If this is your first visit, be sure to check out the FAQ by clicking the link above. You may have to register before you can post: click the register link above to proceed. To start viewing messages, select the forum that you want to visit from the selection below. 



Thread Tools  Display Modes 
#1




inverted spin recovery explanation
.... and don't forget to close the throttle :)
"john smith" wrote in message ... TD wrote: Can someone help me and list the steps to recover from an incipient inverted spin and fully developed inverted spin? It doesn't matter whether you are inverted or upright. If you are in a spin, step on the "HARD" rudder pedal, neutralize the stick. When the rotation stops, the nose will be pointed down. Pull to the nearest horizon. Speed will rapidly increase with the nose low, so don't hesitate. 
Ads 
#3




Dudley Henriques wrote:
established your lower and top gate parameters with a g/altitude/airspeed profile. We're wandering off topic, but yes, the concept of a "gate" is sorely underutilized in the civilian aerobatic world. Most of the people into civilian aerobatics aren't really very big into physics, which is a pity, because aerobatics is really just applied physics. So what happens most of the time is that people experiment, trial and error, and figure out what works, and what doesn't, hopefully at a high enough altitude to recover from any mistakes. The gate is a wonderful  I would opine essential  tool of the lowaltitude aerobatic pilot. You can program an airplane similarly to a computer: same inputs, same outputs. Let's take a reverse outside half cuban eight, for example. We start level, pull to the 45 up (I personally prefer a tad steeper, say 55 deg, to reduce xaxis requirements) and my gate for the push over the top is 1500 feet of altitude and 80 mph in the Pitts. The gate altitude is what determines whether or not I hit the ground, and the entry airspeed determines the G I must pull to obtain the desired radius, because the velocity squared factor in the lift equation is cancelled out the the velocity squared factor in the angular momentum equation at the stalling AOA. Neat, eh? I can enter the maneuver faster (90 mph works nicely), and obtain the same downward radius by pushing more G on the way down, but it's easier on the hardware to minimize the negative G. I can push over slower than 80 mph but I don't like it much  I'm on the edge of a negative stall as the nose pitches down, which doesn't feel good if it's a bumpy day  turbulence can cause you to exceed your stalling AOA and you can get into a drag trap as Cd exponentially soars, which isn't so bad going down except that Cl is reduced. Now, thinking about the start of the maneuver, we have to be able to have enough potential energy to obtain 1500 feet and 80 mph, which means that I'd like to see 160 mph of kinetic energy at 250 AGL before I pull up to the 55. The above really isn't very complicated. A very nice, simple maneuver which has you exiting inverted at 250 AGL. Great view. We do it in wingtiptowingtip formation, which is great fun. Keeping in mind that with a negative AOA the effect of bank is reversed, which is a phenomenon which gets more apparent as the negative G increases. This means that if the wingman gets too close to the lead and absentmindedly slightly spirals away from the lead (a harmless enough adjustment during a positive G formation maneuver such as a loop) the high pressure on the top of the wing will cause the wingman to move *closer* to the lead. It's best to start out doing this stuff with nosetotail clearance for this reason, but that increases the power delta required between the lead and the wing because of the geometry during the vertical maneuvers. What great fun, though!  ATP www.pittspecials.com 
#4




