Mooney Aerodynamic Curves (Nerd Alert)

[KSMooniac]

If you plotted the centerline of the wing, you would see it sweep forward. Optical illusion with the perpendicular leading edge! More obvious with the vertical tail, which is also swept forward. (These are aero definitions...the general non-engineer might argue differently)

Sent from my LG-US996 using Tapatalk

[Chuyg]

55 minutes ago, PT20J said:

Actually,  stall is the point where C_L begins to decrease with increasing alpha. If C_L actually went to zero, the plane would be in free fall.

 

This comment assumes the wing is the same shape throughout its length. Yes, a stall occurs when alpha reaches a critical angle, which is when CL begins to decrease, but the wings do not go from not stalled to stalled in a moment. Flow separation in most GA aircraft, Mooneys included, starts at the root of the wing. Additionally, we know CL will never be zero, as long as a fuselage exists or there is some flow across a wing below 90 degrees AoA.

 

Also since you insist on being pedantic... Free fall doesn't mean what you think it does. You would have a free fall if you had no engine producing trust, wings at a zero-lift AoA, somehow a fuselage/tail that didn't produce any lift when the wings are at zero-lift AoA, and no wind, which Im sure, you know, is not exactly possible.

 

[carusoam]

Welcome aboard, Chuyg.

I was so focused on the tech details in this thread, I missed the new guy come in! 

When you get a chance... put some data in your avatar.  The more the better.

Best regards,

-a-

[jaylw314]

1 hour ago, carusoam said:

PT,

which part of the wing is forward swept?

I get the feeling I am going to learn something new tonight!  

Going on old fuzzy memory, the leading edges are 90° to the cabin... but I didn’t measure them to see if there is some forward sweep there...

The part of the wing I stand on getting in the plane is really wide compared to the fancy wing tips... There is no obvious change to the taper along the way...

Private Pilot asking a question, trying to learn something new about Mooney wings...

Best regards,

-a-

The leading edge is perpendicular to the cabin, but the trailing edge sweeps forward, so the span-wise chord line (or whatever you call it) actually does sweep forwards.  Same could be said for the vertical and horizontal stabilizers

[0TreeLemur]

On 12/11/2018 at 7:04 AM, 1964-M20E said:

The AV-20 does show a digital presentation for a clock which meets 91.205.  I can replace the clock on the panel (minor alteration I do believe) with A&P sign off.  The other features of the AV-20 are what really falls under the NORSEE.  JMHO  Yes if you are connecting it into the pitot static system you need to get a new pitot static check done.

Replace your clock with the AV-20 ( minor mod according to  NORSEE) this adds a back up AI (biggest function IMHO).  All the other bells and whistles are great but they are just lagniappe.  My Davtron clock is there primarily acting as a flight timer.  I have several other timers, clocks etc. on different GPS displays.

I'm thinking of getting the AV-20 and 30.  I just wish the AV-30 could act as a CDI and I could get rid of my KI-209 CDI.

Learned a new word today:  https://www.merriam-webster.com/dictionary/lagniappe

[Hank]

28 minutes ago, Fred_2O said:

Learned a new word today:  https://www.merriam-webster.com/dictionary/lagniappe

What'd you get???

 

What'd you buy to get it?

[0TreeLemur]

9 hours ago, Hank said:

What'd you get???

 

What'd you buy to get it?

Aerovonics AV-20.  A really cool 2-1/2" clock/timer that has a bunch of other features, including a backup AHRS attitude indicator.  For less than 1 amu.

[1964-M20E]

2 minutes ago, Fred_2O said:

Aerovonics AV-20.  A really cool 2-1/2" clock/timer that has a bunch of other features, including a backup AHRS attitude indicator.  For less than 1 amu.

all the other stuff besides the clock that's called lagniappe 

[0TreeLemur]

1 minute ago, 1964-M20E said:

all the other stuff besides the clock that's called lagniappe 

Having a clock/timer that can help save 'yer arse in the event of a vacuum failure is pretty darn cool lagniappe.

[1964-M20E]

I've seen some clocks that are just clocks cost more than the AV-20.

[FastTex]

38 minutes ago, Fred_2O said:

Aerovonics AV-20.  A really cool 2-1/2" clock/timer that has a bunch of other features, including a backup AHRS attitude indicator.  For less than 1 amu.

Nice, now you've got me hooked with this thing! I have been thinking to replace my old mechanical clock on the far left of my panel with something actually useful in this era and age...I think that will do it!

Does anyone know it the pilot can install it or we need to call the A&P to do the work?

 

[0TreeLemur]

8 hours ago, FastTex said:

Nice, now you've got me hooked with this thing! I have been thinking to replace my old mechanical clock on the far left of my panel with something actually useful in this era and age...I think that will do it!

Does anyone know it the pilot can install it or we need to call the A&P to do the work?

 

The AV-20 has NORSEE approval, which means that it may be installed as a minor modification provided that (... see FAA letter at Aerovonics).  I installed it during the annual under supervision of my A&P, who inspected the work and signed off on it.

[carusoam]

Expect to use your mechanic when you are integrating into...

• the ship’s electrical system...
• Using Proper documentation...
• proper log entries...
• proper WnB... if heavy enough...

The Best way to do this yourself, is at annual using Fred’s example.

It really helps to know your mechanic.

Best regards,

-a-

 

[testwest]

Wow, how did I miss this topic? OK, for the OP, I have a very neat drag polar for you (clean). Stand by........

