Stalls in a Mooney Ovation - do speed brakes affect stall speed? Does configuration make a difference?

[Fly_M20R]

I have always “felt” that speed brakes might increase the stall speed in a Mooney. However, never really read anything specific nor does the POH publish any stall speeds with the speed brakes deployed. So, thought I would take to the skies and do a “test” flight. I was a bit surprised and now believe I understand their effect better.

Stalls in a Mooney Ovation - effect of weight and speed brakes.

 

[Graf_Aviator]

I have always “felt” that speed brakes might increase the stall speed in a Mooney. However, never really read anything specific nor does the POH publish any stall speeds with the speed brakes deployed. So, thought I would take to the skies and do a “test” flight. I was a bit surprised and now believe I understand their effect better.
Stalls in a Mooney Ovation - effect of weight and speed brakes.
 

Chris,

I really like your videos and I have subscribed already to your channel on YT quite some time ago.
Very informative

Thank you for taking the time to create all these great Mooney videos…


Sent from my iPhone using Tapatalk

[midlifeflyer]

I'm no aerodynamics guru either but that explanation based on the location of the laminar flow relative to the speed brakes in each configuration makes sense to me. 

[carusoam]

Chris, great video and details…

Thanks for sharing them.

 

Consider a few things we may know…

1) From videos of speed brakes in rain…. The effect of the brakes is about 3X their width…

2) They essentially remove the lift over a swath of about a couple of feet of wing or so… on each side. (Roughly speaking)

3) to make up for the lost lift and maintain altitude, we increase the AOA…

4) the small addition of AOA puts the wing closer to the critical angle of attack…

5) As power gets removed, the AOA gets increased until the critical AOA is achieved…

6) The critical AOA is very much wing design related…

7) What we haven’t seen… any videos of speed brakes in the rain during high AOA flight…

8) We would probably visualize the effects of air flow separation as it moves from the trailing edge towards the leading edge…

9) The air flow separation probably drowns out the effect of speed brakes that are mounted behind the main wing spar….

10) Nice speed prediction calculations… I would have been stuck interpreting the stall speed charts in a linear kinda way…. 

 

Really amazing speed control to make this video possible!

The GI275 really delivered here.

The cool thing about knowing your Vso for the current weight…  you can use 1.3, 1.2, and 1.1 X Vso around the traffic pattern with precision…

How was your landing following this experiment?

Fantastic presentation!

PP thoughts only, not an aerodynamicist…

Best regards,

-a-

[Jeff_S]

Nice video...well done Chris!  What day did you shoot this?  My hangar is just a few steps from Chris's so I can attest that he's out all the time flying around. Just a few comments:

1) Given the only slight variations in stall speeds, I wonder how much of this could be do to measurement or environmental error rather than actual differences. The Vso speeds are slightly higher, so I guess maybe there is some actual difference.

2) Does the type of flap really matter? All flaps tend to promote the pitch down effect to some degree, so I'm curious if it's important that the Mooney's slotted flaps make a difference. Also, would be fun to take my Ovation out with the newer speed brakes to see if there's a measurable difference in effect.

3) Either way, it seems the effects are minimal so there shouldn't be too much consideration about whether or not you're using speed brakes to land. I actually do...this was suggested by Joey Cole when I first got my Ovation, and he said that he feels it reduces float. Given their placement in the air flow at low speeds this may also be negligible, but any little bit can help.  It does become another memory checklist item on go-around, although the plane is certified to fly with speed brakes in any configuration so it's not unsafe.

[Fly_M20R]

Thank you for all the comments and questions guys!! I'll reply in detail a bit later today. Really good questions and comments!!

Chris

[carusoam]

note on landing/stopping distance…
 

Speed brakes at low speeds become less effective… kind of in a non-linear way…

Having them deployed in ground effect probably cuts some more of their effect as well…

It would be interesting to know… if braking improves early on as lift gets removed from the wings… speed brake could help with this…

 

But…  with instrumentation like the GI275 and CloudAhoy with a WAAS source, it’s now measurable by every day pilots, not just test pilots at the factory!

I’m not afraid to use speed brakes to dump a small amount of excess energy on final…

 

PP guesses only…

-a-

[Fly_M20R]

9 hours ago, carusoam said:

Chris, great video and details…

Thanks for sharing them.

