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Author Topic: UK Lakester build G/GL  (Read 101726 times)

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Offline Lemming Motors

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Re: UK Lakester build G/GL
« Reply #435 on: December 11, 2019, 05:28:13 AM »
I am struggling to find good pictures of the relationship of a (single) parachute tube and the tether line anchor point. I have searched the forum and am still somewhat in the dark regarding best practice.

My best option so far seems to be a 6"OD seamless alloy tube with 0.16" wall.

I am building the rear support structure - as I see it there are at least three options to tether the lines:

1. at the front end of the chute tube (i.e. inside the tube). Cons: its potentially getting chewed by the rear lip of the tube if it flaps.
2. Under the chute tube opening, behind the tube. Pros; apart from a short length of steel (push bar) there is nothing to rub on. Cons; the tether line is doubling back on itself prior to deployment so has to travel through 180 degrees on the anchor.
3. Under the chute tube but forward of the opening. Pros; it is already in the correct orientation so cannot hang up on any bracketry as it swivels through 180 degrees (per option 2). Cons; I wont have too much clearance from the underside of the chute tube so it could rub on that during slowdown if the chute flaps up and down.

If anyone can provide some clear pics of a tried and tested relationship (tube / anchor) on a lakester / liner that bodily comes to a point in that area; that would be hugely appreciated.
A Bonneville Lakester please barman.
Certainly sir; a lick of salt, a sip of gas and a twist of Lemming. More Lemming sir?
Just a squeeze.

A Squeeze of Lemming it is sir.

Offline Elmo Rodge

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Re: UK Lakester build G/GL
« Reply #436 on: December 11, 2019, 07:49:39 AM »
John, as I see it, your first task is to figure out the height of your center of mass. Your tether mount should be placed accordingly. That's what I did and I really feel comfortable when my chute hits. I have pictures in my build diary.
Wayno

Offline Elmo Rodge

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Re: UK Lakester build G/GL
« Reply #437 on: December 11, 2019, 08:26:58 AM »
John, look on page 5 of the Build Diaries at Utah Belly Tank. Page 3 has some pictures.  :cheers:
Wayno

Offline Stainless1

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Re: UK Lakester build G/GL
« Reply #438 on: December 11, 2019, 09:45:45 AM »
John, I would not do a through the tube attachment... IMO that creates a lever that can move your car around.  There are a lot of cars that do it that way, but we are outside attachment guys.  We have never had a problem with the tether laying at the bottom of the tube causing a problem, except that it adds several cubic inches of space requirement. 
Our design makes the chute tube structural, the old one was and Pork Pie said this one must be also, so I could not use an alloy tube.  (see build diary)
The tether has never worn or rubbed on the tube and the push bar is above the tube so no issue there either.  Our attach point is in the middle of the mass. 
Draw a line through the center of your mass in the car, the center of the motor and adjust it based on where battery and water mass is located.  This should be very close to where the chute should attach.
Here is a Pork Pie pic of our car
Stainless
Red Hat 228.039, 2001, 65ci, MSA Bockscar Lakester with a little N20 
MSA Bockscar Lakester #1000 my fastest mile 245 and change, 84 ci turbobusa motor... but Corey's 233 MPH H/BFL record is still 3MPH faster than mine.

Offline Lemming Motors

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Re: UK Lakester build G/GL
« Reply #439 on: December 11, 2019, 10:23:33 AM »
Wayno
Thank you for the direction. I just read your entire build diary and almost missed a work call as a result, they do not understand priorities!

Stainless
Thank you. I will go look for the diary.
A Bonneville Lakester please barman.
Certainly sir; a lick of salt, a sip of gas and a twist of Lemming. More Lemming sir?
Just a squeeze.

A Squeeze of Lemming it is sir.

Offline Lemming Motors

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Re: UK Lakester build G/GL
« Reply #440 on: December 16, 2019, 07:03:03 AM »
I did some research based on Wayno's comment (first find the height of your centre of mass) aka Centre of Gravity Height aka CGH and Stainless comments about masses.

