Air Force Question Thread

[hassan1]

CHECK PAF NEW JH-7A AIRCRAFT

PAF JH-7A - Pakistan Defence Gallery

 

[notsuperstitious]

Najam Khan, neat sketches sir.

 

[shehbazi2001]

and last but not the least is it possible if you can post details of all colored birds/display teams used by PAF from Red Dragons till 17 Sqn F-7PG?

The painting of Sabre is not bad but there are some techincal mistakes like the three 0.5 inch (12.7 mm) calibre guns on each side of the fuselage are not in order. The guns are placed in an arrow head type arrangement with the middle gun protuding ahead of the top and bottom gun.

Then it seems that you have placed rocket pods on the wrong pylon. The pylon that you have used is a wet pylon, used for carrying the fuel tank. The inboard underwing pylon was used for rocket pods.

Also you have combined flaps and ailerons, which is wrong in case of F-86. Yes you can add full-span slats on them but not full-span flaps.

 

[Hasnain2009]

Good job Najam!!

 

[Najam Khan]

The painting of Sabre is not bad but there are some techincal mistakes like the three 0.5 inch (12.7 mm) calibre guns on each side of the fuselage are not in order. The guns are placed in an arrow head type arrangement with the middle gun protuding ahead of the top and bottom gun.

Then it seems that you have placed rocket pods on the wrong pylon. The pylon that you have used is a wet pylon, used for carrying the fuel tank. The inboard underwing pylon was used for rocket pods.

Also you have combined flaps and ailerons, which is wrong in case of F-86. Yes you can add full-span slats on them but not full-span flaps.

Thanks for your detailed reply Shehbazi,its always great to acquire knowledge from you guys at Def.pk. I'll make sure these mistakes arent repeated!

Thanks to fateh and Hasnain

 

[spurdozer]

Gr8 job. Najam sir.

 

[spurdozer]

sorry guyys double post.

 

[HAIDER]

Does a plane burnt more gas to sustain lower speed on high attitude ...for example refueling ??

 

[Muradk]

Does a plane burnt more gas to sustain lower speed on high attitude ...for example refueling ??

Nice question
lets start with the basics at low altitude we have more Oxygen more Friction which means more Drag. So at any speed it will suck your tank dry because of the above conditions.
Now when we are at higher altitude we have less Oxygen less Drag so it will not burn more Fuel. If you have noticed that all commercial airlines which are crossing over that Atlantic or any other ocean will be at a higher altitude to cross 5 to 6 thousand miles they climb higher. The longer the trip the higher the altitude.

 

[HAIDER]

We notice second world war plane had frequent problem of stall....is this common technical issue, can we still find this problem in modern fighters. If it happened what are chances of survival for fighter during air combat ???...

 

[Muradk]

We notice second world war plane had frequent problem of stall....is this common technical issue, can we still find this problem in modern fighters. If it happened what are chances of survival for fighter during air combat ???...

Every Fighter has a limit and after that it will stall. Stall means it runs out of air speed, Even fighters like F-22 with such Weight to Thrust Ratio will stall at a certain point.
In war if you stall either you end up in Hell or Heaven there is no 3rd option.

 

[PAFAce]

Every Fighter has a limit and after that it will stall. Stall means it runs out of air speed, Even fighters like F-22 with such Weight to Thrust Ratio will stall at a certain point.
In war if you stall either you end up in Hell or Heaven there is no 3rd option.

Sir, what is the post-stall maneauver, and what is its significance when related to thrust vectoring? I watched a Canadian show in which they told Canadian Air Force recruits not go below 180knots in their CF-18s, and if they did, to dive and build up air-speed to 180knots before continuing. Is that the post-stall maneuver?

 

[Tang0]

Nice question
lets start with the basics at low altitude we have more Oxygen more Friction which means more Drag. So at any speed it will suck your tank dry because of the above conditions.
Now when we are at higher altitude we have less Oxygen less Drag so it will not burn more Fuel. If you have noticed that all commercial airlines which are crossing over that Atlantic or any other ocean will be at a higher altitude to cross 5 to 6 thousand miles they climb higher. The longer the trip the higher the altitude.

Right notion, but wrong explanation good sir.

Sorry, I am an aerospace engineer and I could not resist.

First off, lets ignore propeller driven aircraft because well..It is complicated.
Jets have a similar fuel efficiency for a given thrust all throughout their operational altitudes, so the engine does not really care. Drag is proportional to air density, but so is lift. It is proportional to the square of velocity, but again, so is lift. "Parasite drag" also increases with the square of the velocity. Since: Drag =Parasite Drag + Lift Induced Drag, that means, drag increases faster than lift as you increase velocity, especially as you get past Mach .75.

