Maximum IAS for half flaps on M20J

[Jer]

Folks:

 

My POH says 115 KIAS for Vfe at full flaps but is silent on partial flaps.  Anyone have any comment about a higher allowable speed at half flaps?

 

Jerry

[ilovecornfields]

TL:DR

Lots of comments.

Little definitive guidance.

Conservative approach:  Use 115 KIAS for any degree of faps.

Other approach: Make up an arbitrary speed and choose that as your partial flap setting because - well,  no one said you couldn’t.

 

[PT20J]

We have hashed this out before. The only model that has a higher flap speed listed in the the TCDS and AFM/POH for partial flaps is the M20J/205. All other models only have a single speed listed, so that applies to all flap deflections.

People get confused by the language used in the POH to define Vfe but that is simply the language dictated by the FAA for specifying limitations. But realistically, if there is only one speed listed, how would you know what higher speed would be safe were you to make up your own speed? If you are going to do that, why not go for broke and just put in approach flaps at Vne?

Skip

[ilovecornfields]

2 minutes ago, PT20J said:

We have hashed this out before. The only model that has a higher flap speed listed in the the TCDS and AFM/POH for partial flaps is the M20J/205. All other models only have a single speed listed, so that applies to all flap deflections.

People get confused by the language used in the POH to define Vfe but that is simply the language dictated by the FAA for specifying limitations. But realistically, if there is only one speed listed, how would you know what higher speed would be safe were you to make up your own speed? If you are going to do that, why not go for broke and just put in approach flaps at Vne?

Skip

But, they didn’t explicitly say I couldn’t make up my own speed so I use 9*sqrt(tire pressure) + 1/2 wind gust component because I know better than those dumb lawyers writing the AFM.

[Raymond J1]

3 hours ago, ilovecornfields said:

But, they didn’t explicitly say I couldn’t make up my own speed so I use 9*sqrt(tire pressure) + 1/2 wind gust component because I know better than those dumb lawyers writing the AFM.

With floats, what pressure do you use?... 

[Raymond J1]

3 hours ago, PT20J said:

We have hashed this out before. The only model that has a higher flap speed listed in the the TCDS and AFM/POH for partial flaps is the M20J/205. All other models only have a single speed listed, so that applies to all flap deflections.

People get confused by the language used in the POH to define Vfe but that is simply the language dictated by the FAA for specifying limitations. But realistically, if there is only one speed listed, how would you know what higher speed would be safe were you to make up your own speed? If you are going to do that, why not go for broke and just put in approach flaps at Vne?

Skip

The US POH of an 67F as :

"(d) White Arc- 64 to 105 MPH CAS (Denotes Speed Range in which Flaps may be Safely Lowered)

-Maneuvers involving approach to stalling angle or full application of elevator, rudder. or aileron should be confined to speeds below maneuvering speed.

- No snap maneuvers or whip stalls are approved at any speed.

- No inverted or acrobatic maneuvers, including spins, are approved ."

 

The French POH for the same plane as :

For the flaps : Page IV-20 : "...Ne pas sortir les volets à une vitesse indiquée supérieure à 125 MPH, ne pas dépasser Vi 125 MPH avec les volets sortis...

Page IV-15 : "Cet avion doit être utilisé comme un avion de catégorie "Normale"... Aucune manoeuvre acrobatique, y compris les vrilles, n'est autorisée..."

Page IV-16 : "Vrilles : Les vrilles volontaires ne sont pas autorisées pour cet avion ; Cependant, l'avion peut se mettre en vrille si la sortie de décrochage est retardée ou si l'avion est maintenu en décrochage d'une façon non coordonnée...

En cas de départ en vrille, appliquer immédiatement les consignes de sortie suivantes :

-Ramener les ailerons au neutre et réduire les gaz,

-Pousser le palonnier vivement dans le sens opposé à la rotation,

-Pousser rapidement le volant sur l'avant pour abaisser le nez de l'avion,

-Garder le palonnier à fond dans le sens opposé jusqu'à l'arrêt de la rotation,

-Sortir du piqué qui en résulte.

