Wind Noise

[jonclancy]

[Schoolboy snigger...]

The taller among us might have noticed the amount of wind noise when driving our cars. It's distinct from the induction, exhaust and road noise. I've used foam ear plugs, musicians attenuating full range plugs, wearing my fleece beanie with goggle straps (recently in the colder weather) - and no hearing protection at all.

The latter is fatiguing after a very short while. The fleece works well to reduce the wind noise, and both types of plugs dull the exhaust note, but do little but mask the outside world. The joy of open motoring is quite the opposite of that!!

I've discovered a couple of things:

A hand resting on the top of the screen has the same effect as ducking down a few inches. A massive reduction in wind noise. That's obvious, of course, and an easy fix with some "H" channel ally moulding and some appropriately sized Perspex from eBay. I do recall period pictures with Elevens sporting similar mods.

Another source of wind noise, which I thought was a whine, comes from the round-section wing mirror mount. It all but disappears when I put a hand in front of it while driving. There are suppliers of streamline (not aerofoil, for obvious reasons) tubing. A mild steel profile could be welded to produce a new mount, but the angle of attack would need to be zero and carefully constructed so as to not introduce more turbulence and therefore noise.

I've discovered K&S Precision Metals. They supply profiles and tubing to crafters/ modellers. The supply various sizes or streamline aluminium tube, and, once I can get to a model shop locally, I'd like to use some as fairings on the mirror mounting.

http://www.ksmetals.com/32.html

Anyone got a wind-tunnel I could borrow, please?

[bobwhittaker]

For ultimate wind noise visit " The singing ringing tree " panopticon on the moors above Burnley .

[Westfield 129]

Bucket seats or the bench seat back?

If you have the bench, you can easily re contour the seat so that you fit beneath the windscreen. That will fix your wind noise problem.

[jonclancy]

Hi Bob,

I hadn't heard about the Panopticon. What an impressive work of art.

Reminds me of this beauty I like to spend a few moments gazing at every time I walk past it:

http://www.waymarking.com/waymarks/WMGV ... _Boston_MA

Hi Jan,

Bucket seats for me. I'm just over 6', so the wind deflector should work well....

[alleggerita]

It seems that someone did windtunnel testing on a model that was used for the design of the XI:
http://www.rae-exapprentices.org/measuresmitt1955c.pdf

The author of this document describes having done tests at the Messerschmitt Wind Tunnel in 1955, which is now at the Farnborough Air Science Trust Museum. If you have a scale model of your Eleven you could take it there!

The author was invited to explain the results of his testing to Frank Costin and Colin Chapman. Costin wasn’t fond of wind tunnels and relied more on his own calculation skills backed by testing. Look at the striking picture in the Ortenburger book where you can see Costin strapped to the bonnet of a wind vanes cladded Eleven while being driven at high speed.

I assume if you want to reduce wind noise by reducing turbulence around the indicated areas, you have to make sure not to introduce too much laminar flow, which has a bad influence on your maximum speed.

[Westfield 129]

I dont' know anyone that tall that still has bucket seats in the W11, flat or dropped floor. Seems that they stick out the top too much. My set of buckets (not yet installed), came from a local guy who couldn't stand the turbulance, and needed to get lower in the cockpit. Elminating the seat allows a much lower seating position, with more padding available for the seat squab.

If you get some 3 layer tempurfoam and some hard foam (used for seat forming), you can remove the bucket, and contour a seat that will drop you a few inches into the car. The driving position will be more Lotus 25, but this is actually quite comfortable if you get it right.

Use the 3 layer for the seat squab. You can use the medium and hard tempurfoam for the seatback.

Once you get your head out of the slip stream, the car becomes really comfortable, as there is an almost complete absence of turbulence in the cockpit when the body is fitted with the head rest faring.

[jonclancy]

I'm long in the leg, so the buckets aren't too bad... I do like a bit of a breeze blowing through my luxuriant mane, though. The joy of open top motoring! I'll try the screen deflector and profile first. The bucket seats are very comfy for me, and a bench would mean 'Er Indoors would need to wear platforms to reach the pedals. I reckon an hour's work would sort this, rather than redoing the seat...

I can't recall where I read recently a comment about the head fairing without the single cockpit being a bit of an air brake. Is that why Splat is changing to a standard rear clam? Comment on laminar flow is an interesting aside. My car never gets to max revs in top when I drive it, anyway! Maybe I should be trying harder!

Just reading the full article linked above now. What a gem! Thanks!!

[Westfield 129]

Usually, the long lagged get rid of the buckets as there is a couple of more inches of leg room available with the flat seat back.

On early cars, the forward seat travel is limited by the frame element that holds the alloy floors in place and stiffens the chassis.

Having long legs will ensure that your head is lower in the cockpit with the bench seat back and a semi reclining seating position. As far as platforms being necessary to work the pedals, I split the bench seat back and make one thick, and the other thinner. This usually makes an excellent adjustable seat. As or the wind in the hair, you can easily set that with the seat back contour, or the seat squab thickness.

I always wear a hat and goggles, so I prefer to be down inside the cockpit.

In any case, this eliminates what could be an ugly wickerbill attached to your lovely aero windscreen, and just leaves another thing to grab that can crack it.

My Lotus 7 Series 1 had a split seat back in two thicknesses, as the previous owner was tall, and his wife, who was racing the car, was short. The seat back setup worked perfectly to fit the two drivers.

I doubt that the head faring is much of an air brake. The unfared head is more turbulence inducing, and the fin fixes the problem. The lack of turbulence in the cockpit of a head faring equiped body is indicative of the reduction in drag.

Of course, if you wanted to do a tuft test on the bodywork, you really don't need a wind tunnel. All you need is a few meters of yarn or string, some tape, a road and a camera to record the data.

With my car, the problem is the drag in the engine compartment, as the W11 lacks the under bonnet aero of the original Lotus 11. Getting all the front aperature air flow to go through the radiator and exit beneath the car would help quite a bit. This is likely more of an aero problem for the W11 than the headrest and fin. The bonnet blows up and lifts at speeds much over 120, and my car is still accelerating at that point. I suspect that it will pull redline (6400 RPM, around 130 mph) in top gear if I can keep the air out of the bonnet.

[jonclancy]

120? Blimey! What diff ratio are you running on your 15"?

[alleggerita]

Assuming:
5900 rpm at 120 mph
Gearbox out ratio 1:1 in highest gear
4.5 x 15” tyres, dia 650 mm
You would get a diff ratio of 3.54

From the tests done by Costin we know that the slippery Eleven body needs 9 BHP to run at 60 mph. Extrapolating this to 120 mph requires 72 BHP.

All within normal values I would say, except it probably needs a big heart and a wide lane to test it.