AV8B Altitude limitation - Bad model?

[Brainfreeze]

Hi,

I noticed that the AV8B struggles to fly even at 25k altitude with any kind of armament on.  AOA goes through the roof, airframe is not stable, need 100% RPM to stay in the air.   Surely that is a limitation of the model right? The real thing can fly well even above 25k?

I am not saying it cannot go there or even higher just that the airframe is not stable there.   Fencing-in / doing a G-warm at this altitude is a real challenge...you reach 12 AOA almost immediately upon starting your 90deg turn and have to battle to keep the aircraft stable.

Edited February 13, 2022 by Brainfreeze

[Spurts]

I got to 30k with 10 LJDAMs, 2 Sidewinders, gun pod, and targeting pod.  It takes time but it gets there.  Remember 102% is max continuous power.  I use VREST-Cruise page and climb at the "current alt cruise CAS".  Might work climbing at opt alt cruise CAS too.

[Brainfreeze]

I can get there eventually yes but with no fuel left once I reach it and I can't call it flying out there.  More like attempting to not fall 

[Spurts]

I just did it again.  Plenty of gas remaining.  I did try changing flaps from auto to cruise and it reduced drag (improved climb)  for that final bit. 

[Brainfreeze]

Super.  Well done

[Spurts]

I'll do a set of tests for climb and post the results. 

[Brainfreeze]

57 minutes ago, Spurts said:

I'll do a set of tests for climb and post the results. 

Try fencing in / doing G-warm at this altitude:  90deg turn at 4G/10AOA (whichever comes first) then 90deg 4-6G/12-15AOA.  Standard fencing in procedure.  Easy at 15k, 25k+ is another story here

[Spurts]

No way, lol. Anything over 20 is for transit only. 

[Brainfreeze]

25 minutes ago, Spurts said:

No way, lol. Anything over 20 is for transit only. 

yep my point.  Not sure that is realistic. Hence the thread ... it might be but feels wrong

Edited February 13, 2022 by Brainfreeze

[Wisky]

the harrier is a beast at deck, but the higher you go the harder it will be without any afterburner. The tiny wings on the harrier are great for parking on a carrier and for taking off and landing we have the nozzles and flaps. But the thinner the air the less lift you will get from the wings, and if you try to create lift with flaps its like throwing an anchor.

another factor is the big engine. Its starving for air the higher you go and would easily overtorque if it wouldnt be limited by systems.

at 20.000 ft youre likely reduced to 60% engine power. at 30.000 its maybe 40% left.

 

and iirc plus 38.000 the engine has a chance to just turn off mid air.

Edited February 13, 2022 by Wisky

[Spurts]

Okay I found that targeting the IAS for OPT Cruise in climb give a faster rate of climb than targeting the IAS for Current Cruise up to 20,000.  The higher speed climb then became more effective to 30,000.  This under 98% MGTOW, 42C OAT, adjusting throttle for 102%rpm, Cruise Flap setting, attitude hold on for the duration.  Once up there I did the fencing maneuver.  It was slow but doable.  Flaps Auto is really a boat anchor up there.

I had previously found that targeting the Current Alt Cruise speed when at 20,000ft gives you almost the same estimated range, but in actuality probably even more because you get to power back sooner.

[Brainfreeze]

Would be good to have someone who flew these things for real to provide a sense of wether this is realistic or not 

[Spurts]

I did recently have a former pilot comment on a video of mine that the "slushy" behaviour at altitude with a heavy load was accurate.

[DmitriKozlowsky]

I got it up to almost 40K with 1200 fuel , TPOD centerline, and 2 X AIM-9M. However inflight refueling with 250  KIAS, is much easier at 15K. I just discovered, since last 2.7.10X update that below 250 AGL in Cyprus, there is now significant low level buffeting. So NOE tactical flight is a bit more challenging now, but feels more real.

[Spurts]

I've hit 40k on the RTB phase of my flights, but again the question becomes "is the juice worth the squeeze".  Even after dropping my AG stores I can cruise back to the boat at 30-35k with only 60ppm fuel burn.

[Bog9y]

Read page 206 of the FSG , the section is called "High Altitude Maneuvering". It mentions that between 20-30K ft you can only pull 2-3 G with full power and keeping a constant speed of M 0.7 whilst flying level.   I was told by a former Harrier pilot they would initiate a descent for that 2nd G warm up turn at full power.  And as I understand it, G warmups are normally done below 20k ft. 

 

Ps, what was your loadout that you struggled to reach 25k ft with?

Edited February 15, 2022 by Bog9y

[Brainfreeze]

20 minutes ago, Bog9y said:

Read page 206 of the FSG , the section is called "High Altitude Maneuvering". It mentions that between 20-30K ft you can only pull 2-3 G with full power and keeping a constant speed of M 0.7 whilst flying level.   I was told by a former Harrier pilot they would initiate a descent for that 2nd G warm up turn at full power.  And as I understand it, G warmups are normally done below 20k ft. 

 

Ps, what was your loadout that you struggled to reach 25k ft with?

 

had 4xmk82 +tpod+gun + aim9. I don't 'struggle' per se but the airframe becomes sluggish and G-warm becomes a circus act .  Also better not lose speed as engine power becomes really weak.   I was curious that it happened so early (25k) as cruise rc'd alt is often 40k so thought it might be model weakness vs real thing but looks like it is not. 

[Spurts]

40K?  I only see that recommended when I am "empty".  AIM-9s, four empty ITERS, TPOD, GPOD, <3,000lb fuel remaining. which I guess other than the fuel is pretty similar to your load @Brainfreeze in terms of weight and drag..

Edited February 15, 2022 by Spurts

[deephack]

Flaps in auto at higher altitudes is quite a limiting factor drag wise. I was surprised how much easier it was to fly above 20k with them in cruise.

[Bog9y]

22 hours ago, Brainfreeze said:

had 4xmk82 +tpod+gun + aim9. I don't 'struggle' per se but the airframe becomes sluggish and G-warm becomes a circus act .  Also better not lose speed as engine power becomes really weak.   I was curious that it happened so early (25k) as cruise rc'd alt is often 40k so thought it might be model weakness vs real thing but looks like it is not. 

Ok, with that loadout your drag index should be around 34ish with a total weight of around 26k lbs.  According to the performance manual your optimum cruise alt should be around 35k ft. This does not mean that you can pull 4+ Gs at that altitude, it's an optimal cruising altitude that will be the most efficient for the engine (hence give you the lowest fuel flow).  

With regards to manuevering, have a look at the TAC-000 manual on page 766 you will find the H-M diagrams. Now , I could be completely wrong about this but if I understand these graphs correctly, at 25K ft with a 6 x mk82 loadout+gun+DECM pod, 50% water and 50% fuel you should be able to pull only around 2 Gs at 25K ft. In order to get 5 Gs you should be around 13k ft.   I know this is a  heavier loadout than yours with more drag but it's as good a graph as you're gonna get to see what should be possible. 

 

BTW the sluggish feel you talk about at alt is exactly what the pilots say about the jet when it's loaded out and at alt. 

Edited February 16, 2022 by Bog9y