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By: - 29th October 2016 at 00:02 Permalink - Edited 1st January 1970 at 01:00
There is nothing wrong with the data, the Tomcat is aerodynamically the most efficient fighter ever. The plane was so aerodynamically efficient due to the fact that it had high aspect ratio wings contributed to its turning efficiency so it wasnt producing as much drag as stub wings would at high AoA. The airframe itself contributes a lot to lift and its turning ability is the result of its wings and tail surfaces worked in conjunction to how the lifting area of the fuselage was distributed, the entire fuselage acted like a giant LERX. The fact that the Tomcat could get away with such small tail surfaces indicates how well balanced the aircraft was in the way that the wings and tail surfaces leveraged the large lifting area of the fuselage. So lots of thrust was not needed to maintain energy in a turn like jets with high wing loading like the F-16, it was aerodynamically able to project speed through the turn. If FBW did not exist the Tomcat would still be the top fighter in the world. The main problem with the Tomcat besides the engines were that it was overweight due to the complex fuselage structure to accommodate the swing wing and the weight of the pivot mechanism of the swing wing. The Fuselage suffered from a lot of cracking and was overly complicated to maintain. It should have been designed as a fixed wing and would have been equal or better to the F-15 if it was.
With FBW it is a common now to make fighters with barn door sized tail surfaces that are almost as big as the wings, this layout that is definitely not as efficient without FBW. Even the F-15 used electronic stabilization making it semi-FBW, without it it would not have flown very well.
By: - 29th October 2016 at 00:47 Permalink - Edited 1st January 1970 at 01:00
There is nothing wrong with the data, the Tomcat is aerodynamically the most efficient fighter ever. The plane was so aerodynamically efficient due to the fact that it had high aspect ratio wings contributed to its turning efficiency so it wasnt producing as much drag as stub wings would at high AoA. The airframe itself contributes a lot to lift and its turning ability is the result of its wings and tail surfaces worked in conjunction to how the lifting area of the fuselage was distributed, the entire fuselage acted like a giant LERX. The fact that the Tomcat could get away with such small tail surfaces indicates how well balanced the aircraft was in the way that the wings and tail surfaces leveraged the large lifting area of the fuselage. So lots of thrust was not needed to maintain energy in a turn like jets with high wing loading like the F-16, it was aerodynamically able to project speed through the turn. If FBW did not exist the Tomcat would still be the top fighter in the world. The main problem with the Tomcat besides the engines were that it was overweight due to the complex fuselage structure to accommodate the swing wing and the weight of the pivot mechanism of the swing wing. The Fuselage suffered from a lot of cracking and was overly complicated to maintain. It should have been designed as a fixed wing and would have been equal or better to the F-15 if it was.
Your post doesn't make much sense to me, sorry.
If the F-14 used high aspect wings, while turning. Then both Str and ist would suffer, especially the latter.
If the F-14 used low aspect wing configuration, then you get good its, but str would still be only average, due to severly drag/lift. See SH for clues..
So to claim F-14 is the most aerodynamic fighter EVER is not very correct to say the least.
From your post I see you like F-14, but its aerodynamics had shortcomings.
You can't simply blame it all on T/W ratio.
As been said before a million times, there is no free lunch in the field of Aerodynamics.
By: - 29th October 2016 at 00:56 Permalink - Edited 1st January 1970 at 01:00
If the F-14 used high aspect wings, while turning. Then both Str and ist would suffer, especially the latter.
what youre saying is not true at all, if it was then aerobatic planes would have stub wings which they obviously dont. There is a point where large wing area can outweigh the effects of aspect ratio which is why large delta wing fighters will turn well.
See SH for clues.
Youre comparing an FBW jet with non-FBW, subtract FBW from the SH and what are you left with? A VERY BAD FIGHTER
By: - 29th October 2016 at 01:44 Permalink - Edited 1st January 1970 at 01:00
Turning is all about producing excessive lift. High aspect ratio wings provide the best lift to drag ratio (see sail plane for ex.). It's all about induced drag (refer to your aero book).
