investigating Thrust to weight ratio: confused

[Cmptohocah]

Another thing that might verify thrust/drag, if you guys feel inspired to try it out, is a straight and level flightm, according to the manual, acceleration at 1000m altitude should be:
- 600km/h to 1100km/h in 13.5s

- 1100km/h to 1300km/h in 8.7s

Now the manual doesn't mention anything about the weight and load out, so I would assume that standard Russian setup applies here: 50% fuel 13.000kg weight with 2xR-27R and 2x73.

Edited October 7, 2021 by Cmptohocah

[Ironhand]

32 minutes ago, Cmptohocah said:

- 600km/h to 1100km/h in 13.5s

- 1100km/h to 1300km/h in 8.7s

TAS?

[Cmptohocah]

8 hours ago, Ironhand said:

TAS?

Good question.
Manual doesn't specify this, but I would say probably IAS. The difference at 1000m, between TAS and IAS, is only around 5%.

[Cmptohocah]

From the RL manual:
 

Quote

Each engine at full AB produces thrust of 8300kg...

[Ironhand]

1 hour ago, Cmptohocah said:

From the RL manual:
 

Well…isn’t that interesting…

[bkthunder]

 

Guys this must be the most interesting thread I've been involved in, and this is thanks to your contributions!

 

I carried out the test you suggested: 

 

15 hours ago, Cmptohocah said:

Another thing that might verify thrust/drag, if you guys feel inspired to try it out, is a straight and level flightm, according to the manual, acceleration at 1000m altitude should be:
- 600km/h to 1100km/h in 13.5s

- 1100km/h to 1300km/h in 8.7s

Now the manual doesn't mention anything about the weight and load out, so I would assume that standard Russian setup applies here: 50% fuel 13.000kg weight with 2xR-27R and 2x73.

 

Mig-29A 13000kg GW with 2x R27R and 2x R73

 

- 600km/h to 1100km/h in 13.5s  DCS: 15s

- 1100km/h to 1300km/h in 8.7s  DCS: 10s

 

I couldn't find a way to measure decimals of a second in TacView... 

 

Track and Tacview attached.

MiG-29A acceleration test.trk Tacview-20211008-154129-DCS.zip.acmi

[Ironhand]

1 hour ago, bkthunder said:

I couldn't find a way to measure decimals of a second in TacView... 

 

"Raw Telemetry" under the "Analysis" tab in the payware version. Don't know if the freeware version also has that available, if that's what you use.

 

Edited October 8, 2021 by Ironhand

[bkthunder]

yeah I have the free version.. well, you can check the track and get more precise timings I guess

[Ironhand]

In my own flight, the numbers from the same flight depended on whether measurements were IAS or TAS

 

TAS: 14.49 and 7.96 sec

IAS: 15.38 and 10.48 sec

[Ironhand]

Using your Tacview, I come up with the following:

 

           600--1100 k/h          1100--1300 k/h

 

TAS       14.81 s                          10.19 s

IAS        15.89 s                          15.70 s

 

Wonder why my IAS times are so different.

[bkthunder]

I was using TAS

[Ironhand]

On 10/12/2021 at 7:26 AM, bkthunder said:

I was using TAS

 

I thought as much.

It's interesting. I took all of my flights that were timed to have 13000 kg gross weight at the 600 k/h point and came up with times for the 600-1100k/h section that were roughly 1 second more than the manual's time and the 1100-1300k/h section times were consistently less. The sum of the times in the manual is 22.2 sec. The sum of my times were grouped on either side of that time from 22.0 to 22.7. When, just for chuckles, I made a flight with the 13000 kg weight at 13000k/h, the total time came to just a bit more, 22.99.

Edited October 13, 2021 by Ironhand

[Cmptohocah]

I guess we just need to wait for someone from ED to respond to our findings.

[Flappie]

19 hours ago, Cmptohocah said:

I guess we just need to wait for someone from ED to respond to our findings.

Would you mind summing it up? I started reading the thread but it's hard to follow. What exactly needs to be changed? Thrust? Drag? Weight?

[Ironhand]

4 hours ago, Flappie said:

Would you mind summing it up? I started reading the thread but it's hard to follow. What exactly needs to be changed? Thrust? Drag? Weight?

Speaking for myself, I’m not sure if there is a problem or if there is one, how big it is or what it is. Based on my limited testing, everything seems fine in terms of sustained turn rates. Thrust measured in a steep climb seems close but perhaps a bit low. Thrust measured in terms of straight line acceleration compared to the manual’s chart is lower in the 600-1100k/h speed range but greater than the chart indicates from 1100-1300k/h so that, in the end, the entire range from 600-1300k/h works out to be about right.

