ComNavOps has stated that the role of a carrier and its air
wing is to provide escort and protection for the Tomahawk cruise missile
shooters, the Burkes. Related missions
include clearing lanes for Air Force bombers and establishing local air
superiority for operations. All these
missions require a top end, pure, air superiority fighter.
One of the main characteristics of a useful carrier air
superiority fighter is very long range/endurance.
Let’s look at existing and historical fighter size aircraft
and ranges and see if we can project an achievable maximum range and aircraft
size.
I’ve collected data on a variety of [mostly] fighter
aircraft. Obviously, range is a function
of many factors including aircraft weight – and, of course, engine efficiency,
flight profiles, weapon loads, fuel capacity, and so on. However, weight is the factor we’ll examine
today.
Range (combat radius, to be clear) and weight data are taken
from Wikipedia and other sources and can vary widely. I’ve tried to pick representative
values. I’m not going to debate specific
data. We’re looking at overall trends
not exact values for a specific aircraft configuration and mission. The overall trends are clear regardless of
variations in exact values.
The graph below shows the relationship between aircraft
range (combat radius) and weight, quite clearly. The bigger the aircraft, the greater the
range. This is demonstrating that our
desired long range, air superiority fighter is going to have to be big. This is not really a surprise but the graph
hammers the point home.
Are these jet fighters in the graph below shown in empty, gross or max takeoff weight? Also what is their armament?
ReplyDeleteFrom the post,
Delete"I’ve tried to pick representative values. I’m not going to debate specific data. We’re looking at overall trends not exact values for a specific aircraft configuration and mission. "
What stands out is the 40 year old F15! If only they had progressed with the F15N.
ReplyDeleteThe F-15C doesn't have anything like that radius (and the configuration of F-15E with both conformal tanks and drop tanks that gets that range doesn't have anything like that gross weight). The F-15N would have had worse range, ceteris paribus, than the F-14, and slightly worse maneuverability - there were studies done on this. You could get the range up by turning other knobs (reduce payload, especially the specific requirement to carry 6 of the huge Phoenix missiles along with aerodynamic fairings and launch rails and oil cooling systems to support them, and the gigantic and powerful radar and bespoke fire control system to manage them), but if you're going to play that game you could turn the same knobs on the F-14 with the same result.
DeleteIf you look at the standard aircraft characteristics documents* for the F-15C and the F-14A and F-14B/D, you'll see that the radius for similar missions and similar payloads is very close, with the F-14A usually leading the pack (though losing the the F-14B/D for deck launched intercepts, largely because the F110 engines let the latter do the cat launch and some of the initial fly-out without lighting the blowers). The F-14A had more efficient engines and was more aerodynamically efficient, while the F-15C has a better fuel fraction, largely because it can carry more and better (larger capacity and less drag) drop tanks, and the end result is about a wash between the two.
Of course, none of this really makes a big difference to the pretty-obvious overall trend, which is that for a given mission profile and payload, the following are all true ceteris paribus:
1) a larger aircraft with a larger fuel fraction will have longer range
2) a more aerodynamically efficient aircraft (for the mission profile) will have longer range
3) an aircraft with more efficient engines (in most flight regimes relevant to this discussion, this means higher-bypass turbofans, though there are other factors) will have longer range
* a final quick note about SAC documents: unfortunately, the mission profiles with the same names are _neither_ identical nor equivalent in the SAC documents for different aircraft. Additionally, the set of mission profiles is often different, the external store loadings available are often not close to equivalent, etc. To put the icing on the cake, the SAC documents get revised sometimes, and the revisions are almost uniformly in a more conservative direction wrt. range (eg. because the unstated fuel reserve is increased compared to the initial assumptions), so comparing the SAC document for aircraft A and aircraft B where you are using the initially-released document for A and a document updated after ten years of fleet service for B is often misleading. You almost have to get the -1 or NATOPs and compute the drag index and look up burn rates on range charts yourself to get an accurate comparison.
Worth reading on this subject is Dr Jerry Hendrix's Oct'15 paper 'Retreat from Range' the rise and fall of carrier aviation.