A swing wing fighter enjoy the benefits of a ticker profile. When the wing is swept backward, the relative airfoil is "extended" by the inverse of the cosines of the sweep angle.
Hence: Ticker airfoil, greater aspect ratio-> better lift. And as we have seen, better lift at less drag.
Add the the fuselage lift, the staggered wing concept with the tail surface enhanced by the wing downwash and you have a very efficient aircraft in a turn. You can then reduce the amount of power needed to the point that for a given set of perfs, the extra power of new engines won't see much use if:
. - you don't increase G
. - you allow "some amount" of alt loss in the turn
My 2 cents ;)
By: - 29th October 2016 at 12:52 Permalink - Edited 1st January 1970 at 01:00
But can anyone explain, how can the E-M diagrams be practically not influenced by the 34% increase in static thrust? Or name another example of such situation? Or maybe there is something wrong with the data (even though it is taken from the NAVAIR manuals) or my interpretation of it?
No, nothing wrong about your interpretion. First point is, there is dynamic thrust issue like in the discussion you've mentioned. Increase in 34% static thrust does not mean equally increased thrust throughout the flight regime.
Also, F-14D is heavier by 1747 lbs. To make the same turn wings have to generate more lift, and to do that, AOA requirement increases. This is important as F-14 already has very high wing loading, so a slight increase of AOA may drop L/D drasdically. Also we don't know if there is a CG shift due to this weight increase. F-14 has positive stability, if CG shifts forward, elevators would have to work harder to maintain AOA while turning. Considering major changes from F-14A to F-14D are in avoinics department, this is very likely to be the case as well.
As for another example, its actually applicable to almost any aircraft; Modern versions tend to have usually less maneuverability than the initial aircraft: F-15A PW-100, F-15C PW-220 and F-15E PW-229 comparison:
[ATTACH=CONFIG]249377[/ATTACH]
F-15A has higher STR PW-229 equipped F-15E with 22% higher thrust. Also speaking of dynamic thrust, note that PW-220 engines has the least thrust of all 3, (105,7 kN), but its by far the fastest of all 3 on same aircraft.
Also, at sea level F-16 Blk 30 (20000lbs) has 23 deg/s STR, and 26,2 deg/s ITR but F-16 blk 50 (22000lbs) has 21,4 deg/s STR and 24,8 deg/s ITR despite higher thrust.
Welcome to the forum BTW.
By: - 29th October 2016 at 15:42 Permalink - Edited 1st January 1970 at 01:00
[ATTACH=CONFIG]249365[/ATTACH]
Again, the differences are negligible, with only small advantage for F-14D. It is obvious, that even if the numbers are the same, the Super Tomcat was in another league in comparison to the legacy model, as the F110 allowed much more care-free handling than the stall-prone TF30 (although I think that these E-M diagrams to some extent debunks the myth of sluggish F-14A). But can anyone explain, how can the E-M diagrams be practically not influenced by the 34% increase in static thrust?
You've had a few examples from other aircraft provided in other posts already, but I would add this nuance to the interpretation:
- Looking at the E-M Diagram, higher turn rates will be dominated by aerodynamic performance. Changing the engine out does nothing to change the basic aerodynamics of the airplane, and adding weight only makes all performance parameters worse.
- The lower turn rate portion of the diagram, however, will be dominated by thrust-to-weight ratio. So if you look at the lower g-loading segment, for example, you can see that adding the F110 greatly extended the flight envelope where the 300 fps acceleration margin applied.
In other words, a pilot with a higher-thrust F110-powered F-14D would seek to use his advantage in acceleration at low g-loadings to give him an edge over an F-14A powered by the TF30. The F-14A pilot, in contrast, would seek to lure the F-14D into a low-speed, tight, turning engagement where the F-14A would have the advantage. It's commonly called "dissimilar air combat" (although here there are many more similarities in this example than in most comparisons).
