bigger wing and carries a LOT more payload.  How fast is your M when you have to make 2 trips to bring luggage?

Total fuselage cross-section area is not a huge driver of total drag at these speeds (compressibility is not part of the equations this slow). Al and Dwane didn't have the CFD that we have today.  It was Lopresti (and others) that made the M20 so much faster (other than Al's wood wing of course :) )

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2 hours ago, Blue on Top said:

@0TreeLemur :lol::D:D  I am not bias (it would hurt my company).  Compare all the numbers.  The C has a bigger wing and carries a LOT more payload.  How fast is your M when you have to make 2 trips to bring luggage?

Total fuselage cross-section area is not a huge driver of total drag at these speeds (compressibility is not part of the equations this slow). Al and Dwane didn't have the CFD that we have today.  It was Lopresti (and others) that made the M20 so much faster (other than Al's wood wing of course :) )

And remember, Roy was just going after the low hanging fruit, drag-wise. He was part engineer and part marketeer. His goal was never to get the most speed possible -- it was to get >200 mph on 200 hp. A source of irritation at Mooney was that Lopresti got the credit for the speed improvements when most or all had been designed (but not implemented) before he came on board. What Lopresti did was to design a well-instrumented flight test program to figure out the most cost effective way to meet his marketing goal, and then promote it (kind of like Iacocca and Chrysler).

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3 hours ago, Blue on Top said:

@0TreeLemur :lol::D:D  I am not bias (it would hurt my company).  Compare all the numbers.  The C has a bigger wing and carries a LOT more payload.  How fast is your M when you have to make 2 trips to bring luggage?

Total fuselage cross-section area is not a huge driver of total drag at these speeds (compressibility is not part of the equations this slow). Al and Dwane didn't have the CFD that we have today.  It was Lopresti (and others) that made the M20 so much faster (other than Al's wood wing of course :) )

The C wing is 174 ft2 for a 172 or 177RG, and yes, a different airfoil.   The 172 is fixed gear with struts and fixed pitch, the SP model has the IO360 rated at180 HP.  The 177 is retractable with no struts, and constant speed prop. but 200 HP.   The C177 has a bit more empty weight, and about 100 lb more useful load than the the M20C.  The POH cruise speed of the C177 at 7500 and 70% pwr is listed as 144 kts at 10 GPH.  Our '67 M20C at 7500' does 143 kts at 10 GPH on 70% of 180 HP.   The C177 with its 100 lb more UL isn't going to make me make another trip, I'm going to leave baggage at home. B)

The 172SP at 124 kts and with fixed legs and struts hanging out isn't a fair fight, even though it has the same amount of aluminum in it.  The data comparison in the paragraph above indicates to me that the drag of my M20C at the same airspeed requires 14 fewer horses to move essentially the same load through the air as a C177.  That equates to less drag?  Some of that reduced drag is airfoil, and some is cross-section?

Which C model would you compare against a M20C?   What model of C would be most similar head-to-head.  ?   Note, our M20C does have the lower cowl closure mod but not the 201 windshield.

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On 2/27/2020 at 7:36 PM, 0TreeLemur said:

NGme make another trip, I'm going to leave baggage at home. B)

The 172SP at 124 kts and with fixed legs and struts hanging out isn't a fair fight, even though it has the same amount of aluminum in it.  The data comparison in the paragraph above indicates to me that the drag of my M20C at the same airspeed requires 14 fewer horses to move essentially the same load through the air as a C177.  That equates to less drag?  Some of that reduced drag is airfoil, and some is cross-section?

Which C model would you compare against a M20C?   What model of C would be most similar head-to-head.  ?   Note, our M20C does have the lower cowl closure mod but not the 201 windshield.

@0TreeLemur  Sorry, I know all the C and all the M.  I went new with both.  Both with 300 Hp.

Yes, the strut is draggy, but the structure is much lighter.  The C210 is heavier yet as unlike the M20 with a one-piece wing, the C210 (even strutless) has a break at side of body … the wrong place to put a joint.  The Cessna NGP didn't have a break there … and was significantly wider.

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Had fun today: got to fly a friend’s 1963 M20C. It’s been a lot if years since I flew a C with manual gear and hydraulic flaps and the first time I remember using the Johnson bar from the right seat. That took a few tries to get right. Had it worked out by the fourth takeoff. 

The ailerons aren’t bevelled on this one and they do feel stiffer at small deflections than my J, but not a lot different at higher deflections. This is in line with what I’ve read in the old NACA reports about the effect of bevelling. 

I confirmed that the elevator is streamlined with the stabilizer in cruise unlike my J which trims elevator slightly trailing edge down. Others have reported that long bodies trim slightly trailing edge up. 

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38 minutes ago, cliffy said:

And now the early 210s (strutless) have a new $1850 AD to do immediately looking for corrosion in the wing spar, seems an Aussie 210 shed a wing from a fatigue crack starting at a corrosion pit in the spar. 

@cliffy  I saw that.  Ironically, I know a company that has some cool wing technology.  One of my suggestions to them was to look at re-winging airplanes.  They laughed and said that was a dumb idea.  They could have been ready for this.  Not now.

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  • 2 weeks later...

BEVELED AILERONS (again):

Mooney introduced beveled ailerons in the 1960s and they may have been added to reduce hinge moments (stick forces) for the PC servos. Thickening a control surface and beveling the trailing edge is a method for improving aerodynamic balance and reducing stick forces used ever since the later P-51s.  For some time, I've been trying to understand exactly how they do this. I thought I understood it a while back, but was never completely satisfied. I finally found a good explanation in Airplane Stability and Control  by Abzug and Larrabee. The idea goes like this: Suppose an aileron is deflected down (to raise a wing). The protrusion into the airstream thins the boundary layer on the bottom and thickens the boundary layer on the top. The thinner boundary layer tends to follow the surface contour better, so when the air flowing along the bottom gets to the trailing edge it wants to follow the bevel and deflect upward. Curving the airflow requires a pressure change -- in this case a lowering pressure at the bottom of the trailing edge. The thicker boundary layer along the top surface doesn't follow the bevel well so there is a differential pressure effect that tends to pull the aileron down which is in the desired direction.

NACA report 927 (referenced by Abzug and Larrabee) quantifies the effect:

1260838075_Beveledailerons_20200310_0001.thumb.jpg.b1b8bc08ee6cc5010379eaedbeb8d008.jpg

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On 2/28/2020 at 10:13 PM, PT20J said:

Had fun today: got to fly a friend’s 1963 M20C. It’s been a lot if years since I flew a C with manual gear and hydraulic flaps and the first time I remember using the Johnson bar from the right seat. That took a few tries to get right. Had it worked out by the fourth takeoff. 

The ailerons aren’t bevelled on this one and they do feel stiffer at small deflections than my J, but not a lot different at higher deflections. This is in line with what I’ve read in the old NACA reports about the effect of bevelling. 

I confirmed that the elevator is streamlined with the stabilizer in cruise unlike my J which trims elevator slightly trailing edge down. Others have reported that long bodies trim slightly trailing edge up. 

Skip

Skip I"m curious- do the ailerons on the J extend all the way to the wingtip as they do on the C?  The interaction between the aileron end and the tip vortex add to heaviness in roll.   The later models of M20 put 10" of wing outside the aileron to detach it from the tip vortex.  If the J has that then that will be a factor too.

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