Over and Under or around the sides

[BreezyRacer]

When I was at University ('72 - '75) wingtip vorteces were said to be as a result of the different speed of the air over the top compared to underneath - resulting from the different camber & the angle of attack of the two sides. The diagram you link to was used. The analytical theory showed that mathematically there is circulation of the air about the wing which is shed at the tip. So what should be done here? An aerofoil with different curvature each side or a symmetrical one set slightly off straight ahead? Or do you get them from just about anything. I am aware that smokestacks shed vortexes but they come off one side then the other with opposite rotation & buffet the smokestack badly (hence the spiral rids on the outside to prevent vortex shedding).

That all seems correct but with a wing tip vortex keep in mind that it's the airspeed difference between the air flowing around the wing vs free airflow adjacent to the wing, thus the speed difference, thus the vortex, so even a chord neutral shape works and produces little to no drag.

As for your smokestack example, keep in mind that a round shape produces a large unstable, turbulent wake, whereas an airfoil does not.

[greenpower dude reloaded]

Ok not with a second to spare we managed to get the car ready for the race last Sunday. Which had any of you seen the true extent of what needed to be rebuilt you'd understand why it wasn't finished earlier. Infact to give you an idea it was genuinely a complete rebuild with new components in every area.... Yes my old school managed to wreck it THAT badly.

I was incredibly nervous before we sent my sister out for this race as we had not conducted one single form of load testing on it as time had been that tight. So it was another step in to the unknown this season.

Anyway, We pulled away from the third row (three rows of three) of the grid and after one lap we were already in second place. But unfortunately on the second lap the new heavier duty chain came off. We think it stretched under initial accelleration.

20 minutes later we rejoined the race and were lapping 2 secs a lap off first place but we had unfortunately dropped to dead last, we spend the next hour picking our way through the field to acheive 4th place... 30secs off 3rd argh!

But it was a great race all in all and I'm incredibly proud of my sister who spent the whole race trying as hard as she possibly could, which reflected very well in her lap times.

As you may have noticed I changed the body around a bit, simply didn't have time to do anything worth while mould wise. I've got a couple of changes I'd like to make to it but I don't want to do anything detrimental I only have next weekend to work on it so if anybody thinks they could run a couple of CFD models for us I would really appreciate it.

Just the final left now... the race that in my eyes reallly counts. even if it is too late for us to acheive anything worth while in the championship... It certainly doesn't hurt to show some of these top teams who the boss REALLY is

[Michiba]

Well done mate!

you can only improve from here. And with not too much work, you can change that livery to look like a mouse. Would be cool to see a mouse scurrying around a track,

[greenpower dude reloaded]

HAHA, I could indeed, hadn't realised it looked at all mouselike.

Another interesting point that's worth noting... Our race last year saw us covering 44laps in 1.5hrs to finish 2nd. This year we covered 44laps in 1hour 9 and in all honesty last years car was bloody quick... We were on target for 58laps!!

[BreezyRacer]

Congrats on getting it back out to the track, however your chain is still costing you wins even after multiple failures. What chain are you using exactly? I seriously doubt that chain stretch from "wear in" is your problem. What are your sprocket diameters. You need to spend this week installing an idler wheel or chain tensioner. This kind of failure destroys all your other fine effort.

Do you have any wheel travel and if so, what suspension setup do you have? 4 link, 3 link, etc? Does the chain fall off to the inside of the sprockets or to the outside?

[marcush.]

looks like superswoosh is converging towards ultimate....it starts to look purposeful indeed.
Would love to see it with all the edge radii + VGs in anger...

One point towards ultimate swoosh or whatever to call next years machine:

the current design obviously is creating lift ,and as the lift is in effect a force ,
this Force is going to eat power from somewhere (Batteries).Counteracting to this is the reduced vertical force at speed on the tyres helping reducing losses there .

On the other side ,I assume the tail sweeping down will always induce lift.
wouldn´t it be a possibility to raise the rear deck height to almost horizontal and raise the floor in a double sweep to deck height ?
I´m aware you could not build a rear diffuser proper as the diffuser sides could not taper to the mid axis without increasing drag ,so behind the rear wheels this design would surely lead to more complex shapes out of reach for your current body
work manufacturing recources...still it would converge even more to the boxfish shape then ..and somewhat a halfway house towards the elevated groundclearance car as well ...

the devlopment seems to work on the right variables , doesn´t it ? It is always rewarding to see concepts proving themselves in real contest.sure you can already smell the silverware of the finals already...Make sure you concentrate on having no hickups so preparation of what you have is paramount ,and ONLY if you are getting seriously bored by rechecking everything and still aweeks time I´d try to step up with the car further...I know this is obvious ,but I remember only too good almost blowing a championhip winning final with overambitous last minute projects,luckily we still catched the bowl...In racing you very,very rarely get to race what you think you should go racing with and have to perform the art of the possible instead..

