cyow5
Reader
4/16/21 1:41 p.m.
Go_Gators (Forum Supporter) said:
In reply to cyow5 :
Yea, agree! In the pic i posted today, the rear radiator is in place, below the wing.
I don't think we are agreeing quite yet though - the position in your second pic puts the face of the radiator nearly parallel to the streamlines I drew which would explain the overheating. You drew one blew arrow pointing directly at the face of the radiator, but that arrow is ignoring the massive effect the wing will have on the flow. My suggestion is to place it much higher and more forward, essentially triangulated between the seats and bottom edge of the wing.
Edit: I had to re-read you post a couple times to really digest what your plan with the panel was, and I agree with sleepy's critique that it is too steep and ignores the massive wings. It also ignores the air coming around the sides, so I don't think a fastback is the right approach here without full bodywork, and, well, that puts you in a Corvette, haha. Before trying a bunch of ducting (which certainly would be the most professional approach), I am suggesting more like placement like this (green markup) and ditching the roof. My guess is the roof simply move the same disturbance as the top of edge of the windshield just closer to the wing. Before you do any fab though, run some string back and forth across the tubes, add some tufts of yarn, and see if my green streamline looks correct. If so, that's a pretty simple solution. 
Another thing you can do is "tuft test" to see what the air around and going through the rad does. Also see if there is any turbulence from under the rear of the car or under the wing interfering with the exit of heated air
In reply to cyow5 :
granted. got to try maximizing the flow with the radiator where it is.... moving it would be a great deal off work and put the mass of it higher...
cyow5
Reader
4/16/21 2:03 p.m.
Go_Gators (Forum Supporter) said:
In reply to cyow5 :
granted. got to try maximizing the flow with the radiator where it is.... moving it would be a great deal off work and put the mass of it higher...
I edited my post above while you replied. Maybe you can lean the radiator forward (which I guess is similar to what you said about extending the top of the shroud) to catch some of the air that eventually gets sucked up in the low pressure zone below the wing. Mounting the rad ahead of that low pressure zone would give you a major boost in flow through the rad though compared to where it is now since you'll have relatively high pressure behind the "bumper"
In reply to cyow5 :
certainly moving/growing the shroud is where i think i need to start...
cyow5
Reader
4/16/21 2:15 p.m.
Go_Gators (Forum Supporter) said:
In reply to cyow5 :
certainly moving/growing the shroud is where i think i need to start...
Yup, but also keep in mind the air that feeds the bottom of the wing is possibly more important to it than the air above it. The more you divert to the rad, the more likely the wing will stall, so there will be a balance to be struck.
In reply to sleepyhead the buffalo :
appreciate the thoughts! the transition from the roof to a rear panel would certainly not be smooth, i could round the top panel some, but its still a nearly 90deg turn. Could even add side plates, like NASCAR has before the spoiler, but my hope would be that preventing the flow into the cabin would create flow for the radiator when coupled by a more aggressive shroud...
i kinda ruled out an upper duct/scoop primarily bc the main hoop is already high to ensure a couple inches of clearance between the line from A-piller top to main hoop top and my helmet.
side duct/scoop is not impossible, but getting clearance for 9-10" will require some creative shapes to navigate around the tire and cage.
maybe the best next step would be to cobble together a test rear window panel, try the string test again. If that not significantly better, start further evaluating the construction challenges of side ducting.
Sleepyhead is doing the math to effectively rebuild the nose ducting of the original front-of-car layout. This will be the most intuitive solution. I would lean toward a side inlet split system, which should be less impact on the rear wing assembly. Carry the split duct all the way to the face of the radiator (within a few millimeters to avoid chaffing) and then you don't have to worry about cross-wind/yaw flow bypassing the core. The side inlets could also provide some functionality of a fender to protect you from gravel kicked up by the tires and water spray on wet auto-crosses.
Since the inlet duct ideas are already out there, try this one on for size. Use the low pressure behind the car and under the wing to your advantage. Extend a duct behind the radiator, with an open top. Angle the sides outward as it gets further from the radiator to increase the effective suction. This will not add any visual obstacles and will increase the radiator efficiency somewhat without having to move it. The pictures appear to indicate the water lines would be inside the duct, but that okay, since they are in the hot flow in the nose-mounted configuration. I am not sure if this would be enough to get to a stabilized condition for track days but it is one way to start increasing the cooling. This is not a completely unheard of design, as quite a few aircraft used the ducting behind an exposed radiator.
The air swirling around the roof is a typical issue for open cars and has been know to do things like draw exhaust air forward into the cabin or spatter the back side of the windshield with rain. The panel down the back of the cage will reduced this and provide some sort of protection from hot water in a worst case scenario.
Honsch
Reader
4/16/21 2:53 p.m.
You won't get flow through the radiator unless the air pressure behind the radiator is lower than the air pressure in front of the radiator.
Our car has body panels so we know a bit better where the airflow is. We use side mounted inlet ducts plumbing into a rad box in the trunk with dual 10" outflow ducts. The ducts exit at the rear of the car in a low pressure area.
stafford1500 said:
Sleepyhead is doing the math to effectively rebuild the nose ducting of the original front-of-car layout. This will be the most intuitive solution. I would lean toward a side inlet split system, which should be less impact on the rear wing assembly. Carry the split duct all the way to the face of the radiator (within a few millimeters to avoid chaffing) and then you don't have to worry about cross-wind/yaw flow bypassing the core. The side inlets could also provide some functionality of a fender to protect you from gravel kicked up by the tires and water spray on wet auto-crosses.