Si la manoeuvre de sortie de vrille n'est commencée qu'après un tour complet de vrille, la rotation peut continuer pendant un tour supplémentaire après l'application des consignes sur les commandes.

La perte d'altitude pendant un tour de vrille et la manoeuvre de sortie peut atteindre 2000 ft (610 m), les décrochages à basses altitudes sont donc très dangereux.

Pour l'entrée en vrille, l'avion va partir en roulis, pratiquement comme pour un tonneau barriqué. Les ailes seront presque verticales au premier quart de tour de la vrille. Après environ 1/2 tour, les ailes sont presque horizontales, mais le nez de l'avion sera très bas, presque vertical. Après un tour complet, le nez va un peu se relever. La rotation pendant la première partie de la vrille est très rapide, avec risque de désorientation des occupants...

Il a été démontré que l'avion sort d'une vrille après un décrochage prolongé, jusqu'à 1 tour de vrille. La marge d'un tour est compromise lorsque la manoeuvre de sortie n'est pas entamée à la première détection de l'approche du décrochage.

There is therefore no setpoint on the position of the flaps during the spin, which suggests that they have a "counter" effect.

 

 

 

[mike_elliott]

6 hours ago, ilovecornfields said:

But, they didn’t explicitly say I couldn’t make up my own speed so I use 9*sqrt(tire pressure) + 1/2 wind gust component because I know better than those dumb lawyers writing the AFM.

but that's for knots! unless your ASI is marked in knots you must use mph

[ilovecornfields]

1 hour ago, mike_elliott said:

but that's for knots! unless your ASI is marked in knots you must use mph

Mine is in knots, of course. I’m a pretty smart guy too so when I know I’m going to fly into a busy airport like LAX I overinflate the tires by 20 psi so I get can that first notch of flaps in sooner.

[Ibra]

Somewhere between VFE(full flaps) and VNE(clean flaps), asking what is the speed for 1/2 flap in Mooney is very odd: you can select any flap setting with a continious dial? 50% of cockpit indicator? 50% of flap degrees? 

You can interpolate between VFE and VNE but remember aerodynamic forces go quadratic in speed and you don't want to re-test harmonics and flutter near VNE with partial flaps 

In M20J putting 1/2 flaps down & up at gear extension speed is OK, the ASI white arc says 115KIAS: it's hard to beat the good habit of doing things within the white arc !

There are load of aircraft with discreet flap selection where VFE and VS are published for the various flap angles, that should give you an idea of how much room you have, on that data you could argue VFE+10kts is likely fine for 1/2 flaps while VNE is not OK...

Edited December 19, 2022 by Ibra

[A64Pilot]

9 hours ago, PT20J said:

We have hashed this out before. The only model that has a higher flap speed listed in the the TCDS and AFM/POH for partial flaps is the M20J/205. All other models only have a single speed listed, so that applies to all flap deflections.

People get confused by the language used in the POH to define Vfe but that is simply the language dictated by the FAA for specifying limitations. But realistically, if there is only one speed listed, how would you know what higher speed would be safe were you to make up your own speed? If you are going to do that, why not go for broke and just put in approach flaps at Vne?

Skip

I know someone who accidentally did a 180 kt low approach once with takeoff flaps, he was wondering as he did it why it wasn’t 190 ish kts.

No harm was done, but if done often it’s very likely fatigue would have set in.

But VFE is often just an arbitrary number that a manufacturer picks that they think is good enough then do testing to substantiate that number, they don’t test to failure then back off ten percent very often at all, maybe Boeing does who knows.

‘But example the Thrush was originally a piston airplane, that Serv Air got an STC to put a turbine on, and airspeed numbers stayed the same, Fred Ayres bought Thrush and the STC and started manufacturing turbine Ag planes, that could exceed VNE in level flight.

