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Air Force Question Thread

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.

If I start using Airforce terms my friend will not learn any thing, So I try to stay very basic when it comes to make someone understand, What you said I learned it in When I did my PHD in AeroD in 1984. If I go into deep details that wount help instead make things complicated with more question. What all you said I said it in 1 line. The people asking questions are quite aware when I say Friction or drag.
And please you don't have to say Sorry.
 
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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.



good 1 , i totally agree....Please get involved more, cuz we need people with know how to generate talks......:cheers:
 
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...I learned it in When I did my PHD in AeroD in 1984...

Sir, did you get your PhD from the Air War College or the Air University? I had read that there were programs in place for PAF officers to complete graduate studies, both nationally and abroad. If this is true, then I would definitely consider doing graduate and research work in Pakistan instead of Canada or the US.
 
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Sir, did you get your PhD from the Air War College or the Air University? I had read that there were programs in place for PAF officers to complete graduate studies, both nationally and abroad. If this is true, then I would definitely consider doing graduate and research work in Pakistan instead of Canada or the US.
I dont know how it is on the engineering side, but after trying in a couple of very BIG name Pakistani Institutions and wasting three precious years of my life I had to leave Pakistan to do my PhD abroad. A decision, I always regret why I didn't make earlier.
 
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Sir, did you get your PhD from the Air War College or the Air University? I had read that there were programs in place for PAF officers to complete graduate studies, both nationally and abroad. If this is true, then I would definitely consider doing graduate and research work in Pakistan instead of Canada or the US.


Yar In Pakistan we retire at a early age its not like USA that you retire after 65 and say I am done but after that people do work in USA. I being a fighter pilot retire having a BA in Aerospace Engg and Masters that will not get you a job after retirement. So I did my BA', 2 Masters, 1 Masters in Military Operations, The other 1 in Physics and a PHD. All done in USA except BA.
 
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Yar In Pakistan we retire at a early age its not like USA that you retire after 65 and say I am done but after that people do work in USA. I being a fighter pilot retire having a BA in Aerospace Engg and Masters that will not get you a job after retirement. So I did my BA', 2 Masters, 1 Masters in Military Operations, The other 1 in Physics and a PHD. All done in USA except BA.

Wow..incredible credentials. May I ask what was your topic in PhD?

Btw, expect me to keep bothering you with silly newbie questions as Aerodynamics and military jets seems to be my new-found hobby :D
 
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Yar In Pakistan we retire at a early age its not like USA that you retire after 65 and say I am done but after that people do work in USA. I being a fighter pilot retire having a BA in Aerospace Engg and Masters that will not get you a job after retirement. So I did my BA', 2 Masters, 1 Masters in Military Operations, The other 1 in Physics and a PHD. All done in USA except BA.

Sir, if I were interested in joining the PAF in the R&D departments, would you recommend that I complete at least a Masters from Canada or the US, or will a Bachelor of Applied Science degree be enough? Also, what departments in the PAF hire civillians for R&D work? I know PAC Kamra does a lot of engineering work, but not R&D. CAE is probably one institution that focuses on R&D, along with SUPARCO etc.

Also, what are the chances of the PAF re-opening the GD(P) Graduate Program. Will it be possible to get more information on this?
 
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I was wondering if PAF uses Maverick missile for air to ground attacks basically used to take out tanks and other land based military hardware, can any one with the proper knowledge please answer my question?:pop:
 
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Wow..incredible credentials. May I ask what was your topic in PhD?

