Aerodynamics thread

[Engineer]

good try but already has been proven on aircraft flying, not computer models that turn rates are enhanced

In your own quote, the statement "very slow speed, very high angle-of-attack (AOA) flight regime" implies a near-stall or post-stall situation. That confirms, rather than invalidates what I have said. Look at another source for an elaboration of what "very slow speed" means.

Thrust Vectoring is one of the design elements that can contribute to create a certain advantage during close air combat by generating impressive pitch and yaw rates, but only in a limited portion of the flight envelope at velocities well below “corner speed”.

However, Thrust Vectoring can also transform in a few seconds an energy fighter in a piece of metal literally falling off the sky, making it an easy prey for those who have been able to conserve their energy.

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As for your second link, I quote:

It was not an aim of this project to conclude anything about the use of Thrust Vector Control (TVC) / Post Stall Manoeuvrability (PSM), but rather to purely provide methods for assessing these and other technologies, for aircraft where the engine exhaust nozzles are located at the rear of the aircraft.

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You are engaging in used-car salesman's tactic of cherry picking quotes and misrepresenting what the authors themselves are saying. Nice try.

 

[Air Force Brat]

In your own quote, the statement "very slow speed, very high angle-of-attack (AOA) flight regime" implies a near-stall or post-stall situation. That confirms, rather than invalidates what I have said. Look at another source for an elaboration of what "very slow speed" means..

Every aircraft has a certain speed-range in every configuration where it is happy, most stable, with gear and flaps down, aircraft stalling speed is reduced. For whatever reason, lowering the landing gear increases stability, and usually lowers the calibrated stall speed.

For that reason, if a pilot loses directional control, one of the most effective recovery techniques is to select gear down, even at a high rate of speed, even if doors and actuators are damaged, lowering the gear will often stabilize an aircraft enough for you to regain control..

a "clean" aircraft has the broadest range of stability as to airspeed spread, and a dirty aircraft has the narrowest band of aircraft stability, as you lower flaps and gear, you will have to "retrim" the aircraft pitch for this new configuration. As you lower flaps the center of lift changes and the aircraft will require pitch trim to be changed in order to stabilize the aircraft?? If you lower full flaps you will also have to add power and increase pitch in order to maintain altitude.

Lowering the flaps also increases drag as well, and may enable you to slow your aircraft and regain control, although at an extremely high rate of speed you risk losing a flap and creating an assymetric lift situation, which would really cook your goose.

 

[Air Force Brat]

Every aircraft has a certain speed-range in every configuration where it is happy, most stable, with gear and flaps down, aircraft stalling speed is reduced. For whatever reason, lowering the landing gear increases stability, and usually lowers the calibrated stall speed.

For that reason, if a pilot loses directional control, one of the most effective recovery techniques is to select gear down, even at a high rate of speed, even if doors and actuators are damaged, lowering the gear will often stabilize an aircraft enough for you to regain control..

a "clean" aircraft has the broadest range of stability as to airspeed spread, and a dirty aircraft has the narrowest band of aircraft stability, as you lower flaps and gear, you will have to "retrim" the aircraft pitch for this new configuration. As you lower flaps the center of lift changes and the aircraft will require pitch trim to be changed in order to stabilize the aircraft?? If you lower full flaps you will also have to add power and increase pitch in order to maintain altitude.

Lowering the flaps also increases drag as well, and may enable you to slow your aircraft and regain control, although at an extremely high rate of speed you risk losing a flap and creating an assymetric lift situation, which would really cook your goose.

I have very recently helped the present owner, restore our old 172 to flight status, basically there were a few squawks. The main gear tires were starting to dry-rot from UV exposure, and the seat rails with pin holes to adjust your seat for and aft, had to be replaced as the pin holes to locate the steel pin had elongated, and were out of spec.

That could allow the seat to slide backwards on the rails if you were in a very slow, high angle of attack condition, or conversely allow it to slide forward pushing your yoke forward. If the seat slides to the rear, instinctively you hang on to the yoke which could result in full aft yoke travel and a violent pitch up, if it slides forward you would naturally push forward on the yoke causing a violent pitch down.

 

[Air Force Brat]

I have very recently helped the present owner, restore our old 172 to flight status, basically there were a few squawks. The main gear tires were starting to dry-rot from UV exposure, and the seat rails with pin holes to adjust your seat for and aft, had to be replaced as the pin holes to locate the steel pin had elongated, and were out of spec.

That could allow the seat to slide backwards on the rails if you were in a very slow, high angle of attack condition, or conversely allow it to slide forward pushing your yoke forward. If the seat slides to the rear, instinctively you hang on to the yoke which could result in full aft yoke travel and a violent pitch up, if it slides forward you would naturally push forward on the yoke causing a violent pitch down.

anyway, approach to landing stalls are no sweat, although it requires a little power to get it to "break" and actually stall, it would rather "mush", which morph's into a fairly stable high rate of sink. It will "bite" power on, the old 172s had a straight leading edge before 1973, when a "cusp" was added to the leading edge, taming power on stalls, but our old bird would love to roll-off on a wing, and would spin if you let it??

 

[kurutoga]

Just curious, any one try to move/turn the entire engine as an alternative to TVC? So power is always 100%

 

[PiSigma]

Just curious, any one try to move/turn the entire engine as an alternative to TVC? So power is always 100%

That would be an osprey. Too inefficient and slow response.

 

[PiSigma]

Just curious, any one try to move/turn the entire engine as an alternative to TVC? So power is always 100%

That would be an osprey. Too inefficient and slow response. And with what room on the plane are you going to put the moving full engine?

 

[kurutoga]

That would be an osprey. Too inefficient and slow response. And with what room on the plane are you going to put the moving full engine?

I was thinking just allow 5 degree flexibility and still use the regular Turbofan engines

 

[siegecrossbow]

6th gen requirements have not even been defined. Do you have credible reference source to be speaking in such definitive language with regards to the adoption of TVC in both Boeing and LM's proposal?

From what I've heard both Boeing and LM are actually moving away from the knife-fights for sixth gen. Some of the areas they'll pursue include AI, directed energy weapons, high super-sonic flight, long range and high endurance, and integration with drone network.

 

[Air Force Brat]

I was thinking just allow 5 degree flexibility and still use the regular Turbofan engines

You're using your "thinking cap" and that's good, but your concern about OVT losing massive amounts of thrust is way overblown, in fact on the F-22 I would call the loss of thrust insignificant compared to the agility increase.

Secondly, your 5 degree would be very overly complex, and very inefficient compared to OVT, first the nacelle would have to be oversized?? unless you choose to move the whole nacelle, then you would disrupt your airflow through the engine.

Although if you kicked the aft end of the engine up to increase pitch for high angle of attack, you would also lower the angle of attack of the engine, possibly giving it a better airflow??

and I do think that you would lose some of the tremendous advantage of thrust vectoring by reducing the angles of thrust!