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Spins prohibited

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46 minutes ago, David Lloyd said:

 

Sorry, back to the OP.  Spin testing was done. If the airplane would not come out of a spin under certain circumstances dictated by the FAA, the airplane would not be certified.  There are other things in consideration for not allowing spins, some of which are at the say of the manufacturer.  One would be as others pointed out, a nose low attitude during recovery.  As others have said, aslick airplane builds speed quickly when the nose is pointed straight down.

Most common reason for lack of spin certification is lack of interest by the manufacture. This was the case with Mooney according to Bill Wheat. Its also why brand new Cessna 172's are spin prohibited.

-Robert

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3 hours ago, kellym said:

Uhhem,

Either I misunderstand what you are trying to say or you don't really understand the situation.  The issue with Vne is not while IN a spin, it is during the recovery, after you have stopped the rotation, because you will be at a very nose low attitude, gaining speed rapidly.  Holding a Mooney in a spin isn't the problem, it is getting out of the spin, and it is necessary to both stop the turn and break the stall, which requires forward pitch long enough to break the stall, and then restoring a normal attitude at a rate that doesn't generate a secondary stall and doesn't exceed Vne.  The Mooney rudder is not particularly effective at stopping the turn.  A Cessna takes effort to initiate a spin and maintain it. The Mooney is very different.

A spiral is normally encountered when in IMC and when not realizing you are turning.  It has very little in common with a spin or spin recovery, although I suppose if the turn isn't fully stopped in a spin recovery it could happen. I'd like to hear thoughts on the subject from experienced CFII.

You are referring to a graveyard spiral.  A spiral is defined in AC 61-67C reasonably well.  "Many airplanes will enter a spin but the spin will become more vertical and degenerate into a spiral".  In Bill Kershner's Student Pilot Flight manual he explains the maneuver to the left in part "Once the spin is established, you can maintain it as long you like with full up-elevator and full left rudder.  Relaxing the back pressure will result in some airplanes going from the spin into a spiral".  There is a video of one of his trained CFI's doing a lot of rotations in a C150 from 17500 straight on down, air speed is consistent, rotation is consistent, it is a text book maneuver of a spin.  

There is a fair amount of stuff out there from Bill Wheat and Bob Kromer on spinning a Mooney.  My experience has been if you lose the spin in a Mooney, what happens next happens very fast.  Best not to play around with.

In short a spin is an aerobatic maneuver which is benign in aerobatic airplanes, spirals kill people. 

 

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The Mooney tail is relatively weaker than the wing because it doesn't need to be as strong and adding structure puts weight aft where you don't want it. On any airplane, something is going to break first when you exceed the ultimate load. From an occupant's perspective, it doesn't really matter which part fails.

Regarding spins, the CAR 3 requirement (3.124 - see attached) for a Category N airplane weighing less than 4,000 lbs. is to recover from a one turn spin in one and a half additional turns without exceeding Vne or the limit load factor. Given that the Mooney was designed for transportation and not acrobatics, it would be a waste of time and money for the manufacturer to test beyond the certification requirements. 

My understanding is that a one turn spin is generally considered incipient rather than fully developed. Recovery from a fully developed spin may be more difficult. I have spun a Citabria, Decathlon, C-150 and C-172. A two turn spin in each lost around 1000' if I recall correctly. BTW, according to my C-172S POH, intentional spins are still approved in the utility category.

Bob Hoover used to perform five turn spins in the Shrike as part of his airshow routine until it went flat on him one time and he had to use all his test pilot skills to recover. To quote him, "I had been performing spins in the Shrike for twenty years and would have bet anything that it would not go flat. That experience taught me differently. I omitted the spins from my performance." (Forever Flying, chapter 25). So, if you get away with it once (or a hundred) times, the next one might be different. It's only the last one that counts.

I believe Ron @Blue on Top has some experience in this regard and may have some thoughts to add to the discussion.

