PDA

View Full Version : A bug in droptank rack modelling for Bf 109



jurinko
07-07-2004, 04:43 PM
I have found a bug concerning the Bf 109 series with droptank. Recently I took 75% fuel + 300l droptank on Bf 109 G-6 for long online mission on Virtualpilots map and after releasing it, the plane flew like with it. It flew almost like the bad G-6 from old IL-2 http://ubbxforums.ubi.com/infopop/emoticons/icon_wink.gif

I did some tests offline I started QMB in certain alt and measured time required for reaching 2000m and 3000m without touching the controls except preventing the banking. I tested clean Bf 109 G with various fuel levels and with droptank, which I released immediately after QMB started. Here are the test results:

Configuration 2000m 3000m

25% fuel 0:39 1:33
50% fuel 0:41 1:38
75% fuel 0:43 1:43
100% fuel 0:45 1:50
25% fuel + tank 0:44 1:48
100% fuel + tank 0:55 2:15

The configuration with 25% fuel and dropped droptank climbed almost exactly as the clean configuration with 100% fuel load. Since 25% fuel in Bf 109 means 100l and droptank means 300l, the sum is 400l exact 100% volume of 109´s internal tank. It means that the droptank fuel was moved into the fuselage internal tank.
However, the fuel gauge showed 25% of fuel after the droptank release.
Moreover, if flying with 100% fuel in internal tank and dropping the droptank, the virtual weight of fuel in the plane increases up to 400+300=700l over the internal tank capacity, and exactly, the plane´s climb was the worse from all. I did not tested whether the plane´s virtual weight increase after releasing the droptank depends on how much fuel remains in the droptank, but my feeling from the online flying is, with 75% of internal fuel (300l) and after releasing the 300l (even partially empty) droptank, the plane really felt much heavier than with 100% fuel inside.

I tested and found the same phenomena with Bf 109 G-2. I did not check other planes with droptanks.

Another interesting information resulted, the clean G-2 with 50% of internal fuel reached 2000m in 0:35 and 3000m in 1:22. If we agree that in case of G-6, each 25% of fuel increase (=100l ~ 80kg) adds 2s to reach 2000m, the 2000m time for 50% G-6 is 6s higher than 50% G-2. By extrapolation, the weight of Bf 109 G-2 with the same fuel level is found to be of 3x100l of fuel (240 kg) lighter than G-6, which is nonsense in reality G-6 was heavier of some 50kg. But in FB, G-6 flies exactly like G-2 with SC 250 inside...
The View Objects says the take-off weight for G-2/G-6 is 3100/3153kg (ok) but the empty weight is 2255/2676kg weird 421kg weight increase in case of G-6. Not so far from the calculated weight difference of 240kg, and if we add drastically increased drag model for G-6 (look how HUGE the MG131 bulges are).. then the reason of experienced FM difference between G-2 and G-6 is obvious most probably wrong G-6 weight model.

---------------------
Letka_13/Liptow @ HL

[This message was edited by jurinko on Sat July 10 2004 at 01:13 PM.]

[This message was edited by jurinko on Wed July 14 2004 at 07:22 AM.]

jurinko
07-07-2004, 04:43 PM
I have found a bug concerning the Bf 109 series with droptank. Recently I took 75% fuel + 300l droptank on Bf 109 G-6 for long online mission on Virtualpilots map and after releasing it, the plane flew like with it. It flew almost like the bad G-6 from old IL-2 http://ubbxforums.ubi.com/infopop/emoticons/icon_wink.gif

I did some tests offline I started QMB in certain alt and measured time required for reaching 2000m and 3000m without touching the controls except preventing the banking. I tested clean Bf 109 G with various fuel levels and with droptank, which I released immediately after QMB started. Here are the test results:

Configuration 2000m 3000m

25% fuel 0:39 1:33
50% fuel 0:41 1:38
75% fuel 0:43 1:43
100% fuel 0:45 1:50
25% fuel + tank 0:44 1:48
100% fuel + tank 0:55 2:15

