Radiator drag

[IvanK]

I spent most of today in the UK National Archives collecting info. One snippet I came across was Radiator Drag measurements on Hurricane II. Graph below gives an indication of the real world effect of Radiator Drag:

http://i40.photobucket.com/albums/e215/zulu64/Rad_Drag.jpg

[CaptainDoggles]

Nice find,thanks for sharing.

[Kurfürst]

Thx ivank.

109 data.

I. For what it's worth, French trials of 109E suggest the following figures:

http://kurfurst.org/Performance_tests/109E_French_trials/french_109e_performanceT.html

Bf 109E-3 at 5000m, OPEN radiators, 2400 rpm and 870mm Hg boost: 520 km/h
Bf 109E-3 at 5000m, CLOSED radiators, 2400 rpm and 880mm Hg boost: 570 km/h

II. As per the V15a trials.

the 570 km/h speed was understood with the coolant radiator flaps 1/4 open (radiator flaps in streamlined position) and closed (I guess minimum) oil flaps position.
This was sufficient to maintain a constant, optimal 90° Celsius coolant and 62/82° Celsius oil temperature, at +5 ° Celsius external temperature during level speeds.

Maschine Bf 109 V 15 a D-ITPD W.-Nr. 1774
Motor DB 601 A W.-Nr. 140
Schraube 3 fl. VDM Verstellschraube 9-11081 W.-Nr.17459
Wasserkühler 1/4 geöffnet (Klappe in Straak)
Wassertemperatur konstant = 90°
bei +5° Außenlufttemperatur

Ölkühler Klappe geschlossen
Öltemperatur 62/82°; Öldruck 3,2 kg/cm2
bei +5° Außenlufttemperatur

http://kurfurst.org/Performance_tests/109E_V15a/Geschw_109V15a.html

III. Somewhat related are the figures for Bf 109 G radiator drag.

It should be noted that the top speed of 109's were understood for a condition where the raditor was very slightly open (1/4 open in 109E, 50 mm open on 109F-K) compared to it's minimum opening position, ie. not 'fully' closed (which I believe was impossible to do on 109E anyway). This was usually referred to as 'schnellflugstellung', ie. fast speed setting. Top speed data refer to this setting.

See: http://kurfurst.org/Performance_tests/109G_Leistungzusammenstellung/LZS109G_Blatt24_radiatoreffecton_speed.jpg

CONLCUSION

Therefore, IMHO and based the data in a good and realistic 109E radiator drag setting should look as the following:

Raditor closed: ca. + 5 km/h faster speed (negative drag)
Radiator 1/4 open: no drag = top speed achiavable
radiator 100% open: ca. -35 km/h speed loss at SL, ca. -50 km/h speed loss at 5000m (since drag has greater effect at higher speeds/at full throttle heights)

I am looking forward to see the specs for other aircraft as well.

Picture of 109E coolant radiator in presumably fully open condition.

http://www.ww2aircraft.net/forum/attachments/aircraft-picture-requests/166838d1304831173-me109e-nose-detail-radiator.jpg

[camber]

Very Interesting!

One thing I am not sure of, does Hurri "Flap 6 notches open" correspond to fully open? It seems likely.

So converting to kmh, the Hurri is losing around 8kmh to the rads at a middle-low speed (340kmh)

The 109 is losing around 50kmh at a high speed (570kmh).

As form drag is very nonlinear with airspeed (supported by real data above) it would be fantastic to see this modelled. Poodling around with fully open rads would be fine, but it would be very detrimental trying to get fast. Good pilots would be having to perform rad adjustments.

[Crumpp]

One snippet I came across was Radiator Drag measurements on Hurricane II.

Nice, thanks for posting it.

What were the test conditions?

[Osprey]

Are you about to invalidate it with your expert insight?


