By: Anonymous
- 10th June 2008 at 10:18Permalink- Edited 17th October 2019 at 04:21
Contrary to the West the SU had a high number of medium bombers to fill the capability gap of the Su-24.
Indeed, I remember a Carlos Kopp diagram showing that with cruise missiles like a Kh-15 that the Tu-22M3 could carry twice as many weapons as an F-111 over a similar range.
His diagram showed one Tu22M3 performing the mission of two F-111s with tanker support.
BTW the F-111 carrys extra fuel and a 20mm gun and ammo in its weapons bay. It is not used for other weapons normally.
The Tu22M3s weapon bay on the other hand can carry 6 x Kh-15s on a rotary launcher. With two more carried externally (the brochures claim it can carry 10 missiles, which I would assume means 4 external Kh-15s and 6 internal ones) it carrys 8 missiles, the equivelent F-111 load is 4 missiles per plane and two planes with a 3,000km flight radius with inflight refuelling.
By: Sens
- 10th June 2008 at 10:46Permalink- Edited 1st January 1970 at 01:00
5x640kg X-58 missiles weight 3200kg
2x2400kg external fuel tanks=4800kg
so this is where the 8000kg warload of Su-24 comes (condition: wing swing)
6x2271liter external fuel tanks approximately weight 10800kg but wing fixed
so reduce to 4x2271liter ETT about to 7200kg + bomb bay load 908kg = 8108 kg
(wing swinged)
so when condition is same, warload of Aardvark and Fencer are almost equal.
The conditions are not the same from the start.
There are two main differences, when not comparing pears and apples.
10 tons of fuel inside a Su-24 do generate a range of 100% or whatever number in nm/km you like.
10 tons of fuel inside a F-111 do generate a range of 130 % or ..........
Even when we reduce that difference in SFC to 10% only, there is still a difference in favor of the F-111.
But that is all without the second main difference.
Before going to that, a small example may be a help for better understanding.
When your car has 150 hp/kW installed power and a truck has an engine of the "same" nominal 150 hp/kW too, but both have to haul a load of 15 tons at 80 km/h you will get an idea, that same hp but different torque make u huge difference.
In some sense, the airflow of an jet-engine is something similar like torque.
The TF30 is ~5500 kp in installed dry, when the AL21 is ~8000 kp in installed dry.
The engines in both aircraft are able to give that enough thrust to reach Mach 0,8 till Mach 0,9 in max military or dry with external load.
The difference in installed dry to do so is up to 45 % alone.
But that is not for free, every kp or kN in nominal thrust has to be payed by fuel measured in SFC, when in use.
Where ever you look first, you will find out easily, that there is a huge gap in range capability between the Su-24 and the F-111, related to the propulsion system alone.
Looking into some data only can be very misleading.
So under the most favorable conditions a F-111 can have two times the action radius of a Su-24 with the same weapon-load.
Compared to that yardstick, the Su-24 is close to the Tornado IDS by nearly double the size.
But besides that, it seems that the Su-24 did/does satisfy the needs of the Russian AF, because it was kept and worth an avionic upgrade for some of that till today and the near future, when its replacement, the Su-34 does suffer funding problems.
By: Schorsch
- 10th June 2008 at 11:18Permalink- Edited 1st January 1970 at 01:00
To give an idea about specific fuel consumption for turbofans and turbojets see attached plots.
The TJ-example does not really represent the most advanced TJ, but even if you consider a 10% more efficient engine the conclusion is not dramatically altered.
[ATTACH]162829[/ATTACH]
Shows SFC over power setting for three altitudes (one per plot) and various Mach numbers (lines in each plot). For the typical mission points (low alt, M0.7, max dry thrust; high alt, max dry, M0.8) we see an SFC of ~1.3-1.4 for low level and 1.1-1.2 for the high alt cruise. That is a bit more than for more advanced TJs, but not far away.
[ATTACH]162830[/ATTACH]
Same for the TF-30 (of the F-14 in this case). One can see an SFC between 0.9 and 1 for low alt and M0.9, and about 1 for high alt cruise. That is in line with other turbofans.
In conclusion: the TJ shows a 20 to 40% increase in SFC, depending on altitude, Mach number and power setting. The reduced SFC in afterburner does not really save the day as a typical mission of the F-111 would see the afterburner switched on not more than a few minutes at egress.
Or short: Fitting aircraft with turbojets for subsonic cruise is crap.
For experts or those who want to become it: the often quoted SFC from Wikipedia is normally at M0, 0km altitude and full dry power. So, that would be the lowest line on the right hand plot (while that is still for M0.5 resp. M0.7). You'll see that by this the static SFC values are much lower than real flight SFC values. For civil engines, normally the design point is given. For afterburner SFC max power at sea level Mach 0 is given, again, only truly representative for a taxiing aircraft.
But as I said, don't get confused too much by the complexity of reality.
By: Sens
- 10th June 2008 at 11:58Permalink- Edited 1st January 1970 at 01:00
At least no afterburning TFs.
Still a mistery to me why they didn't retrofit the RD-33 or a derivative of that engine.
To fit an AB to an Tf is no problem, as the example of the R8 from the Viggen showed or later the D-30 for the MiG-31
The AB is injection of fuel into the hot exhaust to use the unburned oxygen still left.
By that you can rise nominal thrust up to 50% at sea-level with a Tj. When that nominal ratio did not change, the practical thrust gains are much higher at height and speed. When the engine itself is affected by the drop of atmosphere pressure in a linear way, the AB is not so to the same degree.
40 kN dry and 60 kN wet at low (start) is 50 % of AB thrust.
High up that does change to 10 kN dry and 20 kN wet or the AB thrust is up to 100 % from the total, besides the gains from the modulated inlet- and outlet-system. To compare that to ground level values, some did use the artifical value of mathematical thrust.
