correct as is Hornet stalls when vertical

[Jonnylap1]

Hello all,
I have a quick question. 
In reality the F-18 can sustain a vertical climb almost indefinitely due to its high thrust to weight ratio. 
However, when I try any steep climbs in DCS I quickly lose speed and eventually stall. 

Am I doing something wrong, or is this a bug maybe?

Any ideas would be really appreciated. 

Thanks for your help!

[Tholozor]

I think you've misunderstood what a thrust-to-weight ratio actually means. TWR is only a single metric regarding an aircraft's performance. Atmospheric conditions, temperature, wind, wing loading, lift-to-drag ratios; all play crucial parts.

These are also air-breathing engines, not solid fuel boosters. Sustained vertical climbing (or even acceleration for that matter) is already a challenge.

Edited August 16, 2023 by Tholozor

[wilbur81]

4 hours ago, Jonnylap1 said:

Hello all,
I have a quick question. 
In reality the F-18 can sustain a vertical climb almost indefinitely due to its high thrust to weight ratio. 
However, when I try any steep climbs in DCS I quickly lose speed and eventually stall. 

Am I doing something wrong, or is this a bug maybe?

Any ideas would be really appreciated. 

Thanks for your help!

All 4th and 5th Gen fighters will stall out in a vertical climb when drag, air density, gravity, etc.. catch up to it....the Hornet sooner than several others due to its lower TWR.

[Temetre]

Another thing is to consider that even the maximum T/W only takes weight in consideration. So even if the engines could lift the weight of the aircraft in a vertical climb, you will have air resistance slow you down.

And the slower you go, the less air gets pushed into the intakes, the less thrust you produce, etc. Thats why almost no aircraft can sustain a vertical climb.

 

Thrust to weight ratios are very misleading, because the thrust of an engine depends a lot on the air coming into the intakes. As a rule of thumb, the only aircrafts that can actually hold their own weight at stillstand are VTOLs, and only when theyre very light (no payload, low fuel).

Edited August 16, 2023 by Temetre

[Jonnylap1]

Maybe T/W ratio is not the correct term.

What I'm confused on is how there are youtube videos of F18s (Including Canadian jets to prove they aren't super hornets) climbing vertically up past 30000' without stalling or slowing, whereas in the game I seem to loose speed far before reaching that kind of altitude. 

I have even tried flying naked without any pylons or external fuel tanks. 

Is this simply a DCS limitation to not fully mirror the capabilities of the F18, perhaps for classified reasons?

Edited August 16, 2023 by Jonnylap1

[razo+r]

It's probably because you do not fly the same profile as they do. You think they fly vertical but they don't.

Or can you show us a video where we can see one of them pointing 90 degrees straight up until 30'000ft?

[Phantom711]

vor einer Stunde schrieb Jonnylap1:

Maybe T/W ratio is not the correct term.

What I'm confused on is how there are youtube videos of F18s (Including Canadian jets to prove they aren't super hornets) climbing vertically up past 30000' without stalling or slowing, whereas in the game I seem to loose speed far before reaching that kind of altitude. 

I have even tried flying naked without any pylons or external fuel tanks. 

Is this simply a DCS limitation to not fully mirror the capabilities of the F18, perhaps for classified reasons?

 

1. What altitude did they start their climb? What speed were they at, when they started to pull up?

2. The F/A-18 is basically a 40 year old airframe. There is certainly not that much secrecy about the performance data alone. (And just to be clear: yes, certain aspects of the avionic systems certainly are secret)

[Jonnylap1]

7 hours ago, Phantom711 said:

1. What altitude did they start their climb? What speed were they at, when they started to pull up?

2. The F/A-18 is basically a 40 year old airframe. There is certainly not that much secrecy about the performance data alone. (And just to be clear: yes, certain aspects of the avionic systems certainly are secret)

The videos I've seen are takeoffs from the runway and they go straight up without losing a beat it seems.

Edited August 17, 2023 by Jonnylap1

[Jackjack171]

4 minutes ago, Jonnylap1 said:

The videos I've seen are takeoffs from the runway and they go straight up without losing a beat it seems.

