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SL top speed issue


Hummingbird

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So eventhough I am no fan of DCS propjobs I decided to buy the Spitfire Mk.IX (in conjunction with the F/A-18 ) anyway as I do love the jets and want to support ED as much as I can.

 

However having now flown the Spitfire IX for a while I cannot achieve the real life top SL speed of the aircraft, maxing out at 520-522 km/h at SL, instead of the real life 537 km/h.

 

Ran at +18 lbs/sq.in. and 3,000 rpm, but no luck.

 

Engine also seems quite fragile seizing rather quickly during combat if run at full boost. Definitely can't seem to make it last the 5 min limit.

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Rads in DCS Spit can be either only full auto, or full opened (when switching to manual mode).

 

I seem to recall the plane could do the advertised SL speed in 1.5.8 and overheating was only a problem in slow manouevres, when going below 180. Haven't tested it in 2.5, though!

i7 9700K @ stock speed, single GTX1070, 32 gigs of RAM, TH Warthog, MFG Crosswind, Win10.

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Nah, you must've left the rads open by mistake, or flown badly out of trim? Curious about your observations, I just fired up the "free flight" mission on Caucasus, taking advantage of already close to ISA conditions (15 degrees ambient temp).

 

With full throttle, the plane got up to 532-534'ish as reported by F2 cam, and that's with a bit sloppy control using keyboard and trims only (didn't bother to plug in flight sim gear only for this short check :D, maybe one could squeeze a little more with smoother inputs?), screens below. Notice that coolant temp doesn't even reach 115 (treshold for auto rad open), so there's no way this will ever result in overheat. Oil temp, however, seems to be redlined indeed, but I didn't fly long enough to see when the engine would blow.

Screen_180211_183149.thumb.jpg.f29ceee949b1358034cdfc78749b38bb.jpg

Screen_180211_183153.thumb.jpg.d392564edce9f62870e224a0e52cd154.jpg


Edited by Art-J

i7 9700K @ stock speed, single GTX1070, 32 gigs of RAM, TH Warthog, MFG Crosswind, Win10.

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Briefly reached 530 km/h TAS by running at 2,800 rpm, but rads opened after being there for 10 sec and speed dropped to a stabil 515 km/h.

 

Using auto rudder as well.

 

 

EDIT: Tried multiple times now, at 2,800 & 3,000 rpm, the speeds always settles at 515 km/h TAS with rads opening fully after just 5-10 sec at 522 (3,000 rpm) or 530 km/h (2,800 rpm). No clue what's going on...


Edited by Hummingbird
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Well it is normal I believe, it is a Spitfire IX after all and it’s not supposed to be very fast. 530ish seems fairly good from it.

 

Or perhaps the current versions is no longer based on and/or tries to match far too optimistic results obtained on one off prototypes or flight tests with weird anomalies present?

http://www.kurfurst.org - The Messerschmitt Bf 109 Performance Resource Site

 

Vezérünk a bátorság, Kísérőnk a szerencse!

-Motto of the RHAF 101st 'Puma' Home Air Defense Fighter Regiment

The Answer to the Ultimate Question of the K-4, the Universe, and Everything: Powerloading 550 HP / ton, 1593 having been made up to 31th March 1945, 314 K-4s were being operated in frontline service on 31 January 1945.

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What is the key combination that gives us TAS readings in F2 ( external view ) ?

 

 

Ctrl+Z you can switch the Bar between IAS+TAS and different Opitions in the F2 View.

Once you have tasted Flight, you will forever walk the Earth with your Eyes turned Skyward.

 

[sIGPIC][/sIGPIC]

9./JG27

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^ It's Ctrl-Y (on standard QWERTY keyboard, MAD-MM, you're using QWERTZ layout I presume).

 

OK, I've got the answer for first half of Hummingbirds problem - the F2 "TAS" is actualy more like a GS (though I recall Yo-Yo's post explainign that it's not really a GS either). The Caucasus free flight mission has some wind added down low (plus a bit of a turbulence when flying REALLY low above sea waves), thus "TAS" readouts are changing depending on your heading - from 520-few to 540-few (!). Clearly for better evaluation, one has to hop into full editor and make a mission with strictly ISA-sea-level-conditions.

 

No idea about second half of the problem, though. The radiators should not open, at least not that quickly - I flew the plane full boost for 8+ minutes (stopwatch measured)... until I closed fuel cock by mistake by hitting "T" instead of "Y" :D. Still, even though probably 5+ minutes were with oil at 100 degrees, the rads didn't open (I recall they're controlled strictly by coolant temp anyway) and the engine was running well.


Edited by Art-J

i7 9700K @ stock speed, single GTX1070, 32 gigs of RAM, TH Warthog, MFG Crosswind, Win10.

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I use Ctrl + Y for switching between IAS & TAS.

 

Art-J, I wish I could get the aircraft to run for 8 min at +18 without opening the rads, but I simply can't achieve it for more than 5-10 secs. I'm flying completely smooth and level, everything perfectly trimmed, the aircraft on rails, but I always end up at 515 km/h TAS.