Before carried away, a bypath engine has a lot of unburned oxygen to rise thrust by injecting fuel into the burner. That start with 60% and higher related to bypath ratio. The higher the bypath ratio, the higher the fuel-burn or the related SFC in AB. Early Tfs with a bypath ratio higher 1 could reach a SFC up to 3.
Modern Tfs are more leaky Tjs, when with an bypath ratio below 0,5 are close to SFC of Tj in AB. The other factors about SFC aside.
When an engine is used most of the time in dry and for short periods in burner, the advantages in fuel consumption are more than obvious.
Burner development did not stand at idle too, like the first ones with all or nothing behavior. The second generation could be used in stages, when the modern ones do allow a smooth movement (FADEC) to every power-setting you wish.
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By: MiG-23MLD
- 10th June 2008 at 12:32Permalink- Edited 1st January 1970 at 01:00
To give an idea about specific fuel consumption for turbofans and turbojets see attached plots.
The TJ-example does not really represent the most advanced TJ, but even if you consider a 10% more efficient engine the conclusion is not dramatically altered.
[ATTACH]162829[/ATTACH]
Shows SFC over power setting for three altitudes (one per plot) and various Mach numbers (lines in each plot). For the typical mission points (low alt, M0.7, max dry thrust; high alt, max dry, M0.8) we see an SFC of ~1.3-1.4 for low level and 1.1-1.2 for the high alt cruise. That is a bit more than for more advanced TJs, but not far away.
[ATTACH]162830[/ATTACH]
Same for the TF-30 (of the F-14 in this case). One can see an SFC between 0.9 and 1 for low alt and M0.9, and about 1 for high alt cruise. That is in line with other turbofans.
In conclusion: the TJ shows a 20 to 40% increase in SFC, depending on altitude, Mach number and power setting. The reduced SFC in afterburner does not really save the day as a typical mission of the F-111 would see the afterburner switched on not more than a few minutes at egress.
Or short: Fitting aircraft with turbojets for subsonic cruise is crap.
For experts or those who want to become it: the often quoted SFC from Wikipedia is normally at M0, 0km altitude and full dry power. So, that would be the lowest line on the right hand plot (while that is still for M0.5 resp. M0.7). You'll see that by this the static SFC values are much lower than real flight SFC values. For civil engines, normally the design point is given. For afterburner SFC max power at sea level Mach 0 is given, again, only truly representative for a taxiing aircraft.
But as I said, don't get confused too much by the complexity of reality.
I think you example is not representative of the Al-21 versus TF-30 without having the real data of both engines something you do not have niether you are presenting.
The SFC given by Russian sources show the AL-21 to be slighly more thirsty than the Al-31 or TF-30 in fact only a Max of 12% and a minimun of 7% at dry military power however at full afterburner the TF-30 seems to be quit thirsty
All your empirical guessing does not prove that the range of the F-111 is the result of the TF-30 being 30% more economical.
You are not proving the F-111 and SU-24 carry the same amount of fuel
Look at this image it shows you very clearly the F-111 is carrying six external fuel tanks, while the Max range claimed for the Su-24 is with only three external fuel tanks, its obvious that the Max ferry range quoted for the F-111 is with six fuel tanks and it is obvoius the lighter Su-24 carries less fuel and this is proven by data taken from the Sukhoi webpage and RAAF
even the max carrying capacity shows it can carry more fuel tanks
Maximum Takeoff Weight F-111F, 100,000 pounds (45,000 kilograms).
Armament Up to four nuclear bombs on four pivoting wing pylons, and two in internal weapons bay. Wing pylons carry total external load of 25,000 pounds (11,250 kilograms) of bombs, rockets, missiles, or fuel tanks.
By: franc
- 10th June 2008 at 13:06Permalink- Edited 1st January 1970 at 01:00
The conditions are not the same from the start.
There are two main differences, when not comparing pears and apples.
10 tons of fuel inside a Su-24 do generate a range of 100% or whatever number in nm/km you like.
10 tons of fuel inside a F-111 do generate a range of 130 % or ..........
Even when we reduce that difference in SFC to 10% only, there is still a difference in favor of the F-111.
But that is all without the second main difference.
Before going to that, a small example may be a help for better understanding.
When your car has 150 hp/kW installed power and a truck has an engine of the "same" nominal 150 hp/kW too, but both have to haul a load of 15 tons at 80 km/h you will get an idea, that same hp but different torque make u huge difference.
There was a story which mes told out what was your logic:
A man went to post office to send a mail. server told him his mail is overweight so he should buy more stamps and affix those stamps on envelop. The man ask back: Isn't more stamps will overweight more?
If there was no misinterpretation, I can understood why you like that man who sent mail in that story thought more fuel carried that oppressed engine working under infaust condition .
:p The more stamps, the more overweight, so the more fuel carried, the more fuel consumption will be in any different flight profile. :cool: I am not laughing at you but even we ratiocinate among your logic, the consequence will rebut yourself: if the range or engine work will be unbenefited from more fuel carried, WHY the range of Fencer is so much less than Aardvark, or put in reverse word, why the range of Aardvark go ahead of Fencer so many??
Now the problem is still here.
In some sense, the airflow of an jet-engine is something similar like torque.
The TF30 is ~5500 kp in installed dry, when the AL21 is ~8000 kp in installed dry.
The engines in both aircraft are able to give that enough thrust to reach Mach 0,8 till Mach 0,9 in max military or dry with external load.
The difference in installed dry to do so is up to 45 % alone.
But that is not for free, every kp or kN in nominal thrust has to be payed by fuel measured in SFC, when in use.
Where ever you look first, you will find out easily, that there is a huge gap in range capability between the Su-24 and the F-111, related to the propulsion system alone.
Looking into some data only can be very misleading.
