Is physical strength required to pull an aeroplane out of a nose dive?

May 6, 2010 2:09 PM

Is physical strength required to pull an aeroplane out of a nose dive?

In films, the hero often wrestles with the controls to pull the plane up from a dive. In reality, is physical strength ever required to do this? Does it depend on what kind of plane?

posted by beniamino to grab bag (10 answers total)

It depends a lot on the plane, elevator trim, and airspeed (if you let the plane speed up too much it would be harder to pull out).

The danger from a nose dive is that high speeds stress the airframe so that it will eventually come apart. Pulling up out of a dive has to be done carefully to avoid too many Gs. There is also the possibility of control surface flutter.

Aircraft certified by the FAA have various requirements force of pilot control inputs (for example, a normal pilot has to be able to overcome the trim, so a particular force in pounds is specified as a limit).
posted by exogenous at 2:18 PM on May 6, 2010

It depends on the type of plane, yes.

Generally, smaller, less-expensive planes are mechanically controlled - meaning that, essentially, the yoke (control stick) is physically connected to the control surfaces of the aircraft by wire/mechanical linkage.

Larger aircraft and more-expensive small aircraft (read: Learjet) are controlled by something called fly-by-wire. This means that maneuvering the yoke inputs electrical signals that change the position of the ailerons and rudder.

So, yes, maneuvering an aircraft with mechanical linkages can require a good amount of strength.
posted by InsanePenguin at 2:19 PM on May 6, 2010

Oh, shoot, meant to add:

So, yeah, mechanically linked planes are akin to driving a car without power steering. If you've ever done this, you'll understand how much power steering can help turning the tires. In a fly-by-wire aircraft, sensors in the plane can decide how much assistance the pilot needs to right the aircraft and increase pressure accordingly.
posted by InsanePenguin at 2:21 PM on May 6, 2010

Some planes are even equipped with stick pushers, in which the plane can sense situations where a stall or other unwanted, dangerous maneuver is about to occur, and the plane will attempt to automatically self-correct, actually sending signals to the manual controls ("oh shit, the pilot is asleep, better push the stick back for him"), and hence to the control surfaces.

These can be overridden by the pilots, of course.
posted by Cool Papa Bell at 2:36 PM on May 6, 2010

The movies that I've seen that utilize this trope frequently have the hero pulling, and pulling, and pulling! and finally the airplane starts to pitch up after several seconds of nerve-wracking terror. This does not happen. Control inputs are noticed immediately, although obviously with a larger aircraft the effects are a bit subtler as you've got a hell of a lot more mass you're trying to throw around.

If you're trying to move a relatively large airplane with a mechanical control system, then I would say it would be more noticeable on your arm muscles to have to suddenly pull back on the stick, but not impossible.

Here's a helpful fact, though - most airplanes (ignoring "specialty" planes like stunt planes or military fighters) want to fly straight-and-level. They're designed to be very stable and will correct themselves in a dive. You'll witness what a paper airplane will do if you folded it properly - dive, flatten out as it picks up speed, slow down, drop the nose, repeat.

The corollary to this is that, if you want to get out of a (recoverable) dive, add power. It seems counter-intuitive ("You want me to fly FASTER into the ground?!"), but it will allow you to recover the airplane more easily. This assumes you a) have a functioning power plant, and b) have not fucked yourself so badly that you've put the plane into an recoverable situation (flat spin, etc.).

Also consider that, from 35,000 you have quite a long time to recover. Gentle backpressure on the controls will lead to a graceful recover and no spilled drinks.
posted by backseatpilot at 2:44 PM on May 6, 2010 [2 favorites]

As I re-read my answer about stick-pushers, I realize that stick pushers are most often used to prevent stalls, so they push forward.
posted by Cool Papa Bell at 2:51 PM on May 6, 2010

It does depend on the plane and also on how quickly one needs to get out of the dive. There's a not particularly well referenced usenet post archived on one of my favorite web sites that gives some stick force examples for a couple of WW2 fighter planes:

P-51D @ 3g = 48 lbs
P-51D @ 5g = 86 lbs

P-47D @ 3g = 16 lbs
P-47D @ 5g = 27 lbs

The P-51D, at least, requires a good deal of physical strength for these types of maneuvers, which would be considered normal things to do in such a plane.

It also depends on whether or not the plane is working properly. For planes with hydraulic controls that have manual reversion, if the hydraulics fail completely you can still fly them, but with much higher stick forces. This is kind of like what happens when the power steering in your car fails.

The Alaska Airlines Flight 261 crash was caused by a failure of the horizontal stabilizer trim mechanism and the pilots had to apply a lot of stick force (both pilots working together) just to keep the plane in the air as long as they did. Ultimately the problem worsened and they lost control, but this sort of thing might be another example where physical strength was needed.
posted by FishBike at 3:33 PM on May 6, 2010

In WWII there was a well-known problem with the P-38 where, in steep dives, the stick would become immovable or close thereto. Someone compared it to having the control stick stuck in concrete.

This, as you can imagine, caused some deaths.

They later fixed this by adding little flaps to a rear stabilizer, but until then it was extremely hazardous to put the plane in a steep dive.
posted by circular at 8:39 PM on May 6, 2010

Ah, here:

During high-speed flight approaching Mach 0.68, especially during dives, the aircraft's tail would begin to shake violently and the nose would tuck under, steepening the dive. Once caught in this dive, the fighter would enter a high-speed compressibility stall and the controls would lock up, leaving the pilot no option but to bail out (if possible) or remain with the aircraft until it got down to denser air, where he might have a chance to pull out.

From Wikipedia.
posted by circular at 8:41 PM on May 6, 2010

So, yeah, mechanically linked planes are akin to driving a car without power steering. If you've ever done this, you'll understand how much power steering can help turning the tires. In a fly-by-wire aircraft, sensors in the plane can decide how much assistance the pilot needs to right the aircraft and increase pressure accordingly.

I think you're conflating fly-by-wire with hydromechanical control systems. Many, many planes use hydraulic actuators to move the control surfaces instead of having a direct wire or linkage between the stick and surface. This is exactly like power steering. It's a direct proportional control, only amplifying the force. This is NOT fly-by-wire, which is a very different thing and is only found in the most sophisticated and expensive aircraft like jet fighters.
posted by Rhomboid at 2:03 AM on May 7, 2010