Hi guys,
I Notice the numbers in the Spit XIV description for stall and climb times are not aligned with the numbers I've found in my own research.
The description lists the power on stall speed as 89 mph at 75% fuel. My POH (1945) gives a POWER OFF stall speed of 85mph @8,375 lbs.
The time to climb is also unduly pessimistic. Our blurb gives over 5 minutes to hit 16 k. That would mean an average rate of less than 3000 feet per minute. According to the charts and data I've seen, the Spit XIV at 18lbs of boost maintained a rate of over 3000 fpm all the way to 25k At 20k, it was still climbing at 3500 or better The data I've seen lists just over 5 minutes to 20 k. Now hmm... The poh lists 12lbs of boost for take off, and does not give a time to climb figure. aND 12LBS is not available in the game. As well, one test report said that the xiv climbed as well at 9lbs as the spit IX did at 12.
RAF performance tests show a time to climb to 20k of 5.5 minutes at 18 lbs boost.
Now... if our numbers are based on 9 lbs of boost, they may well be accurate! They should be lower, as they are in the information blurb. I'll have to test tonight and see how the 14 does at 9 and 18 lbs of boost
I think the level speed numbers are pretty close!
finn

The spit IXe at boost 12lbs (which it can do for 60 minutes) gets to 20 k as fast as the XIV gets to 16k at 9 lbs.
I think we need to dump the 9lb boost and sub in 12lbs. Since the XIV was tested climbing to 20 plus at 18lbs, that also suggests that maybe it's time limit at that boost was more generous. Unsure about that.
Also... here's something weird. I had trouble stalling that xiv power on at a speed lower than power off. Granted I don't fly the 14 as much as the VC or IXe, so it may be I just need more practice. I also had a deuce of a time matching the turn time at SL that is given in the blurb. I averaged around 15-16 seconds best sustained turn. Again, might be a matter of needing more practice. IT's worth checking though.
finn

Time to climb from Test Reports

Spit IXb (merlin 61/63)
-----------------------------------
6m30secs to 20k @ Normal rating +12 (rad flaps open)
5m36secs to 20k @ Combat rating +15 (rad flaps open)

Spit IXe (merlin 66)
-----------------------------------
4m45secs to 20k @ Combat rating +18 (rad flaps open)

Spit XIVe (griffon 65)
-----------------------------------
5m00secs to 20k @ Combat rating +18 (rad flaps open)

+9lbs @2600rpm is the 60 mins climb power limit in the POH.

i.e.

When you set the revs with the throttle lever to 2600rpm, it will give automatically give you +9lbs boost, this power can be maintained for 60 mins before temps means cool down is necessary.

When you set the revs with the throttle lever to 2750rpm, it will give automatically give you +18lbs boost, this power can be maintained for over 5 mins before temps means cool down is necessary with 150 grade fuel, or 5 mins with std fuel.

* with 150 grade fuel, advancing the throttle even further from the normal FTH position will increase available boost to +21lbs

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The Spit 14 should soon have the +18 lb power level reinstated as BST2 and will look something like this,

BST 1 +9lb for 60mins
BST 2 +18lb for 7.5-10 mins
BST 3 +21lb for 5 mins

It should make the plane more usable IMO.

You could override the automatic boost control unit within certain limits.
Hence why you could set 12lb with max rpm 2750 for take off purposes - though they reckoned take off with just normal power +7lbs was fine.

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Is this any help?

http://www.spitfireperformance.com/spitfire-XIV.html

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What we really need is an infinitely variable boost lever between zero boost and WEP through the gate.
I'd say drop 9 pounds for the 14 and go 12, 18 and 21. (25 for the last day or two of the TOD).
If the Spit XIV could climb as well at 9 pounds as the IXe could at 12, and we don't model that for OUR boost 9, then dump it for the sake of performance veracity and go to 12lbs for the XIV as the 1 hour setting. Am I clear as mud? IF boost 9 doesn't allow the spit 14 to reach it's tested real life performance levels in WB, then let's use the setting that DOES allow that performance for 60 minutes.
IF.. we can get the spit 14 to behave as it should at boost 9, then I'm ok with that too.
I'd say 12lbs for 60, 18 lbs for 8-10, and 21 for 5 minutes.
finn
Edited once in the vain hope of achieving clarity.

First of the devil is in the details. The climb numbers in the Vehicle info is at Bst1. That means +9 lbs of boost. The climb numbers stated from POH etc are from +18 lbs tests, so they cannot be compared to the Bst1 climb time.

I have built a +18 boost for the next update. One can calculate the Spitfire XIV's time to climb to 20000 ft from the graph below. The data is at +18 lbs boost at a weight of 8500 lb.
Link for the chart: http://www.spitfireperformance.com/spit14climbchart.jpg





My calculations from the graph show a climb time to 20000 ft of 4m 43s at +18 lbs. I just ran a test on the Spitfire XIVe flightmodel with +18 boost modeled and it reached 20000 ft at 4m 37s, which is almost pinpoint to the numbers from the graph. As such the flightmodel should be very close to real life performance in the climb.

