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Old 05-30-2007, 04:12 PM   #1381
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Ground Effects
I tried this because it was convenient and easy on my chassis and because the full size GTP cars use it. I am aware that the best effects from it are over 100 mph so we may be below the zone where it is useful.

I found no beneficial effects from the lower wing. The car did not tighten (more push)even a little. I use a soft dam in front that actually almost skims the track, so maybe I have no useful air underneath.
I could not use the full straight as there were two puddles (springs really) on it, but I did have access to one high speed right hander just on the near side of the track where I did my tests.
I had a huge crash back end first at high speed into a very solid 2 x 8 board caused by one of the puddles. It popped one of the super heavy Traxxas ball cups but I could push it back one fine. The lower wing survived. All the Panhard bar parts survived. The spur did not.

Wayne-Now if it pushes up does that mean that you have too much downforce in the back, or does it drift up on all four wheels evenly. Thanks for the report. Interesting fact on you rear bumper as Mathijs and I discussed this earlier in the thread.

I still defend my position that the back of most GTP shells do not have to be cut quite so high so that they are a bit stronger in supporting the side dams below the waist of the car. If there was significant wind down there my lower wing would have picked it up. Now this Nissan NPT90 shell has a huge cut below the wing so obviously a high rear cut is needed to clear that air flow.

Boomer- Thanks for the Aero discussion. My findings above.

KcSteringa-as the same spektrum system worked flawlessly, superbly, (best RC invention of the year) in the pan car with both a sphere comp and a Novak GTB controller just before the Mamba installation, I am not so quick to point a finger at it as the source of all my Mamba problems.

New Mamba Max Firmware. No change.

RCsteve93- We should have plenty of range then.

Catcars-Thanks. Welcome aboard.

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Old 05-30-2007, 04:29 PM   #1382
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Aero can work on RC under the car...it just needs more drastic measures. I remember one velodrome car a company made that was a molded graphite chassis with a tunnel and diffuser built in. This car genereated something like 11lbs of downforce and had to pretty much lock up the front suspension to keep it from bottoming out.
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Old 05-30-2007, 07:38 PM   #1383
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i think you will need to add some side dams to those ground effects to help speed up the air like you were saying, other wise its just a panel with air hitting it inconsistently. i think the side pieces will help streamline some flow across the surface. But in the end the ultimate would be a custom laid cf chassis.. basically like the real cars. The one thing to worry about is does it 'dry/wear' out the track faster. you are speeding up the air across the surface so one would have to worry about that if moisture content is a concern (especially on those soaked carpet surfaces lol) I offer that as something to chit chat about, on asphalt it might be okay. on a surface such as carpet or dirt oval where moisture content really effects surface/traction i think its probably best to limit/eliminate excessive ground effects to help keep it the same for everyone..

i was planning on building my own wind tunnel - hey thats what the workshop, i mean garage, is for anyways right?

john if you have a bunch of spare lexan around, try 'sealing' the majority of the area under the chassis, from the front to the back, just cut out around the wheel areas. that will start to get the air flowin. also either use a little extra lexan or put some bends in it to fasten the body tight so it doesn't bow and flex allowing air into the cab. i think 1 or 2 sheets would cover this and you would really find out if a flat surface would work at all. or you could stick something between the lexan and the chassis making a small aerofoil. There are so many ways to do it that i think the message would cut off first before posting it all.
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Old 05-30-2007, 08:26 PM   #1384
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John, back in the late '80's, a company named Dahm's made bodies and acc. they had an undertray that sounds like what Mason is talking about. I tried it but don't really recall that it was of any help, but then I was running stock motors in a TRC Pro 10, on asphalt oval and not travelling at anywhere near the speed you are. Just thought I'd mention it.

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Old 05-30-2007, 11:25 PM   #1385
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losi, back somewhere in the thread we've covered dahms, currently known as vans invent, vansinvent.com . website is still operational but not sure if they are still in bidness. gent was older and seemed to have time to do it so if anyone wants any of their stuff might just email them asking if they have the tray still...
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Old 05-31-2007, 09:05 AM   #1386
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Got my I-Force today... Looks great. I will probably need some pictures though to take me through assembly has been 10 years since I built a pan car with non metric screws...

