flight dynamic changed?

[Magician]

Okay I jumped in and did some maneuvers at that altitude, and at both 500 kts true (~310 kts indicated) and indicated (When I could reach 500 kts indicated, wouldn't do it with drop tanks). And with varying loads from empty, to 8 Slammers, to 3 tanks and heaviest load of missiles out of the stock load outs.

 

All I can think is that you are trying to bank and yank with a full load of missiles and 3 drop tanks, or maybe just 3 drop tanks. Because I could pull a lot of G's at that altitude and airspeed all day without them, even with 8 Slammers, but if I tried a bank and yank with the drop tanks it pretty much maxed out the AOA right away, causing the rolling back and forth. Ease up on the back pressure and it recovers pretty quick.

 

You aren't supposed to do that with drop tanks in any case, and that is why. You can still do gentler maneuvers without any problem though (2-3 G's).

[Stuge]

After a short F-15 test at 30000ft altitude and 500kts indicated airspeed(empty stores, full internal fuel) here are my observations:

 

With full afterburner, a sustained level turn of about 4.5 G is easy to maintain.

 

Maximum G is approximately 7. Try to go much above it, and angle of attack will become too high, causing a spin. 7 G will bleed airspeed, so if you don't loosen the stick pull with the decreasing airspeed, you'll spin as well!

 

Why only 7 G? Why is it so easy to exceed stall AoA and spin the thing?

 

I'm not an expert in aerodynamics so I can't really answer that in a professional way, but I'm quite sure it must be related to the huge difference between indicated airspeed(IAS, indicating the dynamic air pressure on the aircraft's nose) and true airspeed(TAS, the actual speed at which your aircraft is going through the box of air around you) encountered at high altitude flight.

 

At sea level, IAS and TAS are pretty much equal. At, say, 40000ft, TAS is almost double the IAS. Which means the plane is actually going twice as fast through the air than is indicated by your airspeed indicator :D Which in turn means that same G gives a lower turn rate at high altitude. How this affects the required AoA for a particular G load I don't know, maybe someone could shed a light on it?

 

But in conclusion: if you spin it, try not to yank it so hard, be more gentle!

 

EDIT: About spins: any roll input when flying close to stall AoA may trigger a spin, and opposite roll input while in a spin may aggravate the spin, because aileron deflection disrupts airflow on wings asymmetrically. Keep this in mind when doing hard maneuvers, or recovering from a spin ;)

Edited July 31, 2014 by Stuge

[Exorcet]

Why only 7 G? Why is it so easy to exceed stall AoA and spin the thing?

 

I'm not an expert in aerodynamics so I can't really answer that in a professional way, but I'm quite sure it must be related to the huge difference between indicated airspeed(IAS, indicating the dynamic air pressure on the aircraft's nose) and true airspeed(TAS, the actual speed at which your aircraft is going through the box of air around you) encountered at high altitude flight.

Yes, aerodynamics are "constant" for a given indicated air speed. That would be completely true if it wasn't for Mach number, which makes things more complicated.

 

You can see it in the lift formula, L = .5*rho*V*V*CL*A

 

As rho goes down with height, so does lift, unless CL (AoA) and/or V go up (and A, but that usually doesn't change).

 

High'ish altitude flying is now even more unstable and unpredictable than it was with 1.2.8

 

@ 30.000 feet and 500 knots one would expect you can pull 1 G without going in a violent roll

 

I'm finding it far more predictable. I'm easily exceeding 4 g at 30,000 feet.

[Stuge]

I don't think 4.5G sustained at 30000ft is too far from the truth.. In instantaneous turn you can still get 8G, as long as you're going fast enough like 600kts.

 

I agree about firing all missiles from one side first being idiotic :D unless there is some unseen logic there...

[GGTharos]

Yes, it's so idiotic that the real aircraft does it.

 

The F-15C is resistant to these out-of-control rolls with as much weight imbalance as one full fuel tank on one wing - that's 4000-5000lbs. AMRAAMs will amount to maybe 700lbs together on one wing.

[Stuge]

Yes, it's so idiotic that the real aircraft does it.

 

 

Alright.. is there actually a benefit to this or is it just a drawback of how the system is designed?

[blkspade]

Yes, it's so idiotic that the real aircraft does it.

 

The F-15C is resistant to these out-of-control rolls with as much weight imbalance as one full fuel tank on one wing - that's 4000-5000lbs. AMRAAMs will amount to maybe 700lbs together on one wing.

