investigating Thrust to weight ratio: confused

[Exorcet]

12 hours ago, Exorcet said:

Or cutting the engines at high speed at a given altitude and using the deceleration to measure drag directly.

So I did a quick version of this test by cutting engines at 600 knots 30000 ft and timing 500-450 knots. As I thought the FC3 planes were able to keep autopilot running without engines, but the FF planes were more problematic. The F-16 was able to nearly hold altitude so I took down the number. The F-18 went out of control.

 

F-15: 13 seconds

F-16: 21 seconds

MiG: 22 seconds

 

So it seems like the MiG might be similar to the F-16 in terms of drag subsonically. The F-15 is a brick for some reason.

[NineLine]

On 9/5/2021 at 11:10 AM, bkthunder said:

The trk exceeds the allowable file size, can you suggest a sharing service that doesn't require to sign up?

https://wetransfer.com/ works well, but you may want to ping me as the upload is time limited.

[bkthunder]

https://we.tl/t-nLhQ55Bwst

 

I PMd you as well

[Seaeagle]

On 9/16/2021 at 3:44 PM, Wizard_03 said:

Empty T/Ws with AB

 

F-15C - 1.69

X2 F100-PW-220 @ 47540lbs combined

empty weight - 28000lbs 

 

 

F-16C BLK 50 no CFTs - 1.58

X1 F110-GE-129 @ 28984lbs

empty weight - 18238lbs

 

 

F/A-18C - 1.53

X2 F404-GE-402 @ 35400lbs combined

empty weight - 23000lbs

 

 

MiG-29A - 1.51 

X2 RD-33 @ 36680lbs combined

empty weight - 24251lbs

 

Sources: wiki/F-16.net

A little nitpick on the values there:

 

IIRC the F-18 and MiG-29 have the same empty weight almost down to kilo - some 10800 kg ~ 23800 lb, while the max engine output in AFB is:

 

2 x 16000 lbf ~ 2x 7257 kgf for F404-GE-400 equipped F/A-18A and F/A-18C(up to Lot 15)

 

2x 17700 lbf ~ 2x 8022  kgf for F404-GE-402 EPE (F/A-18C from Lot 15 and up)

 

2x 8300 kgf ~ 2x 18300 lbf for the RD-33 (MiG-29 9.12 and 9.13)

 

So the MiG-29 does have a TWR advantage over the Hornet and for the early ones a significant one. Earlier F-16 versions also had engines with a lower thrust rating (IIRC some 23000 lbf), so maybe this also has something to do with this..

On 9/16/2021 at 3:44 PM, Wizard_03 said:

 

Take these with a grain of salt but it seems I was wrong the MiGs perceived performance advantage may have a lot more to do with lift then thrust. Very interesting. 

 

(F-15 though  lol)

...i.e. that the MiG-29 performance advantage stems from a time where it was more pronounced compared with  contemporary adversaries.  The F-15 is a different story of course, but then its also really in a different class.

 

 

 

[Wizard_03]

1 hour ago, Seaeagle said:

A little nitpick on the values there:

 

IIRC the F-18 and MiG-29 have the same empty weight almost down to kilo - some 10800 kg ~ 23800 lb, while the max engine output in AFB is:

 

2 x 16000 lbf ~ 2x 7257 kgf for F404-GE-400 equipped F/A-18A and F/A-18C(up to Lot 15)

 

2x 17700 lbf ~ 2x 8022  kgf for F404-GE-402 EPE (F/A-18C from Lot 15 and up)

 

2x 8300 kgf ~ 2x 18300 lbf for the RD-33 (MiG-29 9.12 and 9.13)

 

So the MiG-29 does have a TWR advantage over the Hornet and for the early ones a significant one. Earlier F-16 versions also had engines with a lower thrust rating (IIRC some 23000 lbf), so maybe this also has something to do with this..

...i.e. that the MiG-29 performance advantage stems from a time where it was more pronounced compared with  contemporary adversaries.  The F-15 is a different story of course, but then its also really in a different class.

 

 

 

Yeah I don't 100 percent trust these figures either, for sure, it was just a quick Google search. 

 

We also have charts for everything BUT the 402 hornet so I wouldn't be surprised at all if the actual static thrust figure is different as well. It was just surprising to me that MIG isn't firmly at the top of that list considering the seat of the pants feeling but it just goes to show the truth is always more complicated.

 

It certainly feels like a rocket compared to the hornet and viper but clearly that's not the whole story 

Edited September 19, 2021 by Wizard_03

[KenobiOrder]

On 9/15/2021 at 6:14 PM, GGTharos said:

Well, if you consider testing like this alone, you're exactly right, you have to somehow remove drag from the equation.

But, you can't even really guarantee that the thrust you're getting is correct.

 

So, at slow speed drag is pretty much not that big of a deal, right?  But at the same time the motors lose a lot of thrust when installed and at slow speed.

 

What we do have or well, ED has for the F-18 and F-16 are acceleration charts.  The eagle and miG-29 have them too, and I'm sure those two aircraft match their charts quite well.  I don't know about the other two though.

