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Thread: Xfsaer wants to build a fan car type FSAE car for autocross type demonstrations

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  1. #1

    Xfsaer wants to build a fan car type FSAE car for autocross type demonstrations

    As per title ... I am thinking of making it also an open source type projects for all those fsaers who are dreaming of being part in a similar project-so polite input and ideas exchange is welcome
    I am searching for photos from the Cornell 1990 fan car for starts - maybe people who designed it and raced it can offer some insights since this tech has been banned for more than 2 decades from FSAE
    Thank you in advance and congratulations for this beautiful forum , tool for knowledge , been a long time lurker
    Last edited by Xfsae; 10-27-2013 at 12:51 PM.

  2. #2
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    I would start with looking up the Cheaparral Corvette that competed in the Grassroots Motorsports $2007 challenge. There is a nice PDF of the how's and why's of what they did along with a bunch of pictures. I was thinking of doing a similar setup with my Impreza. Anyone know where I can get a surplus Abrams blower fan or the manufacturer of one?

    http://www.cheaparral.com/
    Last edited by rjwoods77; 10-27-2013 at 08:24 PM. Reason: added link

  3. #3
    @ RJWoods77 reading through the cheaparral website now - thank you for the link
    They used a fan from M1 tank ...It is one of the intake fans at the back of the tank

    i was trying to see if there was a specific reason for them choosing this fan-12000cfm at 70 pounds weight must be the reason ... It is a 2 stage vane axial design in alloy1-2.JPG

    Some useful info from the corvette "cheaparral" fan car project:


    "Extensive calculations and testing with a proto sled identified the ammount of airflow and vacuum required to stick the car to the ground with 1500 pounds of force (6675 Newton or like 680kg extra) ,the ammount necessary to boost the Vette's rating from 0.9 to 1.4g lateral "

    I wonder how they found that they had to add this ammount of downforce to get this specific increase in lateral acceleration given that the ultra low budget of the project should not allow them to buy tire data - not even new tires- Did they start loading the car with weight and driving around with an accelerometer ? Any idea or suggestion?

    The Abraams intake blower seems to be about 0.4 m in diameter and 0.4m in height judging from the photos of it placed in the Vette and on the tank and was powered by a 33hp snowmobile engine in the cheaparral project

    4.JPG (placed in the codriver seat place on the Vette)

    At 10 inches of water operational vacuum (that is -14.33 psig relative to atmosphere ) they got 1000 pounds (454kg) of downforce
    They measured it with a vacuum meter on the car - not sure how they were deriving the downforce amount

    To maintain traction throughout the suspension travel a 2 piece skirt frame connected by bellows was developed and installed under the car - shopping trolley type of caster wheels attached to the lower frame would maintain a 1/2 inch gap between the skirt and the ground

    untitled.JPG (skirt- trolley wheel photo)

    Z- as always interesting , informative (and entertaining in a cool manner in this case!) post .Thank you

    I was looking in the internet for performance curves ,dimensions and weights for plastic industrial high pressure blowers of the dimension you suggested

    http://www.mkplastics.com/documents/...MARCH_2008.pdf
    http://www.plasticair.com/dat/files/28.pdf

    is what i come up with but they dont seem very promising (in terms of space, weight and power required) ,in comparison to the cheaparal project figures i found and mention above

    can you post a link to the high pressure blower you found?

    George Bowland.JPG

    FSAE fan car boy-George Bowland's leaf blower vacuum assisted B8R A-Mod

    leaf blower said to have been running WOT

    Skirts seem to be of polyethylene or nylon variety -someone mentions them as rubber skirts but i dont know they dont seem like that to me- they seem to be actually touching the ground on the sides - i don't know how they seal front and rear and in the corners
    Last edited by Xfsae; 11-01-2013 at 04:18 PM.

  4. #4
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    I know we had a program in our office that had a picture of it. I think it was pretty straight forward as you didn't have to try to get around any rules against it at the time. These days if you were going to play by the rules I don't see why you couldn't duct the cooling intake of your air cooled engine to the diffuser.
    Any views or opinions expressed by me may in no way reflect those of Stewart-Haas Racing, Kettering University, or their employees, students, administrators or sponsors.

  5. #5
    There can only be one...

  6. #6
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    Quote Originally Posted by exFSAE View Post
    There can only be one...
    Sue for breach of copyright! ;-)

    Pat
    The trick is... There is no trick

  7. #7
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    Xfsae,

    Here is an earlier discussion (2005) from the Off-Topic section...

