RV-6A spins

[Bill Dicus]

David Domeier notes correctly that it can be hard to know if a given airplane has been overstressed and if so how much. The new EFIS's do allow monitoring of g loads. If one wanted to take the trouble a continuous record of airspeed and g loads could be created for a new airframe. THis would be nice to have if the airframe is sold and could be reassuring to a potential buyer. I have seen a tendency for pilots to not mention an inadvertent overstress. Just be quiet and zero the g meter. This is why Neil Williams stressed (pun intended) leaving the g meter tell-tales for the next pilot to see, a good idea!

Bill

[LarryT]

Aluminum and steel have very different fatigue properties. There are legitimate reasons to be concerned about airframe overstress.

There is a stress level, often referred to as the "endurance limit", where a steel part will have infinite fatigue life (assumes no other age/use related affects) when operated below that stress level. A rule of thumb is that the "endurance limit" is about 50% of the steel's yield strength. One significant overstress, e.g. approaching the yield strength, may alter the fatigue life of the steel part to a finite number.

The bad news.

There is no endurance limit for aluminum. Operated long enough at any fatigue cycle stress level, any aluminum part will eventually have a fatigue failure. Because it is necessary for airplanes to be made from aluminum in order to get off the ground, aircraft design engineers have to be especially clever and use (relatively) complicated designs to keep stress cycling low enough for long life. An example is the Piper Cherokee wing spar AD, which came out after two Cherokees used for pipeline patrol had inflight airframe failures. After much DER work, it was determined that in "normal" service, the wings didn't need an inspection until 60,000 airframe hours! That's right, even at Turbo's flight time rates (when does he sleep?), 150 years in service! If memory serves me correctly, the two pipeline planes had airframe hours in the 6,000 range, so the affect of the far greater stress cycling can be seen.

The good news

Fatigue cracks start at the surface. Because airframes are overdesigned, it will take a crack some time to spread. This is the whole point of condition inspections and purchase inspections. There are removeable inspection panels on the aircraft. Use them. If an airframe has been significantly overstressed at some point, there are a number of features that could become evident - well ahead of an inflight failure. These include: rivets that are working; wrinkled skin; fatigue cracks starting to propagate. A crack has to travel a long way before the remaining crossectional area carrying the load is less than 50% (I am deliberately oversimplifying by ignoring notch affects, etc., etc.)

It would be a good sales point for someone, who flies aerobatically to download their EFIS and document the absence of airframe overstress. More realistically, vigilence at prepurchase inspections and condition inspections will help us all keep flying safely.

[zspivey]

About a year ago while trying to climb over a 9500 cloud deck, I allowed my 6A to enter an inadvertant spin. When I felt the stall burble, I thought it was an engine miss due to carb icing so my recovery started off slowly. It took about two turns to identify and start spin recovery. Once I started the correct control inputs, recovery was quick. Including the ensuing dive, I lost about 5,000 ft.
The information I took away from the experience:
1. When climbing, keep your airspeed up and insure the ball is centered
2. Spins at altitude are not frightning.
3. Spins at low altitude will be deadly

[luddite42]

Originally Posted by zspivey

About a year ago while trying to climb over a 9500 cloud deck, I allowed my 6A to enter an inadvertant spin. When I felt the stall burble, I thought it was an engine miss due to carb icing so my recovery started off slowly. It took about two turns to identify and start spin recovery. Once I started the correct control inputs, recovery was quick. Including the ensuing dive, I lost about 5,000 ft.
The information I took away from the experience:
1. When climbing, keep your airspeed up and insure the ball is centered
2. Spins at altitude are not frightning.
3. Spins at low altitude will be deadly

I'm curious about a few things - have you had significant spin training? Which way did you spin? It must have been to the right, because you're holding right rudder in a climb. I find it hard to believe that a true spin developed after a stall from the small amount of right rudder involved, unless you really monkey-footed the rudder somehow. My experience it that it takes practically full continusously held rudder before and after a stall to produce a spin. Also takes the stick held fully back in your gut. The ball being off a little won't do it. Did you just get into a high speed spiral after the stall and just take a while to recover and pull out?

