A question about propeller torque during takeoffs

[_viper_]

Hello!

I'm new on the forum and hopefully I picked up the right discussion board.

As the title says I'm looking for a information about propeller driven airplanes and their behave on the takeoff run. Does the pilot apply diffrential braking when the throttle is being pushed fully open? As fas as I know the propeller torque is major problem in high power piston engine aircrafts, like WW2 eras fighter planes(P-51, Spit, Fw-190, Bf-109)

Another question is about tri gear planes, a good example for a warbird could be a P-39 or for a civil plane an ordinary Cessna. An effect called P-factory doesn't exist on takeoff rolls in these planes but are the still some propeller torque wich pushes the left main gear towards ground. How does the pilot cope with this? does he apply differential braking on his/her right foot?

[Humaround]

In my limited experience, with nosewheel aircraft it isn't usually an issue - easily controllable with rudder/nosewheel correction.

Tailwheel is a whole other issue, and I imagine high powered taildraggers could be a real handful. What happens is that the gyroscopic effect of the prop acts to slew the aircraft as the tail comes up during the ground-run. With an anti-clockwise prop rotation (looked at from the front) the swing is to the left. If coupled with a left crosswind things can get exciting and require differential braking.

This isn't the same thing as the torque effect as the throttle is opened, but that hasn't had much effect on the 2 taildraggers on which I have experience (Emeraude and Vans RV6)

[NutLoose]

As said above, on the Spitfire Mk 14 and 19 the book says you wind on full left rudder trim to assist in counteracting it in the preflight checks, the rest as you surmiss is then done on brakes with a judicious jab to keep it going straight........

On a Twin or 4 engine aircraft, you can have the props rotating in the opposite direction to counter it but not all did, that is one reason why the likes of the Lancaster had the H layout of the tail with twin rudders and fins, this puts the fin and rudder in the airflow back from the inboard engines, that allows the rudder to become effective earlier to assist in handling due to the propwash..

Welcome to the forums

The spit also has different tyre pressures and possibly oleo strut pressures to assist, though not 100 % on the latter......

On a cessna the engine is angled off from centre slightly if one remembers correctly, next time you are near on look at the spinner from the front and it is not plumb centre.

[BelArgUSA]

On airplanes such as 1600 hp Spitfires or Mustangs, an important item is to set the rudder trim to certain value "rudder trim x units" to compensate for the P-factor expected on the takeoff roll, and assist your rudder inputs. I imagine that pilots who check-out in these airplanes are increasing power quite gradually on takeoff. Even a certain amount of rudder trim is normally set in the 450 hp Harvard.
xxx
Machines I never flew, but would love to, to scare myself.

Happy contrails

[BackPacker]

An effect called P-factory doesn't exist on takeoff rolls in these planes but are the still some propeller torque wich pushes the left main gear towards ground.

The effect is called the P-factor, not the P-factory, and it's one of the three effects that the theory says generate a tendency to swing left (with a right-turning engine). The other two are the torque which puts more weight on the left wheel, and the spiraling propwash which hits the fin.

In all lightly powered aircraft such as we fly (up to 200 HP, let's say) this is not an issue at all and can easily be corrected aerodynamically with the rudder. The only aircraft I know about that might require a bit of differential braking is the DA-40, which has a castoring nosewheel. But differential braking is, at the end of the day, braking, so it slows you down. Not something you want during the T/O run.

[_viper_]

Yes of course BackPacker. I had a bit of spelling mistake there. Maybe I've watched too many X-factor videos on youtube lately

Anyway thanks for the answers and as you described there are few general aviation aircrafts which require braking during take off roll. If I'm right a big and powerful engine on a little plane is all over the place if you don't treat it gently. Oh and if things are done correctly the plane doesn't actually go "sideways" at all?

Obviously it requires differential braking as well rudder use?

[SNS3Guppy]

As the title says I'm looking for a information about propeller driven airplanes and their behave on the takeoff run. Does the pilot apply diffrential braking when the throttle is being pushed fully open? As fas as I know the propeller torque is major problem in high power piston engine aircrafts, like WW2 eras fighter planes(P-51, Spit, Fw-190, Bf-109)

Another question is about tri gear planes, a good example for a warbird could be a P-39 or for a civil plane an ordinary Cessna. An effect called P-factory doesn't exist on takeoff rolls in these planes but are the still some propeller torque wich pushes the left main gear towards ground. How does the pilot cope with this? does he apply differential braking on his/her right foot?

If the takeoff is performed correctly, braking isn't required.

