New answers tagged supersonic
5
Neglecting friction does indeed lead to inaccuracies. Those, however, are small for weak shocks, so using the equations for inviscid shocks gives a good approximation. Especially in the times before electronic computers, this was a major simplification while the error was tolerably small.
Stronger shocks should be avoided and replaced by a cascade of weaker,...
0
Most spaceplanes are aerodynamically just hypersonic airplanes. The tailless delta wing with directional stabilising fins on the tips is an optimal solution, especially if you do not want a fin on the fuselage. Directional stability can be elusive and highly non-linear, so types designed before the days of high-speed digital control systems often resorted to ...
0
The North American XB-70 Valkyrie was a Mach 3 bomber which had variable-geometry winglets. Their purpose was most unusual in that they turned vertically down to help reduce drag during supersonic cruise, and returned to horizontal to increase the wing area for takeoff and landing.
The wing of the Valkyrie was a waveriding delta. The engine intakes formed a ...
1
Yes they do use a lot of extra fuel, but the amount is depending on the operating conditions (Mach flight speed and altitude)!
Comparing MIL (military) power setting (maximum power without reheat) to MAX power setting (engine will be in MIL power, but the reheat will be scheduled and the exhaust nozzle opened) you can see that it is not uncommon to have 3 ...
10
To explain if the afterburner makes the engine louder, you must understand what the afterburner does. In the afterburner, the exhaust gases are re-heated by injecting fuel in the afterburner duct. The left oxygen is used to burn the fuel, which results in an increased exhaust gas flow. Note that the engine itself will not spool up faster: this is done by ...
1
From an energy standpoint, the engine produces heat, thrust, and less significantly, sound. Ignore the afterburner for a second and just consider throttling up, whether a jet or your car. The engine gets louder. That's not a law of physics, that's just what happens. There's no theoretical reason why the extra waste energy can't go 101% into heat, and -1% ...
1
If you look at it in terms of thrust vs fuel flow, then yes, they're very inefficient.
However, if you just look at the amount of fuel burnt to get an interceptor from the runway to 30,000ft, then they can be more efficient. Without afterburners the same climb would take significantly longer and could use more fuel.
Without afterburners, you'd need much ...
28
This PDF indicates an increase by ~10 dB for an F-8K in afterburner versus the same aircraft in 100% dry thrust.
This PDF indicates smaller increases:
+5 dB for an F-15
+4 dB for F-22 and F-35
-4
If you are asking if the engine is louder, no it is not. The afterburner and the diversion of the exhaust is what makes it louder. Just like in a car motor running straight pipe to gain horsepower. You can take the same motor and put an exhaust system on it and it will give that motor a different tone.
5
Yes the specific fuel consumption of the afterburner, lbs of fuel used per lb of thrust, is much higher than the core engine. This is because the fuel is being added to a part of the engine where the air is less compressed, so the energy conversion is a lot less efficient. The bright orange flame coming out the tail pipe when in reheat is pretty much all ...
14
I would say definitely yes, because of all the extra energy added to the exhaust flow and it's obvious to anyone who attended enough military airshows. Watch an F-16 depart with reheat on, then reduce thrust to military power (max thrust with reheat off) on the climb out, and it almost sounds like the engine flamed out.
The flow out the nozzle may be ...
24
It has been around 20 years since I've been on a carrier deck, but I recall that it wasn't as dramatic of an increase as you might think. It may have gotten a little bit louder, but what I remember more is that the tone changed. The sound was more "full" when the afterburner was engaged. I realize this is a rather subjective answer.
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