    Z

    (PS. Xfsae vs exFSAE?
    Hmmm..., an "X" is that mysterious, unknown factor, like in those "X-Men" movies. But an "ex" is just a "has-been", innit??? )

  8. #8
    It's true, it's true... I'm a has been.. my student racer career is all washed up. Several years in it and not a 1st place in any competition event - not even the push bar contest. It's a tough life, but guess I'll have to settle on all these wins at the pro level instead.

    Back to the original post.. interesting idea. I think a variety of people have had similar concepts. Some thoughts...
    • Why look for inspiration from a 1990 FSAE car? Or any FSAE car for that matter. I feel like you might be better off just starting completely ground up, open mind (and also being very familiar with the rules for whatever SCCA class or whatever you intend to run)
    • If you intend to make a group or "open source" project - gotta think about a suitable design software (or series of softwares). That may be particularly difficult.
    • Likewise, need to have some lead designer to orchestrate everything. Really, I my gut feeling is that just doing the whole car yourself would be much easier than trying to do group/"open source" route.

  9. #9
    I still feel pretty confident that if you're a graduated, working engineer now.. that you can do significantly better than a 1990-ish FSAE car. I'd still say, don't look to student built stuff for inspiration. Just blank slate it. I find that blank slating and focusing on fundamentals tends to yield better results with fresh perspective than trying to copy something else as a starting point. Often much easier too!

    Not to take anything away from students who have done well in student competitions... but I'd say that shortly after graduating, working professionally, and then looking at student cars afterward - any "wow" factor of what used to be really impressive equipment just evaporated for me. Bottom line all these cars are design and built by folks without engineering degrees [yet] and without much experience. Sometimes surprisingly good stuff emerges, but it could all be better. For what it's worth, upon quick Google search, that "active aero" Cornell car only finished 5th overall of 45. That's not even top 10%.

    With regard to everything else you're covering, all these little specifics, it comes across as way too scattered. If you're serious about doing this then maybe pump the brakes a second and start from absolute basics. Start design at a high level conceptually and all the specifics of piece parts will fall into place. Much better approach than what I feel is typical of FSAE kids or young engineers of being focused on the parts and pieces and trick gizmos first.

  10. #10
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    Quote Originally Posted by exFSAE View Post
    If you're serious about doing this then maybe pump the brakes a second and start from absolute basics. Start design at a high level conceptually and all the specifics of piece parts will fall into place.
    exFSAE (the old one ),

    That really is expert advice!

    (Err..., from "ex" = "a has-been", and "spurt" = "a drip under pressure"... (Z thinks - Oh, no, no, no... you're just digging yourself a deeper hole! Quick, move on... )
    ~~~~~~~~~~o0o~~~~~~~~~~

    Xfsae (the mysterious, unknown one),

    Taking the above very good advice, here are some thoughts.

    GENERAL, BIG-PICTURE STUFF - As indicated on the "Sucker Car" thread (link back on page 1) and covered in more detail below, an FSAE sized active-aero (fan) car should be able to get AT LEAST a ton of downforce, at any speed from zero to Vmax. In fact, I think 3 tons would be quite easy, and 10 tons would be feasible!

    The important point here is that with these numbers the big-picture changes radically. Things like tuning "under/oversteer handling balance at the limit" become irrelevant, because YOU WILL NEVER REACH THE LIMIT.

    Let's consider roughly where "the limit" is. Take the middle figure above of 3 tons downforce (technically ~30 kN downforce). Assume that because of the extra strength that you have to add to the car (more below), the car+driver weighs 1/2 ton (technically ~500 kg mass). And assume racing slicks good for about Mu = ~1.5. The tyres thus have the capability to exert a ~45 kN force horizontally, which will accelerate your car+driver mass at 45,000/500 = 90 m/s.s, or ~9 G!. A lower mass car, with greater downforce, and maybe stickier tyres, are all possible, so even higher Gs possible...

    Bottom line here is that YOUR PROBLEMS ARE MAINLY STRUCTURAL, both for the car and the driver!

    So, toss those girly-boy 68xx thin-ring wheel bearings beloved of FSAE teams. You will need, at the least, wheel bearings off a largish production car. When you really start pushing the envelope you will need something off a light truck (hint - tapered-roller bearings).

    Most definitely toss those Keizer wheel centres from the other thread currently running! Some stout, production-car, steel wheels might be a good start.

    I am not sure what loads typical FSAE tyres will take, but you will certainly need higher than normal inflation pressures (eg. 2 bar, 30psi?). Le Mans style cars weigh ~1 ton, and develop 2 or 3 times that in aero downforce at high speeds, so those wheels and tyres should be strong enough (at your lower downforce numbers!).

    Other chassis structure stuff should also be appropriately up-sized. Main point here is do NOT use typical FSAE-sized parts.