Skip

CAR-PART3.pdf

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8 hours ago, kellym said:

A spiral is normally encountered when in IMC and when not realizing you are turning.  It has very little in common with a spin or spin recovery, although I suppose if the turn isn't fully stopped in a spin recovery it could happen. I'd like to hear thoughts on the subject from experienced CFII.

A spiral and a spin are completely different aerodynamically. In a spiral, the wing is not stalled and the airplane is in a steep descending turn. The outer wing has greater airspeed than the inner wing and is creating a rolling moment that perpetuates the turn. In a spin, the wing is stalled, however the angles of attack are different and this causes the auto rotation. 

A spiral will not become a spin, but improper spin recovery, or botched spin entry, can turn a spin into a spiral. The standard spin recovery technique is PARE - Power to idle, Ailerons neutral, Rudder held opposite the rotation, Elevator forward to reduce angle of attack. The rudder comes first because it is necessary to reduce or stop the rotation before breaking the stall. If the elevator is applied first, there is a possibility that the spin will stop and a spiral begin. A spin will not exceed any load or airspeed limits, but a spiral easily can especially during recovery. The recovery from a spiral is power off, coordinated roll to level the wings, and control pitch with elevator which may require a healthy push if the airspeed has gotten far above trim speed.

Skip (CFII)

Edited by PT20J

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Many planes are not "Spin Certified" and really what's the point unless it is certified in the acrobatic category. Diamond DA 40 NG aircraft are prohibited from spins too but they sure seem to spin pretty well...

 

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I usually don't have much to add do to a lack of knowledge on most threads on the MS and this may fall into that same scenario. Back before my Mooney ownership we were the proud owners of a nice little C150 that I bought to train in. During that time the FAA issued an AW directive advising that intentional spins were prohibited. The reason given was two incidents where following accident investigation found that the rudder could become jammed or caught on the fixed rudder stops on the tail. The two options to resolve the issue was to install larger bumpers on the stops or to mount a placard on the panel stating intentional spins prohibited. IN the two investigationss one was an airplane that was out of annual and the other was undetermined if the stuck rudder was the cause or if it was resultant of the impact. This was two incidents out of a fleet of over seventeen thousand 150's. The consensus was that the addition of the rubber bumpers would in fact reduce rudder athority. As mentioned before it takes very quick and full control deflection to get the 150 into a true spin.  Lots of fun by the way. My point is there are many different reasons for spin restrictions. I opted for the placard on the panel and then from that time forward I would only accidentally spin my 150.

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1 hour ago, bonal said:

 I opted for the placard on the panel and then from that time forward I would only accidentally spin my 150.

:)

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2 hours ago, RobertGary1 said:

Just like the old rumor that twins cannot be recovered from a spin.

It is important I think to make the distinction between performing a maneuver and ending up in an unusual attitude.  A spin as a demonstrated maneuver is PARE and is a non event for the most part.  
 

An inadvertent spin is probably not going going to be recognized prior to proceeding to a spiral or impacting the ground (base to final turn).  Obvious exception is when demonstrating stalls where you can anticipate it which is why it is a required training for CFI’s and the only acrobatic maneuver exempted from chute requirements.

Just like stall training it is to understand and avoid primarily   The odds of actual recovery from an inadvertent spin are not going to be very good in a high performance aircraft. 

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There used to be an eye opening video of some dude in a white shirt with two other people in maybe an F model stalling and inadvertently spinning over a lake on YouTube. Can’t find the link but that was an eye opener. 

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9 minutes ago, bradp said:

There used to be an eye opening video of some dude in a white shirt with two other people in maybe an F model stalling and inadvertently spinning over a lake on YouTube. Can’t find the link but that was an eye opener. 

Here you go...

 

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So much for PARE recovery - that looked like it was not fully developed-  but looked like power was on, right aileron and forward elevator- may not have helped.  Hope the pants weren’t white as well.   It gets away quickly doesn’t it.  