Later he went out of business,  Thrush was bought by new owners and I came  aboard and wanted to modernize the aircraft, GE engine became a thing so we had talks with them and I got to modernize the old Thrush, now the flaps for example were identical on the GE as the old Thrush, but the new VFE was higher than the PT-6 powered VNE as was all the other flight speeds and other things, like gross weight went from 6,000 lbs to 10,500 lbs, but the airframe was the same with relatively minor difference like we tightened up the flight control balance requirement to bump VNE from 158 MPH to 196 MPH if memory serves. But none of the limits were actual limits, every one of them were numbers that were considered to be “good enough”. Other than flutter we don’t know the speeds at which something bad will happen and flutter was only determined by ground test, no one went out and found flutter of course.

Even then that’s not even close to the real VNE, it’s likely well over 200 kts, I mean way over 200 as we had a HUGE flutter margin and the structure is very strong, automotive safety glass windshield for example to take bird strikes. Flutter terrifies me.

But and here is the problem, some limits are real no kidding real limits and the manufacturer had to work hard to get them, but nothing tells you which ones are “real” as in exceed this number and you may kill yourself from the limits that were set as some number that was decided to be plenty. Plus fatigue is a real thing, that dummy that made a low pass at 180 kts with T/O flaps if he did it very often I bet fatigue would break something.

Then CAR 3 airplanes under Certification did not have to test for fatigue, the only requirement was that fatigue had to be considered 

[Fly Boomer]

52 minutes ago, A64Pilot said:

Other than flutter we don’t know the speeds at which something bad will happen and flutter was only determined by ground test, no one went out and found flutter of course.

How do you do a flutter test on the ground?  Big fans?  Wind tunnel?

[Will.iam]

12 hours ago, Jer said:

Folks:

 

My POH says 115 KIAS for Vfe at full flaps but is silent on partial flaps.  Anyone have any comment about a higher allowable speed at half flaps?

 

Jerry

I wonder if people are asking what higher speed they can use partial flaps are wanting to use them to help slow down as they don’t have speed brakes or they would be using those instead. I think this thought process comes from trainer aircraft where their flaps are more effective drag. Mooney flaps offer very little drag in comparison. If you want to slow down and did not plan far enough back to come down at a shallower angle or ATC slam dunk you, throw the gear out. It has a higher extend speed than the flaps and once down and locked a higher speed extended. Plus you will not land gear up as they are already down unless you retract them in the pattern and who does that?The flaps are really for lowering your stall speed so you can fly at a slower speed to land and stop in a shorter distance. Not an issue when you are too fast to even deploy them. 
the A320 airliner is no different in this regard. We plan 3 x your alt + 10 miles so at 35,000 we need to start down 105 + 10 = 115 miles from the airport at normal cruise speeds and 250kts at 10k feet.  The extra 10 miles is what it takes to slow from 250kts to approach speed about 140kts on an middle weight landing A320. If the controller slows our descent then we need more distance away from the airport to get down. Any closer and we have to start using speed brakes.  We tell ATC all the time we can slow down or go down but not both which one do you want? They usually take the get down option and we slow down once we are closer to the airport. But sometimes ATC will vector us so we get the time and distance to get down if we are really too high / fast as no one wants to go around because we were too high or fast to land. 
 

