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#1 Rad air control flaps

Posted: Mon Apr 20, 2020 12:47 pm
by Fspp369
Hi all,
Hope everyone is staying safe.A BIG thank you to anyone working within the widest health care sector, particularly the NHS.

Does anyone know of a source of suitable rubber sheet to remake the flaps on the back of the radiator shroud on an S3. There are two thicknesses of material 1.5mm and 2.00mm the latter is for the “cross” shroud flap at the top, presumably to work at different speeds depending on the air speed coming through the rad under normal driving conditions.
Mine are falling apart with a tear along one side to the middle flap.
Any info appreciated.
Peter.

#2 Re: Rad air control flaps

Posted: Mon Apr 20, 2020 9:25 pm
by Series1 Stu
Try using old inner tubes?

Regards

#3 Re: Rad air control flaps

Posted: Tue Apr 21, 2020 7:49 am
by Fspp369
Mmmmm, thanks for that, I’m not sure if they will be heat stable and oil/fuel/ATF etc resistant.
May try specifically made silicone sheet, or maybe Viton sheet. You see I’m trying to get complicated to solve the problem, but will try the KISS principle. :studyinggray: :scratchheadyellow:

#4 Re: Rad air control flaps

Posted: Tue Apr 21, 2020 1:26 pm
by Colin
Hi Peter
I bought a set from SNG Barratt part number C33960/3 £11.76 in stock inc VAT

I bought mine in 2011 and they were pretty good quality so probably not worth trying to make them for that sort of money

Cheers

Colin
S3 V12 2+2 1973

#5 Re: Rad air control flaps

Posted: Tue Apr 28, 2020 3:54 pm
by Fspp369
Colin, I have great sympathy with that view, but that has never stopped anyone making life complicated has it?
The air control flaps on my rad cowl and two others I’ve measured have different thicknesses. One on the top O/S is almost twice as thick as the others, this leads me to believe that there is a differential in the flow at certain flow rates/air pressures coming through the radiator. The downward flow of the rad may give a temperature gradient such that the lower air flow is through the top, as the stiffer flap would prevent flow.
The central two and the lower N/S flaps open much more easily, at perhaps lower car speeds, enabling more air to pass through the rad/cowl combination to the engine, and that’s where the hottest water is.
When the fans come on they all close together.
So, does anyone on the forum know why these flaps are like this for sure, and what’s the purpose of the differing thicknesses if my wet finger in the air theory is correct.
I did say complicated is good sometimes....I know K.I.S.S. :roll: :scratchheadyellow:

#6 Re: Rad air control flaps

Posted: Sat Jul 25, 2020 10:06 am
by Fspp369
This is the finished cowl with viton rubber flaps and two speed Coolcat type fans.
It works a treat....anyone spot the deliberate change..? I thought I’d try it and it works!
Peter
Image

#7 Re: Rad air control flaps

Posted: Sat Jul 25, 2020 10:09 am
by Fspp369
More pics available if reqd

#8 Re: Rad air control flaps

Posted: Sat Jul 25, 2020 2:57 pm
by jagwit
Fspp369 wrote:
Sat Jul 25, 2020 10:06 am
Image
I once saw this cowling mounted IN FRONT of the radiator by a highly regarded Jag rebuilder here in South Africa. So, yep, we have those too.... :cry:

#9 Re: Rad air control flaps

Posted: Sat Jul 25, 2020 3:37 pm
by Fspp369
Ahh yes but you haven’t spotted the difference.

#10 Re: Rad air control flaps

Posted: Sat Jul 25, 2020 3:47 pm
by jagwit
Fspp369 wrote:
Sat Jul 25, 2020 3:37 pm
Ahh yes but you haven’t spotted the difference.
Sorry, I don't understand.

#11 Re: Rad air control flaps

Posted: Sat Jul 25, 2020 4:41 pm
by Fspp369
Spacers on the ends of the fan mounting “ spiders” to bring the tips of the fans back to assist in air flow ( according to a Cranfield engineer I know, something to do with tip vortex!!.) and the bottom flap is inverted.
Mounting that lot in front of the rad must be an interesting excercise .
Any pics

#12 Re: Rad air control flaps

Posted: Sat Jul 25, 2020 5:11 pm
by jagwit
Fspp369 wrote:
Sat Jul 25, 2020 4:41 pm
Spacers on the ends of the fan mounting “ spiders” to bring the tips of the fans back to assist in air flow ( according to a Cranfield engineer I know, something to do with tip vortex!!.) and the bottom flap is inverted.
Mounting that lot in front of the rad must be an interesting excercise .
Any pics
Original fans also have those spacers, most likely for the same reason.

I can find no reason to deliberately invert the bottom flap. Although the radiator and the cowling is slanted slightly forward, RAM air pressure from the front would easily push that flap rearwards over the vertical. When everything is nice and hot in there, that flap will curve over all the way to look like an inverted U. Once in that position, when the fans run, they will not suck that flap closed but will in fact suck LOTS of air from behind the cowling, then just circulating through the fan, right back into that opening, effectively short-circuiting the RH fan.

I can find only good reasons why it should also hang down just like the top one.

Mounting the cowling in front of the radiator is physically very easy - IF the bonnet is off. Most likely THE reason that car I saw was done like that. But its still a very bad idea!!! First, the fan motors will have to run the other way round to push air, rather than suck, secondly the rubber flaps will then have to be mounted on the INSIDE of the cowling, because if they remain on the outside, the fans pushing will then push them open rendering fan action quite useless. Second, the idea is that those flaps should be pushed open with RAM action, so then they should be mounted on the inside of the cowling, so that ram air will push them open.

That inverted flap is IMO, just not a good idea, period.

#13 Re: Rad air control flaps

Posted: Sat Jul 25, 2020 5:29 pm
by Fspp369
Have you seen viton rubber flaps at the temperatures that are expected?
Have you seen the Coolcat fans on high speed?
Mounting on the front of the rad is therefore a pointless excercise!
Having seen the flaps working,?, they seem to cope .period.

#14 Re: Rad air control flaps

Posted: Sat Jul 25, 2020 6:15 pm
by jagwit
Fspp369 wrote:
Sat Jul 25, 2020 5:29 pm

Mounting on the front of the rad is therefore a pointless excercise!
So we agree!

:-)

#15 Re: Rad air control flaps

Posted: Sun Jul 26, 2020 8:46 am
by Fspp369
Phillip
Don’t recall your replies to my queries.