 

But didn't someone else indicate that it should be right wing first as opposed to the left. Until either the flight model is fixed, or the launching, the best work-around is to use certain mixed loadouts that allow you to sort to the right first.

[GGTharos]

Alright.. is there actually a benefit to this or is it just a drawback of how the system is designed?

 

It is how the system is designed, and I don't know if there are any benefits - in fact I can think of some drawbacks for some limited scenarios using heaters. You can reject a missile and launch from a different pylon if you need to in the real deal.

 

But didn't someone else indicate that it should be right wing first as opposed to the left. Until either the flight model is fixed, or the launching, the best work-around is to use certain mixed loadouts that allow you to sort to the right first.

 

I think that's a really, really minor issue compared to what the flight model is doing.

[blkspade]

It is how the system is designed, and I don't know if there are any benefits - in fact I can think of some drawbacks for some limited scenarios using heaters. You can reject a missile and launch from a different pylon if you need to in the real deal.

 

 

 

I think that's a really, really minor issue compared to what the flight model is doing.

 

Yeah it is technically a minor issue on its own, but it has an effect on the flight model. Which of the two could theoretically be fixed faster, with less debugging, to provide a tolerable result. One could argue the existence of the missile reject switch could be tied to issues of asymmetry, as I find it hard to imagine any other reason beside launch failure.

[GGTharos]

It's tied to reasons of missile failure or instability of any kind - if the missile displays 'degraded' and you have other missiles that are not, you reject that missile.

 

So, no, you can't really argue it's tied to asymmetry, especially since it would have been very easy to address that with automation in the real aircraft.

 

And no, it isn't the right way to fix what's going on. No band-aids.

 

One could argue the existence of the missile reject switch could be tied to issues of asymmetry, as I find it hard to imagine any other reason beside launch failure.

[blkspade]

It's tied to reasons of missile failure or instability of any kind - if the missile displays 'degraded' and you have other missiles that are not, you reject that missile.

 

So, no, you can't really argue it's tied to asymmetry, especially since it would have been very easy to address that with automation in the real aircraft.

 

And no, it isn't the right way to fix what's going on. No band-aids.

 

I didn't say it was right way, but it gets something done. You could only halfway even call it a band-aid if the current functionality is actually wrong and the change further resembles its real life counterpart. Two birds, one stone. Obviously the AFM itself need further work and time, so its not like I'm suggesting something says now they don't have to worry about it.

[Buckeye]

The newly added cockpit/airframe vibrations still put a smile on my face every time I endure them while flying in 1.2.9. It's funny how the little things can make flying that much better in some cases.

[Exorcet]

The newly added cockpit/airframe vibrations still put a smile on my face every time I endure them while flying in 1.2.9. It's funny how the little things can make flying that much better in some cases.

Yes. Could really use them in the P-51, though I haven't flown it in the current patch so maybe it's there.

 

Seems odd that the F-15 will intentionally unbalance itself, even if the plane will correct for it, I don't see why you wouldn't just avoid the problem in the first place. But if it's real, it's real.

[TAW_Blaze]

But didn't someone else indicate that it should be right wing first as opposed to the left. Until either the flight model is fixed, or the launching, the best work-around is to use certain mixed loadouts that allow you to sort to the right first.

 

... and end up firing AIM-9s instead of AMRAAMS because you forgot that the sequence is now 3 long instead of 2, and curse for a few minutes. :megalol:

[NeilWillis]

Isn't it a fact that all modern fly-by-wire airframes are inherently unstable anyway? If the prototype does something a particular way, you can bet your bottom dollar that there is a pretty damn good reason for it.

 

As for the flight envelope, I'd suggest it'll be getting tweaks for a very long time to come. It has to be an incredibly complex chunk of code, and I dare say it'll just keep getting better and better as the reports come rolling in about what feels wrong.

 

I have to chuckle about how all the "experts" here are telling ED how to do their work. I mean, they couldn't possibly have a programme in place to progress their models! Without these inputs I bet they'd be utterly without any sense of direction at all, after all, how have they coped so far???

[NeilWillis]

Isn't it a fact that all modern fly-by-wire airframes are inherently unstable anyway? If the prototype does something a particular way, you can bet your bottom dollar that there is a pretty damn good reason for it.

 

As for the flight envelope, I'd suggest it'll be getting tweaks for a very long time to come. It has to be an incredibly complex chunk of code, and I dare say it'll just keep getting better and better as the reports come rolling in about what feels wrong.

