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Emergency maneuver training / FUN!

J

Jetlinkin

Member
I recently attended APS emergency maneuver training in Phoenix, Az. This was probably the best aviation training that I have ever received! The training was a 3 day course, with 6 flights in the Extra 300L, and the experience was invaluable! A little bio on myself when I attended this course. 5000+ total time, 4 1/2 years part 121 with Expressjet, and now I drive a C550, and of course, the 4. During the 3 day course, there was about 12 hours of ground school which covered a lot of aerodynamics. One interesting tidbit I learned from this training, if you unload your aircraft from 1G to 1/2G, your stall speed decreases by 42% ( it's a good thing to know when you are in a stall). The instructors at APS are top notch (ex military / airline), and their knowledge base is incredible. Unlike regular flight training in the past, where we all have talked about all of the different types of stalls with our CFI, and only do power off and on in the aircraft. During my APS training we actually preformed every type of stall, in every type of attitude, in the aircraft. Instead of what we are used to doing, talking about the "theory" of what is going to happen during ground school, like all of us have in the past, and never preforming the actual maneuver.

For all of us, experiencing these many different types of upsets could possibly save our lives. I can't say enough how invaluable this training was.

This is only the tip of the iceberg during my experience, if you have any questions let me know. Here is the highlight reel from the last 40 minutes of my training.
http://www.youtube.com/watch?v=1fM9_R7H7kY&context=C306fd0bADOEgsToPDskIp-jxB2Rg6NomixB_54kJX
 
very nice.

I have a BFR due in May so I have signed up for a EMT course as part of the flying portion.
 
Jetlinkin said:
One interesting tidbit I learned from this training, if you unload your aircraft from 1G to 1/2G, your stall speed decreases by 42% ( it's a good thing to know when you are in a stall).
Click to expand...
Are you sure you don't mean increases? :confused:
 
Decreases is correct. OTOH, if you increase the G loading up to 2 G's, the stall speed increases. The higher the G, the higher the stall speed, and vice-versa.

At zero G, you can't stall the plane.:cool:

Of course you can't maintain zero G very long, as you end up pointing straight down!
 
Nope...stall speed decreases under low G conditions. At zero G, the stall speed is zero (and the airplane is effectively ballistic). A proper unload can undo a myrid of sins. Any nose rise/slice/stick force lightening or buffet, neutralize control inputs and unload to a 1/4 G condition (my RV-4 is carbuerated), reduce power (to mitigate torque effect) and wait until the velocity vector transits the horizon and airspeed increases through about 100 MPH and then recover. The basic concept is to "unload for control." As long as the ground doesn't get in the way, it works like a champ. Under 1/4 to 1/2G, the engine runs fine, as zero G approaches, it begins to bark and won't operate continuously at zero G. Under low airspeed conditions, when the engine quits, the light weight (Catto) prop will generall stop. In this case, an airstart is required post-recovery.

Post-stall breakdown in the directional control in our RV-4 tends to be in yaw, especially considering prop effects, so generally the first sign of things going astray is uncommanded yaw--perceived as the nose slicing. You also need to be aware of torque effects as the airplane decellerates and not fight an uncommanded roll with a "subconscious" aileron input.

An important part of this technique is to properly neutralize the controls and be patient until the airspeed begins to increase. All RV's accellerate once the velocity vector is below the horizon, especially those equipped with fixed pitch props. Attitude is not important during the recovery, only establishing the low G condition desired for recovery is. For example, if you're inverted in a nose-high condition with airspeed decreasing, you can effectively maintain a low-G condition upside down while the airplane transits a ballistic arc. This could be disorienting if you're not familar with all-attitude/aerobatic flight; but it's not a difficult technique to learn once you've been exposed to it.

Fly Safe,

Vac
 
Vac said:
Nope...stall speed decreases under low G conditions. At zero G, the stall speed is zero (and the airplane is effectively ballistic). A proper unload can undo a myrid of sins. Any nose rise/slice/stick force lightening or buffet, neutralize control inputs and unload to a 1/4 G condition (my RV-4 is carbuerated), reduce power (to mitigate torque effect) and wait until the velocity vector transits the horizon and airspeed increases through about 100 MPH and then recover. The basic concept is to "unload for control." As long as the ground doesn't get in the way, it works like a champ. Under 1/4 to 1/2G, the engine runs fine, as zero G approaches, it begins to bark and won't operate continuously at zero G. Under low airspeed conditions, when the engine quits, the light weight (Catto) prop will generall stop. In this case, an airstart is required post-recovery.

