Is acceleration performance in game wrong?

[SJ_Butcher]

I have always found that acceleration of planes is slow, even in the initial stages where you use the maximum available performance of that plane, leave alone on flight, some planes are real turds accelerating, I was always curious about how fast planes accelerate in real life, its obvius that you will accelerate faster from 250 to 350 than 350 to 450, but the numbers are low... I tried to manage some test and looking into internet I found this from a book.

 

This little test shows the maximum ideal acceleration of some planes at determinated speed, I did the same for example with the A3 and my results were garbage compared with the US Navi Evaluation which shows a best acceleration from 250-350km/h of 12km/s, I did the same and it took me 17 seconds to reach that speed an average of 5km/s what am I doing wrong? because with the big hp to weight ration that this machines have they accelerate too slow. I dont get it...

Edited March 21, 2018 by SJ_Butcher

[=EXPEND=13SchwarzeHand]

Hmm the test was done in Feb 44. Maybe this engine has a different rating then we have in game. MAybe it has teh 1.65 ata clearance.

 

Have you done the test with the G-2 too? This one was tested in July 42. So it should be more comparable to what we have in game

[SJ_Butcher]

Going to test it. But even with 1.65 ATA the difference is almost the double!

[=362nd_FS=Hiromachi]

Could you be so kind and state which book is that ? I'd be fairly interested in reading it myself.

[SJ_Butcher]

54 minutes ago, =EXPEND=SchwarzeDreizehn said:

Hmm the test was done in Feb 44. Maybe this engine has a different rating then we have in game. MAybe it has teh 1.65 ata clearance.

 

Have you done the test with the G-2 too? This one was tested in July 42. So it should be more comparable to what we have in game

 

going to test and come with the numbers

31 minutes ago, =362nd_FS=Hiromachi said:

Could you be so kind and state which book is that ? I'd be fairly interested in reading it myself.

 

sure the book name is : Fighter Aircraft Performance of WW2 By Erik Pilawskii

[Holtzauge]

14 hours ago, SJ_Butcher said:

I have always found that acceleration of planes is slow, even in the initial stages where you use the maximum available performance of that plane, leave alone on flight, some planes are real turds accelerating, I was always curious about how fast planes accelerate in real life, its obvius that you will accelerate faster from 250 to 350 than 350 to 450, but the numbers are low... I tried to manage some test and looking into internet I found this from a book.

 

This little test shows the maximum ideal acceleration of some planes at determinated speed, I did the same for example with the A3 and my results were garbage compared with the US Navi Evaluation which shows a best acceleration from 250-350km/h of 12km/s, I did the same and it took me 17 seconds to reach that speed an average of 5km/s what am I doing wrong? because with the big hp to weight ration that this machines have they accelerate too slow. I dont get it...

 

12 Km/h/s in the above table looks very optimistic but I can run a C++ simulation if you tell me the conditions you had when you measured 17 s acceleration time from 250 to 350 Km/h: I'm assuming it was IAS you had as a base? So I need to know if it was TAS or IAS and at what altitude you did the in-game test. Also weight is important: So you need to specify fuel status and armament status as well. Finally, I'm assuming you used Notleistung 1.42 ata right?

[SJ_Butcher]

I don't have the book, just a extract of it from internet, 12km/h sounds pessimistic to me, a captured plane in who knows what conditions, but as the test shows it indicates that if not specified the altitude, should be at sea level. Using always max ATA

[Holtzauge]

1 minute ago, SJ_Butcher said:

I don't have the book, just a extract of it from internet, 12km/h sounds pessimistic to me, a captured plane in who knows what conditions, but as the test shows it indicates that if not specified the altitude, should be at sea level. Using always max ATA

 

Well if you give me the conditions for your BoX test which as I understood gave an acceleration time of 17 s then I can compare that to what the C++ simulation shows.

[SJ_Butcher]

9 minutes ago, Holtzauge said:

 

Well if you give me the conditions for your BoX test which as I understood gave an acceleration time of 17 s then I can compare that to what the C++ simulation shows.

 

The conditions were:

Kuban Summer, runway, sea level.

FW190 A3, from 250 km/h to 350km/h, 15.5s an average of 6.46km/h/s.

Plane stock load out(100% fuel), 1.42 ATA

[Holtzauge]

Below is a table of the C++ results for these conditions but at 15 deg C (I use standard atmospheric conditions in the simulations) so this will be a bit faster than at summer conditions.

 

To me the results actually look pretty close: First of all the C++ simulation does not model engine spool up but an instantaneous power onset so I would add a couple of seconds to my results to take that into account: so 13.3 +2=15.3 s which is pretty much stop on.

