Most pilot-unfriendly aircraft (cool or not)

In My Humble Opinion
41

The Yak 141 was supposed to be Russia’s answer to the Harrier jumpjet : a VTOL, carrier-bound aircraft. Doubly useful for them, since the Russians never managed to get functional carrier catapults, which really limited the performances of their navy birds at the time (they later managed to work around that).

The catch ? Well, it had the same problem as the Harrier when the thrust nozzle pointed down - one second you’re skimming fine, the next you’re crashing. So, the vertical take-off/landing procedure was set to automatically activate the ejection seat under certain parameters. Apparently, the automated software was finicky, so it also happened at random sometimes, resulting in a very surprised pilot.

42

The Sopwith Camel was, as Cicero noted, notoriously difficult for beginners to get the hang of- you either worked it out pretty damn quick or it killed you.

The problem was the Clerget rotary engine in it- Which resulted in an incredible amount of torque to the starboard side, meaning the Camel could make incredible starboard turns, but not as well to port.

Also, if it stalled, it would invariably go into a spin, which, for a novice pilot, basically meant you were completely buggered.

Having said that, in the hands of an experienced pilot, the Camel was incredibly manoeuvrable and could be trimmed to fly so the pilot could take their hands of the controls and the aircraft would still continue in level flight.

An improved version- the Snipe- saw limited operation use in the closing months of WWI, in case anyone was wondering.

43

IANA gyroplane pilot, but I do hold a Rotary Wing rating in helicopters.

Helicopters are inherently unstable. The fuselage hangs by the mast like a pendulum from the main rotor. Many helicopters have semi-rigid rotors, also known as a teetering-rotor system since the two blades flap as a unit like a teeter-totter. Examples are the Robinson R22 and the Bell JetRanger. Semi-rigid rotor systems have a flapping hinge to allow the blades to move up and down, and feathering hinges to allow the blades to change pitch. Other helicopters have fully-articulated rotor systems, like the Schweizer 300. Fully-articulated systems have flapping hinges, feathering hinges, and lead-lag hinges. (The last is to compensate for the Coriolis effect.) Rigid rotor systems have feathering hinges, and the flapping and lead-lag are handled by the flexibility of the blades.

Some rigid-rotor helicopters can do aerobatics. I’ve just gotten out of bed, so I can’t think of one right now. Some helicopters with fully-articulated systems can do aerobatics as well. I’ve seen video of a guy doing amazing stuff in a Schweizer/Hughes 300, and of a Sikorsky HH-3 ‘Jolly Green Giant’ doing an ‘aileron’ roll.

But these are positive-g maneuvers. See, if you remove G the fuselage will swing in any direction. If you unload the rotor disc, there will probably be mast-bumping. If this is violent enough, it could cause the rotor system to separate from the aircraft. What happens more often is a boom chop. In this situation, the rotor blades strike and sever the tail boom. This is bad. (Boom chop can also occur in low rotor RPM when the retreating blade stalls and results in ‘blowback’ of the rotor system.)

The R-22 seemed to be particularly susceptible to zero-g crashes. The story as I heard it was that one young pilot happened to come from a rich family with connections, and the issue was escalated to the point where the R-22 was to be deemed unsafe. Investigation of crashes revealed that many of the accident pilots recently transitioned from fixed-wing aircraft, and the R-22 was the most popular helicopter for training. It was determined that the aircraft was not at fault, but the pilots’ technique was. The result was that R-22 pilots with less than 400 hours in type were required to undergo recurrent training on how to avoid low-g and low rotor RPM, and all R-22 pilots had to take a safety class.

So why did airplane pilots tend to get into low-g in helicopters? Let’s say you’re flying along and notice you’re losing airspeed and your nose is a bit high. An airplane pilot pushes over, resulting in low- or even zero-g, and all is good – in a fixed-wing. In a helicopter this is exactly the wrong thing to do. Pushing over unloads the rotor disc and allows the fuselage to swing, possibly resulting in a boom chop.