Post-stall breakdown in the directional control in our RV-4 tends to be in yaw, especially considering prop effects, so generally the first sign of things going astray is uncommanded yaw--perceived as the nose slicing. You also need to be aware of torque effects as the airplane decellerates and not fight an uncommanded roll with a "subconscious" aileron input.

An important part of this technique is to properly neutralize the controls and be patient until the airspeed begins to increase. All RV's accellerate once the velocity vector is below the horizon, especially those equipped with fixed pitch props. Attitude is not important during the recovery, only establishing the low G condition desired for recovery is. For example, if you're inverted in a nose-high condition with airspeed decreasing, you can effectively maintain a low-G condition upside down while the airplane transits a ballistic arc. This could be disorienting if you're not familar with all-attitude/aerobatic flight; but it's not a difficult technique to learn once you've been exposed to it.

Fly Safe,

Vac
Click to expand...
Ok, I am going to show my ignorance with my questions concerning this post. I have a few phrases used above that I do not quite understand. Vac, can you expound upon what these phrases mean, or, in some instances, describe how you perform the maneuver you describe?

"A proper unload" - What exactly does the pilot do to perform this?

"Any nose rise/slice/stick force lightening or buffet, neutralize control inputs and unload to a 1/4 G condition" - I am not sure what you mean by "slice" and again what specific action is the pilot performing to "unload to a 1/4 G condition"?

"wait until the velocity vector transits the horizon and airspeed increases" - What is "velocity vector"? What is the pilot observing in this state?

"the first sign of things going astray is uncommanded yaw--perceived as the nose slicing." - Again, here is the phrase "nose slicing". Can you describe this?

"you can effectively maintain a low-G condition upside down while the airplane transits a ballistic arc." - Can you explain HOW a pilot "maintains a low-G condition" whether inverted or right side up? Is the pilot pointing the nose of the aircraft toward the ground in order to "unload" the G-forces?

Thanks for any enlightening you can provide.
 
Very cool

and I just have to say it....... nicely done!

I think that there certainly is a certain aversion to manuvering that settles in after hours and hours of trying to be smooth. You almost begin to forget who is flying who. You begin to compromise with the airplane and just coax it to do what you want it to as long as it does'nt seem to object (or disturb the pax).

Some occasional yanking and banking restores that feeling of positive control back into your mind.

I think that the most demonstrative manuver we used to teach in Navy basic training was the skidded turn stall (I guess essentially a snap roll). Big time cross controlled stall that snaps inverted instantly.

Very valuable training for sure, and as a GIB, I'm glad you got that training!
 
RVbySDI said:
Ok, I am going to show my ignorance with my questions concerning this post. I have a few phrases used above that I do not quite understand. Vac, can you expound upon what these phrases mean, or, in some instances, describe how you perform the maneuver you describe?

"A proper unload" - What exactly does the pilot do to perform this?

"Any nose rise/slice/stick force lightening or buffet, neutralize control inputs and unload to a 1/4 G condition" - I am not sure what you mean by "slice" and again what specific action is the pilot performing to "unload to a 1/4 G condition"?

"wait until the velocity vector transits the horizon and airspeed increases" - What is "velocity vector"? What is the pilot observing in this state?

"the first sign of things going astray is uncommanded yaw--perceived as the nose slicing." - Again, here is the phrase "nose slicing". Can you describe this?

"you can effectively maintain a low-G condition upside down while the airplane transits a ballistic arc." - Can you explain HOW a pilot "maintains a low-G condition" whether inverted or right side up? Is the pilot pointing the nose of the aircraft toward the ground in order to "unload" the G-forces?

Thanks for any enlightening you can provide.
Click to expand...

An aircraft in normal steady state (cruise flight) is under the force of 1g. Remember when your CFI showed you pencils floating in the cockpit to you once? ( I am almost positive they did- most show you that). When the pencils float it is essentially a zero g or negative G maneuver depending on how hard/quick they move controls. Its not just pushing the nose down at 1 G to break out of the stall, its on the verge of an aerobatic maneuver. If done properly you can fly an average piston airplane almost straight up (for a few short moments) without stalling it. It is the same as shooting a bullet straight up into the air or throwing a stone, at the top of the arc it slows down to zero for a moment before starting to fall downward at velocity again.
 
Jetlinkin said:
I recently attended APS emergency maneuver training in Phoenix, Az. This was probably the best aviation training that I have ever received!

For all of us, experiencing these many different types of upsets could possibly save our lives. I can't say enough how invaluable this training was.

This is only the tip of the iceberg during my experience, if you have any questions let me know. Here is the highlight reel from the last 40 minutes of my training.
http://www.youtube.com/watch?v=1fM9_R7H7kY&context=C306fd0bADOEgsToPDskIp-jxB2Rg6NomixB_54kJX
Click to expand...