Time to climb at +18 lbs
ww2 Data: 4m 43s
My test: 4m 37s


Regarding stall speed I've learnt to never fully trust the POH. This from my experience of modeling over 100 flightmodels. POH numbers are often influenced by gauge errors and the test pilot's personal definition of exactly where the stall starts. In Warbirds it can be measured much more precisely than in real life, as we can put the plane on auto-trim level and see exactly the speed when the G's go from 1.0 G's to 0.9 G's, which is my definition of the stall and not the speed at which a wing is dropping etc, which might be used as a definition by a real life pilot, and which will give a lower estimated stall speed. Also the stall speed data often varies from different tests of the exact same aircraft. For the Spitfires the stall speeds vary greatly between the POH's of different models, even though they use the exact same wing and as such should follow a nearly identical stall speed pattern. Below are numbers from the Spitfire IX POH and Spitfire XIV POH. As can be seen the Spitfire IX POH states much higher stall speed numbers than the Spitfire XIV POH. I have plotted these numbers vs the stated weight in the graph below. I have also added my own stall tests at these exact weights to the graph. When setting the stall speed (liftco) for the Spitfires I used all manuals and trials available, from all the different variants of the Spitfires, and tried to wrap my head around this data, as well as using all my experience from other fighters stall speeds at their various wing loadings and wing thickness ratios etc.








<S>
/Robert

Not trust the POH? are you freaking kidding? Pilots bet their lives on the POH. If the POH is incorrect it's usually corrected in pen by the pilot who is given the correct number.
You trust the POH about boost- even tho' boost is infinitely variable in a real spit, and there is no logical reason why a spit 9 should use 12 lbs of boost for an hour, but the XIV can only use 9lbs. Some numbers in a POH are suggestions, some are facts that pilots have to live with.
Stall speed has to be right- within very small limits in the POH. Period.

Your stall numbers for the SPIT 9 are correct...but they apply to the CLIPPED WING Spits only... as is written in the part under the chart that you DON'T show here... Spits with regular wings will stall between 6 mph or 3 kts slower. so the MPH figure for a normal spit would be about 84mph. or 75kts. Further, the stall speed is in IAS. it doesn't change with altitude although the true airspeed does.

finn

For an excellent discussion of the spit's wing design and capabilites, go here:
https://www.aerosociety.com/media/4953/ ... itfire.pdf

The author has made quite a study of the spit versus 109. He's a professor of aeronautical engineering, and I'm just a dumb former pilot and teacher, but his math looks good to me.

finn

<S> sir!
No, I'm not kidding. I've read over 50 POH's, compared them to ww2 trial data, NACA data, calculating the theoretical stall speeds etc while trying to wrap my head around the stall speed for each of the 100 fighters I've remodeled. The POH is not always correct, and in many cases I would say it is correct and not correct at the same time. This for several reasons.

For one the pitot tube might not always give exact measurments for the cockpit's speed gauge. For some ww2 trials there are tables provided to convert the IAS shown on the cockpit speed gauge to the real IAS speed accounting for pitot tube error. The gauge IAS speed shown for the pilot is often slightly lower than the real IAS. The F6F Hellcat is the prime example where Grumman engineers could not understand why the F4U, using the same engine, was so much faster according to the speed gauges, until Vaught borrowed Grumman a F4U to run tests with against the F6F. In these tests it was found that the F6F and F4U had near identical top speeds, flying side by side, and the supposed inferior speed of the F6F was only a misconception owed to turbulent airflow around the pitot tube making the speed gauge of the Hellcat showing a notably lower IAS speed than the actual real IAS speed. Errors like this also affect the stall speed measured in ww2 trials, and it's smarter to write down the speed shown on the cockpit gauge for the POH, than the mathematically correct stall speed. This since the pilot has to rely on the gauge. For building flightmodels however one wants the mathematically correct stall speed since we don't have these pitot tube errors in the sim.

You are correct the Spit XIe numbers are for clipped wings, I had to respond in a hurry so forgot to account for this. As you state the stall speed is then around 84-87 mph (3-6 mph reduction) at 7150 lb. I'll go with a 5 mph reduction for non-clipped wings so this gives 85 mph stall speed at 7150 lb. The Spit XIV POH states a stall speed of 85 mph... at 8375 lb. So assuming the POH can never be wrong... a weight difference of 1225 lb makes none or only a single mph difference? It goes against all known physics though. The Spit IX manual also states a stall speed of 95 mph ( 100 mph for clipped wing) at 8700 lb. Calculating by interpolation this results in a stall speed of 93 mph at 8375 mph for the Spitfire IX's POH if using normal full span wings. The Spitfire XIV's POH still states 85 mph at the same weight. So how do we move on with this if we assume the POH can not be incorrect? Also the 85 mph at 7150 lb in the Spitfire IX POH is for an "aircraft without rear-view fuselage". A spit with rear-view fuselage stalls at 5-17 mph higher stalls speeds. Using these numbers a Spitfire IX would then stall at 106 mph at 8375 lb, which is even further from the 85 mph of the Spit XIV at this weight. Since I'm not 100% sure about the "rear-view fuselage" issue, or why it would increase the stall speed by so much, which seems very strange, let's just stick with 93 mph for the Spit XI at 8375 lb vs the 85 mph of the Spit XIV at this weight. We can also look at other trials. This one for example shows a stall speed of 95 mph at 8145 lb, which should result in around 97 mph at 8375 lb.
http://www.spitfireperformance.com/Spit ... ndling.pdf

