[Healeys] Interesting (?) Photos

[Bob Haskell]

Chris,

African or European?

Cheers,

Bob Haskell
AHCA 3000 MkI registrar
http://www.ciahc.org/registry_3000mk1.php

On 08/01/2018 08:37 AM, Chris Dimmock wrote:
> Hi Perry,
> I suspect the mistake you have made is that the calculations indicate 
> the vehicle is stationary.
> If I use your same calculations for the same column of air (so let's 
> assume the radiator opening is the same size as the fan diameter), but 
> the car is travelling at 60mph:
> 60 mph = 5,280 ft per min, which is also the airspeed velocity of an 
> unladen swallow.
> So then 3.1416 x .390525 x 5,280
> = 6,478 CFM
> 
> Which is why you never have an overheating issue at 60 mph (unless 
> you've put an electric fan in front of your radiator, as happened to 
> several competitors at Bathurst)
> 
> I'm not sure what this all proves, but it shows that you only generate 
> 20% as much airflow stationary in your driveway at 3,000 rpm as you do 
> driving at 60 mph.
> 
> Best
> Chris
> 
> On 1 Aug 2018, at 1:58 am, Perry <healeyguy at aol.com 
> <mailto:healeyguy at aol.com>> wrote:
> 
>> OK this has been bothering me off and on for years and I never did 
>> anything to try to calculate the Cubic Feet per Minute (CFM) of a 
>> stock AH100 radiator fan. In light of the recent discussion of air 
>> flow in the engine compartment
>>
>> (Some text borrowed from the net)
>>
>> According to the general fan law for axial fans, you will need to know 
>> the fan blade diameter and pitch (blade tilt or attack angle) along 
>> with the rpm to calculate CFM. An Austin Healey 100 radiator fan has a 
>> four blades with a 15 inch (1.25 foot) diameter and an 4-inch 
>> effective pitch (one inch pitch times four blades). This means that 
>> each revolution of the running fan blows the 1.25 foot diameter column 
>> of air coming passed the fan 4 inches.  There are efficiency losses 
>> but we are talking generalities here . For the two ends of the 
>> spectrum the engine is idling at 700 rpm or powering along the road at 
>> 3000 rpm. The pulley setup on the AH100 is nearly the same diameter on 
>> the water pump and crank, so the fan rpm is approximately the same as 
>> engine rpm.
>>
>> Calculate the linear velocity of the air through the running fan. If 
>> each revolution moves the air 4 inches, then 700-revolutions per 
>> minute multiplied by 4 means the air is being moved at 2800 inches per 
>> minute, or 233 feet in one minute.  For 3000 rpm engine speed, the 
>> answer is 12000 inches or 1000 feet.
>>
>> Calculate the CFM (volumetric flow of air) at 700 rpm. The volume of 
>> the column of air described above is pi (3.1416) x fan radius squared 
>> (7.5 inches or 0.625 feet squared) times the column length in feet. 
>> This would be 3.1416 x 0.390525 square feet x 233 feet = 285 cubic 
>> feet per minute at 700 rpm. At 3000 rpm the CFM is 1226.
>>
>> I knew that the stock fans do not move much air but my calculation 
>> says it really is horrendous. Suspect my math is off somewhere. Math 
>> teachers and mechanical engineers and anybody else for that matter, 
>> Comments please.
>>
>> Perry
>>
>> To:
>>
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