Thanks for sharing this. I have been a part 121 airline guy for 15 years and only in recent years has there been more emphasis on this.
 
Hi Steve,

Sorry about the lingo, let me see if I can give a better answer than "it depends..."

"A proper unload" - What exactly does the pilot do to perform this?

-Ailerons and rudder neutral, do what it takes with fore/aft stick to make the G-meter read "1/4." If you're mostly right side up, that likely means forward pressure on the stick, if you're mostly upside down, you've got radial G working for you, so that means less forward pressure. The key is to make the meter read "1/4" (or zero, or whatever your target is). Since looking at a G-meter isn't always practical, each of us develops seat-of-the-pants cues to help...if everything is floating up in the cockpit around you and the engine is sputtering, you're probably close to a zero G condition.

"Any nose rise/slice/stick force lightening or buffet, neutralize control inputs and unload to a 1/4 G condition" - I am not sure what you mean by "slice" and again what specific action is the pilot performing to "unload to a 1/4 G condition"?

-These are subtle cues that the airplane gives before it stalls. I'm not familiar with the handling characteristics of the airfoil on your -9, but the 23013.5 section on the 3/4/6/7/8 as a rather abrupt break at the stall (i.e., there is zero.zero doubt when the wing quits flying!). Prior to that point you can experience buffet, nose rise or slice.

Nose rise is tough to perceive unless you're looking for it. It occurs when you're maneuvering and pulling aft on the stick and the nose continues to rise even though you've unloaded a bit to try to stop it. It occurs because the CG is rotating over the top or underneath the aerodynamic center and your pitch stability is decreasing (it's like your elevator suddenly got bigger/more effective). It feels as though the stick just got lighter in your hand.

Nose slice is simply when the nose starts to slide to the left or the right. Again, I'm not familiar with the -9, but when you put our -4 (loaded within aerobatic design limits as specified by Van) into a deep stall, i.e., maintain full aft stick, the nose will slide before the airplane drops off in a spin. In a -4, there is sufficient rudder to counter this slice. The same cue can occur just prior to the stall as well, it's just telling you that your directional control is starting to break down (think of your tail being blanketed or less effective).

Because of the torque effects of the prop, sometimes this slicing gets mixed with some roll as the airplane decelerates. You can experience this when you do a power-on stall. If you do the classic 1 knot/sec decelleration as you approach the stall, the airplane will start to roll to the left a bit, and chances are if you're not looking for it, you may add some right aileron to help out your decreasingly less effective tail, but then when the airplane stalls, the left wing drops suddenly. If, however, you only use your feet to counter roll/slice to the left and quit trying to stop it as you run out of authority, the airplane will stall straight ahead (no wing drop).

"wait until the velocity vector transits the horizon and airspeed increases" - What is "velocity vector"? What is the pilot observing in this state?

-Velocity vector = flight path or where the airplane is going (but not necessarily where its pointing). If the airplane is going in a direction above the horizon, it will slow down. If the airplane is going in a direction below the horizon, it will speed up. This is gravity's contribution to "thrust."

If you unload before a stall (or loss of directional stability), the flight path of the airplane is just a ballistic trajectory (like throwing a ball). If you've got sufficient altitude, eventually the path with get below the horizon and the airplane will start to speed up. After you've got sufficient airspeed, you can recover from any unusual attitude you might be in. 100 is just a nice round number and you've got about 3.3 G's available for maneuvering--likely fast enough to help avoid a secondary stall if you're too quick with back pressure when you try to recover. The real thing to be careful of in any RV is once the nose is down getting too fast, as I'm sure you've experienced.

Hope that helps a bit. Feel free to drop a line if you have any more questions.

Cheers,

Vac
 
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These courses are so important

Mtbguy said:
An aircraft in normal steady state (cruise flight) is under the force of 1g. Remember when your CFI showed you pencils floating in the cockpit to you once? ( I am almost positive they did- most show you that). When the pencils float it is essentially a zero g or negative G maneuver depending on how hard/quick they move controls. Its not just pushing the nose down at 1 G to break out of the stall, its on the verge of an aerobatic maneuver. If done properly you can fly an average piston airplane almost straight up (for a few short moments) without stalling it. It is the same as shooting a bullet straight up into the air or throwing a stone, at the top of the arc it slows down to zero for a moment before starting to fall downward at velocity again.
Click to expand...