ReplyDeletehttps://www.cnas.org/publications/reports/retreat-from-range-the-rise-and-fall-of-carrier-aviation
Be careful of your data sources. ALthough Wiki shows what you have for the F-16 and F-15, it shows the F-16 carrying 4 1000 lb bombs while the F-15 is configured for interdiction mission. What is that? Air to Air or Ground attack? I doubt it is ground attack. Also note no mention of the profile like the F-16 Hi-Lo-Hi. Bombing is a SECONDARY mission for a Fighter and should not be the configuration you use to compare fighters. The wiki F-14 mentions nothing about mission profile or configuration. Although I think few would consider the F-14 to be very good at bombing. It was designed when we had the A-4, 6, 7 specialized attack aircraft.
ReplyDeleteThe services do not want standard missions run to compare aircraft, they might lose budget and programs. Put 4 x 1000 lb bombs on all three aircraft and fly the same profile. Then configure them for their real mission fighting Air-Air and fly the same mission profile. Then let's talk data.
Fuel Fraction is the key to range in aircraft. You are right newer more efficient engines can make up to some extent for lower fuel fraction, but for the same vintage engines, the fuel fraction drives the range. Even the Air Force was embarassed when the range of the F-16 was shown to be more than the protect the home drome.
The next fighter needs to be a single primary mission of fighter with as high a fuel fraction as they can get. It should be cheap as can be, realizing that peer air defenses will take out aircraft. Instead of stealth, in the plane look for enhanced EW escort aircraft that are survivable and can negate the costly stealh technology. Remember the minute you turn on your missile radar they know where you are and where you are going to and coming from. Lastly develop a primary attack aircraft that only carries alot of bombs and guided missiles. You cannot stealth a bomb so you either have internal stores that are small or have to carry alot of external bombs. Again the Fighter should only be used in its secondary attack role when the air defenses have been severely reduced.
"Be careful of your data sources."
DeleteFrom the post,
"I’ve tried to pick representative values. I’m not going to debate specific data. We’re looking at overall trends not exact values for a specific aircraft configuration and mission. "
Unfortunately it is challenging to push engine efficiency much further, remaining gains are pretty incremental. Commercial aircraft trying to vasty increase fuel efficiency focus on more aerodynamic forms (see Celera 500) and/or traveling at higher altitude with thinner air. You can always bleed speed during patrols before contact, that would look something like the F-14 where you change the flight configuration. It would be easier today with electric motors being more reliable than the old pneumatics. Some also think fuel like LNG might help because it is more efficient by mass, but it takes up more volume. It would also require many logistics changes from the Navy.
ReplyDeleteFor the long term you need a better fuel than hydrocarbons, which probably means nuclear isotopes like cobalt-60. I wrote about that on my blog here:
https://austinvernon.site/blog/nuclearseparation.html
The problem with for example swing-wing like the F14 is the weight penalty that is the drawback. The penalty on F14 was around 1000kg if i remember correctly and that would affect the range or the payload. Swing-wing is not a good solution due to the increase in weight and complexity.
Delete/W
The details matter here. If the vast majority of flight time is spent at patrol speeds, then it will add lots of range which a good benefit. And the power density of electric motors and power electronics has improved leaps and bounds since the 1970s. The amount of complexity and weight you add will be much less today. There is an article in these archives about a plan in the 1990s to retrofit the F-14s to dramatically decrease complexity but we retired the planes instead.
Delete"challenging to push engine efficiency much further"
DeleteRegardless of the accuracy of that statement, engines are only one factor. What we need to improve is the overall DESIGN (shaping, maximized lift, reduced drag, conformal tanks, fuel fraction, etc.) to emphasize range. To the best of my knowledge, no one has ever tried to produce the longest range fighter possible. Various designs have emphasized speed or maneuverability or acceleration or supercruise or weapons carry or whatever but none have emphasized range. There are so many factors that impact range that I'm sure we can significantly improve range by optimizing ALL factors for range. Of course, we have to ensure we don't lose combat capability along the way.
https://en.wikipedia.org/wiki/Douglas_F6D_Missileer
DeleteThe F6D Missileer had a 6 hour on station time,
Deleteand long range missiles.