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Problem solved: Mission was set to 20 deg Celcius, when I put it to 15 deg I could achieve a stabile 532 km/h at SL @ 3,000 rpm +18 boost.

 

Another issue was discovered I think though, because as I started turning and water temp exceeded 110 deg the rads opened, however when returning to level flight the rads did not close again once temp was below 110 deg. Infact I ran for 5 min at 95 deg water temp with rads fully open. Only way to get them to close again was to throttle down.

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Interesting. Would it be the case that the real thing only opened up when the temp was becoming really hot, but at the same way, only closed again when it cooled down sufficiently? I.e. there were two separate regulating temperatures, and in between, the shutters were just "off"...?

http://www.kurfurst.org - The Messerschmitt Bf 109 Performance Resource Site

 

Vezérünk a bátorság, Kísérőnk a szerencse!

-Motto of the RHAF 101st 'Puma' Home Air Defense Fighter Regiment

The Answer to the Ultimate Question of the K-4, the Universe, and Everything: Powerloading 550 HP / ton, 1593 having been made up to 31th March 1945, 314 K-4s were being operated in frontline service on 31 January 1945.

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You'd think it would close the moment the temperature fell below the 110 deg limit, but it didn't, not even when the temperature fell below 95 deg. I had to throttle down for the rads to close, and then oddly enough I could immediately throttle back up to full boost with the rads keeping closed.

 

Seems abit odd.

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You would probably have to take a deep look at the control scheme to figure out whether it is correct or not.However, such a system would make sense if the radiator flaps were really just two fixed positions and no intermediate positions like on the 51 or 109. It is a bit crude way to control temp and drag, though.

http://www.kurfurst.org - The Messerschmitt Bf 109 Performance Resource Site

 

Vezérünk a bátorság, Kísérőnk a szerencse!

-Motto of the RHAF 101st 'Puma' Home Air Defense Fighter Regiment

The Answer to the Ultimate Question of the K-4, the Universe, and Everything: Powerloading 550 HP / ton, 1593 having been made up to 31th March 1945, 314 K-4s were being operated in frontline service on 31 January 1945.

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Problem solved: Mission was set to 20 deg Celcius, when I put it to 15 deg I could achieve a stabile 532 km/h at SL @ 3,000 rpm +18 boost.

 

Another issue was discovered I think though, because as I started turning and water temp exceeded 110 deg the rads opened, however when returning to level flight the rads did not close again once temp was below 110 deg. Infact I ran for 5 min at 95 deg water temp with rads fully open. Only way to get them to close again was to throttle down.

 

Check the pilot notes, but I believe the rad was designed to auto open at 115 deg.

In my experience, I find that a few seconds at boost +8 lbs and engine will cool enough for auto operation to close the rad (unless nose too high and speed too low for cooling effect).

Trick is to not fly over 115 deg unless you really need to (perhaps in combat for example); a little under 3,000 rpm may help at times, try 2850 rpm. Pilot notes for most Spits indicate that climb settings are good for combat. Once you have accelerated to speed, climb rpm setting with +18 lbs boost can help with max speed at sea level (yaw and pitch trim, together with minimum movement of stick and control surfaces is essential).

P.S. I am still on 1.5 release version, so have no experience of later versions/patches.

 

Happy landings,

 

56RAF_Talisman

Bell_UH-1 side.png

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Check the pilot notes, but I believe the rad was designed to auto open at 115 deg.

In my experience, I find that a few seconds at boost +8 lbs and engine will cool enough for auto operation to close the rad (unless nose too high and speed too low for cooling effect).

Trick is to not fly over 115 deg unless you really need to (perhaps in combat for example); a little under 3,000 rpm may help at times, try 2850 rpm. Pilot notes for most Spits indicate that climb settings are good for combat. Once you have accelerated to speed, climb rpm setting with +18 lbs boost can help with max speed at sea level (yaw and pitch trim, together with minimum movement of stick and control surfaces is essential).

P.S. I am still on 1.5 release version, so have no experience of later versions/patches.

 

Happy landings,

 

56RAF_Talisman

 

I don't understand the need to throttle down to get them to close though, they ought to close autmatically when temp drops below a certain level. Instead rad closure is currently linked to the throttle, which seems strange.

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I don't understand the need to throttle down to get them to close though, they ought to close autmatically when temp drops below a certain level. Instead rad closure is currently linked to the throttle, which seems strange.

 

Lower throttle = lower boost = lower temps = rad closure at lower temps, under 115 deg.

 

Do what ever you need to do during your flight, the auto rad will open and close to keep your engine temps within limits. Take care that you do not fly too slow, nose too high for too long, in a climb, or the engine will overheat even with rad open.

 

Happy landings,

 

Talisman

Bell_UH-1 side.png

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Lower throttle = lower boost = lower temps = rad closure at lower temps, under 115 deg.

 

You didn't read what I wrote, the rads DON'T close when temperature drops below 115 deg, once open they ONLY close if you reduce the throttle. In other words after the first turn at full boost the rads will open and once I level out the temperature drops steadily to 95 deg, but the rads stay open and the only way to get them to close again is to cut the throttle.

 

In short the automatic radiator system only seems to react to an increase in temperature and not any decrease.

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