 

Consider a few things we may know…

1) From videos of speed brakes in rain…. The effect of the brakes is about 3X their width…

2) They essentially remove the lift over a swath of about a couple of feet of wing or so… on each side. (Roughly speaking)

3) to make up for the lost lift and maintain altitude, we increase the AOA…

4) the small addition of AOA puts the wing closer to the critical angle of attack…

5) As power gets removed, the AOA gets increased until the critical AOA is achieved…

6) The critical AOA is very much wing design related…

7) What we haven’t seen… any videos of speed brakes in the rain during high AOA flight…

8) We would probably visualize the effects of air flow separation as it moves from the trailing edge towards the leading edge…

9) The air flow separation probably drowns out the effect of speed brakes that are mounted behind the main wing spar….

10) Nice speed prediction calculations… I would have been stuck interpreting the stall speed charts in a linear kinda way…. 

 

Really amazing speed control to make this video possible!

The GI275 really delivered here.

The cool thing about knowing your Vso for the current weight…  you can use 1.3, 1.2, and 1.1 X Vso around the traffic pattern with precision…

How was your landing following this experiment?

Fantastic presentation!

PP thoughts only, not an aerodynamicist…

Best regards,

-a-

 

Thank you Anthony! I had a really good time doing this video. Much more fun flying it than editing it though!! 

Hmmmm.... will have to try doing a video like this in the rain to observe what happens with the pattern of rain with speed brakes out. Would be even better to paste some of those little strips that show exactly what the air is doing at any part of the wing. Don't have any and would need some good instruction on how to put them on AND take them off!

My main goal was to have really good speed control and decrease the speed slowly and in a steady fashion. In doing so I ended up descending a bit during each of those stalls. I do not believe the IAS was affected in any way in doing it this way. However could not reliably compare the airplane attitude on the AI and therefore estimate the AOA. Note that with flaps retracted the AOA is the pitch angle (attitude on the AI) plus the angle of incidence which I have not been able to find published anywhere but assume to be some 3 to 5 degrees. Once the flaps are deployed the chord changes from leading edge to the trailing edge of the flap (not the trailing edge of the main wing). I really have no idea of what that angle may be but would also estimate some 3 to 5 degrees. Since critical AOA for our wings is close to 14 degrees according to what I have read, then you can figure the other angles correspondingly.

I have made a spreadsheet that I keep on my phone and iPad on which I can then calculate stall speeds, approach speeds, maneuvering speeds and best glide speeds for any weight of the airplane including fuel, passengers and baggage. Can share although not sure how to share a file on Mooneyspace.

Landing was good even if I flew a bit faster than 1.3 x Vso because of some turbulence on the last part of the final approach. Landed around 700-800 ft beyond the displaced threshold. It's displaced because of trees. 

Chris

[Oscar Avalle]

Chris, really interesting video and well done! I was wondering, and I will try it out, how vortex generators actually impact on the stall speed of my M20C. I do know for sure that the controls are more responsive compared to a stock M20C without the VGs. 

 

Once again, thank you and great videos... I love them.

 

Oscar  

[Fly_M20R]

8 hours ago, Jeff_S said:

Nice video...well done Chris!  What day did you shoot this?  My hangar is just a few steps from Chris's so I can attest that he's out all the time flying around. Just a few comments:

1) Given the only slight variations in stall speeds, I wonder how much of this could be do to measurement or environmental error rather than actual differences. The Vso speeds are slightly higher, so I guess maybe there is some actual difference.

2) Does the type of flap really matter? All flaps tend to promote the pitch down effect to some degree, so I'm curious if it's important that the Mooney's slotted flaps make a difference. Also, would be fun to take my Ovation out with the newer speed brakes to see if there's a measurable difference in effect.

3) Either way, it seems the effects are minimal so there shouldn't be too much consideration about whether or not you're using speed brakes to land. I actually do...this was suggested by Joey Cole when I first got my Ovation, and he said that he feels it reduces float. Given their placement in the air flow at low speeds this may also be negligible, but any little bit can help.  It does become another memory checklist item on go-around, although the plane is certified to fly with speed brakes in any configuration so it's not unsafe.

Hi Jeff!

I flew on 12/29. It was a tad windy on the ground but really smooth at the altitude I did the stalls - 5,500 ft. There was a good amount of wind speed up there but it was smooth. It was from the West and therefore did the stalls either into it or directly away from it.

For those of you who have not met Jeff, he is very knowledgeable regarding his Ovation since he races it and often places first place! He certainly has fun in his plane!!

It is certainly possible that the stall speeds I obtained were subject to some error, and most likely due to environment (i.e. my flying ). However, I can certainly say that the plane felt quite different in landing configuration with speed brakes out vs them being in, and the earlier stall (higher stall speed) with them out is fairly credible. Did not feel that different in clean configuration with them in or out.  

