http://crazypilotman.livejournal.com/ (![[identity profile]](https://www.dreamwidth.org/img/silk/identity/openid.png)
crazypilotman.livejournal.com) wrote in ![[community profile]](https://www.dreamwidth.org/img/silk/identity/community.png)
fandomhigh2008-11-20 10:52 am
crazypilotman.livejournal.com) wrote in fandomhigh2008-11-20 10:52 am
Entry tags:
Aviation & Avionics, Thursday November 20, Period 2
"Hey y'all," Murdock grinned. "I hope you enjoyed the trip last week and may be even learned a few things. It's good that we got a chance to visit there and today we're going to be discussing jet aircraft and engines."
(ocd upin a min)
(ocd up
sign in
Re: sign in
Re: sign in
Re: sign in
Re: sign in
goof-off
Re: goof-off
Re: goof-off
Lecture
Lecture Part I
"During the 50s, one of the Navy's contributions to the Research Airplane Program was the D-558-2 Skyrocket. It gave us critical experimental information for transonic and supersonic sweptwing commercial and military fleets. A decade later, the USAF's North American X-14 flew to nearly Mach 7 above the atmosphere and paved the way for the conquest of space."
"But progress hesitated for many years at Mach 2, the temperature limit of aluminum. Only recently has the promise of the B-70, the SR-71 and X-15 been pursued, stimulated by the resurgence of interest in the Aerospaceplane. They achieved high speeds through advanced materials. For various reasons, operational aircraft, both civil and military, have been frozen at 50s performance level for over 30 years. Instead of improving performance, sophistication of aircraft systems became important."
"And of course, a lot of those developments led us to the jet engine. A jet engine is a reaction engine that discharges a fast moving jet of fluid to generate thrust in accordance with Newton's laws of motion. This broad definition of jet engines includes turbojets, turbofans, rockets, ramjets, pulse jets and pump-jets. In general, most jet engines are internal combustion engines but non-combusting forms also exist."
"In common usage, the term 'jet engine' generally refers to a gas turbine driven internal combustion engine, an engine with a rotary compressor powered by a turbine, with the leftover power providing thrust via a propelling nozzle. These types of jet engines are primarily used by jet aircraft for long distance travel. The early jet aircraft used turbojet engines which were relatively inefficient for subsonic flight. Modern subsonic jet aircraft usually use high-bypass turbofan engines which help give high speeds as well as, over long distances, giving better fuel efficiency than many other forms of transport."
Lecture Part II
"Jet engines make their jet from propellant from tankage that is attached to the engine or from ingesting an external fluid, very typically air, and expelling it at higher speed; or more commonly, a combination of the two sources. The motion impulse of the engine is equal to the fluid mass multiplied by the speed at which the engine emits this mass: I = m c, where m is the fluid mass per second and c is the exhaust speed. In other words, a vehicle gets the same thrust if it outputs a lot of exhaust very slowly, or a little exhaust very quickly." He stopped writing for a moment and turned toward the class. "However, in actuality, parts of the exhaust may be faster than others, but it's the average momentum that matters, and thus the important quantity is called the effective exhaust speed, c here."
He went back to writing, "for example, when a vehicle moves with certain velocity v, the fluid moves towards it, creating an opposing ram drag at the intake: m v . Most types of jet engine have an intake, which provides the bulk of the fluid exiting the exhaust. Conventional rocket motors, however, do not have an intake, the oxidizer and fuel both being carried within the vehicle. Therefore, rocket motors do not have ram drag; the gross thrust of the nozzle is the net thrust of the engine. Consequently, the thrust characteristics of a rocket motor are different from that of an air breathing jet engine, and thrust is independent of speed."
"The jet engine with an intake is only useful if the velocity of the gas from the engine c is greater than the vehicle velocity v as the net engine thrust is the same as if the gas were emitted with the velocity c-v. So the thrust is actually equal to S = m (c-v). This equation implies that as v approaches c, a greater mass of fluid must go through the engine to continue to accelerate, but all engines have a designed limit on this, and also that the vehicle can't accelerate past its exhaust velocity as it would have zero thrust."
Re: Lecture Part II
Talk to Murdock
OOC