147 sunroof wind 'deflector'...?

[johnl]

Driving home tonight with the 'sunroof' open (in quotation marks because I never open it if the merciless sun can then invade the cabin...), and noted the obtrusive wind roar coming from the leading edge of the aperture. Reaching up I experimentally pulled down the articulated pop-up 'wind deflector', and nearly all the unpleasant roaring instantly disappeared. Not only this, but there was no discernable increase in cabin turbulence (only a significantly more pleasant in car ambience).

It seems that this reasonably complicated spring loaded device doesn't actually work as a wind 'deflector' (assuming that be its' intended function, I can see no other) but is in reality a very effective wind noise generator, serving no other function, apparently.  I'll have a look tomorrow to see if it can easily be locked down, out of the airstream.

Can anyone come up with a good reason as to why not try this?

Regards,
John.

[bazzbazz]

The purpose of the deflector is to prevent "Cabin Throb" between 40 & 80 km/h. Faster than that and you get a boundary layer of air running fast enough for it to "skip" across the opening and not enter into the cabin and the deflector is not needed.

I am sure I have seen cars somewhere, where above 80km/h the deflector is retracted/reduced to diminish the noise, obviously expensive cars. 

So you're quite correct in your observations, and at least now you know why it's there. Though there may never seem to be a reason for some sort of engineering on a car, you can always be assured, if it adds cost in any way what so ever it's there for a reason, the bean counters are merciless !   

[Citroënbender]

A few things seem to get past the financial controllers, I've observed aspects of the 147 which are unnecessarily labour-intensive or illogical in respect of serviceability, eg:

Cabin wiring harness goes behind firewall insulation, making a re-loom much slower.
Firewall plate for mounting pedals/booster is not universal, there are manual and Selespeed variants differing only by the punching of a hole and two adjacent mounting points.
The interior trim tactile coating was applied to the ashtray, no surface of which would normally be touched.
The B pillar upper trims are only removable after the scuff plates and lower B pillar trims. This adds unnecessary time and grief to a headlining job.
You need to either lift the car or remove the front bumper to replace the AC drier.

[johnl]

Bazzbazz,
If that's the case then it doesn't seem to work. My car suffers from sonic 'throb' with the roof open, at some speeds not sure what because I've not taken note. The cure is to not have the roof fully open, the throb disappears with the roof about half shut / open.

'Throb' didn't occur when I was manually holding the 'dethrobber' in the closed position. All that happened was significantly less noise. If I can keep it held down (pull ties?), then I suppose I'll find out if there are certain speeds at which unacceptable throbbing occurs without it being 'up'.

I understand your argument re cost, but I suspect not every detail is deeply analysed / scrutinised by the bean counters. Either that or the engineers may defend some feature or other with enough vigour to justify it's retention. I doubt the the accountants personally evaluate every single thing that they may question, for one they are not qualified to do so (that's an engineers skill). In any car company I'm sure there are some epic battles between engineering and accountancy departments (and marketing), but I doubt that the engineers are completely defenceless against the bean counters. I could be wrong...

Regards,
John.

[johnl]

Citroenbender,
There are many things in how cars are put together that are nothing whatsoever to do with ease of access or servicability, or cost associated with that, and entirely to do with what is easy / quick to assemble on the production line, and the cost associated with that...

Regards,
John.

[bonno]

Its all to do with harmonics.

[Citroënbender]

That's a version of "front loading" your fiscal stream; it declines to recognise the probability of repair operations which may fall within warranty period (or even thereafter, giving the car a bad name among techs). Consider how soon the 147 sunroof rear drain nipples started cracking away.

Another pet hate is modern fuel tanks in commercial variants of a car/wagon, where there's no access port for the sender assembly - the manufacturer blithely states you remove the tray liner - which in real life is usually covered in accessories that also require R/R like canopies/bars/roll tops etc.  Not to mention full of junk tools of trade and surplus materials held over! 

[johnl]

So, in the light of day I had a look at the mechanism. The 'deflector' flap is held 'up' by two small springs, one at each side of the flap, which are very quick and easy to remove (and it looks should be equally easy to re-install, which from past experience may be mistakenly dangerous thinking?).

Anyway, I've removed the springs and the flap has dropped down. I haven't driven the car today so speed related sonic throbbing is yet to be tested. I'll see what happens...

Regards,
John.

[bonno]

Hi John
Checked the wind deflector on my 156 and have mot experienced this problem ( upto 110kms). Could it be that the springs have just lost their tension to such a level that the harmonics come in to play. Checked the wind deflector from centre position on mine and there is a considerable amount of resistance to eliminate flapping. Not scientifically, but I would have at a guess at about 300 gms force.

[johnl]

Bonno,
There is no problem as such, the 'device' seems to be working as intended (at least mechanically). The springs are not weak and there is no "flapping" of the 'deflector flap' at any speed, with it being held firmly in the 'up' position. Having said that, I can foresee (not yet having driven the car with these springs removed) at least some possibility that airflow might 'suck' the flap upward, in which case it may "flap" around in turbulent airflow. I suppose I'll find out when I drive somewhere (if the 'flap' does "flap" then I'm sure it could be stopped from doing so in some relatively easy manner).

The issue with my cars' sunroof (and a minor one really) is only that the deflector flap protrudes into the air that is flowing over the car roof, and this creates a significant amount of relatively unpleasant wind 'roar' as the air passes over the protruding flap.

With the springs installed and the 'flap' protruding upward as per stock there is still throbbing at some speeds, despite the flap being designed to prevent it (apparently being its' purpose). Harmonic resonance is what would cause 'wind throb' in the cabin (not the 'roar', which is a different problem) at whatever speed it might occur. 'Throbbing' is worse than roaring, the roar merely being a slight annoyance, but the throb being actively discomforting. 

It remains to be seen whether preventing the flap from rising will result in any throbbing that is worse than the throb that already exists (with springs installed and flap up). I may (or may not) drive the car this afternoon and find out, but in the meantime before I do that I have about 1 hectare of grass to mow, in the hot hot sun. If I don't report back, I may not have survived...

Regards,
John.

[johnl]

So,
As more or less not unexpected, resonant throbbing is worse when the 'deflector' is inoperative (the roof fully open and the windows closed). It kicks in at around 50kmh and stops at about 80kmh. Open one or both windows about 1/4 or more and the throbbing disappears. If the roof is not fully open then it also disappears. My sunroof still causes throbbing when the deflector is working, just less so.

I only open the roof when I want lots of airflow in the car, which means I tend to open it only after I've opened one or both windows. So, the throbbing thing isn't an issue for me since I'm unlikley to often open the roof on its's own (which is the only time the throbbing occurs).

It is nice to have significantly less wind noise at speeds above about 80kmh with the roof and windows open, so for me it makes more sense to leave the 'deflector' springs off and  not have it pop up. If you like having the roof open with the windows closed, then you would definitely want the deflector to pop up when the roof is opened.

Regards,
John.

[Citroënbender]

We experimented with this last week, definitely more bass noise (probably as named throbbing, above) and less roar with it down. Consensus held the roar preferable to the bassy tones, hence the music was turned up.

[Craig_m67]

Is this perhaps related to the clutch dampener ... i only ask as I'm drunk 😵
(My shout)

[Citroënbender]

What's your tipple?

[bazzbazz]

Is this perhaps related to the clutch dampener ... i only ask as I'm drunk 😵
(My shout)

AGAIN ?