Again this is all based on limited testing on my end.

Edited October 14, 2021 by Ironhand
Correct typo from 800 to 600.

[GGTharos]

3 hours ago, Flappie said:

Would you mind summing it up? I started reading the thread but it's hard to follow. What exactly needs to be changed? Thrust? Drag? Weight?

Tuning to get the correct acceleration in the 600-1100kph and 1100-1300kph segments.   This can be thrust, drag or both.

[Seaeagle]

2 hours ago, GGTharos said:

This can be thrust, drag or both.

I was thinking this too - i.e. if both thrust and drag is too low for the MiG-29, then it could appear underpowered in situations where drag is minimal, about right where one equals out the other and overpowered in situations where drag becomes the biggest factor.

[Ironhand]

1 hour ago, Seaeagle said:

I was thinking this too - i.e. if both thrust and drag is too low for the MiG-29, then it could appear underpowered in situations where drag is minimal, about right where one equals out the other and overpowered in situations where drag becomes the biggest factor.

Excellent point.

[Cmptohocah]

On 10/14/2021 at 1:48 PM, Flappie said:

Would you mind summing it up? I started reading the thread but it's hard to follow. What exactly needs to be changed? Thrust? Drag? Weight?

Unfortunately I don't have access to DCS at the moment. I will re-test and verify the results and post them summed up here once done.

[Ironhand]

It occurs to me that running the full range of airspeed's in the sustained turn rate chart would probably provide the answers.

[bkthunder]

On 10/14/2021 at 1:48 PM, Flappie said:

Would you mind summing it up? I started reading the thread but it's hard to follow. What exactly needs to be changed? Thrust? Drag? Weight?

I started the thread because I think raw thrust of the MiG-29 is less than what it should be. 

We have done several tests and they all seem to show the thrust is not about 16000 kgf but around 12500-13000 kgf, as you can see in this and following  posts:

On 10/6/2021 at 11:23 AM, bkthunder said:

 

So I *think* I tested this correctly. 

 

Mig-29A

total Mass: 13770Kg

Flaps up in all tests to reduce drag.

 

first I tested the ground friction as you suggested. 

 

Initial speed: 35 m/s

final speed after 10 seconds: 31.3 m/s

= -0.38 m/s2 deceleration

13770 x -0.38 = -533.58 kgf

 

 

Acceleration test - measurement started when in full AB and no brakes. 

Initial speed: 39.8 m/s

final speed after 10 seconds: 125.2 m/s

= 8.54 m/s2 acceleration

13770 x 8.54 = 11991.57 kgf + 533.58 = 12525.15 kgf

 

 

So:

 

- 12500 kgf vs 16600 kgf (static thrust)

- 12500 kgf vs 16000 kgf according to the chart below

 

 

 

Conclusion: 

 

The MiG-26A lacks 4000 kgf of thrust. 

Can someone confirm my calculations are correct? 

 

 

Thanks

 

  

 

To make things more interesting, it seems also other airplanes are far below the supposed thrust range, but we don't have detailed data for installed thrust as we have for the MiG-29 so, it's hard to tell. What is confirmed is that the MiG-29 has the worst thrust and climb performance compared to F-18, F-16 and F-15, given a GW that should provide the same T/W ratio for all.

The turn rate tests IMO are not very useful because, as someone pointed out again, if the drag is lower than it should be, then with less thrust it could be possible to have correct turn performance. 

Edited October 22, 2021 by bkthunder

[jackmckay]

Interesting topic, I must say. What came to my mind is the number on far end of speed charts.

At max speed in level flight engine T/W ratio is in equilibrium with airframe drag reaching terminal velocity. Weight is irrelevant in this case as it is in equilibrium with lift and matching AoA at max speed conditions to maintain level flight and more weight can only decrease acceleration to terminal. All test subjects are supersonic so airframes are drag polished up for that regimes meaning that all are in same league.

Since initial test were framed in conditions of pure vertical 90deg climb acceleration measurement at T/W>1 (1.2), there should be correlation with airframe max speed (doesn't matter IAS or TAS as those are atmosphere dependent) to evaluate engine performance eliminating lift vectors gain from airfoil in vertical acceleration or climb records in lower climb angles. That's why AoAs are probably different for each climb record but that's not the focus here. There is also factor of different drag values at AoA sweep per airframe that could indicate loss of kinetic energy in turns which is also out of scope of this test. Also there is a factor of engine economy, meaning that the more fuel is consumed the less weight is to counter at climb envelope which means that T/W ratio is accelerated on thirstier engines.

