ajg193 Posted February 12, 2022 Share Posted February 12, 2022 Biggest issue with curing large sections is excess heat generation in the thick areas causing internal delamination/blistering. As Nick says, heat it up nice and slow. Particulate fillers (like talc or calcium carbonate) result in less shrinkage, but can make it more brittle. Fibre fillers could be a good addition with this stuff though as it is pretty brittle (0.65% elongation at failure), and has a stupidly low tensile strength (only 30 MPa, generally epoxies are over 100 MPa). You shouldn't really have any problems with drilling and tapping epoxy but it would be best to use inserts so the fasteners don't clamp onto a constantly relaxing surface. 1 Quote Link to comment Share on other sites More sharing options...
ajg193 Posted February 12, 2022 Share Posted February 12, 2022 Biggest issue with curing large sections is excess heat generation in the thick areas causing internal delamination/blistering. As Nick says, heat it up nice and slow. Particulate fillers (like talc or calcium carbonate) result in less shrinkage, but can make it more brittle. Fibre fillers could be a good addition with this stuff though as it is pretty brittle (0.65% elongation at failure), and has a stupidly low tensile strength (only 30 MPa, generally epoxies are over 100 MPa). You shouldn't really have any problems with drilling and tapping epoxy but it would be best to use inserts so the fasteners don't clamp onto a constantly relaxing surface. Quote Link to comment Share on other sites More sharing options...
Roman Posted February 12, 2022 Author Share Posted February 12, 2022 Another issue I've been thinking about for when I finally get to a trackday. Is to try tame some of the floaty feeling of driving a bean bag shaped car at 180kph+ Currently all of the engine bay air has to go out underneath. The drip tray and windscreen wiper area unbolts, so its easy to remove a big chunk that should flow a bit of air out even if it's not an ideal location. Might do some wool tuft tests and try see where the air wants to go when the whole panel is missing. I am guessing that the engine bay air will mainly want to try escape past the wing mirrors rather than going over the top. 1 Quote Link to comment Share on other sites More sharing options...
ajg193 Posted February 13, 2022 Share Posted February 13, 2022 ^Whoops, I accidentally deleted your pictures when I changed my post contents to NAN, I think oldschool was still in brick mode at the time. (They disappear after doing a ctrl+r reload to clear your cache) Quote Link to comment Share on other sites More sharing options...
shrike Posted February 13, 2022 Share Posted February 13, 2022 23 hours ago, Roman said: Another issue I've been thinking about for when I finally get to a trackday. Is to try tame some of the floaty feeling of driving a bean bag shaped car at 180kph+ Currently all of the engine bay air has to go out underneath. The drip tray and windscreen wiper area unbolts, so its easy to remove a big chunk that should flow a bit of air out even if it's not an ideal location. Might do some wool tuft tests and try see where the air wants to go when the whole panel is missing. I am guessing that the engine bay air will mainly want to try escape past the wing mirrors rather than going over the top. Front air diffuser time? Something like what Barry has? Could also pick up a spare hood to put some holes in and do ducting to bring air up and out through them (spare hoods only 4 bolts right?) Do you have enough space to do a duct from the radiator and out the bonnet? Is there an air duct/dam that goes from the bumper to the airbox/radiator? also having a heat shield separating the pod from the rad may help with temps? Is there enough space to duct the space with the airbox also out a bonnet hole? You could also look at an under tray, though thinking about it now unless you made something that just slid in and out it may be too time consuming to just swap over for a track day Quote Link to comment Share on other sites More sharing options...
Roman Posted February 13, 2022 Author Share Posted February 13, 2022 Nah nothing like that. Will use the drip tray area so it looks a bit more standard / nicer. Maybe a bit of a front lip to reduce the amount of air going straight under though. Interestingly some of the newer shape Yaris rally cars have their engine bay vents very close to the base of the windscreen. 2 Quote Link to comment Share on other sites More sharing options...
flyingbrick Posted February 14, 2022 Share Posted February 14, 2022 Isn't the base of the windscreen a high pressure area? Eg cowl induction hoods actually draw from that area rather than expelling air like you'd think. 1 Quote Link to comment Share on other sites More sharing options...