I ll post some pics when I am done
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Old 05-31-2007, 09:17 AM   #1387
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Jon,

great report on the under wing. I agree, there probably not much down force from the wing.

What really got me thinking on the rear down force, is that one day I was racing flat track oval on a very dusty track, the car was leaving a rooster tail of dust suck up from the track as it went down the straight. I'm talking a 3 foot or more rooster tail. that tells me that there was air under the car being suck out the rear. probably cutting the back out the body with a large rear wing is still the answer. but I keep thinking about creating more downforce with less drag.

I remember that rc downforce chassis runnning at the velo. from what i remember it didn't work to well. the pan cars were still faster and handled better.

when I said push up. it was more like a jump up. it all happened within milli seconds. the car lost traction and just slide up almost instantly. however as my speed hit 50 the rear started to slide. so i'm thinking the rear let go and the front let go almost at the same time and up it went.

I am also thinking at for a high speed run a gtp car may create to much drag from the down force created the foil shape of the body.

Even at the Velodrome with stock car bodies you can year the cars being pressed to the track from the down force.

jon, thanks again for you reports,
they pretty much back up some of my own theories on areo.

yours
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Old 05-31-2007, 09:52 AM   #1388
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When you think about roostertails or any other "lifting" of dust or debris at the back of the car, remember that you're creating a pretty big vortex behind the spoiler. There is nothing behind this big "wedge" you've created - we're not running a real Group-C type of airfoil where there is air able to come back down the back of the car - we are a complex wedge shape. (I can't say that without thinking WEDGIE!!! sigh. . .)

This wedge is more effective the higher the rear of the wedge - OR the longer the wedge - but both create drag, and the longer (without support) is less stable and thus less effective.

The reason why it's more effective is because, according to Milliken, of the vortices created. The vacuum created behind the rear spoiler (the entire rear of the car, essentially) helps create the downforce at the rear. No height at the rear, no rear DF.

Now - the roostertails aren't an indication of airflow under the car. They are indicators of two things - first they indicate the vortices behind the car disturbing debris on the track. This type of "roostertail" would be the "cloud" type of tail following the car. The second is caused by those two big meats you have at the end of the car - those sticky tires, even covered by dust, will pick up crap and throw it high in the air.

Combine these two and you've got wonderful roostertails.
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Old 05-31-2007, 10:23 AM   #1389
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Thanks for the discussions guys, I'lll add a couple more notes. After my run through the water the lower wing was wet on the bottom. I took it to the compressor and blew it off from the leading edge underneath. I got good laminar flow of air accross the wing, nice and straight. The water droplets aligned themselves lengthwise and were straight all the way to the back end of the lower wing. The air followed the smooth bend very well. If I had good airflow under the wing it should have done what I wanted and diffused the air creating some additional vacuum. I would probably have to raise my front soft dam to get some airflow under the car and maybe do some sealing that Wayne talked about. If this Lexan was easier to join and work with I would probably try some more things. I am not encouraged at this point to continue.

I have one dusty corner where my car will leave rooster tails. I used the plural because there are two very distinct tails, one coming off each tire. Not much happening in the middle. I do have good evidence of the vacuum created by the wedge body though. If there is moisture in the cracks that is not visible on the suface (wayne talked about this) My car will suck this out and coat the body and chassis with water droplets.

Inspgdt-Now about that 11lbs of downforce. How much does the standard body without ground effects make. I imagine a lot.

Boomer-Speaking of those vortices, you can actually see this region of disturbed air in the videos that I posted previously of my pan cars running. This air distorts the video image behind the car and up to about 3 feet back(six feet back on the straight). It is a weird looking disturbance that follows the car. I though maybe it was an anomally of the camera when panning, but it happens when it is not panning also, so I think it's the disturbed hot air, behind the car, distorting the image of the road. You have to view it full screen to see this distortion.

http://hometown.aol.com/johnstranahan/PanvsTouring.wmv

Note that my wide pan car is about 1.5 seconds faster per lap now with the 3 link with Panhard bar rear suspension and dual dynamic A-arm dampened front suspension than it was in this video.

