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Speed with 2x Tanks (empty)


Captain Orso
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Lode-out is 4x Sidearms, DECM, and 2x fuel tanks, which are empty.

 

At 16,000 feet, straight and level flight (also with AFC) with engine at 100%, flaps on cruise, and trimmed for level flight, I cannot break 420 kn IAS.

 

Is this normal?

When you hit the wrong button on take-off

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Given your drag index, which should be (if I didn’t screw up calculating) somewhere between 35 and 40 with that loadout, and looking at the low altitude cruise charts, I don’t find your numbers surprisingly low. You’re doing 520 KTAS or Mach .83 in your example.

 

But I might be wrong, of course.

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Is 16,000 feet low altitude? :huh:

 

I'm used to running around 500+ kts in level flight at even lower altitudes and lower engine output.

 

The tanks might have a fairly large diameter, but they are long and aerodynamically designed. It seems excessive to me, but I am just guessing.

When you hit the wrong button on take-off

hwl7xqL.gif

System Specs.

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System board: MSI X99A GAMING 9 ACK Memory: 16GB DDR4-3000 G.Skill Ripjaw System disk: Samsung SSD 970 EVO Plus 1TB
CPU: Intel Core i7-5820K @ 3800MHz PSU: Corsair AX860i PSU Monitor: ASUS MG279Q, 27"
CPU cooling: Noctua NH-D15 Graphics card: Zotac Nvidia GeForce GTX 1080 Ti Amp! Extreme VR: Oculus Rift CV1
 
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Compared to 40000 it is.:)

 

Don’t forget the increasing difference between Indicated Airspeed and True Airspeed with increasing altitude.

A rule of thumb is that, with every 1000ft of altitude the difference increases by 2%.

That means, at 10000ft 100KIAS would equate to 120KTAS.

 

So, the lower you fly, the higher your indicated airspeed would be, but that wouldn’t make you fly faster actually.

 

For the additional drag created by external loads I recommend to have a look at the A1-AV8BB-NFM-400 performance manual.

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Is 16,000 feet low altitude? :huh:

I'm used to running around 500+ kts in level flight at even lower altitudes and lower engine output.

 

In addition to Herby's comments regarding IAS v TAS, I would also point out that saying you are using lower engine output at lower altitudes might not be correct; what I mean is that the engine at 100% RPM at 16k is producing much less thrust than the engine at SL at 100%. Aerodynamics for Naval Aviators shows that a fixed geometry turbojet will be capable of producing 67 percent of it's sea level, ISA rated thrust at 16,000 feet. Obviously this wouldn't be an exact representation of the Pegasus engine, but the concept is the same. Air density decreases exponentially with altitude (recall that ~ half of the earth's atmospheric mass is at FL180 and below) so as soon as you start climbing, you are losing available thrust on a similar exponential curve.

 

All that said, I don't have the Harrier NATOPS (yet) but hitting .83 mach on an aircraft with a .90 redline while hauling 4 missiles and a pair of tanks in the teens sounds reasonable to me. I could certainly be mistaken there though, I would be interested to crawl into the books on it.


Edited by tom_19d
Edited first sentance for clarity and tone

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T(h)anks for the answers.

 

I guess I'll just have to get used to being the slow-poke in the Harrier :noexpression:

 

I'm setting up a mission and using the KC-135 MPRS. I set the KC to circle in a race track course at 550 kts, knowing that it would be far slower in IAS, but I didn't calculate out what that would be, and I thought, "hey I can easily do 500 IAS, easy-peasy" :noexpression:

 

After taking off from the Tarawa with 4k-lbs fuel and empty tanks, I tried to rendezvous with the KC, but I gained soooo slowly, that my tanks were literally dry before I could catch up :cry:

 

I've now got the KC circling at 500 kts :D

When you hit the wrong button on take-off

hwl7xqL.gif

System Specs.

Spoiler
System board: MSI X99A GAMING 9 ACK Memory: 16GB DDR4-3000 G.Skill Ripjaw System disk: Samsung SSD 970 EVO Plus 1TB
CPU: Intel Core i7-5820K @ 3800MHz PSU: Corsair AX860i PSU Monitor: ASUS MG279Q, 27"
CPU cooling: Noctua NH-D15 Graphics card: Zotac Nvidia GeForce GTX 1080 Ti Amp! Extreme VR: Oculus Rift CV1
 
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T(h)anks for the answers.

 

I guess I'll just have to get used to being the slow-poke in the Harrier :noexpression:

 

I'm setting up a mission and using the KC-135 MPRS. I set the KC to circle in a race track course at 550 kts, knowing that it would be far slower in IAS, but I didn't calculate out what that would be, and I thought, "hey I can easily do 500 IAS, easy-peasy" :noexpression:

 

After taking off from the Tarawa with 4k-lbs fuel and empty tanks, I tried to rendezvous with the KC, but I gained soooo slowly, that my tanks were literally dry before I could catch up :cry:

 

I've now got the KC circling at 500 kts :D

 

You're tanker should be at 275 indicated. You'll have to do some tweaking to get the right speed. But at around 20,000 feet you're looking at around 390 knots, it all depends on the conditions in your mission though. But that should help you out a bit.

 

The Pegasus, and by extention the Harrier does EXTREMELY well in the low altitude region, the thrust that engine puts out is actually quite remarkable. But as others have said, when you start to climb in this jet, especially while loaded with ordinance, you'll start to see a big drop off in performance climbing above ~12,000.

 

I fly it a lot in Normandy, usually hitting a tanker after leaving Lessay, most of my transits are around 15,000 (unless I need to avoid SAM threats) and I try to work targets around 10-14,000 to make use of the engine. I will usually weigh around 28-30K at takeoff but with no TERs, so single store per pylon to save on some of the drag.

 

It's a bit of a funny jet in terms of performance, but flight it in the right part of the sky, it's not slow. Take it too high, and well yeah, the drag catches up with you quick.

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I have been continuing to think about this issue, and while I don't have access to my gaming machine at the moment, I did acquire the AFMs for the AV8.

 

Strangely, I can't seem to find a practice problem that shows how to work out the drag index, so I'm not sure if I am calculating correctly. I'll attach my work for Capt Orso's load out though, would any of the SMEs here be able to tell me where I need to make changes?

 

I am arriving at a DI of 53.5. The constant mach cruise charts for an AV8 using the -408 engine show that a .80 mach cruise in the original situation posed is possible, but no charts are published for a faster mach. The low altitude cruise series of charts only go up to 12,000 feet. According to these charts, given an ISA day and the load out proposed, the aircraft should be able to reach 420 KCAS but not be able to achieve 450 KCAS at 12,000 feet. (this is assuming a gross weight of ~24000 lbs, which I what I think Capt Orso's aircraft should weigh, but as I said I don't have access to my machine to check with DCS).

 

Sources

A1-AV8BB-NFM-000 15 Sept 2001

A1-AV8BB-NFM-400 1 Feb 2003

189687969_DragIndex.jpg.423a5c5936dc9ef20a6bdbcbcf484bdf.jpg

Multiplayer as Variable

 

Asus Z97-A - I7 4790K - 32 GB HyperX - EVGA GTX 1080 Ti - Corsair 750i PSU

 

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