"Andrew Boyd" wrote in message om... Dudley Henriques wrote: established your lower and top gate parameters with a g/altitude/airspeed profile. We're wandering off topic, but yes, the concept of a "gate" is sorely underutilized in the civilian aerobatic world. Most of the people into civilian aerobatics aren't really very big into physics, which is a pity, because aerobatics is really just applied physics. So what happens most of the time is that people experiment, trial and error, and figure out what works, and what doesn't, hopefully at a high enough altitude to recover from any mistakes. The gate is a wonderful  I would opine essential  tool of the lowaltitude aerobatic pilot. You can program an airplane similarly to a computer: same inputs, same outputs. Let's take a reverse outside half cuban eight, for example. We start level, pull to the 45 up (I personally prefer a tad steeper, say 55 deg, to reduce xaxis requirements) and my gate for the push over the top is 1500 feet of altitude and 80 mph in the Pitts. The gate altitude is what determines whether or not I hit the ground, and the entry airspeed determines the G I must pull to obtain the desired radius, because the velocity squared factor in the lift equation is cancelled out the the velocity squared factor in the angular momentum equation at the stalling AOA. Neat, eh? I can enter the maneuver faster (90 mph works nicely), and obtain the same downward radius by pushing more G on the way down, but it's easier on the hardware to minimize the negative G. I can push over slower than 80 mph but I don't like it much  I'm on the edge of a negative stall as the nose pitches down, which doesn't feel good if it's a bumpy day  turbulence can cause you to exceed your stalling AOA and you can get into a drag trap as Cd exponentially soars, which isn't so bad going down except that Cl is reduced. Now, thinking about the start of the maneuver, we have to be able to have enough potential energy to obtain 1500 feet and 80 mph, which means that I'd like to see 160 mph of kinetic energy at 250 AGL before I pull up to the 55. The above really isn't very complicated. A very nice, simple maneuver which has you exiting inverted at 250 AGL. Great view. We do it in wingtiptowingtip formation, which is great fun. Keeping in mind that with a negative AOA the effect of bank is reversed, which is a phenomenon which gets more apparent as the negative G increases. This means that if the wingman gets too close to the lead and absentmindedly slightly spirals away from the lead (a harmless enough adjustment during a positive G formation maneuver such as a loop) the high pressure on the top of the wing will cause the wingman to move *closer* to the lead. It's best to start out doing this stuff with nosetotail clearance for this reason, but that increases the power delta required between the lead and the wing because of the geometry during the vertical maneuvers. What great fun, though!  ATP www.pittspecials.com See Aeroplane Monthly Feb. issue 2004 Article "Precision Decision" by Col (now Gen) Des Barker. In it, Gen Barker covers fairly completely my comments on the issues involved in high gating and it's effect on low altitude vertical recoveries in the P51 Mustang. You might find the article interesting. Hope you guys are having a good season. I understand your dad was Canadian Forces. Ask him if he knew Greg Bruneau. I flew the #10 bird as a guest of the Snowbirds back in the 70's with Greg. Great guy, and a wonderful team. You two remind me of another father and son team from back when. Don't know if you would remember Bill and Corkey Fornof. They put together the first F8F civilian Bearcat team ever. Bill is gone now, but Cork is still out there doing movies. Just emailed with him last week. Doing fine! All the best, Dudley Henriques International Fighter Pilots Fellowship Commercial Pilot/ CFI Retired For personal email, please replace the at with what goes there and take out the Z's please! dhenriquesZatZearthZlinkZdotZnet 
#5




Andrew, do you compensate for density altitude when you define your gates?

#6




Jay Smith wrote:
Andrew, do you compensate for density altitude when you define your gates? As a formation team, we are far more sensitive to density altitude than solo performers, who are free to improvise as they go along. Some of our maneuvers  like our opening noroll vertical eight, which has an outside loop on the bottom and an inside loop on the top  simply wouldn't be possible at say a 3,000 foot elevation airport on a 100F day. We'd drop the top (slow, high AOA) inside loop, and just do a vanilla outside loop instead, which is also what we do for our low (not flat) show with low ceilings. Frankly what bothers us mostly with higher density altitudes is power loss. We try to deal with that by trading potential energy for kinetic: for example, on a hot day we will plan to exit the opening vertical eight at 400AGL instead of 250AGL and let the nose drop to 250AGL before the push to the following outside cuban, which I have to be very gentle over the top to avoid outside snapping in close formation. Giving away the 150 feet of altitude also unloads the wing and gives us another 10 mph entry speed for the outside cuban, which is worth gold to me on wing over the top. At higher density altitudes you will definitely see higher TAS and larger radiuses, and if you're going to airshows under those conditions, you will DEFINITELY want to pad your gate altitude. I live way too far north, but can't stand to not fly during the winter. When it's 20C (dunno what that is in F, probably below zero) you wouldn't believe the aircraft performance: engine, prop and wing all love that cold, thick air. I can get 2,000 feet of vertical from the surface to the hhead kick in my stock S2B, which is simply not possible in summer. P.S. Even though there's no heater, your toes don't get cold  just pull some G, and they warm up just fine :) P.P.S. Apologies for being offtopic,  ATP www.pittspecials.com/images/oz_inv.jpg 
#7




