SuperBuickGuy
Well-known member
how much down force is on the splitter? to make the framework, I don't want to overbuild....
Plastic Fantastic 2
- Thread starter SuperBuickGuy
- Start date
phantomjock
Well-known member
Quick - SWAG (bar-napkin analysis).
You probably expect 800 - 1200 pounds in the rear from the wing, is that about what the folks told you?
So to keep the nose down - you'll want the same up front - else go "flippy."
Those values would be at the 120-ish range I expect.
Guessing that your fuel pump is good to 700Hp, with that as a limit, we can guess how fast the car "might" go:
[Again, close enough for 0500 work!]
http://www.wallaceracing.com/Calculate HP For Speed.php
You can use "real HP" if you'd like to recalculate.
Now at 240 mph, you'll generate more downforce (and drag of course).
Recall the SuperBird (over in the the other thread) was at about 1200 pounds - so, not far off.
Build for 1200 pounds 4 struts(?) 300 each, backing plates should be good to go.
(Add a bit of pad for the wife and dog, eh Pappy?)*
Cheers - Jim
*Obscure reference to calculating final approach speeds.
Cheers - Jim
You probably expect 800 - 1200 pounds in the rear from the wing, is that about what the folks told you?
So to keep the nose down - you'll want the same up front - else go "flippy."
Those values would be at the 120-ish range I expect.
Guessing that your fuel pump is good to 700Hp, with that as a limit, we can guess how fast the car "might" go:
[Again, close enough for 0500 work!]
http://www.wallaceracing.com/Calculate HP For Speed.php
You can use "real HP" if you'd like to recalculate.
Now at 240 mph, you'll generate more downforce (and drag of course).
Recall the SuperBird (over in the the other thread) was at about 1200 pounds - so, not far off.
Build for 1200 pounds 4 struts(?) 300 each, backing plates should be good to go.
(Add a bit of pad for the wife and dog, eh Pappy?)*
Cheers - Jim
*Obscure reference to calculating final approach speeds.
Cheers - Jim
phantomjock
Well-known member
So, got my walk in, and 3rd cuppa, here goes.
Let's assume 2000lbs maximum downforce on the splitter. So if 1000 is closer to "real" that gives a 2x safety factor.
Using 1/4 inch Stainless steel aircraft cable - you'd have 6400 lbs breaking strength available in each cable.
3/8" 7x19 Stainless Steel Aircraft Cable - 12000 lbs Breaking Strength
1/4" 7X19 Stainless Steel Aircraft Cable - 6400 lbs Breaking Strength
You could use skinny turnbuckles - about the same. It will come down to how many to install - four seem to be the "typical number." That is overkill for strength, but the important feature is not the individual strength - but "Pull-Through." That is a tough one to get answered- and depends on what you mount to. Here is one mounted with three struts:
Variables to consider; LOAD, laminate thickness, number of supports, fastener diameter, and fastener head/bearing surface. In a test in the UK they found the main failure mechanism was diagonal shear cracking of the composite. Seems reasonable, if you have adequate bearing area on the fiberglass. If you are mounting to steel - well, no problem. In the picture above - I'd be concerned about those mounting points.
Assuming 2000 lbs with 4 attachments (on fiberglass structure), that is simple math - 500 pounds each. Do you want fender washers - or a bar? A 1/4 inch bolt at 500 lbs on a aluminum backing plate "ought" to be sufficient - or overkill. I'm guessing here, but would add something behind the factory (fiberglass) fastening locations, unless you are confident you could put 300-500 pounds pull on each and not pull through. The bolts would be good - but the surrounding fiberglass may not. If using washers - round would give better edge breakout protection vs square (sharp edge corners). If you could distribute the load over more area - all the better.
From a Rabbit Hole - for bolts mounted in epoxy grout - like garage floor to calculate the pull-out:
Let's assume 2000lbs maximum downforce on the splitter. So if 1000 is closer to "real" that gives a 2x safety factor.
Using 1/4 inch Stainless steel aircraft cable - you'd have 6400 lbs breaking strength available in each cable.
3/8" 7x19 Stainless Steel Aircraft Cable - 12000 lbs Breaking Strength
1/4" 7X19 Stainless Steel Aircraft Cable - 6400 lbs Breaking Strength
You could use skinny turnbuckles - about the same. It will come down to how many to install - four seem to be the "typical number." That is overkill for strength, but the important feature is not the individual strength - but "Pull-Through." That is a tough one to get answered- and depends on what you mount to. Here is one mounted with three struts:
Variables to consider; LOAD, laminate thickness, number of supports, fastener diameter, and fastener head/bearing surface. In a test in the UK they found the main failure mechanism was diagonal shear cracking of the composite. Seems reasonable, if you have adequate bearing area on the fiberglass. If you are mounting to steel - well, no problem. In the picture above - I'd be concerned about those mounting points.