    As for the driver, well cornering at 9 G would be like lying on your side while your favourite football team jumps on top of you! The sides of the cockpit should be very well padded. And lest the G forces rip the driver's head off his shoulders, I suggest a very effective "Head And Neck Restraint System" (preferably something much better than the conventional "HANS", which is just a few strings tied to the helmet).

    "Centrepoint" steering would be good (ie. Offset/Trail/SAI/Castor = 0), but even then you will probably need power-steering. Think about how fast those slalom corners will be coming at you. Do NOT worry about "steering feel". Remember, you are unlikely to get close to the tyre's limits, and I doubt you would have time to notice if you were.
    ~~~o0o~~~

    THE FAN - You have the choice of axial-flow fans (like an aeroplane propellor, or a domestic fan, or on the Chaparral 2J, or the (two-stage) Abrams-tank fan linked to by Rob on page 1) or radial-flow fans (like the compressor on a "turbo", or many industrial units). Either of these can be compounded (put in series) for greater pressure difference, and some fans are partly axial, partly radial-flow.

    Briefly, I suggest a radial-flow fan for the following reasons. Generally, for pumping a given amount of air, axial-flow fans are smaller and more energy efficient (ie. less input power required). BUT (!!!), once the airflow is reduced past a certain limit (say, your "skirts" start to seal really well), the fan "stalls" and the pressure difference disappears! Also, the blades must be accurately "aerofoil" shaped, and the incoming airflow must be "straightened" for good operation (ie. to prevent stalling).

    On the other hand, radial-flow fans are "STALL-PROOF". They operate by "centrifugal force", not by subtle "aerodynamic" means. As a result they can be made very simply, such as from fabricated sheet metal, like the majority of industrial "blowers". Even with very simple design (eg. just radial, sheet-steel vanes inside a sheet-steel, snail-shaped housing) they still have reasonable efficiency, and generally higher pressure difference capability than the axial-flow fans.

    As confirmation of above, I have just conducted an extensive series of tests (err, while the jug boiled for my next cup of coffee...). My oldish domestic vacuum cleaner has a small radial flow fan in it (not sure which way the blades are curved, probably radial or backward). It has a hose nozzle of ~34 mm diameter, so about 9 sq.cm area. The suction from this vacuum-cleaner comfortably picked up a plastic drink bottle with ~1 litre water in it.

    So the "stalled" suction is about 1 kg/9 sq.cm, or 0.11 bar, or 11 kpa, or 1+ ton per square meter. Keep in mind that a column of air 1 metre square at its base, and reaching from ground level up to the edge of space, weighs about 10 tons (or "atmospheric pressure" = 10 tons/sq.m). I put a few 1+mm thick toothpicks between the suction nozzle and the drink bottle, to simulate skirts that are "off-the-ground", and I could still comfortably pick up 0.5 litres of water. So still ~0.5 ton/sq.m lift (or downforce).

    Google radial-flow fans and you should see that much higher pressure differences are possible with commercially available, off-the-shelf, relatively inexpensive fans. 3 tons per square metre (0.3 x atmospheric pressure) should be a feasible...
    ~~~o0o~~~

    THE VACUUM-BOX - From the above, a "vacuum-box" of about 1 to 2 sq.m plan-area should suffice. This can have "skirts" that are either held just off the ground, or else allowed to lightly touch the ground and gradually wear away (say, made of something plasticky, like polycarbonate, UHMW-HDPE, or even plywood). For some comformability of the four wheels and the vac-box to uneven ground, and also for a smoother ride for the driver, I reckon it would be best to mount the vac-box "unsprung".

    The easiest way I can think of to do this would be by using beam-axles front and rear. Longitudinal beams running down each side of the car (just inboard of the wheels) would hang off the beam-axles and form the side-skirts (possibly with flexible plastic extensions, like "side-splitters", for better sealing). Similar cross-beams at front and rear would seal the ends of the vac-box. The front might best be V-shaped (like a ship's bow) to help sweep away gravel, etc. In fact, "broom-like" skirts at the front might be a good idea.

    The whole, roughly rectangular, vac-box should be allowed to twist to give more equal wheel loads on uneven ground (ie. a soft "twist-mode"). The several tons of down load on the roof of the box will help this, and should also be considered when building said roof! The rest of the car, namely chassis, engine, driver, etc., can now be softly sprung above the vac-box. So at least you get some vertical ride comfort, if not horizontal.

    This whole arrangement is very similar to UWA's 2012 car, just with the active-aero added. Oh, and another couple of hundred kilos of structure, to keep it all together...

    Enough for now...

    Z
    Last edited by Z; 10-29-2013 at 11:16 PM.

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