# Why don't prop planes need to counter the prop like a helicopter? **URL:** \ **Category:** Factual Questions\ **Created:** [May 14, 2004, 3:17pm UTC](https://boards.straightdope.com/t/why-dont-prop-planes-need-to-counter-the-prop-like-a-helicopter/245119 "2004-05-14T15:17:16Z")\ **Posts on this page:** 20\ **Page:** 2
**Author:** ![Broomstick](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/broomstick/32/246_2.png) [@Broomstick](https://boards.straightdope.com/u/Broomstick)\ **Post date:** [May 15, 2004, 2:18am UTC](https://boards.straightdope.com/t/why-dont-prop-planes-need-to-counter-the-prop-like-a-helicopter/245119/21 "2004-05-15T02:18:44Z")
For some reason I feel a strange compulsion to point out that not all single-engine prop planes have _left_ turning tendencies - some designs with props rotating the opposite direction have _right_ turning tendencies for all the same reasons, just in mirror-image. ---
**Author:** ![Llama\_Llogophile](https://avatars.discourse-cdn.com/v4/letter/l/49beb7/32.png) [@Llama\_Llogophile](https://boards.straightdope.com/u/Llama_Llogophile)\ **Post date:** [May 15, 2004, 2:28am UTC](https://boards.straightdope.com/t/why-dont-prop-planes-need-to-counter-the-prop-like-a-helicopter/245119/22 "2004-05-15T02:28:27Z")
Another aspect of aircraft design that helps correct for the left turning tendencies of a single engine prop plane: the engine is often offset to the right. Take the cowling off of a Piper Warrior and look at the engine and you can see it. I also recall reading something about an Italian WWII fighter plane that had one wing longer than the other to offset some of the engine torque. ---
**Author:** ![Berkut](https://avatars.discourse-cdn.com/v4/letter/b/a88e57/32.png) [@Berkut](https://boards.straightdope.com/u/Berkut)\ **Post date:** [May 15, 2004, 2:36am UTC](https://boards.straightdope.com/t/why-dont-prop-planes-need-to-counter-the-prop-like-a-helicopter/245119/23 "2004-05-15T02:36:46Z")
> [@Jinx](#): > > 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 It’s not uncommon for twins to have counter rotating props. ---
**Author:** ![dqa](https://avatars.discourse-cdn.com/v4/letter/d/d6d6ee/32.png) [@dqa](https://boards.straightdope.com/u/dqa)\ **Post date:** [May 15, 2004, 2:41am UTC](https://boards.straightdope.com/t/why-dont-prop-planes-need-to-counter-the-prop-like-a-helicopter/245119/24 "2004-05-15T02:41:52Z")
> [@BrotherCadfael](#): > > “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!” Can you translate this? Why is having counter-rotating props a bad thing? ---
**Author:** ![Richard\_Pearse](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/richard_pearse/32/13144_2.png) [@Richard\_Pearse](https://boards.straightdope.com/u/Richard_Pearse)\ **Post date:** [May 15, 2004, 2:45am UTC](https://boards.straightdope.com/t/why-dont-prop-planes-need-to-counter-the-prop-like-a-helicopter/245119/25 "2004-05-15T02:45:17Z")
> [@Berkut](#): > > It’s not uncommon for twins to have counter rotating props. Yeah, some do, some don’t. Preferably they all would have counter rotating props, but that means the engine manufacturers have to produce two versions of their engines which adds cost. ---
**Author:** ![David\_Simmons](https://avatars.discourse-cdn.com/v4/letter/d/9de053/32.png) [@David\_Simmons](https://boards.straightdope.com/u/David_Simmons)\ **Post date:** [May 15, 2004, 2:49am UTC](https://boards.straightdope.com/t/why-dont-prop-planes-need-to-counter-the-prop-like-a-helicopter/245119/26 "2004-05-15T02:49:28Z")
> [@pilot141](#): > > 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. Sure, if you think about it there has to be some method of roll control at hover independent of any engine effects. Just wind gusts and lateral weight unbalance would demand it. ---
**Author:** ![pilot141](https://avatars.discourse-cdn.com/v4/letter/p/e0b2c6/32.png) [@pilot141](https://boards.straightdope.com/u/pilot141)\ **Post date:** [May 15, 2004, 2:59am UTC](https://boards.straightdope.com/t/why-dont-prop-planes-need-to-counter-the-prop-like-a-helicopter/245119/27 "2004-05-15T02:59:41Z")
> [@David Simmons](#): > > Sure, if you think about it there has to be some method of roll control at hover independent of any engine effects. Just wind gusts and lateral weight unbalance would demand it. Ummm, right. But the same system that is used for compensating for wind gusts and weight imbalances is ALSO used for the (very minor) problem of torque. As **Berkut** points out, the Harrier has a pretty slick engine design. And thanks for letting me know that compressor air is used for the control nozzles. I suspected as such, but wasn’t sure. ---
