need track replay Aircraft has too much drag

[Tiger-II]

The basic airframe appears to have too much drag.

Atmosphere was set to standard. Caucasus map. OAT +15 deg. C.

Aircraft was put in a 25 degree dive from 7000 ft at 300 kts. Aircraft would not accelerate past 400 kts. Barber pole increase to over 500 kts, but good luck ever getting close to that. It just seems to hit a wall and won't accelerate anymore.

Once you start hanging stores off this thing, it becomes a total dog, and getting much over 250 kts becomes difficult. This of course, has rammifications for its maneuverability.

Edited August 9, 2022 by Tiger-II

[BIGNEWY]

Please include a track replay and any public evidence. 

thank you

[Tiger-II]

Hi,

I found this chart regarding expected A-10A INDICATED airspeed values. I know we're flying the C model, but I'm sure one of the points of the C model was it had more power (= more payload capability).

Attached is a track where I don't do much. Takeoff, level acceleration to a point where it is clear she's not going to go much faster, then a half-loop to 10000 ft to show level acceleration there, then a 30 degree dive, some light maneuvering, another half-loop, a 20-degree dive, then some harder maneuvering to show what happens with the speed trend.

Overall, she seems to be lacking, remembering this is a clean jet with full gun and fuel only.

Has an F-5 type mix-up happened with the A-10C II? The F-5 was incorrectly using ground speed for some parameters within the flight model. The A-10C II seems to hit the numbers if you look at GROUND SPEED, but these are supposed to be INDICATED AIRSPEED VALUES! e.g. she's supposed to make 350 kts in level flight, not 315-ish. That is quite a significant degredation in performance.

https://simhq.com/forum/ubbthreads.php/topics/3150118/re-a-10c-speed-and-flight-dynamics#Post3150118

A-10C II Drag Issue.trk

Edited August 11, 2022 by Tiger-II

[Yurgon]

8 hours ago, Tiger-II said:

I found this chart regarding expected A-10A INDICATED airspeed values.

Awesome, that's some solid data for a comparison!

8 hours ago, Tiger-II said:

I know we're flying the C model, but I'm sure one of the points of the C model was it had more power (= more payload capability).

Do you have any source to back that up?

As far as I'm aware, the A-10 has used the same engines with the same thrust rating pretty much since its inception.

8 hours ago, Tiger-II said:

Takeoff, level acceleration to a point where it is clear she's not going to go much faster

Cool! I've seen 345 KIAS in the HUD.

So, going to the chart, with a gross weight of 38,000 pounds (not that gross weight matters, but that's what the mission editor gives for a fully fueled jet with full gun ammo and no external stores attached to the pylons), at a pressure altitude of 400 feet, which I'll just call sea level, and a drag index of 0 (give or take), at 15°C sea level temperature, we should be seeing a maximum indicated airspeed at maximum thrust in level flight of round about 345 to 348 knots.

8 hours ago, Tiger-II said:

10000 ft to show level acceleration there

The document you linked doesn't provide acceleration data, only max speed.

I see 312 KIAS in the HUD (creeping up to 314 after a while) at round about 10,000 feet pressure altitude. At a slightly lower gross weight (800 pounds of fuel have been burned), still drag index 0 and still 0 degrees temperature variation from a standard 15°C day, the A-10A should be reaching a max speed of some 315 KIAS.

Thanks for taking the time to show that in both these tests the A-10C is within 1% of the document you linked.

[Jel]

Somehow related but not quite, watch the narration of his speed and altitude, pretty interesting:

 

[Tiger-II]

7 hours ago, Yurgon said:

Awesome, that's some solid data for a comparison!

Do you have any source to back that up?

As far as I'm aware, the A-10 has used the same engines with the same thrust rating pretty much since its inception.

Cool! I've seen 345 KIAS in the HUD.

So, going to the chart, with a gross weight of 38,000 pounds (not that gross weight matters, but that's what the mission editor gives for a fully fueled jet with full gun ammo and no external stores attached to the pylons), at a pressure altitude of 400 feet, which I'll just call sea level, and a drag index of 0 (give or take), at 15°C sea level temperature, we should be seeing a maximum indicated airspeed at maximum thrust in level flight of round about 345 to 348 knots.

The document you linked doesn't provide acceleration data, only max speed.

I see 312 KIAS in the HUD (creeping up to 314 after a while) at round about 10,000 feet pressure altitude. At a slightly lower gross weight (800 pounds of fuel have been burned), still drag index 0 and still 0 degrees temperature variation from a standard 15°C day, the A-10A should be reaching a max speed of some 315 KIAS.

Thanks for taking the time to show that in both these tests the A-10C is within 1% of the document you linked.

Thanks for the reply, but DCS has a history of chronically under-performing aircraft and higher drag profiles than reality. The F-5 is still wrong to this day, with no sign of it being corrected.

Is it correct that it takes several minutes to achieve these speeds? In the case of 10000 ft, it is over double the time of sea-level.