The configuration with 25% fuel and dropped droptank climbed almost exactly as the clean configuration with 100% fuel load. Since 25% fuel in Bf 109 means 100l and droptank means 300l, the sum is 400l exact 100% volume of 109´s internal tank. It means that the droptank fuel was moved into the fuselage internal tank.
However, the fuel gauge showed 25% of fuel after the droptank release.
Moreover, if flying with 100% fuel in internal tank and dropping the droptank, the virtual weight of fuel in the plane increases up to 400+300=700l over the internal tank capacity, and exactly, the plane´s climb was the worse from all. I did not tested whether the plane´s virtual weight increase after releasing the droptank depends on how much fuel remains in the droptank, but my feeling from the online flying is, with 75% of internal fuel (300l) and after releasing the 300l (even partially empty) droptank, the plane really felt much heavier than with 100% fuel inside.

I tested and found the same phenomena with Bf 109 G-2. I did not check other planes with droptanks.

Another interesting information resulted, the clean G-2 with 50% of internal fuel reached 2000m in 0:35 and 3000m in 1:22. If we agree that in case of G-6, each 25% of fuel increase (=100l ~ 80kg) adds 2s to reach 2000m, the 2000m time for 50% G-6 is 6s higher than 50% G-2. By extrapolation, the weight of Bf 109 G-2 with the same fuel level is found to be of 3x100l of fuel (240 kg) lighter than G-6, which is nonsense in reality G-6 was heavier of some 50kg. But in FB, G-6 flies exactly like G-2 with SC 250 inside...
The View Objects says the take-off weight for G-2/G-6 is 3100/3153kg (ok) but the empty weight is 2255/2676kg weird 421kg weight increase in case of G-6. Not so far from the calculated weight difference of 240kg, and if we add drastically increased drag model for G-6 (look how HUGE the MG131 bulges are).. then the reason of experienced FM difference between G-2 and G-6 is obvious most probably wrong G-6 weight model.

---------------------
Letka_13/Liptow @ HL

[This message was edited by jurinko on Sat July 10 2004 at 01:13 PM.]

[This message was edited by jurinko on Wed July 14 2004 at 07:22 AM.]

NegativeGee
07-08-2004, 02:36 AM
2676kg (or thereabouts) is an often quoted empty weight value for the G-6, so I don't think that is wrong in itself if that weight is used for the FM in FB.

"As weaponry, both were good, but in far different ways from each other. In a nutshell, I describe it this way: if the FW 190 was a sabre, the 109 was a florett, or foil, like that used in the precision art of fencing." - Günther Rall

http://www.invoman.com/images/tali_with_hands.jpg

Look Noobie, we already told you, we don't have the Patch!

jurinko
07-08-2004, 02:44 AM
ok, then the G-2 weight is too low. Whether G-2 should fly closer to G-6 or vice versa I do not know, but the difference existing now is too big.

---------------------
Letka_13/Liptow @ HL

butch2k
07-08-2004, 10:43 AM
Actually 25% + droptank should not be possible... Indeed IRL fuel from the droptank replaced fuel pumped from the main tank, fuel was not pumped directly from the DT.
So 25%+DT means 100% in the main tank and an empty DT which is exactly what you test proves http://ubbxforums.ubi.com/infopop/emoticons/icon_wink.gif.
50%+DT means 100% internal fuel + 33% of the DT still filled up.

HIH

p1ngu666
07-08-2004, 10:59 AM
did the droptank have the pump inside it?
germans asked for the drop tanks back also, u got a reward for returning them, and pilots also got a bonus

http://www.pingu666.modded.me.uk/mysig3.jpg
<123_GWood_JG123> NO SPAM!

Fillmore
07-08-2004, 03:47 PM
"I tested clean Bf 109 G with various fuel levels and with droptank, which I released immediately after QMB started."

Dropping the droptank doesn't make the plane clean, it still has the rack. Last time I tested it the rack dropped topspeed by 12kph if I remember correctly. It also had noticeable difference in turn, acceleration and general E-bleed kind of stuff.

OsA_FW
07-09-2004, 07:54 AM
S!

