Engine quastion about He-177

[rousseau]

I've known that two engines was crowded cramed in one nacelle on He-177 per se. So cause a serious problem about how to cooling the engine. I think both of air-cooling and liquid-cooling was used on He-177's engine nacelles but still hard to make them works well. Therefor, I was wondering, why Nazi didn't set engins as fore-and aft? Such layout of engine has had already used on Farman 222 before He-177 was born. Both problems of head-on area of engine and cooling engine would be solved.
Here invite your thoughts

[Parmigiano]

I'm not a super-expert, but I think that the fore and aft layout would probably had simplified the gearing of the 'powertrain' (possibly at the expense of a less optimized aerodynamics of the wing/nacelle) but I don't see how it could have (alone) improved the cooling, especially for the water cooled DB.

[DerAdlerIstGelandet]

The whole reason behind the coupled engines was to allow the aircraft to be perform Dive Bombing duties.

[Njaco]

Adler, I just noticed your comment under your siggy and I'm cracking up!!!

Adler is right, it was to streamline the plane for dive-bombing purposes. After all the problems Ernst went on his own and tried a conventional four engine design.

[ccheese]

fly boy said: "isn't that the first jet bomber? becasue i have flown one in a flight sim before and i know how it handles.

Good one, Adler..... I love it...

Charles

[Kurfürst]

The He 177s DB 610s problem was not cooling related but lubrication related. It was a problem early DB 605s suffered from (the DB 610 were really just two 605s coupled together), also in other airraft like Bf 110, 109..

It was solved in the automn of 1943 by adding an oil de-aerator.

[Njaco]

Kurfurst wasn't there also a problem with leaking fuel or maybe oil that collected in the cowlings and caught fire from the heat at times? maybe another plane.

[rousseau]

Originally Posted by DerAdlerIstGelandet

The whole reason behind the coupled engines was to allow the aircraft to be perform Dive Bombing duties.

I think a tandem setting engine could get a smaller head on area for diving but no reduce the amount of engines.

[Graeme]

Originally Posted by rousseau

I think a tandem setting engine could get a smaller head on area for diving but no reduce the amount of engines.

Would such an arrangement destroy the aerodynamics of what was meant to be a high performance multi-role bomber?

I've also read (somewhere) that a pusher configuration is less efficient than a tractor. Maybe someone more knowledgeable in this area can confirm/deny this.

[HoHun]

Hi Graeme,

>I've also read (somewhere) that a pusher configuration is less efficient than a tractor.

Actually, the pusher tends to be more efficient as the tractor accelerates the airflow over the fuselage/nacelle/wing, and the faster airflow means more drag.

However, the same faster airflow can be an advantage when it comes to take-off and landing as it means more lift, and depending on the layout also better controllability by provding a slipstream to keep the tail aerodynamically effective.

With regard to WW2 aircraft, the Dornier Do 335 had different single-engine characteristics depending on it flew on the tractor front engine or on the rear pusher engine

According to Eric Brown, it was faster on the rear engine.

Regards,

Henning (HoHun)

[SoD Stitch]

Originally Posted by Graeme

I've also read (somewhere) that a pusher configuration is less efficient than a tractor. Maybe someone more knowledgeable in this area can confirm/deny this.

Actually, as HoHun said, it's the other way around; there is no parasite drag on a pusher propeller, but there is on tractor propeller. I know that the Do 335 was faster with the front (tractor) propeller feathered, flying on the rear (pusher) propeller, than the other way around. Also, our Cessna 337 Skysmasher was faster on just the rear engine than it was on just the front engine.

[Graeme]

Originally Posted by HoHun

Actually, the pusher tends to be more efficient as the tractor

Originally Posted by SoD Stitch

Actually, as HoHun said, it's the other way around

So much for my memory. Thanks HoHun/SoD Stitch.

Why then don't we see more 'pushers' (with regards to props) in the sky?

[HoHun]

Hi Graeme,

>Why then don't we see more 'pushers' (with regards to props) in the sky?

The standard single-engine tractor layout naturally allows good propeller ground clearance in take-off and landing attitude. If you go for a pusher, you introduce the risk of propeller ground strikes when the angle-of-attack is increased too far.

To keep the landing angle within limits, it's sensible to add particularly effective flaps not necessary on a similar tractor aircraft. If you plan on achieving the same low take-off and landing speeds as with the tractor aircraft, you have to make the flaps yet more effective, introducing even more cost, complexity and weight to the airframe. (Dornier's early patents on a Do 335-style push-pull aircraft actually included a variable incidence wing for that purpose - talk about complexity!)

You also need a stiffer fuselage if you're going to use a pusher propeller in the tail (unless you go for a canard ... Rutan VariEze - Wikipedia, the free encyclopedia ). Willy Messerschmitt's Me 109 layout - with engine, wings, main gear and fuselage all joined through a single structural member, the firewall - illustrates the advantage of the traditional tractor layout. For a pusher layout, you'd need something like an Airacobra with the extension shaft going aft to a pusher propeller behind the tail ... and if you have seen drawings of the structure of the P-39's fuselage structure, you have probably noticed that quite a bit of metal went into that.

For multi-engined aircraft, it's probably a bit easier to design for pusher engines as ground clearance is a minor issue. However, for multi-engined aircraft, take-off and landing distances tend to be important, and the benefit of the accelerated airflow from the propellers increasing lift is a point designers like to employ to improve the low-speed characteristics of their aircraft. The B-29 for example used tractor engines, while the B-36 built for the same role used pushers. The B-29 used a relatively small high-aspect ratio wing of high wingloading, while the B-36 used a relatively larger, lower aspect-ratio wing which I guess was not quite as advantageous for long range as the B-29's wing.

In short, it comes down to the propeller configuration being a the result of a compromise inspired by the intended purpose of the specific type

Regards,

Henning (HoHun)

[Graeme]

Very informative answer HoHun! Thanks.

One last query. The ducted propeller. So many promising designs. Generally 'pusher' in layout with the propeller protected. Yet to my knowledge no large scale manufacture ever occurred for any of them. I would have thought that the General Aviation market would have embraced the idea. Any thoughts as to why success evaded them?

[rousseau]

So a dim conclusion here may be is that designor of He-177 was never aware of tandem setting engine is actually useful layout for their trouble?