The fastest way down
 

Fly like a fighter: Down we go...

(AOPA Online, 12/30, L. Brown) "...Aside from drag devices, fighters also have the option of performing a low-power but high-G descending spiral to keep the airspeed under control while making a rapid descent. But, alas, not all of these options are available in our general aviation airplanes. From cruise at 8,000 feet to 12,000 feet msl, would you consider ripping your throttle to idle to expedite your descent? Not a good idea since shock cooling a piston engine is not a healthy choice. Most GA airplanes don’t have speed brakes, and most already have the gear extended. We do have an added trick that doesn’t work as well in fighters--the forward slip. Overall, though, what is your best option? Follow the guidance of “proper prior planning prevents pretty poor performance” and you will pre-plan your descent point in your aircraft for your particular flight that day. If you do get behind, then go ahead and make a 360-degree turn (or two) to allow you to descend comfortably and not rush your arrival..."

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This article reminds me of the knife-edge spiral some skydive dropzone pilots use in Cessna 182s. Close cowl flaps, set power to 15, bank to ~85, kick full opposite rudder, and adjust attitude using aileron (not elevator) to stay in yellow arc, adjust g's using elevator to hold about 3.5 on the meter. This is the fastest way to get down short of using a drag chute plus speedbrakes. It is faster than forward slipping or a full-flap descent. Shock cooling does not occur using good power management technique as any drop zone owner knows, although a digital engine meter helps fine tune it. Many drop zone Cessnas have ten thousand hours on the same engine doing this with no problem. I had a thread on it some time ago, see below. You do not want to do it without a good bit of practice because it involves pretty fine adjustments of attitude, speed, and power. Also, never attempt without proper training, parachute, and g-meter lest you overstress the airframe and find yourself without one.

Knife Edge

Similarities, and Applied Aerodynamics
 

The high-g profile described in the article works because fighters are generally low-aspect ratio wings. At high g (AOA), there are huge drag penalties due to tip-losses/vortices.

The same principle works in GA aircraft, as you have noted, just not quite as well. Most fighters have an aspect of about 6; GA is usually around 10-12, if memory serves. GA losses due to vortices are a much smaller percentage of the drag on the airplane.

The article said fighters can't use a slip: I have, and continue to do so (this is in the F-4 and the T-38). Fly-by-wires may not cooperate as much, but I think it can still be done (ie, step on the rudder in an F-16, and it deflects---but the ailerons would auto-deflect to prevent the roll that happens in swept-wings with yaw).

I did an emergency decent in the sim (for a checkride) simulating cabin-pressure loss in the Lear 35 a little differently than the book. We normally just went to idle, dropped the gear, popped spoilers, and held it straight-ahead at redline speed. From 40,000 ft, it took about 7 minutes to get down to 10,000.

I did all that, but went into a 60-degree-bank turn and used bank to keep the pitch at its normal mark (I think it was 10 degrees). IE, I was holding 2-gs.

The Sim guy said "Hey, what are you doing?" I had my FO give the "ATC, we are orbiting at present position in our descent" call.

When we levelled off, the Sim Instructor said "Wow...you got down in half the time of normal.......you're going to have to explain to me how you did that...." ;)

I've seen cross-controlling use to slow closure too. Usually the result of poor closure control to start out with :) - but effective.

USMCFLYR

This maneuver of course is all about converting potential energy (altitude) into kinetic energy (motion) by wasting it at the stress limits of the airframe. AoA gives lift which is wasted to the side as well as induced drag which wastes energy in the form of wingtip vortices as mentioned. The added value of a slip or knife edge is you get the rudder adding to it through unused yaw and associated drag, while it angles the fuselage to get form drag as well. All this challenges the structures, but I used to see minus 5,000 fpm in the C182 without speed brakes or evidence of any rivet stress. Fly-by-wire may be why they do not use it as much in military jets. I am guessing, but you guys would know.

When training guys in tbms or meridians I would use this setup, max safe(simulated versus actual situation) speed, 45 bank, and point that nose down! Very effective when the only concern is just getting down. Now if there's some distance to still cover I'd say keep the wings level, but everything is situational.

Very interesting stuff. Gets into some advanced aerodynamics and you'd better know what you are doing. There are a couple of jump operations closer to where I operate out of and since we are located in a TSRA area I doubt they use techniques such as this to get down.
On a similar note, please forgive me if the said note is dissimilar to what we are discussing here. I was giving a photo flight and the gentleman (who was an Air Force pilot) wanted to take a "vertical shot" of the target since the gear of the Skyhawk would be in the way. We were at 1,000 foot AGL surrounded by mountainous terrain and he wanted me to "try doing a crab" for which I scratched my head. I have received adequate spin training and I was not about to "crab" or be uncoordinated at 1,000 ft. AGL so I refused such a maneuver and settled for a 45 degree bank. I actually climbed to 2,000 AGL and made a descending 45 degree bank to 1,000 ft. AGL. If I would have tried to crab or be uncoordinated in the name of getting the landing gear out of the way, I think I would have found a very fast way to get down indeed.