AllTorque Posted February 14, 2022 Share Posted February 14, 2022 Yaris might be more aerodynamic than a 69 Camaro. 2 1 1 Quote Link to comment Share on other sites More sharing options...
Roman Posted February 14, 2022 Author Share Posted February 14, 2022 I think "it depends" If you have a long flat bonnet and a steep upright windscreen. Then its more likely to be a high pressure area there. Which is where cowl induction works good. Echo has a tiny short bonnet, and a very shallow angle from bonnet to windscreen. Similar to the rally car I posted which has its vents right up the back. What I was thinking is that I will retain the lower half of the drip tray, and add some one way flaps like in baffled sumps or radiator shrouds. So they only open if pressure in the engine bay is higher than the outlet area. But for starters I can just have the whole tray out and see what happens with some wool tufts or a manometer. 8 Quote Link to comment Share on other sites More sharing options...
shrike Posted February 14, 2022 Share Posted February 14, 2022 19 minutes ago, Roman said: I think "it depends" If you have a long flat bonnet and a steep upright windscreen. Then its more likely to be a high pressure area there. Which is where cowl induction works good. Echo has a tiny short bonnet, and a very shallow angle from bonnet to windscreen. Similar to the rally car I posted which has its vents right up the back. What I was thinking is that I will retain the lower half of the drip tray, and add some one way flaps like in baffled sumps or radiator shrouds. So they only open if pressure in the engine bay is higher than the outlet area. But for starters I can just have the whole tray out and see what happens with some wool tufts or a manometer. https://youtu.be/iK23hiI4m-E?t=50 1 Quote Link to comment Share on other sites More sharing options...
Roman Posted February 15, 2022 Author Share Posted February 15, 2022 Okay soooo The wool tufts dont go mostly up or mostly down, just mostly just nearly flat towards the base of the windscreen but with lots of wiggling around. Maybe because the open area is so large, it can just equalize the pressure top and bottom no problem. Doesnt seem particularly conclusive, but maybe it needs some more context with more dangly bits on surrounding areas. Or maybe I should just fit a pressure sensor under the bonnet instead, as that's the real issue (or not) 5 Quote Link to comment Share on other sites More sharing options...
flyingbrick Posted February 15, 2022 Share Posted February 15, 2022 @Roman please draw a side profile of the car and run it through a virtual wind tunnel/fluid dymanics stuff (Which i know you know how to use) and show us pretty colors to represent pressures at base of windscreen. 1 Quote Link to comment Share on other sites More sharing options...
flyingbrick Posted February 15, 2022 Share Posted February 15, 2022 Or use some kinda snorkel system to bring the hoods outlet up into an area of known low pressure. Quote Link to comment Share on other sites More sharing options...
ajg193 Posted February 15, 2022 Share Posted February 15, 2022 You're wasting your time, Toyota already did all the measurements on these 40 years ago 2 2 3 Quote Link to comment Share on other sites More sharing options...
shrike Posted February 15, 2022 Share Posted February 15, 2022 1 hour ago, Roman said: Okay soooo The wool tufts dont go mostly up or mostly down, just mostly just nearly flat towards the base of the windscreen but with lots of wiggling around. Maybe because the open area is so large, it can just equalize the pressure top and bottom no problem. Doesnt seem particularly conclusive, but maybe it needs some more context with more dangly bits on surrounding areas. Or maybe I should just fit a pressure sensor under the bonnet instead, as that's the real issue (or not) I think the real issue is that you don't have enough wool tufts over the whole car, and your current results are clearly inconclusive 1 Quote Link to comment Share on other sites More sharing options...
Popular Post tortron Posted February 15, 2022 Popular Post Share Posted February 15, 2022 8 3 Quote Link to comment Share on other sites More sharing options...
Muncie Posted February 15, 2022 Share Posted February 15, 2022 Reminds me of this. Has anyone put a jelly bean in a wind tunnel before maybe you could scale up for the Echo? I would love to see this thing turbocharged on E85 with the 13:1 comp ratio. 3 1 Quote Link to comment Share on other sites More sharing options...
