"WHY ROLL?" Topic

Have to confess to a good deal of confusion about this maneuver.

Can anyone summarize the advantages/disadvantages an aircraft gets from rolling.

I realise there must be different types of rolls – I've heard 'snap roll' and vector roll/barrel roll etc.

Do not be afraid to assume I know nothing – because that is about the state of play.

Hoping folks can help yet again.

A roll will often be a prelude to a change of direction. As the pilot you generally want to pull the nose up (generating positive G forces) rather than down (negative g forces). This will also allow the pilot to see where he is headed as in most cases you can't look down through the aircraft.

Rolls can also be used to try and throw off an attacker's aim with unguided weapons. It can also be used to move a shorter straight line distance without bleeding off to much speed, useful to make or counter a reversal. Hope that helps. Much easier to explain wit hand gestures tan in text :)

That's a helpful start.

Does a roll result in much if any lateral change of position?

E.g. If the pilot rolls to the right [left wing up and right wing down] does the aircraft move to the right at all? It will obviously keep going the direction it was when the pilot began the roll – but does it end up any further to the right than it otherwise would?

Afraid that one exceeds my grasp of the concept :) Watching stunt pilots barrel roll I expect there can be based on how tightly or not the roll is executed.

A roll helps your spotting also

A roll is simply spinning the aircraft around its longitudinal axis. It doesn't change your position laterally. A barrel roll consists of pulling the nose up, rolling the wings to the desired angle then pulling on the stick. This results in a corkscrew displacing the aircraft laterally. The barrel roll can be used to move onto an enemy planes tail if you are off angle in a turning fight. It can also be used to lose a bit of speed. It can b e used defensively with a fighter that has gotten close and has a closure rate higher than the defensive aircraft.

The only roll related maneuver not mentioned previously is the 'split S'. It was a favorite for breaking off (or attempting to at least) and for radically changing direction (180 degrees) quickly. Starts with a snap lateral roll into the upside down/inverted position then a hard pull back on the stick for what is essentially an inverted climb/dive. As you pull up/level off you end up facing the opposite direction very quickly. If poorly executed it can leave you more vulnerable, and of course it costs altitude.

The reason most missiles don't roll is that they don't have a pilot to gray out or red out through g forces.

Airplanes roll to keep blood in the pilot's head as the bird maneuvers.

It seems like I'm confusing a 'roll' where the a/c simply rotates about its centre of gravity with a barrel roll or vector roll.

Split S and Immelmann turns do involve rolling too.

With early aircraft, you need to roll before manoeuvring as the wings can only take the stresses in one direction. So for a steep dive you go inverted then pull the stick back. If you don't , you'll tear the wings off.

Yep – that and the pilot is more comfortable with a mild +ve G force than the -ve G force if you push the nose down and then keep diving steeper and steeper. Some Engines don't like the -ve G too – IIRC.

Well… In normal flight, a secondary effect of rolling will be a turn to the left or right, depending which way you've rolled (unlike a boat, you can't turn an aircraft simply by applying rudder, using only yaw).

To tighten up a turn, the pilot can roll the aircraft closer to 90 degrees of bank and pull back on the stick, thereby adding the effect of elevators to the turn.

To simply roll around the longitutinal axis (i.e. to perform an 'Aileron Roll') is actually quite a difficult manouevre and takes some skill to pull off. It requires the pilot to start with the nose slightly above the horizon, then apply some opposite control to counteract the tendency of the aircraft to turn in the direction of the roll. Most notably, the aircraft will always try to turn an Aileron Roll into a Split S at the halfway-point, so it takes some effort to keep the roll going and the nose slightly above the horizon.

Note that aileron rolls are far easier to perform in modern combat aircraft and aerobatic aircraft than they are in traditional piston-engined aircraft, though don't underestimate the potential for disaster in such an apparently simple manoeuvre.

A Barrel Roll is essentially like an elongated loop and like a loop, needs some speed on the clock to perform successfully (or a lot of power in reserve). The pilot the nose up above the horizon, and then draws and imaginary circle on the horizon with his nose, essentially describing a corkscrew through the air. If performed successfully, the aircraft will not have lost any height and will still be heading in the same direction, though it will have bled off a lot of speed.

