What is the advantage of a tri-engine aircraft?

[tyrodtom]

A pair of machineguns or 20mm cannon can be sychronized to fire through the center engine prop if prop shafts aren't hollow.

Did anyone do that on a trimotor ?

 

[parsifal]

No they didnt, moreover having a fixed forward firing armament is quite limited. What cn this arrangement do to combat an attack by fighters from the forward quarter. A flexible forward firing mount at least gives the gunner the aibility to train his guns on the oncoming attacker. If the twin is manouverable, like a Mossie or a Ju88, ther is some hope of aerobatting the a/c to achieve a firing solution. For the older style and (usuay) unprotected trimotor configurations, this was not really a viable option.

The conclusion....trimotors tend to be more vulnerable to certin types of attack

 

[Shortround6]

By the time you hang 3 engines on an airplane the ability to maneuver like a fighter (even a poor one) is pretty well gone. Which rather limits the use of fixed forward firing guns even if the SM 79 had one. The SM 79 was only about 25,000lb and had three 9 cylinder engines ( 27 total) compared to most twins two 12s or 14s ( 24 cylinders or 28). Three 12s or 14s, let alone three of most peoples 18s make for rather large planes.

Many early twins, especially with fixed pitch propellers could not maintain height on one engine, The triples offered a measure of security in case of engine failure. As planes got cleaner (less drag) and got controllable pitch or constant speed propellers their ability to maintain height and make it to an airfield instead of putting down in a field or meadow got a lot better.

Tri-planes usually had a worse view over the nose, had more vibration in the cockpit (if not the entire fuselage) had higher maintenance costs than twins of equivalent power.

 

[davebender]

By the time you hang 3 engines on an airplane the ability to maneuver like a fighter (even a poor one) is pretty well gone.

I agree.

German Ju-252 and Ju-352 cargo aircraft carried some defensive weapons but I suspect they wouldn't have been terribly effective. Fighter escort is the only way to protect transport aircraft from enemy aircraft.

 

[R Pope]

Still seen as a viable concept in some respects. There were a number of DC3's with three turboprops installed for use in the north country, don't know if any are still being used. One version was called the Tri-Turbo Three.

 

[R Pope]

Still seen as a viable concept in some respects. There was a DC3 with three turboprops installed for use in the Arctic, I believe it was called the Conway or Conroy Tri Turbo Three. It's now a derelict hulk, I think.

 

[R Pope]

Still seen as a viable concept in some respects. There was a DC3 with three turboprops installed for use in the Arctic, I believe it was called the Conway or Conroy Tri Turbo Three. It's now a derelict hulk, I think. Then there was the post-war Northrup Raider, 13 built.

 

[davebender]

DC-10 passenger liner has three engines. One under each wing and one in the tail.

 

[wuzak]

DC-10 passenger liner has three engines. One under each wing and one in the tail.

As did the Boeing 727 and Lockheed Tristar

 

[davebender]

de Havilland Australia DHA-3 Drover
de Havilland Australia DHA-3 Drover - Wikipedia, the free encyclopedia

Britten-Norman Trislander
Britten-Norman Trislander - Wikipedia, the free encyclopedia

 

[vikingBerserker]

Now that's a pretty interesting bird.

 

[ShVAK]

The Trislander looks really odd. Never seen a trimotor prop aircraft with the centerline engine in the tail rather than the nose.

 

[parsifal]

very unusual pics dave. well done

 

[MiTasol]

The Drover was a nightmare - did not perform at all well with one engine out, especially in tropics.
Qantas lost one in the water off Lae in PNG when an engine failed. No survivors
This is one of the hundreds of accidents that Qantas claim they never had.

Mi

 

[dedalos]

I wonder for years ,if the tri Motor configuration could be a solution for germany. Since germany failed miserably to provide powerful emgines for its medium bombers, another approach could be interesting
A JU 188 version with three Jumo 211 J/N, no ventral gondola and the bulged bomb bay of the Ju 88A 15, the tail remote control turret, a smaller cocpit with lower drag canopy. I believe that even with the bigger and stronger airframe ,three jumo s 211 N could deliver better power to weight ratio than 2 BMW 801s and lower specific fuel consuption, especially if the BMW use B4 fuel, as it was the case in bomber use

 

[tomo pauk]

Three Jumo 211 will provide ~4000 HP for take off in 1941, that being equivalent of 2 x Jumo 222 (1st versions) or two R-2800 from 1942-44. At altitude it is about 3100 HP - not peak power, but 30 min rating. The 3 Jumos will be draggy as about 2 R-2800?
I'd go maybe for two engines on wings, 3rd behind the wing as a pusher? Granted, a new airframe is needed. Sorta cross between Mosquito and Mixmaster. Should work for the Americans, too.

 

[Shortround6]

Adding a 3rd engine to an existing airframe may be possible, it is a lot easier to take one away.

By the time all is said and done, adding a 3rd Jumo 211 engine is going add around 2000lbs (1 ton) to the empty weight of an aircraft. Ju 88/188 had a fuel problem as it was. Feeding a 3rd engine is going to call for being really creative in regards to fuel storage.

What was teh fuel consumption of the Jumo 211 and BMW 801s per hp/hr at cruise settings? not full power.