Diving acceleration seems pretty low, too, and it takes nothing for the aircraft to bleed off speed. The video linked by Jel is interesting - pulling +4 g should allow the A-10 to "maintain energy" - that means no excess energy is lost as the result of simply pulling g beyond what would be lost as a result of a vertical maneuver. In a level turn this would mean little speed is lost pulling +4 g vs. say +2 g.

It seems to be a common "sim-ism" that anything over +1 g causes an aircraft to dump speed like it is flying through treacle, and that straight and level flight at idle means an aircraft should decelerate to stall speed in about 1 NM. This simply isn't true at all, but we see it all too often.

If you have any data on glide performance (both engines shutdown) then it would be worth testing that. I'll bet the aircraft falls short.

[Yurgon]

1 hour ago, Tiger-II said:

Is it correct that it takes several minutes to achieve these speeds? In the case of 10000 ft, it is over double the time of sea-level.

I don't know. My only frame of reference is being a passenger in an airliner.

On one hand, the thinner air at 10,000 ft creates less drag. On the other hand, I assume it provides less thrust. So it may be correct. We'd need an acceleration chart to compare this against.

1 hour ago, Tiger-II said:

Diving acceleration seems pretty low, too, and it takes nothing for the aircraft to bleed off speed. The video linked by Jel is interesting - pulling +4 g should allow the A-10 to "maintain energy" - that means no excess energy is lost as the result of simply pulling g beyond what would be lost as a result of a vertical maneuver. In a level turn this would mean little speed is lost pulling +4 g vs. say +2 g.

Again, we'd need some solid and hard data for comparison. Demos are usually flown with little fuel and no gun ammo (and a counter-weight in the forward landing gear bay to make up for the lack of gun shells, so the C/G isn't too far off), making the aircraft as nimble and maneuverable as it gets. A-10 demo jets often have some of the pylons removed, giving them less drag (or a negative drag index, when we look at the TO). Pretty sure they don't have flare and chaff dispensers loaded, and even that can have a little bit of a drag index impact.

What I'm saying is, we shouldn't be comparing apples and oranges. Personally, I have absolutely no way to tell whether or not the A-10C in DCS is performing correctly; the closest I've ever been to an A-10 was about half a mile away at an airshow in the late 80s or early 90s (what a demo that was indeed!).

So far you provided one chart that says the DCS A-10 does extremely well.

If I recall correctly, drag used to be an issue with the DCS A-10C and was corrected a couple of years ago, bringing some of the aircraft's performance parameters closer to the original documentation. For acceleration, I guess they'd need really good data to change the flight model again.

1 hour ago, Tiger-II said:

If you have any data on glide performance (both engines shutdown) then it would be worth testing that. I'll bet the aircraft falls short.

I'm aware of a long-standing problem that the engines still provide hydraulic pressure when wind-milling in flight, which they shouldn't.

As for glide performance, it would be great to have some solid data to compare the DCS A-10 against. Otherwise, any change to the flight model would be a shot in the dark.

[Snoopy]

On 8/11/2022 at 2:51 PM, Tiger-II said:

Hi,

I found this chart regarding expected A-10A INDICATED airspeed values. I know we're flying the C model, but I'm sure one of the points of the C model was it had more power (= more payload capability).

 

 

That isn’t correct, C and A models have the same exact engines and performance.

On 8/12/2022 at 3:59 AM, Jel said:

Somehow related but not quite, watch the narration of his speed and altitude, pretty interesting:

 

You can’t use the demo bird as proof…not only does it have items removed (like pylons) it also flies with the minimum fuel load.

[MiG21bisFishbedL]

1 hour ago, Snoopy said:

That isn’t correct, C and A models have the same exact engines and performance.

 

I can neither find any indication that the TF34s saw anything other than overhaul between the A and the C. 

[Jel]

vor 5 Stunden schrieb Snoopy:

[...]

You can’t use the demo bird as proof…not only does it have items removed (like pylons) it also flies with the minimum fuel load.

I´m not saying you should take that demo "use as proof"  Just saying it´s somewhat related to the topic and may be interesting to watch. I didn´t know there was need for clarification here regarding the loadout and fuel on a demo bird, so i´m sorry if there are any misconceptions.

Edited August 16, 2022 by Jel

[Ephedrin]

Am 12.8.2022 um 14:30 schrieb Tiger-II:

Thanks for the reply, but DCS has a history of chronically under-performing aircraft and higher drag profiles than reality. The F-5 is still wrong to this day, with no sign of it being corrected.

Is it correct that it takes several minutes to achieve these speeds? In the case of 10000 ft, it is over double the time of sea-level.

Diving acceleration seems pretty low, too, and it takes nothing for the aircraft to bleed off speed. The video linked by Jel is interesting - pulling +4 g should allow the A-10 to "maintain energy" - that means no excess energy is lost as the result of simply pulling g beyond what would be lost as a result of a vertical maneuver. In a level turn this would mean little speed is lost pulling +4 g vs. say +2 g.