Andrew, do you compensate for density altitude when you define your gates?
An interesting fact, which is not obvious to many folks, including some aerobatic pilots (judging by the number of loop into the ground accidents) is that the radius of any turn, up, down, sideways or whatever, is a function of the square of TRUE airspeed, which is of course a function of density altitude and calibrated airspeed. So, if the density altitude increases your true airspeed by 5mph, you get a 5mph^2 impact on your radius. This kind of change in radius can ruin your day if you are playing down near the dirt. This velocity^2 thing is also why the reverse cuban or loop down is a real killer. If you start the pull with X knots too many, you will use X^2 more radius for the 1/2 loop, throw in an increase in TAS of say Y due to density altitude and you are into (X+Y)^2 more radius ... not good. If you have not left margin either in terms of available G or altitude you are either gonna high speed stall on the way down (and hit the ground) or hit it on the arc. This sort of question is on the ICAS exam now if I'm not mistaken. Peter 
#8




Peter AshwoodSmith CGZRO wrote:
Andrew, do you compensate for density altitude when you define your gates? An interesting fact, which is not obvious to many folks, including some aerobatic pilots (judging by the number of loop into the ground accidents) is that the radius of any turn, up, down, sideways or whatever, is a function of the square of TRUE airspeed, which is of course a function of density altitude and calibrated airspeed. So, if the density altitude increases your true airspeed by 5mph, you get a 5mph^2 impact on your radius. This kind of change in radius can ruin your day if you are playing down near the dirt. This velocity^2 thing is also why the reverse cuban or loop down is a real killer. If you start the pull with X knots too many, you will use X^2 more radius for the 1/2 loop, throw in an increase in TAS of say Y due to density altitude and you are into (X+Y)^2 more radius ... not good. If you have not left margin either in terms of available G or altitude you are either gonna high speed stall on the way down (and hit the ground) or hit it on the arc. This sort of question is on the ICAS exam now if I'm not mistaken. Peter Hence the reason I asked the question. Thank you, Andrew and Peter. The original ICAS/FAA ACE proposal required a PhD in Aeronautics and computational fluid dynamics software to answer the questions. Fortunatly, the program was changed and common sense prevailed. Sadly, there are still many acro pilots out there who have no understanding of how density altitude affects their flight and refuse to be educated. 
#9




"Peter AshwoodSmith CGZRO" wrote in message m... Andrew, do you compensate for density altitude when you define your gates? An interesting fact, which is not obvious to many folks, including some aerobatic pilots (judging by the number of loop into the ground accidents) is that the radius of any turn, up, down, sideways or whatever, is a function of the square of TRUE airspeed, which is of course a function of density altitude and calibrated airspeed. So, if the density altitude increases your true airspeed by 5mph, you get a 5mph^2 impact on your radius. This kind of change in radius can ruin your day if you are playing down near the dirt. This velocity^2 thing is also why the reverse cuban or loop down is a real killer. If you start the pull with X knots too many, you will use X^2 more radius for the 1/2 loop, throw in an increase in TAS of say Y due to density altitude and you are into (X+Y)^2 more radius ... not good. If you have not left margin either in terms of available G or altitude you are either gonna high speed stall on the way down (and hit the ground) or hit it on the arc. I think this may need a little more explaining even if only for my understanding. I am very new to aerobatics. So if I normally commence a loop at 100 knotts but get the entry speed wrong and start at 105 knots then my loop (assume horizontal plane and constant speed for simplicity) will be New_Loop_Diameter=Old_Loop_Diameter x New_Speed ^2 / Old_Speed ^2 i.e. a factor of 1.103. A bad entry of 15 knots over speed would have a factor of 1.323. But a target speed of 200 but entry of 215 would have a factor of 1.156. If my understanding is not correct then please explain why. I prefer to understand the physics/maths before I attempt some of these manoeuvres. Anyone care to formulate what happens when speed ( or "G") are not constant? This sort of question is on the ICAS exam now if I'm not mistaken. Peter 
#10