So under the most favorable conditions a F-111 can have two times the action radius of a Su-24 with the same weapon-load.
Compared to that yardstick, the Su-24 is close to the Tornado IDS by nearly double the size.
Sorry I didn't see what you mean? Because where ever I look the Raven is dark, so unexceptionallly the Raven always be dark?
:diablo:
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By: MiG-23MLD
- 10th June 2008 at 13:16Permalink- Edited 1st January 1970 at 01:00
The conditions are not the same from the start.
There are two main differences, when not comparing pears and apples.
10 tons of fuel inside a Su-24 do generate a range of 100% or whatever number in nm/km you like.
10 tons of fuel inside a F-111 do generate a range of 130 % or ..........
Even when we reduce that difference in SFC to 10% only, there is still a difference in favor of the F-111.
But that is all without the second main difference.
Before going to that, a small example may be a help for better understanding.
When your car has 150 hp/kW installed power and a truck has an engine of the "same" nominal 150 hp/kW too, but both have to haul a load of 15 tons at 80 km/h you will get an idea, that same hp but different torque make u huge difference.
In some sense, the airflow of an jet-engine is something similar like torque.
The TF30 is ~5500 kp in installed dry, when the AL21 is ~8000 kp in installed dry.
The engines in both aircraft are able to give that enough thrust to reach Mach 0,8 till Mach 0,9 in max military or dry with external load.
The difference in installed dry to do so is up to 45 % alone.
But that is not for free, every kp or kN in nominal thrust has to be payed by fuel measured in SFC, when in use.
Where ever you look first, you will find out easily, that there is a huge gap in range capability between the Su-24 and the F-111, related to the propulsion system alone.
Looking into some data only can be very misleading.
So under the most favorable conditions a F-111 can have two times the action radius of a Su-24 with the same weapon-load.
Compared to that yardstick, the Su-24 is close to the Tornado IDS by nearly double the size.
But besides that, it seems that the Su-24 did/does satisfy the needs of the Russian AF, because it was kept and worth an avionic upgrade for some of that till today and the near future, when its replacement, the Su-34 does suffer funding problems.
You allusion forget the F=MxA, the F-111 is heavier it needs to use the engine at higher power settings if it needs to fly at the same speed, You can say perhaps the F-111 has a better lift/drag ratio but also has heavier max take off.
in fact at any max weight you see a difference of 7000kg to 5000kg difference in the max take off of the Su-24 and F-111. that difference alone reflexes the difference in fuel tankage, the Su-24 never was tested to its max speed and only achieved slightly more than Mach 2.1 however the design was supposed to be able to reach mach 2.4 as part of the original requirements so you can not say it has worst lift drag ratio without real data
By: franc
- 10th June 2008 at 13:22Permalink- Edited 1st January 1970 at 01:00
See the combat radius of Aardvark without any external fuel tank is about to 530 NM in the picture MiG posted
with only internal fuel, the radius of Ardvark won't be over 1000km approximately.
almost be equal to Su-24 Fencer with two 3000 liters external fuel tanks.
So if Aardvark's range is 4000km, which is right, then the Fencer's range is 2775km with 2x3000liter fuel tank externally, which must be wrong! The gap won't be such large, ever.
The 2775 km must be internal fuel only. or say with internal fuel only that range 2775km is credible
By: Schorsch
- 10th June 2008 at 13:31Permalink- Edited 1st January 1970 at 01:00
There was a story which mes told out what was your logic:
A man went to post office to send a mail. server told him his mail is overweight so he should buy more stamps and affix those stamps on envelop. The man ask back: Isn't more stamps will overweight more?
If there was no misinterpretation, I can understood why you like that man who sent mail in that story thought more fuel carried that oppressed engine working under infaust condition .
:p The more stamps, the more overweight, so the more fuel carried, the more fuel consumption will be in any different flight profile. :cool: I am not laughing at you but even we ratiocinate among your logic, the consequence will rebut yourself: if the range or engine work will be unbenefited from more fuel carried, WHY the range of Fencer is so much less than Aardvark, or put in reverse word, why the range of Aardvark go ahead of Fencer so many??
Now the problem is still here.
I am getting serious doubt on your willingness to understand, even though Sens now has arrived at very basic level.
F-111:
NTOW is 37.6t
OEW is 21.6t
Internal fuel is given with 5040 gallons, makes 5040*3.8*0.8 = 15.3t fuel.
That gives a useful payload of 700kg (=2x B61 nuclear bomb).
Aircraft is clean.
Fuel fraction is .41 (that is close to a B747)
Su-24:
NTOW is 38t
OEW is 22.3t
Internal fuel is 11.1t
Add 2x2000kg and you have 15.1t.
Useful payload is 600kg, or two nuclear bombs.
Fuel fraction is .4.
Aircraft is not clean (~+20-30% drag)
SFC +25% (conservative)
Fuel Flow = SFC * Glide Ratio * Weight
Now, we assume for the F-111:
SFC = 1 (fictional value)*
Glide Ratio = 1/10 (fictional value)
Avg Weight = 29.6t
Fuel Flow: 3.0t/h
In case of the Su-24:
SFC = 1.25
Glide Ratio = 1/8 (20% more drag)
Avg Weight = 30.2t
Fuel Flow: 4.7t/h (50% more than F-111)
So, after roughly 5 hours the F-111 is out of fuel, while the Suchoi radios Bingo after a little over three. At an average ground speed of 900km/h the F-111 has 4500 km behind it and the Suchoi 24 is somewhere at 2830km.
Somebody might be tempted to doubt some numbers, however, I will only respond to people who take the effort and show me that a 20% less fuel efficient engine and a 20% draggier aircraft can come out somewhere close to the aircraft being clean and more fuel efficient.
----------------
The values for SFC and glide ratio are taken just as they look good and you can make by hand.