So at 8375 lb we now have the Spitfire's stall speed stated as 93 mph and 85 mph from two different POH's, and 97 mph from a ww2 trial. Looking at even more trials we'd get even more different numbers for the stall speed for the same airplane. The chaos has just started! I'm willing to commit blashpemy and say that one or both of the POH's might actually be incorrect.

What makes it unwise to compare the POH stall speed to the stall speeds from my tests though, is that the stall speed in the POH is made from real life pilot tests, while mine are made on auto-pilot with the HUD telling me the exact milisecond where the G's go from 1.0 to 0.9 G's. This would be impossible to measure in a real life test. And it would be near impossible to keep the airplane flying perfectly right at 1.0 G's to start with. In a perfect stall test I get the power ON stall speed of the Spitfire XIV to 89 mph at 75% fuel. If turning off the sound for the stall buzzer though (in real life ww2 planes didn't have a stall buzzer), and flying manually trying to feel the stall, I would have estimated it that the Spit XIV starts to fall out the sky at 79-84 mph, since this is where I can actually notice the nose and wings starting to drop. This is 5-10 mph below the mathematically correct stall speed I get from a perfect auto-pilot test, and can explain why a ww2 stall test shows lower numbers than the stall number I've presented in the vehicle info. This can also explain why the stall speed varies between different ww2 tests for the same plane, since it's up to the test pilot to define the exact milisecond where he estimates the plane is stalling, and near stall the airspeed is decreasing rapidly so every split of a second extra will result in a lower estimated stall speed. In real life there are also small differences in quality between the planes.

What I can say is that the best way I've found is to collect all stall data I can find for a flightmodel, try to make sense of it since all tests will often show a different number, then compare it to the stall speed I get from using my method of calculating it. For the P-39 Airacobra there is very detailed calculated/tested NACA stall data available. The method I use for mathematically estimating the stall speed of a flightmodel matches perfectly to the NACA data for the P-39, and has also given correct results vs other NACA tests and relative stall numbers when comparing different fighters. I have retested the Spitfires and compared them to all the other fighters, setting the weight to match a wingloading of 30.0 for all airplanes so that I can measure their relative stall speed, looking at the max AoA, airfoil and wing thickness ratio etc. Looking at these tests I believe the Spitfire's stall speed is where it should be compared to all the other flightmodels I've remodeled. Lowering it by several mph would not make sense relative to the other fighters as the Spitfire's stall speed at 30.0 wingloading would then be lower than what planes with thicker wings and a higher max AoA have at the same wingloading.

Here is an example from a very thurough NACA report on the Spitfire V that shows the difference in the IAS that the pilot sees on his gauge (which would be used for stall speeds in the POH), and the correct IAS, which is what we use in the game (No pitot errors in Warbirds).




When modeling the Spitfires I found many different stall speeds for the various variants. Not always clear if power ON or OFF. Some of those were:
64 mph - 5804 lb
78 mph - 6050 lb
73 mph - 6172 lb
81 mph - 6917 lb
85 mph - 7150 lb
88 mph - 7800 lb
95 mph - 8700 lb
85 mph - 8375 lb
95 mph - 8145 lb

Plotted in a graph we get quite an arbitrary picture




I now however remember how I finally determined the stall speed (liftco) for the Spitfire series. It was by doing my own estimations, and comparing these to the very detailed NACA test of the Spitfire V. This test is as thorough as it gets, and stated a stall speed of 77 mph power ON at 6184 lb. If you take a Spitfire Vb and use 45% fuel (6184 lb), you can go autopilot, turn off the engine, and see that the very moment where the G's meter in the HUD goes from 1.0 to 0.9 G's, is exactly at 77 mph for the Spitfire series, as per the NACA tests. (In Warbirds the stall speed doesn't vary with engine ON/OFF, so we're using power ON as a basis for all flightmodels). The whole Spitfire series uses the liftco setting that was used to match the NACA test and as such the Spitfires in Warbirds should be quite on par with their real life stall speeds. This liftco setting results in an 89 mph stall speed at 8288 lb, which is the weight of the Spitfire XIV at 75% fuel.

You can find this NACA test at:
https://ntrs.nasa.gov/archive/nasa/casi ... 092581.pdf





Cheers!
/Robert