Spit IX - max level speed at sea level?

Hi mate, yeah SoW is looking very seriously at DCS now... we're all playing DCS regularly and exploring what options there might be for an SoW-style campain/ server.

 

The sooner the better Phil! :pilotfly:

 

OD

Official testing is done with 18lb boost, 3000rpm and radiator flap closed (minimum drag position).

 

So that is what I have used throughout.

 

Runs are 5mins below 50' ASL, rad in auto.

 

First one rad open: 318 mph.

 

Second one rad closed: 333 mph.

 

Official speed testing is always done with the rad. closed.

 

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Official testing is done with 18lb boost, 3000rpm and radiator flap closed (minimum drag position).

So that is what I have used throughout.

Runs are 5mins below 50' ASL, rad in auto.

First one rad open: 318 mph.

Second one rad closed: 333 mph.

Official speed testing is always done with the rad. closed.

..

 

I agree that 330 is possible with rad set to auto, as per my second video.

However, that said, I was unable to get 330 with the radiator set to auto, unless I used lower RPM (or a dive) to get past the 315 mark though, then, once past about 320 I could get 330.

 

Also, you should do the tests over the black-sea water, not land. Land is above sea level (and at higher altitudes you can get more speed, until about FTH), and you will be able to get much closer to sea-level over the water. The Black sea is at 0m AMSL.

 

See this:

Edited February 21, 2017 by philstyle

I agree that 330 is possible with rad set to auto, as per my second video.

However, that said, I was unable to get 330 with the radiator set to auto, unless I used lower RPM (or a dive) to get past the 315 mark though, then, once past about 320 I could get 330.

 

Also, you should do the tests over the black-sea water, not land. Land is above sea level (and at higher altitudes you can get more speed, until about FTH), and you will be able to get much closer to sea-level over the water. The Black sea is at 0m AMSL.

 

See this:

 

I'm at 18' ASL, how low do you want me to go?

 

14' ASL.

 

 

 

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Edited February 21, 2017 by Holbeach

I'm at 18' ASL, how low do you want me to go?

14' ASL.

..

 

Grass in the radiator please! :megalol:

I'm at 18' ASL, how low do you want me to go?

 

14' ASL.

 

 

 

..

 

Hi Holbeach,

 

To add to Phil's point, the land undulates and has obstacles, so to run level to test sustained best speed for 15 minutes +, the sea provides a much more equal and sound test environment.

It is too easy to move up and down more over the land, which can alter results. I can easily get to speeds higher than 330 mph for a while if the nose is almost unperceptively slightly down, but I try and resist logging such speed and take the level at which I can truly sustain for a good amount of time. So, if I occasionally make 335, 332 or 331 mph, but never drop below 330 for a long period and 330 is the lowest most common figure, then I call it 330 as my best sustained speed. Of course, this is just me testing my way in DCS and I am not claiming real life conditions, just trying to get the best in DCS.

Following real life tests at 3000 rpm never seems to work for me in simulators. Also, I seem to remember reading somewhere that, for some technical mathematical reason, real life 3000 rpm will not give best sped at sea level anyway (perhaps someone with more knowledge could chime in on this one as I may be remembering it wrong). So perhaps whatever the 3000 rpm max speed figure is, we should be able to go faster at a slightly lower rpm anyway.

 

Happy landings,

 

56RAF_Talisman

Grass in the radiator please! :megalol:

 

You can't get rid of me like that. That grass will slow me down.

 

Talking of radiators.

 

Our Spit is fitted with an air filter.

This reduces sea level speed by 3 mph and high alt. around 16 mph. (when not used).

This would make up the difference below the 336 mph on the Boscombe Down tests.

 

I think the team have done a good job on this one. :thumbup:

 

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Interesting that you have the carb intake fully back.

I can get 330 mph with it full forward, do you see an air-speed gain in having it back?

 

Hi Phil,

 

Real life manual says forward for take off and landing (filter activated to protect engine from dust and crap, particularly at make-shift airfields), and lever back to de-activate filter in flight. I have presumed that with the filter in operation, as for take off and landing, there would be more drag. Therefore I have assumed that with the filter de-activated (lever fully back) the aircraft will travel faster. But perhaps I am wrong about this. Perhaps someone with accurate knowledge could chime in on this point and educate some of us.

 

P.S. I have not speed tested with carb intake lever full forward.

 

Happy landings,

 

56RAF_Talisman

Hi Holbeach,

 

To add to Phil's point, the land undulates and has obstacles, so to run level to test sustained best speed for 15 minutes +, the sea provides a much more equal and sound test environment.