wrote:
So if I normally commence a loop at 100 knotts but get the entry speed wrong and start at 105 knots .... Anyone care to formulate what happens when speed ( or "G") are not constant? Your speed and G are NEVER constant during a loop. A vertical maneuver is always low and fast, then high and slow, then low and fast again, etc. You continually convert your kinetic energy at the bottom, to potential energy at the top, then back to kinetic energy on the downline. A hhead (aka stall turn) is a perfect example of this. You go straight up until you stop, then pivot, and fly down and gain airspeed again. Given a constant density altitude, additional entry speed implies additional G to make the same radius, assuming you fly at (or near) the stalling AOA which generates Clmax. Think of it this way: given that you fly at Clmax: 1) the radius of the vertical maneuver is a function of the aircraft stall speed (Vs), and 2) The G you must pull or push is a function of the entry speed. Does that make sense? It's not completely true  it will not withstand a rigorous proof, but practically speaking, it's what you really need to know to yank and bank down low. The tbird F16 (famous canopy pic) that dug a hole this year doing a vanilla reverse inside 1/2 cubaneight is a perfect example of this: he blew his gate  he was 1000 feet low. It didn't matter how much G he pulled, or what speed he flew, the F16 was simply not capable of that tight a radius. However, the Pitts with it's lower stall speed would have been easily capable of it  1500 feet is plenty for me, because my stall speed is roughly half of his. This is worth repeating: for a gate at the top of a vertical maneuver (with downwards energy vector) such as a splits or reverse cubaneight: 1) the altitude determines whether or not you hit the ground (your radius is a function of your true stall speed, which in turn is a function of density altitude) and, 2) the entry speed determines how much G you will have to pull (or push, if it's outside) to attain Clmax which results in the minimum radius. Hopefully this G is less than ultimate load! I am assuming that everybody reading this is familiar with a fundamental equation of aerodynamics, which is crucial for understanding aerobatics: Vs(G) = sqrt(G) x Vs(1G) There is a fundamental relationship between speed and how much G you can fly. A wing stalls at the pretty much the same AOA, which can be attained at a variety of airspeeds. N.B. The above is easily derived from the lift equation. I will do so for the lowly price of a beer P.S. One doesn't need a Phd (piled higher and deeper) to understand this stuff. It's mostly high school physics with a smattering of first year college/university mechanics. Remember all that crap about weightless ropes and frictionless pulleys? :) I had forgotten about it too, until years later I ran across a brainless pulley, but that's another story :) P.P.S. Good luck trying to find an aerobatic instructor who has both a solid practical background and an understanding of the theory involved, and who can explain both. They are few and far between!  ATP www.pittspecials.com 

Thread Tools  
Display Modes  


Similar Threads  
Thread  Thread Starter  Forum  Replies  Last Post 
AOPA Stall/Spin Study  Stowell's Review (8,000 words)  Rich Stowell  Aerobatics  28  January 2nd 09 03:26 PM 
Accelerated spin questions  John Harper  Aerobatics  7  August 15th 03 07:08 PM 