Remarkable difference between Kurfursts 109 data and the Hurricane. The rads are very different though, the Hurricane is a single rad in the propwash so gets perhaps more airflow than outside the wash I would think??? citation needed....
Plus the 109 has twin rads, are they in the propwash, they are on the edge....

[JG52Uther]

Can you please stop sniping at each other.

[Osprey]

Sorry, I was just trying to save time ;) :D

[Crumpp]

Sorry, I was just trying to save time

No you were not Osprey. You just don't like the fact I don't agree with you on some things.

Grow up.

First of all, it does not make a bit of difference to "test" something and then completely invalidate the effort because of ignorance.

I am not calling anyone ignorant so don't turn it into that. There is a reason why aeronautical engineering efforts are teams in the real world. There is a lot of details that can bite you.

Now, there are some knowledgeable and experienced people on these boards.

You want the dev's to listen and make your favorite gameshape as easy for you to live out your ace fantasy as possible, right? ;)

1C knows what they are doing in terms of aircraft performance. The fact they have adjusted the FM's once says they are concerned. Now, you are saying after all the time they just spent adjusting things....it is completely wrong. Based on what??

Whines waste time and more importantly money to a company. The people at 1C are paid and the company estabilished the boards to save some of that money by cutting down on the number of wild goose chases they send their people on.

If you want to be listenend too then raise legitimate issues. The first thing is is to determine if there is an issue in the first place.

Aircraft performance is dependant upon conditions. Without the conditions, what IvanK posted is interesting like an art gallery is interesting but not very useful for making any conclusions about specific aircraft performance.

1. Determine the atmospheric conditions in the game- that is the first priority. If it is not correct, anything else is a pointless waste of time.

[bongodriver]

1. Determine the atmospheric conditions in the game- that is the first priority. If it is not correct, anything else is a pointless waste of time


and the reason we can't enjoy the fruits of your very qualified analysis is because?...............

[Osprey]

I see you took on board what Uther was saying then Crumpp.

[phoenix1963]

1. Determine the atmospheric conditions in the game- that is the first priority. If it is not correct, anything else is a pointless waste of time.

What twaddle, Crumpp you need to distinguish between first and second order effects. Some simple corrections for the "actual" CloD atmosphere are not difficult. Some slight error in a model based on this data would have negligible effect on overall peformance in the scheme of things.

What is lovely about this is some REAL data on a small part of the contribution to performance. However it looks like the data in (winter?) temperate climes has been extrapolated to others, maybe a prediction for overseas performance. Perhaps the basis for a sensible extrapolation to other altitudes in the CloD models.

The very fact that it's labelled "temperate" should suggest to you that small variations in temperature are a fairly minor effect on drag due to the radiator, compared to overall drag - a second order effect.

Get a grip on what is and isn't important!

56RAF_phoenix

[Crumpp]

The very fact that it's labelled "temperate" should suggest to you that small variations in temperature are a fairly minor effect on drag due to the radiator, compared to overall drag - a second order effect.


What twaddle?? The only twaddle is people being agressive and running their mouth without facts.

Conditions in England in August are not far from standard depending on the time of day.

http://www.wunderground.com/history/station/03772/1996/8/1/DailyHistory.html?req_city=NA&req_state=NA&req_statename=NA

So the graph is meaningless without specific information.

[CaptainDoggles]

So the graph is meaningless without specific information.

Not sure if I would go that far. The results appear to be parallel, i.e. linearly translated, so it would seem to me that we can conclude that differing conditions do not have a significant effect on radiator drag. The relative difference between Closed and Open 6 Notches remains about 5 mph at approx. 20000 feet in each curve.

What I would like to see is a comparison for different altitudes.

[Crumpp]

109 data.

I. For what it's worth, French trials of 109E suggest the following figures:

http://kurfurst.org/Performance_test...formanceT.html

Bf 109E-3 at 5000m, OPEN radiators, 2400 rpm and 870mm Hg boost: 520 km/h
Bf 109E-3 at 5000m, CLOSED radiators, 2400 rpm and 880mm Hg boost: 570 km/h


If you line up the altitudes and look at the manifold pressures the French recorded, they used higher manifold pressure's when the closed radiator test was conducted.