Whell I can only agree that diference beetwen BF109/G2 compared to G6 is to big and it shouldnot be that MUCH .

my opinion :-)

enoy

KroatJG1_OsA

LLv34_Flanker
07-10-2004, 12:43 AM
S!

Butch2k, do U have weights of the centerline rack of the Bf109G? Would be interesting to compare the weight with and without it + then test results to see how much difference there is when it is on/off the plane...

---------------------------

Flanker
1.Lentue p¤¤llikk¶ / TO
Lentolaivue 34

"Let Chaos entvine on defenseless soil!"
~Dimmu Borgir~

jurinko
07-10-2004, 08:45 AM
<BLOCKQUOTE class="ip-ubbcode-quote"><font size="-1">quote:</font><HR>Originally posted by butch2k:
Actually 25% + droptank should not be possible... Indeed IRL fuel from the droptank replaced fuel pumped from the main tank, fuel was not pumped directly from the DT.
So 25%+DT means 100% in the main tank and an empty DT which is exactly what you test proves http://ubbxforums.ubi.com/infopop/emoticons/icon_wink.gif.


HIH<HR></BLOCKQUOTE>

yep understand but try start flying with 100% of internal fuel and with droptank and release that droptank: the plane will fly as it carries weight of 400+300l fuel.

More, if starting with 25% fuel in internal tank and full droptank is released, why the weight of plane is as with 100% fuel (ok if all fuel was moved to the internal tank), but the gauge and range is like with 25% fuel?

"50%+DT means 100% internal fuel + 33% of the DT still filled up."
in FB, 50% plus 300l tank means after throwing the tank away, plane will be burdened with 200+300l of gas (500l) but the gauge will keep showing only 50% fuel.

Solution - when flying with tank, the internal tank gauge should show immediately the sum of internal tank and DT, and if DT with abundance of fuel is thrown away, the weight of that gas which remained in DT will not be added to the plane weight.
Now it is possible to have plane heavy like with 100% fuel and with 25% range.

---------------------
Letka_13/Liptow @ HL

jurinko
07-10-2004, 08:48 AM
<BLOCKQUOTE class="ip-ubbcode-quote"><font size="-1">quote:</font><HR>Originally posted by Fillmore:
"I tested clean Bf 109 G with various fuel levels and with droptank, which I released immediately after QMB started."

Dropping the droptank doesn't make the plane clean, it still has the rack. Last time I tested it the rack dropped topspeed by 12kph if I remember correctly. It also had noticeable difference in turn, acceleration and general E-bleed kind of stuff.<HR></BLOCKQUOTE>

thats not only the problem of the rack - the aerodynamics should be affected maybe, but it should not affect much turn and E bleed. According to my tests, the turn and bleed is caused by weight increase, the weight of gas which was already thrown away with the droptank.

---------------------
Letka_13/Liptow @ HL

Kurfurst__
07-10-2004, 10:18 AM
<BLOCKQUOTE class="ip-ubbcode-quote"><font size="-1">quote:</font><HR>Originally posted by p1ngu666:
did the droptank have the pump inside it?
germans asked for the drop tanks back also, u got a reward for returning them, and pilots also got a bonus

http://www.pingu666.modded.me.uk/mysig3.jpg
&lt;123_GWood_JG123&gt; NO SPAM!<HR></BLOCKQUOTE>

Nope, the fuel from the DT was 'pumped' into the main tank by compressed air.

The supercharger provided compressed air, which was fed with an air line into the DT. The pressure forced the fuel into the main tank via a fuel line - it could be observed directly through a transparant glass on the line that went throgh the cocpit. It was always from the main tank the engine fed from.

The MW 50 system worked the same way BTW - compressed air from the supercharger forced it into the supercharger intake. Compressed air was also used to operate the MK 108 cannon, though I am not sure what exactly they used it for.

http://www.x-plane.org/users/isegrim/fat-furred%20tigerB.jpg

"We've got the finest tanks in the world. We just love to see the German Royal Tiger come up on the field".
- Lt. Gen. George S. Patton, Jr. Febuary 1945.