for my mooney planning descent from 12,500 ft I use 500ft vvi going down. This puts me at 180kts in the descent. This allows me to keep the power up to not shock cool the engine and regain time lost in the slow speed the climb was at the begging of the trip. At 180kts you are traveling 3 miles a min and at 500ft per min descent to a 1000ft pattern alt above a sea level based airport is going to take you 23 mins or 69 miles in light winds. If you have a strong head or tail wind you adjust accordingly but you also have to slow down at 180 down to 80 I find takes about 7 or 8 miles depending on how far back on the manifold pressure you pull by now in that long descent your cyl temps are well below 350 and most of mine are below 310 so no shock cooling now  if  you miscalculated and need to goto idle to really slow down at 1000ft above the field. And if a straight in to land and i bump the distance back another 5 miles for descending the last 1000ft to land. So I start my descent to land from 12,500 at 83 miles out! This keeps me from having to use speed brakes and avoids shock cooling the engine. If it’s going to be bumpy i plan same 500 vvi descent but use 150kts so 2.5 miles per min. If very bumpy 120kts so 2 miles a min i use speed brakes here to keep my engine power up but using gear at 120 kts works very well too. 

[PT20J]

Bob Kromer told me that the reason for not carrying the higher takeoff flap setting speed forward from the 205 to later models was that the need for a higher flap speed was obviated by the speed brakes.

Mooney flaps are more effective in reducing stall speed than a lot of other single engine airplanes, but they produce less drag than many. This is why people used to Cessnas think that the Mooney flaps are ineffective.

Skip

[exM20K]

2 hours ago, PT20J said:

Bob Kromer told me that the reason for not carrying the higher takeoff flap setting speed forward from the 205 to later models was that the need for a higher flap speed was obviated by the speed brakes.

Interesting, and that makes sense to me.  

Speed brakes are good for 20ish KIAS all other stuff being unchanged.  This permits a very quick slow-down to gear speed from the descent.

[A64Pilot]

4 hours ago, Fly Boomer said:

How do you do a flutter test on the ground?  Big fans?  Wind tunnel?

You hire a Flutter DER of which there aren’t many, but they take large drivers, think great big Woofers that instead of a speaker cone drive a rod, ones our guy used were actually made by JBL, you attach them to different spots on the airplane with it on jacks and he shakes the airplane, oh it has accelerometers mounted to the aircraft too, he’s looking for vibration frequencies that excite the natural frequency of the flight control and wings etc, you do this at different weights too. Called a GVT for ground vibration test

Contrary to common belief it’s not a guaranteed science, but it’s pretty darn close, but once in a while they miss so you still have to go out and do dive tests to validate the ground vibration tests, and once in a blue moon you can get flutter and sometimes the time interval from onset of flutter to disintegration can be very short, even less than 1 sec. so sometimes there is nothing a pilot can do but hopefully get out.  But there are others forms of flutter like whirl flutter which is a propellor flutter, even if you change props a vibe survey must be done, Hartzell has so much data that most often they can do that by analysis.

But apparently the natural harmonic frequencies found on the airframe and flight controls can be attributed to airspeeds. For whatever reason, I think stiffness is key, but the Thrush is very unlikely to get into flutter.

[Will.iam]

8 minutes ago, A64Pilot said:

You hire a Flutter DER of which there aren’t many, but they take large drivers, think great big Woofers that instead of a speaker cone drive a rod, ones our guy used were actually made by JBL, you attach them to different spots on the airplane with it on jacks and he shakes the airplane, oh it has accelerometers mounted to the aircraft too, he’s looking for vibration frequencies that excite the natural frequency of the flight control and wings etc, you do this at different weights too. Called a GVT for ground vibration test

Contrary to common belief it’s not a guaranteed science, but it’s pretty darn close, but once in a while they miss so you still have to go out and do dive tests to validate the ground vibration tests, and once in a blue moon you can get flutter and sometimes the time interval from onset of flutter to disintegration can be very short, even less than 1 sec. so sometimes there is nothing a pilot can do but hopefully get out.  But there are others forms of flutter like whirl flutter which is a propellor flutter, even if you change props a vibe survey must be done, Hartzell has so much data that most often they can do that by analysis.

But apparently the natural harmonic frequencies found on the airframe and flight controls can be attributed to airspeeds. For whatever reason, I think stiffness is key, but the Thrush is very unlikely to get into flutter.