That means the speed gap between open and closed due to radiator drag is not as wide as their results.

[Crumpp]

What I would like to see is a comparison for different altitudes.

That is what I am looking at but without the conditions, the information is useless.

[Kurfürst]

If you line up the altitudes and look at the manifold pressures the French recorded, they used higher manifold pressure's when the closed radiator test was conducted.

That means the speed gap between open and closed due to radiator drag is not as wide as their results.

I don't think 10 Hgmm boost difference would change anything. In real life, that's well inside measurement/manufacturing/modelling tolerance.

From the practical standpoint its not too relevant either, since 1/4 open is the speed referenced point, the temperature is stable. Fully open position has only relevance as a speed break or on the ground for example, in prolonged run up.

In short, technically it might not reach up to modern engineering standards, but its more than good enough to model a flightsim with apprx. good values.

[Crumpp]

In real life, that's well inside measurement/manufacturing/modelling tolerance.


I agree it is not going to make much difference. I just noticed it and wanted to point that out.

Fully open position has only relevance as a speed break or on the ground for example, in prolonged run up.


Exactly.

I did not think the overheat modeling was realistic at all. In general these airplanes are designed to fly with radiators closed or in the least drag position (straak) and keep the engine cooled at maximum continuous and below.

It is only in overboost conditions, high density altitude, and stressful operations such as climbing that the engine temperature becomes an issue. I tried the Spitfire Mk I out and it ran at maximum temperatures in level flight in cruise settings.

[pstyle]

Hopefully the mythical patch update will give us some radiator drag modelling.

We red's have been running about with rads wide open for months now, with no effect on airspeed... I think, in the interests of historicity that this should be fixed... ;)

[TomcatViP]

Hopefully the mythical patch update will give us some radiator drag modelling.

We red's have been running about with rads wide open for months now, with no effect on airspeed... I think, in the interests of historicity that this should be fixed... ;)

That's the problem of some behaviour in IL2 sim world.

Personaly I never did that and used the rad as if they were not bugged (but I am so sure they induced drag that I am thinking you are one of those that are constently midling their prop with no top perf achieved).

Hence IMOHO, it's more a bug in the behaviour of some players that the only patch that will makes this debate vanish is your own grandma modeled back on your shoulder just like the days when she caught you the finger in the jam.

[pstyle]

but I am so sure they induced drag that I am thinking you are one of those that are constently midling their prop with no top perf achieved
.
ooooooh, handbags.....

[TomcatViP]

To get back to the graph posted by IvanK it show us that the drag effect of the rad flap in the free stream is negligible. Most of the drag come from the free stream of air impacting the actual radiator surface inside the duct (the duct being the encasing sheet metal).

Lowering the flap increase the exit area allowing a greater mass of air to circulate trough the radiator. Since the geometry of the rad system is fixed, in the inlet portion, the air is less decelerated and then impact the rad at a higher speed. This increasing the drag of the system (but adding more cooling effect obviously).

Concerning the FM of CoD, it could be interesting to use this same value for the Spit.

[klem]

Not sure if I would go that far. The results appear to be parallel, i.e. linearly translated, so it would seem to me that we can conclude that differing conditions do not have a significant effect on radiator drag. The relative difference between Closed and Open 6 Notches remains about 5 mph at approx. 20000 feet in each curve.

What I would like to see is a comparison for different altitudes.

And so we should not start splitting hairs. There are considerably larger incorrect level speed figures in the Hurricane at the moment (nearly 60mph @ 20,000ft?). 5mph might matter in a tail chase but in terms of combat performance it means almost nothing. It may be more significant at lower altitudes though.

[CaptainDoggles]

Agree 100%