I assume he meant "sideslip" rather than crab.

Sideslips/forward-slips (same thing, just differences in the relative wind direction and path along the ground) are used by all sorts of GA aircraft all the time to land! Many people teach this as a technique to get better visibility of the ground, but I never went crazy with it, as being uncoordinated is usually not the best thing for passengers and you need to pay attention to maneuvering speeds when making control deflections obviously. Still, I would have my students do it at times. Don't let your speed drop excessively low, but realize that sideslips and forward-slips are done all the time close to the ground. Remember that a spin requires a yawing moment, if you aren't yawing when you stall, it will not really start to spin (unless the stall then causes a strong yaw, but this can usually be managed). Use good judgement, don't let your speed get dangerously low, but it can and is done safely all the time. You might not be able to maintain altitude for long while doing this, so it's best to limit it for a while, climb back up, repeat if necessary. Obviously each aircraft is different and not all will react the same, but you can do this all day in standard cessna single engine, and while I may not want to stall in some other aircraft while being "uncoordinated", the airspeed and any POH/AFM limitations are really key here. I've had people come to me and say they were never taught to do full forward-slips to landing in that airplane with full flaps, and while a tail-oscillation buffet is possible (it's been very rare for me), it does not result in loss of control and as long as you got fuel in both tanks, you can do this all day too, not restricted in the manual or anything.

On the other hand, flying low over mountainous terrain is something that has to be managed correctly. There are things you can get away with, and then the right way to do things. If you didn't feel comfortable getting low/not having an exit, then more power to you.

Testing the operating envelope of an airplane requires a higher degree of skill and knowledge. The topic at hand in this post certainly says that. I have and teach the use of slips constantly and quite frankly I enjoy doing them especially when landing with no flaps on a Skyhawk. The combination of high terrain, and low altitude, made me feel like a recipe for a disaster to try being uncoordinated. I just did not feel comfortable. I listened to that infamous inner feeling that said "don't do it."

It's knowing the airplane and knowing your skills. Slips with the 40 degree flap setting in the 172 is not good - that's why the newer models only go to 30. I'd let pax know, "we're a little high, so I'm going to turn the airplane sideways to get down, it's better to be too high than too low".

I was taught to use slips whenever needed in every plane I've flown and have done so (on final only, not at altitude or in the 3 other legs of the pattern)

Somewhere in the recesses of my brain, I remember hearing of a 737 (? big jet, regardless) driver slipping to get down.

Great thread - I've enjoyed the Lear and jump driver posts especially

From my limited aerobatics experience, I was taught that you cannot spin the airplane from a slip, but only from a skid. If stalled while in a slip, the plane will do a "falling leaf" maneuver. Quite a weird feeling to hold it in one, but the falling leaf is pretty unstable and can oscillate to a skid pretty easy and start a spin if you're not careful.

Being experimental, I've tried slips in a 182 with 40 degrees of flaps. It pitches the nose down pretty violently. Before I tried it, I heard in a lecture, at an ESP CFI seminar, that the violent nose pitch is the reason planes are placarded for no flap slips (he was an FAA examiner so I'll consider it a credible source).

And that knife edge maneuver is awesome!

Due to swept-wing aerodynamics, slipping an airliner is universally a very bad idea. These guys ran out of options:
http://en.wikipedia.org/wiki/Gimli_Glider

I had a boss many years ago who was rated in the Lear. He told me (not sure if this was BS or not) that when they practiced getting down to altitude from a catastrophic decompression, this was way before simulators, Lear 20 series, that they pulled the power, rolled the airplane inverted, dropped the gear and out with the speed brakes. This way going into it inverted, as the nose came down, they would only pull positive G's. He told me this story once, but like I said, I did not know if he was pulling my chain.

Not Quite Right
 

The two prerequisites for a spin (in any airplane) are a stalled wing, and yaw. Doesn't matter if the yaw is "Forward-slip" or "Side-slip."

I found that previous training colored my perception (and made for pre-conceived notions) regarding aerobatics and post-stall maneuving. I started flying in General Aviation. Stalls were straight-ahead to 30 degree bank maneuvers, and slow. Spins were something entered from low-speed, low-power, and deliberate (with full-aft wheel and full rudder).

The resultant aircraft behavior was also pre-conceived: in stalls, a Cessna 150 would pitch down (classic stall-break). Spins would increase bank, and settle at about 20 degrees down. And, I believed that once stalled, an airplane could not be maneuvered, per-se. (In my mind, the recovery was mostly about the addition of POWER, and trying to figure out how to stop that horrible Cessna stall horn from going "bleeehhhhhhh!")

