A helicopter needs a tail rotor or it will rotate around the main rotor. Since a center-mounted prop plane is the same basic layout but rotated 90 degrees, how do they deal with the problem?
I don’t know but I’m subcribing so I don’t miss the answer.
I’ve never flown a plane with an engine 
but my guess is that you trim the ailerons to counter the amount of rotational force from the prop.
IIRC powerful single engined planes like WWII fighters could be quite a handful if you cranked the throttle on the ground.
Plenty of pilots here. We’re waiting. . .
That is part of it. The other part is the tail unit (and for that matter the wings) resist the torque generated by the props.
Still the rotation of the prop does have an effect, some older planes need a foot on the rudder at all times to counteract its force.
Quick answer: right rudder.
Longer answer: A helicopter needs to counteract the torque effect of the main rotor because the rotor is the sole provider of lift, and needs to spin to generate that lift. Also, if I’m not mistaken, the rotor is fairly heavy compared to the weight of the helo.
On a fixed-wing aircraft, the propeller is relatively light compared to the weight of the plane, but the torque effects are still there. On a single-engine plane, the prop usually turns clockwise (from the back), so the rest of the plane would have a slight left-turning tendency. The pilot would compensate for this effect by adding a little pressure on the right rudder, which will cause the plane to bank slightly right.
The other single-engine plane pilots here know you also add right rudder to compensate for things like P-factor (asymmetric prop loading) and corkscrewing air when at high angles of attack. The four left-turning tendencies all have the same cure, basically.
(On preview: most small planes, Cessnas at least, don’t have aileron trim…)
On at least some twin-engine planes, the props spin in opposite directions, so as to cancel each other’s torque. Hence the old Air Force song:
“Don’t give me a P-38, with props that counter-rotate
They’ll loop, roll and spin but they’ll soon auger in
Don’t give me a P-38!”
I was a radio-electrical assembler for Cessna for a decade, and av8rmike is right about the smaller models lacking aileron trim (which probably explains the popularity of the optional ARC-200A autopilot, essentially a wing leveler).
Anyway, this got me to reminiscing. Seems to me that on at least one single-engine model (maybe the 180/185 “taildragger”) the vertical tail actually sat slightly askew. If so, I suppose that would provide an “automatic” counter to the engine torque.
It’s been a couple of decades, so don’t hold me to this. . . .
Well as a matter of fact the airplane does counter the engine/propellor torque. The plane is trimmed to fly straight an level at a certain airspeed. This is done by slightly increasing the lift on the left wing and off-setting the vertical stabilizer slightly to counteract the engine/propellor torque. At all other flight conditions than the one for which the plane is trimmed the pilot has to make adjustments to aileron and rudder controls either manually or by setting moveable trim tabs to do the job. It gets to be automatic.
As Small Clanger and av8rmike have surmised, we’re looking at two issues:
[ol]
[li]Primary torque moment about longitudinal (roll) axis[/li][li]Secondary effects of torque on yaw axis[/li][/ol]
The relationship between power, and torque, and prop speed is P = T*N (applying the correct unit conversions when necessary). A lightplane engine running at 180 horsepower and 2500 RPM (typical for a newer Cessna 172 at takeoff) will produce 380 foot pounds of torque. A helo rotor generates more torque for a given power input simply because it’s spinning more slowly; the weight of the rotor disc is irrelavent.
If the plane could be suspended without wings, the reaction to the torque would slowly (relative to the prop) and continuously roll the plane to the left. To stop this roll, you need to apply another torque moment counter to the motion; this is where the wings come into play. On the 172 with a 36-foot wingspan, the engine torque can be countered by an 11 pound force at the tip of each wing (or the equivalent distributed across the length of the wing). For an airplane whose wings carry a load of at least 2500 pounds (it has to for the plane to get off the ground), this is easy to counteract with aileron trim, wing levelers, or designing the wings to produce a slight counter-rolling tendency.
IIRC some WWI fighter planes were sufficiently light, with sufficiently powerful engines that without a fair amount of effort would tend to roll and fly into the ground on takeoff. Now planes are heavier, better designed, and with better control systems
Many WWI planes used rotary engines. Rotaries are kind of like an inverse radial - instead of having a circular ring of cylinders fixed to the fuselage with the prop attached to the spinning crankshaft in the centre, a rotary has the crank fixed to the fuselage and the cylinders spinning. This makes for a big, heavy gyroscope hanging off the front of your plane, and some planes, like the Sopwith Camel, were notorious for killing inexperienced pilots because of torque effects.
Why anyone ever thought rotary engines were a good idea is beyond me.