"One day a Tiger Royal got within 150 yards of my tanks and knocked me out. Five of our tanks opened up on him at ranges of 200 to 600 yards and got 5 or 6 hits on the front of the Tiger. They all just glanced off and the Tiger backed off and got away. If we had a tank like that Tiger, we would all be home today."
- Sgt. Clyde D. Brunson, US Army, Tank Commander, February 1945

Yellonet
07-10-2004, 11:53 AM
If we're talking droptanks, what about the P-40s droptank? It hangs in the air under the plane! I guess there should be som bars or something to hold the tank, but there isn't.


- Yellonet

Fillmore
07-10-2004, 01:38 PM
"the aerodynamics should be affected maybe, but it should not affect much turn and E bleed"

Huh? not maybe, definitely. All speed charts show differences in top speeds between planes with and without bomb racks (and from the 190 charts I have seen 12kph seems reasonable.

Turn performance (as well as acceleration) must certainly be affected by aerodynamics.

I can't say how accurately modelled all the various effects of having the rack are, but that the rack actually should have those effects is unquestionable, it is just a matter of to what degree.

Also note that the droptank itself (I was flying alot in an online war where we had to use droptanks on 109G2s as we had to stay in the air so long, so I did a bunch of tests with droptanks) actually contributes less drag than just the rack, the rack drops top speed by 12, while tank+rack drops by 22. Oleg has noted before that weight has negligible affect on level flight top speeds, so we can figure that most if not all of this loss in top speed is a reflection of the drag (E-bleeding drag) produced by these items.

jurinko
07-10-2004, 02:19 PM
ok even the rack causes some drag (which should affect max speed but not the turn rate too much), the bug still exists:
even the weight of fuel from droptank is added to the plane weight after throwing the DT away, the usable gas content in the fuselage tanks remains the same - plane is heavier of the droptank fuel but its range is based on no-changed fuselage fuel.
More, it is possible to transfer the whole weight of DT fuel into the fuselage tank even it is already full (400l) and plane behaves like with 400+300l but has actually only 400l of fuel aboard.

---------------------
Letka_13/Liptow @ HL

Fillmore
07-11-2004, 04:16 AM
I'm not sure what makes you think your test shows the weight of the fuel is kept after the tank is dropped, I see nothing that would indicate that. The drag from the rack lowers climb rate. Try climbing clean with radiator closed, then again with radiator open and you will see what effect that drag has on climbrate (as well as turnrate etc.).

Take 25% fuel+droptank, drop the tank and test climb.

Then take 25% fuel+bomb, drop the bomb and test climb.

If both are the same then you can see that it is purely the rack and not any weight from fuel, if not then you have shown something may be amiss.

You may also want to try it with different bomb weights incase you might think the weight of the bomb is kept after the bomb is dropped.

jurinko
07-11-2004, 09:24 AM
If I fly with 100% of internal fuel, I reach 3000m from start in 1:50 min.
If I start with 100% fuel and 300L droptank and I release the droptank immediately after start, my climb time to 3000m rises to 2:15 min.
Even the ETC rack has some drag and weight, it can not increase the climb time of 25s.. it is the weight of already dropped droptank which still burdens the plane.

---------------------
Letka_13/Liptow @ HL

Jetbuff
07-11-2004, 11:03 AM
I guess a simple way to test this would be to time your climb to Xm:

a) with droptanks on + 100% fuel
b) with droptanks on + 100% fuel, releasing drop-tank immediately
c) with droptanks on + 25% fuel
d) with droptanks on + 25% fuel, releasing drop-tank immediately
e) with 100% fuel only

If there is no difference between a and b or c and d then you are right. If there is a difference then something else is causing the discrepancy. Also, if d = e then, again, it confirms your suspicions (25% fuel:100L + Droptank:300L = 400L = 100% fuel) while if b = e, it negates your theory.

http://members.rogers.com/teemaz/sig.jpg

jurinko
07-11-2004, 12:15 PM
hi Jetbuff, those tests I did.. results are in the first post. Exactly, the clean G-6 with 100% fuel flies (climbs, turns) visibly better than 100% full G-6 with 300l tank which was released immediately after the mission start. The rack causes some drag and may slow the plane down of 12kph (fully open rads slowed planes down of 50kph) but the plane behaves like it still carries that droptank fuel.
And if the speed loss with droptank is really only 10kph (and additional 12kph due to the rack), it is another bug - open rad slows plane down of 50kph and big fat tank only of 10kph?