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During filming of the movie "Boots", I asked the late Mike Miles [beloved Mooney test pilot] about doing spins in the Mooney.   Mike said yeah, he did all kinds of configurations for spins and many were video recorded  from chase planes..............cause nobody wanted to ride along with him.........LOL!

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I love all the previous discussions … Yes, I went all the way back through the 2013 posts and attachments :) .  Yes, I'm a total aero  geek.

So, all the previous discussion is very typical of everyone talking about stalls, spins and spirals.  Mooney people are no different in that respect.  Then @PT20J (Skip) comes along and ruins all the "There I was, flat on my back" stories :lol: with the regulations (reality).  Yes, the M20 (and all aerodynamic model changes) had to pass the 1-turn "spin" and recovery tests.  These are called spin tests because they are in that section of the regulations.  At one turn, the airplane has not advanced into a developed spin yet.  More on this shortly.

During the stall testing, the airplane is not allowed to roll more than 15 degrees OR pitch down more than 30 degrees (or it would be noted in the POH) with normal use of the flight controls and without exceptional pilot skill (iow, you and me flying).  If your airplane can't do this, something needs to be looked at/adjusted.  Now let's go after the spin/spiral.

Odds of spinning (and not spiraling) are low - unless you continue to input pro-spin controls.  With that said, both events are extremely frightening the first many times.  Most pilots when the nose drops 30 degrees will tell the story that they were pointed straight down.  The stories get bigger in a spiral as the nose is much lower … still not pointed straight down.  Here's how we tell the difference (and the DA video is good to watch).  If airspeed is near stall speed and not increasing, the airplane is in a spin (stalled).  If the airspeed is increasing, the airplane is in a spiral (not stalled).  Recovery from a spin is into a spiral (you must lower the nose to reduce the angle of attack (AOA).  Yes, the angle of pitch will be very nose down, and pushing at that point is counter intuitive (which is why people don't do it … and we have fatalities), but that is what is required.  So, the airplane will recover very nose low (good video over the lake).

Once the airplane is in a spiral (and as others have mentioned), it will pick up speed rapidly (drag of the airplane is not a huge factor … more soon).  Roll wings level and pull, now.  If you want to know the force you will need to pull, try to pull 3.8G in a level turn.  It will surprise you how heavy that is.

Now for the drag vs. "pick up speed rapidly" follow up.  Think of how long it takes for the airplane to accelerate in level flight from 70 knots to Vh (maximum level speed).  The propeller is producing (I'm guessing here … and it depends greatly on your model) 600 down to 200 lbs. of thrust (the faster you go, the less thrust is produced).  Now, let's look at the physics of the airplane.  In level flight, the weight is producing no "thrust" (force along the longitudinal axis).  At an AOP (angle of pitch) of -7 degrees, the weight is producing a "thrust" of 10% of the weight of the airplane (~250 lbs.).  When the nose is down 45 degrees, the weight is giving a "thrust" of 70% of the weight of the airplane (1,500 lbs.).  You get the idea.  The weigh component at 70 degrees nose down is >> than the thrust of your propeller … even statically (where propeller thrust is the highest).  The airplane no matter how draggy will gain speed very rapidly.

Bottom Line: It is not during the spin that things may wrinkle, it is in the recovery (spiral) that speed will be increasing very rapidly.

Hope this helps.  Civil bantering appreciated.

Keep the Blue on Top.  -Ron 

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There was a brief mention of aileron use very early in this thread, and it reminded me of the first stalls I experienced as a pre-solo student in a C-152.

My instructor had me doing departure stalls and kept talking about using rudder to keep the wings level (she had not to that point told me why - I was about to provide that lesson for myself). I did what had worked for me up to that point and used the ailerons to keep wings level. Just before the wing stalled, it quite working, the wing dropped, and it seemed like I was staring straight down through the windshield. My instructor took over and recovered before a spin developed. 

I learned from this that increasing the AOA of a wing at the point of a stall by the use of ailerons results in the wingtip stalling first and potentially a spin entry. In more than 2500 flight hours from then to now, in many different airplanes, when practicing stalls, I use the rudder to keep the wings level.