From what I have read and superficial knowledge I have obtained it appears as if Fowler type flaps (which extend the most beyond the trailing edge) have the most effect on lift because they do increase the wing surface. Flaps that just "go down" only affect the camber and the cord and don't add that much to the wing surface. The camber change also increases lift and moves the center of lift somewhat aft. It is more pronounced with Fowler flaps.

Let me know what you find after the test flight in your newer Ovation with the Series 2000 brakes. I plan to fly Jack's Bravo which has the series 2000's and test it  out. Will do a video of it when I fly.

Yep, the speed brakes certainly reduce the float on landing. When landing we usually do so with flaps fully deployed and therefore the effect of the speed brakes would be to reduce some lift as per my findings. Having less lift may translate into less float. 

See you at the airport! 

Chris

[Fly_M20R]

22 minutes ago, Oscar Avalle said:

Chris, really interesting video and well done! I was wondering, and I will try it out, how vortex generators actually impact on the stall speed of my M20C. I do know for sure that the controls are more responsive compared to a stock M20C without the VGs. 

 

Once again, thank you and great videos... I love them.

 

Oscar  

Hi Oscar!

Did you install the VG's after you got the plane or were they already installed? Your short field landings must be on a dime!! Did they change the airspeed indicator to reflect the change in stall speeds?

Yep, you should go out and do some stalls and calculate what the stall speed should be per the formula I showed. I would use the original stall speed (Vso and Vs) published for your plane without the VG's in the formula and that way you can determine if they really make any difference. Really curious as to what you find. 

Thank you and happy flying!!

Chris

 

[Oscar Avalle]

48 minutes ago, Fly_M20R said:

Hi Oscar!

Did you install the VG's after you got the plane or were they already installed? Your short field landings must be on a dime!! Did they change the airspeed indicator to reflect the change in stall speeds?

Yep, you should go out and do some stalls and calculate what the stall speed should be per the formula I showed. I would use the original stall speed (Vso and Vs) published for your plane without the VG's in the formula and that way you can determine if they really make any difference. Really curious as to what you find. 

Thank you and happy flying!!

Chris

 

Chris,

BTW I love your videos. I am seriously thinking of putting some voice on the ones I produce in light of how interesting I find yours. My only concern is that you are so good at it that I would never reach your level of proficiency...

I installed the VGs after I got my plane. I was using my plane to fly into grass strips and shorter runways. My field was also at 5,000 feet and density altitude was often an issue. On several occasions I was taking of and landing with 8,000+ feet density altitude and it was an issue. So I decided to install them. I feel that I may have lost some knots... may be 3 or 5, but I gained so much control that I don't regret it. 

As soon as I go flying again I will do some stalls and report back.

 

Oscar 

[carusoam]

Chris,

Sharing a file around here is pretty easy….

Find the download area… and upload the file…

 

Somebody did this for T/O and landing calculations for the Ovations as well… it is an excel spreadsheet that uses another app that allows the spreadsheet to be used like an app….   Really nice from a user point of view to calculate details for today’s flight….

 

Best regards,

-a-

[Fly_M20R]

8 hours ago, carusoam said:

Chris,

Sharing a file around here is pretty easy….

Find the download area… and upload the file…

 

Somebody did this for T/O and landing calculations for the Ovations as well… it is an excel spreadsheet that uses another app that allows the spreadsheet to be used like an app….   Really nice from a user point of view to calculate details for today’s flight….

 

Best regards,

-a-

Thank you Anthony!

Will upload soon.

Chris

[Fly_M20R]

On 1/18/2022 at 6:14 PM, Oscar Avalle said:

Chris,

BTW I love your videos. I am seriously thinking of putting some voice on the ones I produce in light of how interesting I find yours. My only concern is that you are so good at it that I would never reach your level of proficiency...

I installed the VGs after I got my plane. I was using my plane to fly into grass strips and shorter runways. My field was also at 5,000 feet and density altitude was often an issue. On several occasions I was taking of and landing with 8,000+ feet density altitude and it was an issue. So I decided to install them. I feel that I may have lost some knots... may be 3 or 5, but I gained so much control that I don't regret it. 

As soon as I go flying again I will do some stalls and report back.

 

Oscar 

Hi Oscar,

Crazy that you find that I am good at the videos I do because I definitely struggle all the time to try to make them more broadly appealing. I feel that what is required is being the playwriter, producer, director, actor, prop guy, sound and music guy (I am not musically capable at all and so have no idea as to what music may be good to insert) and editor all at once to make a reasonably appealing video. 

You definitely have had challenging landings and takeoffs from what you describe and seems as you would need some VG's if you want to have a Mooney and be able to use those fields. 

Looking forward to your report.