I don't fly the P51 or the spitfire, but I do fly the Air Tractor AT-802, a single engine tailwheel airplane which develops typically 1,350 hp on takeoff, and has a powerplant capable of up to 2,000 hp on takeoff. By comparison, the P51B developed 1380 hp on takeoff. Empty weights are similiar, though the Air Tractor is capable of much heavier takeoff weights.

The WWII veterans like to describe the P51 as a monster when it came to torque, talking about how it could take the airplane right out of the pilot's hands, and how it could cause a turn on takeoff that couldn't be controlled. This isn't true...it's legend and lore talking.

If one applies power gradually into the takeoff from a standing start with no brakes, it's just not an issue. If instead one stands on the brakes, brings the engine up to full power and releases the brakes to start rolling, it's still not an issue...and this with full power developed and the airplane ready to go.

If braking is used, it's typically used for steering only, as most larger tailwheel airplanes of this type don't use steerable tailwheels; it's differential braking up until the rudder gains effectiveness.

In that respect, one might say that rudder is required for the takeoff, but it really isn't...it's occasionally required for directional control, but generally that's more a function of crosswind in the early stages, and then typically only with a strong crosswind. Remember that the rudder receives considerable prop blast with which to be effective, at takeoff power, and this means the rudder becomes effective early in the takeoff roll (a significant difference, sometimes, between taking off and landing with a crosswind).

P-factor isn't a function of torque. Torque is something different, it's a rolling tendency which may or may not be down the longitudinal axis of the airplane. Torque is the equal and opposite reaction to spinning the propeller, and it's transferred from the motor through the motor mounts to the aircraft longerons (the airplane structure); the whole airplane wants to turn opposite to the propeller...and it has nothing to do with the aerodynamics of the propeller, save for drag. It has everything to do with the engine spinning the propeller. Torque increases with the load on the propeller, and as the constant speed propeller takes a bigger bite of the air and thus experiences more drag, it's harder to turn, and more torque (twisting force) from the engine is required to turn it at a given speed...the harder it is to turn the propeller out there (the more torque), the more the engine twists in the opposite direction, and that's what's felt by the airplane.

You mentioned one gear being pushed down harder against the ground. You could say that's happening with torque, but it's not significant enough to be needing to drag a brake. It's usually handled with opposite rudder, and in some airplanes some slight steering brake might be used...though typically little, if any, and not all the time.

P-factor is an assymetrical thrust produced by the propeller disc when the airplane is flying at a positive pitch angle...which is most of the time. The descending blade meets the oncoming slipstream at a higher speed (not angle), and an increase in effective thrust occurs on the side of the propeller disc with the descending blade. For airplanes which experience a propeller disc turning clockwise as seen from the cockpit, then the descending blade is on the right side of the airplane. If one is flying for a significant period of time, one will often see the side of the airplane with the descending blade become dirtier.

The following site has some pictures, though I don't think they're spectacular, that may help illustrate how this works: Untitled Document

P factor isn't particularly significant during the early takeoff roll, and it's effects actually increase with forward velocity and RPM. P factor is far less significant on airplanes with the long axis of the airplane aligned with the direction of travel on takeoff, such as nosewheel airplanes, but more significant on tailwheel airplanes which have a built in angle between the longitudinal axis and the direction of travel...the propeller disc already sits at an angle when the takeoff roll starts (when the tail is down), and thus the descending blade, or the side and bottom of the prop arc, see a higher velocity airflow than the retreating blade (rising blade...left side and top of prop arc on a propeller spinning clockwise as seen from the cockpit).

Spiraling slipstream has an effect which is much more pronounced on single engine airplanes than multi engine airplanes for a variety of reasons...the chief one being that its' right down the long axis of the airplane, and right where it can have a big impact on the rudder.

Spiraling slipstream is blown out of proportion too, as the air doesn't continue to spin around like it did from the propeller rotation. It does have some rotation motion, but to keep spinning like a propeller as it moves aft, the propeller blast would have to defy more than one of newton's laws of motion. It has some effect in rotation, but not as much as one might think when looking at diagrams in a book. It's enough, however, that if one were to tack a yaw string to the windshield of a single engine airplane, it tends to lean to one side, particularly on takeoff, and particularly if it's placed in the airstream forward of the windscreen and above the cowling (instead of right down on the cowling).