---------------------
Letka_13/Liptow @ HL

Fillmore
07-11-2004, 12:17 PM
"Even the ETC rack has some drag and weight, it can not increase the climb time of 25s.. "

So far your test shows that it does. If it can't and shouldn't (and you have documentation showing as much) then send a bug report to Oleg about excessive drag from the rack.

If you really want to isolate the rack and eliminate the possibility of fuel weight, then do as I suggested and try with bomb instead of fuel. My guess is that you will find that it is purely the drag from the rack that causes all the performance loss.

If you really feel the drag from the rack is excessive then use closed radiator and compare it to different amounts of open radiator so that you have a known quantity to compare the drag to, then you will have a radiator setting which corresponds to the same drag as the rack, and Oleg can verify if that is the correct amount of drag.

When the FM was reworked for FB, radiator drag was overlooked and was wrong with FB. This was corrected in a patch. Perhaps there is an error with the rack, perhaps not, but there is no way to know until more thorough testing is done.

Fillmore
07-11-2004, 12:24 PM
"If there is no difference between a and b or c and d then you are right."

No. You are neglecting the rack, the drag from the rack will decrease climb times even without weight. Compare with a bombrack to factor out fuel weight, then compare with radiator positions to quantify the drag. As noted make sure you have a fully patched version as the radiator drag was at one time way too high, but was corrected in a patch.

jurinko
07-11-2004, 12:51 PM
neee, the effect of rack should be constant doesn´t matter how much fuel is carried in the internal or external tank. That 12kph loss due to its aerodynamical drag is reasonable. But the wrong dependancy observed is, the fuel from removed droptank adds its weight to the plane, but it is not present in the internal tank (gauge still shows 25% after the tank is removed but the plane behaves like with 100% fuel), and sometimes the total fuel weight even exceeds the internal tank capacity.

---------------------
Letka_13/Liptow @ HL

Willey
07-11-2004, 04:25 PM
You didn't do what Jetbuff proposed...

Take the G-6 with a droptank and keep it, don't drop it. Then take the same one again and drop it right at the start. If it doesn't differ here, we have it.

Fillmore
07-11-2004, 05:49 PM
"But the wrong dependancy observed is, the fuel from removed droptank adds its weight to the plane, but it is not present in the internal tank (gauge still shows 25% after the tank is removed but the plane behaves like with 100% fuel), and sometimes the total fuel weight even exceeds the internal tank capacity."

You don't seem to get that your test does not isolate the weight of the plane from the drag of the rack. It doesn't "behaves like with 100% fuel" it "behaves like with a rack". That is why you need to try it with a bomb that you drop rather than fuel, so that you can see that it is only the rack, not any weight from fuel that is making the difference (or rather that makes it almost the same with 100%-fuel-no-rack vs 25%-fuel-with-rack).

Willey's test does not isolate the drag of the droptank from the weight of the plane. If you keep the tank then you will get reduced performance, but you cannot isolate that as being due to weight of fuel or drag from droptank.

jurinko
07-12-2004, 12:30 AM
<BLOCKQUOTE class="ip-ubbcode-quote"><font size="-1">quote:</font><HR>Originally posted by Willey:
You didn't do what Jetbuff proposed...

Take the G-6 with a droptank and keep it, don't drop it. Then take the same one again and drop it right at the start. If it doesn't differ here, we have it.<HR></BLOCKQUOTE>

that one with the tank will be worse for sure - the aerodynamical drag of droptank will be added. I didn´t say the plane after tossing the DT flies exactly like with it - it lacks the tank drag now, but it flies like if all the weight of the fuel from DT had moved into internal tank, but
1) the gauge doesn´t show it
2) in some cases (&gt;25% of fuel starting with and removed DT) the overall weight of plane is bigger than with full internal tank. If the DT will replenish the fuel in main tank, it can not fill it up to more than 400l: but the plane flies like with 700l (when starting with 100% of internal fuel).
The rack itself should not affect the climb rate so much - it can lower the max speed a bit. The weight of the rack can not be equal to 300l of fuel.
But the idea with the bomb is good, I will test it.