Because, IIRC, it was the only way they could make an engine with a lot of cylinders fit in a short space. They hadn’t perfected V- technology, and to make an engine with a bunch of cylinders makes it really long. I think the Germans may have had success with the big, long engines, but I could be mistaken. And a rotary engine probably didn’t vibrate as much as a in-line or V- configuration.
You need to distinguish between the radial engine and the rotary engine.
The radial engine had the cylinders mounted in a fixed engine block, equally spaced about a rotating crankshaft.
The rotary engine had the cylinders, and, indeed, the entire engine block, rotating around a stationary crankshaft.
My understanding is that the radial engine was much more widely used than the rather bizare rotary engine.
Rotary engines were much more reliable, too, since they had greatly simplified lubrication systems. Just drip the oil into the crankcase and it will be forced out to the cylinders, evenly distributed between cylinders. They did spray a fine mist of oil off the heads, forcing the installation of guards over the upper halves to keep from blinding the pilot - that’s the quickest way to identify a plane with a rotary. Fuel and ignition systems were almost as simple.
On the other hand, they couldn’t speed up or slow down quickly enough to be useful, so to decelerate the pilot had to blip the throttle to intermittently stop fuel flow. A rotary-engined plane being landed always sounded like it was about to die.
Radials gained popularity, once their reliability improved, mainly because they allowed the plane to be turned about as easily in either direction. A fighter pilot who got into a superior position dogfighting a rotary-powered opponent could predict what he’d do.
Good explanations so far.
To back up to the very basic reason that airplanes don’t need some sort of mechanism to counteract the torque: Its because they need airspeed to stay airborne.
When a helicopter is hovering, the only way to counteract rotor torque is to generate some force on your own - hence a tail rotor.
For airplanes, torque is handled during the takeoff run by a combination of steering and rudder/aileron. Once airborne, the airplane has an always available “force” mechanism - airflow over the control surfaces. Just deflect the rudder/ailerons a little into the airstream and voila: the torque is counteracted.
Yes, it’s a simplified explanation. We could talk Vmcg and Vmca, but everyone casually reading the thread would have their eyes glaze over.
To continue the rotary-engine hijack…
Rotary engines had one other advantage over radial-type engines of the day, because the cylinders rotated, this provided some additional cooling at low air speeds. They did not use a throttle, nor was engine speed regulated (they were run AFAIK at "full-throttle at all times) by metering the fuel. Rather, the pilot had a switch to kill the ignition and would “blip” the switch when less than full power was required.
Most rotary engines were lubricated with mineral oil, and even with the “engine guards” in place, the pilots would be breathing a fine mist of mineral oil throughout their flight. Occasionally, the laxative effects if this mist would become, er…, urgent. I have heard reports of pilots cutting the ignition as soon as the wheels of their plane touched the ground, exiting the cockpit with the plane still in motion and making a mad (hopefully, successful) dash for the latrine.
–SSgtBaloo
Which brings up a question. The compressor section of a turbojet has to generate some reaction torque on the airframe. The compressor blades are working against the resistance of the air to its being compressed and that resistance is applied to the airframe producing a torque.
The Harrier jet can hover stationary in the air with no airflow over the control surfaces so how is that torque opposed? Harrier pilots?
Do we have a Harrier pilot on the Dope?
Anyhow, small airplane pilot checking in, confirming most of the above. The tail of many single engine prop planes IS set slightly askew, and most of them I’ve seen have a little flange of aluminum on the back end of the rudder that can be bent to allow further fine tweaking. The Cessna C150 has 1 degree more dyhedral (which I’m sure I’ve misspelled) on one side than the other to help combat left-turning effects. You do hold rudde on take off to counter-act turning tendencies on take off, during high angles of attack, and other situations where they become noticable - but if the pilot’s good the passenger isn’t likely to notice them doing this.
The short answer is that in fact prop planes DO need to counter the effects of the prop - it’s just that it’s done differently than on helicoptors.
Well, to be a Harrier pilot in the US you need to be a Marine so that rules out any response that involves writing.
I kid, I kid!! Sorry Marines, I luv ya, I really do!
IIRC the Harrier has ducting that runs out to the wingtips to provide roll control during hover. The ducting takes high-pressure engine air (I don’t know if it’s compressor air or exhaust air) and ports it to nozzles on the wingtips that react (ie open or close) based on pilot input. Combine that with four exhausts pointed down and you can overcome any torque from a spinning motor.
I haven’t flown in a puddle jumper in quite awhile, but I do seem to recall how the props spin in opposite directions. The forces must balance out…don’t know much more. - Jinx
The Harrier’s engine is a turbofan with counter rotating compressors to fight the gyroscopic effects.
Very nifty engine. Bypass air goes out the front nozzles, while exhaust gas goes out the aft nozzles.
The small nozzles at the wingtips, nose, and tail, use bleed air from the high pressure compressor.