However, 1 for SFC and 10 for glide ratio is not that far of reality.
By: Schorsch
- 10th June 2008 at 13:34Permalink- Edited 1st January 1970 at 01:00
So if Aardvark's range is 4000km, which is right, then the Fencer's range is 2775km with 2x3000liter fuel tank externally, which must be wrong! The gap won't be such large, ever.
The 2775 km must be internal fuel only. or say with internal fuel only that range 2775km is credible
Wrong.
See my latest post.
Trust the engineers as they understand aircraft.
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By: MiG-23MLD
- 10th June 2008 at 13:42Permalink- Edited 1st January 1970 at 01:00
I am getting serious doubt on your willingness to understand, even though Sens now has arrived at very basic level.
F-111:
NTOW is 37.6t
OEW is 21.6t
Internal fuel is given with 5040 gallons, makes 5040*3.8*0.8 = 15.3t fuel.
That gives a useful payload of 700kg (=2x B61 nuclear bomb).
Aircraft is clean.
Fuel fraction is .41 (that is close to a B747)
Su-24:
NTOW is 38t
OEW is 22.3t
Internal fuel is 11.1t
Add 2x2000kg and you have 15.1t.
Useful payload is 600kg, or two nuclear bombs.
Fuel fraction is .4.
Aircraft is not clean (~+20-30% drag)
SFC +25% (conservative)
Fuel Flow = SFC * Glide Ratio * Weight
Now, we assume for the F-111:
SFC = 1 (fictional value)*
Glide Ratio = 1/10 (fictional value)
Avg Weight = 29.6t
Fuel Flow: 3.0t/h
In case of the Su-24:
SFC = 1.25
Glide Ratio = 1/8 (20% more drag)
Avg Weight = 30.2t
Fuel Flow: 4.7t/h (50% more than F-111)
So, after roughly 5 hours the F-111 is out of fuel, while the Suchoi radios Bingo after a little over three. At an average ground speed of 900km/h the F-111 has 4500 km behind it and the Suchoi 24 is somewhere at 2830km.
Somebody might be tempted to doubt some numbers, however, I will only respond to people who take the effort and show me that a 20% less fuel efficient engine and a 20% draggier aircraft can come out somewhere close to the aircraft being clean and more fuel efficient.
----------------
The values for SFC and glide ratio are taken just as they look good and you can make by hand.
However, 1 for SFC and 10 for glide ratio is not that far of reality.
Your data is twisted to prove something not true, the max take off weight of the F-111 is not as you claim it is close to 43000 or 50000kg as the RAAF quotes
General Dynamics F-111 technical specifications Manufacturer General Dynamics
Role Long-range strike fighter
Crew Pilot and navigator, who also operates the weapons systems
Engine Two Pratt and Whitney TF-30 turbofans (9,500 kg thrust each)
Airframe Length: 23m, height: 5.3m
Wingspan 21.3m extended, 10.3m swept
Weight 24,000kg basic, 51,846kg fully loaded
Speed Supersonic at sea level, Mach 2.5 at altitude
Range Ferry range in excess of 5,500km
Ceiling Above 50,000 feet
http://www.airforce.gov.au/aircraft/f111.htm
see they say 51846kg fully loaded do you want me to believe that 5000km range is gotten at 37 tons as you claim;), you now it is not true and Sukhoi claims a max weight of 43 tons so therefore there is is a difference in fuel of very likely 6000kg and only a 3000kg of payload (whcih can be used as external fuel tanks)
Note source is from the RAAF not wikipedia
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By: MiG-23MLD
- 10th June 2008 at 13:44Permalink- Edited 1st January 1970 at 01:00
Wrong.
See my latest post.
Trust the engineers as they understand aircraft.
By: franc
- 10th June 2008 at 13:47Permalink- Edited 1st January 1970 at 01:00
I am getting serious doubt on your willingness to understand, even though Sens now has arrived at very basic level.
F-111:
NTOW is 37.6t
OEW is 21.6t
Internal fuel is given with 5040 gallons, makes 5040*3.8*0.8 = 15.3t fuel.
That gives a useful payload of 700kg (=2x B61 nuclear bomb).
Aircraft is clean.
Fuel fraction is .41 (that is close to a B747)
Su-24:
NTOW is 38t
OEW is 22.3t
Internal fuel is 11.1t
Add 2x2000kg and you have 15.1t.
Useful payload is 600kg, or two nuclear bombs.
Fuel fraction is .4.
Aircraft is not clean (~+20-30% drag)
SFC +25% (conservative)
Dear friend:
Who told you, add 2 external fuel tanks which means add 20-30% drag?
Fuel Flow = SFC * Glide Ratio * Weight
Now, we assume for the F-111:
SFC = 1 (fictional value)*
Glide Ratio = 1/10 (fictional value)
Avg Weight = 29.6t
Fuel Flow: 3.0t/h
In case of the Su-24:
SFC = 1.25
Glide Ratio = 1/8 (20% more drag)
Avg Weight = 30.2t
Fuel Flow: 4.7t/h (50% more than F-111)
Where did you get the fuel flow? How did you get 50% fuel flow more than F-111?
By: Schorsch
- 10th June 2008 at 13:56Permalink- Edited 1st January 1970 at 01:00
Dear friend:
Who told you, add 2 external fuel tanks which means add 20-30% drag?
Experience from having looked at several flight manuals, several aircraft types, several flight regimes. A pair of large subsonic fuel tanks gives you another 10 to 15% of drag in pure subsonic and about 15 to 25% in transonic (start M0.8) regime.