Lets ignore the transonic region as well though.

The issue essentially amounts to how fast you want to get somewhere. For lift to be equal to weight(IE to "fly"), if we increase velocity, to stay in level flight, we need to decrease the air density. Otherwise, we climb, which has the side effect of decreasing the air density anyway.

If you do the calculations, you find that the most fuel efficient flight path is slow, near the ground, at around 120% of stall speed.

This ignores atmospheric turbulence that you get at lower altitudes, but that is situational. The issue is of course, no-one wants to sit and wait for 5 hours, when they could get to their destination in 3. So, if you want to go faster and still be relatively fuel efficient (In steady level flight), you climb.

Long story short, most airlines fly between 30% and 60% faster than the most fuel efficient speed, and at higher altitudes because of that. In addition, higher altitudes get you more consistent wind magnitudes and direction along with less turbulence.

The reasons for fast, high altitude flight do not however relate directly to an increase in fuel efficiency.

 

[Tang0]

Sir, what is the post-stall maneauver, and what is its significance when related to thrust vectoring? I watched a Canadian show in which they told Canadian Air Force recruits not go below 180knots in their CF-18s, and if they did, to dive and build up air-speed to 180knots before continuing. Is that the post-stall maneuver?

Stall is a technical definition meaning: The point at which, because of low velocity of the wing relative to the air stream, you stop generating significant lift. This happens because of not enough thrust, too low speeds, or high angles of attack. Basically, aerodynamic forces are no longer the most important, and gravity does its thing. Falling is bad, especially as the plane is not designed to be stable while falling.
Post stall maneuvering is anything that happens after you stall, but before lift takes over again. Usually, it is some variation on the dive, but you could do anything. With enough thrust, you can complete a turn, or in the case of the F-16, even gain altitude.
Generally, stalling your aircraft is a bad plan. And in a dogfight, slows you down enough for the enemy to gain altitude and get the drop on you.

Muradk I am sure could come up with some better examples.

 

[Muradk]

Sir, what is the post-stall maneauver, and what is its significance when related to thrust vectoring? I watched a Canadian show in which they told Canadian Air Force recruits not go below 180knots in their CF-18s, and if they did, to dive and build up air-speed to 180knots before continuing. Is that the post-stall maneuver?

Below 180 it will stall and will not recover, With TV you have so much power that the fighter can stay in air suspended drop its nose and not go into a flat spin with TV technology Flat spin recovery is easy. The following is in a way a few ways to do PSM

STALL TURN:
To execute a Stall Turn, the aircraft must start in level flight and nose up to a vertical flight path until it comes to a stop. At which point the model aircraft yaws through 180 degrees, then dives and finally recovers straight and level on a flight path in the opposite direction to the entry. Entry and exit should be at the same height. Low powered aircraft types would be expected to execute a shallow dive at full throttle in order to pick up the necessary speed before commencing the maneuver. The Stall Turn will allow players to regain the offensive position.

The Herbst Maneuver

The Herbst Maneuver another classic post-stall maneuver. The goal of the maneuver is to quite simply reverse the aircraft’s heading angle and to complete the reversal at the same point and velocity that the maneuver was started from. The maneuver typically resembles the one illustrated; the aircraft pitches to a high AOA to stop the forward component of its velocity, puts in rudder at the top of the climb to point the aircraft down, and then dives to regain speed as it returns to the starting point, enabling a rapid direction change.

The Cobra

The Cobra is yet another post-stall maneuver. The two primary characteristics of this maneuver are 1 a rapid pitch-up to near 90 degrees AOA and 2 a rapid decrease in velocity by 50-75%. (The latter is due to the fact that the aircraft is flying through the air on its tail when at 90 degrees AOA, and therefore is incurring a huge drag penalty.) The maneuver also results in an increase in altitude due to the lift generated at AOA values greater than zero.

The Kulbit

An aircraft could shoot an opponent directly behind them by extending the Cobra past 90 degrees to a full 180 degrees. The aircraft actually pitches all the way from 0 to 360 degrees AOA while flying in a nearly straight line, except for the altitude increase as before with the Cobra. This allows for ideal missile shot positioning. But It depends on a the fighter which is locked in a dog fight this move is good but have to bring the boggy close and then pull it , if the boggy is 1500 to 2000 ft behind you and you pull this you are dead. He is go for full breaks and a missile shot or guns.