Jump to content

Mooney Aerodynamic Curves (Nerd Alert)


0TreeLemur

Recommended Posts

In the Sept. issue of MAPA Log Trey Hughes asserted that Mooneys were "built by engineers for engineers".   As one of those, I proudly wear my nautical mile wide nerd streak on my sleeve.   When re-designing the panel in our M20C earlier this year, a spare 2-1/2" diameter hole was created for a small accessory.  I found that the good old Davtron 811B served great as a clock/timer and bagel toaster/watt waster, but not much else.  Then I read about the AV-20-S from Aerovonics, which includes engine run time based on bus voltage, flight time based on V>40 kts from pitot-static, count-down and count-up timers, GMT, local time, density altitude, true airspeed, plus AHARS standby artificial horizon, and sensorless AOA, all in a tiny 2-1/2" package.  The sensorless AOA display requires calibration.   I've spent some time looking for lift and drag (Cl and Cd vs. alpha) coefficient curves for the M20 series, but have not been able to find it yet.   Does anyone have such info?   Old design reports?  Would it be worthwhile to contact the company?  Of course I want it for the C, but would take it for the E or F.  Thanks.

Link to comment
Share on other sites

11 minutes ago, Fred_2O said:

In the Sept. issue of MAPA Log Trey Hughes asserted that Mooneys were "built by engineers for engineers".   As one of those, I proudly wear my nautical mile wide nerd streak on my sleeve.   When re-designing the panel in our M20C earlier this year, a spare 2-1/2" diameter hole was created for a small accessory.  I found that the good old Davtron 811B served great as a clock/timer and bagel toaster/watt waster, but not much else.  Then I read about the AV-20-S from Aerovonics, which includes engine run time based on bus voltage, flight time based on V>40 kts from pitot-static, count-down and count-up timers, GMT, local time, density altitude, true airspeed, plus AHARS standby artificial horizon, and sensorless AOA, all in a tiny 2-1/2" package.  The sensorless AOA display requires calibration.   I've spent some time looking for lift and drag (Cl and Cd vs. alpha) coefficient curves for the M20 series, but have not been able to find it yet.   Does anyone have such info?   Old design reports?  Would it be worthwhile to contact the company?  Of course I want it for the C, but would take it for the E or F.  Thanks.

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!

  • Like 1
  • Thanks 1
Link to comment
Share on other sites

25 minutes ago, Fred_2O said:

In the Sept. issue of MAPA Log Trey Hughes asserted that Mooneys were "built by engineers for engineers".   As one of those, I proudly wear my nautical mile wide nerd streak on my sleeve.   When re-designing the panel in our M20C earlier this year, a spare 2-1/2" diameter hole was created for a small accessory.  I found that the good old Davtron 811B served great as a clock/timer and bagel toaster/watt waster, but not much else.  Then I read about the AV-20-S from Aerovonics, which includes engine run time based on bus voltage, flight time based on V>40 kts from pitot-static, count-down and count-up timers, GMT, local time, density altitude, true airspeed, plus AHARS standby artificial horizon, and sensorless AOA, all in a tiny 2-1/2" package.  The sensorless AOA display requires calibration.   I've spent some time looking for lift and drag (Cl and Cd vs. alpha) coefficient curves for the M20 series, but have not been able to find it yet.   Does anyone have such info?   Old design reports?  Would it be worthwhile to contact the company?  Of course I want it for the C, but would take it for the E or F.  Thanks.

Are you just curious about the lift and drag coefficients?  You don't need them to calibrate the AOA.

Link to comment
Share on other sites

I may still have some drag polars a Mooney engineer sent me in the early 90's for the M20J when I was trying to determine stability derivatives for a flight simulator. I'll look for it when I get to the office. Mooney didn't have much data on earlier models -- just what was required for certification. But Lopresti did a lot of aerodynamic modelling for the 201 and they took more data.

You might want to get a copy of Performance of Light Aircraft by John T. Lowry. He has an interesting (and pretty technical) approach to getting at performance data with a minimum of flight testing.

Skip

  • Thanks 1
Link to comment
Share on other sites

18 hours ago, PT20J said:

I may still have some drag polars a Mooney engineer sent me in the early 90's for the M20J when I was trying to determine stability derivatives for a flight simulator. I'll look for it when I get to the office. Mooney didn't have much data on earlier models -- just what was required for certification. But Lopresti did a lot of aerodynamic modelling for the 201 and they took more data.

Skip

Oh, if you can find the drag polars, please share them - those would be cool to see.  

