Turbocharger

[A380800]

Hey guys,

I was recently studying performance and power augmentation and while doing so i came across a point which stated that turbochargered engines power output decrease as altitude increase? I wanted a little clarity

I understand that turbocharged engines produce increased back pressure but how?

[Radix]

..........

[mustafagander]

A388,
My take on this phenomenon you're asking about is that all piston engines lose power as density altitude increases - it's the nature of the beast.

Turbo charging as well as increasing power for T/O also maintains a higher air pressure in the induction system, ie a lower density altitude so you have more power. Hence better take off performance on hot, high D/A, days. Eventually you "run out of puff" as altitude increases and the turbo is maxed out so D/A starts to increase with further climb. A benefit of turbos is the recovery of waste energy going down the exhaust pipe, especially heat which is recovered as the exhaust gasses expand through the turbine. But nothing for nothing and it costs due to higher back pressure in the exhaust reducing overall efficiency a bit. Superchargers (mechanically driven) have similar benefits excluding the heat recovery but they tend to cost a bit more energy to run.

Turbos can and often are optimised for the mission so sizes vary on otherwise similar engines - look at engines powering, say, a Beech Duke and a Piper Chieftain, different planned cruise regimes mean different turbo sizing. Look also at Piper turbo normalised Seminoles which use small turbos mainly to help take off performance as D/A rises.

[Chu Chu]

If you removed the piston engine part of a turbo-compound (leaving the shaft connecting the supercharger and the turbine), and replaced it with a simple combustion chamber, you'd have a turboprop. Of course, you'd probably want to rearrange a few other things as well . . .

[ThreeThreeMike]

The compound engines of the B29 used exhaust turbines to add more torque to the crank shaft. These engines were also supercharged by a crank driven supercharger, so you can think of them as being indirectly turbo charged. Whether that was better than simply pointing the un-tapped exhaust backwards (like Merlins did) is debatable. It was certainly heavier, more complex and less reliable. It was probably more efficient though; on a slow aircraft like a B29, jet exhaust is not as efficient as putting a bit more power into the prop.

The B-29 was not engined with the Wright R-3350 turbo compound radial. It was a standard supercharged version. The postwar Boeing B-50 was powered by the P&W 4360, but not a turbo compound version. Wright was the only company to place the turbo-compound engine into production.

The Wright turbo-compound radial was not fully developed until after the war. It was fitted to military and civilian aircraft, the Douglas DC-7 and Lockheed Constellation being two civilian examples.

[Old Fella]

The Turbo-Compounding certainly added to the power of the Wright 3350. It did, unfortunately, lead to the loss of at least one aircraft and eight crew members to my knowledge. In February 1959 a RAAF Neptune was lost as a result of an uncontained Power Recovery Turbine failure which led to an uncontrollable fire which was of such intensity as to burn through the wing resulting in the aircraft crashing into the bank of the Hawkesbury River, short of the airfield.

[jimjim1]

Napier Nomad - Wikipedia, the free encyclopedia (http://en.wikipedia.org/wiki/Napier_Nomad)

Designed from the outset to be a compression ignition (diesel) turbo compound engine.

Was never in production but development continued until 1955. The pure jet and turbo jet won out and the project was eventually canned.

[RVF750]

All engines lose power as the air density and pressure reduce, not just piston ones.


At 39,000ft the CFM is burning only 1.1tonnes per hour. this is because it's not getting much air in the front and not making much power, ram effect or not! Probably explains the time it gets to drag your ass to 41,000ft......