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Posts:
1,800
From:
Walnut, CA
Registered:
1/3/03
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(1 of 17)
How come the three Engine configuration was not widely exploited?
Sep 29, 2009 2:37 AM
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Hi all,
This got me curious. We have the standard two or four engine configuration ranging from fighters to heavy bombers. My question is, how come the three engine configuration was never exploited by Japan, America or even Germany?
If I remember correctly the only country that exploited this configuration was Italy and the least known aircraft the CRDA/CANT Z.1007 Alcione. I also seem to recall early before the war Fokker used a Commercial Airline with a three engine configuration.
Thoughts anyone?
-GINO
--
"God Bless and God Speed to our Boys who are now overseas."
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Posts:
6,344
Registered:
2/27/03
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(2 of 17)
Re: How come the three Engine configuration was not widely exploited?
Sep 29, 2009 6:42 AM
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Don't forget the Ju52-3m, one of the great transports of all time though eclipsed by the C-47. As I understand it this originated as a single-engine plane and was then given the wing motors and the 3m designation.
For bombers etc. the obvious thoughts are that the nose was valued for bombsights or armament. Vi-bration and forward visibility for the pilot may also be concerns.
Ed. note - apparently vi-bration without the - violates community standards.
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Posts:
876
Registered:
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(3 of 17)
Re: How come the three Engine configuration was not widely exploited?
Sep 29, 2009 7:54 AM
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One of the reasons, as Carronade correctly pointed out, is that putting the engine on the nose of a bomber or transport aircraft is simply taking up space that could be better utilized. Bomber aircraft use the nose for guns and/or bombsights. Transports generally have the cockpit as far forward as practical to maximize cargo area in the fuselage. The nose-mounted engine additionally complicates the design by requiring to get fuel to that engine.
Another aspect of nose- vs. wing-mounted engines is Center-of-Gravity (CG). The weight of the engine must be balanced by weight behind the CG. The CG envelope must be considered in the cases of the aircraft being loaded and unloaded, and the nose weight places restrictions on the CG envelope. Conversely, wing-mounted engines are applying their weight at or near the CG and do not place the same restrictions on aircraft loading.
The Ford Tri-motor was one of the more successful early transport aircraft. However, the advantages of wing-mounted engines became apparent as transport aircraft evolved.
--
Illegitimis non carborundum, "Vinegar Joe" Stilwell
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Posts:
4,563
From:
Southern California Foothills
Registered:
9/10/99
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(4 of 17)
Sep 29, 2009 9:40 AM
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>If I remember correctly the only country that exploited this configuration was Italy and the least known aircraft the CRDA/CANT Z.1007 Alcione.<
Actually, MOST Italian bombers were of the tri-motor configuration. The famous SM-79 Sparviero torpedo bomber, the Cicogne floatplane, etc. The Italian engines of the time were producing about 2/3rds the horsepower of other nations, so..... they put three engines on instead of just two, and accepted the consequences.
PS--I made a fanciful "what if" 1/72 aircraft model of an imaginary late-war trimotor JET fighter for Italy, and I guess it was so convincing (to the lazy and gullible) that a recently-published book on "Turbojets of of WW II" had MY picture of MY model in it relating the aircraft as a real Italian jet project (and hadn't contacted me about my picture or my source of "facts"). They even used my name for the craft--the "Caproni Bologna" and apparently didn't catch on to the fact that "Bologna" is "Baloney". OOPS!!
WHAT A HOOT!
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Posts:
171
Registered:
5/6/09
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(5 of 17)
Re: How come the three Engine configuration was not widely exploited?
Sep 29, 2009 9:53 AM
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Uh.,., you OWN the copyright on your design, your picture, your "sample" model, your naming it, etc.., and you have actionable rights that they have breached. You might be able to get financing for " Bologna II " from them. You should at least send them notification that your rights were violated. After all.., the author may have been innocent, but don't forget the publisher and book stores are profiting from YOUR work.
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Posts:
1,829
From:
Melbourne, Australia.
Registered:
10/3/02
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(6 of 17)
Re: How come the three Engine configuration was not widely exploited?
Sep 29, 2009 1:38 PM
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Gino,
Another was the Fokker Tri-Motor', which became the first plane to fly the Pacific, piloted by Sir Charles Kingsford-Smith and Charles Ulm.
John.
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Posts:
5,573
Registered:
9/19/99
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(7 of 17)
Sep 29, 2009 4:12 PM
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A single-engine plane using a propellor driven by a reciprocating engine will tend to turn in the direction of the rotation of the propellor, which is almost always the rotation direction of the engine. Mujlti-engine aircraft tend to fly straight if their engines are equally distributed as to direction of rotation (some British-ordered P-38s to the contrary). A three-engined aircraft will have a bias of 2/1 or 3/0 depending on the rotation of the engines. This only becomes a real problem at take-off under full power on a narrow runway or in other such conditions of low-speed, high-power settings. But the airframe must be built in consideration of thedisparity in torque. A failure of the one engine that rotates against the other two would be a serious event during take-off...