Where did you get the fuel flow? How did you get 50% fuel flow more than F-111?
if you see that the Su-24 with 2 fuel tanks it can achieve 2775km, the F-111 can achieve 5500km with six fuel tanks and a max takle off weight of 51464kg you see that both Sukhoi and the RAAF are saying with an extra 8000kg the F-111 achieves slightly more than 30% more range it is obvious why, fuel and not SFC as the main reason for that difference
Schorsch does not understand that the Su-24 never was fitted with another engine simply because the AL-21 was a fine one and not as he claims a superfuel thirsty engine
By: Schorsch
- 10th June 2008 at 14:00Permalink- Edited 1st January 1970 at 01:00
Weight 24,000kg basic, 51,846kg fully loaded
If you take the OEW as 24t instead of 21.6, put the additional weight on TOW, you basically arrive at similar numbers.
Any additional ton of average weight increase fuel flow by 100kg/h. So, you can stuff in another 15t OEW (for example: glue a Tornado IDS on top of it), before the F-111 gets close to the Suchoi 24 in terms of fuel flow.
By: Schorsch
- 10th June 2008 at 14:04Permalink- Edited 1st January 1970 at 01:00
[Schorsch does not understand that the Su-24 never was fitted with anotehr engine simply becasue the AL-21 was a fine one and not as he claims a superfuel thirsty engine
Schorsch understands the difference between different engine types, the influence of external loads on overall performance and the dependence on mission profile.
Schorsch also knows how a seemingly small difference can add up and become a huge difference in the end. Guess why GE and Boeing sell their GrandMa if necessary to get 3% less drag, 4% less OEW or 5% better SFC. It adds up to 20% better economics in the end.
Schorsch is an engineer. You are obviously not.
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By: MiG-23MLD
- 10th June 2008 at 14:11Permalink- Edited 1st January 1970 at 01:00
Schorsch understands the difference between different engine types, the influence of external loads on overall performance and the dependence on mission profile.
Schorsch also knows how a seemingly small difference can add up and become a huge difference in the end. Guess why GE and Boeing sell their GrandMa if necessary to get 3% less drag, 4% less OEW or 5% better SFC. It adds up to 20% better economics in the end.
Schorsch is an engineer. You are obviously not.
But schorsch also avoids the fact the Su-24 also weighs similar to the F-111 at normal take off and both aircraft weights have a difference of 8000kg at max take off and he continues avoiding that that difference explains the F-111`s FERRY range with six fuel tanks of more than 5000km, that difference of 2500km extra simply implies that a Su-24 with 3 fuel tanks and less fuel will have a shorter range because with an inflight refueling can achieve also 5000km, the inflight refueling makes for the difference in max take off weight Schorsch avoids to see
By: Sens
- 10th June 2008 at 14:13Permalink- Edited 1st January 1970 at 01:00
There was a story which mes told out what was your logic:
A man went to post office to send a mail. server told him his mail is overweight so he should buy more stamps and affix those stamps on envelop. The man ask back: Isn't more stamps will overweight more?
If there was no misinterpretation, I can understood why you like that man who sent mail in that story thought more fuel carried that oppressed engine working under infaust condition .
:p The more stamps, the more overweight, so the more fuel carried, the more fuel consumption will be in any different flight profile. :cool: I am not laughing at you but even we ratiocinate among your logic, the consequence will rebut yourself: if the range or engine work will be unbenefited from more fuel carried, WHY the range of Fencer is so much less than Aardvark, or put in reverse word, why the range of Aardvark go ahead of Fencer so many??
Now the problem is still here.
Sorry I didn't see what you mean? Because where ever I look the Raven is dark, so unexceptionallly the Raven always be dark?
:diablo:
Despite your claim, I will try to stay serious for the benefit of the others.
When you have a truck with a gasoline engine to haul a load of 10 tons at 80 km/h, you are in need of some power to do so.
In case A you have 80 hp and the related torque to do so and 10 litre of fuel. Now you can find out how far you can go with the load, at the speed.
In case B you have a diesel of 55 hp which delivers the torque in need to do the demanded.
The "clever-one" will start that a single hp of the gasoline-engine is in consumption close to that of a hp from the diesel-engine.
But here the "clever-one" stops, because he has proven, there is not much difference in SFC between both engines.
What do you miss about that, when it comes to range?
Something that math does proof, whatever value you like to use.
80*0,9= 72 total use
55*0,8= 44 total use
When 72 is 100% base value 44 is 61% of that.
When A can go 100 km with 10 litre,
B can go how many km with 10 litre by that?
By: Sens
- 10th June 2008 at 15:06Permalink- Edited 1st January 1970 at 01:00
See the combat radius of Aardvark without any external fuel tank is about to 530 NM in the picture MiG posted
with only internal fuel, the radius of Ardvark won't be over 1000km approximately.
almost be equal to Su-24 Fencer with two 3000 liters external fuel tanks.
So if Aardvark's range is 4000km, which is right, then the Fencer's range is 2775km with 2x3000liter fuel tank externally, which must be wrong! The gap won't be such large, ever.
The 2775 km must be internal fuel only. or say with internal fuel only that range 2775km is credible
By: Anonymous - 10th June 2008 at 10:18 Permalink - Edited 17th October 2019 at 04:21
Indeed, I remember a Carlos Kopp diagram showing that with cruise missiles like a Kh-15 that the Tu-22M3 could carry twice as many weapons as an F-111 over a similar range.
His diagram showed one Tu22M3 performing the mission of two F-111s with tanker support.
BTW the F-111 carrys extra fuel and a 20mm gun and ammo in its weapons bay. It is not used for other weapons normally.
The Tu22M3s weapon bay on the other hand can carry 6 x Kh-15s on a rotary launcher. With two more carried externally (the brochures claim it can carry 10 missiles, which I would assume means 4 external Kh-15s and 6 internal ones) it carrys 8 missiles, the equivelent F-111 load is 4 missiles per plane and two planes with a 3,000km flight radius with inflight refuelling.