Welcome to the forum, Lolek.
By: - 29th October 2016 at 15:55 Permalink - Edited 1st January 1970 at 01:00
Changing the engine out does nothing to change the basic aerodynamics of the airplane, and adding weight only makes all performance parameters worse.
Shouldn't having more thrust increase the STR? The more thrust you have the more you can sustain a turn at high Gs and the more lift the wings will generate during the turn.
By: - 29th October 2016 at 19:14 Permalink - Edited 1st January 1970 at 01:00
Thanks guys for your answers, I must say that I find them all really informative.
The main problem with the Tomcat besides the engines were that it was overweight due to the complex fuselage structure to accommodate the swing wing and the weight of the pivot mechanism of the swing wing. The Fuselage suffered from a lot of cracking and was overly complicated to maintain. It should have been designed as a fixed wing and would have been equal or better to the F-15 if it was.
It is another interesting matter for me, was a VG design a mistake in the case of the Tomcat? It is quite common that people are talking about weight penalty connected to the variable geometry configuration, however most of the books says that the VG was often chosen to allow weight savings. For example, probably we all know the story of Grumman 303F fixed wing design which was considered during F-14 development. In the words of the designers: "The 303B was modified to become the contract-award-winning E, which we then ran off against the fixed-wing 303F. The F lost for 2 reasons:
Also, in the book on the F-14 by David Baker there was a small discussion about VG design, here are some of the most important points:
[ATTACH=CONFIG]249379[/ATTACH]
So how it really is with the variable-geometry, was it a technological dead-end, or there was really something into it (let's neglect the maintenance problems connected with this idea)? Or maybe just the introduction of FBW and other aerodynamic advances made the VG obsolete?
Also we don't know if there is a CG shift due to this weight increase.
Well, there is some indication of the CG shift, as the glove vanes were deleted in the D model. Partially it was dictated by lower cost of maintenance, but they were also deemed unnecessary for pure aerodynamic reasons.
Shouldn't having more thrust increase the STR? The more thrust you have the more you can sustain a turn at high Gs and the more lift the wings will generate during the turn.
This is something I also still don't fully understand, although I see that it is not as simple as I originally thought. However one thing that bothers me is the fact, that opinions on superiority of F-14D over F-14A were quite unanimous. Were the differences noted by fltgshdw significant enough to justify them?
By: - 29th October 2016 at 20:24 Permalink - Edited 1st January 1970 at 01:00
It is quite common that people are talking about weight penalty connected to the variable geometry configuration, however most of the books says that the VG was often chosen to allow weight savings. For example, probably we all know the story of Grumman 303F fixed wing design which was considered during F-14 development. In the words of the designers: "The 303B was modified to become the contract-award-winning E, which we then ran off against the fixed-wing 303F. The F lost for 2 reasons:
Also, in the book on the F-14 by David Baker there was a small discussion about VG design, here are some of the most important points:So how it really is with the variable-geometry, was it a technological dead-end, or there was really something into it (let's neglect the maintenance problems connected with this idea)? Or maybe just the introduction of FBW and other aerodynamic advances made the VG obsolete?
I was actually not aware of the 303F and Im surprised it performed so poorly compared to the swing wing version although my idea of a fixed wing F-14 would be freezing the wing geometry at mid sweep. Of course part of the idea of VG wings is to compensate for shifting CoL, especially at high speed. But I think that idea has been found to be a non-issue as the drag reduction for super sonic cruise by reducing tail surface downforce has been negligible. So my thought is that an F-14 with wings fixed at mid sweep would would work just as well as the full swing wing design, similar to how the wing angle is set to a stationary angle on a mig-23 for maximum manoeuvrability.
By: - 29th October 2016 at 20:27 Permalink - Edited 1st January 1970 at 01:00
There is nothing wrong with the data, the Tomcat is aerodynamically the most efficient fighter ever. The plane was so aerodynamically efficient due to the fact that it had high aspect ratio wings contributed to its turning efficiency so it wasnt producing as much drag as stub wings would at high AoA.
