better to climb then cruise or cruise low?

[Dirty Rotten Flieger]

It appears to be better to spend the fuel to climb to high altitude and then cruise in the thin air rather than save the climbing fuel and cruise at low altitude.

 

If I was in a long range plane I would say this is true for sure but the MIg21 is quite short range so I'm not really sure if I am doing it right.

 

Any thoughts on this with the Mig21?

 

Should I use the burner to climb to 10000m and then cruise or no burner in the climb?

 

I'll have to test it myself but I'm sure there are better informed people here to help.

 

I have been shot down in a mission and I respawned and took off again and flew fast and high to get back in the fight. So when I get over the fight. I am 10000m and very fast and I know there are phantoms down there on the deck maneuvering with my wing men. I did some supersonic zoom and boom attacks with the burner on. I'f I'm lucky I get a radar lock and a missile off and if I can't spot anything I climb back right back up. Well after a few of these runs I noticed my fuel seems to be going down much slower than if I had stayed low and tried to maneuver with the enemy with burners on.

 

Is this what the north vietnamese Mig21 pilots did? I had heard they would engage the phantoms with Mig17s and then Mig21s would do a high speed attack, fire some missiles and blow through. I had assumed they were at low altitude the whole time but now I stumble on this supersonic zoom and boom thing I wonder if thats how they did it?

 

It's pretty fun to do after being used to doing zoom and boom in a bf109 !!

 

Maybe one day I can get a supersonic gun run at the bottom of a 10000m dive! :D

 

I doubt it though

[Vedexent]

In general - not just the MiG-21 - this is the case: high thin air = less fuel than lower thick air.

 

Real world pilots will usually operate up near their operational ceiling (or as close as ATC will assign them), for this reason.

[panzerd18]

You also don't need to use afterburner in the MIG-21 in the climb. 95% throttle is recommended holding 600km/h indicated airspeed.

 

If you look in the manual you will see a table that details the fuel burn at a certain altitude. The higher you go, the less fuel burn. The higher you go the thinner the air, meaning less drag and better efficiency.

[Hadwell]

It mostly depends on where, and what, rather than efficiancy...

 

Flying really high up against F-15's and SU-27's is less smart than burning fuel down on the deck, where you can use mountains and hills to at least shorten their radar range if not make you invisible to anyone that's not up in the stratosphere.

 

but from what i can recall north Vietnamese pilots used to zoom in at high speed, launch some missiles, and leave, not even stay and fight, they were a lot more rare and valuable than the mig-19/17, and they didn't want to risk them in dogfights.

Edited February 7, 2015 by Hadwell

[Exorcet]

Low altitude = drag. Jet engines have compressors, so while air density drops with height, the thrust loss isn't as great as the drag loss. Temp also drops with height and that is another benefit for engines.

 

Any time you want to achieve range or endurance you should gain height. I don't know specifics for the MiG-21 but for a fighter I'd expect good performance around 30,000+ ft.

 

I was doing tests on the F-15 a while ago, I should go back and finish them.

 

http://forums.eagle.ru/showthread.php?t=130100

[Justin Case]

95% throttle is recommended holding 600km/h indicated airspeed.

 

I believe it's more efficient to climb at a throttle setting just below afterburner, I've only seen those 95% mentioned once in the manual but then it seemed to be a recommendation for a "first flight" smooth climb.

 

Edit: Unless there's an engine limit I've missed.

Edited February 7, 2015 by Justin Case

[JorgeIII]

I choose altitude for cruising depending the distance I m going to travel:

 

*Under 100 km I keep my altitude. If your at sea level you can burn between 300L / 100 km at 550 km/h IAS up to 1200L / 100 km at 1300 km/h IAS. So I choose my speed accordingly to how much fuel i got left and want to use.

 

*If I have to travel a distance over 200 Km I will always climb (from 9000 m to 13000 m), if it´s save. You will use up to 800L in a climb from sea level using full AFT and about 450 L / 100 km cruising at 2100 km/h TAS at 12000 m (that´s very fast and not so much fuel).

 

If I have to travel between 100 km and 200 km I evaluate the situation.

 

If Im very low in fuel I always keep my altitude and calculate 330 L for every 100 km (Cruising at sea level at 550 to 650 km/h IAS) plus 300 L for landing.

 

I dont have the numbers for cruising slowly (650 km/h) without the AFT at high altitude, might be a nice option. Tried a while a go and you couldnt even cruise without AFT over 7000m, I think this is solved now buy angle of attack and drag still increases with altitude at same IAS.

Edited February 8, 2015 by JorgeIII

[Dirty Rotten Flieger]

Thanks Jorge III

 

this is exactly the stuff I am learning to thinking about. I been playing the over the hump missions and they are all about 200km or just under i guess. I have to climb at least enough to get over the mountains and very often find myself having to disengage from a fight so I have enough fuel to make it home...

 

Sometimes I even have jettisoned all my unused missiles to lower drag so I can pull away from the F4 chasing me with full racks of missiles slowing his acceleration. If I can just get over the mountains and glide down to Nanchick with a little bit of fuel left for a powered landing. quite tense!