**Author:** ![Berkut](https://avatars.discourse-cdn.com/v4/letter/b/a88e57/32.png) [@Berkut](https://boards.straightdope.com/u/Berkut)\ **Post date:** [May 15, 2004, 3:08am UTC](https://boards.straightdope.com/t/why-dont-prop-planes-need-to-counter-the-prop-like-a-helicopter/245119/28 "2004-05-15T03:08:22Z")
> [@dqa](#): > > Can you translate this? Why is having counter-rotating props a bad thing? It’s a good thing. Most twins that use counter rotating props are designed so that as the engine turns, the descending blade is closest to the fuselage. This is good for controllability if one engine fails. However, most of the P-38s had counter rotating propellers that turned outwards due to problems with buffeting. Still corrects for P-factor, but not as good if you happen to lose an engine. ---
**Author:** ![David\_Simmons](https://avatars.discourse-cdn.com/v4/letter/d/9de053/32.png) [@David\_Simmons](https://boards.straightdope.com/u/David_Simmons)\ **Post date:** [May 15, 2004, 3:21am UTC](https://boards.straightdope.com/t/why-dont-prop-planes-need-to-counter-the-prop-like-a-helicopter/245119/29 "2004-05-15T03:21:51Z")
> [@Berkut](#): > > It’s a good thing. Most twins that use counter rotating props are designed so that as the engine turns, the descending blade is closest to the fuselage. This is good for controllability if one engine fails. Could you explain why this is good for controllability? And as a side note, the P-38 had in-line, liquid cooled engines which turned at relatively high rpm and required a gear reduction between engine and propellor. This made counter-rotating props a cinch; all that was required was an idler somewhere in the gear train to reverse the prop direction. With radial engines an entirely different engine would have to be built and stocked resulting in added logistic complexity. It’s just simpler to let the pilot worry about the torque since all of them are already trained to do so. And of course on the radial engine planes where torque is really a problem, single engine fighters, counter-rotating props are not an option. ---
**Author:** ![Richard\_Pearse](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/richard_pearse/32/13144_2.png) [@Richard\_Pearse](https://boards.straightdope.com/u/Richard_Pearse)\ **Post date:** [May 15, 2004, 3:35am UTC](https://boards.straightdope.com/t/why-dont-prop-planes-need-to-counter-the-prop-like-a-helicopter/245119/30 "2004-05-15T03:35:08Z")
> [@Berkut](#): > > It’s a good thing. Most twins that use counter rotating props are designed so that as the engine turns, the descending blade is closest to the fuselage. This is good for controllability if one engine fails. > > However, most of the P-38s had counter rotating propellers that turned outwards due to problems with buffeting. Still corrects for P-factor, but not as good if you happen to lose an engine. And the reason having the props turn outwards is not so good? The thrust from a prop is offset towards the side of the prop disc where the blades are going down. If you have a clockwise rotating prop (as viewed from behind or the cockpit), the thrust line is shifted to the right rather than coming straight through the centre. On a twin engine aircraft with props rotating away from the fuselage, an engine failure on either side will result in an operating engine that produces thrust further out from the aircraft centre-line than if it was rotating the other way. This means that more rudder is required to counter the turning moment produced by the offset thrust. As control effectiveness reduces with airspeed, more rudder is needed to keep the aircraft flying the slower you go. On the above aircraft, you will run out of rudder control at a higher airspeed than if the prop was rotating the other way. You have less useful airspeed range available to you. ---
