Talk:Turboprop

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TurboShafts are helicopter engines they go through a gear reduction more then once to allow proper speed for rotor rotation

on the Jet engine page, turboprop is listed as a type of jet engine. On the Turboprop, turboprop is contrasted with a jet engine.

I changed it to Turbofan.

Contents 1 First Turboprop Aircraft 2 Turboprop illustration 3 Merge 4 Efficiency versus Piston Engine?

[edit] First Turboprop Aircraft

"The first turboprop engine was the Rolls-Royce RB.50 Trent, a converted Derwent II fitted with reduction gear and a Rotol 7' 11" five-bladed propeller. Two Trents were fitted to Gloster Meteor EE227 - the "Trent-Meteor" - which became the first turboprop powered aircraft."

I've removed the 2nd sentance from the article as the Gloster Meteor article, and pictures, appear to clearly contradict this. Could someone with better knowledge of aircraft write a replacement sentance. --Myfanwy 09:30, 23 Jun 2005 (UTC)

The Trent-Meteor was a converted Meteor I which had its Derwent jet engines replaced with two of the converted Derwents (Trents) Trent-Meteor It was therefore the worlds first turboprop powered aircraft. I'll add a line or two to the Meteor page stating this and restore the original sentence. Ian Dunster 11:55, 9 November 2005 (UTC)

I don't understand, why are turboprops more eficient at low velocity, than turbojets?

The efficiency of a turbojet increases as it's speed through the air increases, because that forward speed allows for more efficient compression of the air inside the engine. The SR-71's engines, for example, were more efficient (less fuel burned per mile) at Mach 3.2 than at Mach 2.8. The efficiency of a turboprop, however, decreases the fast it goes, because the the fast you go, the propeller must increase in pitch to maintain the same thrust. But because drag is higher, the prop must be increased an additional amount just to overcome that drag. There's a practical limit at any given propeller rotation speed, but you can't just increase the prop rotation speed, as doing so can mean the propeller tips go supersonic, and that not only creates a lot of noise, but it creates a lot of drag, as well. Mugaliens 20:04, 13 August 2006 (UTC)

[edit] Turboprop illustration

While the picture is very nice, I can't think of a single turboprop aircraft that angles its exhaust so as to prevent residual thrust. That thrust is beneficial. 66.35.138.9 05:31, 3 January 2006 (UTC)

Yes, I don't understand that either. --Hooperbloob 23:46, 1 April 2006 (UTC)

While flying, yes, and it's why the turboprop directs the thrust aft. But the elimination of residual thrust is primarily for ground power units, ship's turboshaft engines, etc. Most have additional turbine sections to scavange nearly all of the pressure differential before the gasses are exhausted, as that's more efficient. But for turboprops, you're right - that residual thrust is beneficial, and about 25% of the thrust comes from it. Mugaliens 20:11, 13 August 2006 (UTC)

Most PT6 applications do not get any thrust from the exhaust. This is due to the way the engine is built with the intake at the back of the engine and the exhaust at the front. King Airs are great example. While the exhaust does face back, the actual thrust gained from it is negilable since most of the thrust is used to turn the prop and running the generators. Xnuiem 12:47, 19 January 2007 (UTC)

"This enables the propeller to rotate freely, independent of compressor speed." From the current illustration I don't see how this can happen since the prop shaft is geared to the turbine shaft.--Hooperbloob 23:46, 1 April 2006 (UTC)

The illustration depicts a geared turboprop engine. There is another type of turboprop which isn't illustrated that uses a free power turbine to drive the propeller. 66.35.138.9 06:52, 4 April 2006 (UTC)

[edit] Merge

Turboprop and turboshaft -Ste|vertigo 19:24, 16 May 2006 (UTC)

Disagree... they are different things. Turboprop=geared off main shaft. Turboshaft=different shaft. See Turboshaft. 00:11, 24 July 2006 (UTC)~

Disagree with the proposed merger. Turboprops are a gas-turbine engine who's principle work drives a propeller connected directly to the engine via mechanical gearing. It's almost always a constant-speed prop, and as the throttles are advanced or retarded, the pitch is changed to maintain a constant rotational velocity. A turboshaft, on the other hand, generates an exhaust stream that drives an impeller which may or may not be coaxial with the engine. That impeller is in turn connected to generators, air blowers, the shafts of a ship's props, a helicopter's rotor blades, etc. The key difference is that a turboprop is constant speed, while the devices a turboshaft drives have a need to maintain a variety of rotational velocities, or will see a variety of changing loads. Mugaliens 19:56, 13 August 2006 (UTC)

Amazingly, it just hit me - there's another key difference between turboprops and turboshafts. The turboprop drives the aircraft's propeller, (hence, turboprop), while the turboshaft is just the engine itself, and can drive many different things. So again, do not merge. Rather, both need to be cleaned up to reflect this. Mugaliens 10:34, 20 August 2006 (UTC)

By the way, I think this idea has been killed. Let's remove the proposed merger sign. Mugaliens 10:36, 20 August 2006 (UTC)

[edit] Efficiency versus Piston Engine?

However, turboprops are far more efficient than piston-driven propeller engines.

BSFC for a piston airplane engine is typically around 0.45 lb/hp-h while BSFC for a turboprop it is typically around 0.65 lb/hp-h. So the above statement is not true when referring to fuel efficiency. However, the overwhelming popularity of turboprops for commercial aviation applications suggests that overall efficiency (taking into consideration all costs) is better.

The above statement should either be removed or, more beneficially, expanded into a fuller discussion of the overall difference in cost of the two types of engines.

I removed it for now. Frankly, it's been so long since large aircraft were designed with piston engines that it's hard to know how efficient a large piston airliner would be. My guess would be "probably a fair bit more efficient", but the big barrier is safety. Turboprops and turbofans are incredibly reliable; piston engines were less so back in the old days. --Robert Merkel 05:32, 31 October 2006 (UTC)