Good points. Let me add my 2c!:)

You can fly an aircraft straight up until you stop, kick the rudder to turn and fly straight down toward the ground and pull out, and never come anywhere close to stalling the aircraft. You can also fly the aircraft straight up, let it get on it's back slightly, stall inverted, kick the rudder and go into an inverted spin. You can easily stall the aircraft when it's going straight at the ground. (This all being done in an aircraft that is strong enough to withstand backward airflow, and higher g-loads of course.) Stall speed has nothing at all to do with the aircraft's attitude in relation to the ground, and everything to do with the angle of attack. With enough experience you can feel when the wings have an angle of attack, either positively or negatively loaded. You can also feel when the wings have no angle of attack, just as you can feel yaw from the rudder.

For example, a common mistake many pilots make when doing a hammerhead is to not unload the wing when in the vertical. When you pull from straight and level to vertical during the first part of the hammerhead, the aircraft often still has a slight positive angle of attack, because even though the attitude is vertical, there is still a slight horizontal component from the aircraft's momentum. You can get a zero angle of attack by "popping" the stick forward slightly after reaching the vertical. If done properly, you will feel yourself float out of your seat as the aircraft goes straight up. If you don't do this, the wing is still flying, and that can make the aircraft want to roll even more than usual in the turn at the top, more than the aileron can prevent. Another common mistake for new acro pilots is to let the aircraft get on it's back ever so slightly as it's in the vertical. If you do this, and then misjudge the time to kick, if the aircraft starts to fall backward you will now have a negative angle of attack on the wings which can stall even at a very slight angle (because your airspeed is so low). If you kick the rudder as this happens, you can get into a nice inverted spin pretty quickly. Even if you kick early and fly it over the top, if you have let the aircraft get slightly on it's back, it can still have a negative angle of attack and go into an inverted spin.

Once you have some experience with this, it's easy to tell when it's going to happen. You can feel the aircraft's angle of attack, and if you keep it at zero, then even at zero airspeed you will not stall. But if you develop even a slight angle of attack at a very low airspeed, and impose any sort of g load, it's very easy to stall.

I know that most people will probably disagree with me, but in my not so humble opinion ;), courses like these should be required for anyone who wants to fly with trusting non-pilot passengers.
 
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Here's a reference

For those wishing to know a lot more about this stuff, here is a good reference

https://www.cnatra.navy.mil/pubs/folder5/T34C/P-354.pdf

This is the out of control flight instruction manual for Navy basic training in the T-34C. The T-34 has performance/flight characteristics similar enough to RV's to be usefully comparable.

By the way, I highly recommend other CNATRA (Navy Training) publications. The basic Flight Training instruction - https://www.cnatra.navy.mil/pubs/folder5/T34C/P-330_CH9.pdf is excellent, particularly in regards to the emergency engine out procedures. This lays out the High Key - Low key pattern that is oft discussed here on the forum. Also describes really good landing pattern procedures from downwind to landing - including correct waveoffs and the whole nine yards.

All of these documents can be found here https://www.cnatra.navy.mil/pubs/ppub_t34_pri.htm

Your tax dollars at work!!! might as well get some valuable info for your money. Might save your bacon and will definately make you a better pilot.
 
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Mike,
Thank you for the clarifications. Since I am not into aerobatics (hey I fly a non-aerobatic 9) I am not really looking to go experience this in my plane but I am interested in understanding these concepts. The truth is I am not really interested in intentionally doing these maneuvers for the pleasure of aerobatic flying like many RV fliers out there. However, I would like to be experienced in the theory and would like to have an opportunity to practice them for the purpose of emergency recovery.

By the way, you commented that you were not familiar with the characteristics of the 9 in stall. The 9 also has a distinct abrupt break at the stall. In addition, I have not heard other 9 pilots comment before about this but, with my particular 9, there is a very distinct "stick shacking" prior to the stall. This is a very unmistakable sudden and distinct shaking that occurs to the stick just prior to the break. There is absolutely no way a pilot could miss this shaking prior to the stall. Now with the 9 being non-aerobatic I have not tested nor experienced this in any inverted attitude but in every other "normal" attitude I have had my plane in it is there. Power on and power off both produce this shaking. Because of this I am very confident I have ample warning of impending stalls.

Again, thank you for the information. I love this forum for this specific reason. I love the fact that I have access to people with this kind of experience that I can learn from.
 
PCHunt said:
Decreases is correct. OTOH, if you increase the G loading up to 2 G's, the stall speed increases. The higher the G, the higher the stall speed, and vice-versa. At zero G, you can't stall the plane.:cool:
Click to expand...
Right... I think I was confusing the *margin* between airspeed and stall speed, with the stall speed itself.
 
Sorry... aerobatics nut here!