In pure vertical climb free body diagram, lift is replaced with thrust force countering the gravity force, and booth the drag and thrust are altitude codependent.

What this test simplified looks like, for me, is pure rocket climb test, core engine power against gravity at same T/W start conditions enabling positive acceleration.

 

If some airframe has greater max speed and lower fuel economy, doesn't that indicates better acceleration at T/W ratios greater than 1, considering engine max performance already proved against supersonic drag?

 

Edited November 1, 2021 by jackmckay

[Cmptohocah]

Comparing engine thrust from the manual to real-life performance

In this RL MiG-29 takeoff video, it takes a Fulcrum weighing around 13300kg 14000kg (11000kg EW + 3000kg fuel) to accelerate from 100km/h to 200km/h around 3.76s at MIL power (max dry thrust), which gives an acceleration of around 7.39m/s^2 and calculated thrust (per engine) of around 5010kgf 5272kgf.

This is slightly above what manual states This verifies the value from the manual which states that at MIL power, each engine should provide 5040kgf.

I guess now it would be a matter of performing the same test in DCS now.

JavaScript code used for calculations:

const g = 9.81; // m/s^2

const m = 14000; // [kg]

const framesToSecond = frame => frame / 25;

const kphToMs = kph => kph / 3.6;

// 00seconds:00frame
const deltaT = (t0, t) => {
  const time = t.split(':');
  const time0 = t0.split(':');
  
  return (parseInt(time[0], 10) + framesToSecond(parseInt(time[1], 10))) - (parseInt(time0[0], 10) + framesToSecond(parseInt(time0[1], 10)))
};

const dt = deltaT('02:03', '05:22');

const v0 = 100; // [km/h]
const v = 200;  // [km/h]

const a = (kphToMs(200)-kphToMs(100))/dt;

const f = m * a;

const thrustEngine = f / g / 2;

console.log('It takes MiG-29 weighing ' + m + 'kg, ' + dt + 'seconds to accelerate from ' + v0 + 'km/h to ' + v + 'km/h.');
console.log('Acceleration is ' + a.toFixed(2) + 'm/s^2. Single engine thrust equals ' + Math.round(thrustEngine) + 'kgf.');

Output:

• "It takes MiG-29 weighing 13300kg, 3.76seconds to accelerate from 100km/h to 200km/h."
• "Acceleration is 7.39m/s^2. Single engine thrust equals 5008kgf."
• "It takes MiG-29 weighing 14000kg, 3.76seconds to accelerate from 100km/h to 200km/h."
• "Acceleration is 7.39m/s^2. Single engine thrust equals 5272kgf."

Edited November 1, 2021 by Cmptohocah
Fixed calculation error.

[stefasaki]

I don’t think that the current discrepancy is enough to start a rework... afterall it is within 5% in most circumstances. Also experience tells us that not much has been done even in cases of obvious and ridiculous differences in acceleration for FC3 aircraft (su-27.....there’s already a thread on this) so I am afraid that nothing will come out of this... the only difference here is that the performance charts are public domain and it’s easy to point out various errors, as opposed to the flanker. Actually I appreciate the level of detail in the fulcrum’s flight model, it’s one of the most detailed (and accurate) ones and actually depends on temperature, which has a huge impact on acceleration and top speed (at the moment a lot of modules, like the f-15 for example, are not influenced at all by this).

[Cmptohocah]

41 minutes ago, stefasaki said:

I don’t think that the current discrepancy is enough to start a rework... afterall it is within 5% in most circumstances. Also experience tells us that not much has been done even in cases of obvious and ridiculous differences in acceleration for FC3 aircraft (su-27.....there’s already a thread on this) so I am afraid that nothing will come out of this... the only difference here is that the performance charts are public domain and it’s easy to point out various errors, as opposed to the flanker. Actually I appreciate the level of detail in the fulcrum’s flight model, it’s one of the most detailed (and accurate) ones and actually depends on temperature, which has a huge impact on acceleration and top speed (at the moment a lot of modules, like the f-15 for example, are not influenced at all by this).

A this point max. we can do is to report and hope for the best.

Would be great if you can share some critique on the test methods. If I remember corectly you have a background in aerodynamics. 

Our preliminary results show a difference that is close to 20% compared that of the manual.

Edited November 5, 2021 by Cmptohocah