 

Video please! Add to that, the HUD footage that shows going past 30,000. What you see in a YT video and reality are 2 different things. No aircraft on the planet can go vertical almost indefinitely. Eventually, you run out of airspeed. This also depends on the profile flown, weight and other factors called out by the others replying as well. Please reproduce the footage with more solid information other than you saw a YT video! 

[Jonnylap1]

Thanks anyways people. It's clear what the consensus is. 

[TimRobertsen]

It would be fun if TWR worked like that

Regardless:

Try setting the mission to 1. feb, minimum temperatures, and maximum air pressure. Take off from Batumi towards the sea, with 2k lbs of fuel, no pylons, nu gun ammo. Get to 500 knots, keeping 200-300 feet of altitude, and then pull up. That is probably the closest you'll get

[GGTharos]

10 hours ago, Jonnylap1 said:

Maybe T/W ratio is not the correct term.

It is.

10 hours ago, Jonnylap1 said:

What I'm confused on is how there are youtube videos of F18s (Including Canadian jets to prove they aren't super hornets) climbing vertically up past 30000' without stalling or slowing, whereas in the game I seem to loose speed far before reaching that kind of altitude. 

I have even tried flying naked without any pylons or external fuel tanks. 

Is this simply a DCS limitation to not fully mirror the capabilities of the F18, perhaps for classified reasons?

You're simply missing some information.   No aircraft can go vertical and not lose speed.   Near the ground, at low altitude where the pressure is high enough and if you start at high speed, you might be able to accelerate vertically for a short time - but the pressure will drop quickly and the amount of thrust generated by the engines depends on that very pressure - so it's that plus the speed.  So you lose pressure by altitude, you lose indicated airspeed, and thus all you're doing by going up is starving the engines of the very air they need to maintain this thrust.

So to sum up, you need to ram air into the engine to get more thrust.  Less air (lower density + lower airspeed) = less thrust.

[Temetre]

vor 7 Stunden schrieb Jonnylap1:

The videos I've seen are takeoffs from the runway and they go straight up without losing a beat it seems.

The image can be a bit misleading on video, the climb is probably not fully vertical. The plane might also lose speed during the climb and its not that apparent.

Or are you talking about airshow planes? Those are often very different from "combat ready" planes, much lighter, might have tuned engines and flight control systems. Those usually have a pre planned coreography to maximize the planes performance for stunts, drive it to the final edge. Thats very different from the expected combat performance usually, espeically with payload.

[Foka]

I heard that next mission to the moon will be with a legacy Hornet.

[TheFreshPrince]

If you're really trying to maintain around 90° nose up, you can go some way until you stall (I don't remember the max. height, but i started slow):

IRL I think you wouldn't climb with 90°, maybe at an airshow. But then you don't climb that high or else the spectators will lose sight . You can also see the plane already slowing down in this vid:

 

Edited August 18, 2023 by TheFreshPrince

[Temetre]

Am 18.8.2023 um 18:25 schrieb TheFreshPrince:

IRL I think you wouldn't climb with 90°, maybe at an airshow. But then you don't climb that high or else the spectators will lose sight . You can also see the plane already slowing down in this vid:

And the Hornet spends quite some time accelerating over the runway. Frankly, this looks quite a bit slower than our DCS Hornet?

[Hulkbust44]

And the Hornet spends quite some time accelerating over the runway. Frankly, this looks quite a bit slower than our DCS Hornet?

Well he wasn't in full blower...

Sent from my moto g stylus 5G (2022) using Tapatalk

[Tom Kazansky]

I'm not at my PC but I bet even with a light F-15C which has an even better T/W ratio than the Hornet you couldn't climb 90° after take off to 30k feet because of the reasons others posted above. (Has anybody tried this? I will...)

[Tom Kazansky]

On 8/20/2023 at 8:45 AM, Tom Kazansky said:

I'm not at my PC but I bet even with a light F-15C which has an even better T/W ratio than the Hornet you couldn't climb 90° after take off to 30k feet because of the reasons others posted above. (Has anybody tried this? I will...)

