Author Topic: Frontal Area / Cd numbers  (Read 75063 times)

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Offline robfrey

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Re: Frontal Area / Cd numbers
« Reply #255 on: May 31, 2019, 08:31:46 PM »
Even if you do not plan on running SCTA you will probably want to have a second chute.
Btw, chute tubes do not need to be round.
When you get closer, I will send you one of my spare chutes so you can experiment with how you can fold up shroud lines to fit in your tubes and adjust design if necessary to fit.
Oh yeah, they grow a bit during a week at the salt even though you will rinse them after every use. Can’t explain it but it seems to consistently happen so leave yourself a little extra room.


Rob Freyvogel
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Offline robfrey

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Re: Frontal Area / Cd numbers
« Reply #256 on: May 31, 2019, 08:36:20 PM »
Another thing I noticed about this design that uses a clamshell door is that the chute’s come out a little lazy. There is a giant low pressure area created on the backside of the clamshells. Naturally the chute does not want to go from low pressure to high pressure so you will need to get it forced out pretty good to get it into clean air and it will still probably bounce off the ground.
Were you planning on using a drogue chute?


Rob Freyvogel
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Offline robfrey

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Re: Frontal Area / Cd numbers
« Reply #257 on: May 31, 2019, 08:41:17 PM »
When looking at the car from the top view, as the air comes between the fuselage and the wheel pants and gets towards the rear of those items, there will be a low pressure area created since it is opening up like a Venturi.
Low pressure area above your wing is not good.
The fix is to shorten up the wing cord wise.
You may want to extend the leading edge of the wing where it meets the fuselage to compensate for the shorter cord.


Rob Freyvogel
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Offline SPARKY

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Re: Frontal Area / Cd numbers
« Reply #258 on: June 01, 2019, 12:34:47 AM »
I definitely vote for a small  pilot chute that can be shot into the slip stream  up or side ways   to pull the main chute out---bouncers are not fun and will get you written up for late chute
Miss LIBERTY,  changing T.K.I.  to noise, dust, rust, BLUE HATS & hopefully not scrap!!

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Offline robfrey

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Re: Frontal Area / Cd numbers
« Reply #259 on: June 01, 2019, 08:59:09 AM »
I am very happy about how we did our chutes by ejecting them straight up into clean air. I barely have to think about touching the lever and the chute is at full snatch.
Our design is sort of a jack-in-the-box approach and the entire chute package is thrown out of the box.
This system does not use a drogue.
Initially we had a drogue and not a sprung bottom. The problem that we were experiencing was that the cords were actually getting burned by friction when existing the radiused edge of box.
The only thing I would change is to make the chute door on the primary a two piece design that opened at the center. With the one piece design, the door is a little big and I am concerned about the air breaking it off at over 500. So far so good at 420 but we do have a couple of spare doors made just in case.


Rob Freyvogel
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Offline kiwi belly tank

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Re: Frontal Area / Cd numbers
« Reply #260 on: June 01, 2019, 04:17:53 PM »
You might want to look at changing it to a soft flexible material to save damage to you or somebody else running over some of it.
  Sid.

Offline Simspeed

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Re: Frontal Area / Cd numbers
« Reply #261 on: June 02, 2019, 04:12:07 PM »
I had a great meet up with Stainless, John Boy and the crew yesterday in Denver...great bunch of guys.  Stainless had his new chassis in tow for body work and I had a test fit which was definitely tight just in the bare chassis.  I can see the need to rethink how best to design around the driver with helmet and driving suit as many here have stated.  For now we'll continue with what we have dimension-wise for this concept stage but eventually we'll have to scale everything up for production drawings once the final concept is nailed down.  Thanks again Stainless...fun day and highly educational. Best of luck to you and the crew with the new Bockscar 2.0 lakester... 

Offline 4-barrel Mike

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Re: Frontal Area / Cd numbers
« Reply #262 on: June 02, 2019, 07:11:52 PM »
 :cheers:  :cheers:

Mike
Mike Kelly - PROUD owner of the V4F that powered the #1931 VGC to a 82.803 mph record in 2008!

Offline Stainless1

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Re: Frontal Area / Cd numbers
« Reply #263 on: June 02, 2019, 11:43:28 PM »
Yea we tried to lead Terry astray... but he is smarter than the average bear... errr racer...
I think the test fit was a good experience.... it will be a lot tighter in a SFI 20 and Snell 20 (future), than blue jeans and a shirt.
Enjoyed our talk... see you at the salt with any luck
Stainless
Red Hat 228.039, 2001, 65ci, Bockscar Lakester #1000 with a little N2O

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Re: Frontal Area / Cd numbers
« Reply #264 on: June 03, 2019, 12:28:13 AM »
Terry, It was nice to spend time bench racing. Thanks again for dinner. If you are coming to the city again it would be great to see you again. We dropped the Bockscar II off to get the aluminum panels fabricated.