[greenpower dude reloaded]

Unfortunately due to other commitments, Namely girlfriend having moved to Uni last weekend (to study engineering ) I am left with but 2days to work on the car. In this time the plan is to set the tracking up properly and to check bearings and the suchlike.

I would ideally also like to minimise the cockpit opening and re position the wing mirrors for small gains. Given the time I will also attempt to sharpen the trailing edge on the roll bar which is currently square.

I may also try and run the gearbox control off an auxilary battery rather than the main. NuVinci say it takes a maximum of 5amps, which out of 20amps is too many!! any battery suggestions? it needs to run for 1.5hours and be light! oh, and easy to charge.

It is now going to be at least next season before it is going to have a body with rounded edges. but that should be a substantial step in the right direction.

AHH! and Laura (part time sister, part time Driver) has said IF we build another car she'd want it to be called Wonder Whoosh.. to follow on from Swoosh, Whoosh, Super Swoosh (and this new version of swoosh that we raced on sunday I have been calling Super Swoosh 3000 just thought it sounded cool.)

We are using 3/8" pitch chain, we used to use standard bike chain up until this new incarnation of SS personally I think it has done the trick. I think the trailer journey down may have slackened it off a touch too..

[BreezyRacer]

Unfortunately due to other commitments, Namely girlfriend having moved to Uni last weekend (to study engineering ) I am left with but 2days to work on the car. In this time the plan is to set the tracking up properly and to check bearings and the suchlike.

I would ideally also like to minimise the cockpit opening and re position the wing mirrors for small gains. Given the time I will also attempt to sharpen the trailing edge on the roll bar which is currently square.

I may also try and run the gearbox control off an auxilary battery rather than the main. NuVinci say it takes a maximum of 5amps, which out of 20amps is too many!! any battery suggestions? it needs to run for 1.5hours and be light! oh, and easy to charge.

It is now going to be at least next season before it is going to have a body with rounded edges. but that should be a substantial step in the right direction.

While the rounded edges will reduce drag they INCREASE lift because the high pressure air will spill over onto the sides of the body creating a low pressure area on the top.

Your GF is an engineering student? Have HER look at the chain issue then. You have GOT to solve that.

[marcush.]

Unfortunately due to other commitments, Namely girlfriend having moved to Uni last weekend (to study engineering ) I am left with but 2days to work on the car. In this time the plan is to set the tracking up properly and to check bearings and the suchlike.

I would ideally also like to minimise the cockpit opening and re position the wing mirrors for small gains. Given the time I will also attempt to sharpen the trailing edge on the roll bar which is currently square.

I may also try and run the gearbox control off an auxilary battery rather than the main. NuVinci say it takes a maximum of 5amps, which out of 20amps is too many!! any battery suggestions? it needs to run for 1.5hours and be light! oh, and easy to charge.

It is now going to be at least next season before it is going to have a body with rounded edges. but that should be a substantial step in the right direction.

AHH! and Laura (part time sister, part time Driver) has said IF we build another car she'd want it to be called Wonder Whoosh.. to follow on from Swoosh, Whoosh, Super Swoosh (and this new version of swoosh that we raced on sunday I have been calling Super Swoosh 3000 just thought it sounded cool.)

We are using 3/8" pitch chain, we used to use standard bike chain up until this new incarnation of SS personally I think it has done the trick. I think the trailer journey down may have slackened it off a touch too..

WonderWhoosh ,that really does it .. I guess she will have to be craned out of the machine after each run next year refusing to turn back into sister ...

Setting toe: do you compensate for dynamic toe due to flex in the system?
I suppose the best thing would be to do coastdown runs to see which is best in terms of rolling resistance?
hows the steering geometry of the super swoosh ?
(Ackerman,scub radius etc ) I bet there is also a lot(of speed) to be lost steering the car at speed ...

[greenpower dude reloaded]

She is indeed, she always says it should have been me head off to uni when I finished college 3years ago I just didn't get the grades... ah well. I hope to test the car briefly in a week or so, Just doing practise starts to see what happens. I think it was just a case of re-tensioning it. It made some awful noises under accelleration off the start line and for its first lap or two. Once retensioned it was fine under accelleration out the pits (which I must say was with gusto!)

this newest version we made sure the sprockets were all lined up, we've introduced more teeth and strengthened the area around it significantly.

At the final we have the advantage of the car being there the night before so I can actually work on it. As I may have explained before, I became a member of the team that run these events last year I obviously can't spend any time on race days looking at this car at all. I like to think we'd be darn close to winning this championship this season if I still lived at home and had kept my job as a coachbuilder....

