Impact of Engine Layouts on Aircraft Characteristics

[Scott Kenny]

If you lack space on top of the engine, try what North American did. Image of A-36 with 0.5in machine gun below the engine:
View attachment 734312
There could be some drawbacks to this solution, I can't recall any other single-engine aircraft type with guns below the engine.

That's certainly the only such installation I know of with guns down there.

 

[sienar]

Most planes don't have the thrust line passing through the CG.

 

[OliverSedlacek]

Quoting from "The Secret Horsepower Race" Daimler and Jumo produced inverted V engines because the RLM put that in the requirements. They considered the ease of maintenance as sufficiently important to offset the drawbacks.

 

[HoHun]

Hi,

Quoting from "The Secret Horsepower Race" Daimler and Jumo produced inverted V engines because the RLM put that in the requirements. They considered the ease of maintenance as sufficiently important to offset the drawbacks.

For DGLR Report 88-01, Wolfram Eisenlohr was interviewed by Kurt Grasmann, and that's what Eisenlohr had to say on the topic back then (in 1987):

The requirements for large aero engines were formulated by Sachse of the Heereswaffenamt in cooperation with Eisenlohr, aided by feedback from Kamm of the DVL and Jelinghaus of the Deutsche Lufthansa, and issued to the industry in 1928.

The new large aero engine had to fulfill the following new requirements (somewhat summarized, not a direct translation):

1) Inverted Vee layout resulted in a narrower shape in the field of vision of the pilot. All six cylinder in each row were to run in a single cast light alloy block with inserted cylinder liners.
2) Low lying exhausts, which was good for visibility and helped against contamination by exhaust fumes. Additionally, the aircraft fuselage is wider at the bottom anyway.
3) Propeller reduction gear, to reduce the relatively high speed of the crankshaft for driving the propeller.
4) A free line of fire through the propeller hub, which could be used by a MG or a 20 mm cannon. This arrangement resulted in significantly better chances of hitting the target because on one hand, the aircraft axis was identicial to the bore axis, and on the other hand the large mass of the engine stabilized the weapon. Additional (unnamed) factors also contributed.
5) Altitude supercharger, single-stage with two gears for 2.5 and 4.5 km equal pressure height (I assume this means equivalent to sea level pressure).
6) Fuel injection. This could be postponed for the initial introduction and added later.
7) High temperature cooling of up to 115 - 120 °C. This had been introduced for the BMW VI after extensive testing, and it permitted the use of radiators of just a bit more than half the size of the those used with previous standard temperature of about 80 °C. The temperature difference from the engine into the coolant was reduced and additionally the temperature difference between radiator and ambient air was increased.

This resulted in the Jumo 210 and DB 600/601 engines. It seems the RLM aimed for a 30-liter engine, but also asked for a 20-liter engine to be used in smaller aircraft.

Regards,

Henning (HoHun)