 

Happy landings,

 

56RAF_Talisman

 

Nice try RAF, but where I go it's at 0' ASL and is as flat as the sea, in fact it is just green sea and is easier to maintain a rock solid speed, no fluctuation until the petrol runs out.

 

Regards..

Nice try RAF, but where I go it's at 0' ASL and is as flat as the sea, in fact it is just green sea and is easier to maintain a rock solid speed, no fluctuation until the petrol runs out.

 

Regards..

 

Fair enough. Looking at your screenshots in full-screen it is clear you're not flying over elevated terrain :)

Intersting stuff about the Carb-air Talisman.

 

 

Holbeach and Talisman:

 

So, maybe time for another, final test!

 

If I can maintain 333mph with the carb-air lever back, 18lb and 2850rpm or so with the radiator set to the "auto" position then this would make perfect sense given the -3mph penalty from the air-filter - (the target speed from Boscombe Down without the filter being 336).

I don't understand why I cant find more speed benchmarks and cruise speed benchmarks with lower RPM Ranges it is allways 3000 RPM. hopefully we will get some benchmarks that where taken from the fighter collections plane.

Intersting stuff about the Carb-air Talisman.

 

 

Holbeach and Talisman:

 

So, maybe time for another, final test!

 

If I can maintain 333mph with the carb-air lever back, 18lb and 2850rpm or so with the radiator set to the "auto" position then this would make perfect sense given the -3mph penalty from the air-filter - (the target speed from Boscombe Down without the filter being 336).

 

I am using the latest patch to DCS version 1.5. The map I use is the Spitfire in-game instant mission named 'Free Flight'. I spawn in with the air-start, drop slowly down over the sea and start testing. Always the same place, as sometimes it seems to me I get different results from different maps. I can't do another test today, but if anyone else is able to test on the same map with the same DCS version 1.5, over the sea, then we might actually be able to check apples with apples. Also, perhaps at least 10 to 15 minutes for the test from the point the speed reaches what appears to be a sustainable speed.

 

Happy landings,

 

56RAF_Talisman

I don't understand why I cant find more speed benchmarks and cruise speed benchmarks with lower RPM Ranges it is allways 3000 RPM. hopefully we will get some benchmarks that where taken from the fighter collections plane.

 

I can only guess that the manufacturers needed to test all engines with the same set of parameters and 3,000 rpm was the max rpm for the engines, so it made sense to test each time at max rpm for comparison purposes as engine types were modified and/or advanced. I also guess that using 3,000 rpm provided something of an additional stress test in real flight.

I stand to be corrected, but I don't think we are aware of the fine detail of how each different nation or manufacturer tested best sea level speed. For example, did they do a timed trial over a long course like the Schneider Trophy, or did the pilot just read his instruments in flight over a period of time (what period of time might that be?), write them down and then work out an average? Or perhaps the highest speed at any one time was claimed? For all we know we may be comparing apples with oranges as far as test procedures, results and max sea level speed claims are concerned between different nations and manufacturers. Remember the old adage of "lies, damn lies and statistics", lol. Was there some international rule for speed tests followed by all of both the Axis and Allied nation powers?

Finally, I am still not convinced that a propeller configured for full power max rpm (3,000 in this case) will deliver the fastest possible sustained speed a sea level. But I stand to be corrected. I would love for someone with more concrete knowledge to contribute to this thread.

As for DCS, I suspect that they do their best to gather as much reliable data as possible, apply the mathematics and science and then make reasonable decisions as expert and knowledgeable people for each model. We then give them our feedback and they have to decide how much to take that into account. A hard job to do well I think, but I am grateful for the developers work and passion.

 

Happy landings,

 

56RAF_Talisman

ISA - that's the key point, because all tests was reduced to ISA.

 

Many thanks Yo-yo, but I could not open to view the youtube clip.

 

However, found this:

 

http://www.universalweather.com/blog/2014/09/international-standard-atmosphere-how-it-affects-flight-understanding-the-basics/

 

As a side note, the following is an interesting extract:

 

"Be aware that aircraft may not perform exactly as listed in the manufacturer’s tables, and some sort of bias may need to be factored in."

 

I would not want the above to be a red herring to this discussion, but I find it interesting that, even in the modern day, there is a caution against aircraft manufacturers bias, LOL.

 

Happy landings,

 

56RAF_Talisman

Whichever way you look at it, the Spitfire is an absolute beauty.