Chris

 

[Fly_M20R]

On 1/18/2022 at 5:15 PM, Fly_M20R said:

Hi Jeff!

I

From what I have read and superficial knowledge I have obtained it appears as if Fowler type flaps (which extend the most beyond the trailing edge) have the most effect on lift because they do increase the wing surface. Flaps that just "go down" only affect the camber and the cord and don't add that much to the wing surface. The camber change also increases lift and moves the center of lift somewhat aft. It is more pronounced with Fowler flaps.

 

Your comment re slotted vs Fowler flaps got me to read more about them and it seems that true Fowler flaps extend much more than what our Mooney flaps do. Our Mooney flaps do add up to a couple of inches to the length of the wing when looking at it from the top which is why I called them "Fowler" type. But it is not the same mechanism as true Fowler flaps. Both Fowler and slotted have "slots" which allow the air from below the wing to get above the flap and therefore add lift. It would also appear that since they do add some length to the wing they also increase the wing surface. Slotted then?

Chris

[Oscar Avalle]

16 hours ago, Fly_M20R said:

Hi Oscar,

Crazy that you find that I am good at the videos I do because I definitely struggle all the time to try to make them more broadly appealing. I feel that what is required is being the playwriter, producer, director, actor, prop guy, sound and music guy (I am not musically capable at all and so have no idea as to what music may be good to insert) and editor all at once to make a reasonably appealing video. 

You definitely have had challenging landings and takeoffs from what you describe and seems as you would need some VG's if you want to have a Mooney and be able to use those fields. 

Looking forward to your report.

Chris

 

Hi Chris,

I had a great laugh when I read your response, because my challenge is how to write and interesting script and of course how to sound engaging. Let me share with you what I do in my videos and you will see what I mean. 

 

[PT20J]

Nice video @Fly_M20R. It's always great when someone takes the time to perform an experiment and posts the results. I'll let @Blue on Top comment on the aerodynamics.

A couple of points:

1. According to the S&MM, the angle of incidence is 2.5 deg

2. According to the graphs supplied me by a Mooney engineer years ago, the wing stalls at 16 deg AoA clean and 17 deg with 33 deg flaps (this data was for a M20K, but should be representative of all the M20 series). For engineering purposes, the chord line doesn't change as function of flap deflection.

3. If the speed brakes had any appreciable effect on stall speed, it would have been noted in the AFMS.

A lot of electronic flight displays will display a velocity vector. It should be possible to estimate angle of attack in level flight by placing the velocity vector on the zero pitch line and noting the pitch attitude and then adding the angle of incidence.

Skip

M20K Aerodynamic Coef - Flaps 0.pdf

M20K Aerodynamic Coef - Flaps 33.pdf

[Blue on Top]

1 hour ago, PT20J said:

Nice video @Fly_M20R. It's always great when someone takes the time to perform an experiment and posts the results. I'll let @Blue on Top comment on the aerodynamics.

2. ... the chord line doesn't change as function of flap deflection.

3. If the speed brakes had any appreciable effect on stall speed, it would have been noted in the AFMS.

Skip

First and foremost, GREAT videos to both @Fly_M20R and @Oscar Avalle!

 If all y'all want to know more aerodynamics, I submit the following: (work with me I'm an aero/flight test geek/nerd ... and proud of it). 

Skip's "2)" above separates the aerodynamicist from the pilot (aerodynamicist wanna-be).  The chord line, length, angle, etc. doesn't change with flap, slat, etc. changes.  Another point along those lines, real aerodynamicists know that laminar flow is unrealistic (past 15-20% on the upper surface ... at best ... for ALL airfoils ... except in the computer or wind tunnel).  Please talk about airflow in one of two conditions: attached (turbulent) or separated (no longer "attached" to the surface).  Technicalities out of the way.  Whew!

Great job on the videos and stall testing.  One consideration is that entry rate changes the stall speed.  In other words, if the airplane is slowed very, very slowly (as you did), the stall speed will be higher.  If the airplane is slowed rapidly, the stall speed will be lower.  We call these Vmin stall speeds (1G stall speeds are different).  The regulations (what is in your POH) is for 1 knot/second deceleration.  In addition, the stall speeds are done at forward CG with the airplane trimmed at 1.4Vs (by today's regs).  Stabilizer position will matter also, if there is/was not enough elevator power to stall the wing.

Speed brake effect will vary between models because the stall strip location is different and the wing twist is different, too.  Your results @Fly_M20R look great!  Since the speed brakes (really spoilers as they are only on the top of the wing) are not factory installed, the data will not be in the POH.  It is also typical that if the speeds don't change by 3 knots, they are not required to be published (or operation be limited below XX feet AGL).  