[SJ_Butcher]

2 minutes ago, Holtzauge said:

Below is a table of the C++ results for these conditions but at 15 deg C (I use standard atmospheric conditions in the simulations) so this will be a bit faster than at summer conditions.

 

To me the results actually look pretty close: First of all the C++ simulation does not model engine spool up but an instantaneous power onset so I would add a couple of seconds to my results to take that into account: so 13.3 +2=15.3 s which is pretty much stop on.

 

How can that be close when the source I Iinked is the half of that, in 5 seconds he reached what we achieve in 15 secs

Edited March 21, 2018 by SJ_Butcher

[Holtzauge]

What I meant is that BoX seems to model this exactly the same as I do, i.e. we seem to agree on how a Fw-190A3 should accelerate.

 

The source you linked, how do you connect that to the above test results? There are no test conditions specified as far as I can see......

Edited March 21, 2018 by Holtzauge

[SJ_Butcher]

5 minutes ago, Holtzauge said:

What I meant is that BoX seems to model this exactly the same as I do, i.e. we seem to agree on how a Fw-190A3 should accelerate.

 

The source you linked, how do you connect that to the above test results? There are no test conditions specified as far as I can see......

 

and how do you know your simulation is correct? where is the formula, how do you calculate that? I bought the book recently to see the whole conditions but looks like our values are wrong.

 

 

 

 

Here are the test from FW 190 A3

[AndyJWest]

An 'extrapolated performance' of 'best anticipated acceleration' isn't test data.

[=EXPEND=13SchwarzeHand]

It‘s a simulation not a formula. I would have to say that there are a lot of unknown variables in the test you cited e.g. fuel load, what engine exactly etc...

 

If Holtzauge gets the same result, relying on a test with uncertain variables and half the measured time does not seem right.

Edited March 21, 2018 by =EXPEND=SchwarzeDreizehn

[SJ_Butcher]

Well in a part of the book the quoted IL2 forgotten battles claiming that performance there were very wrong, as soon as I have the book I will figurate what all of this means, still I don't understand how you dont think the acceleration values are way too slow

[Holtzauge]

Of course I can't say my results are a 100% correct but I also have close agreement with the Finnish accelerations tests on Me-109G2 MT-215.

 

If you want to believe my results or not SJ_Butcher I leave up to you but you asked in the OP if the game acceleration is wrong and to me it looks pretty much spot on.

 

Also, while a nice compilation of numbers on the A3 that table hardly supports the 12 Km/h/s accelerations figure just like AndyW and Schwarze13 pointed out above.

[SJ_Butcher]

But how even a car can accelerate faster than a combat plane with 1600hp, I don't get how you get those results 

[AndyJWest]

The book SJ_Butcher is citing is published by Lulu.com, an online print-on-demand, self-publishing and distribution platform.  I see no particular reason to assume that the author has any particular expertise, despite his attempts to dismiss any criticism in advance:

 

This isn't the sort of comment I'd expect to see from any academic historian, or from any expert in aircraft design. 

 

 

 

 

[=EXPEND=13SchwarzeHand]

Which car goes from 250 to 350 in 15 seconds?? If you mean the acceleration from 0 to 100, stick your head out the window at 250km/h and and at 0km/h and you will know where (at lease part of) the  difference in required power comes from

Edited March 21, 2018 by =EXPEND=SchwarzeDreizehn

[Holtzauge]

9 minutes ago, SJ_Butcher said:

But how even a car can accelerate faster than a combat plane with 1600hp, I don't get how you get those results 

 

Numerical integration to calculate acceleration is actually pretty easy and so is estimating the drag in this case. Calculating turn rates is much harder. But I get the feeling you have make up your mind about this so I think we will simply have to agree to disagree.

[SJ_Butcher]

lets continue this discussion when the books arrive and are the doubts will cleared out, I am sure that this guy can't be soo wrong

[AndyJWest]

A word of advice to SJ_Butcher: it is unwise to cite a book you haven't read. Particularly so when said book (or substantial portions of it) can be viewed online via Google Books. The author explicitly states that the formula he uses for "best anticipated acceleration... has not been broadly accepted in aerodynamic theory...". He also makes it clear that this extrapolation "represents the aircraft's maximum score" and is "not representative of the machine's behaviour over its entire flight envelope".

 

 

[Holtzauge]

Just now, SJ_Butcher said:

lets continue this discussion when the books arrive and are the doubts will cleared out, I am sure that this guy can't be soo wrong

 

Well based on the snippet from the book AndyW posted I would not be too sure about that.