It wasn't until I did the very thorough aerobatic training in the Air Force that I realized: I could stall in any attitude, at any speed. Spins: any attitude, and a wide range of speeds. And airplanes (depending on type) could be maneuvered after the stall.

Example: while doing a loop, you can stall while going straight up, upside down at the top, or when going straight down. The resultant (temporary) aircraft motion differs, but the principles are the same.

Do a loop while going straight-up, pull on the stick until the airplane is stalled, and stomp the rudder: you just entered a spin while going straight-up. Horizontal plane? Snap-roll. These resultant maneuvers are temporary, and given enough time, would end in a familiar stabilized spin.

Back to the two prerequisites. In a spin, usually the inside wing is stalled, and the other is not (or "Less-stalled"). The difference in drag on the two wings (more drag on the stalled side) is what keeps the yaw stabilized.

In most GA aircraft, the recovery is to unload (reduce AOA) to "un-stall" the inside wing, and apply opposite yaw. When it stops spinning, recover from whatever attitude you are in.

In jet fighter-types, it may be a little different: apply full-aft stick to make both wings equally stalled. Rudder-yaw may or may not be available (usually not) as fighters have short tail moment-arms, usually have limited deflection available when the gear is up (to prevent overstress at high speed), and are often in disrupted air behind the spinning fuselage.

You should be able to yaw a GA airplane for photos without worry. Slip a little, and if losing airspeed or altitude, add power. If you are at the max allowable power, slip less.

Learn it at higher altitude until it is natural before trying it down low.

Yep, did it extensively in a job I had flying GPS grids for photo work at low altitude. The grids often ran right into hillsides and we would skid to turn around quickly. I had a huge post worked up telling all the gory details, then the software lost my work before I could post it. Could not even use the back button to find it. The lesson is to make small posts apparently. :(

Some points:

• Skidding creates tons of drag. Your airplane will probably start a gradual descent even using full power.
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• When you skid under full power, the prop disc will undergo partial stall. This creates huge stresses on the prop and makes a loud noise. It probably is bad for the prop but in hundreds of operational hours doing this on 3 blade props, I never saw a failure or got a bad report from a mechanic. Your mileage may vary.
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• Full-bore skidding is hard on the flight controls. You will see rising maintenance costs for rigging work.
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• You are much safer in regard to spins than you would guess. The airplane will mush before spin most likely. My photo firm tested this extensively, and found that only a gross attempt to stall the airplane in a skidding configuration with full power using back elevator would produce a spin. It was a safe maneuver even at low altitudes done with care.

I've done slips all the time in 182s with full flaps, just pitch down more, in fact most people do not do this enough because they are trying to replicate their "normal" landing pitch while slipping, and they tend to get slow. I'll even go as far to say that most people should not land these with 40 degrees of flaps and they do not make an approach that is appropriate. Why are you going to follow the VASI at 40 degrees of flaps and 12" of MP? How does it make sense to power in at a high-AOA and high power seting during landing? How much extra power will you now have when you hit some wind shear or downdrafts? If you are going to use the 40 degrees you need to come in at an AOA and speed that are approrpiate (usually going to be pretty steep). This airplane is a drag-queen with 40 degrees, but you can still slip. Don't get slow, think about your descent rate and transitioning to normal landing later on. Never had it "pitch down" on me like you describe in any situation. Think about it, how would that be possible?

You can find a lot of crazy things stated by examiners, less by inspectors, and less depending on the experience, knowledge and ability of whomever you are talking to. Realize that examiners are kind of out there "on their own" by contract from the FAA. They sometimes have some pretty interesting/crazy ideas. Think about their reasoning and do some research.

Newer single engine cessnas only go to 30 degrees because it's way too hard to power out of a rejected landing with 40 degrees in certain conditions. I can fly that old C182 with 40 degrees at some pretty crazy slow speeds given it's weight and size, but with that much induced drag you just can't maintain altitude at all. With these aircraft there was also the issue of the flaps blanking out the tail when speeds decrease during landing, resulting in flat/hard landings as well. Limiting to 30 degrees helps with both. I don't believe it had anything to do with slips.

Hopefully with good instruction students won't have to wait until an experience like this to make this realization. When I do spin training I deliberatly pull up from the resultant dive fast enough that I'm getting some accelerated stall buffeting, to minimize building up load factors. I'm basically on the edge of a stall while pointing straight down. And then there's the accelerated stalls that can demonstrate the point IF you do them correctly (one IP taught to do them in a bank and simply get slow in the bank until you stall..great for not scaring people, um...poor to demonstrate the point that you can stall at any pitch attitude). You can even do these things with a cessna 150, although it helps to have an aerobat :)

Me too....a Solution
 

Cub:

That's happened to me, too (when APC times-out on me while writing a lengthy diatribe, and I mis-type my name or password getting back in).

