James
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| posted on 10/5/11 at 11:39 PM |
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F1: Calculating temperature change from air friction
Been letting my brain have some thoughts this evening- never wise!
Wondering what sort of temperature change you'd get from the friction caused by air flowing over the front wing?
I know that high speed planes suffer from this but that's at Concorde's sort of speeds. Would there be a measurable affect at your average
F1 speed of about 150mph?
Cheers,
James
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"The fight is won or lost far away from witnesses, behind the lines, in the gym and out there on the road, long before I dance under those lights."
- Muhammad Ali
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Ninehigh
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| posted on 11/5/11 at 12:14 AM |
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Interesting... However I have driven a couple hundred miles at 70+ and the car's not warmed up outside... I'd guess that if it does have
any effect then it would be a degree or two
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coyoteboy
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| posted on 11/5/11 at 12:42 AM |
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Friction would have to counteract the forced convection that normally takes the heat away. Anyone know the friction coefficient of air? 
A quick scan of some NASA literature shows they do calculate it but don't show the calculations and cross-relate it to actual test data from
early re-entries.
It'll be in the order of 0.01 of a degree, they're not even close to the 20,000mph of initial re-entry and drag increases with the square
of speed IIRC, so you'd be looking at 100^2 reduction in effect at least. Shuttle wing temps hit ~1200ishC.
[Edited on 11/5/11 by coyoteboy]
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britishtrident
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| posted on 11/5/11 at 06:08 AM |
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Only a tiny change in temperature at such low speeds, on aircraft the temperature rise only becomes significant when compressibility occurs ie from
the transonic range upwards.
Basically at speeds below about 500 mph the air in front of the aircraft has enough time to be diverted around the aircraft, but as the speed
rises closer to the speed of sound the air over some parts will become supersonic before the aircraft speed becomes supersonic. At supersonic
speeds the air in front of the aircraft doesn't have enough time to move out the way of the object and the air is compressed. As with any gas
compression process a lot of work is done on the air and as result the temperature rises sharply.
At speeds of Mach 2 and upwards the temperature increase is really significant.
[Edited on 11/5/11 by britishtrident]
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T66
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| posted on 11/5/11 at 07:35 AM |
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Its all relative - higher you go colder the air gets, the calculation is an ever moving thing. For people with large brains and foreheads to work
out....
Anyway seeing as you like to get your brain going, I got a subscription to rc engineering- top quality read, which covers in depth race related
engineering and theory.
http://www.racecar-engineering.com/
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hughpinder
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| posted on 11/5/11 at 08:08 AM |
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You'll have significant heat removal as you're moving through the air pretty quick - you'd have to calculate increaing heat loss
from this effect against heat gain from friction.
Heat loss (by convection from a surface to a fluid) is proportional to kinematic viscosity of the fluid and speed of fluid over the surface.
Heat gain by skin friction is proportional to viscosity and speed squared.
There will be thermal conduction and radiation/viscosity changes to allow for too, skin coef of friction, turbulent mixing depends on various
factors.... and lots of other variables too. When I did my degree in chemical engineering many years ago and was pretty good with multivariable
calculus, I could probably have had a decent stab at this, (but that was almost 30 years ago!)
In the real world, and at well below supersonic velocity, I'm guessing the skin cooling is the dominant factor and the car stays at pretty much
at the mean air temperature (except for heat soak from the engine of course).
Regards
Hugh
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JC
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| posted on 11/5/11 at 08:57 AM |
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For aircraft, the RAM air temperature felt by objects protruding into the airflow, is as follows:
Ram Rise (°C) = (TAS x 0.0115)² - where TAS is true air speed.
This means than for an aircraft travelling at 200 knots, at sea level, the heating effect would be 5.29 degrees!
Therefore, the heating effect on an F1 car is not significant I would suggest, but am prepared to be proved wrong by greater brains than a simple
pilot!
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hughpinder
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| posted on 11/5/11 at 09:17 AM |
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Ok, so 200 knots is about 232mph. At 150 then the temp change will be about 2.2 DegC (proportional to speed squared)
Regards
Hugh
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nick205
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| posted on 11/5/11 at 09:22 AM |
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Ease up chaps you're giving me brain fade 
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James
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| posted on 11/5/11 at 11:10 AM |
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T66,
Great link. If I get that job I'll consider a subscription!
Okay, thanks everyone, all interesting stuff.
Disappointing that it's so small as I was hoping I might have found a clue to how Red Bull are flexing their wing... could it have inside a
substance that's solid at normal temperature (hence passing scrutineering load tests) but that liquifies with the change in temperature of fast
corners. Whilst liquid the wing could flex as we've seen but it would cool on the slow down lap and solidify again ready for post race
testing.
But if it's 2°C that's not enough to compensate for air changes througout a race and unless the liquid is seriously 'tunable'
at the point it switches it would work at some races and not others where the air is hotter/cooler.