Btw, expect me to keep bothering you with silly newbie questions as Aerodynamics and military jets seems to be my new-found hobby :D

PhD in Aerodynamics and my son is doing his PhD in Astrophysics.
Son I have been teaching all my life regardless of my rank. I used to pick up the least experienced pilot and say ok Son Show me what you got out of 69 students I have never raised my voice always had a smile which made them easy in the cockpit but I admit 1 student who is now a very big person in PAF I have broken his bones because he being selected for BPT quite on me that people say that I look like a mouse so I want to quit PAF and I picked him up and started beating him and didn't stop while beating him I was crying more than him because he was more than a son too me. After the thrashing he flew with one of the worst people in the history of PAF a man who thought he was the best and used to fire SQD Cmd on the spot, my student flew with him and won the BPT.
So you can ask me anything regardless of what you think is a stupid question, is actually not stupid. knowledge is knowledge no matter what others say. There are a very few people who have really seen a Fighter let alone fly one, You might be very educated but sitting a flying is a totally separate thing and having a couple of boogies under your belt makes hell of a difference.
So ask anything except weapons I will not go into details unless PAF has openly told everyone. I hope you can understand. So fire away sometimes I am busy with job and grandkids so reply might be late which I appologise my wife has already said that Defence.pk is my Sawtan:lol::lol:A waring for NEO and ASIM if she lands in your city vanish :lol: it takes her 1 sec from becoming a good house wife to bruce lee:rofl::rofl:.
 
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Sir, if I were interested in joining the PAF in the R&D departments, would you recommend that I complete at least a Masters from Canada or the US, or will a Bachelor of Applied Science degree be enough? Also, what departments in the PAF hire civillians for R&D work? I know PAC Kamra does a lot of engineering work, but not R&D. CAE is probably one institution that focuses on R&D, along with SUPARCO etc.

Also, what are the chances of the PAF re-opening the GD(P) Graduate Program. Will it be possible to get more information on this?

Look I don't want to discourage you person with the name Nisar was asked by Gen Zia to join DR Q. And nisar was the most educated person in that field at that time he quit his job from USA and joined Mr Q he left the job in 3 months because he was a civilian and his advice was taken as crap. Same person who loved Pakistan left a 6 figure job in USA now hates Pakistan because how he was treated and he is now one of the top people in NASA today.
you can join PAC by sending your resume to CPD JF-17 don't surrender your nationality you might need it. Again Who an I to tell you if you want to join do it we need good people .
This year they will not take GDP Applications because they have qualified people on waiting list. My advise join CAE and change to GDP after 2 months. After hiring GDP Cadet most leave within a month a space is open you can convert your course from CAE to GDP. Academy likes to keep a higher ratio of cadets in the pilot field.
 
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I was wondering if PAF uses Maverick missile for air to ground attacks basically used to take out tanks and other land based military hardware, can any one with the proper knowledge please answer my question?:pop:


Yes in a video/song of PAF, we see Mavericks with F-16s. Now I dont know which version of Maverick PAF has bought.........may be the TV-guided AGM-65A or improved AGM-65B.

TV-guided Mavericks can't be used if the weather is not clear or if its night or darkness............

For night ground-attack , there is an IR-guided Maverick version......

For all-weather attack, there is a laser-guided version of Maverick....

For all-weather/round-the-clock capability, you need a wide variety of weapons.........
 
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PhD in Aerodynamics and my son is doing his PhD in Astrophysics.

Actually my question was about your topic...like the exact area you worked on in your PhD or better asked, "what was the title of your dissertation report?"

If its available online, you can save the explanation and throw in the link or any of your research papers.

So you can ask me anything regardless of what you think is a stupid question, is actually not stupid. knowledge is knowledge no matter what others say. There are a very few people who have really seen a Fighter let alone fly one, You might be very educated but sitting a flying is a totally separate thing and having a couple of boogies under your belt makes hell of a difference.

That's very kind of you.

So ask anything except weapons I will not go into details unless PAF has openly told everyone. I hope you can understand.

Oh, don't worry, my questions are rather about aerodynamics than PAF and any PAF specific question would be general. I can understand that things in the armed forces are pretty sensitive and sometimes even things we may consider normal as classified.