Solution (at least, what I have done):

Write your post in Word, then copy and paste. ;)

"Example: while doing a loop, you can stall while going straight up, upside down at the top, or when going straight down. The resultant (temporary) aircraft motion differs, but the principles are the same.

Do a loop while going straight-up, pull on the stick until the airplane is stalled, and stomp the rudder: you just entered a spin while going straight-up. Horizontal plane? Snap-roll. These resultant maneuvers are temporary, and given enough time, would end in a familiar stabilized spin."

That's a very good point. I was meaning to point out, from a straight and level perspective, that "the slip" is relatively stable while "the skid" is not (in high wing stable airplanes). Once again the example is the falling leaf maneuver.

"Never had it "pitch down" on me like you describe in any situation. Think about it, how would that be possible? "

I actually have no idea. I'd lightly slip all the time with 40 degree flaps because it was a very tight runway. The nose down would usually happen if I applied full rudder and held it. Assuming a CG at its forward limit and airspeed constant.

A REAL internet guru can read a thread, log on, work up a 1,000-word content-perfect post in 10 minutes or less, hit the little "send" button and be back to the ladies before the server even thinks about dumping their little discourse on the subject. That's the test of internet manhood. I'm getting old. :)

wizepilot

I don't know if he was pulling your chain, but he was certainly foolhardy and not very wise about flying jet aircraft. First, anything close to a catastrophic decompression raises the real chance of the structure being damaged--not a situation you would want to be rolling inverting and pulling. Maintain the airspeed at the time of failure and go down slowly. At least one B707 wa lost when it had an explosive decompression due to a bomb and the crew did the classic "high dive" and ripped the tail off.

Second, doing aerobatics like that in a plane not tested or cert'd for them is asking for HUGE trouble. Too many incidents to mention here--several Hawkers have been rolled with nasty structural damage, for one.

Third, I suspect a Lear pointed straight down would not have enough drag not to get into a serious overspeed or get seriously damaged. Overspeeds in Lears are proven killers--loads of examples there.

GF

I'm going to have to agree with galaxyflyer on this. The early Lears had a nasty high-speed mach tuck tendency that has claimed a few lives over the years. They're great airplanes, but not ones you want to be rolling inverted at FL400+ in a possibly compromised airframe.

I'll stick with the procedures established by the manufacturer to meet certification guidelines.

It's not just the 20-series. The 35, 36, and I believe 31 are the same in regards to tuck. Get over M0.82? Good luck.

It worked well in the 727 too,...as long as you wemt about it smoothy.

A rapid descent at any bank angle... Are you flying it in circles or kicking the rudder in to go straight down in a slip ?

In jets I'd presume all rapid descents are in circles because slipping a wing like that could be asking for trouble.

Thanks. I thought he was full of s$$t. He's gone now anyway. Ran into a tree driving drunk.

Speaking for Cessna 182s, you fly in circles doing a full slip with nose slightly above the horizon. So a left one would be, left wing tip on the ground using ailerons, full right rudder to the stop to make a slip. Pull the yoke to adjust g's but adjust ailerons a bit too, no hard rule on that but technically g's go to infinity at 90 degrees according to the math and we don't want that, while an outright dive will overspeed the airframe pretty fast, so you are treading a fairly fine line near 90 degrees of bank. It's a walk and chew gum at the same time kind of a thing and I used to train new pilots to do it with about half of them washing out of this very maneuver. I never thought it was that hard to do personally, and I am not hero pilot either, but many guys would get un-nerved about an extended unusual attitude and they would often screw it up. Since the maneuver was at the limits of the airframe and screwups could not be tolerated we generally had to fire them if they did not get it pretty quick. That said, I know many jump pilots used this maneuver for decades without issue, although from what I hear it is getting less popular to do it at drop zones because the early 182s they use are wearing out and the last few thousand hours can only be extracted by gentle means.

Well, only if maintaining level flight

I don't mean this disrespectfully as I've never flown jumpers, but high load factors coupled with maximum sideslip sound like a recipe for problems unless the pilots have aerobatic experience. Is this technique common?

The maneuver is as good as the pilot and yes, it has been done for ages in C182s. RickT86 or one of the other former jump pilots will tell you. You do this maneuver 30 times a day from 14k down to 1k for years at a time, not a stressed rivet in sight. I worry about pilots who have no feeling for things more than those who do and fly using their experience, knowledge. common sense and intuition. Fly like you love it and know what you are doing. No problems that way, none at all. What are the g's telling you? What are the airframe sounds telling you? How do the flight controls react? How would you feel if you were the airplane right now? What does the science tell you? Does the science agree with your experience? Why or why not? That is the way to think about any performance maneuver. Never fly mechanically.