 

These fuel calculations are not a simple thing in combat. 450L/100km at 2100km/h at 12000m wow ! the distance traveled makes it actually economical in a way. certainly worth it when time is short.

 

Really enjoying learning to think about such high energy flying and constant fuel awareness.

[panzerd18]

Here is so real data I found.

 

For maximum range.

 

Fully loaded 10,000m altitude and Mach 0.83. I have found this requires around 93-95% N1 throttle setting.

 

Clean 11,000m altitude and Mach 0.84. I have found this requires around 88-90% N1 throttle setting.

[gezahu]

It depends. To climb to 11000m (where you have max range with a given amount of fuel at 510 IAS) takes about 700l of fuel (no matter if you use afterburner or not). To do so you need to accelerate to 0,8M and start to climb with that speed, slowly accelerating further, you should reach 1M at about the hight of 8000 at be at 1.1 at 11000. That way you will be at 11000 for about 3 mins and 50 km distance at the cost of 700l fuel. The point is that you first accelerate to 0,75-0,8M and the start to climb slowly accelerating further. many make the mistake of gaining altitude with too low initial speed.

 

At sea level where you burn fuel most efficiently at 670IAS you burn 3,5l fuel for each km (at 11000m you burn 1,65l/km), which means with 700l (which it takes to climb to 11000) you can fly abut 200km at sea level. You anyway fly 50km with climbing to 11000 with afterburner so the difference is 150km. So at 11000m you burn 1,65l/km and you are 150km behind the plane which stayed at sea level and burns 3,5l/km you both have 2000l fuel now. The high flying buddy can cover 1200 further km the low flying buddy can cover 555km which totals 1250km for the high flying and 755km for the low flying buddy. Where they even out as far as fuel consumption is concerned would be about 330km, so less to cover than that stay low, more to cover progressively climb higher.

 

I have attached a graph to be more visual on range (fuel consumption per km covered) at sea level, 5000 and 11000 as you can see the tipping point between 5000 and 11000 for example is more like 400 km.

Edited February 17, 2015 by gezahu

[gezahu]

To use burner or not? According to the Russian technical data it does not rally matter, or you are slightly better off with burner. With burner it is 625l and 3 minutes and 50 km distance, without burner it is 670l 130km and 11 minutes.

[Hadwell]

with or without having to worry about radar, and getting shot down?

 

flying low and using anything you can to keep the enemy from picking you up on radar is far more important than a few KM here and there...

 

if all you're doing is ferrying the plane, then yeah sure, climbing is better....

 

and afterburner is probably better cause you go more distance in less time, that includes the climb to altitude, except you won't have as long on station if you have to slow down and circle an area before you go to land, because it's easier to lose energy than get it back.

 

so if you have to loiter on bulls eye, or on a TA, then not using afterburner is better, if you're trying to catch a target at 10.000+ meters, awacs, or a tanker, etc... and you already know where it is, then afterburner is better.

 

Try it on the VA server, if you climb correctly, you can get to mach 2 with the center tank just about empty, fly clear across the map in record times...

Edited February 18, 2015 by Hadwell

[JorgeIII]

 

At sea level where you burn fuel most efficiently at 670IAS you burn 3,5l fuel for each km (at 11000m you burn 1,65l/km), which means with 700l (which it takes to climb to 11000) you can fly abut 200km at sea level. You anyway fly 50km with climbing to 11000 with afterburner so the difference is 150km. So at 11000m you burn 1,65l/km and you are 150km behind the plane which stayed at sea level and burns 3,5l/km you both have 2000l fuel now. The high flying buddy can cover 1200 further km the low flying buddy can cover 555km which totals 1250km for the high flying and 755km for the low flying buddy. Where they even out as far as fuel consumption is concerned would be about 330km, so less to cover than that stay low, more to cover progressively climb higher.

 

 

Thanks Gezahu.

Notice that those are official manual numbers. I tested it in DCS and the mig will use and average of 200 l / 100 km ( from 1,8 to 2,2 L /km instead of the 1,65l/km from the manual), loaded whith 2 missiles, cruising @ 12000m and 520 km/h IAS, almost full mil power, no AFT. So you will get even at around 400 km (Sea level slow vs 12000 slow). At 12000m of altitude your 520 km/h IAS will be around 900+ km/h TAS.

 

The thing is, being the Mig a Mach 2 fast mover, who wants to fly it so slowly for so long?

 

I only fly so slowly when I RTB low on fuel.

 

If I have extra fuel I always use all the after burner I can.

 

In most of the missions, if TA is under a 150 km distance, I will go to TA at 80-95% power at low altitude (IAS 650 to 1050 depending how much fuel i want to use).

If its over 200 Km and its safe I will climb an fly high and fast to TA. Then, if Im still alive, I would RTB low and choosing the speed that will make me arrive at the airport with 200 to 700 l of fuel left.

[gezahu]

Good strategy. Fuel usage is a very complex mathematics from temperature to air pressure wind etc. must be taken into account, no blame on leatherneck that there are simplifications it is still far the most advanced model I have seen. And regardless to the theoretically most efficient regime tactical reality dictates all the time.

My biggest problem is arriving to landing at about 700l remaining, I usually always arrive with more and have to burn some before land which is a planing issue on my side :)