Ah well! Bang goes that theory! 
Cheers,
James
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"The fight is won or lost far away from witnesses, behind the lines, in the gym and out there on the road, long before I dance under those lights."
- Muhammad Ali
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matt_gsxr
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| posted on 11/5/11 at 12:08 PM |
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Re F1 wing. Isn't it just a force thing and clever engineering thing?
The wing is tested with a 50kg weight and with that isn't allowed to flex (more than a tiny bit).
But at speed things are much stronger.
So, for example if they incorporated a flexible strut in compression that supports the wing, then this could be strong enough to handle the 50kg with
no deflection, then once the forces are strong enough to deform that (Euler strut maths) then if would collapse to a new set-point. The interesting
thing about a strut is that its ability to recover is much less than the force required to start collapsing it.
I am not saying this is what they are doing, but it wouldn't be that hard if you had the budget.
If you get the chance, accidentally stand on the wing and see if it flops or not. My guess is it will have that nasty non-linear "have I broken
it" feel.
Matt
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TimEllershaw
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| posted on 11/5/11 at 01:23 PM |
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quote:
Originally posted by matt_gsxr
Re F1 wing. Isn't it just a force thing and clever engineering thing?
The wing is tested with a 50kg weight and with that isn't allowed to flex (more than a tiny bit).
But at speed things are much stronger.
So, for example if they incorporated a flexible strut in compression that supports the wing, then this could be strong enough to handle the 50kg with
no deflection, then once the forces are strong enough to deform that (Euler strut maths) then if would collapse to a new set-point. The interesting
thing about a strut is that its ability to recover is much less than the force required to start collapsing it.
I am not saying this is what they are doing, but it wouldn't be that hard if you had the budget.
If you get the chance, accidentally stand on the wing and see if it flops or not. My guess is it will have that nasty non-linear "have I broken
it" feel.
Matt
I believe "Aero-Elasticity" is all quite common in most forms of motorsport. They create parts with interesting carbon layup techniques
that are designed to flex in a non-linear way. In the old days the whole rear wing would tilt backwards at speed. In the case of the RBR front wing,
each side deforms by <10mm at 50kg load as per FIA test, but at speeds of 70-80mph each side would have a load of around 100kg and will deform to
25-35mm.
Tim.
[Edited on 11/5/2011 by TimEllershaw]
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James
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| posted on 11/5/11 at 01:44 PM |
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I agree it probably is aero-elasticity.
Very interesting article about it here:
http://mccabism.blogspot.com/2011/04/how-red-bull-simulate-front-wing.html
But I just wondered if there could be anything else going on.
Read this:
http://mccabism.blogspot.com/2011/05/red-bulls-front-wing-cables.html
Now I dont think the wires do anything themselves. But it got me thinking, could they be activating something inside the wing that makes it more
flexible when required?
Could something be liquifying and making the wing more flexible? Like a viscous clutch on a Pinto fan? The wires dont look thick enough to supply much
current to heat the substance and as we've discussed above, the wing itself doesn't heat enough from friction to do the job so guessing
it's not that.
But what about a substance that liquifies with a small current. I know there are liquids that go solid with current, can you do this in reverse?
Cheers,
James
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"The fight is won or lost far away from witnesses, behind the lines, in the gym and out there on the road, long before I dance under those lights."
- Muhammad Ali
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Neville Jones
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| posted on 11/5/11 at 03:15 PM |
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Your mates at McLaren in a bit of a quandry, eh James?
F1's are fitted with strain gauges all over the place. The cables mentioned in the links above are probably for the gauges. They are also fitted
with other sensors, more cables.
The wing flexibility is probably a lot simpler than all the armchair professors want to make out.
When you put different materials together, and given differing moduli, then the bending is easily achievable. It wouldn't be done with carbon,
as the modulus is way too high. And straight resin would crack and fail. The answer is somewhere between the two.
As for the bent/not bent situation, it wouldn't be done with layup alone, and is again, easily achievable with simple mechanical structural
design. Done on raceboats all the time. Nothing a turned on engineer with good composite knowledge couldn't do.
F1 is not as high tec as some may want you to think.
Cheers,
Nev.
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hughpinder
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| posted on 12/5/11 at 07:34 AM |
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Perhaps the wings are 'just' stiff enough to pass the 50kg test. They may then be too flexible at high speed, so how about using one of
the magnetic ferrofluids (like in the audi suspension) to 'set' the wing when its bent enough? E.g wing meets scrutineering at the start,
drive off, wing starts to deform and computer switches on the current to make the wing rigid when the speed reaches whatever speed you have previously
determined to give best results. The wing then stays that shape until you turn the current off at the end of the race. Is that possible and within the
allowed rules?
Hugh
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coyoteboy
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| posted on 12/5/11 at 04:41 PM |
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F1 is alllll about rule bending in engineering, a great game. Far more exciting than watching the cars being pointed round the tarmac!
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