Toughbeard-good luck. Your car is similar to the pantoura, see the first couple of pages of this thread for the photos you need.
John

Last edited by John Stranahan; 05-31-2007 at 10:50 AM.
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Old 05-31-2007, 12:30 PM   #1390
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Not as much as you might think...I don't remember the specific numbers that well from when I talked to them as it was over 10 years ago. For some reason only the 11Lbs stuck in my mind and that it was significantly more then just the body alone. Either way it was enough downforce to nearly bottom out the car on front arm flex alone with the older style nylon arms on the dynamic strut front end. I saw the guy here on RC Tech somewhere. If I can find him I'll see if I can get more accurate numbers.
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Old 05-31-2007, 02:44 PM   #1391
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hmmm, 10 years ago, we were running bodies which were nowhere near as good as they are now.

And with John having that front lip, there's much more of a vacuum underneath which would make the bodies much more effective and any under-ground-effects less.
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Old 06-01-2007, 09:09 AM   #1392
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I have pretty much abandoned the under body stuff, went back to old school wing and cut out rear for now.

I have tried the flexible lower valence on an old superspeedway car, at the old Carson Velodrome. the car was hooked up and I believe it did ad to the vacume. I'm not sure if I will use it at the Encino Velo. to many bumps. I think on that for a while.

enjoyed all the comments.

and re the rooster tails. last night the thought that the tires would kick up dust did enter my mind.

one last thing, the shape of the body will affect your speed. we have tried high down force bodies at the velo and they stick to the ground so well the speeds dropped of dramatically. you can hear the tires being smashed into the track.
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Old 06-01-2007, 09:20 AM   #1393
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Yep - we had the same experience the first time we really began running 6 cell mod (9x2) - the rear spoiler would actually buckle slightly, the body just front of the rear wheels would scrape. . .etc.
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Old 06-01-2007, 06:57 PM   #1394
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Boca Bearings , Robinson Racing Gold Pinions

I received my order from Boca Bearings. The yellow sealed bearing at top left is a rubber sealed high RPM bearing that I am going to try on the Novak 3.5R. The high RPM model with shields is just below. You can see part numbers and Boca information in the photo. My theory is that without dirt inside, this bearing is going to last 10 times longer than a non sealed bearing. I will see.

At the top and right are the green sealed axle bearings that I am going to try. These are rubber sealed also. I found no teflon sealed bearings in these two types at Boca.

Center low are a few pinions in good better best position, good on top.
The upper pinion is a Corally. These are hard and last well, but are too narrow for the spur and invariable cause a power robbing fuzzy area of spur next to their edge. 13 tooth is the smallest. The middle Robinson Racing Nickel Plated pinion is just almost wide enough. You end up with a little motor endplay driving the setscrew onto the gear area in spite of your best efforts. This creates nice little power robbing divots evenly space every 4-5 teeth on the spur. The 12 tooth model wears way to fast. 2 runs. Now the best I have found is this Titanium Nitride Gold Pinion from Robinson Racing. It is wide, very hard, long wearing and no longer in production. Stormer racing has made an effort to resupply us with these so I though I would go ahead and report it again. They show 6 of each in stock yesterday long after my order. I bought enough for myself (I think its called hoarding).

Novak 4.5R and the Mamba Max
I got pretty proficient with this combination on a slippery track today. The gear I like in my current car is 87/14. Top speed was super with the Thunder Power Battery, but I was not near as fast, lap time wise, with it as with a GTB controller and the Novak 3.5R. I'll try the Mamba with the 3.5R tomorrow now that I have the proper 12 tooth pinion. I am also going to try 50% brakes at the controler and more brakes at the radio to see if this will soften the brake pulses any. This is a continuing problem for me. I am awaiting anxiously for the Return of my GTB, or the instock notice on the LRP TC edition 80750. I have 12 runs on the ThuderPower Battery. 12 or so more and I'll retest it.

John
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Old 06-01-2007, 07:39 PM   #1395
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if i move back to Florida as i expect to in august/september, i'll get you some pinions plated that will never wear out.. my cousin works for an outfit that has a proprietary system for nickel/boron plating on things.. he was going to do some piston/sleeve sets for me before i gave up nitro...
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