So fire away sometimes I am busy with job and grandkids so reply might be late which I appologise my wife has already said that Defence.pk is my Sawtan:lol::lol:A waring for NEO and ASIM if she lands in your city vanish :lol: it takes her 1 sec from becoming a good house wife to bruce lee:rofl::rofl:.

Let's hope she doesn't read this part :D


My first question:

This question arises from rumors about JF-17 will possibly have a future twin-tail version. Its been rumored around by all and sundry but also reported by some rather respectable people that we "should expect a twin-tail version in the future".

So the question is : What advantages would a light weight ,twin-tail, presumably single engine plane offer to the airforce?

The bolded part seems interesting (to me). My limited knowledge tells me at a first glance that twin tails may have several advantages...like reduction in height ... which is helpful in putting them in a hanger (particularly interesting for Navy), reduction is RCS , shorter take off because a canted twin-tail also have the vertical component of the airflow that might add to the lift, helpful in maintaining balance in twin-engine if one engine fails or provides unequal thrust, etc but has a disadvantage in that it increases weight which is of significant importance to a light weight aircraft.

All the above features (with the exception of reduction in RCS) suits the Navy better. No wonder F-14, F-18, was mostly in the US Navy use (although they were used by airforces of other nations like Iran , Australia, Spain,etc). Infact, and if I am not wrong, the F-16 and the F-18 were in direct competition at the design stage both hoping to impress the forces for their then next generation light-weight fighter. The USAF chose the F-16 while the US Navy preferred the F-18 both with slight modifications.

Other twin-tail fighters, however, have been used by airforces like the Sukhoi Su-27, F-22, F-35, etc but atleast all these and the one used by the Navy were twin engines and heavy weight (OK, F-35 has one but a mammoth one) .Of these, the Su-30 and the F-15 both had pure vertical twin-tails unlike the hornet. Here I have omitted older designs because presumably with advances in understanding of aerodynamics, later designs are much more optimized. I also excluded the the F-14 having vertical tails because it has another unique feature in that it can change its aspect ratio.

Light/medium weight single engine popular design do not use the twin-tails e.g F-16, EF-2000, Rafale, Grippen, JF-17, J-10, LCA, etc.

In summary, the question(s) is/are:
- what advantages or disadvantages would a twin-tail design give to the JF-17 or any other signe-engined fighter?

- How do these advantages/disadvantages compare with primary role of airforce/Navy in addition to what I have stated? (like in why USAF went with F-16 while USN with F-18 while other airfroces did opt for F-18)

- How does a vertical twin tail / canted twin tail relate to other features like aspect ratio, wing design,dihedral angle, sweep angle etc and characteristics of the plane like flight regime?


I presume the answer to each of these sub-questions would be rather long, so please take your time and if you wish you can answer one part at a time. Also, if you have some online resource for easy reference or know of any video lectures, graphical explanation on any of these topics, it would be highly appreciated.

Many thanks in advance.


P.S. Oh, just a note...Mods/ Admins, if this thread isn't the right place for this discussion, you can move it to a more appropriate place since this thread is primarily related to air force questions rather then aerodynamics of planes.
 
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Jets have a similar fuel efficiency for a given thrust all throughout their operational altitudes, so the engine does not really care.

Engine does care. Aircrafts have different ranges at different altitudes, why? because the engine does care. Thats why the designers optimise an engine for a given altitude.

The engines of Tornado are optimised for low-level flight and their performance at medium level is not impressive. Air superiority fighter engines are designed for medium level altitudes and they burn more fuel at low altitudes, reducing their range at low level.

At higher altitudes, air density is lower, which can cause a reduction in thrust, if engine is not optimised for this altitude. A reduction in thrust for a given fuel increases the specific fuel consumption (sfc). But then the engines of airliners are designed for cruising heights, which are themselves at medium altitudes.


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.

Hard for me to digest. Aircrafts regularly accelerate to supersonic speed while remaining at level flight. Increasing velocity does not mean that we must climb (to reduce air density).
 
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