These various factors, torque, P-factor, and spiraling slipstream, account in parts for the left or right turning tendency of propeller driven aircraft (and in some centerline jets, torque also accounts for some tendency, too, though not nearly as much). How much of a role they play varies with the type of aircraft and the installation (centerline, assymetrical like a twin, etc), type of engine and propeller, amount of power, and perhaps most importantly, the phase of flight. They don't each contribute the same values to turning tendencies all the time; it varies with power setting, airspeed, and phase of flight, as well as other factors.

The most important thing to know is that the airplane is capable, as it's designed, to handle whatever these forces may be; the stories about taking wild rides because of extreme torque and big engines are legends perpetuated by pilots who either didn't know enough, got behind their airplanes and lost control, or simply wanted to inflate the airplane larger than life. When a pilot talks about these airplanes being so powerful they run away on takeoff...the pilot should be embarassed, because he's not talking about an airplane that's really so powerful...he's talking about a pilot who failed to control his airplane. But...it feeds myths and legends, and perhaps that's good enough.

[Crash one]

Thank you Mr Guppy sir, I am now beginning to understand why many people think tailwheelers are flown by supermen & yet I have no problems with mine.

[IO540]

With most planes, even higher end IFR tourers, below say 350HP, the torque reaction is not an issue, and is easily countered during takeoff with rudder trim, or a liberal application of the right boot if you don't have a rudder trim.

It is again noticeable if doing steep turns, e.g. the chandelle, when the rudder is again used to keep the ball in the middle.

However, on the more powerful stuff, and the faster turboprops like the TBM, one does have to watch it because if you slow down to just above Vs and then (as in e.g. a go-around from the end of an ILS) whack the power to 100%, there won't be enough aileron authority to stop the roll... one needs to use the rudder too and preferably go easy with the throttle as well Several TBM crashes are believed to have been caused by pilots forgetting this, and no doubt the placing of the radar dome on the left wing does not help in this case.

[Jucky]

There are four forces that are generated by the engine and propeller.
Torque
Slipstream Effect
P-Factor
Gyroscopic Effect
The first three being expertly explained by SNS Guppy. The force that nobody seems to have mentioned is Gyroscopic effect. This is the one that affects the big piston engine fighters the most at the initial stages of the take off roll. Remember a propeller is a large gyroscope. The three factors that affect the magnitude of gyroscopic force are;
Diameter
Mass
Speed of rotation
Of these, diameter has the biggest effect. Propellers on piston engine fighters have bags of all three, particularly the Seafury. Don't forget that when a force is applied to a gyroscope it will precess 90deg. Therefore if you yaw the aircraft you will get a pitching motion and conversely if you pitch the aircraft you will get a yawing motion. So getting back to the take off roll, as the tail is raised you will get a yawing motion, hence you will need a boot-full of rudder to keep the aircraft straight and on some aircraft a dab of brake as well.

Regards,

Jucky

[_viper_]

SNS3Guppy, thanks a bunch for the detailed explanation. So if I managed to follow your text's message there should not be big problems for the pilot to counteract the prop torque? When you said that it will not be an issue I still thought that the torque effect hasn't disappeared anywhere, its not that big as some WW2 veterans discribe.

I base on my statements on the www. sites, for example this Aerospaceweb.org | Ask Us - Propeller Torque Effect site seems to be pretty well made and reliable .I mean that there are still prop torque etc. which is corrected via ailerons and rudder but its not that big what some veteran's memories might say?

I remember reading a book where a finnish Bf 109G ace told that during takeoff he kept right foot almost welded on the pedal during the climbout ;P

[BackPacker]

as the tail is raised you will get a yawing motion, hence you will need a boot-full of rudder to keep the aircraft straight and on some aircraft a dab of brake as well.

Really? I'm not a taildragger pilot but it would seem to me that you only raise the tail once you have sufficient aerodynamic authority in the rudder to counteract the gyroscopic force.

Jabbing the breaks while raising the tail sounds like generating more problems instead of solving them.

[RatherBeFlying]

The Grumman AA-5's have a free castoring nosewheel, while your average Cessna or Piper has a sprung linkage between the nosewheel and rudder pedals. The taildraggers I know also have a sprung linkage between the tailwheel and rudder.

So with most SEPs pressing the rudder pedals will help steer the nose/tailwheel.

With the Grumman AA-5x on takeoff, you would need gentle brake pressure on the upwind wheel in the early part of the takeoff run in a crosswind situation -- and remember to get off the brake once the rudder was up to the job of keeping the a/c straight.