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2 hours ago, flyer338 said:

I learned from this that increasing the AOA of a wing at the point of a stall by the use of ailerons results in the wingtip stalling first and potentially a spin entry. In more than 2500 flight hours from then to now, in many different airplanes, when practicing stalls, I use the rudder to keep the wings level.

@flyer338  Thanks for the real world example!

This is also a great example of where pilots and aerodynamicists think differently.  I'm hoping all y'all teach me enough guidance so that I do not upset the FAA and pilot organizations when I tell them that changing the AOA/chord line is really not how it works :).  As a pilot (and the FAA, currently … and I wear both those hats, too), it is being taught that when a flap or aileron goes down, it increases the angle of attack.  Yes … and no.  One could say that the LOCAL AOA has increased (but it is not proportional to the actual, physical new chord line (line drawn from the leading edge to the new trailing edge).  The situation is simply not that simple.  Allow me to clarify.

Aerodynamicists plot a curve of local stall AOA (relative to a singular aircraft AOA) versus wing span location.  In other words, at what aircraft AOA will that section of the wing stall.  We design the wing through changing airfoils, thicknesses, chord lengths, twist, stall strips, etc. to have the wing stall progress from inboard to outboard (so the ailerons remain effective through the stall).  I know that's a lot in a couple sentences.  Basically, we think of the aircraft AOA required to stall that local area.  Why?  We only know/measure one, singular AOA that is measured locally and converted to the aircraft as a whole.

If one thinks of a down aileron (or flap) as the AOA increasing, one is forgetting that the camber is also changing and/or a slot may be opening, etc. In other words, it's a different airfoil completely.  We can agree that the wing is being asked to work harder in that area and will therefore stall at a lower angle of attack.

Let the volleys begin :) 

PS.  Bonus information: As a word of caution, current regulations do not require stall warning to give any warning before a departure initiated by the ailerons.  Follow-on:  A stall initiated the ailerons will develop into a spin (the down aileron causes asymmetric yaw .. the second ingredient required for a spin (the stall being the first)).

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I was looking at the specs in the M20J service manual and noticed something I never noticed before. In addition to changing the airfoil from root to tip, there is also a geometric twist of -1.5 deg. BTW, I know aerodynamicists are just making educated guesses when they design some of these parameters because I never see something like  -1.387 degrees ;)

Cessna singles have relatively longer span, shorter chord ailerons than Mooneys. How does that affect roll control at and near stall?

Skip

 

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54 minutes ago, PT20J said:

I was looking at the specs in the M20J service manual and noticed something I never noticed before. In addition to changing the airfoil from root to tip, there is also a geometric twist of -1.5 deg. BTW, I know aerodynamicists are just making educated guesses when they design some of these parameters because I never see something like  -1.387 degrees ;)

Cessna singles have relatively longer span, shorter chord ailerons than Mooneys. How does that affect roll control at and near stall?  -Skip

@PT20J  Skip: So … we don't always say all we know? :lol::D:lol:  There's not enough time :D.  Sure glad MooneySpace doesn't count these emojis :lol::lol::lol:!  Let's start with the basics.

The stated airfoil on an airplane is typically the base or starting airfoil.  If (when) a company modifies that airfoil, it probably won't tell the public (or anyone outside of that small design group); it's company (or even department) proprietary data.  The airfoil is modified to produce a certain CLmax, Cm (pitching moment) and/or CDcruise for that airplane.  In Advanced Design, the airfoil, wing planform, twist, dihedral, etc. are varied to produce the final wing (and expected coefficients).  Although the M10 wing is physically straight tapered, it was designed to produce a perfect, elliptical lift distribution.