Marcush,

Our original car had lovely kingpins that included KPI to minimise scrub radius. they were however totally unsuitable for this season, so we lifted the ones from our 2nd car Whoosh! these only included ackermann and now 10degs of castor. We only have very minimal lock and also only a short wheelbase which helps keep the speed up as the wheels don't need to turn at such an extreme angle in order to corner...

We don't set any toe. We set all wheels to run dead straight there is ver little weight over the front axle and so the steering typically doesn't flex. I always set it with at least the batteries in anyway.

I'm going to get a lesson on this from a Caterham team this week.

[Carlos]

Very good effort. Great to see you out there and your perseverance. A simple chain tensor as simple as a bracket and lever and idler sprocket. with a spring from the sprocket lever to the bracket, could do the trick.

[CMSMJ1]

Sorry, am not clever enough to contribute particularly to this, but suffice to say this thread is superb.

best of luck with the car..it is great

[Ciro Pabón]

Well, I don't know how simplistic is this suggestion, but, what the heck: if the chain falls inside, you could use a Chain Watcher. I have one in my bike. So, if you try one, my recommendation (after years of using it) is: do not buy the american version but the chinese one (sorry, you american dudes: I picked a picture with that flag, to prove I'm not against US industry but against Third Dog chain watcher). The chinese version is cheaper and works better, the plastic is more resistant.

Chain watcher: it's useful when the chain has some slack (or, I imagine, by the large torque of your electric motor, you "stretch" the chain in acceleration and then it "rebounds": it's going to move towards the inside of the chain gear).


If you don't know where is moving, or if it's derailing towards the outside, you could use a ring guide. The version in the picture is very good (the "incomplete" one, that doesn't have a complete circle, but has a "cut off" section: you don't need the frontal part, the chain is not going to derail in that section, so it's lighter).

[greenpower dude reloaded]

It was the National Final on Sunday and so I thought I should keep you posted on the final results. Again, good and bad news. We were definitely one of the fastest cars. Having been lapping at 4 mins 15 secs quite consistently at the start, and using only 71% of the power we were drawing a few weeks prior at Dunsfold Park, as we had changed the Shift Map from running at 1700rpm to 1750rpm instead, because we just aren't capable of completing race distance on that sort of power, we turned up the wick after 20mins downtime at Dunsfold. I think 1700rpm translates to about 34amps, 1750 is about 27.

It's amazing how much of a difference the setup makes. I got somebody to show me how they do the tracking in most racing series up to F3. It's dead simple. Only needs two bits of box section and some fishing line and that made a vast difference in speed, we'd always done it simply with a tape measure, and it always appeared spot on before, turned out to be a long way out.

4minutes 15 is also a full minute faster than we were at the start of the season. So I think we have improved a fair bit this year...

We did however face a really odd problem where by the batteries kept dropping in voltage and then spiking back up again. My only thoughts on that are duff batteries or a loose connection, but connections had been checked on the saturday night. After about 15-20 minutes Laura's lap times had slowed down so much she came in the pits to establish the problem. Off load they read 23.9 that worried us a bit but sent her out and she picked up again setting a few sub 5minute laps.

Anyway our final result this year was 7th. Not at all what we hoped for as we were aiming for top 3 both in this race and the championship, it looked entirely likely that that would happen at one point as we were sat in third being chased by 4th and 5th who were drawing more current than they could sustain for the whole race.

We have however equaled our personal distance record of 43.2miles in 1.5hours and achieved our big aim of the season to break the 5min barrier around Goodwood, which I think you'll agree we smashed with 4mins 15.

BUT the good news is! we have a great reliable chassis and the makings of a good plug, I know we can gain an extra few mph with just a modified version of this years car should be able to shake off a fair bit of weight too...

Next year our aim is to be the F24+ Champions, a target that is in all honesty entirely realistic and one that could have been this year but only had a total of about 100 man hours from it's conception to actually finishing the season as an all new car rebuilt midseason.

Most cars take a minimum of 500hrs for construction between a team of roughly 12, rather than 100 between, me, myself and I.

I would like to thank you all for your support this season and will be posting updates very shortly on development.

Stage one will be evaluation of the current body and evolving this shape for better results.

[Saribro]

Stage one will be evaluation of the current body and evolving this shape for better results.

Not to criticise your inspired and inspiring work, but considering your race reports, wouldn't it be more logical to sort out your mechanicals (chain/batteries/engine operating point/...) first, or does the shape of the car have notable repercussions on said mechanicals?
The old: In order to finish first, first you have to finish. (or in endurance terms, keep your car on the track).
In any case, good luck.