Assuming 2000 lbs with 4 attachments (on fiberglass structure), that is simple math - 500 pounds each. Do you want fender washers - or a bar? A 1/4 inch bolt at 500 lbs on a aluminum backing plate "ought" to be sufficient - or overkill. I'm guessing here, but would add something behind the factory (fiberglass) fastening locations, unless you are confident you could put 300-500 pounds pull on each and not pull through. The bolts would be good - but the surrounding fiberglass may not. If using washers - round would give better edge breakout protection vs square (sharp edge corners). If you could distribute the load over more area - all the better.
From a Rabbit Hole - for bolts mounted in epoxy grout - like garage floor to calculate the pull-out:
F = D x 3.1415 x L x 800 psi
F is bolt pull-out force
D is the grout hole diameter in inches
L is the length of the grout hole
[800 psi is the epoxy strength resisting pull]
Hope that helps and doesn't muddy the waters,
Cheers - Jim
phantomjock
Well-known member
Sorry - one more...
I wanted to check my assumptions of downforce of the rear wing.
But, I had to make some other assumptions - but this may "bound" your solution. For simplicity I used a Joukowski Airfoil (no endplates).
Downforce = 623 lbs
Drag = 139 lbs
Endplates increase efficiency and will increase lift (Downforce!) and change the vortex sheets.
Same wing data at various speed can be had here (NOTE: No change in AOA):
I noted that going from -10 AOA to -14~15 AOA, you get a maximum of around 650 lbs downforce, and Drag up to about 150 Lbs. After that, it stalls and downforce falls off precipitously [Always liked that word].
YMMV!
NOTE:
If you'd like, pass along the wing chord and span - I'll rerun. After lunch maybe.
It going to be nice outside today - I gotta go do some work. Maybe glue up the front fenders...or, who knows?
Cheers - Jim
I wanted to check my assumptions of downforce of the rear wing.
But, I had to make some other assumptions - but this may "bound" your solution. For simplicity I used a Joukowski Airfoil (no endplates).
Then, I inverted it for our needs and ran some numbers:
- Wing set at minus 10 degrees Angle of Attack (AOA)
- Camber -20 percent (of chord)
- Thickness 10 percent (of chord)
- Wing Area 6 sq-ft; 12 " chord, 6 foot span
- 120 mph sea level - standard temp/pressure (STP)
- Free-stream - not mounted on car
Drag = 139 lbs
Endplates increase efficiency and will increase lift (Downforce!) and change the vortex sheets.
Same wing data at various speed can be had here (NOTE: No change in AOA):
I noted that going from -10 AOA to -14~15 AOA, you get a maximum of around 650 lbs downforce, and Drag up to about 150 Lbs. After that, it stalls and downforce falls off precipitously [Always liked that word].
YMMV!
NOTE:
If you'd like, pass along the wing chord and span - I'll rerun. After lunch maybe.
It going to be nice outside today - I gotta go do some work. Maybe glue up the front fenders...or, who knows?
Cheers - Jim
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SuperBuickGuy
Well-known member
oooohh, my brain.... I'm 2 cuppas behind you, but thank you.... so very, very, very helpful. thank you
mfain
Well-known member
I'll put in my $.02 worth (not adjusted for inflation). The actual downforce created by a splitter ( lbs.) is not all applied directly to the splitter surface. The downforce produced is a result of airflow re-direction across the nose of the car and results in aerodynamic force being applied to exterior surfaces of the vehicle, including negative force on the lower surface of the splitter including the portion of the splitter behind the leading edge of the car (front belly pan). This is especially true if you incorporate diffuser tunnels (very effective) in the lower splitter surface. The ACR, for example, uses two front support struts that are mounted (at the top) to part of the steel bumper support structure. They use through bolts at the bottom. However, there are also two additional steel cables further back supporting the splitter extension a foot or so behind the leading edge. This arrangement allows the splitter to "flex" upward in case of impact on speed curbs. I have seen a couple of front strut failures generally caused by impact damage (running over speed curbs). The failures are generally broken mounting bolts (1/4"). I recently observed a "pull-through" on a home-built splitter, and he ran a few laps with one end of the splitter sucking down to the ground on the higher speed sections of the track. Splitter supports that are too rigid absorb a lot of abuse on track. While a good front splitter may result in a 1000# or more of downforce on the nose of the car, that force is not all directly applied to the exposed surface of the splitter. Generally, if you can stand on your splitter and it doesn't do damage, it will handle the aero downforce.