But it will also provide less lift at similar sweep angle
the entire fuselage acted like a giant LERX.
No it doesnot ,the purpose of LERX is to create vortex and provide lift , the entire fusalage of F-14 doesnot create vortex
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The fact that the Tomcat could get away with such small tail surfaces indicates how well balanced the aircraft was in the way that the wings and tail surfaces leveraged the large lifting area of the fuselage.
I dont know why would you think F-14 have a small tail , its tail is massive
So lots of thrust was not needed to maintain energy in a turn like jets with high wing loading like the F-16
I dont see how well balanced the aircraft is has anything to do with how much thrust required to overcome drag in a turn.
By: - 29th October 2016 at 20:37 Permalink - Edited 1st January 1970 at 01:00
Talking about turn rate, an engineer made a similar comparision between USAF 4-5 gen aircraft ( equalize combat radius and weapon load )
http://www.f-16.net/forum/download/file.php?id=22895&sid=fceea8e076beb5734e1905ae96dd3c30
By: - 29th October 2016 at 21:08 Permalink - Edited 1st January 1970 at 01:00
I was actually not aware of the 303F and Im surprised it performed so poorly compared to the swing wing version .
Here it is, I must say it's a very pretty beast:
[ATTACH=CONFIG]249382[/ATTACH]
Talking about turn rate, an engineer made a similar comparison between USAF 4-5 gen aircraft ( equalize combat radius and weapon load )
Interesting. When compared with the E-M diagram for the F-14D it looks quite good. However, some of his findings look questionable to me, like comparison of the range between F-14D and F/A-18E (F-14D is considered inferior by him), as from what I heard the Tomcat was far superior in this aspect.
By: - 29th October 2016 at 21:18 Permalink - Edited 1st January 1970 at 01:00
But it will also provide less lift at similar sweep angle
no it wouldnt, the high aspect ratio wings provide more efficient lift compared with stub wings of equal area
No it doesnot ,the purpose of LERX is to create vortex and provide lift , the entire fusalage of F-14 doesnot create vortex
Youre taking me too litterally, of course the fuselage does not match the exact same purpose as LERX in that its not providing an over-wing vortex. But the fuselage area does provide lift forward of the CoL of the wings, and in that way provides increased leverage in a turn the same way the LERX on say the Mig-29 provide ahead of CoG lift in which to lever against.
I dont know why would you think F-14 have a small tail , its tail is massive
I guess I overemphasized the of the tail surfaces being small in proportion to the wings and overall size of a/c, I guess Im comparing it more with modern 5th gen fighters like the F-22.
I dont see how well balanced the aircraft is has anything to do with how much thrust required to overcome drag in a turn.
I never said the purpose of distribution of lifting surfaces reduced drag
By: - 30th October 2016 at 01:29 Permalink - Edited 1st January 1970 at 01:00
I was actually not aware of the 303F and Im surprised it performed so poorly compared to the swing wing version although my idea of a fixed wing F-14 would be freezing the wing geometry at mid sweep. Of course part of the idea of VG wings is to compensate for shifting CoL, especially at high speed. But I think that idea has been found to be a non-issue as the drag reduction for super sonic cruise by reducing tail surface downforce has been negligible. So my thought is that an F-14 with wings fixed at mid sweep would would work just as well as the full swing wing design, similar to how the wing angle is set to a stationary angle on a mig-23 for maximum manoeuvrability.
No, it wouldn't work at all. An F-14 with fixed wings at mid sweep would neither be able to take-off and land on a carrier nor would it have acceptable supersonic performance. In other words it would be completely useless.
Swing wings were a great solution to get high performance and good low speed handling required for carrier ops. The reason swing wings have gone out of fashion is not because of aerodynamic performance but complexity and cost (and stealth nowadays). It also limits the life of an aircraft, though thats not an issue for a carrier jet as its life is limited by the number of landings anyway.