I don't want to make this post long (I should be writing the February "The Mooney Flyer" article on pitot-static systems.  BUT, I want you to ask ANY and ALL questions you are curious about.   My goal is to educate.

I will be coming to Florida for Sun-N-Fun and would LOVE, LOVE, LOVE to work with both of you!  Let's talk before then, and I would enjoy doing several tufting programs on your airplanes!  For the Ovation owner(s), I can definitely make your airplanes faster.

 

[Fly_M20R]

10 hours ago, Oscar Avalle said:

Hi Chris,

I had a great laugh when I read your response, because my challenge is how to write and interesting script and of course how to sound engaging. Let me share with you what I do in my videos and you will see what I mean. 

 

Hi Oscar,

Nice video!! Have some comments and questions about it but haven't had the time to write them out. Will do so this weekend.

Chris

[Fly_M20R]

On 1/20/2022 at 3:44 PM, PT20J said:

Nice video @Fly_M20R. It's always great when someone takes the time to perform an experiment and posts the results. I'll let @Blue on Top comment on the aerodynamics.

A couple of points:

1. According to the S&MM, the angle of incidence is 2.5 deg

2. According to the graphs supplied me by a Mooney engineer years ago, the wing stalls at 16 deg AoA clean and 17 deg with 33 deg flaps (this data was for a M20K, but should be representative of all the M20 series). For engineering purposes, the chord line doesn't change as function of flap deflection.

3. If the speed brakes had any appreciable effect on stall speed, it would have been noted in the AFMS.

A lot of electronic flight displays will display a velocity vector. It should be possible to estimate angle of attack in level flight by placing the velocity vector on the zero pitch line and noting the pitch attitude and then adding the angle of incidence.

Skip

M20K Aerodynamic Coef - Flaps 0.pdf 1.99 MB · 5 downloads

M20K Aerodynamic Coef - Flaps 33.pdf 190.25 kB · 3 downloads

Hi Skip,

Great info. Thank you!

A few questions  and comments arise using my rusty college engineering background and my layman's aerodynamic knowledge:

1) I thought that the chord with flaps up was from the leading edge of the wing to the trailing edge of the flaps up and that with flaps down the chord changed to being from leading edge of the wing to the trailing edge of the flaps (now down) and therefore the chord line did change accordingly which could be some 3 or maybe more degrees. (???). Appears as if the engineers opted not to consider this change in their calculations.

2) The AOA with flaps at 0 deg ("AOA_Flp_0" is the pitch angle we observe on the AI (call it "Deg_AI") plus the angle of incidence ("Deg_Inc"):

         [  AOA_Flp_0  =  Deg_AI   +  Deg_Inc ]

3) The AOA with flaps at 33 deg ("AOA_Flp_33" is the pitch angle we observe on the AI (call it "Deg_AI") plus the angle of incidence ("Deg_Inc") plus the chord angle increase delta with flaps down ("Deg_chord_delta_Flp_33"):

         [  AOA_Flp_33  =  Deg_AI   +  Deg_Inc  +  Deg_chord_delta_Flp_33  ]

                                **** Note that we should observe a smaller pitch on the AI with flaps down  ****

                                 **** The unknown (for me) in this formula is the added angle to the chord with the flaps down.   ****

4) Based on the critical AOA you provided on the M20K looks like the slightly higher critical AOA_flp_33 of 17 deg vs 16 for flaps up would be a combination of delta degrees of the chord and ability to fly at higher AOA at same airspeed with flaps down. 

5) The wing on an M20K is the same wing as on the Ovation since you can calculate the stall speeds for an M20K with its gross weight with the formula I gave plugging in the M20K's gross weight for current weight and 3,368 lbs for the Ovation. Vs and Vso at gross in the Ovation are 66 and 59 respectively. Or, you can go the other way around: flip the weights in the formula and put the Vs and Vso of the K as the stall speeds at gross. I know it works quite closely for the J models as well. 

6) Obviously don't have a velocity vector on the GI 275, however one might be able to estimate the angle based on the VSI. I was descending somewhere between 100 and 200 fpm during the stalls since it was easier to control the airspeed changes that way. Wish I had done it at perfectly level flight to get a better idea of the actual pitch at the time of stall and therefore get a good ballpark of the critical AOA. .... Next time I'll have to do the fine speed control with finer throttle adjustments combined with smooth yoke back pressure. A bit more of a challenge...

7) Apparently, there is no need to note speed brake effects on stall speed in the AFMS as long as they are less than 3 kts, which is what I found. This is according to a post on Beechtalk by someone who was part of the design team for the Series 2000 Precise Flight speed brakes. Guess that explains it.