The point of the preceding paragraphs is that in most rotorcraft you want to avoid low-g. That includes most helicopters, and not gust gyroplanes.

Now, what about the horizontal stab? The purpose is to help maintain the fuselage angle in forward flight. Some can be trimmed, but on the R-22s and Schweizers I’ve flown they are not. (Incidentally, have you ever noticed the spoiler above the cockpit on the Hughes/Schweizer 269 series (this includes the 300s, as the 300s are built under the 269 type certificate)? On earlier models there were crashes at high speed when the fuselage would ‘tuck’, much as described in the OP – but because of high speed, and not because of low-g. The spoiler fixes that.)

A horizontal stab will help keep the fuselage from ‘tucking’; but the solution really is to ‘dont get into a zero-g situation’.

44

I thought it was the Yak-38 that had the worst problems, incl. with the automatic ejection seat. The 141 didn’t even make it into full production.

45

Only about two dozen pilots flew the various Gee Bees; 8 died in them. That’s got to be a a difficult percentage to beat.

46

I’m possibly conflating the two, since they shared many characteristics if I’m not mistaken. Or was it that the 141 was supposed to do away with the 38’s issues, but didn’t ? I don’t remember, to tell you the truth.

47

I wonder how many pilots flew the BD-10? Only five were built, and three crashed, killing the pilots.

48

I just asked him. The 727 has no noticeable pitch response to a power change. On the 10, the simulator instructors just loved to kill #2 on takeoff to see if the pilot could prevent the nose from rising too far.

49

This is enough to strike fear into any pilot.
The Tarrant Tabor.

50

The 141 program was cancelled in 1991 thanks to the breakup of the Soviet Union. It sort of lives on in the sense that BAe bought the rights to certain aspects of the design and development data and incorporated it into the F-35B.

51

First part true for helicopters. Not quite as true for gyro’s. This may be because the helicopter rotor is directly powered a motor. In a gyro, it is not and the gyro is pushed or sometimes pulled by a propellor through the air just like a normal airplane. But thats more a nitpick by me and to be honest I havent thought through the heavy physics to really be sure about my position on that.

The bolded part is DEFINITELY not true for gyro’s. Or is at least extremely misleading if you dont really understand the physics. As soon as you get zero or negative G you arent “hanging” from anything. Hence the problem for gyro’s with no stabilizers.

And its a two fold problem for such gyro’s. First,since the gyro rotor isnt directly mechanically powered, as soon as it isnt providing lift, by definition, it isnt being powered and starts slowing down (unlike a helicopter rotor). Rotors going too slow are unstable and weak and often break up themselves or chopp off aircraft parts in short order. Negative G’s are even worse and start a negative feedback loop of badness.

The second part of the problem is the real killer though. As mentioned, the gyro is pushed or pulled through the air like an airplane. When you enter zero G, that pushing or pulling is still going on. If your thrust/pull line does NOT pass directly through the center of mass, THAT high level of thrust is going to instead try to rotate the craft about its center of mass. If you have a significant miss alignment of thrust in relation to the center of mass, that rotation can take only a second or so. And you don’t even have to have a major rotation until you’ve rotated it enough that its unrecoverable, and it all over but the falling and dying. Even the military and military test pilots would probably say that something that requires a reaction time that quick is unacceptable (or at least without DAMN good reason).

This thrust problem is also an issue (but generally lesser) with the center of drag as well as the center of mass, and the center of drag varies as a function airspeed.

But this problem can EASILY be solved by doing two things. Run the thrust line through the center of mass. And put on a horizontal stabilizer. This configuration allows to you to survive brief periods of zero G with enough time for you to either ride it through, or manuever in such a way to get out of the zero G situation.

And there are no good reasons to NOT do these two things.

As for the “don’t get into zero G” part. Yeah, don’t do it on PURPOSE for sure. But people screw up for one thing. For another, you can get a downdraft that will PUT you a zero G situation through no fault of your own. Ask any weekend fixed wing flyer how often they get even an unplanned brief period of zero G. Then ask them if they would keep flying if every time that happened they had a very high chance of dieing.