With that awareness I did some research and came across a calculator for finding CGH on the interweb in the Longacre Racing website - hope this link works and is useful to others wondering this:

http://www.longacreracing.com/technical-articles.aspx?item=42586

I also came across a video by VTEC Academy that showed some drag and LSR cars with front or rear wheels off the ground (it was mostly focusing on Honda Civics and CRZ's) and that had some data suggesting long chute lines /small chute would be a low angle (from tether mount through CGH) vs. short lines / large chute at a higher angle.

They had 45' lines at 3 degrees vs. 20' lines at 8 degrees.

First pass calculation based on some extrapolated weight assumptions would be a 32' line for Squeeze of Lemming so around 5 degrees angle - hope my CGH does not turn out to be high or too far forward or I will be mounting the tether line half way up the tail fin  lol8

Thanks Wayno and Stainless for guiding me to be able to ask the right questions of Mr. Google.  :cheers:
A Bonneville Lakester please barman.
Certainly sir; a lick of salt, a sip of gas and a twist of Lemming. More Lemming sir?
Just a squeeze.

A Squeeze of Lemming it is sir.

Offline Lemming Motors

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Re: UK Lakester build G/GL
« Reply #441 on: December 16, 2019, 07:31:24 AM »
I printed out the Pork Pie pic of Bockscar 1 and although it was quite small scale I make the tether line angle 3 degrees.

Is the chute line length from attachment to the back of the chute or to where they attach to the chute .....?

By making some ill-informed Bockscar dimension assumptions I get the chute length from attachment to the back of the chute at 33' - does that sound about right?
A Bonneville Lakester please barman.
Certainly sir; a lick of salt, a sip of gas and a twist of Lemming. More Lemming sir?
Just a squeeze.

A Squeeze of Lemming it is sir.

Offline Interested Observer

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Re: UK Lakester build G/GL
« Reply #442 on: December 16, 2019, 08:33:16 AM »
Lemming:  While the Longacre method of CG determination is useful for a completed car, perhaps in your case with only a partially finished car another method may be more useful.  This would consist of calculating the moments of various components about a chosen location relative to the car, and then resolving those into an average.  For instance, choosing a convenient coordinate system reference point, perhaps at ground level, rear axle centerline and chassis centerline with x going forward, y going vertically, and z going laterally to the right side of the car, one can do the following:  for each significant mass, identify its mass amount (or weight) and the coordinate position of its individual CG.  If you are only concerned about the height of the composite CG, only y coordinates need be addressed, however, the same process can be used to find the longitudinal CG location by doing the same for x coordinates, etc.  Once the ?masses? and locations are identified, the following calculation will yield the coordinate of the composite CG.    Xe = (m1x1 + m2x2 + ...mnxn)/ (m1 + m2 + ...mn)   Similarly for Ye and Ze.
This, of course, is easily incorporated into a spreadsheet so that as the build progresses and different items are added or accounted for or modified, the new numbers are easily produced.

Offline Lemming Motors

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Re: UK Lakester build G/GL
« Reply #443 on: December 16, 2019, 10:48:25 AM »
Thanks IO.

I have been keeping a record of weights (actual and calculated) so I can estimate CG in the X axis (front to rear) and am keeping an eye on that.
I see what you mean about calculating their moments in the y (vertical) to get the CGH - I had not thought of that.

I am waiting for some engine parts to arrive, the tires from the US are not in my hand yet (Wayno - do you even remember the discussion about you getting yours so quickly months ago - its a long saga) and my rear axle is not finished so I was planning ahead to keep myself occupied.
A Bonneville Lakester please barman.
Certainly sir; a lick of salt, a sip of gas and a twist of Lemming. More Lemming sir?
Just a squeeze.

A Squeeze of Lemming it is sir.

