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F-16.net Editor Joined: Sep 23, 2003 Posts: 2862

dwightlooi wrote:

The F-35 also has superior range compared to the Raptor, a superior strike ordnance capacity and superior overall sensor package. It'll need less maintenance and less logistical support. Most importantly, it'll cost 1/3 as much to build. So the question really is whether 1 Raptor is preferable to 3 F-35s.

But not superior survivability in a stiff IADS.

RE: Range. That we don't know. A big part of that is what ever a good fuel econ lower speed super-cruise is for the F-22. Calculate the relationship between KIAS and TAS super-cruising at 60,000ft and you will come up with some monstrously fast.... ground speed figures. That is what really tells you how fast you are moving over the map. And not to mention at that height near nonexistent wind and weather to deal with. So in the end the figures for a CTOL JSF and F-22 should be close. CV has more gas but also has more Max gross weight issues vs. what it can carry, Put max gas in the CV with 2ea 2000lb 'ers and then ad the gun pod (drag) and you are reaching your max load. In the non stealth mode where if you want it to look like an A-7 all loaded up, then you will have to trade gas for ordnance. Of course in a fighter or ISR mission with max gas no big deal and CV should have some really great range. Consider though that the best econ cruise for JSF is subsonic.

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Elite 1K Joined: Aug 01, 2006 Posts: 1003 Status: Offline

elp wrote:

But not superior survivability in a stiff IADS.

No, not every bit as survivable, but survivable enough. The biggest reason the F-22 is survivable is not because of the height or speed it can fly at. The biggest reason it is survivable is that the enemy sensors cannot acquire it at more than about 1/10 th distance it can acquire an F-16 for instance.

elp wrote:

RE: Range. That we don't know. A big part of that is what ever a good fuel econ lower speed super-cruise is for the F-22. Calculate the relationship between KIAS and TAS super-cruising at 60,000ft and you will come up with some monstrously fast.... ground speed figures. That is what really tells you how fast you are moving over the map. And not to mention at that height near nonexistent wind and weather to deal with. So in the end the figures for a CTOL JSF and F-22 should be close. CV has more gas but also has more Max gross weight issues vs. what it can carry, Put max gas in the CV with 2ea 2000lb 'ers and then ad the gun pod (drag) and you are reaching your max load. In the non stealth mode where if you want it to look like an A-7 all loaded up, then you will have to trade gas for ordnance. Of course in a fighter or ISR mission with max gas no big deal and CV should have some really great range. Consider though that the best econ cruise for JSF is subsonic.

This I think we can be pretty sure of this. The fuel load of the F35 is about 8.3 tons whereas the F-22 carries about 10~10.5 tons. Having half as many engines, a significantly smaller and lighter airframe and an engine with a higher bypass, the fuel burn in economical cruise for the F-35 will be less than the difference in fuel load. And we are assuming that both are flying at economical speeds (subsonic). Super cruising always burn more fuel than subsonic cruise, so it always reduces range and never improves it.

In the absence of a head or tail wind, your TAS is your ground speed. The only thing that changes with altitude is your Mach number for a given absolute velocity. But even this stops changing at about 40,000 ft above which temperature no longer falls (it becomes ~constant). The Jet stream is typically at around 30000~35000 ft. Sometimes it can go as low as 20000 and as high as 50000 ft but that is not the norm. Both aircrafts will have the ability to climb above the jet stream or get in it to maximize tail wind assist.

F-16.net Editor Joined: Sep 23, 2003 Posts: 2862

I think you need to review your numbers. I would not assume an F-22 will subsonic cruise at extreme altitude. And... your effective ground speed is much greater at 60,000ft than it is at 50 or 40 or 30 etc.

Example a wag of 400KIAS = 700TAS at 60,000ft which is about 806 mph going across a map. What we don't know is how long and at what rate that push can be done to get those kind of results with the F-22 as it pertains to fuel economy.The real number could be higher than that or lower. Mach depends a big part on the temp but, given it is really cold at that alt. Laughing

etc etc.