“dont get into a zero G situation” is like saying don’t wear your seatbelt as a race car driver. Just don’t get in an accident and no harm , no foul. Something bad happens, your dead. The seatbelt doesnt hurt a thing, so wear it!

“The gyros dont need centerline thrust or horizontal stabilizers” crowd is the gyro communities equivalent of the anti-vax crowd. The only difference is the anti-vax crowd hasnt killed anyone yet. Hundred of gyro deaths have happened because of this.

And why these people think gyro’s don’t need em when (virtually?) every helicopter flying has one is beyond me. Especially given that gyros are probably more sensitive to zero G in some ways than helicopters.

52

Once again I’m posting right out of bed, and before I’ve finished a cuppa joe. Not all of the synapses are firing yet, but I’ll try to address this.

I disagree. The fuselage hangs like a pendulum on a gyroplane just as it does on a helicopter. Even high-wing airplanes are said to have ‘pendulum stability’. In a helicopter or gyroplane there’s the added complexity of a ‘universal joint’ connecting the lifting surface and the airframe; which is why the weight-and-balance envelope tends to be fairly narrow, and why the pilot has to figure lateral CG as well as longitudinal. Google ‘gyroplane’ or ‘autogyro’ and ‘pendulum’ for a lot of cites. For example:

You are correct that rotors with low RPM can chop the boom; but I disagree that they ‘break up’. It’s true that most of the strength of a rotor system comes from rotation. If you were to suspend a rotorcraft from the (non-rotating) blade tips they probably would break. But if your rotor stops in flight you’ve got bigger problems to worry about.

It doesn’t matter that a helicopter’s rotors are powered and a gyroplane’s aren’. When a helicopter enters autorotation the rotor system is not connected to the engine. And they definitely do slow down, which is why it’s critical to lower the pitch immediately. Aerodynamically, there is a ‘driving section’ and a ‘driven section’ of the rotor system. The air passing over the driving section keeps the blades turning. The driven section provides the lift. Forward speed to keep all of this working is provided by gravity. In a gyroplane it is provided by thrust from the engine. If you were to have an auxiliary engine just for thrust on a helicopter, then it would fly as a gyroplane. If you were to cut the engine in a gyroplane, it would glide just like a helicopter in autorotation. Basically, a gyroplane is flying in autorotation all of the time.

You’ll get no argument from me that zero-g kills. As I said earlier, so many people died after zero-g crashes that the FAA imposed additional training for the R-22. People who fly JetRangers tend to have a lot more experience than R-22 drivers, so they know to avoid zero-g. I think that the problem with gyroplanes is that the people who crash them tend to be low-time gyroplane pilots. That is, it’s not really the aircraft; but the pilots.

As for ‘a second or two’ being too little time to reasonably expect a pilot to react, helicopters have the same issue. The R-22s and Schweizers in which I have experience have ‘low-inertia rotor systems’. That is, their blades aren’t very heavy. Upon loss of power (and the resulting decoupling from the engine) they slow down right now. This is why it is critical for the pilot to act immediately. By ‘immediately’ I mean less than a second. I’ve been through a lot of unexpected throttle-chops, and it’s easily done. In hovering autorotations (you’re three feet off the ground and you lose your engine) you have to wait a second before pulling the collective to cushion the landing. A second can seem like a very long time.

53

The Pendulum thing is WRONG. Dead wrong. “LIKE a pendulum” is not the same thing as “IS JUST LIKE or is a pendulum”.

Imagine a pendulum. It has a mass down below a pivot point. That mass may oscillate fore and aft of that pivot point but barring extreme input the mass will stay below the pivot point and want to return to that position. And it takes more and more force to get it farther and farther from its stable position of straight down. Release those forces and it returns to that position.

A gyro (without a horizontal stabilizer or center line thrust) in zero G can easily get its mass above the pivot point. Additionally, when it rotates, it doesnt rotate above the pivot point (rotor), it rotates about its center of mass. Pendulums dont do that.