[SNS3Guppy]

However, on the more powerful stuff, and the faster turboprops like the TBM, one does have to watch it because if you slow down to just above Vs and then (as in e.g. a go-around from the end of an ILS) whack the power to 100%, there won't be enough aileron authority to stop the roll... one needs to use the rudder too and preferably go easy with the throttle as well Several TBM crashes are believed to have been caused by pilots forgetting this, and no doubt the placing of the radar dome on the left wing does not help in this case.

I hear that from time to time, but I've not seen it. I've run out of airspeed in mountain sheers and rotors during drops and put in eleven hundred to sixteen hundred horsepower, well past two thousand pounds of torque--up to 4,000 lbs or more...without running out of rudder. Aileron isn't much of an issue at all. I can't imagine that the TBM and other aircraft with considerably smaller engines are so poorly designed that they do run out of aerodynamic control authority.

If you're talking about a spin, then yes, adding power is very bad. Applying power at the wrong time approaching a spin may help the airplane over the top. However, just like tales of airplanes running out of control on takeoff due to torque and other turning effects...most of the time in flight, even with a large high-torque motor and big propeller turning out there...you're not going to have issues with running out of rudder or aileron. It's simply a matter of flying the airplane.

Therefore if you yaw the aircraft you will get a pitching motion and conversely if you pitch the aircraft you will get a yawing motion. So getting back to the take off roll, as the tail is raised you will get a yawing motion, hence you will need a boot-full of rudder to keep the aircraft straight and on some aircraft a dab of brake as well.

Gyroscopic forces tend to be manifest largely in hard maneuvering such as in aerobatics, and they're most felt not by the pilot, but by the engine as crankshaft stresses. I don't think I've ever paid much attention to the rudder required as the tail comes up, but it's never been significant enough to require attention, even when light.

A heavy airplane is far easier to control than a light one when it comes to pulling a lot of power. A typical light takeoff weight in the Air Tractor or Dromader, for example, is about 6500 to 8000 lbs, vs a max takeoff weight of about 16,000 lbs. At A light weight, it's going to take more rudder, and more delicate rudder control, than at a heavy weight.

When the tail comes off the ground, the airplane has already got good rudder authority, and you're gaining rudder authority as the tail comes up. The airplane becomes more streamlined, it's moving fast enough and has enough rudder authority to bear control properly, and it doesn't happen rapidly enough to cause a massive gyroscopic yawing motion.

There are times when brake may be used, typically with a strong crosswind, but especially in a conventional gear (tailwheel) airplane, judicious and careful use of brakes is essential.

A free castering tailwheel or nosewheel doesn't give the same directional stability as a steerable one, or in the case of a tailwheel, a lockable tailwheel. With proper handling brake shouldn't be necessary under calm conditions, but where brake is used for steering, it becomes a tool for use like anything else.

As far as rudder trim goes...it can be set for takeoff, but this is strictly a comfort issue, not a controllability issue. Full rudder throw is always available; like other trim, it's simply a matter of the legpower required. Generally it's preset to a given value only to reduce the fatigue for one's leg in the initial climb, and then adjusted as necessary shortly after takeoff...and with each power change.

[Jucky]

Gyroscopic forces tend to be manifest largely in hard maneuvering such as in aerobatics, and they're most felt not by the pilot, but by the engine as crankshaft stresses. I don't think I've ever paid much attention to the rudder required as the tail comes up, but it's never been significant enough to require attention, even when light.

Agreed. But I am not referring to modern aerobatic aircraft. The OP was asking about WWII era piston engine fighters, of which I am referring to. Although the Seafury FB11 wasn't exactly a WW11 fighter it was pretty much the last of the piston engine fighters and pretty good example to use. It had a 5 bladed metal prop with a diameter of 3.9m driven by a Bristol Centaurus producing 2480hp @2700RPM. Diameter is the biggest factor when it comes to gyroscopic precession. Not forgetting it has a large mass with a high speed of rotation. All of which are perfect for helping gyroscopic precession. How many modern single engine tailwheel aircraft have props this big? In comparison the AT-802 has only a 2.9m diameter five bladed prop being driven by a PT6A giving 1295 SHP@1700RPM, I would also imagine the mass of the propeller is substantially less. At low speed, powerful gyroscopics on older aircraft will overcome aerodynamics. Therefore if you raise the tail too early before aerodynamics get a chance to take over you are going to get a yawing motion in reaction to the pitching motion. In modern aircraft this isn't a factor anymore because they have smaller diameter, lighter props.

Of course all of things are easily overcome by good pilot training and judicious use of control inputs during critical stages of flight.

Viper, the biggest problems the Me109 had on take off was due to poor directional stability due to the narrow track undercarriage. This dogged the aircraft throughout its life and was the cause of many accidents.

