Junkers Ju288 as four engine bomber

[Carl Schwamberger]

This gives me the glorious vision of Ju-288s being hunted over the Atlantic by roving pairs of YB-40 (with engines upgraded to the R-1820-74W, giving them 1,500hp per engine compared to the -65 1,200hp) creating the most bizarre dogfights in the history of powered flight.

Was not what I was thinking, but yeah its 1940s Punk, lets go with it.

How soon before you see AEW Sunderlands or VLR Liberators over Bay of Biscay?

I don't know about the Sunderlands, but prototype Liberators were flying in 1940. All it takes is someone with the vision & power to make it happen.

 

[riggerrob]

when the "power system" scenario did not work for JU-288 wonder if a trimotor arrangement might have served? (using the Jumo 211s)

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One possible configuration for a tri-motor would have two engines on the left wing but only one engine on the right wing. The key is having clockwise rotating (as seen from the tail) propellers on the left wing and a counter-clockwise turning propeller on the right wing. This places the down-ward propeller blade closer to the centre line to minimize yaw if one engine quits. At steep angles of attack (e.g. climbing) the descending prop blade creates more thrust.
They would probably ask Richard Vogt to explain the finer points after all of his experience with the asymmetric, single-engined Blohm & Voss 141 recce plane. Vogt sketched another dozen asymmetric airplanes but none were built. BV 141 was only made in small numbers because it’s BMW801 engines were desperately needed for FW190 and Do217.
Prolific British pilot Eric “Winkle” Brown briefly flew a BV 141 after the war and reported that it handled fine. He only curtailed his test flight because of a rough-running engine.

More recently, Burt Rutan built and flew his asymmetric Boomerang twin with two different engines. All the passengers sat in the right-hand fuselage. Baggage and fuel went in the much-slimmer left-hand fuselage.
Rutan also built and flew the ARES prototype with the anti-tank cannon barrel protruding from the right side of the nose, while the single engine intake was on the left side to avoid investing muzzle blast.
Note that early A-10 prototypes had problems with engines surging when they fired their anti-tank cannon.

 

[Dynasoar]

Presumably building on my post #48, which suggested adding a third engine on the wing of an underpowered twin Ju 288, riggerrob offers the following, which emphasizes minimizing direct propeller yawing moment under engine-out climbing flight:

[QUOTE="riggerrob,

One possible configuration for a tri-motor would have two engines on the left wing but only one engine on the right wing. The key is having clockwise rotating (as seen from the tail) propellers on the left wing and a counter-clockwise turning propeller on the right wing. This places the down-ward propeller blade closer to the centre line to minimize yaw if one engine quits. At steep angles of attack (e.g. climbing) the descending prop blade creates more thrust. (Quote)

This is fine as far as it goes however a few observations- I had suggested installing a center section to mount the additional engine (on whatever side of the aircraft). Since the aircraft presumably will spend more time in cruise flight than in desperate attempts to survive engine out emergencies, I put some emphasis on coordinated (minimum drag) flight where each thrust vector points straight ahead from the prop center of rotation. Here, the location of each engine on the wing (regardless of direction of rotation) is key.

For simplicity let's use the following example, where we have 1000HP/engines and are flying at 375 MPH where one HP equals one pound of thrust. Prop diameter is 10-feet, and in the twin configuration, engine center lines are 10 feet from the fuselage center line. Each prop in this example produces 1000 pounds times 10 feet- a moment of 10,000 pound feet and each cancels the other. Remember the center section which will introduce the third engine- assume it extends 15 feet to the left of the aircraft centerline, with the propeller CL 10 feet out. The yaw moments become 10,000 + 20,000 (the existing wing-engine mounted to the stub wing) pound feet for a total moment of 30,000 pounds feet. To eliminate adverse yaw in cruise, the single engine on the opposite wing must be located 30 feet to the right of the fuselage CL to develop the same (opposing) moment and eliminate any need for yaw correction under cruise conditions. These minimum changes in existing wing,engine and landing gear, would require an assymetric center section of 40 feet span, less fuselage width. Assuming fuselage width of seven feet and modest clipping of wing tips, possibly eight feet per side, new span would be about 17 feet longer, with improved aspect ratio and wing area appropriate to new payload. All other mods would be confined to the new wing centersection.

About loss of an engine during takeoff or climb- the really critical engine would be the single one on the right, regardless of direction of rotation; the two remaining on the left would simply convey the aircraft to the scene of the crash. Since the standard direction of rotation is CCW viewed from the front, yaw would be generally to the left in climb, with the angle of relative wind shifting the apparent location of the thrust vector origin toward the fuselage ( the side with the downgoing blade) which renders each of these engines the "less critical". Thus all engines could be of standard rotation and no outer wing structure has to be redesigned from scratch to graft on the additional engine. Again, the key point is optimizing cruise performance.

Dynasoar

edited for punctuation, units and singnage