Look at all the carrier borne fighters. All the high performance fleet defenders had some sort of high lift device. F-8 had adjustable wings, F-4 had boundary layer control, F-14 had swing wings. F-18 and F-35 have nothing and consequently their supersonic performance is poor. A fixed wing F-14 would have required some other high lift device, as the book says. Either that or give up on state of the art kinematics and go the F-18E/F route.
By: - 30th October 2016 at 01:36 Permalink - Edited 1st January 1970 at 01:00
Well, there is some indication of the CG shift, as the glove vanes were deleted in the D model. Partially it was dictated by lower cost of maintenance, but they were also deemed unnecessary for pure aerodynamic reasons.
Well yes, not the glove vanes were deemed unnecessary per se, but the performance they allowed for was no longer required. F.e., the F-14A could pull 7.5G at Mach 2 with the help of the glove vanes. The F-14D could not. If the F-14D would have been required to have the same performance, the glove vanes would have remained. Lower maintenance cost was more important.
Btw. the F-14A manual says maneuver devices on AUTO, F-14D has them disabled. That might have some negative effect.
By: - 30th October 2016 at 02:25 Permalink - Edited 1st January 1970 at 01:00
Talking about turn rate, an engineer made a similar comparision between USAF 4-5 gen aircraft ( equalize combat radius and weapon load )
http://www.f-16.net/forum/download/file.php?id=22895&sid=fceea8e076beb5734e1905ae96dd3c30
thankies.
didnt realize the F-35C was so much a better performer than the A and B
By: - 30th October 2016 at 04:21 Permalink - Edited 1st January 1970 at 01:00
All the high performance fleet defenders had some sort of high lift device. F-8 had adjustable wings, F-4 had boundary layer control, F-14 had swing wings. F-18 and F-35 have nothing and consequently their supersonic performance is poor. A fixed wing F-14 would have required some other high lift device, as the book says. Either that or give up on state of the art kinematics and go the F-18E/F route.
While I agree that ship-borne aircrafts generally feature some sort of high lift devices, not all of them carry the same level of weight/cost penalty as the swing wing. Look at Rafale-M, which almost exclusively relies on its low wing loading to achieve low speed performance.
By: - 30th October 2016 at 05:53 Permalink - Edited 1st January 1970 at 01:00
Low speed and bring back are two different things. Lately you saw the Raf M taking off with on single CM when the Adl'A did with two...
Add 30 days of strikes, near peer attrition losses and you get a clearer picture. ;)
By: - 30th October 2016 at 06:56 Permalink - Edited 1st January 1970 at 01:00
While I agree that ship-borne aircrafts generally feature some sort of high lift devices, not all of them carry the same level of weight/cost penalty as the swing wing. Look at Rafale-M, which almost exclusively relies on its low wing loading to achieve low speed performance.
you forget the canards which add flow control over that nice delta wing which result in a significantly lower landing speed (at an acceptable AoA) than without. Compared with a Mirage 2000, you have an approach speed below 120kts, which would mean stall speed below 92kts, while the Mirage is @ 140kts approach and stall around 110kts (while being lighter than the Rafale)
By: - 30th October 2016 at 07:24 Permalink - Edited 1st January 1970 at 01:00
you forget the canards which add flow control over that nice delta wing which result in a significantly lower landing speed (at an acceptable AoA) than without. Compared with a Mirage 2000, you have an approach speed below 120kts, which would mean stall speed below 92kts, while the Mirage is @ 140kts approach and stall around 110kts (while being lighter than the Rafale)
You can add Carnards and make it a tri-plane like Su-33 or No Carnards at all like Mig-29K wit Kruger flaps, And keep other stuff like variable air-inlet as well for performance wise. Those two jet can do whatever the Other CV jets can do. Its just pure acedemics. Ski-jump or steam rails.
You increase the size of some control surfaces. Add some 1000Ib of weight/strenght and you get a jet that has far less "compromise" that F-14 had.