Note also here, would be an advantage if the JSF could get up to higher alts as we only have to look at F-104 drivers super-cruising at 70,000ft in their P-suits to see an incredible ground speed vs. fuel economy combo.

Where you will be doing subsonic cruise with JSF. What ever that scale is.

I will put my money on that JSF and F-22 will be close on range.

Elite 1K Joined: Aug 01, 2006 Posts: 1003 Status: Offline

elp wrote:

I think you need to review your numbers. I would not assume an F-22 will subsonic cruise at extreme altitude. And... your effective ground speed is much greater at 60,000ft than it is at 50 or 40 or 30 etc.

Example a wag of 400KIAS = 700TAS at 60,000ft which is about 806 mph going across a map. What we don't know is how long and at what rate that push can be done to get those kind of results with the F-22 as it pertains to fuel economy.The real number could be higher than that or lower. Mach depends a big part on the temp but, given it is really cold at that alt. Laughing

etc etc.

Note also here, would be an advantage if the JSF could get up to higher alts as we only have to look at F-104 drivers super-cruising at 70,000ft in their P-suits to see an incredible ground speed vs. fuel economy combo.

Where you will be doing subsonic cruise with JSF. What ever that scale is.

I will put my money on that JSF and F-22 will be close on range.

The ONLY reason ground speed can be different from airspeed is if there is wind involved. Otherwise they are the same regardless of altitude. 800mph is 800 mph. It is not different with altitude. If you have a head wind of 100 mph then the ground speed is 700mph if its a tail wind of 100mph then the ground speed is 900 mph. Winds are the flight altitude is the ONLY reason air speed is not equal to ground speed.

Air temperature actually stays pretty much constant above 40,000 ft for altitudes relevant to jet aircraft. Temperature drops to about -55 deg C as you go up in altitude to ~30,000 ft. It then stays pretty much constant at ~-55 deg C till ~60,000 ft. It then RISES again! At about 140,000 ft it is a pretty mild 0 deg C again.

Below is an altitude/temperature graph... there are nicers ones out there, but I am too lazy to look.

The engine differences between the F-22 and F-35 (0.57 vs 0.20 bypass) will not be the determining factor as to their ceiling altitude. Boeing 747s fly at up too 45,000 feet and that is with 5.0~6.0:1 bypass fans. Control authority will be and in this aspect the presence of thrust vectoring gives the F-22 much better ability to handle itself at extreme altitudes. But the F-35 has larger control surfaces compared to aircrafts like the F-16 and hence handling at high altitudes can be expected to be better. F-16 class aircrafts has a service ceiling of about 57,500 ft. The F-35 can be expected to be a little higher. But flying at those altitudes is one thing, being great handling is another.

F-16.net Editor Joined: Sep 23, 2003 Posts: 2862

Duh...

We are talking indicated airspeed... calculated to True Air Speed(TAS) and True Air Speed converted to ground speed ( in the final part I converted Knots to miles ) And yes final ground speed is determined by wind influence on TAS. But for the general study I'm not going to include wind because I have no idea where the example is taking place....

250 Knots Indicated Airspeed (KIAS) ( what for example the pitot tube gathers ) gives different True Air Speeds (TAS)by... Altitude. ( Fact ) Have a pilot explain it to you. Checklists and procedure that have to do with handling of the aircraft more times than not refer to (KIAS). ( Have a pilot explain that to you too if you don't believe me ).

250KIAS will yield different True Air Speeds at 10,000ft , 20,000 ft (or use the FLs if you like ) 40,000ft etc. This usually means more effective ground speed meaning you move across the map at a faster rate based on KIAS being the same.

Once you figure that out, let me know.