**Author:** ![Richard\_Pearse](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/richard_pearse/32/13144_2.png) [@Richard\_Pearse](https://boards.straightdope.com/u/Richard_Pearse)\ **Post date:** [May 15, 2004, 3:43am UTC](https://boards.straightdope.com/t/why-dont-prop-planes-need-to-counter-the-prop-like-a-helicopter/245119/31 "2004-05-15T03:43:23Z")
> [@David Simmons](#): > > Could you explain why this is good for controllability? Reference my above post. The closer the thrust line is to the aircraft centre line, the easier it is to control the aircraft. A single engine aircraft has only a slightly offset thrust line (due to the down going blades producing more thrust) and is very controllable. A twin operating on one engine with props rotating inwards has a significanlt offset thrustline and is controllable but care must be taken. A twin on one engine with the prop going outwards has a thrustline further offset and is still controllable but more care must be taken and there is less margin for error. ---
**Author:** ![Richard\_Pearse](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/richard_pearse/32/13144_2.png) [@Richard\_Pearse](https://boards.straightdope.com/u/Richard_Pearse)\ **Post date:** [May 15, 2004, 3:47am UTC](https://boards.straightdope.com/t/why-dont-prop-planes-need-to-counter-the-prop-like-a-helicopter/245119/32 "2004-05-15T03:47:39Z")
Sorry, meant to include this: It can be seen that the third scenario is the worst. On a twin with counter-rotating props turning outwards (P38), an engine failure will always produce scenario 3. An engine failure on a twin with counter rotating props turning inwards will always produce scenario 2 (a good thing). On a twin with props rotating in the same direction as each other, there is a 50/50 chance of scenario 2 or 3. ---
**Author:** ![Berkut](https://avatars.discourse-cdn.com/v4/letter/b/a88e57/32.png) [@Berkut](https://boards.straightdope.com/u/Berkut)\ **Post date:** [May 15, 2004, 4:04am UTC](https://boards.straightdope.com/t/why-dont-prop-planes-need-to-counter-the-prop-like-a-helicopter/245119/33 "2004-05-15T04:04:07Z")
> [@David Simmons](#): > > Could you explain why this is good for controllability? Certainly. A single engine propeller aircraft with a “standard” clockwise rotating propeller has a left turning tendency at high angles of attack. One of the reasons for this is that the descending blade of the propeller has a higher angle of attack than the ascending blade, and is producing more thrust. This tries to yaw the airplane to the left, which you can correct for with right rudder. Now, imagine the same thing on a multi-engine airplane, with a clockwise engine on each wing. You will have the same left turning tendency, which you can correct for with right rudder. But what if one of the engines decides to quit? With the engines mounted on the wing, away from the aircraft’s centerline, the airplane will try to yaw into the failed engine, because all your thrust is on the other side. Now on your twin with two CW engines, it’s much worse to lose the left engine than the right one. The reason for this is that your right engine’s descending blade is towards the outside of the wing, away from the fuselage. The farther away your thrustline is from the centerline of the aircraft, the worse off you are. It makes your asymmetric thrust situation worse. However, a loss of your left engine won’t be as bad, since the descending blade (with its greater thrust) is closer to the centerline of the fuselage, reducing the tendency to turn into the dead engine. The obvious solution to this is to make it so both engines have their descending blades closest to the fuselage centerline (counter rotating). That way, no matter which one you lose, you are keeping the thrustline closer to the fuselage. But, on the P-38, the descending blades are farther away from the fuselage centerline. Single engine performance suffers. > [@](#): > > And as a side note, the P-38 had in-line, liquid cooled engines which turned at relatively high rpm and required a gear reduction between engine and propellor. This made counter-rotating props a cinch; all that was required was an idler somewhere in the gear train to reverse the prop direction. Yeah, too bad they put them on the wrong wings. 🙂 But, they had their reasons. ---
**Author:** ![Berkut](https://avatars.discourse-cdn.com/v4/letter/b/a88e57/32.png) [@Berkut](https://boards.straightdope.com/u/Berkut)\ **Post date:** [May 15, 2004, 4:07am UTC](https://boards.straightdope.com/t/why-dont-prop-planes-need-to-counter-the-prop-like-a-helicopter/245119/34 "2004-05-15T04:07:54Z")
Or, what he said. 🙂 Really, every little bit in a light twin helps. When you lose an engine in a twin, you don’t lose 50% of your performance, it’s more like 80%. Counter rotating props (when turning the right way) help out a lot. ---