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By: Sens - 10th June 2008 at 10:46 Permalink - Edited 1st January 1970 at 01:00
The conditions are not the same from the start.
There are two main differences, when not comparing pears and apples.
10 tons of fuel inside a Su-24 do generate a range of 100% or whatever number in nm/km you like.
10 tons of fuel inside a F-111 do generate a range of 130 % or ..........
Even when we reduce that difference in SFC to 10% only, there is still a difference in favor of the F-111.
But that is all without the second main difference.
Before going to that, a small example may be a help for better understanding.
When your car has 150 hp/kW installed power and a truck has an engine of the "same" nominal 150 hp/kW too, but both have to haul a load of 15 tons at 80 km/h you will get an idea, that same hp but different torque make u huge difference.
In some sense, the airflow of an jet-engine is something similar like torque.
The TF30 is ~5500 kp in installed dry, when the AL21 is ~8000 kp in installed dry.
The engines in both aircraft are able to give that enough thrust to reach Mach 0,8 till Mach 0,9 in max military or dry with external load.
The difference in installed dry to do so is up to 45 % alone.
But that is not for free, every kp or kN in nominal thrust has to be payed by fuel measured in SFC, when in use.
Where ever you look first, you will find out easily, that there is a huge gap in range capability between the Su-24 and the F-111, related to the propulsion system alone.
Looking into some data only can be very misleading.
So under the most favorable conditions a F-111 can have two times the action radius of a Su-24 with the same weapon-load.
Compared to that yardstick, the Su-24 is close to the Tornado IDS by nearly double the size.
But besides that, it seems that the Su-24 did/does satisfy the needs of the Russian AF, because it was kept and worth an avionic upgrade for some of that till today and the near future, when its replacement, the Su-34 does suffer funding problems.
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By: Schorsch - 10th June 2008 at 11:18 Permalink - Edited 1st January 1970 at 01:00
To give an idea about specific fuel consumption for turbofans and turbojets see attached plots.
The TJ-example does not really represent the most advanced TJ, but even if you consider a 10% more efficient engine the conclusion is not dramatically altered.
[ATTACH]162829[/ATTACH]
Shows SFC over power setting for three altitudes (one per plot) and various Mach numbers (lines in each plot). For the typical mission points (low alt, M0.7, max dry thrust; high alt, max dry, M0.8) we see an SFC of ~1.3-1.4 for low level and 1.1-1.2 for the high alt cruise. That is a bit more than for more advanced TJs, but not far away.
[ATTACH]162830[/ATTACH]
Same for the TF-30 (of the F-14 in this case). One can see an SFC between 0.9 and 1 for low alt and M0.9, and about 1 for high alt cruise. That is in line with other turbofans.
In conclusion: the TJ shows a 20 to 40% increase in SFC, depending on altitude, Mach number and power setting. The reduced SFC in afterburner does not really save the day as a typical mission of the F-111 would see the afterburner switched on not more than a few minutes at egress.
Or short: Fitting aircraft with turbojets for subsonic cruise is crap.
For experts or those who want to become it: the often quoted SFC from Wikipedia is normally at M0, 0km altitude and full dry power. So, that would be the lowest line on the right hand plot (while that is still for M0.5 resp. M0.7). You'll see that by this the static SFC values are much lower than real flight SFC values. For civil engines, normally the design point is given. For afterburner SFC max power at sea level Mach 0 is given, again, only truly representative for a taxiing aircraft.
But as I said, don't get confused too much by the complexity of reality.
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By: Sens - 10th June 2008 at 11:58 Permalink - Edited 1st January 1970 at 01:00
To fit an AB to an Tf is no problem, as the example of the R8 from the Viggen showed or later the D-30 for the MiG-31
The AB is injection of fuel into the hot exhaust to use the unburned oxygen still left.
By that you can rise nominal thrust up to 50% at sea-level with a Tj. When that nominal ratio did not change, the practical thrust gains are much higher at height and speed. When the engine itself is affected by the drop of atmosphere pressure in a linear way, the AB is not so to the same degree.
40 kN dry and 60 kN wet at low (start) is 50 % of AB thrust.
High up that does change to 10 kN dry and 20 kN wet or the AB thrust is up to 100 % from the total, besides the gains from the modulated inlet- and outlet-system. To compare that to ground level values, some did use the artifical value of mathematical thrust.
Before carried away, a bypath engine has a lot of unburned oxygen to rise thrust by injecting fuel into the burner. That start with 60% and higher related to bypath ratio. The higher the bypath ratio, the higher the fuel-burn or the related SFC in AB. Early Tfs with a bypath ratio higher 1 could reach a SFC up to 3.
Modern Tfs are more leaky Tjs, when with an bypath ratio below 0,5 are close to SFC of Tj in AB. The other factors about SFC aside.
When an engine is used most of the time in dry and for short periods in burner, the advantages in fuel consumption are more than obvious.
Burner development did not stand at idle too, like the first ones with all or nothing behavior. The second generation could be used in stages, when the modern ones do allow a smooth movement (FADEC) to every power-setting you wish.
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By: MiG-23MLD - 10th June 2008 at 12:32 Permalink - Edited 1st January 1970 at 01:00
I think you example is not representative of the Al-21 versus TF-30 without having the real data of both engines something you do not have niether you are presenting.
The SFC given by Russian sources show the AL-21 to be slighly more thirsty than the Al-31 or TF-30 in fact only a Max of 12% and a minimun of 7% at dry military power however at full afterburner the TF-30 seems to be quit thirsty
All your empirical guessing does not prove that the range of the F-111 is the result of the TF-30 being 30% more economical.