A more accurate description is “a gyro sorta acts like a pendulum until it quits acting anything like a pendulum”. Just enough similarity to be dangerously misleading IMO.

I have no doubt you a helicopter guru and pilot (seriously). But gyros are a bit different. I am just a armchair guy that has spent hundreds, if not thousands of hours reading about gyros. And not just the fluffy, cool story stuff either.

I’ll just point you in the direction of a, if not THE gyro guru. Chuck Beaty. Google rotary gyro forum. Its the one powered by vbulletin. Anything written by him is physics/technology/aerodynamic gold. He knows his stuff, knows how to write, is more logical than Spock, and is good with simple analogies as well.

There are hundred if not thousands of pages of plenty of people asking questions and misunderstanding how gyros really work and behave. Chuck and a few other really bright and patient others explain this stuff over and over and over and over. It makes the gun and simliar threads here on the SDMB pale in comparison.

Of course Dennis Fetters post there as well, who is probably responsible for more helicopter and gyro deaths than any other single person on the planet due to some questionable understanding of physics as well as the inability to ever admit he is wrong about anything. There is probably a special place in aeronautical hell reserved just for him.

Happy reading.

54

I guess I’m not being clear. If a helicopter is in a hover, then it is suspended below the rotor disc from the hub. Since the pilot properly worked out the W&B, the fuselage hangs more-or-less level below the rotor disc like a rock tied to a string. A gyroplane can’t hover (at least not for very long), but the fuselage is still hanging below the rotor disc like a rock on a string.

So you’re flying along in a helicopter and you push over hard enough to get zero-g. Here’s where the pendulum effect breaks down. Obviously the center of mass is well below the rotor disc. But not it’s no longer hanging from the rotor disc. The ‘string’ has gone slack. You are correct there. Since there is no rigid connection, such as on fixed-wings, the rotor disc does what it does, and the fuselage does what it does. In a gyroplane you have the engine moving the fuselage, and in a helicopter there is inertia with the added complication of the tail rotor that is trying to rotate the airframe.

I tend to assume people know what I’m talking about, and I often use ‘shorthand’ analogies that are perfectly clear in my mind but don’t make it to the keyboard. In positive-g flight, the airframe is like a pendulum below the rotor disc. In negative-g it isn’t. When I said it acts like a pendulum it was a poor analogy. I just meant that the fuselage swings relative to the rotor.

Also, as an aside, low/neg-g and low rotor RPM are two different things.

But my main point is this: Aircraft have limitations, and they have to be flown within them. A gyroplane pilot who flies an aircraft without a horizontal stab needs to know these limitations and take steps to avoid flying outside of the envelope just as the pilot of any other aircraft needs to in his aircraft. Sometimes it can’t be avoided, such as suddenly flying into severe wind shear. But in normal operations it’s more a factor of pilot technique than aircraft design.

Some aircraft are poorly designed and dangerous. Take the BD-10 mentioned earlier. It had a habit of breaking up in flight due to flutter. But if flown below the speed at which flutter occurs, it can be flown safely. Unfortunately it was specifically designed to go fast and the vertical stabs weren’t up to the task. A gyroplane or helicopter is not designed to fly in neg-g. So unlike the ill-fated Bede, they are safe when flown within their design parameters.

Would a horizontal stab be beneficial on your gyro? From what you say, it sounds like it would. But as designed, it shouldn’t be a problem to a pilot experienced in-type.

55

A couple people up-thread asked a few questions about 727s. In no particualr order:

  1. I never did anything interesting, like fly them in Africa or … . I did a bunch of charters to smaller airports here in the US, where we were by far the biggest thing on the field that month. That often led to comic or mildly dangerous interactions with the locals.
  2. Theories about why 727s were hard to land were a dime a dozen.

The main gear location vs CG was one of the most common but always seemd to me to be particularly unlikely. Unlike the contemporary 707 and 737, the 727 had a problem with tipping up on its tail if the rear cargo compartment was loaded too soon or too heavy. The tail stairs were often lowered during loading as a preventative measure. That would indicate to me an airplane with the main gear to close to the CG, not one with the main gear too far aft of it.