 

Finally, I would like to say that I erroneously called the flaps as "Fowler" flaps instead of "Slotted" because I noted that they did extend by 1-1/2 to maybe 2 inches behind their original position and took the definition of Fowler literally without taking into the account that true Fowler flaps extend significantly more than what we have in our planes. Appears as if Fowler ones also go back horizontally first and then curve down as in the "scareliners"... 

 

Thank you again for your great feedback Skip!

Chris

 

[Fly_M20R]

On 1/20/2022 at 12:23 PM, Oscar Avalle said:

Hi Chris,

I had a great laugh when I read your response, because my challenge is how to write and interesting script and of course how to sound engaging. Let me share with you what I do in my videos and you will see what I mean. 

 

Hi Oscar,

I really enjoyed your video and the music was perfect! 

The following comments come from me as still a beginner in videography:

I actually still find it a bit difficult to "be myself" when I do my videos but that is what comes through best. One appears fairly rigid when trying to "act" in a "professional" manner or what one imagines the audience would like to see. I often find myself acting a bit different than "me". Of course, it is important to enunciate well otherwise one does not come through intelligibly (I can tend to mumble at times). It appears as if the audience does like to see one's face every once in a while rather than just panel or outside view. Need to get over stage fright!! We all have stage fright!

You can record your transmissions and actions during your takeoff, parts of cruise and landing. 

How long was your flight on this video? I ask because the outside cameras can be controlled to record and stop recording via their own wifi network but still use up battery during idle time and I found it difficult to get more than maybe 1-1/2 hrs out of them. If your flight was longer than that then how did you preserve battery? Great views!!

I think that having the landing at 1x recording speed would have been nicer than at 2x (or 3x) as you had. People enjoy watching landings! I have a framed caricature that says "Flying is man's second greatest thrill. Landing is the first"!!

Chris

[PT20J]

4 hours ago, Fly_M20R said:

Hi Skip,

Great info. Thank you!

A few questions  and comments arise using my rusty college engineering background and my layman's aerodynamic knowledge:

1) I thought that the chord with flaps up was from the leading edge of the wing to the trailing edge of the flaps up and that with flaps down the chord changed to being from leading edge of the wing to the trailing edge of the flaps (now down) and therefore the chord line did change accordingly which could be some 3 or maybe more degrees. (???). Appears as if the engineers opted not to consider this change in their calculations.

2) The AOA with flaps at 0 deg ("AOA_Flp_0" is the pitch angle we observe on the AI (call it "Deg_AI") plus the angle of incidence ("Deg_Inc"):

         [  AOA_Flp_0  =  Deg_AI   +  Deg_Inc ]

3) The AOA with flaps at 33 deg ("AOA_Flp_33" is the pitch angle we observe on the AI (call it "Deg_AI") plus the angle of incidence ("Deg_Inc") plus the chord angle increase delta with flaps down ("Deg_chord_delta_Flp_33"):

         [  AOA_Flp_33  =  Deg_AI   +  Deg_Inc  +  Deg_chord_delta_Flp_33  ]

                                **** Note that we should observe a smaller pitch on the AI with flaps down  ****

                                 **** The unknown (for me) in this formula is the added angle to the chord with the flaps down.   ****

4) Based on the critical AOA you provided on the M20K looks like the slightly higher critical AOA_flp_33 of 17 deg vs 16 for flaps up would be a combination of delta degrees of the chord and ability to fly at higher AOA at same airspeed with flaps down. 

5) The wing on an M20K is the same wing as on the Ovation since you can calculate the stall speeds for an M20K with its gross weight with the formula I gave plugging in the M20K's gross weight for current weight and 3,368 lbs for the Ovation. Vs and Vso at gross in the Ovation are 66 and 59 respectively. Or, you can go the other way around: flip the weights in the formula and put the Vs and Vso of the K as the stall speeds at gross. I know it works quite closely for the J models as well. 

6) Obviously don't have a velocity vector on the GI 275, however one might be able to estimate the angle based on the VSI. I was descending somewhere between 100 and 200 fpm during the stalls since it was easier to control the airspeed changes that way. Wish I had done it at perfectly level flight to get a better idea of the actual pitch at the time of stall and therefore get a good ballpark of the critical AOA. .... Next time I'll have to do the fine speed control with finer throttle adjustments combined with smooth yoke back pressure. A bit more of a challenge...

7) Apparently, there is no need to note speed brake effects on stall speed in the AFMS as long as they are less than 3 kts, which is what I found. This is according to a post on Beechtalk by someone who was part of the design team for the Series 2000 Precise Flight speed brakes. Guess that explains it.