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Posts:
4,563
From:
Southern California Foothills
Registered:
9/10/99
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(8 of 17)
Sep 29, 2009 5:11 PM
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>A single-engine plane using a propellor driven by a reciprocating engine will tend to turn in the direction of the rotation of the propellor, which is almost always the rotation direction of the engine.<
I always thought it was the other way around, that the rotation of the aircraft was OPPOSITE the engine/prop rotation. It wouldn't make sense, from the conservation-of-angular-momentum angle, to have it otherwise.
Can you verify/deny this?
From a wiki site (we all know how "off" they can be!) :
"According to Newton's law, "for every action there is an equal and opposite reaction," such that the propeller, if turning clockwise (when viewed from the cockpit), imparts a tendency for the aircraft to rotate counterclockwise. Since most single engine aircraft have propellers rotating clockwise, they rotate to the left, pushing the left wing down."
At "Aerospace.org":
"According to Newton's law, "for every action there is an equal and opposite reaction," such that the propeller, if turning clockwise (when viewed from the cockpit), imparts a tendency for the aircraft to rotate counterclockwise. Since most single engine aircraft have propellers rotating clockwise, they rotate to the left, pushing the left wing down."
There is an illustrative drawing here:
http://www.aerospaceweb.org/question/dynamics/q0015a.shtml
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Posts:
2,714
From:
Washington state
Registered:
9/10/99
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(9 of 17)
Re: How come the three Engine configuration was not widely exploited?
Sep 29, 2009 10:21 PM
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There were also several tri-motor flying boats, where the engines could be supported on the high wing, or in the case of biplanes, between the wings, solving the problems caused by the engine in the nose.
Examples would be the French Breguet 521 and Loire 70, and the German Blohm and Voss Bv 138 and Dornier Do 24.
As far as the S.79, probably the most successful land-based tri-motor aircraft of the war, goes, it's interesting that Savoia Marchetti was unable to interest any other country to buy the aircraft (unless you count Spain, who kept the ones the Italians left behind after the Civil War) until they made a twin-engined version, the S.79B. They were then able to sell the twin-engined aircraft to Iraq, Brazil, and Rumania. Only Yugoslavia bought the tri-motor version.
--
TV interviewer: Why do you think people love Doctor Who so much?
Russell T. Davies: Because it's the best idea ever invented in the history of the world!
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Posts:
876
Registered:
12/20/00
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(10 of 17)
Sep 30, 2009 5:08 AM
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Yes, torque is applied to the airframe in the opposite direction of prop rotation. However, except in high powered aircraft, and generally only at low airspeed and with sudden large changes in power setting (think Corsair in the groove attempting to 'go around'), torque has a minimal effect on the turning tendencies of propellor driven aircraft.
Most US built piston engines turn clockwise when viewed from the cockpit. The left-turning tendency of clockwise rotating props is mainly cause by "P-Factor", spiral slipstream, and gyroscopic precession.
"P-Factor" is a phenomenon at high angles of attack, in which the decending prop blade (on the right side of the a/c) has a higher angle of attack to the relative wind than the accending blade on the left. The result is a yaw force on the aircraft to the left.
Spiral slipstream is a rotation of the air leaving the propeller in a clockwise manner around the airframe. Thus the spiralling air is striking the left side of the vertical stabilizer, pushing it to the right, and thus trying to turn the aircraft left.
When a force is applied to a rotating mass (the prop is acting similar to a flywheel) gyroscopic precession applies a force to the mass at 90 degrees from the initiating force. This is most notable in tailwheel aircraft on takeoff. The aircraft is at high power and low airspeed when the tail is raised to takeoff position. Raising the tail generates a precession force that turns the aircraft to the left.
At low airspeeds, torque applies a downward force on the left wing. At higher airspeeds, it has a small relative effect and is easily balanced by aerodynamic forces.
Many twin-engined aircraft have counter rotating props to mitigate the danger of loosing the "critical" engine. If both engines of a twin turn clockwise, loosing the left engine presents the most danger. The thrust of the right engine being off the center line of the aircraft, coupled with the normal left turning tendencies, can cause yaw and roll to the left beyond the pilots ability to control it in certain flight regimes. If the right engine were to rotate counter-clockwise instead, the asymetric thrust would be somewhat offset by the then right turning tendency of that engine.
Back to the tri-motors, both the Ford and Fokker tri-motors had all three engines turning clockwise. Likewise the 4-engined B-17 and B-24 had all turning clockwise. Counter rotating props are most prevalent in twins.