I'm also surprised you could have actually let a "departure" stall happen. Given the 22,000' or so ceiling of an RV, how was a 9500' climb challenging your ability to avoid a the stall? Did the engine truly miss or cut out, because to do a full power stall in an RV even at altitude involves a ridiculous nose high attitude. Unless you had engine problems, it's hard to believe you could allow this to happen. Are you at risk of stalling and spinning at lower altitudes? Would you be dead if you ever accidentally stalled the airplane at 5,000'?

Also, if you were disoriented enough not to recognize the stall/spin for a bit, how could you have possibly kept track of how many turns you did before recovering? It takes some spin experience, good ground references, and deliberate attention to maintain situational awareness enough to precisely keep track of your rotations. Highly unlikely in the event of an accidental spin. To use up 5,000' ft, you must have done a lot more rotations than 2 or so. I noticed a two-turn spin for me in the RV used up 1000'. This was at lower altitude, but not enough lower to cause this much of a gap in altitude loss. Spins at low altitude (subjective) are not deadly...accidental spins at low (pattern) altitude are deadly...especially if you're inexperienced with spins.

[jrs14855]

In 40 years+- of competetion aerobatic flying in the IAC era, I don't recall a single incident of anyone spinning into the ground during a sanctioned contest. Unlimited category routinely does 1 to 1 1/2 turn spins from 1200 feet.
the important thing to remember in contest flying is that there must be a visible vertical down line after the spin. This uses up a lot more altitude than a non competetion spin recovery.
I have to agree that there is no way a two turn spin is going to use up 5000 feet. A training type spin in the Pitts S2B uses 450 feet for a one turn spin. A Piper J3 uses at least 300 feet, so unless you get into heavier aircraft or aircraft with nasty stall characteristics, the above numbers are typical.

[Kiwi]

Originally Posted by luddite42

I'm curious about a few things - have you had significant spin training? Which way did you spin? It must have been to the right, because you're holding right rudder in a climb. I find it hard to believe that a true spin developed after a stall from the small amount of right rudder involved, unless you really monkey-footed the rudder somehow. My experience it that it takes practically full continusously held rudder before and after a stall to produce a spin. Also takes the stick held fully back in your gut. The ball being off a little won't do it. Did you just get into a high speed spiral after the stall and just take a while to recover and pull out?

I'm also surprised you could have actually let a "departure" stall happen. Given the 22,000' or so ceiling of an RV, how was a 9500' climb challenging your ability to avoid a the stall? Did the engine truly miss or cut out, because to do a full power stall in an RV even at altitude involves a ridiculous nose high attitude. Unless you had engine problems, it's hard to believe you could allow this to happen. Are you at risk of stalling and spinning at lower altitudes? Would you be dead if you ever accidentally stalled the airplane at 5,000'?

Also, if you were disoriented enough not to recognize the stall/spin for a bit, how could you have possibly kept track of how many turns you did before recovering? It takes some spin experience, good ground references, and deliberate attention to maintain situational awareness enough to precisely keep track of your rotations. Highly unlikely in the event of an accidental spin. To use up 5,000' ft, you must have done a lot more rotations than 2 or so. I noticed a two-turn spin for me in the RV used up 1000'. This was at lower altitude, but not enough lower to cause this much of a gap in altitude loss. Spins at low altitude (subjective) are not deadly...accidental spins at low (pattern) altitude are deadly...especially if you're inexperienced with spins.

Valid questions and I do hope the original poster feels comfortable enough to answer. Such a discussion benefits everyone.

What I have noticed with spin accidents is that it is always like this. How did that happen? They actually seem unexplained. zspivey's experience seems typical.

Over the last few years we have had a number of fatal and serious injury spin accidents here in New Zealand. Being a small country you tend to sit up and pay attention when something happens, particularly as often you'll either know or know of the participants. The de Havilland Tiger Moth has been the most common aircraft. Because the pilots have either been dead or have no recollection of the events it has simply not been possible to figure out what happened, particularly when others have gone up and tried to replicate things at altitude and found the plane would not spin.

Over on supercub.org there have been discussions on this issue, and some very experienced pilots have reported the same experience. Against all odds and against all expectations the plane has spun on them.