 

Finally, I would like to say that I erroneously called the flaps as "Fowler" flaps instead of "Slotted" because I noted that they did extend by 1-1/2 to maybe 2 inches behind their original position and took the definition of Fowler literally without taking into the account that true Fowler flaps extend significantly more than what we have in our planes. Appears as if Fowler ones also go back horizontally first and then curve down as in the "scareliners"... 

 

Thank you again for your great feedback Skip!

Chris

 

Chris,

I think it is important to realize that a lot of physical parameters are simply arbitrary definitions created to best serve the purpose of the author. In the case of describing how flaps work to someone unfamiliar with aerodynamic concepts, it is convenient to point out that lift is created when an airfoil passes through the air at a positive angle of attack. An oversimplified way of explaining the effect of flaps is to redraw the chord line showing an increased angle of attack and thus increased lift.

For an engineer, such a definition needlessly complicates things. Angle of attack (alpha) is so fundamental to aerodynamic calculations that it is usually considered to be an independent variable, and it would be inconvenient if its definition depended on other parameters. As an example, consider someone trying to determine the effect of flaps on an airfoil mounted in a wind tunnel. A reasonable approach would be to start with the flap up and zero alpha and measure lift, drag, and moment, and then deploy flap and repeat the measurement. This process could be repeated at incrementally increased alpha until the stall. This is exactly what the NACA did to quantify the performance of various airfoils. But, if the definition of alpha changed with flap deflection, it would complicate the analysis enormously because now the measurement would be a function not only of alpha but of alpha and flap position.

Angle of attack (alpha) depends on where you measure it. Many texts for pilots incorrectly show the air streamlines approaching the airfoil in a straight path and being deflected downward after passing over the wing. This is done because the author wishes to explain lift by stating that the wing forces air down and, according to Newton's third law this must force the wing up (exactly what physical mechanism forces the wing up is never explained). But, this diagram is incorrect. The wing creates a pressure pattern in advance of it's arrival and the result is an upwash ahead of the wing. Numerically, half the lift is due to the upwash ahead of the wing and half is due to the downwash behind the wing. So when defining angle of attack it is important to note whether you are talking about the airflow near the leading edge or the free air far in advance of the wing.

While zero pitch on a properly calibrated attitude indicator indicates level flight, it does not indicate zero alpha. In level flight, the wings must generate enough lift to balance the weight and the tail down force. This will generally result in a positive alpha dependent on airspeed. The tail down force can be calculated by knowing the arm to the tail and the airplane moment, but taking 10% of the airplane weight is probably good enough for a rough estimate. Thus, the lift would be 1.1 x the aircraft weight and the coefficient of lift can be determined by solving the lift equation for it: L = 1/2pV²C_LS where p is the air density, V is the TAS, C_L is the coefficient of lift and S is the wing area. S can be obtained from the Service Manual. Once you have the coefficient of lift, you can use the curve I supplied earlier to figure out alpha.

I hope this helps. @Blue on Top might want to chime in -- he's a real aeronautical engineer that does this for a living. I'm just an electrical engineer that just enjoys trying to understand things.

Skip

 

[Fly_M20R]

11 hours ago, PT20J said:

Chris,

I think it is important to realize that a lot of physical parameters are simply arbitrary definitions created to best serve the purpose of the author. In the case of describing how flaps work to someone unfamiliar with aerodynamic concepts, it is convenient to point out that lift is created when an airfoil passes through the air at a positive angle of attack. An oversimplified way of explaining the effect of flaps is to redraw the chord line showing an increased angle of attack and thus increased lift.

For an engineer, such a definition needlessly complicates things. Angle of attack (alpha) is so fundamental to aerodynamic calculations that it is usually considered to be an independent variable, and it would be inconvenient if its definition depended on other parameters. As an example, consider someone trying to determine the effect of flaps on an airfoil mounted in a wind tunnel. A reasonable approach would be to start with the flap up and zero alpha and measure lift, drag, and moment, and then deploy flap and repeat the measurement. This process could be repeated at incrementally increased alpha until the stall. This is exactly what the NACA did to quantify the performance of various airfoils. But, if the definition of alpha changed with flap deflection, it would complicate the analysis enormously because now the measurement would be a function not only of alpha but of alpha and flap position.