[testwest]

OK! For the OP, Fred₂O, here is the drag polar for the M20J, derived from the data in the 1220G POH (which was applicable to our Mooney, a 1977 M20J):

Each one of the little "+" symbols is a line in the POH cruise data. For this POH, the best fit to the aggregate data is from the 6000' best power cruise data at 2740 lb GW, and the pink "+"s are from that particular data set.

So the zero-lift drag coefficient is .01654, and the best-fit straight line above gives C_D = .01654 +.082 C_L²

Pretty close to what Skip wrote... that Mooney provided the clean polar as C_D = 0.0164 + 0.072C_L²

It took a LONG time to enter all that data into Benchmark.....but it could be done for the other models from the POH data. The M20J data are really good though. Curt Lopresti told me during a conversation once about how his dad was so proud of the torque meter they had installed for direct measurement of installed power for the M20J certification, and of course the other two secret weapons were legendary flight test engineers Fen and Dorothy Taylor.

So to overcome drag, you need thrust. How much? Using the data set above and about 75% best power cruise, here is what is happening at the prop:

Lots of eye candy here. 6000 feet, 75% best power cruise, 150 hp into the prop, 131.2 comes out due to prop efficiency. Even the old McCauley C212 is pretty good at about 87.5% efficiency. To describe this to jet jocks, the M20 goes ~163 knots on ~262 pounds of thrust.

This translates to the airplane speed chart for these conditions, here:

Cool stuff. Hope you guys like it.

 

[carusoam]

@Fred₂O Norm left you some details...^^^^

Somewhere around here is Norm’s paper/treatise/big doc needed to graduate...

Best regards,

-a-

[Hank]

Welcome back, @testwest! Long time no see! I am glad to see that you made good use of the propellor data I sent you.

@Fred₂O, it's worth searching this site for Norman's PhD dissertation, but I'll warn you, it's not casual reading with an after-dinner drink . . . . But it is loaded with good information and he has helpfully completed all of the hard math.  

P.S.--to this simple Mechanical Engineer, "hard math" doesn't start until after integral and differential calculus, of which recent experience will speed your reading and comprehension of Norman's paper.

Edited February 28, 2019 by Hank

[testwest]

Haha, thanks Hank! But just for the record, the paper was a Master's thesis, not a PhD dissertation. And I am glad to be back, I also made my donation for this year!

[0TreeLemur]

On 12/9/2018 at 2:38 PM, M016576 said:

As an engineer, perhaps you’d like to try your hand at a little “test piloting” to find the curves for your airframe yourself.

Take your Mooney up at a known gross weight, find the stall point at level flight.  Note the nose high attitude (ie- separation of the whiskey line to the actual horizon). Then work your way back up the curve from there, documenting your attitude in relation to the horizon to find the critical angle of attack.  The POH has some documentation that can help you determine where Cl vs Cd max is from an airspeed/power perspective- establish yourself there, stabilized, and note the attitude again.  To verify that you are actually at the top of Cl/Cd max curve, note that additional attitude won’t allow for a climb on the backside (only power will, which you may or may not have)... but attitude will allow for a climb on the front side of the power curve.  Could be a fun afternoon!

Did that with #1 son right around Christmas, 2018.   Used inclinometer app on iPhone to measure pitch angle.  We were able to identify the angle of attack for max Cl of 12 degrees within about 1 degree in level flight, but unable to calibrate the AV-20S AoA sensor.   It seems to be uncalibratable.

[jaylw314]

15 hours ago, testwest said:

Cool stuff. Hope you guys like it.

 

Ho.  Ly.  Crap. 

We are not worthy! 

[Hank]

1 hour ago, jaylw314 said:

Ho.  Ly.  Crap. 

Yeah, that's why I chose a Capstone Project rather than a thesis for my MSE. The written part was only ~40 pages plus bibliography, etc. (including unpublished papers from two companies).

[0TreeLemur]

@testwest what is that software you used to do all those magical calculations and figures?   Is it public domain?    I want to play with it!

Thx.

-Fred

[testwest]

Hi Fred

Benchmark is a free app on the Mac App store, here: https://itunes.apple.com/us/app/sequoia-benchmark/id1244483544?mt=12

And the primary support and information page is here: http://www.seqair.com/benchmark/index.html

There is a massive amount of information on the info page, be sure to get the 1.0 Manual at the very bottom of the page, even though the interface has been updated, the basic computations behind the program are explained here: http://www.seqair.com/benchmark/BenchmarkManual.pdf

Be forewarned, however! If you are the least bit aerodynamically curious, I just ruined this coming weekend for you.

[0TreeLemur]

10 hours ago, testwest said:

Hi Fred

Benchmark is a free app on the Mac App store, here: https://itunes.apple.com/us/app/sequoia-benchmark/id1244483544?mt=12

And the primary support and information page is here: http://www.seqair.com/benchmark/index.html

There is a massive amount of information on the info page, be sure to get the 1.0 Manual at the very bottom of the page, even though the interface has been updated, the basic computations behind the program are explained here: http://www.seqair.com/benchmark/BenchmarkManual.pdf

Be forewarned, however! If you are the least bit aerodynamically curious, I just ruined this coming weekend for you.

I looked over the information page.   Just what I was looking for.  Thanks- sadly I have no access to a Mac...  With your modeled data I might be able to do some numerical experiments.

[testwest]

I was not a Mac guy until this program came out. It was so compelling I had to get a Mac to run it.