Edit: The cables I mentioned are behind the grill in the areas I circled. Notice how the outer splitter braces are angled out to support the end of the splitter and designed to absorb some impact from below without breaking. This splitter extends back to the front axle centerline and has large diffuser tunnels just inboard of the tire on each side. It aero-balances the ACR wing (that produces 2200# of downforce at 177 mph) quite well.
Edit: The cables I mentioned are behind the grill in the areas I circled. Notice how the outer splitter braces are angled out to support the end of the splitter and designed to absorb some impact from below without breaking. This splitter extends back to the front axle centerline and has large diffuser tunnels just inboard of the tire on each side. It aero-balances the ACR wing (that produces 2200# of downforce at 177 mph) quite well.
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phantomjock
Well-known member
Good cover Pappy. Your point is clear, else the Wright brothers and all WWI aircraft could have never flown with fabric wings! The total downforce is over the entire surface, wing, splitter, canard, tunnels, belly pan, etc.
I am concerned regarding the support structure for the splitter. What would be required to keep from pulling through the lower valance? [My nose structure is long gone so have no idea what is/is not there for mounting] The "Pull through" you noted;do you recall was it at the splitter or body mounting? Was it material failure (plywood/aluma-core/pvc), or too small a bearing surface? I think selecting the material is easy enough, and the stand on it an OK test. A "point load" of 200# 2 size 12s would give 200psi - good - but maybe not enough for transferring the ultimate load to the attachment points.
You are "spot-on" with adding diffuser/tunnels to a splitter. I think I've posted that over in https://www.vettemod.com/threads/internal-body-aerodynamics.11568/page-8 post #153. Incorporating that feature can reduce the "lip-size" - overhang of a splitter - a specified maximum in some associations- while retaining the same amount of downforce. With a deadline of track time this week, SBG might forego that to get some time. The expansion diffuser/tunnels could be cut in next week (post track) if needed without trimming the splitter for even more DF if needed.
Cable install gives the advantage of not "Punching Through" if/when the splitter bottoms out - just as nasty as a "Pull Through" I'd reckon. I've "toyed"with the idea of "lift struts" that might be rigid enough and when struck they compress - but that is a whole bucket of worms in itself. [Eg., would need to be concerned with the possiblity of buckeling if they didn't compress.]
In any case, the "Blue-Nose" up in post #1843 above is going to have some problems. Wonder if it ever made the track? I can't find the original source doc so who knows?
Cheers - Jim
I am concerned regarding the support structure for the splitter. What would be required to keep from pulling through the lower valance? [My nose structure is long gone so have no idea what is/is not there for mounting] The "Pull through" you noted;do you recall was it at the splitter or body mounting? Was it material failure (plywood/aluma-core/pvc), or too small a bearing surface? I think selecting the material is easy enough, and the stand on it an OK test. A "point load" of 200# 2 size 12s would give 200psi - good - but maybe not enough for transferring the ultimate load to the attachment points.
You are "spot-on" with adding diffuser/tunnels to a splitter. I think I've posted that over in https://www.vettemod.com/threads/internal-body-aerodynamics.11568/page-8 post #153. Incorporating that feature can reduce the "lip-size" - overhang of a splitter - a specified maximum in some associations- while retaining the same amount of downforce. With a deadline of track time this week, SBG might forego that to get some time. The expansion diffuser/tunnels could be cut in next week (post track) if needed without trimming the splitter for even more DF if needed.
Cable install gives the advantage of not "Punching Through" if/when the splitter bottoms out - just as nasty as a "Pull Through" I'd reckon. I've "toyed"with the idea of "lift struts" that might be rigid enough and when struck they compress - but that is a whole bucket of worms in itself. [Eg., would need to be concerned with the possiblity of buckeling if they didn't compress.]
In any case, the "Blue-Nose" up in post #1843 above is going to have some problems. Wonder if it ever made the track? I can't find the original source doc so who knows?