Angle of attack (alpha) depends on where you measure it. Many texts for pilots incorrectly show the air streamlines approaching the airfoil in a straight path and being deflected downward after passing over the wing. This is done because the author wishes to explain lift by stating that the wing forces air down and, according to Newton's third law this must force the wing up (exactly what physical mechanism forces the wing up is never explained). But, this diagram is incorrect. The wing creates a pressure pattern in advance of it's arrival and the result is an upwash ahead of the wing. Numerically, half the lift is due to the upwash ahead of the wing and half is due to the downwash behind the wing. So when defining angle of attack it is important to note whether you are talking about the airflow near the leading edge or the free air far in advance of the wing.

While zero pitch on a properly calibrated attitude indicator indicates level flight, it does not indicate zero alpha. In level flight, the wings must generate enough lift to balance the weight and the tail down force. This will generally result in a positive alpha dependent on airspeed. The tail down force can be calculated by knowing the arm to the tail and the airplane moment, but taking 10% of the airplane weight is probably good enough for a rough estimate. Thus, the lift would be 1.1 x the aircraft weight and the coefficient of lift can be determined by solving the lift equation for it: L = 1/2pV²C_LS where p is the air density, V is the TAS, C_L is the coefficient of lift and S is the wing area. S can be obtained from the Service Manual. Once you have the coefficient of lift, you can use the curve I supplied earlier to figure out alpha.

I hope this helps. @Blue on Top might want to chime in -- he's a real aeronautical engineer that does this for a living. I'm just an electrical engineer that just enjoys trying to understand things.

Skip

 

 

Hi Skip,

It is always a pleasure to interact with very knowledgeable people like you. Since my background was electrical engineering and computer sciences I actually abhorred mechanical engineering, thermodynamics and fluid dynamics. Otherwise would have gone into mechanical engineering...  However, have not done any engineering in a very long time. Therefore, I am a basically a "student" in aerodynamics at this time and really enjoy learning from people with more experience. Nevertheless, I will also go out and perform an experiment on whatever concept I may or may not be clear about such as the video I made on stalls. 

I see your point on chord line remaining the same with or without flaps. I was definitely aware of the need for angle of incidence in order to have some positive alpha at cruise with close to zero pitch. As I mentioned in my prior post I plan to go out and do another flight maintaining level flight while doing the stalls so I can compare the pitch attitude for both configurations. Simply add the 2.5 deg of incidence to the pitch and that will be the critical AOA (alpha). Won't even try to estimate the theoretical (and as you say not necessary) added alpha of the supposed new chord with flaps down. It will simply be a comparison of critical AOA for the main portion of the wing in both configurations.

Based on various comments I have explored some more aerodynamic theory doing more in-depth reading, etc.  In my wanderings I found this NACA wind tunnel video that shows how slotted flaps actually delay the separation of airflow on top of the wing, which can explain how speed brakes actually increase stall speed by interfering with the now more "attached" airflow. I am including the link to the video starting at 7:37 which shows the effect of slotted flaps.

Hope @Blue on Top chimes in....

Regards,

Chris

https://youtu.be/ZpoK0InPciM?t=457

[Oscar Avalle]

19 hours ago, Fly_M20R said:

Hi Oscar,

I really enjoyed your video and the music was perfect! 

The following comments come from me as still a beginner in videography:

I actually still find it a bit difficult to "be myself" when I do my videos but that is what comes through best. One appears fairly rigid when trying to "act" in a "professional" manner or what one imagines the audience would like to see. I often find myself acting a bit different than "me". Of course, it is important to enunciate well otherwise one does not come through intelligibly (I can tend to mumble at times). It appears as if the audience does like to see one's face every once in a while rather than just panel or outside view. Need to get over stage fright!! We all have stage fright!

You can record your transmissions and actions during your takeoff, parts of cruise and landing. 

How long was your flight on this video? I ask because the outside cameras can be controlled to record and stop recording via their own wifi network but still use up battery during idle time and I found it difficult to get more than maybe 1-1/2 hrs out of them. If your flight was longer than that then how did you preserve battery? Great views!!

I think that having the landing at 1x recording speed would have been nicer than at 2x (or 3x) as you had. People enjoy watching landings! I have a framed caricature that says "Flying is man's second greatest thrill. Landing is the first"!!

Chris

Chris,

For work I have been interviewed on TV several times and I had to deliver statements etc. You are absolutely right the best thing it to be yourself. Next video I am going to try to speak and comment what is going on... let's see how it goes.

The flight was close to 3.5 hours. My main problem was always battery life for the outside cameras. I tried the wifi option but somehow it never really worked. I found some cheap, very simple, cameras that have a battery life of about 4 hours. No thrills, but decent video quality at 4K. The brand is "Drift". I turn them on before I get into the plane and then I leave them on until I arrive. Tons of video footage. 

Good advice on not accelerating landings. You are absolutely right. I always enjoy watching others land their planes. 

Oscar