**Author:** ![pilot141](https://avatars.discourse-cdn.com/v4/letter/p/e0b2c6/32.png) [@pilot141](https://boards.straightdope.com/u/pilot141)\ **Post date:** [May 15, 2004, 4:11am UTC](https://boards.straightdope.com/t/why-dont-prop-planes-need-to-counter-the-prop-like-a-helicopter/245119/35 "2004-05-15T04:11:09Z")
> [@1920s Style Death Ray](#): > > Sorry, meant to include this: > > It can be seen that the third scenario is the worst. On a twin with counter-rotating props turning outwards (P38), an engine failure will always produce scenario 3. An engine failure on a twin with counter rotating props turning inwards will always produce scenario 2 (a good thing). On a twin with props rotating in the same direction as each other, there is a 50/50 chance of scenario 2 or 3. Yes. The first airplane I flew for the AF after pilot training was the [C-27A](http://www.airliners.net/open.file?id=062868&WxsIERv=QWxlbmlhIEMtMjdBIFNwYXJ0YW4gKEctMjIyKQ%3D%3D&WdsYXMg=VVNBIC0gQWlyIEZvcmNl&QtODMg=U2FuIEpvc2UgZGVsIEd1YXZpYXJlIChTSkUgLyBTS1NKKQ%3D%3D&ERDLTkt=Q29sb21iaWE%3D&ktODMp=SnVuZSAxOTkz&BP=0&WNEb25u=UmljaGFyZCBPbGl2ZXI%3D&xsIERvdWdsY=OTEtMDEwMw%3D%3D&MgTUQtODMgKE=KGNuIDQxMDIpLiBVU0FGIEMtMjdBIFNwYXJ0YW4gaW4gQ29sb21iaWEu&YXMgTUQtODMgKERD=NjUw&NEb25uZWxs=MjAwMC0wMS0xOA%3D%3D&ODJ9dvCE=&O89Dcjdg=&static=yes). (Bonus: I took that picture!) The props on that thing were NOT counter-rotating: they both rotated left (looking forward). This made a right engine failure more critical than a left engine failure (even more so during a single-engine go-around when the operating engine is at max torque). Guess which engine was always “lost” during checkrides? 🆒 ---
**Author:** ![Richard\_Pearse](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/richard_pearse/32/13144_2.png) [@Richard\_Pearse](https://boards.straightdope.com/u/Richard_Pearse)\ **Post date:** [May 15, 2004, 5:54am UTC](https://boards.straightdope.com/t/why-dont-prop-planes-need-to-counter-the-prop-like-a-helicopter/245119/36 "2004-05-15T05:54:44Z")
Yeah, while doing my Instrument Rating, their favourite was to fail the left (critical) engine in the Beech Baron midway through the (left) base turn of an NDB approach. ---
**Author:** ![David\_Simmons](https://avatars.discourse-cdn.com/v4/letter/d/9de053/32.png) [@David\_Simmons](https://boards.straightdope.com/u/David_Simmons)\ **Post date:** [May 15, 2004, 6:11am UTC](https://boards.straightdope.com/t/why-dont-prop-planes-need-to-counter-the-prop-like-a-helicopter/245119/37 "2004-05-15T06:11:44Z")
I suppose in theory, and maybe with today’s high performance planes with their greater power and much steeper climbouts than with piston engined aircraft, there is a significant difference in up and down propellor blades. However, in my copy of the Pilot’s Operating Flight Instructions for the Martin B-26 (which I have open before me right now) I find no mention of any difference in controllability depending upon which engine fails on take-off. In training for this aircraft and for the equivalent Douglas A-26 there was no mention of this effect either. My guess is that for aircraft of that era, like the P-38, the effect was so small compared to all the others in the case of engine failure on take-off that it faded into insignificance and was not mentioned. ---
**Author:** ![Richard\_Pearse](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/richard_pearse/32/13144_2.png) [@Richard\_Pearse](https://boards.straightdope.com/u/Richard_Pearse)\ **Post date:** [May 15, 2004, 6:37am UTC](https://boards.straightdope.com/t/why-dont-prop-planes-need-to-counter-the-prop-like-a-helicopter/245119/38 "2004-05-15T06:37:32Z")
You don’t mention whether the B-26 has contra-rotating engines or not. If it does then it is a moot point as there will be no critical engine. It has nothing to do with extra performance or anything like that. Any aircraft may have an angle of attack at low speeds as high as 15-20 degrees. That is, the angle between the wing and the relative airflow, not to be confused with the angle between the wing and the ground, climb angle is irrelevant. In cruise flight the angle of attack may be around 4 degrees. this all translates to the engine itself sitting at an angle to the airflow and so the down going blade will have a high angle of attack than the up going blade and will produce more thrust, hence the thrust is offset towards the down going blade. This is a factor for all prop driven aircraft from 60hp Piper Cubs to a C130 Hercules. ---