John   
John Gowetski, red hat @ 221.183 MPH MSA Lakester, Bockscar #1000 60 ci normally aspirated w/N20

Offline Simspeed

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Re: Frontal Area / Cd numbers
« Reply #265 on: June 03, 2019, 03:59:20 AM »
Terry, It was nice to spend time bench racing. Thanks again for dinner. If you are coming to the city again it would be great to see you again. We dropped the Bockscar II off to get the aluminum panels fabricated.

John   

Hey John Boy...I'm excited to see the body wrapped in tin with the nose cone in place.  It's amazing the record speeds you guys have achieved with such small engines.  Stainless is doing a great joy updating what has proven to be a well designed record setting machine.  I look forward to our next get together.  God bless...

Offline Bratfink

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Re: Frontal Area / Cd numbers
« Reply #266 on: June 05, 2019, 04:16:18 PM »
Just caught up on this thread. Some seriously excellent work here!

I can assist with Aero testing should you choose. The subject is far too expansive to put into one post here, but if you ping me at abracabratby@yahoo.com and we can discuss. The type of testing is really going to be dependent on your budget and needs.

CFD is the most obvious choice, but not all CFD is created equal, everything from boundary conditions to the type of cores you run the solver on all have an effect on the results.

Windtunnels are tricky for streamliners because all the facilities that you would want to test at (i.e. full moving ground) are not capable of positioning the wheel pads at the narrow tracks and long wheelbases that you typically run. That leaves fixed ground facilities that can leave big question marks on the results.

Anyhow, message me if you like.
James

Offline Simspeed

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Re: Frontal Area / Cd numbers
« Reply #267 on: June 06, 2019, 06:10:01 PM »
Just caught up on this thread. Some seriously excellent work here!

I can assist with Aero testing should you choose. The subject is far too expansive to put into one post here, but if you ping me at abracabratby@yahoo.com and we can discuss. The type of testing is really going to be dependent on your budget and needs.

CFD is the most obvious choice, but not all CFD is created equal, everything from boundary conditions to the type of cores you run the solver on all have an effect on the results.

Windtunnels are tricky for streamliners because all the facilities that you would want to test at (i.e. full moving ground) are not capable of positioning the wheel pads at the narrow tracks and long wheelbases that you typically run. That leaves fixed ground facilities that can leave big question marks on the results.

Anyhow, message me if you like.
James

Hi James...thanks for the offer.  I'll get back to you when we've reached a consensus on the drive layout and body shape we think is best suited to the unique drive train I've introduced.  Essentially we'll be looking to compare the best inboard and outboard drive wheel body geometry to see what the drag penalty is for receiving the added benefits of vertical stabilization, increased traction potential, and added downforce or weight loading of an active aero wing flap on the outboard wheel design.  As I mentioned previously, the outboard design more than doubles frontal area but we're still less than 8 sq.ft. total.  Not great when we consider the inboard wheel design is only 3.6 sq.ft.  Thanks... Terry
« Last Edit: June 06, 2019, 06:32:27 PM by Simspeed »

Offline Simspeed

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Re: Frontal Area / Cd numbers
« Reply #268 on: June 06, 2019, 06:42:15 PM »
When looking at the car from the top view, as the air comes between the fuselage and the wheel pants and gets towards the rear of those items, there will be a low pressure area created since it is opening up like a Venturi.
Low pressure area above your wing is not good.
The fix is to shorten up the wing cord wise.
You may want to extend the leading edge of the wing where it meets the fuselage to compensate for the shorter cord.


Rob Freyvogel
#496
AA/BFS

Hi Rob...I'm working on a redesign of the chutes, wing, flap and various chassis parts to compensate for adding two chute packs.  Not sure just yet how best to get the chutes out into the air stream.  I should have something to show in a few days.  Thanks... Terry

Offline Simspeed

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Re: Frontal Area / Cd numbers
« Reply #269 on: June 07, 2019, 01:17:27 AM »
Here is the redesign of the chute system allowing for two full size packs.  The tail cone in this design is ejected and acts as the pilot chute to pull out the main chute using a short tether cord. The shroud lines run from inside the body fitted packing can back to a formed steel loop that's bolted to the frame rails for the anchor point. We'll probably use two bolts in shear rather than thread tension to retain the anchor loop.

The tail cone itself would be rotomolded high density plastic that sets into the tail stock with spring loaded trigger pins.  The front edge of the tail cone would pop up into the air stream and be flipped backward away from the car pulling the chute out with it. The second chute could be pulled out by a second tether cord affixed to the shroud lines of the main chute near the end of its full extension.  That would keep the main chute lines clear to full deployment before the second chute leaves the car for it's deployment.  The second chute could always be independently ejectable if need be.