It seems to be a common "sim-ism" that anything over +1 g causes an aircraft to dump speed like it is flying through treacle, and that straight and level flight at idle means an aircraft should decelerate to stall speed in about 1 NM. This simply isn't true at all, but we see it all too often.

If you have any data on glide performance (both engines shutdown) then it would be worth testing that. I'll bet the aircraft falls short.

It‘s not the G force that brakes aircraft in a turn, it‘s the angle of attack that comes with pulling the airplane around. Most aircraft have their lowest drag at around 2 degrees AOA, give of take. If you become slower at a high GW you will fly at a higher AOA than if you were light at the same speed or faster at the same weight. This will cause higher drag and hence worse acceleration and performance. 
 

All in all the A10 with its mounted pylons, the half retracted wheels and the twin rudder tail is an extremely draggy airplane, it will not go fast. But if you fuel it as low as in the video with all munition removed (gun too!) it will be able to perform the same stunts. Being less than 5% within real specifications throughout the whole flight model is a great achievement already but providing data from another aircraft won‘t help much. The A10C is much heavier (see above) with no change to its shape and regardless if it has received a power update or if it carries its nose higher than the A model it will always suffer from more drag, simply due to aerodynamics. 
 

This does NOT mean that it‘s not underpowered, I simply can‘t evaluate that. I don‘t know the real aircraft. The F5 has btw been announced to receive a big update, I guess it‘s just not feasible to updtae it now before that. 

[jaylw314]

8 hours ago, Ephedrin said:

It‘s not the G force that brakes aircraft in a turn, it‘s the angle of attack that comes with pulling the airplane around. Most aircraft have their lowest drag at around 2 degrees AOA, give of take. If you become slower at a high GW you will fly at a higher AOA than if you were light at the same speed or faster at the same weight. This will cause higher drag and hence worse acceleration and performance. 
 

All in all the A10 with its mounted pylons, the half retracted wheels and the twin rudder tail is an extremely draggy airplane, it will not go fast. But if you fuel it as low as in the video with all munition removed (gun too!) it will be able to perform the same stunts. Being less than 5% within real specifications throughout the whole flight model is a great achievement already but providing data from another aircraft won‘t help much. The A10C is much heavier (see above) with no change to its shape and regardless if it has received a power update or if it carries its nose higher than the A model it will always suffer from more drag, simply due to aerodynamics. 
 

This does NOT mean that it‘s not underpowered, I simply can‘t evaluate that. I don‘t know the real aircraft. The F5 has btw been announced to receive a big update, I guess it‘s just not feasible to updtae it now before that. 

I'm pretty sure the A-10 won't fly without the gun.  Heck, I thought I recalled the empty casings are retained mostly to prevent the plane going out of CG limits.

Is the max gross weight for the C significantly higher than the A??  I would have thought they'd be the same, there's no airframe structural change, right?

[ASAP]

3 hours ago, jaylw314 said:

I'm pretty sure the A-10 won't fly without the gun.  Heck, I thought I recalled the empty casings are retained mostly to prevent the plane going out of CG limits.

Is the max gross weight for the C significantly higher than the A??  I would have thought they'd be the same, there's no airframe structural change, right?

It’s the same gross weight. The only thing they did was add in a lot of wiring and replaced some of cockpit components with computers. Whatever weight difference is negligible. Engines didn’t change at all. 
 

the aircraft cannot fly without the gun, they can fly without bullets but they add in ballast plates in the nose to compensate so there’s not much of a difference in gross weight either. 
 

the interesting part of the demo video is the pilots first ops check when he calls out he’s only got like 3000 lbs of fuel. That’s why he’s so much more maneuverable and has so much G available. 

Edited August 16, 2022 by ASAP

[jaylw314]

2 hours ago, ASAP said:

the aircraft cannot fly without the gun, they can fly without bullets but they add in ballast plates in the nose to compensate so there’s not much of a difference in gross weight either. 
 

LOL, neat! 

[Ephedrin]

vor 23 Stunden schrieb ASAP:

they can fly without bullets but they add in ballast plates in the nose

Yep but that‘s still a huge difference to what we do with 1150 live rounds. ^^ 

 

good to know that A and C have the same weight though, thanks!

[ASAP]

5 hours ago, Ephedrin said:

Yep but that‘s still a huge difference to what we do with 1150 live rounds. ^^ 

 

good to know that A and C have the same weight though, thanks!

I have no idea how much each ballast plate weighs but they sure look pretty heavy. Although… they are far forward of where the ammo drum is (in the nose gear well vs the ammo drum aft of the seat) so I’d guess that probably lets them get away with the ballast being lighter than the ammo and still keep the CG in limits. So I dunno.

[Snoopy]

We fly without ballasts at Whiteman.  Every other squadron I’ve been in we always installed them when gun was empty.

Edited August 22, 2022 by Snoopy