[_viper_]

Jucky, nice additional info for me again So the rudder is a very important when it comes to the prop torque / gyroscopic precession and its correction

Yes I've read that the Me 109 was an extemelly hard plane to takeoff and land because its landing gear. For example the "Butcher Bird" Fw-190 was much rugged when it comes to landing gears. You can only imagine poor airfields in the middle of nowhere during wartime.

Oh and you also confirmed my thoughts about prop torq. And the Seafury isn't the only fighter plane wich has a huge engine and propeller. A Grumman F8F Bearcat is also a mean looking killing machine http://lh3.ggpht.com/_f_j2zqBPCpk/SN...k/IMG_0078.JPG and the prop diameter is pretty impressive. It's also a pretty nimble, span is only 10,92 m or 35 ft 10 in combined with 2100 hp 46 litres 18 cylinder P&W. And these two planes are just few examples.

Aerospaceweb.org | Ask Us - Propeller Torque Effect
That web site also says that "A more common example comes from the operation of piston aircraft from aircraft carriers. When a pilot misses the landing wires on a carrier deck, he goes to full power to take off again and go around for another attempt. This sudden increase in power also generates a sudden increase in torque that the pilot may not be prepared to compensate for. Complicating the issue even more is that landing occurs at relatively low speeds. When the speed of the air flow passing over the aileron and rudder is slow, these surfaces loss much of their effectiveness and may not be able to counteract the torque."

So is this just exaggerated as SNS3Guppy told before?

[SNS3Guppy]

It's actually 1350 hp with the -67AG, at over 4,000 ft-lbs of torque (it's torque that makes things go, rather than horsepower...as the saying goes, "it's horsepower that sells airplanes, but torque that makes them go"). However, the -67 is capable of up to 2,000 hp, and the 1350 hp is a derate. It's comprable to the P51 takeoff power.

The biggest problem older airplanes of the WWII era had wasn't excessive gyroscopic tendencies, nor excessive torque, nor excessive P factor, nor excessive spiraling slipstream...but inexperienced pilots. Seldom were mishaps the result of too much airplane, but instead, too little pilot.

['Chuffer' Dandridge]

At the risk of sounding condescending, all this talk about jabbing the brakes to keep straight is total guff. If you need to add brakes on takeoff in any aeroplane other than with a castoring nose or tailwheel, it's probably too late!

Why apply the brakes on takeoff? Surely it can only extend the take off roll, and risk a nose over. It's the gyroscopic (& crosswind) effects that are the problem, and if you factor these in, then keeping straight on takeoff is no problem.

On high power aircraft such as the P51 Mustang, the HUGE 12ft metal propeller acts like a gyroscope, not only in trying to turn the aircraft, but when a force is added to it (i.e. when lifting the tail on takeoff), precession takes over and tries to swing the aircraft to the left. Add a crosswind, P factor and asymmetric slipstream effects etc and it can get a lot worse..

So in any high power warbird type with, for example, a RR Merlin, think about where the crosswind is and have it opposing the swing effect if possible. Use the appropriate amount of rudder trim for the type and apply the initial T/O power (40” in the P51) gently. DO NOT raise the tail until you have good rudder authority and can remain dead straight. In fact, my own technique is to not raise the tail but let the aeroplane do it for me. Once the aircraft is tracking straight and under control, apply the rest of T/O power (50”). Apply aileron if required to keep the weight on the up going wheel, as the torque will also try to lift one wing. As somebody has also said, adding rudder trim is a comfort issue and takes some of the legwork out of the equation. Those pilots who fly both Merlin and Griffon engined Spitfires normally set it neutral in case they forget the correct setting.

Swinging on takeoff is just letting the aeroplane (of any type) get ahead of the pilot..... When converting pilots to tailwheel aeroplanes, and they ask which way it swings, I tell them to just deal with it when it happens and keep it straight. It’s what the rudder pedals are for.

[mr. small fry]

Early Spits, pussy cats. Treated with respect P51 a pussy too. Fly a Harvard from back seat and both will be a delight for most to fly, and not as challenging as most would expect. Griffin Spits - treat with great respect, and do not pour it all in at once - you may keep it straight, but you might just run out of roll authority if it gets up before you are ready for it!

[Them thar hills]

Which brake

#13 Ratherbeflying
Re Grummans and other aircraft with castoring nosewheels etc etc,
Not wishing to be unconventional, I'd go for some brake on the downwind wheel...until the rudder comes alive......(I'd hope thats what you really meant !)
tth