Could a tandem twin-engine configuration ever have worked

[Marcel]

I was reading up on the Fokker D.23 and noticed they never solved the heating problems on the rear engine. I read a comment on the Do-335 in the "double engine" thread remarking that it had cooling problems on the rear engine as well.
So was this tandem configuration a bad idea? Could it have worked, or did it work on another fighter?

Fokker D.23

Do 335:

 

[GregP]

The cooling problems were easy to solve but the solution added drag. You must supply sufficient cooling air to the rear engine and that means an intake scoop and an exhaust area taht adds drag. All this conspires to lower the top speed, but would be required for a service aircraft.

I think it could have succeeded, but the real question is would it have been any better than the service aircraft used? I think the answer is no, there is no inherant benefit aside from torque elimination, and there are disadvantages.

The center mass reduces the maneuverability in pitch enormously and precludes installation of significant armament in the fuselage.

While I have nothing against a tandem twin, give me a P-38 or Mosquito until the tandem twin is proven in combat, and I don't want to be in the trial squadron that proves it.

 

[tomo pauk]

If an added cooling drag is, say, 10% and the 'saving' by removing the engines from wings installing them in the fuselage is 20%, the net drag is lower. A long-fuselage, well streamlined design should keep a rear prop working at proper efficiency
The push-puller should perform faster rolls than a conventional twin, since it does not have added weight away from the longitudinal axle.
As for armament, if a country has weapons that can be decently synchronized, and/or the ability to fire through the prop, heavy centrally-located armament should be no issue. As proved by the very Do-335.
Between the what-could-beens, a B-26-like airframe with 2 x V-3420 looks like a true performer for me.

 

[vikingBerserker]

I would think the rear prop would not be as efficient as the front one since the air has been disturbed. I know there have been succesful tandem planes where speed is not critical.

 

[cimmex]

The efficiency of a pusher prop is better than a puller. In a one engine flight the Do335 was faster with only the rear engine on than the front only.
cimmex

 

[vikingBerserker]

But what about both being on. The front would disturb the one in the back. I've only flown a front enginened plane, but I know the prop wash effects the tail surfaces.

 

[Shortround6]

Some of this depends on the particular installation. On the Do 335 the propellers are a good distance apart. While there are fins in front of the rear propeller the radiator airscoop seems a good distance away and the air hitting the working sections on the propeller blades seems to fairly clear to my eye. Compare to the Fokker 23 and how the rear end of the nacelle/engine compartment blocks part of the propeller disc fairly close to the propeller. or the rather disturbed airflow the rear propeller/s were going to get on the Fokker F 32.

http://upload.wikimedia.org/wikipedia/commons/thumb/0/05/Fokker_F.32.jpg/1024px-Fokker_F.32.jpg

Does the better airflow to the rear propeller on a good installation make up for the extra weight of the longer fuselage extension shaft and/or remote gearbox?
Not all engines could be used as pushers without some redesign/modifications to the thrust bearing in the gear box or "front" main bearing in a non-geared engine. Not really hard to do but it means that not all engines were interchangeable front to back.

 

[vikingBerserker]

Very cool, thanks for the education!

 

[cimmex]

Not all engines could be used as pushers without some redesign/modifications to the thrust bearing in the gear box or "front" main bearing in a non-geared engine. Not really hard to do but it means that not all engines were interchangeable front to back.

at the Do335 the heavy bearing of the extension shaft took over the thrust load and the motor reduction gear was not affected at all.
cimmex

 

[cimmex]

Not all engines could be used as pushers without some redesign/modifications to the thrust bearing in the gear box or "front" main bearing in a non-geared engine. Not really hard to do but it means that not all engines were interchangeable front to back.

at the Do335 the heavy bearing of the extension shaft took over the thrust load and the motor reduction gear was not affected at all.
cimmex

 

[davebender]

I don't consider "bad" as the proper description.

Propellor aircraft technology was advancing very rapidly during 1935 to 1945. Many new ideas were tried and tested. Some just didn't work. Others worked but did not prove cost effective. Tandem engine configurations such as the Do-335 were tried but did not prove worthwhile compared to other options. That's why the Do-335 and other such aircraft did not enter mass production.

 

[tomo pauk]

One may wonder about the two other principles of the tandem arrangements, like all-front (Kawasaki Ki-64) or all-back (Douglas Mixmaster, more correctly side-to-side engines). These two examples were quite the performers, but so was the Do-335.
IMO all three principles had merit, but were tested far to late in ww2.

 

[wuzak]

I don't consider "bad" as the proper description.

Propellor aircraft technology was advancing very rapidly during 1935 to 1945. Many new ideas were tried and tested. Some just didn't work. Others worked but did not prove cost effective. Tandem engine configurations such as the Do-335 were tried but did not prove worthwhile compared to other options. That's why the Do-335 and other such aircraft did not enter mass production.

Not sure that it could be claimed that the Do-335 was "not worthwhile". It was certainly late in the war, which affected development and the numbers of aircraft that were produced/went into service.

 

[wuzak]

One may wonder about the two other principles of the tandem arrangements, like all-front (Kawasaki Ki-64) or all-back (Douglas Mixmaster, more correctly side-to-side engines). These two examples were quite the performers, but so was the Do-335.
IMO all three principles had merit, but were tested far to late in ww2.

Dornier were certainly working on a tandem twin with contra-rotating pusher props.

http://www.luft46.com/dornier/3bd252.gif
http://www.luft46.com/dornier/3bd252-3.gif
http://www.luft46.com/dornier/do252-4.gif

That last one shows the engines much closer together than in the Do-335, either side of the main fuel tank, which, presumably, sits on or near ths CoG. The wing is position between the engines too.