Rich

Link to comment
Share on other sites

NORSEE allows installation *in addition to* existing, required instruments in the cockpit.  We are working guidance on how to potentially replace a legacy, analog clock which may be considered a required instrument in some aircraft.  (GPS units often have a clock that meets FAR requirements.)

 

That toaster you are berating and being mean too was your ticket to IFR.  I think you should apologize to her.

With your updated panel you probably have another clock ;)

  • Haha 1
Link to comment
Share on other sites

4 minutes ago, TheTurtle said:

NORSEE allows installation *in addition to* existing, required instruments in the cockpit.  We are working guidance on how to potentially replace a legacy, analog clock which may be considered a required instrument in some aircraft.  (GPS units often have a clock that meets FAR requirements.)

 

That toaster you are berating and being mean too was your ticket to IFR.  I think you should apologize to her.

With your updated panel you probably have another clock ;)

I’m not sure I trust the accuracy of that GPS clock over my trusty second hand sweep 1985 clock. (Sarcasm)

 

this is brings a serious question- are the clock specs for IFR in the type certificate or somewhere else?  Ie What’s the FAR requirement you mention?  

Link to comment
Share on other sites

9 minutes ago, 81X said:

I’m not sure I trust the accuracy of that GPS clock over my trusty second hand sweep 1985 clock. (Sarcasm)

Look at you with the fancy 1985 clock.  :D

91.205

(6) A clock displaying hours, minutes, and seconds with a sweep-second pointer or digital presentation.

The argument is the device above does that.  The fact it isnt an "authorized" replacement for original equipment is the issue and I dont know what FAR that is...

  • Thanks 1
Link to comment
Share on other sites

Here's what I got from Mooney for the M20J drag polars:

Cruise clean: C= 0.0164 + 0.072CL2

Climb, clean: CD = 0.0224 + 0.0697CL2

Climb, gear down, flaps 15 deg.: CD = 0.942 + 0.073CL2

M20K wing aerodynamic coefficient curves attached (quality isn't great: it's a crappy fax from 1991.)

Enjoy,

Skip

 

Mooney.pdf

  • Like 3
  • Thanks 1
Link to comment
Share on other sites

8 hours ago, PT20J said:

Here's what I got from Mooney for the M20J drag polars:

Cruise clean: C= 0.0164 + 0.072CL2

Climb, clean: CD = 0.0224 + 0.0697CL2

Climb, gear down, flaps 15 deg.: CD = 0.942 + 0.073CL2

M20K wing aerodynamic coefficient curves attached (quality isn't great: it's a crappy fax from 1991.)

Enjoy,

Skip

 

Mooney.pdf

I’m surprised the lift continues past the critical AOA (16°) to 18°, I thought laminar flow wings stop producing lift entirely?

Link to comment
Share on other sites

12 hours ago, TheTurtle said:

Look at you with the fancy 1985 clock.  :D

91.205

(6) A clock displaying hours, minutes, and seconds with a sweep-second pointer or digital presentation.

The argument is the device above does that.  The fact it isnt an "authorized" replacement for original equipment is the issue and I dont know what FAR that is...

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.

Link to comment
Share on other sites

5 hours ago, teejayevans said:

I’m surprised the lift continues past the critical AOA (16°) to 18°, I thought laminar flow wings stop producing lift entirely?

I wonder if that curve was calculated with the stall strips in place. The wing doesn't let go until 18º but Mooney wants you to do something about it at 16º.

Link to comment
Share on other sites

6 hours ago, teejayevans said:

I’m surprised the lift continues past the critical AOA (16°) to 18°, I thought laminar flow wings stop producing lift entirely?

IIRC, the critical AOA is the angle at which lift starts decreasing instead of increasing.  The wing still produces lift above that AOA, but it's producing less and still making more and more drag.  It's generally not a sudden loss of lift, although laminar flow wings will probably go through that transition faster than the short, stubby Hershey-bar wings.

Edit: er, now I'm thinking I remember it's the lift coefficient that starts decreasing, not total lift, but at this point I've confused myself:rolleyes:

Link to comment
Share on other sites

3 hours ago, 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.