--
Illegitimis non carborundum, "Vinegar Joe" Stilwell
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Posts:
4,563
From:
Southern California Foothills
Registered:
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(11 of 17)
Sep 30, 2009 9:37 AM
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>Thus the spiralling air is striking the left side of the vertical stabilizer, pushing it to the right, and thus trying to turn the aircraft left.<
As I recall, the P-51 Mustang had its vertical stabilizer angled slightly to the left (a few degrees left of the centerline of the aircraft as seen from behind the aircraft) to help counteract that tendency (or other torque/yaw tendencies to go left).
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Posts:
4,563
From:
Southern California Foothills
Registered:
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(12 of 17)
Sep 30, 2009 9:43 AM
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>Uh.,., you OWN the copyright on your design, your picture, your "sample" model, your naming it, etc.., and you have actionable rights that they have breached.<
Maybe. I don't know quite where the "public domain" aspect comes into play, as the picture and "story" were up on the Internet on a private modeler's website. The guffaw that I, and others that know my modeling work, experience when I (they) see the picture and story in the book is, in itself, a "priceless" treasure.
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Posts:
171
Registered:
5/6/09
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(13 of 17)
Re: How come the three Engine configuration was not widely exploited?
Sep 30, 2009 11:31 AM
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" Maybe. I don't know quite where the "public domain" aspect comes into play, as the picture and "story" were up on the Internet on a private modeler's website. The guffaw that I, and others that know my modeling work, experience when I (they) see the picture and story in the book is, in itself, a "priceless" treasure. '
My understanding of the copyright laws ( I do some photography ), is that it is not public domain, unless YOU give it away. A lot of copyright stuff has tightened up, with all the digital downloading of music. You used to have to copyright stuff.., but I believe now, it has turned the other way, in that you "own" the rights to your creation, without formal papers being filed with the government agencies.
I mean.., you give the example, that it was up on an internet web site. That sure doesn't fly if / when you get caught downloading music.
I understand your amusement with what happened and I agree it's priceless.., but the book store and publisher sure don't give away the book for free. They HAVE a price for what you feel is priceless.
Just a thought. What would / will YOU ever do, if YOU decide to use YOUR OWN WORK in an article or magazine.., and the book publisher or author SUES YOU for copyright infringement on HIS book ? Strange.., but possible.
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Posts:
2,714
From:
Washington state
Registered:
9/10/99
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(14 of 17)
Sep 30, 2009 12:30 PM
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> >Thus the spiralling air is striking the left side of
> the vertical stabilizer, pushing it to the right, and
> thus trying to turn the aircraft left.<
>
> As I recall, the P-51 Mustang had its vertical
> stabilizer angled slightly to the left (a few degrees
> left of the centerline of the aircraft as seen from
> behind the aircraft) to help counteract that tendency
> (or other torque/yaw tendencies to go left).
The Bf 109 also had an offset fin/rudder.
--
TV interviewer: Why do you think people love Doctor Who so much?
Russell T. Davies: Because it's the best idea ever invented in the history of the world!
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Posts:
1
From:
Texas
Registered:
10/31/09
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(15 of 17)
Re: How come the three Engine configuration was not widely exploited?
Oct 31, 2009 5:30 AM
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In the 14 previous messages, most of the discussion has centered on P-Factor (http://en.wikipedia.org/wiki/P-factor), which is not the reason why tri-motors didn't persist in aircraft design.
In aircraft design, the triple considerations of performance, reliability, and cost drives design.
Tri-motors gained in popularity when airframe design exceeded powerplant design, specifically engine reliability and power. Airframe designers were attempting to create commercial aircraft that could haul profitable loads other than airmail. Airframes became larger, requiring more power, and available engines had neither the power or required reliability, hence three engines. Note that this was a compromise solution. Four engine aircraft were built, but at the time, the two outboard engines created other problems not satisfactorily resolved by airframe designers of the period (pre WW2).
Just before WW2, engine power and reliability increased to the point that two engines did the required jobs, reduced complexity, and gave multi-engine reliability. Tri-motors died because three engines were more costly to maintain than two. By the end of WW2, the standard configuration was one, two, or four engines - because of compromises already noted. Aircraft design today is still driven by these criteria: note that as larger engines become available, the trend of commercial aircraft design is to reduce the number of engines to two. There was a resurgence of tri-motor design in the jet age and, for the same reasons, as more powerful (and less costly) engines became available, airframe engines were reduced to two.
On a personal note, as a pilot, I hate tri-motors. In most instances, particularly the Ford Tri-Motor, the center engine was shut down during flight anyway, because the heat would turn the cockpit into a broiler, handy during arctic operations, but otherwise a real disadvantage.
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