You are not proving the F-111 and SU-24 carry the same amount of fuel
Look at this image it shows you very clearly the F-111 is carrying six external fuel tanks, while the Max range claimed for the Su-24 is with only three external fuel tanks, its obvious that the Max ferry range quoted for the F-111 is with six fuel tanks and it is obvoius the lighter Su-24 carries less fuel and this is proven by data taken from the Sukhoi webpage and RAAF
http://www.n-e-c.ru/foxbat/maks/su24_poland/su24_poland_01.htm
see this fact
F-1111F range 3,565 miles (3,100 nautical miles) with external fuel tanks
http://www.fas.org/man/dod-101/sys/ac/f-111.htm
even the max carrying capacity shows it can carry more fuel tanks
Maximum Takeoff Weight F-111F, 100,000 pounds (45,000 kilograms).
Armament Up to four nuclear bombs on four pivoting wing pylons, and two in internal weapons bay. Wing pylons carry total external load of 25,000 pounds (11,250 kilograms) of bombs, rockets, missiles, or fuel tanks.
http://www.ausairpower.net/APA-NOTAM-051107-1.html
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By: franc - 10th June 2008 at 13:06 Permalink - Edited 1st January 1970 at 01:00
There was a story which mes told out what was your logic:
A man went to post office to send a mail. server told him his mail is overweight so he should buy more stamps and affix those stamps on envelop. The man ask back: Isn't more stamps will overweight more?
If there was no misinterpretation, I can understood why you like that man who sent mail in that story thought more fuel carried that oppressed engine working under infaust condition .
:p The more stamps, the more overweight, so the more fuel carried, the more fuel consumption will be in any different flight profile. :cool: I am not laughing at you but even we ratiocinate among your logic, the consequence will rebut yourself: if the range or engine work will be unbenefited from more fuel carried, WHY the range of Fencer is so much less than Aardvark, or put in reverse word, why the range of Aardvark go ahead of Fencer so many??
Now the problem is still here.
Sorry I didn't see what you mean? Because where ever I look the Raven is dark, so unexceptionallly the Raven always be dark?
:diablo:
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By: MiG-23MLD - 10th June 2008 at 13:16 Permalink - Edited 1st January 1970 at 01:00
You allusion forget the F=MxA, the F-111 is heavier it needs to use the engine at higher power settings if it needs to fly at the same speed, You can say perhaps the F-111 has a better lift/drag ratio but also has heavier max take off.
in fact at any max weight you see a difference of 7000kg to 5000kg difference in the max take off of the Su-24 and F-111. that difference alone reflexes the difference in fuel tankage, the Su-24 never was tested to its max speed and only achieved slightly more than Mach 2.1 however the design was supposed to be able to reach mach 2.4 as part of the original requirements so you can not say it has worst lift drag ratio without real data
Posts: 620
By: franc - 10th June 2008 at 13:22 Permalink - Edited 1st January 1970 at 01:00
See the combat radius of Aardvark without any external fuel tank is about to 530 NM in the picture MiG posted
with only internal fuel, the radius of Ardvark won't be over 1000km approximately.
almost be equal to Su-24 Fencer with two 3000 liters external fuel tanks.
So if Aardvark's range is 4000km, which is right, then the Fencer's range is 2775km with 2x3000liter fuel tank externally, which must be wrong! The gap won't be such large, ever.
The 2775 km must be internal fuel only. or say with internal fuel only that range 2775km is credible
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By: Schorsch - 10th June 2008 at 13:31 Permalink - Edited 1st January 1970 at 01:00
I am getting serious doubt on your willingness to understand, even though Sens now has arrived at very basic level.
F-111:
NTOW is 37.6t
OEW is 21.6t
Internal fuel is given with 5040 gallons, makes 5040*3.8*0.8 = 15.3t fuel.
That gives a useful payload of 700kg (=2x B61 nuclear bomb).
Aircraft is clean.
Fuel fraction is .41 (that is close to a B747)
Su-24:
NTOW is 38t
OEW is 22.3t
Internal fuel is 11.1t
Add 2x2000kg and you have 15.1t.
Useful payload is 600kg, or two nuclear bombs.
Fuel fraction is .4.
Aircraft is not clean (~+20-30% drag)
SFC +25% (conservative)
Fuel Flow = SFC * Glide Ratio * Weight
Now, we assume for the F-111:
SFC = 1 (fictional value)*
Glide Ratio = 1/10 (fictional value)
Avg Weight = 29.6t
Fuel Flow: 3.0t/h
In case of the Su-24:
SFC = 1.25
Glide Ratio = 1/8 (20% more drag)
Avg Weight = 30.2t
Fuel Flow: 4.7t/h (50% more than F-111)
So, after roughly 5 hours the F-111 is out of fuel, while the Suchoi radios Bingo after a little over three. At an average ground speed of 900km/h the F-111 has 4500 km behind it and the Suchoi 24 is somewhere at 2830km.
Somebody might be tempted to doubt some numbers, however, I will only respond to people who take the effort and show me that a 20% less fuel efficient engine and a 20% draggier aircraft can come out somewhere close to the aircraft being clean and more fuel efficient.
----------------
The values for SFC and glide ratio are taken just as they look good and you can make by hand.
However, 1 for SFC and 10 for glide ratio is not that far of reality.
Sources:
http://en.wikipedia.org/wiki/F-111
http://en.wikipedia.org/wiki/Su-24
http://home.att.net/~jbaugher1/f111_1.html
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By: Schorsch - 10th June 2008 at 13:34 Permalink - Edited 1st January 1970 at 01:00
Wrong.
See my latest post.
Trust the engineers as they understand aircraft.