---------------------
Letka_13/Liptow @ HL

Aaron_GT
07-12-2004, 08:59 AM
The rack shouldn't increase climb times very much. Drag scales with the square of the speed, and that is low when climbing. You can open your radiators when climbing without a huge effect on climb times.

jurinko
07-12-2004, 03:37 PM
so I run another set of tests and both sides were partially right http://ubbxforums.ubi.com/infopop/emoticons/icon_wink.gif

The immense increase in the climb time is really caused by the pure presence of the bomb/droptank rack. I tested the same G-6 in clean version, with dropped sc250 and with dropped droptank and both bomb and tank versions had the same, much worse, climb times.

(time to climb to 2000m/3000m)

clean G-6 0:42 1:39 (without the rack)
G-6 with dropped sc250 0:46 1:57 (with the rack)
G-6 with dropped droptank 0:46 1:57 (with the rack)
(all with 50% fuel)

so no 300l weight of fuel transfers into the main tank, but the ETC rack itself has the same effect like 240kg of gasoline (G-6 with 25% fuel and rack clims like clean G-6 without the rack).

Tested Fw 190 F-8 without the bomb and after dropping the bomb - same results. The rack is there by default.

tested the same with Bf 109 E-4/B and E-7/B - those planes have the bombrack by default. Planes climbed at the same rate doesn´t matter whgether starting empty, with droptank dropped or with sc250 dropped - tank is there by default and its effect is the same. But E-7/B flies quite reasonably with it.

The bug: ETC bombrack on 109G series has overmodelled weight effect. The aerodynamical drag causing 12kph loss is reasonable.

---------------------
Letka_13/Liptow @ HL

Fillmore
07-12-2004, 08:19 PM
One more series of tests to do and you will have the data you need to submit a bug report (if there really is a bug).

Pick a fuel load (doesn't matter which, but it will be the same for all these tests).

1. Test level speed. No Rack. Radiator closed (not auto).

2. Test level speed. With Rack. Radiator closed (if nothing has changed since last I tested, expect a difference of about 12kph from test 1, at least on a 109G2 anyway).

3. Test level speed. No Rack. Radiator Open. Goal is to find a radiator setting that drops the top level speed the same as just the rack. If fully open is still faster than with rack then use that for further tests, otherwise use lower open settings to find which is closest to rack.

4. Test climb time. With Rack. Radiator Closed.

5. Test climb time. No Rack. Radiator Open (to the setting you found in test 3 that most closely replicated drag of rack).

Now look at results of 4 and 5. If you found a radiator setting that reduced top speed same (or at least fairly close) as what rack does, but tests 4 and 5 give significantly different results, then mission control, we have a problem. Make .NTRKs and send bug report to Oleg. Otherwise, move along folks, nothing to see here.

If you really want to be thorough and cover all bases test with a dropped SC500 to be sure it gives same results as a dropped SC250.

Fillmore
07-12-2004, 08:32 PM
Oh, and something on the tests that may help clarify the results, as your tests show just 18 seconds max difference in climb times. Use a higher climb speed (thus lower climb rate and higher overall climb times). This will amplify the difference that drag makes, as the purpose of these final tests is to determine if the drag of the rack is modelled differently than drag from radiator (which we know was at one time wrong and was recently corrected, so if there is a difference we would assume the error is with the way the rack is modelled rather than with the radiator). This may be important if there is no radiator setting which gives exactly the same speed loss as the rack. If you have a choice between a radiator setting that gives slightly more speed loss or one that gives slightly less, then compare with setting that gives slightly more speed loss than rack, as this will more clearly show a problem if it climbs better than with the rack.

I do not know all that much about aerodynamics of airplanes, but it occurs to be that the fuselage may contribute lift, and that the rack could spoil that and thus hurt your climb/turn more than your topspeed in comparison to radiator drag??