I'll start by saying I'm an aerobatics nut, and have spent quite a bit of time not flying straight and level. I see one thing repeated over and over again here that is causing confusion and is increasingly important in "all attitude flying" that this idea be understood! Everything I have seen so far says "Stall Speed." Airplanes don't stall because of speed (I know you all know this), it stalls at an AOA. I can stall my Extra at 200 knots (ouch...), I can also fly (not stall) it at 0 airspeed.

When we bore holes in the sky maintaining one G flight, straight and level, the speed that CORRELATES to the critical angle of attack is relevant. However, as soon as you start pulling Gs (think a steep turn from base to final) SPEED BECOMES IRRELEVANT, you cannot know your precise stall speed at a given flight load and weight unless you moonlight as a calculator/genius/nuclear physicist... (point taken?) This is why it becomes important to maintain a safe margin above the published stall speed (1.3 times Vso commonly) when maneuvering low and slow. Where this takes another turn (and when you REALLY start flying) is when you begin to maneuver for something other than landing, i.e. AEROBATICS. Most everything in aerobatics is done by sight, sound, and feel. It takes A LOT of time and experience to start to feel the stall coming, but once you begin to know all of the indicators (previously explained as Buffet, Nose Rise, and Slice, but also can include sounds like the distinctive whistle the Extra makes before it stalls, or when it is ready for you to kick at the top of a Hammerhead) that "specific stall speed" means less and less. I know this seems like rambling, but here is my point. As you explore the flight envelope of your airplane (as it relates to stalling tendencies) you will be able to KNOW when the airplane is close to the stall. Rather than having to do rapid integration in your head to CALCULATE a stall speed at .25G going 150 knots at 1700 pounds, you KNOW that buffet means trouble is brewing. Not to mention this "research" is insanely fun (and addictive)! Just make sure you get good and appropriate training, and explore away! I think EVERYONE should go through a similar training experience, it is very unique to fly and airplane in which you can go and DO everything you talk about in ground school. It brings practical instruction to a whole new level! Fly Safe guys, keep the blue side down as much as you can!
 
also a fan of acro.

I spent a while trying to get my 7a (with CS prop on a 2.25" prop extension) to spin inverted...No chance!

Then one day I was doing the hammerhead fell off the back at the top and bang, the thing snapped over into a very impressive invert spin.

I rode it down a little just for kcks and it wound up pretty quickly (for a spinning RV).

I guess this is why self taught aerobatics is a bad idea eh?...:)

Frank
 
frankh said:
also a fan of acro.

I spent a while trying to get my 7a (with CS prop on a 2.25" prop extension) to spin inverted...No chance!

Then one day I was doing the hammerhead fell off the back at the top and bang, the thing snapped over into a very impressive invert spin.

I rode it down a little just for kcks and it wound up pretty quickly (for a spinning RV).

I guess this is why self taught aerobatics is a bad idea eh?...:)

Frank
Click to expand...

Yes indeed. When I ride with students who do this, I can always tell when this is going to happen. They are almost always surprised when it does.

For those of you who are frightened by the very thought of unusual attitudes, I will say this:

When I was first getting my CFI back in the early eighties, I thought it might be nice to take an aerobatic course in case a student "did something crazy."

I signed up for a ten hour course with Duane Cole. For the first two hours I was terrified, everything was a blur.

After five hours I was more relaxed, and at the end of the course I was loving it so much I went home and bought a Citabria! (Paid $7500 for it, those were the days!)

My point is, if you can get past the initial nervousness and fear, the rewards of learning aerobatics are numerous. You will have a much better feel for your aircraft, your confidence level will go up quite a bit, and you will simply be a much better "stick".

Plus, as others have said, it's a lot of fun, and if you become interested in competition, the IAC is filled with really cool people!

If you just aren't up to the G's, and some folks aren't, even after trying for a while, even an unusual attitude course as the OP talks about can be invaluable, building both skill and confidence, and feel for your aircraft.
 
Small Thing

Jetlinkin said:
....One interesting tidbit I learned from this training, if you unload your aircraft from 1G to 1/2G, your stall speed decreases by 42% ( it's a good thing to know when you are in a stall).....
Click to expand...

The decrease is "only" 29%, not 42%. Still significant but you might want to go back and check other arithmetic factoids they taught.

(The decrease itself is 29% of the original speed. It's 41% of the lower speed, and that's how they made their error. The extra 1% is a goof.)

Dave
 
Jetlinkin said:
One interesting tidbit I learned from this training, if you unload your aircraft from 1G to 1/2G, your stall speed decreases by 42% ( it's a good thing to know when you are in a stall).
Click to expand...

I'm not going to comment on the accuracy, validity, or value of this statement, BUT...exactly how does one stall an airplane without more than 0.5G showing up on the G-meter?
 
