[REPORTED] serious headwind/tailwind bug

Just wanted to know if this bug is going to be fixed (and preferable if it affects the F/A-18 as well)

If you fly in a 90kts tailwind you need e.g. 81% RPM to maintain 250kias but only 71% in the same headwind to maintain the same 250kias which is of course totally unrealistic.

This bug furthermore seriously affects top speed and high altitude performance.

I dont see this.

At least in Nevada, in which I just tried, full MIL gives me 550kn IAS either in both tail- and headwind.

The engines can stall though, in tailwind conditiones. Maybe thats your issue? That will happen when you turn into a strong tailwind from headwind at low IAS.

It does not affect the F/A-18. ground speed increases but IAS remains the same.

At which altitude did you test? High enough to achieve a 90kts tail/headwind? Testing at MIL thrust doesn't show this problem very well due to the high drag at high IAS, that's why I mentioned only the test at a much lower IAS.

I tested at the Caucasus map at 7000ft. At MIL I get 545kias in a headwind and 550kias in a tailwind.

A (steady) tail or headwind has zero effect on the airplane or its engines concerning IAS and TAS. Tailwind (at least IRL) affects (some) engines only during starting with the airplane steady on ground.

So we still don't know if the F/A-18 suffers from this bug as well.

Here's a short track which shows this weird bug.

F5_wnd_bug.trk

I did my tests and couldn't confirm a bug (90kts wind, flight at 10000ft, engine at 92% RPM, trim at 1, IAS stabilized at ~480kts). One thing I did notice however was that if you start in the air, the waypoint speed you set in the editor is ground speed - so the initial IAS will be different depending on the wind. And the aircraft will be trimmed for that initial IAS. That means, if you don't touch the trim throughout the test, you'll be putting a different amount of force on the stick to stay level and that might account for a few kts of IAS. Once I made sure my trim was the same in all the tests, I got the same performance out of the aircraft.

How do you want to confirm a bug if don't make the same test? In my reply to Sven Dellepude I mentioned already that this bug isn't as obvious at high IAS and high power setting.

Trim can't play any role because the F-5 doesn't have trim tabs. If you fly straight and level the stabilizers are in exactly the same position, if you are in trim or out of trim and you have to maintain pressure on the stick.

We are not talking about a few knots!

If you fly 250kias at 71% RPM in a headwind and you turn 180deg, you will stall and drop out of the sky with the same 71% in the (now) tailwind!!!

On the other hand if you fly 250kias at 81% in a tailwind and you turn around, your IAS will increase by slightly more than 100kts!!!

This is serious IMO.

How do you want to confirm a bug if don't make the same test?

I had a total of 15 minutes of free time yesterday. I recalled you reported this problem - without the specifics - and I tried to quickly verify it (rather than spend my time on something actually fun) in order to help you and BST get to the bottom of. I didn't recreate the problem but I had an observation about the trim I decided to share. Even if it turned out irrelevant here... why the attitude? You want to fight this battle alone so badly, or do you want people to actually help you?

I didn't see it this way. So, thanx for trying :)

Sorry, I certainly didn't want to upset you!

Thanks for understanding and sorry if I seem a little on edge. Tough week. Anyway, I'll try to do a test with your parameters once I have the time.

:):):thumbup:

Post the mission here so we can test please.

good idea! Thanx for the input :)

F-5_90kts.miz

I tried your mission and got the same result. At 7000ft I needed 71% to keep 250kts into the wind, 81% to keep 250kts with the wind and 76% to keep 250kts perpendicular to the wind. I tried each direction twice. I can definitely see that there is a problem here.

Thanx for taking time to do these extended tests. Highly appreciated! :)

Btw, the same test with the F/A-18 would be very interesting.

I have encountered this bug with the F-15 as well but it doesn't always happen and it's not predictable, hence it's not possible to confirm it.

edit: test performed and I can confirm that this bug doesn't exist with the absolutely magnificent F/A-18 :)

Now it would be nice if BST could confirm and fix this very strange bug.

I think i might have got somewhere with this bug...

I have a feeling it might be related to the engines taking groundspeed as their air-intake speed rather then airspeed.