Hum that is interesting. Was sure you were going to say big wind tunnel.

[Fly Boomer]

8 minutes ago, A64Pilot said:

You hire a Flutter DER of which there aren’t many

Wow!  Never knew there was such a thing.  Thanks.

[A64Pilot]

3 minutes ago, Will.iam said:

Hum that is interesting. Was sure you were going to say big wind tunnel.

Back when it was North American Rockwell the Thrush became the only Ag plane to be put in a wind tunnel, apparently there is a full size one at NASA / Langley
https://ntrs.nasa.gov/citations/19790052733

But that was before my time so I didn’t see it, but they did a lot if testing on aerodynamics to include a razor back that greatly improved aerodynamics of the fuselage and led to the dual cockpit version.

[Pinecone]

HP used to have a system that could do this.  It had sensors that were attached at various locations, then you tapped on the structure with a little hammer that had force and acceleration sensors.

It would do a vibrational analysis.

It wasn't designed for aircraft, but it would work.

[A64Pilot]

1 hour ago, Pinecone said:

HP used to have a system that could do this.  It had sensors that were attached at various locations, then you tapped on the structure with a little hammer that had force and acceleration sensors.

It would do a vibrational analysis.

It wasn't designed for aircraft, but it would work.

The hammer thing is also done in a GVT, not sure why, I watched and he was too busy to talk much, I did ask a few questions and you could tell he wasn’t in a talkative mood. He didn’t hit it hard but did smack it in different locations, dead blow hammer.

[Jer]

Thank you all for sharing your thoughts.  Ibra commented that it was strange I ask about "half" flaps when the application of the flaps is continuous.  I was really referring to "takeoff" flaps as indicated on the indicator, and as per other comments, yes I was contemplating throwing these in along with the gear when decelerating through Vlo in an effort to slow the plane.  Per the numerous comments stating that the Mooney flaps don't offer much drag, I really don't see the point in pressing the issue.  I must confess that recently I neglected retracting the flaps from the takeoff setting and got into  cruise which exceeded Vfe significantly.  The poor performance finally tipped me off and I retracted the flaps.  I looked for damage and noted none, but I don't intend to do that again.

Jer

 

 

[Pinecone]

15 hours ago, A64Pilot said:

The hammer thing is also done in a GVT, not sure why, I watched and he was too busy to talk much, I did ask a few questions and you could tell he wasn’t in a talkative mood. He didn’t hit it hard but did smack it in different locations, dead blow hammer.

It sets up vibrations and the sensors read this and can pick out resonance frequencies.

I was working for HP at the time (computer side) and got to be good friends with one of the instrument guys.  He had done a glider.  I tried to get my flying club to let us do one of the 172s, but they declined.

For the glider, the screen had a wire frame graphic and you could input excitations in and what the structure out do.  Hit a resonant frequency, and WOW.

[kortopates]

Thank you all for sharing your thoughts.  Ibra commented that it was strange I ask about "half" flaps when the application of the flaps is continuous.  I was really referring to "takeoff" flaps as indicated on the indicator, and as per other comments, yes I was contemplating throwing these in along with the gear when decelerating through Vlo in an effort to slow the plane.  Per the numerous comments stating that the Mooney flaps don't offer much drag, I really don't see the point in pressing the issue.  I must confess that recently I neglected retracting the flaps from the takeoff setting and got into  cruise which exceeded Vfe significantly.  The poor performance finally tipped me off and I retracted the flaps.  I looked for damage and noted none, but I don't intend to do that again.
Jer
 
 

You wouldn’t be able to see possible damage, if any, from outside the plane. It won’t hurts the flaps but can crack the subspar and flap motor bracket. A proper inspection requires removing the belly pan and inspecting from under. Don’t worry though, we’ve all done it, hopefully it wasn’t long. But i won’t use any flaps till flap speed. aircraft that have a higher partial flap speed have the Vspeed for it listed.


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