Lost my own bet to some extent.

Tried it with a clean F-15C but needed to reduce fuel to 10% (means almost empty), which allowed only the climb (right after take off) and a save landing right after "falling" down.

 

But: The F-15C just reaches 30k feet within a stall regime and has to use the altitude to recover to a stable flight.

So, my conclusions:

1.) Even the T/W ratio of the F-15C is not enough to play starship - certainly not in normal/safe configurations. So the Hornet wil be doing worse by design.

2.) Everything what is posted here to explain why "T/W >1" does not mean you have a VTOL aircraft is correct.

(Will repeat this with the Eurofighter/Typhoon as soon as I get my hands on it )

Edited August 21, 2023 by Tom Kazansky
typo

[Qiou87]

One thing I didn't see mentioned, but T/W is not a constant. As you fly it will actually continously evolve, as thrust is not the same at all altitudes, atmospheric conditions and flight profiles as has been explained, and weight also varies a lot for a fighter jet depending on configuration and fuel load (T/W will actually slightly improve at sea level as you burn your fuel...). So the T/W ratio of your aircraft upon take-off is changing constantly as you pull the nose up and gain altitude rapidly.

 

This is often misunderstood as websites with limited technical background like to produce baitclick lists of "thrust-to-weight ratios of fighter aircraft" and whatnot, presenting fixed values based on theoretical values from brochures. This sadly propagates a deep misunderstanding among the public and enthousiasts about what to expect from a fighter jet.

 

I would also like to add that our Hornet's flight model has been tested with the help of former Hornet pilots and it seems to be quite a close match. Of course, no simulation is going to be 100% accurate, but if it's close enough for them, it's close enough for me. I'll take their word over my "impressions based on a YT video" anyday.

Edited August 21, 2023 by Qiou87

[Hiob]

1 minute ago, Qiou87 said:

One thing I didn't see mentioned, but T/W is not a constant.

That was mentioned at least three times before.....  I think OP got it by now.... 

[TheFreshPrince]

Am 21.8.2023 um 10:26 schrieb Tom Kazansky:

Lost my own bet to some extent.

Tried it with a clean F-15C but needed to reduce fuel to 10% (means almost empty), which allowed only the climb (right after take off) and a save landing right after "falling" down.

 

But: The F-15C just reaches 30k feet within a stall regime and has to use the altitude to recover to a stable flight.

So, my conclusions:

1.) Even the T/W ratio of the F-15C is not enough to play starship - certainly not in normal/safe configurations. So the Hornet wil be doing worse by design.

2.) Everything what is posted here to explain why "T/W >1" does not mean you have a VTOL aircraft is correct.

(Will repeat this with the Eurofighter/Typhoon as soon as I get my hands on it )

 

Apparently the F-15E should be able to do this. I bet the Eurofighter can also do this easily. 

 

[Tom Kazansky]

7 hours ago, TheFreshPrince said:

Apparently the F-15E should be able to do this. I bet the Eurofighter can also do this easily. 

 

He said "without conformal fuel tanks". Our F-15E can't go 90° to 30k after take off. I tried.

I also expect a Eurofighter can do it, not only because of the thrust to weight ratio but also because of the fact that its engines are optimised for high altitudes.

[howie87]

The main factor here is that as the air gets thinner, thrust decreases with altitude.

An engine with 17,000lbs of thrust at sea level might only produce 5,500lbs at 30,000ft.

[Tom Kazansky]

5 minutes ago, howie87 said:

The main factor here is that as the air gets thinner, thrust decreases with altitude.

An engine with 17,000lbs of thrust at sea level might only produce 5,500lbs at 30,000ft.

Yeah, I got that. And there is no fuel burning engine that will change that without carrying its own oxygen with it like a rocket.

As I mentioned before my tests don't contradict what is correctly stated before about t/w ratio.

They just show whether the thrust combined with the energy gained before t/w drops below 1, by thin air, is enough to get to 30k feet.