IMO imagine them operate off a US super carrier..
Posts: 54
By: Lolek - 28th October 2016 at 19:24 - Edited 2nd October 2019 at 11:40
Hello everyone. I had been a reader of this forum for years, however it was the recent discussion in "What's the difference between energy–maneuverability theory & Supermaneuverability" that encouraged me to finally join the forum community. I must admit that I'm a complete novice in the topic of aerodynamics, since my main interest lays usually in history of aviation programs. Nevertheless the discussion in the mentioned topic (especially at the beginning) gave me a hope that I will be able to get answers to some of the questions that are of high interest for me.
One of my all-time favorites is the F-14 Tomcat. For a long time I was looking for the E-M diagrams of this plane, as it seemed to me that there is a lot of argument considering its maneuverability. From what I see, the consensus is that while it represented a step ahead in comparison to the previous generation of fighters e.g. F-4 or MiG-21, it is not considered to be on par with the rest of teen-fighters or MiG-29 and Su-27. For a long time the only E-M diagram which I was able to find was this one:
[ATTACH=CONFIG]249362[/ATTACH]
It is the one from the NAVAIR 01-F14AAP-1.1 manual for F-14D with General Electric F110 engines. It should be noted, that the diagram is for the configuration with 4 AIM-9 and 4 AIM-7, what translates to the drag index equal to 44. I was really surprised, as after comparison with the E-M diagrams for e.g. F-16 block 50 for similar configuration (Drag index equal to 50):
[ATTACH=CONFIG]249363[/ATTACH]
it turned out, that the Super Tomcat enjoyed the low-speed advantage in ITR up to about 0.65M (even with the Navy imposed 6.5G limit, which was far from both projected structural limit of about 7.5G and 9G limit during test flights). Similar situation can be observed for the STR, where F-14 again reaches its maximum at relatively low speed of 0.6M (15 deg/s), while the F-16 clearly dominates the higher speeds with STR of 14.3 deg/s at about 0.85M (where Tomcat is below 13 deg/s). While of course it can be argued, that the maneuverability at higher speeds is more desirable, I think it is safe to say that overall the F-14D is more or less in the same class in terms of turn rates.
Still, we are talking about D-version, the one that finally get a suitable engine. The F110-GE-400 delivered about 28200 lbs on reheat, what translates into TWR at gross weight of about 1.01. But what about the legacy version? The F-14A was equipped with the TF30-P414A engines with the maximum thrust of 20900 lbs (a rather optimistic value taken from the book by David Baker), what at gross weight of 53873 lbs (the F-14A was slightly lighter) gives TWR of 0.78. While of course these are values calculated for static thrust values, one can expect a drastic difference in terms of agility between F-14A and F-14D. However, after long searches I was finally able to find E-M diagrams for F-14A and to my surprise they turned out to be nearly identical at 5000 feet. Here is the comparison:
[ATTACH=CONFIG]249364[/ATTACH]
The differences are marginal, the F-14D enjoys a slight advantage for each value of specific excess power, but it doesn't translate into higher maximum STR values. I started to wonder, what is wrong? The TF30 was known for its good performance at low level, with the values of installed thrust at sea level (at speed of 0.9M) being given by Stevenson at 28000 lbs, so maybe the small differences at low level can be justified to some extent. However, at high altitudes (e.g. 25000 fts) the advantage of F110 should be clearly visible. But guess what:
[ATTACH=CONFIG]249365[/ATTACH]
Again, the differences are negligible, with only small advantage for F-14D. It is obvious, that even if the numbers are the same, the Super Tomcat was in another league in comparison to the legacy model, as the F110 allowed much more care-free handling than the stall-prone TF30 (although I think that these E-M diagrams to some extent debunks the myth of sluggish F-14A). But can anyone explain, how can the E-M diagrams be practically not influenced by the 34% increase in static thrust? Or name another example of such situation? Or maybe there is something wrong with the data (even though it is taken from the NAVAIR manuals) or my interpretation of it?