 

[tomo pauk]

The BMW 801A and -C will provide 1170 PS @ 4.5 km on max. continuous, while consuming 280 g/PSh of fuel, or 327.6 kilograms of fuel per hour. On max cruise, 990 PS at 225 g/PSh -> 222.7 kg/h at 4.2 km.
BMW 801D makes 1180 PS on max cont @ 5.5 km, 265 g/PSh -> 312.7 kg/h. On max cruise, it is 985 PS @ 5.4 km, 210 g/PSh -> 206.9 kg/h.
Jumo 211F on max continuous will give 900 PS at 5.3 km, for 218 g/PSh, or 196.2 kg/h. Alternatively can use over-revving to 2400 RPM at 5.9 km, making 920 PS and consuming 224 g/PSh, or 206.1 kg/h.
The Jumo 211J will do 1020 PS at 5.1 km, or 1030 PS at 5.6 km, same specific consumption as 211F, total consumption 222.4 kg/h or 230.7 kg/h, respectively.

I don't have the data about the consumption of the Jumo 211 on max cruise at the moment. If it is 2/3rds of the ratio, like we observed for the BMW, it will be some 140-150 kg/h, for powers of 80% of max continuous power, or something along 720-820 PS.
Thus three Jumo 211 will consume 420-450 kg/h for 2200-2500 PS, two BMW 801A/C will consume 445 kg/h for 1980 PS, two BMW 801D will consume 414 kg/h for 1970 PS. The BMW 801A or C will be forced to cruise at lower altitudes than other engines, thus making lower mileage. Three Jumo powerplants (211F was at 720 kg dry weight) will also weight perhaps 1000 kg more than two BMW 801, that is quite a weight. Bigger wing is needed, that will negate many of benefits.

 

[dedalos]

The BMW 801A and -C will provide 1170 PS @ 4.5 km on max. continuous, while consuming 280 g/PSh of fuel, or 327.6 kilograms of fuel per hour. On max cruise, 990 PS at 225 g/PSh -> 222.7 kg/h at 4.2 km.
BMW 801D makes 1180 PS on max cont @ 5.5 km, 265 g/PSh -> 312.7 kg/h. On max cruise, it is 985 PS @ 5.4 km, 210 g/PSh -> 206.9 kg/h.
Jumo 211F on max continuous will give 900 PS at 5.3 km, for 218 g/PSh, or 196.2 kg/h. Alternatively can use over-revving to 2400 RPM at 5.9 km, making 920 PS and consuming 224 g/PSh, or 206.1 kg/h.
The Jumo 211J will do 1020 PS at 5.1 km, or 1030 PS at 5.6 km, same specific consumption as 211F, total consumption 222.4 kg/h or 230.7 kg/h, respectively.

I don't have the data about the consumption of the Jumo 211 on max cruise at the moment. If it is 2/3rds of the ratio, like we observed for the BMW, it will be some 140-150 kg/h, for powers of 80% of max continuous power, or something along 720-820 PS.
Thus three Jumo 211 will consume 420-450 kg/h for 2200-2500 PS, two BMW 801A/C will consume 445 kg/h for 1980 PS, two BMW 801D will consume 414 kg/h for 1970 PS. The BMW 801A or C will be forced to cruise at lower altitudes than other engines, thus making lower mileage. Three Jumo powerplants (211F was at 720 kg dry weight) will also weight perhaps 1000 kg more than two BMW 801, that is quite a weight. Bigger wing is needed, that will negate many of benefits.

Well, lets start with the Ju 388K airframe, essentialy a Ju 188 with the bulged bomb bay of the Ju 88A15. With two BMW 801 s had an empty weight of 10250kgr.
In the 1943 time frame they would be the -D version. If we accept that C3 would be available for the bombers,it would be 3400 PS
If we accept three Jumos 211N of 1943, would add 1000kgr thats about 10%. They would deliver 4350PS. Thats 30% more take off power than the 2 BMWs and even more importantly ON B4 FUEL.
Furthermore i would like to notice that BMW 801s were really not available for ju 88 production until late 1943. Also ,in service, often the fuel consuption of the 801 was higher than in the manuals
Drag wise, three jumos 211s with anular radiators should be very comparable with the wider BMWs
Additional fuel could be a problem.The additional power could permit the standart use of external 900 lt drop tanks , and/or reduce the Internal bomb load from 3000kgr to still respectable 2000kgr and use the space for fuel.
2 20mm cannons would be possible to be installed in the front of the bulged bay,synchronized to fire through the central propeller disc
Finally such an aircraft could recieve a further performance boost, by using MW50 in 1944 for 1600-1650 take off power.

Also i would expect such an aircraft to have much more chance to survive after losing an engine

 

[tomo pauk]

The engine-out situation certainly favors a 3-engine aircraft much more than a 2-engined. My guess is that's why such a popularity between the wars, until the 4-engines aircraft were more widespread.

I've proposed before the 'Ju-88 airframe' (whether it's Ju 88, 188 or 388, does not matter) with a narrow, but long bomb panier, and DB 603A. The weight penalty should not be that big vs. Jumos, max cruise power was at ~1170 PS at 5 km (20% more than BMW 801D along with less drag and use of B4; maybe 30% greater power than of Jumo 211). The similarly heavy Jumo 213A was installed in some Ju 188s and even heavier engines were to be installed in the Ju 388 .
Problems - availability reliability in 1943; not a tri-motor (ie. not for this thread).