My suspicion is that it has something to do with induced drag, but it could be alot of things. Ive tested straight line drag in the hornet and it seemed to check out. But in dogfights right now its out-rating everything...and not by a little bit. It also has absurd energy retention...or something. Right now in competitive groups the hornet is basically dominating everything, including the Eagle and even in energy fights at higher altitudes.

[NineLine]

20 hours ago, bkthunder said:

https://we.tl/t-nLhQ55Bwst

 

I PMd you as well

Thanks, as busy as this weekend has been, I needed to two reminders

[bkthunder]

Yet the point is really quite simple, at least in my tests: 

 

All aircraft were set for a 1.2 T/W ratio. That means they should all maintain airspeed if not slightly accelerate when in a vertical climb. 

Drag is definitely part of the equation, but not at the very low speed at which I tested and certainly cannot justify the MiG-29 bleeding speed rapidly in all scenarios, while all other airplanes gain airspeed in the same conditions, with same T/W ratio. 

 

So IMO it might well be the MiG-29 has a lower thrust than it should have, but also lower drag and higher lift than it should have, which can explain why the top speed and horizontal acceleration are ok, while in a climb it performs far below the rest. 

 

 

 

 

[GGTharos]

If there are low altitude acceleration charts for the MiG-29, you can easily find out if the engine power is correct or not.

[draconus]

3 hours ago, bkthunder said:

All aircraft were set for a 1.2 T/W ratio.

Which is only true for max thrust on paper.

Real values are here on page #11:

https://www.digitalcombatsimulator.com/upload/iblock/dcc/DCS FM principles plus MiG-29 P-47 F-16.pdf

[bkthunder]

18 hours ago, draconus said:

Which is only true for max thrust on paper.

Real values are here on page #11:

https://www.digitalcombatsimulator.com/upload/iblock/dcc/DCS FM principles plus MiG-29 P-47 F-16.pdf

 

So, if I understand correctly: 

 

• I have tested at sea level, so I take the H=0 line - correct?

If yes:

• In the first test, I start to pull up at 300 KCAS / 0.46M  = 8000 Kgf x2 = 16000 Kg of thrust = 35273lb vs GW of 30358lb set in the mission. T/W ratio of 1.16
• In the second test, I started at 200 KCAS / 0.3M = 7700 Kgf x2 = 15400 Kg of thrust. 33951 lb vs GW of 30358 set in the mission. T/W ratio of 1.12

In both test I am well above a T/W ratio of 1, so especially in the second low-speed test the aircraft should maintain speed for a bit while climbing. It doesn't. 

 

 

Edited September 26, 2021 by bkthunder

[Cmptohocah]

@bkthunder if you would like to check MiG-29A's trust to drag ratio, you can perform tests for sustained turn rates and compare them to the RL manual.
Total mass of the airplane should be 13.000 kg and turns performed with max afterburner (A2A stores play no role).

Horizontal axis is indicated airspeed in km/h and the vertical axis in the normal load expressed is Gs.
For example: at 5km altitude you should be able to sustain 6.5G at around 860km/h, or at 8km alt 4.5G at around 730km/h.

Edited September 26, 2021 by Cmptohocah
Forgot to add second altitude reference.

[draconus]

Maybe we can ask @Yo-Yo for an explanation?

[Spurts]

What is your speed at the END of the pull up?  At sea level 200KTAS is still ~1100lb of drag, 250KTAS is ~1700 and 300KTAS is ~2500 (assuming 0.02 Cdo, ballpark for standard config fighters)

[NineLine]

19 hours ago, draconus said:

Maybe we can ask @Yo-Yo for an explanation?

I've asked him to take a look here, but he did say he doesnt believe there is an issue, I will bump this thread to him.

[GGTharos]

On 9/26/2021 at 1:26 PM, bkthunder said:

In both test I am well above a T/W ratio of 1, so especially in the second low-speed test the aircraft should maintain speed for a bit while climbing. It doesn't. 

 

 

The margins when considering drag are narrow.  How long would you expect it to climb before altitude-induced loss of thrust occurs?  Are you looking at CAS or TAS?

[Ironhand]

On 9/26/2021 at 1:26 PM, bkthunder said:

…In both test I am well above a T/W ratio of 1, so especially in the second low-speed test the aircraft should maintain speed for a bit while climbing. It doesn't…

I wonder if it’s a question of methodology. About a year ago Grim Reapers tested climb rate (Fast Jets: Max Comparable Climb Rate) to see which of the DCS jets made it to altitude the quickest. The MiG-29 was the winner. Not the same thing, I know but…

[Ironhand]

It seems to have a positive TW ratio. I increase speed up until about 1500m altitude, then it starts to slowly drop. TRK attached.

MiG-29 TW Ratio.trk

[bkthunder]

22 hours ago, GGTharos said:

 

The margins when considering drag are narrow.  How long would you expect it to climb before altitude-induced loss of thrust occurs?  Are you looking at CAS or TAS?

All other aircraft tested were accelerating up to about 6000ft, then the thrust decreases. The MiG-29A drops speed immediately. 

[GGTharos]

The 29's motors have fairly poor performance at slow speeds IIRC.  Anyone someone posted the thrust curves here, I don't know how that lines up against your tests.