**Author:** ![pilot141](https://avatars.discourse-cdn.com/v4/letter/p/e0b2c6/32.png) [@pilot141](https://boards.straightdope.com/u/pilot141)\ **Post date:** [May 15, 2004, 6:42am UTC](https://boards.straightdope.com/t/why-dont-prop-planes-need-to-counter-the-prop-like-a-helicopter/245119/39 "2004-05-15T06:42:08Z")
From [here](http://www.csd.uwo.ca/~pettypi/elevon/baugher_us/b026-18c.html): > [@](#): > > Unfortunately, many of the pilots trying to master the Marauder at these fields had no previous twin-engined experience. In 1942, a series of training accidents took place stateside which placed the future of the entire Marauder program in doubt. Most of these accidents took place during takeoff or landing. The increases in weight that had been gradually introduced on the B-26 production line had made the wing loading of the Marauder progressively higher and higher, resulting in higher stalling and landing speeds. Veteran pilots in combat overseas had enough experience that they could handle these higher speeds, but new trainees at home had serious problems and there were numerous accidents, causing the Marauder to earn such epithets as “The Flying Prostitute”, “The Baltimore Whore”, “The Flying Vagrant”, or “The Wingless Wonder”, these names being given because the B-26’s small wing area appeared to give it no visible means of support. Other derisive names being given to the B-26 were “The Widow Maker”, “One-Way Ticket”, “Martin Murderer”, “The Flying Coffin”, “The Coffin Without Handles”, and the “B-Dash Crash”. In particular, there were so many takeoff accidents at MacDill Field during early 1942 that the phrase “One a Day Into Tampa Bay” came to be a commonplace lament. It sounds like the B-26 was a handful for new pilots to learn how to fly. What’s the date on that flight manual? The saying in aviation is that every rule is written in blood; my father’s T-38 manual (Dash -1) is a heck of a lot different than the one I got 14 years ago, and I’m sure that mine is different than what the students are getting now. As lessons are learned, warnings are added. ---
**Author:** ![David\_Simmons](https://avatars.discourse-cdn.com/v4/letter/d/9de053/32.png) [@David\_Simmons](https://boards.straightdope.com/u/David_Simmons)\ **Post date:** [May 15, 2004, 6:57am UTC](https://boards.straightdope.com/t/why-dont-prop-planes-need-to-counter-the-prop-like-a-helicopter/245119/40 "2004-05-15T06:57:44Z")
> [@pilot141](#): > > It sounds like the B-26 was a handful for new pilots to learn how to fly. > > What’s the date on that flight manual? The saying in aviation is that every rule is written in blood; my father’s T-38 manual (Dash -1) is a heck of a lot different than the one I got 14 years ago, and I’m sure that mine is different than what the students are getting now. As lessons are learned, warnings are added. The manual I quoted was for the B-26 F and G models which were the last off the line. However, traning was in B-26A, B, C models. The A version was the original, 65 ft. wingspan version which was increased to 71 ft. for B and subsequent models. The early problems in training were the result of several factors. Lack of experienced instructors. Most of them were not long out of cadet school themselves, all the experienced pilots being overseas. Difficulties with the Curtis Electric Propellors which tended to run away. Lack of engine power. The A model had 1850 HP Pratt and Whitney engines which were later changed to 2000 HP engines. In addition the airplane was more critical of weight and balance than the Army was accustomed to; maintenance personel were insufficiently trained. All of this comes from the book _The Martin B-26 Marauder_ by J.K. Havener who was a pilot in the 497th Sqdn., 344th Bomb Group, a B-26 outfit. Jimmy Doolittle was given the task of straightening out the problems and he selected Capt. Vincent Burnett, who Doolittle knew from barnstorming days, to actually do the job. After Burnett got done the Army knew how to fly, instruct for and maintain the plane and it had the lowest loss record of any WWII bomber. Nevertheless, there is no mention in the handbook, as of 15 February 1944, of a difference in single engine performance depending upon which engine is out and there was no mention of it training in the airplane. [Previous page](https://boards.straightdope.com/t/why-dont-prop-planes-need-to-counter-the-prop-like-a-helicopter/245119.md?page=1) [Next page](https://boards.straightdope.com/t/why-dont-prop-planes-need-to-counter-the-prop-like-a-helicopter/245119.md?page=3)