 

18lbs, 3000 rpm, rad flaps closed. 333 mph sustained @ Sea Level, standard ats.

 

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Edited February 23, 2017 by Holbeach

ISA - that's the key point, because all tests was reduced to ISA.

I only perused the thread, but was about to say that. Every time I see you people talking about speeds always forget to say in which conditions that took place.

 

 

Just as a reminder, IAS = TAS @ SL (but sea level, not 500, 200 or 1000 ft), only when atmosphere is set to standard values, 15º Celsius, 1013,25Mb(= 29,92" Hg = 760mm Hg , I guess in DCS ME).

Any other values means not only IAS ≠ TAS, but TAS can be either higher or lower than current IAS.

 

 

Whenever you all make a test with a same atmospheric values you can start comparing those max. speeds you get, but not sooner.

 

 

Whichever way you look at it, the Spitfire is an absolute beauty.

Whichever atmosphere, that's out of discussion :D.

 

 

S!

Just as a reminder, IAS = TAS @ SL (but sea level, not 500, 200 or 1000 ft), only when atmosphere is set to standard values, 15º Celsius, 1013,25Mb(= 29,92" Hg = 760mm Hg , I guess in DCS ME).

Any other values means not only IAS ≠ TAS, but TAS can be either higher or lower than current IAS.

!

 

This has been taken account of in the discussion. In the videos the effect of termperature, air pressure and altitude is mentioned a few times.

 

And, the differences are really almost negligable at low altitude.

For example:

At 5 degrees C, 950 Hpa outside air pressure a 320 mph IAS is 325 TAS

At 35 degrees C, 1050 Hpa outside air pressure the same 320 IAS is now 327 TAS

 

So, even with a 30 degree air-temp change and 100 HPa difference, it's only 2mph variation between IAS to TAS conversion.

 

You need to really hammer the temps or the air pressure to throw the calibration out. Climbing by 1000 feet has more than triple the effect than simply moving about the map globally or conducting the test on a warmer day.

Edited February 22, 2017 by philstyle

All of my tests were done at standard values.

 

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You need to really hammer the temps or the air pressure to throw the calibration out. Climbing by 1000 feet has more than triple the effect than simply moving about the map globally or conducting the test on a warmer day.

Well, as this is a simulator it depends on the settings you use in ME, but IRL warmer days means usually also lower pressures, and no, it's a huge difference flying in warm (low pressure) days, than cold (high pressure) ones.

 

Well, may be in Northern Europe where you don't usually see the Sun :D it's not a big difference, but it's for instance here in Spain@300sunnydaysayear. In particular where I live, Seville@48ºCintheshadowinsummer, the same C152 can either take off in 400m in winter while in summer the whole 1000m runway isn't enough to get airborne… it's a difference mate. But you're right, it's pressure (so density) what makes greater difference than Temperature itself.

 

 

S!

Well, as this is a simulator it depends on the settings you use in ME, but IRL warmer days means usually also lower pressures, and no, it's a huge difference flying in warm (low pressure) days, than cold (high pressure) ones.

 

Well, may be in Northern Europe where you don't usually see the Sun :D it's not a big difference, but it's for instance here in Spain@300sunnydaysayear. In particular where I live, Seville@48ºCintheshadowinsummer, the same C152 can either take off in 400m in winter while in summer the whole 1000m runway isn't enough to get airborne… it's a difference mate. But you're right, it's pressure (so density) what makes greater difference than Temperature itself.

 

 

S!

 

And moist too - to sum-up: Pressure Altitude...

 

But one thing that DCS World's weather model models, and we do not have in the Civil Sims is the effect of cold air on geopotential height.

 

I do not guess to what level they model it ( probably a fixed table or formula for just a generic variation ? ).

 

You can check it easily by creating a mission with the exact same QNH, but fly it between a cold Winter day and a warm Summer one... If there are mountains around you'll easily notice the difference, otherwise you can compare the altimeter readings with the F2 displayed alt...

Edited February 22, 2017 by jcomm

I quickly did these test comparisons last January :

https://docs.google.com/spreadsheets/d/1CJBvekYA9qW38hxM5GKPsvqiBjTqsABOU3bCQkzikpE/edit?usp=sharing

Speed in kph, alt in feets. Tests were rather quick so prone to a certain margin of error. That gives a rough idea, though.

 

Max speed was determined as "max sustainable speed", ie, slight dive until reaching target altitude, then record at which speed the plane stabilize at intended regime.