Phlyan Pan said:
Have a very slow airspeed?
Click to expand...

Airspeed is unrelated to AOA. You can have zero airspeed and also zero AOA. I'm just curious exactly how you would exceed critical AOA (stall) with 0.5G on the meter. This whole 1/2G thing doesn't make much sense to me. It's kinda like saying that at 2G, your stall speed doubles. It doesn't. Stall speed is unrelated to load. It's a combination of airspeed AND load. You can't separate the two. You could pull 2G at 75 mph, or you could pull 2G at 175 mph. Again, I don't understand how load alone relates to stall speed, since at 75 mph, you won't stall at much more than 2G, but at 175 it might take more G-load than the airframe can handle in order to stall. I don't see how 0.5G can be anything but a shallow parabolic arc (no stall).
 
Totally agree.

The limited acro training I had saved my bacon once when CMH tower decided to squeeze out a 7x7 between me and the DC-9 I was following (hazy memory) without advice to me and I rolled inverted practically over the numbers.

N355DW said:
Yes indeed. When I ride with students who do this, I can always tell when this is going to happen. They are almost always surprised when it does.

For those of you who are frightened by the very thought of unusual attitudes, I will say this:

When I was first getting my CFI back in the early eighties, I thought it might be nice to take an aerobatic course in case a student "did something crazy."

I signed up for a ten hour course with Duane Cole. For the first two hours I was terrified, everything was a blur.

After five hours I was more relaxed, and at the end of the course I was loving it so much I went home and bought a Citabria! (Paid $7500 for it, those were the days!)

My point is, if you can get past the initial nervousness and fear, the rewards of learning aerobatics are numerous. You will have a much better feel for your aircraft, your confidence level will go up quite a bit, and you will simply be a much better "stick".

Plus, as others have said, it's a lot of fun, and if you become interested in competition, the IAC is filled with really cool people!

If you just aren't up to the G's, and some folks aren't, even after trying for a while, even an unusual attitude course as the OP talks about can be invaluable, building both skill and confidence, and feel for your aircraft.
Click to expand...
 
luddite42 said:
I'm not going to comment on the accuracy, validity, or value of this statement, BUT...exactly how does one stall an airplane without more than 0.5G showing up on the G-meter?
Click to expand...

One way in vertical maneuvers- After a hammerhead turn where you are at a extremely low airspeed in it?s beginning down hill acceleration and pull the stick past the critical AOA and a little rudder- bingo, a stall/spin with maybe .5 Gs on the meter
 
Lud

I don't think any thing you are saying contradicts anything Vac said. What ever you want to call it - reduced AOA, 1/2 G, flying a ballastic parabolic, or combinations there of - they are all forms of unloading. And a way to avoid a stall (and the attendent post stall gyrations which are much harder to recover from, and eat up lot's more altitude, and bend airplanes, and break aviators).

All same same, I think.

In Brad's example if going up, the stall can occur somewhere around nearly 0 AOA and nearly zero airspeed and near 0 G. In the case of extremely nose high attitudes, no amount of un-load will save it and avoid the post stall gyration, but at least the velocity vector will soon be transiting the horizon!!
 
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luddite42 said:
Airspeed is unrelated to AOA. You can have zero airspeed and also zero AOA. I'm just curious exactly how you would exceed critical AOA (stall) with 0.5G on the meter. This whole 1/2G thing doesn't make much sense to me. It's kinda like saying that at 2G, your stall speed doubles. It doesn't. Stall speed is unrelated to load. It's a combination of airspeed AND load. You can't separate the two. You could pull 2G at 75 mph, or you could pull 2G at 175 mph. Again, I don't understand how load alone relates to stall speed, since at 75 mph, you won't stall at much more than 2G, but at 175 it might take more G-load than the airframe can handle in order to stall. I don't see how 0.5G can be anything but a shallow parabolic arc (no stall).
Click to expand...

Hard to talk about, easy to show with models.

First off, it's important to understand that the critical angle of attack changes with changes in airspeed. In other words the angle of the wing in relation to airflow at which the air quits flowing smoothly over the wing changes as the airspeed changes, it is not the same angle at all airspeeds. At higher airspeed the angle it takes to exceed the critical AOA is a much larger angle than at low airspeeds.

So, at zero G, the angle of attack is zero. At anything more than zero G, there is an AOA, however slight it might be. Another way to think about it is, if you feel pushed into your seat or against the seatbelt, that means either the direction the aircraft is traveling is changing, or gravity is pulling on the aircraft, or both. In all these cases, either with gravity or change of direction, you will have an AOA on the wing. Anytime you feel G's, however slight, that means the wings have an AOA. (Except maybe in a really nice tailslide or torque roll, but that's another discussion!)