Since the inlet duct ideas are already out there, try this one on for size. Use the low pressure behind the car and under the wing to your advantage. Extend a duct behind the radiator, with an open top. Angle the sides outward as it gets further from the radiator to increase the effective suction. This will not add any visual obstacles and will increase the radiator efficiency somewhat without having to move it. The pictures appear to indicate the water lines would be inside the duct, but that okay, since they are in the hot flow in the nose-mounted configuration. I am not sure if this would be enough to get to a stabilized condition for track days but it is one way to start increasing the cooling. This is not a completely unheard of design, as quite a few aircraft used the ducting behind an exposed radiator.
one thing I hadn't gotten around to writing is that it looks like the radiator is "set down" in the rear frame area... which probably isn't helping exit flow.
so, a reposition of the radiator is probably something to consider. And if you could re-orient it to be closer to "horizontal" (might take adapting the fill port to swan neck up)... then you could bring the side entrances between the frame and the "front face" of the radiator (which would be pointing down)... the the rear of the radiator is pointing up. you'd probably still want a bit of a duct up/back from the exit of the radiator to about 1/2 to 3/4 of the wing and then the wing will help pull air out of the radiator. If we can get the inlet into a "high pressure enough" area at the side of the car, this method plus the expansion in area from the inlet to the face of the radiator should create a nice high pressure zone at the face.
also, doing this should lower the CG of the radiator
edit:
other than that, I agree with stafford
thanks guys. not sure i am picturing the a behind the radiator duct/shroud... is this what yall are thinkin (top being only open surface):
looking at the pictures and amount of space between the roof panel, mirror sight line and seating area. i think its plausible that a ~6" x 24" channel could be turned down in the roof and the main hoop roll bar would create the top of the duct. the red lines would be the transition in the roof panel. the green being partially clear polycarbonate, between the upbars of the cage, meeting the red roof transition.
if it needed to be enclosed into a duct, the blue line form could start at the main hoop and run to the top of the radiator...
between the red and green forms, i could make it a fairly curved transition...
i dont like the blue structure (rear view would then be through two sheets of polycarbonate), but the red/green components wouldnt be intrusive at all..
Why not do an inverted version of a P-51 duct?
Start the top at the cage, with the outlet at the back of the bumper?
Do you have anything at the front of the car diverting or directing the air that goes under the car? Either way the air under could effect the air exiting the rear. Again, "tuft test" to see what the air around and going through the rad does.
In reply to Go_Gators :
Use air wisely. The rear wing will force some air down and a efficient fan pulling will help with that. Now all that coolant up high will cause rear roll center issues.
A kart by it's nature is very turbulent . Figuring out where the air is effective is more trial and error than calculated.
Go_Gators (Forum Supporter) said:
thanks guys. not sure i am picturing the a behind the radiator duct/shroud... is this what yall are thinkin (top being only open surface):
Yes, that is the basic idea. Add to that the scoop you sketched up and add in a little of Appleseeds P51 idea and you will have a very effective cooling system.
The downside of all that is a much more complicated assembly that will be fiddly to build and service. The intent of the car is simplicity, so make a simple system to get controlled flow to the radiator first.
In reply to stroker :
Actually, it worked fine, just wouldn't pass tech
stafford1500 said:
Go_Gators (Forum Supporter) said:
thanks guys. not sure i am picturing the a behind the radiator duct/shroud... is this what yall are thinkin (top being only open surface):
Yes, that is the basic idea. Add to that the scoop you sketched up and add in a little of Appleseeds P51 idea and you will have a very effective cooling system.
The downside of all that is a much more complicated assembly that will be fiddly to build and service. The intent of the car is simplicity, so make a simple system to get controlled flow to the radiator first.
appreciate all the input. it will be tricky and take some planning to make sure it is simple enough to deal with, but i think it can be done!
it'll be a project for the early summer, will post of pictures of progress when i get there!
making some progress... rear partition is done. roof is mostly done. Posted a lot of pictures on my build thread. Here are a couple.
I am going to start a top section to enclose the tunnel from the main hoop down to the radiator. what i am debating is whether the scoop at the very top (at or above the roll cage main hoop) can terminate at the main hoop height or whether it should protrude above it to collect more air. the opening from the bottom of the main hoop to the sloped back of the new roof is 5" and its 33" wide. so, 165sqin. i could easily make a small scoop, inside the parrellel rails running forward to aft and increase the general opening to about 260sqin. Any more than that would require going above the main hoop with the yet to be built tunnel cover. I really dont want to do that...
thoughts?
In reply to Go_Gators (Forum Supporter) :
Rad!
*edit*
No pun intended.
In reply to Go_Gators :
Do you know how ground effects work? Air is trapped between the bottom of the car and side skirts. The bottom is shaped like the top of a wing and the result is the car is sucked down to the ground. Increasing cornering speed.
Part of why it works is the air is helped to the rear by an increasing area. Thus lowering pressure and encouraging air to flow through.
You can capitalize on that by placing your radiator in that area. Put a big sucking fan behind the radiator to help pull air through.
In reply to frenchyd :
problem is frenchyd, the air down there... right above the track... is also the hottest. not so great for cooling.
In reply to Go_Gators (Forum Supporter) :
Based on the 165sqin, and my earlier math, I don't think you'll have to go too high. You might add a small flange at 45deg up/forward to the bit of aluminum angle you've added to the roll hoop. That way, if we need to add a bit of height/rounded scoopy entry, it'll be easy to tack on. but, I doubt you'll have to go higher than the aluminum sides that you've already fabbed.
seeing all that in the flesh, with those pics... I'll caution you to 'feel' out if you're getting oversteer now; and keep in mind that you might end up having to raise the rear wing up.