The unpleasant effects of positive G on the pilot and engine might be one reason for rolling before turning, but more important is the need to observe a target or potential collision hazard.

Remember that with any turn or manoeuvre, the pilot ideally wants to see where he's going. The two things that get in the way are a. the nose and b. the wing. It therefore is in the pilot's best interest to roll before turning, in order to move the wing/nose out of the way and better observe the target or any potential collision hazard.

The first rule of airmanship is 'Keep a Good Lookout!'

Very helpful post JF.

I figure that if the pilot rolls the aircraft to the right – say – the wings will apply impetus to move the aircraft to the right. The pilot can compensate for this I suppose.

If they keep rolling the wings will continually apply their lift force in whichever direction they are working. This will cause the aircraft to wobble about in a fairly unpredictable manner – thereby throwing off the aim of any attacker.

The point about seeing where you are going is also well-noted.

Some Engines don't like the -ve G too – IIRC.

Any engine using a carburetor with floats, actually, which is why most WW2 fighters used annoyingly-complex 'pressure carburetors'** and why modern aerobatic planes use fuel injected engines.

**Basically an all-mechanical fuel injection system, usually with fuel injected at the throttle body.

airplanes roll to change the direction of their lift to turn. for a plane to turn right it changes some of the vertical lift which is always perpendicular to the wings into horizontal lift. so when talking about roll rate a better roll rate allows you to start and end a turn faster. then there are full rolls. why do it? they are fun. but really there are several types of these as well, the barrel roll which is like a corkscrew. the snap roll which is basically a horizontal spin (ask if you want the arodynamics), the slow roll, the aileoron roll.

to make a really tight turn like a fighter pilot: roll 90 degrees and pull on the stick. of course the harder you pull on the stick the more g-forces you will "load up"

And since we are on a WWII board this was one of the reasons the FW-190 was so deadly, in a sustained turn ie one already started a spitfire (at least the spit IX anyway) could out turn a FW but if the FW could get the jump on a turn by getting his airplane rolled and thus the turn started he could have a head start then roll the other way and turn again before the spit could catch up in the turn. This was also why when fighting a zero you did not get slow if you wanted to live. at high speeds it was heavy and slow to get a roll started giving the US planes with their much slower turn radius than a zero a much better chance.

Turning with just the rudder, in horizontal flight is very slow.

Thanks desert war. Another piece of the puzzle.

Turning with rudder only is also EXTREMELY difficult to perform, as it places the fuselage sideways-on to the airflow, causing a lot of turbulent air, loss of lift and usually an adverse roll away from the direction of turn. It's not something that a pilot would ever normally do. I know a guy who did it when he had a complete aileron failure – it was so unusual and so difficult that he won an AOC's Commendation for Airmanship.

I'm really only confused about the 'over and over' roll maneuver – what it actually was and what the benefit was.

I'm guessing harder to target a rolling a/c…and some lateral movement in the direction of the roll. So if the left wing goes up the a/c moves to the right – a bit. How much and how fast is a bit of a tricky area.

Do a/c with a high roll rate move more laterally? Or is that not what it's all about.

desert war's point re the Fw190 is well noted.

On turning with the rudder only. it is possible to turn with only the rudder, using only the rudder will usually cause the airplane to roll a little, I've used the doors to turn a Cessna 152. but turning both with the rudder (and doors as well) is a slow way to turn. and enemy fighter would have you dead to rights if you turned that way. it also causes the airplane to be uncordinated. without going into advanced arodynamics again it causes a skidding turn meaning one wing is going faster than the other. if you get slow which tends to happen because of an increase in drag and stall you will spin. never a good thing when low to the ground. for a nice cordinated turn you roll with the stick or yoke raising the allearon on the inside of the turn thus dumping some lift and lowering it on the outside, thus increasing lift. a byproduct of lift is a form of drag called induced drag. to overcome the drag on the outside wing a pilot adds rudder. once a turn is established, ie no longer rolling the alleaons are closed to neutral thus no or little rudder is needed.

You can do straight rolls, as in around a straight, long cylinder.

Usually though, the pilots trying to avoid attacks would attempt to roll erratically, and/or to one side or the other, in order to avoid the bullets/shells from pursuing aircraft, so yes, their progress would be lateral, as well as forward.