If the airspeed is, say ten mph, over the wing, it won't take much of an angle to reach critical AOA. This is the same as saying it won't take much G force to exceed the critical AOA. A nice example of this might be a vanilla humpty bump (pull up, pull over the top, pull out). If, when nearing the top of the humpty, I pull back on the stick to do my half loop at about sixty mph, by the time I reach the apogee I might be only indicating twenty mph. At this point I am still flying even though the stall speed of my plane might be up around 60 or better. I am also close to zero G with a very low angle of attack. But I could easily add a 1/2G, or less possibly, pull on the stick because maybe I am in a hurry to get back to the vertical down line at the top of the humpty, and exceed the critical angle of attack and feel the wing buffet. I know, because I have done this many times.

So G is more an indication of the AOA of the wing to the airflow. At low G, the AOA is less, and at high G it is much greater. If your airspeed is low, then at low G, or low AOA, you can stall the wing. If your airspeed is high, you can pull more G, or have a greater AOA without stalling

Hope this helps, I might be confusing myself here!:)
 
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N355DW said:
Hard to talk about, easy to show with models.

First off, it's important to understand that the critical angle of attack changes with changes in airspeed. In other words the angle of the wing in relation to airflow at which the air quits flowing smoothly over the wing changes as the airspeed changes, it is not the same angle at all airspeeds. At higher airspeed the angle it takes to exceed the critical AOA is a much larger angle than at low airspeeds.

So, at zero G, the angle of attack is zero. At anything more than zero G, there is an AOA, however slight it might be. Another way to think about it is, if you feel pushed into your seat or against the seatbelt, that means either the direction the aircraft is traveling is changing, or gravity is pulling on the aircraft, or both. In all these cases, either with gravity or change of direction, you will have an AOA on the wing. Anytime you feel G's, however slight, that means the wings have an AOA. (Except maybe in a really nice tailslide or torque roll, but that's another discussion!)

If the airspeed is, say ten mph, over the wing, it won't take much of an angle to reach critical AOA. This is the same as saying it won't take much G force to exceed the critical AOA. A nice example of this might be a vanilla humpty bump (pull up, pull over the top, pull out). If, when nearing the top of the humpty, I pull back on the stick to do my half loop at about sixty mph, by the time I reach the apogee I might be only indicating twenty mph. At this point I am still flying even though the stall speed of my plane might be up around 60 or better. I am also close to zero G with a very low angle of attack. But I could easily add a 1/2G, or less possibly, pull on the stick because maybe I am in a hurry to get back to the vertical down line at the top of the humpty, and exceed the critical angle of attack and feel the wing buffet. I know, because I have done this many times.

So G is more an indication of the AOA of the wing to the airflow. At low G, the AOA is less, and at high G it is much greater. If your airspeed is low, then at low G, or low AOA, you can stall the wing. If your airspeed is high, you can pull more G, or have a greater AOA without stalling

Hope this helps, I might be confusing myself here!:)
Click to expand...

an airfoil only has one lift curve slope with a critical AOA somewhere near the point where the lift curve slope starts to turn negative. This is independent of airspeed. Doesn't matter if you have 1mph or 1000mph the critical AOA will be the same regardless. With any velocity above (or below) zero an AOA exists - by definition. AOA which provides zero lift is the x intercept of this curve... symmetrical airfoils will have zero lift at zero AOA. Any other airfoil will still have lift at zero degrees AOA due to camber and would require negative AOA to achieve a zero lift condition (if positively cambered).
AOA is the angle formed between the cord line and the relative wind, simple as that.
 
RVbySDI said:
Mike,
Thank you for the clarifications. Since I am not into aerobatics (hey I fly a non-aerobatic 9) I am not really looking to go experience this in my plane but I am interested in understanding these concepts. The truth is I am not really interested in intentionally doing these maneuvers for the pleasure of aerobatic flying like many RV fliers out there. However, I would like to be experienced in the theory and would like to have an opportunity to practice them for the purpose of emergency recovery.
Click to expand...

http://www.amazon.com/Better-Aeroba...1402/ref=sr_1_1?ie=UTF8&qid=1328828807&sr=8-1

This is the best book on acro I've ever read and will explain a lot of the concepts being described in this thread. Zero g can get you out of trouble in a lot of situations and even if you don't do acro, it is invaluable to know in a situation such as an engine out where you have no choice but to turn around.
 