Cheers - Jim
SuperBuickGuy
Well-known member
I really like the idea of offsetting - seems so simple but if it hadn't been mentioned, I'd have missed it... giving it some 'flex' is a really good tip
blanking plate to direct air to the radiator
metal
installed-ish
welding aluminum is so easy
getting closer
now to decide how much splitter... the blue lines are potential cut lines
about Wednesday. I'm driving Britney. The track wasn't thrilled about their instructor riding in the C3 (yeah, I know, but in the end they agreed).... but that wasn't the biggest deal - I get licensed to solo on Wednesday - which is good enough for Optima to let me run in Intermediate class - which means I can pass... Otherwise I'll get whatever the follow-the-leader time is in Novice. I suspect dead last in Intermediate will still be faster then Novice.... so there is that.... with that said, I really should keep my eyes open for better brakes and sway bars for her... she is a hoot on the track
blanking plate to direct air to the radiator
metal
installed-ish
welding aluminum is so easy
getting closer
now to decide how much splitter... the blue lines are potential cut lines
about Wednesday. I'm driving Britney. The track wasn't thrilled about their instructor riding in the C3 (yeah, I know, but in the end they agreed).... but that wasn't the biggest deal - I get licensed to solo on Wednesday - which is good enough for Optima to let me run in Intermediate class - which means I can pass... Otherwise I'll get whatever the follow-the-leader time is in Novice. I suspect dead last in Intermediate will still be faster then Novice.... so there is that.... with that said, I really should keep my eyes open for better brakes and sway bars for her... she is a hoot on the track
phantomjock
Well-known member
Size of splitter? Maybe; "Stand on the shoulders of..." Here is one that is/has been running. This looks like where you might be headed.
I'd suggest that #28 might be the "right size"-- if racing organization rules met. It barely extends beyond the nose. As a note, the image file is called "bremsetest" That is German for "Brake Test." We can guess it might be under braking - looks like some front compression. A trackside video would be useful.
Looks like they have retained the size and shape - Mar 2021, " First Rollout " video:
A little look at your "wing makers" shows only a small air dam. Did you see it run ? How was it. Might suggest a smaller size. But, you could always bring a saber saw to the track. [I've done that before!]
We "know" the Greenwood's (blue at masthead)...
Cheers - Jim
I'd suggest that #28 might be the "right size"-- if racing organization rules met. It barely extends beyond the nose. As a note, the image file is called "bremsetest" That is German for "Brake Test." We can guess it might be under braking - looks like some front compression. A trackside video would be useful.
Looks like they have retained the size and shape - Mar 2021, " First Rollout " video:
A little look at your "wing makers" shows only a small air dam. Did you see it run ? How was it. Might suggest a smaller size. But, you could always bring a saber saw to the track. [I've done that before!]
We "know" the Greenwood's (blue at masthead)...
Cheers - Jim
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SuperBuickGuy
Well-known member
I'll bring up the other car we admired
SuperBuickGuy
Well-known member
I'm glad you said that about Richard's car....
no splitter, just air dam, even the 24 hour Corvette.... very minimal
even Danny Popp's car
it looks like the most is on the 24 hour Corvette - and even that is minimal. Thinking that is the route I'll go - maybe a 3" extension and call it good, put a bit more on the parts that are outside the fenders to get some 'free' downforce but ultimately make it channel the air away from the underside rather then directly provide downforce....
thoughts?
no splitter, just air dam, even the 24 hour Corvette.... very minimal
even Danny Popp's car
it looks like the most is on the 24 hour Corvette - and even that is minimal. Thinking that is the route I'll go - maybe a 3" extension and call it good, put a bit more on the parts that are outside the fenders to get some 'free' downforce but ultimately make it channel the air away from the underside rather then directly provide downforce....
thoughts?
SuperBuickGuy
Well-known member
the other C3 at Willow Springs
I am finishing the area above the sidepipes as well....
I am finishing the area above the sidepipes as well....
phantomjock
Well-known member
Your splitter mount could double as an air dam. Just need to work what material and how to multi-configure it.
Else, the combination as you mention in the other thread should play well together.
Else, the combination as you mention in the other thread should play well together.
SuperBuickGuy
Well-known member
and more fitting, but this time with a grinder
it will be black when it's done - but I still have a bit more welding to do
it will be black when it's done - but I still have a bit more welding to do
SuperBuickGuy
Well-known member
brake air intakes
here they are.... not going to use them
the issues are too wide and they aim down.... and take up a lot of room
so just holes
was planning on these at the wheels but they'll work quite well here
some 3" tube to aim the flow at the rotors
paint the blanking plate
here they are.... not going to use them
the issues are too wide and they aim down.... and take up a lot of room
so just holes
was planning on these at the wheels but they'll work quite well here
some 3" tube to aim the flow at the rotors
paint the blanking plate
phantomjock
Well-known member
Wow! Did you fill the rectangular holes? Nice job. No, I mean F-in Amazing job!