Offline Elmo Rodge

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Re: UK Lakester build G/GL
« Reply #444 on: December 16, 2019, 11:31:42 AM »
I was lucky. Building everything myself, if I got held up on one thing there was always something else to work on.  :cheers:
Wayno

Offline ronnieroadster

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Re: UK Lakester build G/GL
« Reply #445 on: December 16, 2019, 12:49:02 PM »
John when my car was configured as a Lakester and now as a RMR I attached the chute tether to at a point that was no higher than the crankshaft center line. Upon chute deployment at speeds over 220 MPH theres no feeling of the car being disrupted in any manner especially no nose lift.
 As a lakester using the chute in tube design the tubing I used was irrigation piping used in farming. The aluminum tubing is a large enough diameter to allow easy chute packing with plenty of length as needed. I located a company that sold new and used irrigation supplies they sold me a length of pipe to fit what I was doing. Maybe some farmers in your area would have some pipe like that available for a small price.
 Ronnieroadster
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Offline Lemming Motors

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Re: UK Lakester build G/GL
« Reply #446 on: January 20, 2020, 07:05:41 AM »
The rebuilt rear axle finally arrived (new axle tubes, different end flange) so it was time to add some brackets and mock thinks up properly.
A Bonneville Lakester please barman.
Certainly sir; a lick of salt, a sip of gas and a twist of Lemming. More Lemming sir?
Just a squeeze.

A Squeeze of Lemming it is sir.

Offline Lemming Motors

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Re: UK Lakester build G/GL
« Reply #447 on: January 20, 2020, 07:20:14 AM »
The turnbuckle / push rod for the shocks will be moved outward slightly; its not clear in the pic but I mounted it vertically to see if anything binds or contacts. I was pleased to note that at full bump and droop of the wheel (limited by the shock stroke at this stage) everything is in harmony. The push rods will have a better approach to the bell crank in the final iteration.

Something that is obvious if you think it through (which I did not): by having a wide-ish track and the push rods inboard, then on single wheel bump you activate both shocks, the one on the bump side at 100% of the motion ratio and the other one (in my application) nearly 50%. I guess normal cars do this to a much lesser degree but I had never given it any thought - when I hoicked one end of the axle to full stroke it was really obvious given the shocks are side by side mounted across the chassis.

Now - about spring load / rate.

My best strategy is to put a toad in a jar, print out today's horoscope, pick a number between 400 and 1,000 (lb in), turn around twice, stand on one leg while reciting the mantra spring rate and spring load are not the same, play Led Zeps Rain Song really loud (you are the springtime...), fit the springs, release the toad, burn the horoscope, bounce on the fitted end of the car, repeat.

What step am I missing?
A Bonneville Lakester please barman.
Certainly sir; a lick of salt, a sip of gas and a twist of Lemming. More Lemming sir?
Just a squeeze.

A Squeeze of Lemming it is sir.

Offline ggl205

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Re: UK Lakester build G/GL
« Reply #448 on: January 20, 2020, 08:15:05 AM »
John:

As to spring rate; there are probably better ways to do this but here is how I did it.

First, you need to know corner weights and desired ride height. Calculate actual motion ratio of your rockers (dampers are at some angle other than 90 degrees to rockers so it affects motion ratio. Also remember your rockers work in arcs so how you set them up could give you rising or falling spring rates. You want rising rate and it looks like you have it.) and see how much one inch of vertical axle movement relates to damper movement. If you want to hold a maximum half inch of axle movement in bump, while at speed, you will need a spring rate at least equal to corner weight to start. It helps to have a road racing friend with several spring sets to borrow for this. What you are shooting for is to hold ride height at speed and restrict vertical movement in bump to whatever value you choose.

I made the mistake of setting initial ride height too low and used springs equal to corner weight with a true 1:1 motion ratio. The track was rough and the result was a front end bottoming out with every small bump. I eventually raised ride height sufficiently to keep from bottoming but springs rates were insufficient to hold half inch of vertical travel i.e., ride height too high to accommodate axle travel. I now have rockers with an effective 1:1.35 motion ratio giving my 400 pound springs 540 pounds per inch of compression. Last thing is to figure in any spring compression with car on ground. That will add a little spring rate to the mix.

John
« Last Edit: January 20, 2020, 08:57:34 AM by ggl205 »

Offline Lemming Motors

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Re: UK Lakester build G/GL
« Reply #449 on: January 20, 2020, 10:18:36 AM »
Thanks John

I will let the toad go  :-)
A Bonneville Lakester please barman.
Certainly sir; a lick of salt, a sip of gas and a twist of Lemming. More Lemming sir?
Just a squeeze.

A Squeeze of Lemming it is sir.