Other people believed the fore-aft CG range was particularly broad and handling differed a bunch depnding on CG vs weight.

Others blamed the lack of wing mounted engines and excessive or anomalous reactions to ground effect.

Some thought the gear travel was just too short, while others explained it was because of the lack of a 4-wheel bogie letting you down gently as it rotated to a flat position.

Me? I just admitted I couldn’t see any one theory as having much predictive power. So I just tried to accept the usual heavy clunk-on with the same grace as the occasional smoothy or real pranger.
3. The 727 did not have trailing link main gear. Just a big beefy oleo about 8" in diameter. directly in line with the two main wheels / tires on each side.
4. Landing accidents: IIRC, the 727 never had a bad accident record on landing. Right at introduction, it did garner a poor accident record on approach. As had the 707 and DC8 before it. And as would the DC9 a couple years later.

The 727 was the first jet aricraft flown by many of the second tier airlines of the time. The Nationals, North Easts, Capitals, etc. All names long gone since deregulation.

The first pilots flying jets were the most senior. These were guys (no gals yet) who learned to fly when the DC3 was state of the art.

Approach and landing in a swept-wing jet with very slow-responding engines is quite different from doing the same thing in a Connie or DC7 or Martin 404. Which is what these guys were transitioning from. The 727 also flew the traffic pattern about twice as fast and the approach and landing about half again as fast as the speeds used by the prop liners.

A lot of current industry practice was learned the hard way as guys flew themselves into corners they couldn’t fly out of.

On the Helo stuff mentioned by Johnny … minor war story.

I (a USAF fixed wing pilot) had a chance to fly a US Army OH-58 during a deployed exercise. I’d read about the basic control setup, the interaction of the three axes, and all the rest. I’d flown a lot of light airplanes, and the OH-58 was similar in speed, weight, etc. The Army pilot was a real pro and we were just going for a short ride around the local area at a decent altitude. So I thought I was in a pretty low-risk, high-enjoyment situation.

Turns out I understood just enough about helos to be (very) dangerous.

The Army helo pilot took off, then gave me the controls at ~150 ft. We climbed up to 500 & cruised the local AO enjoying the sights. Did a few turns, tried accelerating and slowing, climbs and descents. Hey, this is at least as much fun as I thought; I gotta get one of these myself.

Then we hit some pretty good short, sharp, bumps and I instinctively applied forward cyclic and dumped some collective to unload, as one would in a fixed wing.

The Army pilot shouted, grabbed the controls and wouldn’t let me fly the rest of the flight. My transient inputs were over and done long before he got his hands on.

On the ground he couldn’t quite bring himself to chew me out, my O-3 outranking his WO-2 by a bunch. But he did say something about “mast-bumping” and to not *ever *do that again in a helo.

I looked up mast bumping and the rest of helo aerodynamics when I got back to civilization. I always wonder how close I came to killing us both.

56

One more 727ism …

  1. As noted by others upthread, there was very little pitch reaction to power changes, and what there was in the correct direction. i.e. pull power and the nose would drop a smidgen.

The DC9 was the opposite; for whatever reason, pulling power off created a definite pitchup and vice versa. I never flew the -9 enough to get really good with it, and they were pretty run out old junkers when I got to them, but they always seemed to me to be barely 1/2 the plane a 727 was. It seemed to me like a 1965 Chevy vs. a 1965 Toyota. Rock solid vs tinfoil.

The long-time DC-9 drivers loved the thing, so maybe I just didn’t give it a chance. Or maybe they just didn’t know any better.

57

Not a pilot, but I have to agree with the ME-163. Any plane where you leave your landing gear behind on take off has to be bad. Wonder if the guys who designed it expected anyone to live long enough to try to land. I can see them thinking, if we have them leave the landing gear behind we can reuse it on the next one. That will help lower building costs.

-Otanx

58

Actually, the did have landing gear. A center skid.

59

Which was designed to save weight. How much weight would a center wheel have weighed versus a retractable skid?

60

Good question.