You interpret that differently than I do.  91.205.(d).(6) requires a clock with a sweep second hand or digital equivalent for instrument flight.  NORSEE allows installation in addition to, not in replacement of, required instruments.  The Aerovonics page does not say that only parts of the instrument are NORSEE approved.  The entire instrument is NORSEE approved.  The way I interpret that is that I could keep my clock and add the AV20-S, but I cannot use the AV20-S to replace my clock.  That's why I'm waiting for Aerovonics to get approval for use as a required clock.  While using the AV20-S to replace a clock meets the spirit of the law, I do not think it meets the letter of the law.  Is anyone going to say something?  Probably not.  Will it ever matter?  Highly unlikely that a clock would have anything to do with an accident/incident.  But I want to comply with the letter of the law.  That's why we also installed a nav source indicator for our GTN650 so we could legally fly IFR.

My GTN650 will display time, but only hours and minutes unless I want to dig all the way down through the menus to a settings page.  It will show me a timer including seconds, but the requirement is not for a timer, but a clock.

Link to comment
Share on other sites

1 minute ago, aviatoreb said:

This is my kind of thread.

you geeks.

fellow geeks.

fellowship of the geeks.

I've already got my daughter plugging numbers into XFOIL and wondering why the airfoil numbers don't match the measured data.  I think we may have you beat in the geek department.

Rich

  • Like 1
Link to comment
Share on other sites

3 minutes ago, rahill said:

I've already got my daughter plugging numbers into XFOIL and wondering why the airfoil numbers don't match the measured data.  I think we may have you beat in the geek department.

Rich

Dude - ... love it!

Warning - that is how my middle son became an aero major.  He is in his Junior year.  May the Force Be With You.  And your geek daughter.

  • Like 1
Link to comment
Share on other sites

I've already got my daughter plugging numbers into XFOIL and wondering why the airfoil numbers don't match the measured data.  I think we may have you beat in the geek department.
Rich
XFOIL is a 2-D airfoil code that is useful for some work, but not for 3-D/finite wing comparisons, or whole aircraft performance predictions.

Sent from my LG-US996 using Tapatalk

  • Like 2
Link to comment
Share on other sites

16 hours ago, 81X said:

I’m not sure I trust the accuracy of that GPS clock over my trusty second hand sweep 1985 clock. (Sarcasm)

 

this is brings a serious question- are the clock specs for IFR in the type certificate or somewhere else?  Ie What’s the FAR requirement you mention?  

I once got a chance to visit CERN - the high energy particle accelerator between countries through Switzerland.  I was impressed that they use GPS in their under ground experiments for its universal time stamp to time stamp their experiments events. (Obviously they have an antenna poking up above the rock).

Link to comment
Share on other sites

3 minutes ago, KSMooniac said:

XFOIL is a 2-D airfoil code that is useful for some work, but not for 3-D/finite wing comparisons, or whole aircraft performance predictions.

Sent from my LG-US996 using Tapatalk
 

But...it is fantastic for a budding young engineer girl to be.  Its not just about professional level engineering - there is the pedagogy motivation aspect too.  My son also played with xfoil A LOT in High School.  And he was always making custom extra pointy airplanes in xplane with massive engines to see how fast they would go.  Today he can tell you and me both about what is good and what is insufficient about xfoil better than you and me combined.  I think its great she's come to the geek side!

Edited by aviatoreb
  • Like 1
Link to comment
Share on other sites

But...it is fantastic for a budding young engineer girl to be.  Its not just about professional level engineering - there is the pedagogy motivation aspect too.  My son also played with xfoil A LOT in High School.  And he was always making custom extra pointy airplanes in xplane with massive engines to see how fast they would go.  Today he can tell you and me both about what is good and what is insufficient about xfoil better than you and me combined.  I think its great she's come to the geek side!
Absolutely! I just wanted to point out that there are several non-trivial steps between XFOIL output and trying to correlate it to whole-airplane performance data.

testwest has some incredible data and whole-Mooney models with Benchmark software by Sequoia for Macs.

Sent from my LG-US996 using Tapatalk

  • Like 2
Link to comment
Share on other sites

8 minutes ago, KSMooniac said:

Absolutely! I just wanted to point out that there are several non-trivial steps between XFOIL output and trying to correlate it to whole-airplane performance data.

testwest has some incredible data and whole-Mooney models with Benchmark software by Sequoia for Macs.

Sent from my LG-US996 using Tapatalk
 

I know.  Sometimes typing is a terrible forum for having fun agreeing with each other.  Lest we agree violently.  I knew we were agreeing and I was just emphasizing the pedagogy side.

  • Like 1
Link to comment
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

×
×
  • Create New...

Important Information

We have placed cookies on your device to help make this website better. You can adjust your cookie settings, otherwise we'll assume you're okay to continue.