[Spridgets] Boot lid and spoiler

[WeslakeMonza1330 at aol.com]

Hi Mike,   
 
A good question that no-one else has asked and which isn't in any of the  
data I've released!
 
Wind tunnel testing can be at any speed up to the maximum rating of the  
tunnel.  At the tunnel I used it was also possible to have the data  
automatically calculated at a higher speed than the test speed.
 
The answer to your question is probably at any speed above 50 mph with  
increasing effectiveness at higher speeds.  Why 50 mph?  Well, at 50  mph I'm 
guessing the grip of the tyres is making a bigger difference than   the aero. 
 I'm also guessing the lighter the Sprite/Midget the greater the  
difference.  Some of this may be in the book, eg: I didn't notice  front end pitch on 
my car when it weighed about 20 Kg more than it does  now.  Put another 
way, the aerodynamic forces were the same when it weighed  20 Kg more but were 
simply less/not at all noticeable.
 
Drag reduction is always most noticeable at top speed simply because it  
allows a higher top speed.  The lift reduction will probably be most  
noticeable at about 80 mph upwards because that's when driving through my  
'reference fast curve' I start to think about whether the car feels like it has  
enough grip to press on to about 100 mph after which I get more cautious.   I'm 
guessing that when I drive my 'reference fast curve' the car will feel more  
'planted' from 80 mph upwards and at 100 mph I'll feel a lot more confident 
to  proceed to a higher speed than was previously the case.  Put another 
way,  at the present time I don't know what 30 lbs less lift will feel like 
other than  it will remove the pitching down at about 110 mph that it 
currently has.
 
Regards
 
 
Daniel
 
 
In a message dated 12/05/2017 20:17:53 GMT Daylight Time,  
rrengineer.mike at att.net writes:

Out of curiosity, at what speed does it become effective?
Mike MacLean






 
 
On Friday, May 12, 2017 9:31 AM,  WeslakeMonza1330--- via Spridgets 
<spridgets at autox.team.net>  wrote:




 
 
Hi List,
 
My new boot lid has just been delivered.  The lid is a new steel  frame, 
skinned in aluminium and incorporating a spoiler based on the design I  tested 
in the full scale wind tunnel.  It's seen here placed rather than  fitted 
to my car for a photo before I get it painted.  It weighs in about  230 
grammes less than a steel lid without a spoiler but after painting I'm  guessing 
the saving will be about zilch.  Short of my unexpectedly having  a large 
sum of spare money  it will be several years/never before I can  have it 
tested in the wind tunnel.  However, in the light of the 4 tests  I made with the 
'mule' boot lid and spoiler its very likely to put 2 mph on  the top speed 
and reduce lift by 30 lbs at the rear.
 
Regards
 
Daniel







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