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Unload for Control

The basic concept is to simply "unload for control." Perhaps the easiest way to think about the concept is that at zero G, you're simply not asking the wing to do any work (i.e., produce lift). Think back to the basic lift equation that you learned in ground school, the "pounds of lift" side of the equation becomes effectively zero. To establish the condition, you are simply reducing the angle of attack to a very low number. The purpose for neutralizing the rudder and aileron is to simply avoid a spurious input that could impart any yaw. The airplane will continue in a "ballistic" condition and gravity will eventually start to pull it down, then it will accelerate. Once sufficient flying speed is available, it's possible to begin maneuvering again and recover from any subsequent "unusual" attitude. A target G is one way to establish the condition, but a target AOA is even better if you have the proper gauge in your cockpit.

The real trick is to do this before you've lost directional stability, i.e., fall off into a spin, etc. Sometimes, an unload is just momentary and not a complete "knock-it-off and recover" type of maneuver--just enough to get you through whatever maneuver it is you're attempting to do without stalling.

"Unload for Control" was a film that was produced by a young engineer named Burt Rutan, who was part of a crew of folks to help develop handling techniques that could be adopted by F-4 crews to help avoid mishaps. The F-4 has some pretty nasty departure characteristics if you exceed 30 cockpit units of AOA (about 20 degrees of alpha)...and it doesn't recover from a spin nearly as nicely as the RV-4. The F-15 was a much better ride, but it too lost directional stability at high AOA. Even fly-by-wire types suffer excursions...

So that's the bottom line: if you reduce the AOA, the wing can't stall. The zero G condition is just a good seat-of-the pants cue to get you to that low AOA.

Fly safe,

Vac
 
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RV8R999 said:
an airfoil only has one lift curve slope with a critical AOA somewhere near the point where the lift curve slope starts to turn negative. This is independent of airspeed. Doesn't matter if you have 1mph or 1000mph the critical AOA will be the same regardless. With any velocity above (or below) zero an AOA exists - by definition. AOA which provides zero lift is the x intercept of this curve... symmetrical airfoils will have zero lift at zero AOA. Any other airfoil will still have lift at zero degrees AOA due to camber and would require negative AOA to achieve a zero lift condition (if positively cambered).
AOA is the angle formed between the cord line and the relative wind, simple as that.
Click to expand...


My bad! Hmm, well perhaps I can fly it but not describe it correctly. Even worse I have been instructing incorrectly, so I need to make sure I get this right!

At low air speeds it takes much less G loading than high speeds to get the airflow to leave the wing. And the Pitts I flew did not have completely symmetrical airfoils, but the Extras did. I had assumed that the angle changed as a function of the airspeed, but what you are saying is the critical AOA is the same, only at lower air speeds it is easier to reach this angle with less G. So over the top of the humpty at 25mph when I pull with half a G and buffet, that angle between the chord and the relative wind is exactly the same as when I pull 6 G's at 150 mph and buffet? It's coming back now I hope! The G force results because I am changing the attitude of the aircraft in relation to the direction in which it is traveling, and the higher the airspeed, the higher the force required to change the angle between the chord of the wing and the relative airflow, no?

It was always instinctive for me to unload the wing whenever I felt it get near the critical AOA, either positive or negative. The Extra does have a symmetrical, or very near symmetrical wing.

Thanks for correcting me!
 
N355DW said:
My bad! Hmm, well perhaps I can fly it but not describe it correctly. Even worse I have been instructing incorrectly, so I need to make sure I get this right!

At low air speeds it takes much less G loading than high speeds to get the airflow to leave the wing. And the Pitts I flew did not have completely symmetrical airfoils, but the Extras did. I had assumed that the angle changed as a function of the airspeed, but what you are saying is the critical AOA is the same, only at lower air speeds it is easier to reach this angle with less G. So over the top of the humpty at 25mph when I pull with half a G and buffet, that angle between the chord and the relative wind is exactly the same as when I pull 6 G's at 150 mph and buffet? It's coming back now I hope! The G force results because I am changing the attitude of the aircraft in relation to the direction in which it is traveling, and the higher the airspeed, the higher the force required to change the angle between the chord of the wing and the relative airflow, no?

It was always instinctive for me to unload the wing whenever I felt it get near the critical AOA, either positive or negative. The Extra does have a symmetrical, or very near symmetrical wing.

Thanks for correcting me!
Click to expand...

I think your statement is essentially correct in that at low airspeeds your stick force per degree of elevator travel will be lower, and so will your pitch rates, also in unloaded or near zero lift flight, your pitch moments are reduced making your elevator control power APPEAR to be more effective as it no longer has to counter the downward pitch moment of the loaded wing. So in the vertical with some airspeed and unloaded, the elevator forces will be lighter, produce less force, but also have less force to counteract the net result is it feels easy to pull through the top.
 
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