[FTC_DerSheriff]

39 minutes ago, =EXPEND=SchwarzeDreizehn said:

Which car goes from 250 to 350 in 15 seconds?? If you mean the acceleration from 0 to 100, stick your head out the window at 250km/h and and at 0km/h and you will know where (at lease part of) the  difference in required power comes from

and furthermore, if we are talking about the acceleration 0-100kph in a car, you have much more friction to the medium you are accelerate on. Physics and stuff

Edited March 21, 2018 by DerSheriff

[SJ_Butcher]

11 minutes ago, DerSheriff said:

and furthermore, if we are talking 0-100, you have much more friction to the medium you are accelerate on. Physics and stuff

 

finally someone understand my point, thats initial acceleration like the data I shared...

[FTC_DerSheriff]

1 minute ago, SJ_Butcher said:

 

finally someone understand my point, thats initial acceleration like the data I shared...

No I think you didn't understood me since my wording was not really good. A car accelerates much better too 100 because the tires have a much better grip on the road compared to a propeller to air.
Air is a really bad medium to accelerate on. Therefore we need 1500hp engines in warbirds to get them going.

[216th_Jordan]

simply put:

 

Acceleration is the result of the combined force vector of an object divided by its mass.

 

F_comb = F_prop - F_dragparasitic - F_draginduced

All those forces are depending on different parameters, mostly airspeed. parasitic drag rises with airspeed while induced drag reduces with airspeed. The lowest drag is therefore at the intersection of F_dragparasitic & F_draginduced over airspeed. If the prop has the same force no matter the airspeed, the airspeed of the lowest drag will be the airspeed of the highest acceleration. But as a prop has nonlinear force characteristics and in general a quite bad efficiency at all airspeeds the value is going to lie above or below.

In other words what other have already said: accleration will be different for every airspeed and atmospheric condition.

 

 

Usually you can assume the best speed for climb to be the speed for the highest acceleration.

 

 

Edited March 21, 2018 by 216th_Jordan

[s9723]

I happen to know a post-war report that test level acceleration of several aircrafts. 

https://es.scribd.com/document/324696219/Flight-Test-Comparison

 

Their engine ratings are lower than war-time rating.

[=362nd_FS=RoflSeal]

9 hours ago, s9723 said:

I happen to know a post-war report that test level acceleration of several aircrafts. 

https://es.scribd.com/document/324696219/Flight-Test-Comparison

 

Their engine ratings are lower than war-time rating.

Seems that the P-51D was modified heavily for civilian use, obvious thing being removal of tank for a second seat, which requires a different canopy that looks draggier

 

Also on pg 53 of the document, it says the Mustang has very high elevator forces of 20lbs/g. This strikes me as very odd considering during the war, manuals said the Mustang had very light stick forces, and this is back by documents i have posted earlier which give a precise break down of elevator forces, and various other  wartime T.Os on modifying the Mustang to create heavier stick forces for the rudder and elevators as they were seen to be too light.

 

I believe this is because when flights were done with 65gal rear tank removed (as stated) but without any weights placed to bring the CG back

Edited March 23, 2018 by RoflSeal

[Holtzauge]

10 hours ago, s9723 said:

I happen to know a post-war report that test level acceleration of several aircrafts. 

https://es.scribd.com/document/324696219/Flight-Test-Comparison

 

Their engine ratings are lower than war-time rating.

 

That is an interesting figure and thanks for posting it!

 

Does the article say anything about the weight status? While drag is one issue like RoflSeal mentioned above, the weight is another big factor in this so it would be good to know how heavy the planes used in the tests were. Also the engine power used in the test: It's one thing what the engine is rated for and another what was actually used in the tests.

[s9723]

2 hours ago, Holtzauge said:

 

That is an interesting figure and thanks for posting it!

 

Does the article say anything about the weight status? 

Yes, table 1 mentions takeoff weight in the test. 

 

Both P-47 and F4U have wing pylons (one each wing).

 

Acceleration test were conducted using METO power. I think that mean normal (continuous) rating of the engine. 

 

~1625HP for r-2800

 

 

Edited March 23, 2018 by s9723

[Panthera]

2 hours ago, RoflSeal said:

Seems that the P-51D was modified heavily for civilian use, obvious thing being removal of tank for a second seat, which requires a different canopy that looks draggier

 

Also on pg 53 of the document, it says the Mustang has very high elevator forces of 20lbs/g. This strikes me as very odd considering during the war, manuals said the Mustang had very light stick forces, and this is back by documents i have posted earlier which give a precise break down of elevator forces, and various other  wartime T.Os on modifying the Mustang to create heavier stick forces for the rudder and elevators as they were seen to be too light.

 

I believe this is because when flights were done with 65gal rear tank removed (as stated) but without any weights placed to bring the CG back

 

They don't need to change the canopy to add the seat, they just need to remove the rear tank and wartime radio equipment.

 

This is the Mustang in question:

http://www.warbirdregistry.org/p51registry/p51-4511586.html

 

 

 

 

2 hours ago, Holtzauge said:

 

That is an interesting figure and thanks for posting it!