In any case, like the round fittings.
Cheers - Jim
In any case, like the round fittings.
Cheers - Jim
SuperBuickGuy
Well-known member
that was paint
another track day completed.... I had the Cadillac airborne.... so much fun (and yes, I knew I'd go airborne)... did a nice 100 mph 4 wheel drift... nothing to see here, moving along
SuperBuickGuy
Well-known member
in other news, painted the spoiler
and installed the block
Soooo, next Friday, I'm doing a Track Night in America at Portland International Raceway.... but
forecast has snow in it. Granted, it's supposed to be 'just' rain by Friday (the weather witches are just guessing) - however, that's not better because rain cancels.... and honestly, that 2 1/2 mile track would be nothing but standing water and stained underpants if it was doing anything but mist.....
I really want to do this track night for a couple reasons - 1) it's where I'm doing Optima this year - thus it's like a free practice, but then 2) noise. I want actual data on noise. I think I have it solved - but the 'if it's not' is I'm building new sidepipes with a far different design... and that will take a solid month to build... I plan on doing this next winter - it will have oval exhaust because Chad (old timers know this story).... but the benefit of new headers is I think these 4' primary pipes destroy power...
Next winter, I plan on pulling the motor then building new headers/sidepipes and putting some kind of port EFI.... get near 900 hp but more importantly, a wider power band....
and installed the block
Soooo, next Friday, I'm doing a Track Night in America at Portland International Raceway.... but
forecast has snow in it. Granted, it's supposed to be 'just' rain by Friday (the weather witches are just guessing) - however, that's not better because rain cancels.... and honestly, that 2 1/2 mile track would be nothing but standing water and stained underpants if it was doing anything but mist.....
I really want to do this track night for a couple reasons - 1) it's where I'm doing Optima this year - thus it's like a free practice, but then 2) noise. I want actual data on noise. I think I have it solved - but the 'if it's not' is I'm building new sidepipes with a far different design... and that will take a solid month to build... I plan on doing this next winter - it will have oval exhaust because Chad (old timers know this story).... but the benefit of new headers is I think these 4' primary pipes destroy power...
Next winter, I plan on pulling the motor then building new headers/sidepipes and putting some kind of port EFI.... get near 900 hp but more importantly, a wider power band....
SuperBuickGuy
Well-known member
it looks nice
too bad it's too low
and all the harpies are rejoicing....
so, it's opportunity. The holes in that valence are a problem for aerodynamics - and it was rightly suggested I block them.... so I will the calculation for cooling is you need 1/3 the radiator surface in grill opening... worst case scenario is I put a vent in the closing panel... the problem is it will be hard to create access for the bolts.... and a bit shorter spoiler.... 3 1/2" was not enough.... the other choice might be to make it flexible with reinforced rubber....
In other news
- I filled the gas tank, no leaks, no smells
- oh and we're moving .... this should be fun (3 hours east)....
too bad it's too low
and all the harpies are rejoicing....
so, it's opportunity. The holes in that valence are a problem for aerodynamics - and it was rightly suggested I block them.... so I will the calculation for cooling is you need 1/3 the radiator surface in grill opening... worst case scenario is I put a vent in the closing panel... the problem is it will be hard to create access for the bolts.... and a bit shorter spoiler.... 3 1/2" was not enough.... the other choice might be to make it flexible with reinforced rubber....
In other news
- I filled the gas tank, no leaks, no smells
- oh and we're moving .... this should be fun (3 hours east)....
SuperBuickGuy
Well-known member
So Sunday, I'll remake the lower valence out of aluminum without air intakes. If I do need intakes, I'll craft some kind of scoop so that it provides downforce to low pressure to the radiator core. I've also thought of making those scoops active so they could be adjusted or even closed.
I also will make a spoiler but seriously considering just a reinforced rubber one.... I need brake cooling so it will be wide enough for the air intakes.... I considered before to put those intakes next to the turn signals (behind the grill but also higher in the body).. this would help with clearance... still need to spend more time on how 'tall' to make it... 3 1/2 was too much but only just barely - the bend came from the step into my shop and may have been caused by an earlier scrape....
learnin'
I also will make a spoiler but seriously considering just a reinforced rubber one.... I need brake cooling so it will be wide enough for the air intakes.... I considered before to put those intakes next to the turn signals (behind the grill but also higher in the body).. this would help with clearance... still need to spend more time on how 'tall' to make it... 3 1/2 was too much but only just barely - the bend came from the step into my shop and may have been caused by an earlier scrape....
learnin'