Fillmore
07-13-2004, 12:18 AM
Ok, I did steps 2 and 3. I have found radiator position 8 with no rack to have the same top speed at 50m over the water on Crimea map QMB with a 109G-6 (518kph TAS, reached from a lower speed), as closed radiator with rack under the same conditions, setting the radiator to 6 makes it measurably faster than with rack, radiator fully open is measurably slower than with rack.

So your task now is to do your climb tests comparing a plane with a rack and with radiator closed, to one without a rack and with radiator set to position 8. If there is no difference then it is all in the simple drag, if there is a difference then I think it would be worthy of a bug report.

jurinko
07-13-2004, 07:15 AM
Hi Fill, the climb rate should not depend much on the rack drag - the drag lowers the speed of 12kph at max speed, but the usual climbing speed is less than half (260-290kph) and the drag is then 4x less (it rises with the square of speed). The weight, however, affects the climb rate very much.
If you climb with radiator at position 2 and with position on auto, you don´t see noticeable difference in climb time - plane just may be slowed down of few kph.
Anyway I wwill test a bit.

---------------------
Letka_13/Liptow @ HL

Fillmore
07-13-2004, 09:13 AM
I don't know how things should be, i'm mainly concearned with finding out exactly how they are (I used to do tons of testing myself but got burned out on it).

If you do find a problem, and the climb times with rack+closed radiator are much different then no rack+radiator position 8, then you should make another final test, which is to compare performance after dropping SC250 to performance after dropping SC500. If there is a difference there then you have isolated the problem as one of weight calculation, but if there is no difference there, but is a difference between 4 and 5 above then it would seem the difference is in how the drag is modelled under different flight conditions rather than one of weight.

jurinko
07-14-2004, 12:54 AM
I tested it..

the clean G-6 with rads set to 8 increased the climb time from 1:39 to 1:48

the rack-equipped G-6 with rads closed decreased its climb time from 1:57 to 1:52

However, the similarity of track/radiators drag should be done at climb speed, not max speed - 300-360kph instead of &gt;500kph.

If we suppose that the speed decrease at 330kph is cca 5kph and the climb trajectory is the same, there should be a difference of 150m (or 2sec of flight) after 1:50 climb test. More, open radiators acted as flaps which should make the climb steeper and the climb time shorter (but that effect of rads is obviously not modelled.)
I will do normal climb test from 0 to 5000m but I expect the climb time to be dramatically increased by presence of the rack which shouldn´t be realistic.

---------------------
Letka_13/Liptow @ HL

Fillmore
07-14-2004, 10:21 AM
"More, open radiators acted as flaps which should make the climb steeper and the climb time shorter (but that effect of rads is obviously not modelled.)"

That makes no sense at all. Are you saying a plane should have a better climbrate by lowering flaps? So I should be climbing with landing flaps?

I tested level speed and rack/radiator position 8 lowers it by 14, not 12 on the 109G-6.

The 1:39 time represents 30.3 m/s, 1:48 is 27.8 m/s, so radiator 8 reduces climbrate by 2.5m/s. 1:52 is 26.8m/s, so rack reduces climbrate by 3.5m/s. 14kph is 3.9m/s. So both radiator position 8 and the rack (seperately not both together) reduce max level speed by 3.9m/s (14kph), but the radiator reduces climbrate by 2.5m/s while rack reduces it 3.5m/s. Seems a bit severe, but I don't really know what to make of it.

"However, the similarity of track/radiators drag should be done at climb speed, not max speed - 300-360kph instead of &gt;500kph."

But you aren't looking for similarity, you are looking for difference. If we take two numbers, like 6 and 8, we have a difference of 2. If we double both numbers to 12 and 16 then we double the difference to 4. If you make your test such that climbtimes are doubled (you can use a lower power setting rather than higher speed if you want to keep the speed low) then this will make any differences easier to see.

It looks to me like it would be worthwhile to test a dropped SC500 to see if it is different from a dropped SC250, as this could isolate the problem as one of weight calculation if it turns out they are different.