Hyperblade Posted February 15, 2022 Share Posted February 15, 2022 On 12/02/2022 at 18:26, Roman said: Another issue I've been thinking about for when I finally get to a trackday. Is to try tame some of the floaty feeling of driving a bean bag shaped car at 180kph+ Currently all of the engine bay air has to go out underneath. The drip tray and windscreen wiper area unbolts, so its easy to remove a big chunk that should flow a bit of air out even if it's not an ideal location. Might do some wool tuft tests and try see where the air wants to go when the whole panel is missing. I am guessing that the engine bay air will mainly want to try escape past the wing mirrors rather than going over the top. As has been pointed out removing the drip tray won't help you as to close to the windscreen, the WRC Yaris are further away, plus they have designed it in wind tunnel. Couple of vents in front of bonnet would work extremely well. Could try and vent engine bay into wheel wells, but then you need to get that air out so would need vents in the front guards. Front splitter just to brute force pressure at front to cancel out the lift. Another option that isn't as drastic might be to add a front bumper lip. My thinking being your trying to reduce the air going under the engine bay, which allows more of the engine bay air to go out under the car, overall dropping the pressure, hence less lift. Bonus is I have a brand new roll here that I never used which you can have, pm me your address and I'll send it up if you want it for this. 1 Quote Link to comment Share on other sites More sharing options...
Roman Posted February 16, 2022 Author Share Posted February 16, 2022 4 hours ago, mopig said: Jesus, i've literally just read all 32 pages of this. all i can say is, captivating. totally the best build and fun experience for very little cashflow. but what has made this is your skill - most normal or even clever folk couldn't achieve these results like you have. i've seen it at the drags a few times recently while there with the older v8 fellas and it's always a laugh watching you peel that thing down the strip. Thanks for the kind words! Yes lots of experimenting and failures on the path to good results but then very satisfying when it all comes together. Worth noting that I couldn't have achieved a lot of this without some incredible generosity and support from a wide variety of people who have also pitched in. Which has been incredible. Come say hi some time next time at the drags! Which hopefully wont be too far off. I'll promise to try not to talk about 32 pages worth of Echo stuff... Maybe. 2 Quote Link to comment Share on other sites More sharing options...
Roman Posted February 16, 2022 Author Share Posted February 16, 2022 2 hours ago, Hyperblade said: As has been pointed out removing the drip tray won't help you as to close to the windscreen, the WRC Yaris are further away, plus they have designed it in wind tunnel. Couple of vents in front of bonnet would work extremely well. Could try and vent engine bay into wheel wells, but then you need to get that air out so would need vents in the front guards. Front splitter just to brute force pressure at front to cancel out the lift. Another option that isn't as drastic might be to add a front bumper lip. My thinking being your trying to reduce the air going under the engine bay, which allows more of the engine bay air to go out under the car, overall dropping the pressure, hence less lift. Bonus is I have a brand new roll here that I never used which you can have, pm me your address and I'll send it up if you want it for this. Oh yeah, I'll give it a go with that lip trim stuff! Will send you a PM, thank you. Yeah I'm not yet completely convinced that the drip tray area is as awful as I'd first suspect though, because of shape of the car. In saying all of this, since half of the point of this car is that parts are cheap and readily available. It would be interesting to get a spare bonnet and cut lots of holes in it, then fit one way flaps that cover over them. So it'll show where's good for vents or not. However I'm not all that keen on having bonnet vents on the car, for visual reasons. Something else that's interesting, is just how little pressure it needs to make a big difference in lift. If my bonnet was 1m squared, and there was 1psi pressure difference from one side to the other. Then there's 1550 square inches in a square meter. so 1550 pounds of pressure? 700 odd kg? Or is that not how it works... Seems like heaps! Or is the actual pressure difference for aero stuff only very small? I cant imagine there being anywhere close to that amount of pressure causing lift. I've got this in the shed, which is about size of a dinner plate: plus or minus two inches of water is only a tiny amount, total usable range about 0.14 psi Will be interesting to see if it shows anything on that sort of scale or if it's too sensitive. A normal 0-5v MAP sensor is definitely not going to have enough sensitivity though. 1 1 Quote Link to comment Share on other sites More sharing options...
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