I don't think that's a fair way of delineating between the kinds of jet engines. Multi shaft turbines are common in all types of turbine installations.
Turbofans are always at least dual, and sometimes three spindle engines. Though in at least two cases, the "fan" part, isn't coaxial with the gas generator section. Turbofans are defined by some fraction of the air moved by the engine, not going through the hot section. Turbofans have even made it down to "small" sizes, in engines such as the FJ33. Turbojets, have all of their air, pass through the hot section. Turbojets are very uncommon these days in bigger installations. Even fighters are using turbofans now. Larger turbojets all tend to be multi spool. To be multi spool, engines need to be of a certain size. Practical limits to size come into play there. Turboprops come in two styles. Free turbine, and .. I'm probably getting the term wrong here, direct drive. And of the popular models, they're about 50/50. Free turbine are much like a turbofan, in that they have second shaft, sitting in the exhaust of the gas generator section, that independently spins the prop gearbox. The gas generator section may or may not be multi shaft. This sort of turboprop is typically started with the prop feathered. Direct drive tend to be a single shaft. The driveshaft to the prop, is the same as the shaft that the compressor and turbines are on. This is a simpler design. But the prop is always a load on the turbine. These turboprops are started with the prop at it's flattest pitch. The number of spools doesn't necessarily directly relate to efficiency. Turbine efficiency is more directly related to compression ratio. Usually called pressure ratio in turbines. Higher pressure ratios give you better thermal efficiency. And bypass ratio, higher bypass ratios mean you're moving more air for the amount of fuel burned. All of this isn't all that relevant in the power regions that say, a KR could use. KR's need 60-200 hp. Turbines of that size, are very, very tiny. As combustion chambers shrink, and turbine wheel sizes shrink, thermal losses become a big factor, also there is leakage around the tips of turbine blades, and that starts to become a major factor. I really do want a 100hp range turboprop... :-) On Wed, Nov 4, 2015 at 7:57 AM, jon kimmel via KRnet <krnet at list.krnet.org> wrote: > Turbo fans and turboprops typically are dual spindle with the aft turbine > section driving the fan or prop and the forward turbine section driving the > compressor...true jets are typically single spool...pretty inefficient. > > https://sites.google.com/site/mykr2stretch/ > https://sites.google.com/site/mykr2stretch/parts-for-sale > On Nov 4, 2015 7:34 AM, "JAMES DUFF via KRnet" <krnet at list.krnet.org> > wrote: > > > That's correct Bill, > > > > > > A gas turbine producing thrust via a propeller is a turbo prop. A turbo > > jet uses a Newtonian reaction from exhaust gases for thrust. > > > > Sent from Yahoo Mail on Android > > > > From:"Bill Wood via KRnet" <krnet at list.krnet.org> > > Date:Wed, 4 Nov, 2015 at 13:30 > > Subject:KR> Jet vs Turbo prop? > > > > Ok guys.. now I am a little confused.. > > > > I am new at this game, I just finished my ground school and going over my > > class work we went thru power plants for air craft. > > > > The picture that I saw of the KR was a gas turbine with a prop on it.. > Yes? > > > > So, correct me if I am wrong, that would indicate that it is a turbo > prop? > > Correct? > > > > Otherwise, if it was a jet, it would use exhaust thrust out the rear and > > wouldn't have a prop? Correct? > > > > Bill > > > > > > > > > > > > jet engine > > > > > > > > > On Nov 2, 2015, at 4:43 PM, Chris Prata via KRnet < > krnet at list.krnet.org > > <mailto:krnet at list.krnet.org>> wrote: > > > > > > > > > > are we talking jet engine, or turboprop (original remarks)? > > > > > > > > > > > > _______________________________________________ > > > > Search the KRnet Archives at http://tugantek.com/archmailv2-kr/search. > > > > To UNsubscribe from KRnet, send a message to KRnet-leave at list.krnet.org > > <mailto:KRnet-leave at list.krnet.org> please see other KRnet info at > > http://www.krnet.org/info.html see > > http://list.krnet.org/mailman/listinfo/krnet_list.krnet.org to change > > options > > > > > > > > _______________________________________________ > > Search the KRnet Archives at http://tugantek.com/archmailv2-kr/search. > > To UNsubscribe from KRnet, send a message to KRnet-leave at list.krnet.org > > please see other KRnet info at http://www.krnet.org/info.html > > see http://list.krnet.org/mailman/listinfo/krnet_list.krnet.org to > change > > options > > > > _______________________________________________ > > Search the KRnet Archives at http://tugantek.com/archmailv2-kr/search. > > To UNsubscribe from KRnet, send a message to KRnet-leave at list.krnet.org > > please see other KRnet info at http://www.krnet.org/info.html > > see http://list.krnet.org/mailman/listinfo/krnet_list.krnet.org to > change > > options > > > _______________________________________________ > Search the KRnet Archives at http://tugantek.com/archmailv2-kr/search. > To UNsubscribe from KRnet, send a message to KRnet-leave at list.krnet.org > please see other KRnet info at http://www.krnet.org/info.html > see http://list.krnet.org/mailman/listinfo/krnet_list.krnet.org to change > options >