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By: MiG-23MLD - 10th June 2008 at 13:42 Permalink - Edited 1st January 1970 at 01:00
Your data is twisted to prove something not true, the max take off weight of the F-111 is not as you claim it is close to 43000 or 50000kg as the RAAF quotes
General Dynamics F-111 technical specifications Manufacturer General Dynamics
Role Long-range strike fighter
Crew Pilot and navigator, who also operates the weapons systems
Engine Two Pratt and Whitney TF-30 turbofans (9,500 kg thrust each)
Airframe Length: 23m, height: 5.3m
Wingspan 21.3m extended, 10.3m swept
Weight 24,000kg basic, 51,846kg fully loaded
Speed Supersonic at sea level, Mach 2.5 at altitude
Range Ferry range in excess of 5,500km
Ceiling Above 50,000 feet
http://www.airforce.gov.au/aircraft/f111.htm
see they say 51846kg fully loaded do you want me to believe that 5000km range is gotten at 37 tons as you claim;), you now it is not true and Sukhoi claims a max weight of 43 tons so therefore there is is a difference in fuel of very likely 6000kg and only a 3000kg of payload (whcih can be used as external fuel tanks)
Note source is from the RAAF not wikipedia
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By: MiG-23MLD - 10th June 2008 at 13:44 Permalink - Edited 1st January 1970 at 01:00
I trust the RAAF that flies the F-111
Weight 24,000kg basic, 51,846kg fully loaded
http://www.airforce.gov.au/aircraft/f111.htm
and sukhoi that built the aircraft
Takeoff weight:
- normal, kg 38,040
- maximum, kg 43,755
http://www.sukhoi.org/eng/planes/military/su24mk/lth/
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By: franc - 10th June 2008 at 13:47 Permalink - Edited 1st January 1970 at 01:00
Dear friend:
Who told you, add 2 external fuel tanks which means add 20-30% drag?
Where did you get the fuel flow? How did you get 50% fuel flow more than F-111?
:confused::confused::confused:
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By: Schorsch - 10th June 2008 at 13:56 Permalink - Edited 1st January 1970 at 01:00
Experience from having looked at several flight manuals, several aircraft types, several flight regimes. A pair of large subsonic fuel tanks gives you another 10 to 15% of drag in pure subsonic and about 15 to 25% in transonic (start M0.8) regime.
Fuel Flow [kg/h] = SFC [kg/(daN*h)] * Inverse Glide Ratio [-] * Weight [daN]
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By: MiG-23MLD - 10th June 2008 at 13:59 Permalink - Edited 1st January 1970 at 01:00
Ferry flight range with 2xPTB-3000 external fuel tanks, km:
- with PTB external fuel tanks dropped 2,775
- with one in-flight refuelling 5,000
http://www.sukhoi.org/eng/planes/military/su24mk/lth/
if you see that the Su-24 with 2 fuel tanks it can achieve 2775km, the F-111 can achieve 5500km with six fuel tanks and a max takle off weight of 51464kg you see that both Sukhoi and the RAAF are saying with an extra 8000kg the F-111 achieves slightly more than 30% more range it is obvious why, fuel and not SFC as the main reason for that difference
Schorsch does not understand that the Su-24 never was fitted with another engine simply because the AL-21 was a fine one and not as he claims a superfuel thirsty engine
with three external fuel tanks it can achieve the range of 3050km
see Перегоночная дальность, км 3055
http://www.airwar.ru/enc/bomber/su24.html
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By: Schorsch - 10th June 2008 at 14:00 Permalink - Edited 1st January 1970 at 01:00
If you take the OEW as 24t instead of 21.6, put the additional weight on TOW, you basically arrive at similar numbers.
Any additional ton of average weight increase fuel flow by 100kg/h. So, you can stuff in another 15t OEW (for example: glue a Tornado IDS on top of it), before the F-111 gets close to the Suchoi 24 in terms of fuel flow.
Lame attempt.
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By: Schorsch - 10th June 2008 at 14:04 Permalink - Edited 1st January 1970 at 01:00
Schorsch understands the difference between different engine types, the influence of external loads on overall performance and the dependence on mission profile.
Schorsch also knows how a seemingly small difference can add up and become a huge difference in the end. Guess why GE and Boeing sell their GrandMa if necessary to get 3% less drag, 4% less OEW or 5% better SFC. It adds up to 20% better economics in the end.
Schorsch is an engineer. You are obviously not.
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By: MiG-23MLD - 10th June 2008 at 14:11 Permalink - Edited 1st January 1970 at 01:00
But schorsch also avoids the fact the Su-24 also weighs similar to the F-111 at normal take off and both aircraft weights have a difference of 8000kg at max take off and he continues avoiding that that difference explains the F-111`s FERRY range with six fuel tanks of more than 5000km, that difference of 2500km extra simply implies that a Su-24 with 3 fuel tanks and less fuel will have a shorter range because with an inflight refueling can achieve also 5000km, the inflight refueling makes for the difference in max take off weight Schorsch avoids to see
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By: Sens - 10th June 2008 at 14:13 Permalink - Edited 1st January 1970 at 01:00
Despite your claim, I will try to stay serious for the benefit of the others.
When you have a truck with a gasoline engine to haul a load of 10 tons at 80 km/h, you are in need of some power to do so.
In case A you have 80 hp and the related torque to do so and 10 litre of fuel. Now you can find out how far you can go with the load, at the speed.
In case B you have a diesel of 55 hp which delivers the torque in need to do the demanded.
The "clever-one" will start that a single hp of the gasoline-engine is in consumption close to that of a hp from the diesel-engine.
But here the "clever-one" stops, because he has proven, there is not much difference in SFC between both engines.
What do you miss about that, when it comes to range?
Something that math does proof, whatever value you like to use.
80*0,9= 72 total use
55*0,8= 44 total use
When 72 is 100% base value 44 is 61% of that.
When A can go 100 km with 10 litre,
B can go how many km with 10 litre by that?
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By: Sens - 10th June 2008 at 15:06 Permalink - Edited 1st January 1970 at 01:00
http://www.sukhoi.org/eng/planes/military/su24mk/lth/
Some proper reading from producer is enough.