Here is a simple way to figure out TAS. Take your KIAS (lets say 300KIAS) take half of your Flight Level, lets say you are at FL300 ( 30,000ft ), Half of 300 is 150, add (150) to your KIAS (300), 300KIAS at FL300 is a TAS of 450 knots. Add or subtract wind speed to get your ground speed. I then convert naudical miles to statue miles, for the purpose of looking at generic maps.

Enthusiast Joined: Nov 23, 2006 Posts: 29 Status: Offline

Since I fly for a living I can offer some info I suppose. ELP is correct, TAS varies with temperature and altitude (and moisture too but its affect is smaller). So while it is correct that in the stratosphere the temperature basically stabilizes, the pressure continues to drop, in fact the pressure almost halves itself, from about 200hPa to around 100hPa. So for the same given IAS, you’ll have a higher TAS at 60K than at 40K.

It is again correct that all of our airspeeds that we work with in flying the jet (V speeds, climb segments, cruise (usually Mach unless we have short leg and are down low) and descent.) are IAS/Mach but we do refer to our GS for fuel burn, ETA etc. (Ok, the computer does it for us but it’s necessary to check out actual winds vs. predicted to keep tabs on actual fuel burn).

BTW- no transport category aircraft fly above FL410, they aren’t certified to do so (O2 requirements). Except the Concorde of course. They might be able to get up there, but it will be a very slow climb. In such a case you run the risk of flirting with your 1.3/1.5 G buffet boundaries. The jet I fly, the 1.5G boundary at FL410 is small, about .03-.05 Mach, and the trend gets progressively smaller out of around FL340 so that indicates that you are quickly approaching a coffin corner -- for maneuver margins anyway -- above FL410.

http://www.flightplan.za.net/trueAirspeed.php

This link illustrates the differences in altitude and TAS. Here’s an example:

Temp: -50C
Alt: 40,000’
EAS: 227kts
Mach: 0.80
TAS: 465kts

Temp: -50C (leaving it the same of illustrative purposes)
Alt: 60,000’
EAS: 227kts
Mach: 1.29
TAS: 751kts

At 60K and M1.5 the F-22 would have a TAS of 873kts and at 40K and M0.80 the F-35 would have a TAS of 465kts.

BDF

Enthusiast Joined: Mar 13, 2007 Posts: 98 Status: Offline

Here's a nice little summary of the coveted much improved and greatly advanced stealthly features of the F-35 (low and slow aint the way to go and light up a radar screen or IR seeker):

(you might have to right click and save to your desktop to read it)

Elite 1K Joined: Aug 01, 2006 Posts: 1003 Status: Offline

fox100 wrote:

Here's a nice little summary of the coveted much improved and greatly advanced stealthly features of the F-35 (low and slow aint the way to go and light up a radar screen or IR seeker):

(you might have to right click and save to your desktop to read it)

So, you have the opinion of an Aussie who does not like the F-35; an opinion that he did not substantiate to any convincing degree. That's supposed to be gospel?

There is no reason why the F-35 has to go low, and there is no reason why it must go slow. 55,000 ft vs say 65000 ft isn't really LOW. And you can fly an ingress into a SAM battery's effective zone at Mach 1.7 if you want to, you just have to burn 2.5x as much fuel while you are doing it.

There is also two thins in that statement that borders on total BS. The first being the assumption that F-35 stealth measures is in ANY WAY narrow in effective bandwidth than the F-22. That is the unfounded and unsubstantiated opinion of various individuals. I can claim that the reverse is true and it'll be equally unfounded and unsubstantiated. The degree of LO differences between the F-22 and the F-35's rear quarters is also questionable. Straight on in the back, both will have significant RCSes from the engine internals, somewhat off center, it is unclear if there will be huge differences.

Newbie Joined: May 11, 2007 Posts: 4 Status: Offline

the operative phrase being 'so far'

the F-35 will enter service in 2012. By then there'll be plenty of armaments that are both modern and suited to the F-35

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