Yes, an interesting thread.

Andrew.

[steve91t]

Originally Posted by zspivey

About a year ago while trying to climb over a 9500 cloud deck, I allowed my 6A to enter an inadvertant spin. When I felt the stall burble, I thought it was an engine miss due to carb icing so my recovery started off slowly. It took about two turns to identify and start spin recovery. Once I started the correct control inputs, recovery was quick. Including the ensuing dive, I lost about 5,000 ft.
The information I took away from the experience:
1. When climbing, keep your airspeed up and insure the ball is centered
2. Spins at altitude are not frightning.
3. Spins at low altitude will be deadly

Let me just say, I have so much respect for you. It's not easy to openly talk about your mistake.

What I like about this, is you are here to learn more about what happened and how to prevent it from happening again.

Honestly, I'm impressed that you came forward with your story. Not only will everyone here help you figure out how to keep yourself safe, but it could help someone reading this stay out of trouble.

Steve

[David Z]

In Canada, a spin is an item on the commercial flight test and must be demonstrated from entry to recovery. Examiner calls the recovery, typically around 1 rotation.
For the Private License, spins need to be performed by the student, but not demonstrated on the flight test. From what I've gathered, a Canadian Private Pilot has had the same spin training as an American CFI.

[zspivey]

I had spin training some 40 years ago. From my experience with spin training, you know you are going to spin and which way you will rotate. In aerobatic maneuvers, you know you are going to spin and which way you will rotate. In each of the previous cases, the pilot does not have to figure out what is happening; he put it into a spin and he or his instructor knows what to do to recover. That is not true for the poor soul who gets into one accidentally. Too many times it happens near the ground and the pilot doesn't live to tell of his experience. Fortunately, I was at altitude, knew enough to recover and my wife and I walked away from it. The good news is, she will still fly with me if we are going somewhere she wants to go.
I will admit, sometimes I have been sloppy and didn't hold enough right rudder in a climb. The incident seems to have cured that problem.
As for the 22,000 ft service ceiling, I suggest you try to get a 6 with a 160hp engine to that altitude; it ain't gonna happen.

[luddite42]

Originally Posted by zspivey

I had spin training some 40 years ago. From my experience with spin training, you know you are going to spin and which way you will rotate. In aerobatic maneuvers, you know you are going to spin and which way you will rotate. In each of the previous cases, the pilot does not have to figure out what is happening; he put it into a spin and he or his instructor knows what to do to recover. That is not true for the poor soul who gets into one accidentally. Too many times it happens near the ground and the pilot doesn't live to tell of his experience. Fortunately, I was at altitude, knew enough to recover and my wife and I walked away from it. The good news is, she will still fly with me if we are going somewhere she wants to go.
I will admit, sometimes I have been sloppy and didn't hold enough right rudder in a climb. The incident seems to have cured that problem.
As for the 22,000 ft service ceiling, I suggest you try to get a 6 with a 160hp engine to that altitude; it ain't gonna happen.

Vans specifications state the ceiling of the 6 with 160 hp is 21,500'.

For the benefit of others, I was hoping you could describe in more detail exactly what happened and how you got in the situation you did. You said you were not holding enough right rudder. I've never been able to get any airplane to enter and maintain a spin without nearly full pro-spin rudder held in...but then I never tried to spin the RV from a full power entry with no rudder. Which direction were you spinning? I assume left, if you say it was a result of not enough right rudder? So you were spinning at full power with no left rudder being held? You must have had the stick very far back to produce a stall. I assume you then reduced power and unloaded the stick at some point. Did you reduce power before or after you unloaded the stick? Or did you unload the stick before applying anti-spin rudder? If you unloaded the stick first before stopping the spin with power in (or off even), you'd have pretty much been in a continuous downward snap roll, possibly with airspeed and stress building if power was not pulled. Probably would have been very disconcerting if you didn't recognize what was happening. 5000' is a huge altitude loss for a plane like an RV. Just curious if you had any additional insights or understanding after the fact exactly what inputs caused this, and what inputs may have delayed the recovery to such an extent. Thanks