 

Does the article say anything about the weight status? While drag is one issue like RoflSeal mentioned above, the weight is another big factor in this so it would be good to know how heavy the planes used in the tests were. Also the engine power used in the test: It's one thing what the engine is rated for and another what was actually used in the tests.

 

It's quite interesting to note the similar take off distance between the P-47 & P-51 too.

 

That said I think there can be little doubt that the aircraft weren't run at max power, and since the data was all KIAS as well it's sadly next to impossible to determine anything precise from it :-/

Edited March 23, 2018 by Panthera

[unreasonable]

8 hours ago, s9723 said:

Yes, table 1 mentions takeoff weight in the test. 

 

Both P-47 and F4U have wing pylons (one each wing).

 

Acceleration test were conducted using METO power. I think that mean normal (continuous) rating of the engine. 

 

~1625HP for r-2800

 

 

 

ETO = Emergency Take Off : see bottom right in second table. Question is does the M in METO mean "Military" or "Modified"? (Or Monday's"?)  I would guess Military. 

[GridiroN]

Planes used to accelerate MUCH faster before the FM re-do...

[s9723]

8 hours ago, unreasonable said:

 

ETO = Emergency Take Off : see bottom right in second table. Question is does the M in METO mean "Military" or "Modified"? (Or Monday's"?)  I would guess Military. 

 

AFAIK, METO means "Maximum Except for Take Off".

Edited March 24, 2018 by s9723

[Dakpilot]

As said above METO is maximum except for takeoff, generally nowadays it is referred as MCP maximum continuous power

 

I actually remember the first time I got to say the phrase to my flight engineer, calling for METO power on climb out after take off (having read it so many times in manuals and listened to my  Captain's use it) 

 

but I am a bit sentimental and sometimes childish like that so it sticks in the memory  

 

Cheers, Dakpilot

[Holtzauge]

20 hours ago, s9723 said:

Yes, table 1 mentions takeoff weight in the test. 

 

Both P-47 and F4U have wing pylons (one each wing).

 

Acceleration test were conducted using METO power. I think that mean normal (continuous) rating of the engine. 

 

~1625HP for r-2800

 

 

 

I ran a C++ simulation for the P-47 acceleration at 10,000 ft with the additional data you provided, and taking the same speeds as was in the OP, i.e. going from 250 to 350 Km/h IAS (135 to189 KIAS) or from 301.5 to 422.1 Km/h TAS as I need to input it into the code, I get an acceleration time of 43 s which looks about right if you compare to the figure you posted earlier.

 

So thanks again for the data: This is really helpful for tweaking and validating the C++ modeling and since detailed acceleration data is much more scarce than speed and climb data, this type of info is gold when you can get it!

 

So this only strengthens my belief that there is nothing wrong with the in-game Fw-190 A3 acceleration since the result I posted here tabs pretty well with the one we have in-game.

Edited March 24, 2018 by Holtzauge

[SJ_Butcher]

Just now, Holtzauge said:

 

I ran a C++ simulation for the P-47 acceleration at 10,000 ft with the additional data you provided, and taking the same speeds as was in the OP, i.e. going from 250 to 350 Km/h IAS (135 to189 KIAS) or from 301.5 to 422.1 Km/h TAS as I need to input it into the code, I get an acceleration time of 43 s which looks about right if you compare to the figure you posted earlier.

 

So thanks again for the data: This is really helpful for tweaking and validating the C++ modeling and since detailed acceleration data is much more scarce than speed and climb data, this type of info is gold when you can get it!

 

So this only strengthens my belief that there is nothing wrong with the in-game Fw-190 A3 acceleration since the result I posted here tabs pretty well with the one we have in-game.

 

Could you share your code? 

[Nocke]

On 21.3.2018 at 10:23 PM, 216th_Jordan said:

simply put:

 

Acceleration is the result of the combined force vector of an object divided by its mass.

 

F_comb = F_prop - F_dragparasitic - F_draginduced

All those forces are depending on different parameters, mostly airspeed. parasitic drag rises with airspeed while induced drag reduces with airspeed. The lowest drag is therefore at the intersection of F_dragparasitic & F_draginduced over airspeed. If the prop has the same force no matter the airspeed, the airspeed of the lowest drag will be the airspeed of the highest acceleration. But as a prop has nonlinear force characteristics and in general a quite bad efficiency at all airspeeds the value is going to lie above or below.

In other words what other have already said: accleration will be different for every airspeed and atmospheric condition.

 

 

Usually you can assume the best speed for climb to be the speed for the highest acceleration.

 

 

just curious: is it really drag force, or drag coefficient thats plotted here? Is it possible that drag forces decreases with speed, at least in a certain speed range?