This layout is better for use as a nightfighter. It allows for a better radar installation, and also allows a better weapons fit. While synchronised guns work on aircraft with puller props (like the Do-335) the rate of fire is reduced and the selection of guns that can be used must surely be smaller (as not all can be synchronised).

Dornier were also drawing aircraft with single engine pushers, as were Focke Wulf and Henschel.

http://www.luft46.com/dornier/dop247.html
Henschel Hs P.75 Luft '46 entry

The Ki-64 mentioned by you is another way of using tandem engines.
http://www.ww2aircraft.net/forum/album/aircraft-cutaways/p18647-kawasaki-ki-64.html

The cutaway shows synchronised guns, but I'm thinking good luck since the front and rear engines aren't connected (as far as I am aware), so that they could have different rpms.

Not sure how well the Ki-64 engines were cooled.

http://www.ijaafpics.com/JB&W/Ki-64-1s.jpg

There doesn't seem to be a lot in terms of radiators. Though the cutaway does show evaporative surface cooling on the outer wings.

Bugatti also used tandem engines for their P.100 racer, driving contra-rotating tractor props.
http://sobchak.files.wordpress.com/2009/11/bugatti100cut.jpg

The engines were offset and angled from the centreline so that the driveshafts could pass either side of the cockpit.

Arado came up with a different way of using side by side engines.

http://www.luft46.com/arado/are654-3.jpg
http://www.luft46.com/arado/are654-2.jpg
http://www.luft46.com/arado/3ba654.gif
http://www.oocities.org/unicraftmodels/germ/ar561/ar561-col.jpg

 

[davebender]

If the Do-335 entered mass production it would be during the summer of 1945. Jets aside, it would face stiff competition from other late war piston engine aircraft. The Ta-152 is arguably just as good a fighter while costing a lot less money. The Me-410 is a superior light bomber and probably costs no more then a Do-335.

 

[wuzak]

If the Do-335 entered mass production it would be during the summer of 1945. Jets aside, it would face stiff competition from other late war piston engine aircraft. The Ta-152 is arguably just as good a fighter while costing a lot less money. The Me-410 is a superior light bomber and probably costs no more then a Do-335.

Depending on the source, the Me410 either carries a 2000kg load (2 x SD1000) or 100kg (says wiki) at 388mph. The Do335 carries 1000kg nearly 100mph faster (474mph) at best altitude (c. 21k ft for Do-335, c.22k ft for Me410) using essentially the same engines (DB603A).

The Do335 could not be considered in the same fighter class as an Fw190D or a Ta152 - it was a heavy fighter, though initially its armament wasn't so heavy.

Where the Me410 wins over the Do335 is the ability to carry a 5cm cannon in the bomber destroyer role - nowhere to stick that on the Do335.

 

[wuzak]

Of course the Me410 was developed from the Me210 and appeared some 2 years earlier.

 

[Denniss]

The Me 410 had an internal bomload capacity of one special 1t bomb or two 500kg. I don't know if they had ever used external bombracks because this would greatly affect speed the Me 410 needed for survivability. With full load, max speed was clearly lower than 388mph.
The Do 335 was just ~60 mph faster with the same engine type - it required alt-optimized and higher-power engines like the 603E to come anywhere near this 470mph claim.
The Do 335 doesn't need a 5cm cannon to kill bombers - ever heard of the R4M? Three 3cm MK 103 were planned for a later version - heavy punch and long range to finish-off bombers crippled by R4M.

 

[wuzak]

Smith, Creek, Roletschek, Dornier Do 335 Pfeil Arrow - The Luftwaffe's Fastest Piston-Engine Fighter gives the maximum speed as 455mph @ 23,294ft (7.1km) at 9,500kg (20,944lbs) weight. 9500kg equates to a full load of fuel (1850kg/4078lbs), pilot, oil, ammo (2 x 200 20mm rounds, 1 x 70 30mm rounds), etc, but without any bombs.

Alternatively it equates to 1350kg fuel with 1 x 500kg bomb.

Fast cruise is listed as 437mph @ 6.6km (21,653ft) at the same weight. Range based on that cruising speed at 6km (19,685ft) is given as 858 miles. For a slow cruise of 286mph at those weights and altitudes gives 1336 miles range.

 

[wuzak]

The Me 410 had an internal bomload capacity of one special 1t bomb or two 500kg. I don't know if they had ever used external bombracks because this would greatly affect speed the Me 410 needed for survivability. With full load, max speed was clearly lower than 388mph.
The Do 335 was just ~60 mph faster with the same engine type - it required alt-optimized and higher-power engines like the 603E to come anywhere near this 470mph claim.
The Do 335 doesn't need a 5cm cannon to kill bombers - ever heard of the R4M? Three 3cm MK 103 were planned for a later version - heavy punch and long range to finish-off bombers crippled by R4M.

"Just" 60mph faster!

No, never heard of the R4M. Is that the 30mm cannon mounted on each wing? Which would make the total armament 2 x 20mm + 3 x 30mm?

Surely the Me410 could have been fitted with a similar array of guns?

Interestingly, the book I mentioned lists the weight of the 30mm Mk103 as 145kg and 73kg for 70 rounds. So, 1.04kg/round. Each extra gun is equivalent in weight to 139 rounds. Assuming that there is enough space to carry those rounds, woud it be better to cary the extra rounds rather than the extra guns?

I suppose not - get better rate of fire from 3 guns so more chance of a hit.