Tandem prop configuration

Fallschirmjager · 13 August 2010, 07:31 AM

Perhaps someone could answer this question for me, as I can't seem to come up with the proper mathematic equation myself: How much more thrust is achieved by a tandem prop configuration (one tractor/one pusher) on the typical inline engine ? I am not taking into account such variables as aircraft weight, configuration of wings, placement of engine nacelle on wings, number of blades on the props and their length,etc... purely the tandem configuration. I have often wondered about the practicality (or lack thereof) of this configuration regards some of the early big planes, particularly Russian. Is there truly a significant enough boost of thrust achieved to warrant the load on the engine and the propensity for burning up a drive shaft quicker ? Any thoughts ?

sobrien · 13 August 2010, 08:57 AM

Not sure about the math, but it is a concept that has been revisited again and again. The WW2 Germans built one, the Dornier Arrow. Cessna built the Skymaster, which got used in VietNam. Burt Rutan built a few. It must have some merit.

Sean

Fallschirmjager · 15 August 2010, 08:44 PM

The Dornier Do-335 was actually a twin-engined aircraft, with the tail prop powered by a second Daimler engine mounted in the fuselage just aft of the wing trailing edge. It was actually the fastest piston-engined aircraft of WWII, but it weighed as much as a B-25 bomber. My query is regarding a single engine powering the tandem arrangement on a single drive shaft. The Russians and Germans approached this arrangement on a few models, but barring props with blades of enormous length and drastic curvature, I have never seen the practicality of this arrangement.

Greybeard · 16 August 2010, 01:56 AM

Increase in engine power requires bigger airscrews and more blades.

Higher diameter may have limits in available space for propeller rotation.

A four blades airscrew has about 2% less efficiency, in respect of a two blades one.

So may be effective to couple two two-bladed airscrews on same shaft: although this arrangement reduces efficiency of rear propeller, this could be still better than a four-bladed one.

Regards,
GB