 

/Irony on/ I have to chuckle about how all the "experts" here are telling ED how to do their work. I mean, they couldn't possibly have a programme in place to progress their models! Without these inputs I bet they'd be utterly without any sense of direction at all, after all, how have they coped so far??? /Irony off/

[lunaticfringe]

Isn't it a fact that all modern fly-by-wire airframes are inherently unstable anyway?

 

That would like, you know, matter...

 

...if the F-15C were actually fly-by-wire.

 

If the prototype does something a particular way, you can bet your bottom dollar that there is a pretty damn good reason for it.

 

And in some instances this is due to lack of data, or a lack of SMEs having push the regimes in question to throw up red flags.

[pauldy]

In regards to the Missile launching sequence.. By default, the left outboard AIM-120 is selected. I tend to select an AIM-9 then back to AIM-120. Then the new selected missile becomes the right outboard Slammer.. continue switching between missiles cycles all the AIM-120s & AIM-9s except the left outboard..

 

For some reason the left outboard Slammer can no longer be selected unless the right outboard is fired..

 

That way I avoid flying right wing heavy.. but I assume all missiles can be selected in the real aircraft right?

[blkspade]

That way I avoid flying right wing heavy.. but I assume all missiles can be selected in the real aircraft right?

 

Well according to the -1 the real F-15 has a switch position that selects GUN, SRM, or MRM. After that there is another button that rejects the current selected missile of that type.

[blkspade]

... and end up firing AIM-9s instead of AMRAAMS because you forgot that the sequence is now 3 long instead of 2' date=' and curse for a few minutes. :megalol:[/quote']

 

I more or less rely on the HUD or audible cue to know what I'm firing as opposed to counting button presses in my head. If I have 120B's loaded I might end up firing one when I wanted a C.

[SDsc0rch]

don't mix bravos and charlies

 

why would you do that

 

pick one and go with it

 

why burden yourself with so many missile options - all you need to have in mind is "heat" or "radar"

[TAW_Blaze]

I more or less rely on the HUD or audible cue to know what I'm firing as opposed to counting button presses in my head. If I have 120B's loaded I might end up firing one when I wanted a C.

 

Me too, usually. Usually :D

[blkspade]

don't mix bravos and charlies

 

why would you do that

 

pick one and go with it

 

why burden yourself with so many missile options - all you need to have in mind is "heat" or "radar"

 

I also sometimes bring sparrows. I bring bravos because there are scenarios where they'll do what I want them to do better than charlies. Seeing as there are a number of flaws in the different missiles that some people have been very good at exploiting, the mix complicates things for them. Having bandits plow through your actives from 8-12nm after you've cranked or gone defensive gets old real fast. Also on those occasions where you have a frog foot trying to run SEAD on your base, bravos and sparrows intercept those anti-radiation missiles better.

[LJQCN101]

But in conclusion: if you spin it, try not to yank it so hard, be more gentle!

 

EDIT: About spins: any roll input when flying close to stall AoA may trigger a spin, and opposite roll input while in a spin may aggravate the spin, because aileron deflection disrupts airflow on wings asymmetrically. Keep this in mind when doing hard maneuvers, or recovering from a spin

 

As for the spin recovery technique in real life F-15C. Under high AOA conditions, rudder is less effective in creating yaw moment (Cn, aka Yawing momentum) than ailerons. For example:

 

 

In normal conditions, a left rudder input will make the nose of the aircraft slice to the left. However in high AOA regions, to make the nose slice to the left, rudder input is ineffective. To many people's surprise, a right stick input will make it. Yeah, in the opposite direction. And that phenomenon is called "Adverse Yaw".

 

So in real life, the proper spin recovery technique in a F-15C is, as proposed by T.O. 1F-15A-1, full lateral stick in the direction of spin. Rudder is useless. As opposed to what is suggested in the DCS F-15C manual.

 

And you're right, opposite roll input while in a spin does aggravate the spin.

Edited August 10, 2014 by LJQCN101

[theropod]

 

So in real life, the proper spin recovery technique in a F-15C is, as proposed by T.O. 1F-15A-1, full lateral stick in the direction of spin. Rudder is useless. As opposed to what is suggested in the DCS F-15C manual.

 

with the old 1.2.8 flight model ,you can use same technic for spin recoveries, rudder was not effective to recover it

while in flat spin, you have to push the stick with the same direction of spin movement to recover it,but with new patch spins are not exist.

aircraft can handle spin recovery with it self

Edited August 10, 2014 by theropod