[Ironhand]

20 minutes ago, bkthunder said:

All other aircraft tested were accelerating up to about 6000ft…

I accelerated up to around 5000 ft, if I’m doing the conversion right. I believe my initial starting speed was much lower than yours, though.

 

Edit: Just checked. After the pull, my airspeed dropped to TAS 314 km/hr. It then slowly increased to 346 with a climb angle of roughly 70-75 degrees depending on the AoA.

Edited September 28, 2021 by Ironhand

[bkthunder]

3 hours ago, Ironhand said:

It seems to have a positive TW ratio. I increase speed up until about 1500m altitude, then it starts to slowly drop. TRK attached.

MiG-29 TW Ratio.trk 47.75 kB · 2 downloads

 

17 minutes ago, Ironhand said:

I accelerated up to around 5000 ft, if I’m doing the conversion right. I believe my initial starting speed was much lower than yours, though.

 

 

You have run the test with 25% fuel, giving you a GW of 26264 lb and a T/W ratio of 1.3. 

I tested with a T/W ratio of 1.2 (80% fuel). 

 

But again this shows my point even more. 

In your test with 25% fuel the MiG-29 still has far worse performance than any of the other planes I tested with a T/W ratio of 1.2. You gained 3-4 knots vertically which stopped at around 3500ft. 

31 minutes ago, GGTharos said:

The 29's motors have fairly poor performance at slow speeds IIRC.  Anyone someone posted the thrust curves here, I don't know how that lines up against your tests.

 

 

This is how it lines up:

On 9/26/2021 at 7:26 PM, bkthunder said:

 

So, if I understand correctly: 

 

• I have tested at sea level, so I take the H=0 line - correct?

If yes:

• In the first test, I start to pull up at 300 KCAS / 0.46M  = 8000 Kgf x2 = 16000 Kg of thrust = 35273lb vs GW of 30358lb set in the mission. T/W ratio of 1.16
• In the second test, I started at 200 KCAS / 0.3M = 7700 Kgf x2 = 15400 Kg of thrust. 33951 lb vs GW of 30358 set in the mission. T/W ratio of 1.12

In both test I am well above a T/W ratio of 1, so especially in the second low-speed test the aircraft should maintain speed for a bit while climbing. It doesn't. 

 

 

 

 

[GGTharos]

So veeery ballpark but, you're going to eat a bunch of drag when you pitch up, and then you're already sunk by zero-aoa drag when you hit 1km (amd 0 aoa drag is not all you have, you have some induced).   Looks right to me, but maybe I'm not seeing the whole picture or I miscalculated.

 

Your only opportunity to accelerate or even maintain speed is between 0 and 1km, and even there your margins are slim.

Edited September 28, 2021 by GGTharos

[Ironhand]

1 hour ago, bkthunder said:

 

..But again this shows my point even more. 

In your test with 25% fuel the MiG-29 still has far worse performance than any of the other planes I tested with a T/W ratio of 1.2. You gained 3-4 knots vertically which stopped at around 3500ft…

Well…not exactly. It’s less than you expect but still positive TW ratio. If I get an opportunity this evening I’ll play around with 80% (?) fuel to see if it holds.

 

OTOH, I gained about 12 knots vertically, or more if you start counting earlier and speed stopped increasing at 1426 meters. Make sure your reading speed in TAS.

 

Edit: BTW, I‘m not implying that there isn’t an issue. Nor am I certain that there is one.

 

Edit 2: The results you get (in the MiG, anyway) will depend on how cleanly and precisely you fly it. As soon as you do anything to increase drag during the climb, you’re toast. The TRK was my 2nd attempt. My first was less clean and the results less satisfactory. And the TRK I posted was still far from clean.

Edited September 28, 2021 by Ironhand

[Ironhand]

At this point I'm not sure anyone is still interested. It took longer than I thought it would to find the time to fly and analyze the results. So everyone might have moved on.

 

I only made the single Mach 0.8 flight but, it certainly seems to coincide with the Thrust-Speed-Altitude chart posted earlier in this thread. On the surface, at least, the MiG-29's TW Ratio in flight matches the chart pretty well. Since Tacview provides fuel quantity during the flight, I used the diminishing fuel wright in the formulas for a more accurate TW Ratio. I want to note that I wasn't completely anal in trying to stop Tacview exactly on the meter mark. But I was within 30 m of the mark for each measurement.

 

 

Since BK took exception to my not using 80% fuel, I made the test flight with 80% fuel as seen in the spreadsheet. After the pull up, I started recording data once the aircraft was on the established climb angle. So it starts at 1000 meters altitude. I charted BK's flight using the Tacview he provided in his first post in the same manner, though in his case I had to start slightly before he was on his established climb angle. At that point he was already down to a 1.1 TW ratio.

 

I've attached the spreadsheet, TRK, and Tacview.

 

 

Tacview-MiG-29 TW Ratio 80pc-M 0.8.acmi MiG-29 TW Ratio 80pc-M 0.8.trk MiG-29A TW Ratio Test Flight.xlsx

Edited October 2, 2021 by Ironhand