Yes, exactly the point I was trying to make. The gains in jet fuel powered craft have to come from the overall system. Better aero, a patrol configuration that allows very efficient slower speed flight (hard when engines tend to have narrow optimal efficiency ranges), higher fuel fraction etc. Massive improvements in modeling software and better electronics/motors are newer technologies that could power significant improvements besides the we haven’t tried hard enough aspect.
DeleteUltimately other fuels besides jet fuel are going to give better performance while possibly lowering costs and we should be working on them in the lab.
The adaptive engine is an example of potential engine improvements however when we examined it, it was questionable (see, "Adaptive Engine".
DeleteWhen designing a aircraft what is intended as a multi-role or in “PR-language” onmirole. The design should always start as a pure fighter. It is easy to convert a fighter design to bomber, see F15 but impossible to convert a bomber to a good fighter, see F35 or Tornado ADV.
ReplyDeleteIf the design should do the mission described in this post I do believe that the weapon load the F22 carries internal is not enough for the mission described, more AA missiles would be needed. External pylons on a F22 design could would solve this, however stealth would then be lost. The option still exist to only use internal weapons if stealth would be critical. Hard to see that the stealth coating could be maintained at see over time. To increase the range super-cruise would be the design to strive for. Super-cruise is supersonic speed, ~M1.2 and above on MIL-Power.
Another interesting question would be the design target size, smaller size would give room for more aircraft and in a combat situation be able to absorb losses better. However weapon load and range would be the trade off.
/W
I was going to contribute the link but am actually in need of it. Does anyone have the hyperlink to the U.S. military aircraft characteristics pdfs? Great info on most old planes from WWII and the Cold War. Thanks!
ReplyDeleteI would point out the F-14 happened because the F-111B was among other things considered too big for the flight deck with a max cat weight of like 84,000lbs and MTOW of 88k. I think the A-3 was the actual in service weight champ finally with an 84k cat launch. F-15 and F-22 are about as big as it will get.
You did see on the chart that the F-15 is about 45,000 lbs gross weight while the F-22 is about 65,000 lbs? The F-22 is about 45% heavier than the F-15.
DeleteYeah, I don't care about the chart and gross weight. I care about empty weight and MTOW.
DeleteWhen was the last time we had a pure fighter? Even the F-4 and F-14 did air to ground missions, despite ostensibly being fighters.
ReplyDelete“One hopes that aircraft engines have developed to a point that we can squeeze out additional range simply from having more modern, more fuel efficient engines in addition to emphasizing whatever other design characteristics might contribute to enhance range (shaping, maximized lift, reduced drag, conformal tanks, etc.).”
ReplyDeleteSome quick back-of-the-envelope calculations.
Range varies linearly with SFC using the Breuget equation, so we can make some estimates:
The A5 (nee A3J) used J79’s with a SFC of 0.84 at Mil Power, the F-119s in an F-22/F-35 are about 0.7, so we see a 16% increase over about 40 years development.
Range varies a bit more subtly with the L/D combination, but improvements of somewhere between 10-15% would be a reasonable guess…say 12.5%.
So a notional modern ‘Vigilante-2’ would have a range extension of 1.16 x 1.125 = 1.305, or about 31%.
We also get some pluses for engine T/W improvements, less weight means a smaller angle of attack in steady flight, and thus a decrease in drag…hard to quantify for ‘as installed’ and since engines are a relatively small fraction of MTOW…maybe 4%?
Which brings us to 35% better range than a late 50s/early 60s design, all else being constant.
Which you can use to increase payload or range - desirable of course, or reduce a/c size and signature for the same mission, also desirable.
A slightly related thought. One reason (at least that's my impression) that fighters have to be so maneuverable is that you have historically needed to point the entire plane at the target in order to fire at it. But given the existence of off-boresight missiles, that's no longer true. Would that fact possibly reduce the requirement for maximizing maneuverability, at least to an extent?
ReplyDelete"reduce the requirement for maximizing maneuverability, at least to an extent?"
DeleteNO!!! Off-boresight is not magic. Every degree off the perfect position reduces the pK. A pilot still has to maneuver for the best possible shot or risk wasting his few, precious missiles on low probability shots.
Just as important is the need for extreme maneuverability in defense. Sooner or later, the pilot is going to be on the receiving end of a missile and will need to maneuver to escape.
Maneuverability - offensive and defensive - is a universal constant in aerial warfare.