If you create a mission with maximum allowable wind speed all the way up to 26000 ft. Spawn a F5 at say 26k and fly with the wind, set power at say 85%, let the speed stabilise. Now turn 180 degrees to fly against the wind... You may notice that engine RPM drops... This suggests to me that the engines are seeing a substantial reduction air intake speed and therefore thrust.

I tried stalling the aircraft both into wind and with the wind and the ASI read the same speed in both cases, So I don't believe the wind is having an incorrect effect on the FM itself, I just think its having an effect on the engines which is leading to a knock-on effect with the aircrafts airspeed into and with the wind.

Just something to think about.

I have found wind to highly compromise handling of the F-5 and F-18, to the point I need to disable it.

The aircraft should not fly any different with or without wind. The only difference will be when the wheels are on the ground, and in ground speed when flying.

As you rightly point out, 500 kts IAS is 500 kts IAS. The RELATIVE WIND at the aircraft in flight is ZERO.

Examples:

50 kts headwind. Aircraft stationary on ground and facing into wind, IAS reads 50 kts. Takeoff roll is shorter, but the required takeoff speed is IDENTICAL. Aircraft "feels" no wind once flying.

50 kts tailwind. Aircraft stationary on ground and facing away from the wind. IAS reads 0 kts. Takeoff roll is much longer, but the required takeoff speed is IDENTICAL. Again, once flying, the wind disappears.

A quick and dirty way to check it's working correctly is set a wind of 200 kts straight down the nose of the aircraft. Pulling back on the stick should cause the aircraft to lift-off the same as during takeoff.

I have no problems with wind in F-18. What issues are you seeing there?

Primarily on the ground, it reacts to even a slight crosswind requiring full rudder inputs to maintain the centerline. A 5 kts wind feels more like 50 kts.

In the air it feels OK.

Related question: does the aircraft feel to have a lot of drag, particularly at higher IAS??

Primarily on the ground, it reacts to even a slight crosswind requiring full rudder inputs to maintain the centerline. A 5 kts wind feels more like 50 kts.

 

In the air it feels OK.

huh.. Thats odd.. You do know that nosewheel steering should be kept on during the takeoff roll? I have zero issues keeping straight in some quite strong crosswinds.

From page III-7-24 in A1-F18AC-NFM-000:

"Nosewheel steering is used to maintain directional control throughout the takeoff roll. Differential braking alone may not be adequate to maintain directional control on takeoff. Also, the drag of the brakes increases the length of the takeoff roll."

Yes, I already knew that. NWS is connected to the rudder pedals. ;)

I do get full rudder motion in both directions, and can steer normally on the ground.

Yes, I already knew that. NWS is connected to the rudder pedals. ;)

 

I do get full rudder motion in both directions, and can steer normally on the ground.

Well.. It was a fair question, you could be disabling it before/during takeoff, as I've known some people to do. I can takeoff in 30knot crosswind with no issue btw - Just did it.

Well.. It was a fair question, you could be disabling it before/during takeoff, as I've known some people to do. I can takeoff in 30knot crosswind with no issue btw - Just did it.

No problem! I'll give it another try!

I think i might have got somewhere with this bug...

 

I have a feeling it might be related to the engines taking groundspeed as their air-intake speed rather then airspeed.

 

If you create a mission with maximum allowable wind speed all the way up to 26000 ft. Spawn a F5 at say 26k and fly with the wind, set power at say 85%, let the speed stabilise. Now turn 180 degrees to fly against the wind... You may notice that engine RPM drops... This suggests to me that the engines are seeing a substantial reduction air intake speed and therefore thrust.

 

I tried stalling the aircraft both into wind and with the wind and the ASI read the same speed in both cases, So I don't believe the wind is having an incorrect effect on the FM itself, I just think its having an effect on the engines which is leading to a knock-on effect with the aircrafts airspeed into and with the wind.

 

Just something to think about.

Yes i think same, engine performance change on tail/head wind.

Isn’t this a MASSIVE flaw that should be promptly addressed by ED? How is it possible that they didn’t do anything about, didn’t even see this thread probably!