So on the twist (and as you estimated), twist is typically input in whole degrees and then 0.5 degrees after we get close.  Smaller increments are a waste of time.  But, with the current desk top CAD and CFD programs, we can run many iterations in a day (Al and Art didn't have that luxury).  In Al and Art's days, the twist was also linear.  IOW, if a wing was twisted 2 degrees, it would be twisted 1 degree at half span, 0.5 degrees at 1/4 span, etc.  You get the idea.  With the speed and modeling capabilities we have today, we also tailor where twist occurs spanwise.  For example, the wing may not have any twist in the flap section (much easier to manufacture the wing, flap, flap tracks and flap operating mechanisms) and have all the twist in the aileron section (smaller loads and smaller parts).  Plus, we are only trying to protect stalling the aileron section (at the price of cruise drag).

So, Cessna SE flap/aileron ratios are planform/manufacturing driven.  As one can look at the larger Cessna SE airplanes where they tried to continue the flap into the outboard, tapered section, hence the flap becomes more of a "best" compromise solution.  Higher percentage chord ailerons, especially with lower Rn (smaller tip chords), work the airflow harder and are more likely to separate at a lower aircraft AOA.

I'll repeat an earlier warning, regulations do not require full and rapid aileron input at or near stall.  As a direct result, there are airplanes that will depart controlled flight (stall with an incipient spin entry) without any stall warning.  Good CFD departments today will analyze this condition in CFD to validate that the wing won't stall due to this flight control input.

The tip of the iceberg has been exposed.

Keep the Blue on Top -Ron

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thanks Ron!

You answered a question that I didn’t finish asking...
 

the following is a raw unfinished post... :)

-a-
 

If...

A -1.387° twist was required for an airplane to fly...

Would it be possible to build something with enough exactness and not cost 1Kamus..?

After 50 years, would it still be flyable..?

It appears... 

1) we are trained one thing...

2) The plane is more robust than we expect....

3) Unfortunately, when we are wrong... there are no do-overs...

 

On MS we have seen all kinds of... inexactness...

1) excess hangar rash...

2) Go-pro cameras mounted everywhere...

3) Painted control surfaces that haven’t been weighed or balanced...

 

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10 hours ago, carusoam said:

A) If... A -1.387° twist was required for an airplane to fly...

B) Would it be possible to build something with enough exactness and not cost 1Kamus..?

C) After 50 years, would it still be flyable..?

It appears... 

1) we are trained one thing...

2) The plane is more robust than we expect....

3) Unfortunately, when we are wrong... there are no do-overs...

 

On MS we have seen all kinds of... inexactness...

1) excess hangar rash...

2) Go-pro cameras mounted everywhere...

3) Painted control surfaces that haven’t been weighed or balanced...

A) Twist is not a requirement; it is a compromise between cruise drag and stall characteristics (which can also be modified by other variables … like stall strips … which are also a compromise between stall characteristics and cruise drag).  But, we'll continue on with "A)" is true.

B) Yes, the tooling would have to be precise.  Precision costs money but could be minimized if the tool was designed correctly.  There must be some tolerance.  A goal of engineers is to have as few parts and dimensions be critical and/or tight tolerance.

C) Good question.  Most likely yes in this case as aerodynamics are pretty tolerant of little changes (stall strip vertical position and laminar flow are exceptions).

1) Yes  2) Definitely  3) LOL.  Sad but true.

MS1) Hangar rash will definitely change aerodynamics, and here a little might mean a lot … or not (one has to know why, where and how much).  For example while backing your airplane into the hangar, you hit an elevator or aileron on the roof support pole.  Will it change the airplane?  Yes.  The surface will "float" to a  different angle.  Does it matter?  That depends on the amount and direction the TE of the surface was bent.

MS2) These installations are approved through FAA guidance, which is good and I am glad about it being easy.  BUT (and this is not bragging, Don :)), I know a bit more about the effect, and I'll limit the airplane operating envelope if applicable.

MS3) Some airplanes are more tolerant of surface balance.  In a Bonanza, this has proven fatal in some cases in the past.  We write ICA manuals for a good reason … and they're not easy.

Thanks, Ron

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