McLaren M20#73

Hi Andy, watching your progress with this is fascinating. But it makes me remember when you picked up your body and stuff off me what seems like just yesterday ??? do you remember our chat about how long this would take. At the time I was 8 years in and you said, I,m thinking a couple or 3 years as I don't have to make the body, Wheels or uprights so I'm well ahead. Its been 5 and counting. I'm sure you will be well under my 12yrs and boy will it be worth it. You are making a fantastic job of this, makes mine look quite tradesman like. Keep up the standard my friend you are inspiring us all. Cheers Leon
 
I do Leon, the last couple of years I haved been dragging my feet a bit. The prospect of Fibreglass and body filler is 1 aspect of the build that I least enjoy. But the realisation is you have to get it done. Working on a project that takes longer than 3 years, there’s a high failure rate. I wont be one.
Both rear brake ducts are complete.
I have been milling up a couple of rear radial brake calliper mounts, there’s a lot of handle spinning, no cnc, nearly done.
Will be increasing the the hub drive pin size from 7/16” tp 1/2” as they’re to puny.
Looking forward to constructing the rear wing.
Andrew
 

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Finished up the rear clip, topside brake ducting complete. Transaxle air intake complete, Engine cowling complete and both rear clip halves are all as one.
Mounted 4 Aero clips to the front edge to give adequate support. They work nice.
Now rear wing time.
 

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Made the rear wing struts out of 12mm 7075. Bullnosed the leading edge and tapered the rear. Turned up some bushes for the top and bottom of struts.
Turned up some bushes for the side fences.
Shot a laser line horizontal and vertical to get the top strut centres.
Will do a twin rod end under wing brace support, bit like the JCB M8F car.
Have a week off next week to get into the wing. Hopefully make a bit more progress.
Andrew.
 

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Neil

Supporter
Made the rear wing struts out of 12mm 7075. Bullnosed the leading edge and tapered the rear. Turned up some bushes for the top and bottom of struts.
Turned up some bushes for the side fences.
Shot a laser line horizontal and vertical to get the top strut centres.
Will do a twin rod end under wing brace support, bit like the JCB M8F car.
Have a week off next week to get into the wing. Hopefully make a bit more progress.
Andrew.
What profile will you use on your rear wing?
 
That's a fine question there Neil, 3 years ago I was looking into aerofoil design and liked the Reynolds S1223 but the trailing edges where too thin to make into aluminum (in my opinion) probably better suited to composite construction. I found a design that I liked but I'm buggered if I can find it online again, it's a blend of a Seagull & S1223.
It's quite interesting to note the use of wings started back in 1956 with Michael May mounting a big inverted wing above his Porsche 550 beating the factory team, whom promptly got it banned. Jim Hall resurrected in 1963 in his LeMans car and here we are.
Andrew.
 

Neil

Supporter
That's a fine question there Neil, 3 years ago I was looking into aerofoil design and liked the Reynolds S1223 but the trailing edges where too thin to make into aluminum (in my opinion) probably better suited to composite construction. I found a design that I liked but I'm buggered if I can find it online again, it's a blend of a Seagull & S1223.
It's quite interesting to note the use of wings started back in 1956 with Michael May mounting a big inverted wing above his Porsche 550 beating the factory team, whom promptly got it banned. Jim Hall resurrected in 1963 in his LeMans car and here we are.
Andrew.
A bit of information- when I joined an informal lunch get-together group of :car guys" here in Tucson, I mentioned that I had built a small sports racer called a Sable Mk III and had built an aluminum wing for it. John Horsman asked what profile I had used and I said "NACA 4412". He approved and told me that JWAE had consulted with aerodynamicist Ron Ayres about wing profiles and received a lengthy tutorial on the subject. Ending the lecture, he added "Or you could just use a 4412.":) I was fortunate enough to later meet Ron Ayres at Bonneville when he was there with the JCB "DieselMAX" streamliner. Nice fellow.
 
Hi Andy, good to see more progress and as always beautiful workmanship. Interesting to see the research you did on wings, I just drew up what i thought was a nice profile and blow me down with a feather it looks exactly like that NACA 4412 profile, so I fluked that one.

Cheers Leon.
 
I am using the Seagull shaped aerofoil.
Theres a few online comparisons Seagull vs Naca4412.
Made 2 rib forms out of left over 20 & 12mm 7075 plate. Sandwiched 2mm 5052 H34 between them and hamered the tabs 90 deg. 2mm for the rib is quite stout.
Made the end plates out of 3mm 5083 and welded on 20 x 2mm tabs.
Reinforced the pivot points with 3mm plates.
Going to weld on a16mm tube as a leading edge to add strength.
Need to take the 1.2 mm 5052 H34 outer cover sheet to the sheet metal shop to get leading edge brake press 16mm radius and the rear edge folded, and some shape rolled in. My machine is too small. Going to be 1 piece outer cover sheet, so its got to be accurate. Not using any stringers as I think the shape will provide enough stiffness.
Andrew
 

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Hi Andy
As usual you are doing an exeptional good work !!
May I suggest one detail you are thinking to cover with an 1.2mm thick foil ; you can use an 0.8 one and you will have only the edge to bend over a tube , then the cover will take easily the form just pusching and "clecoing" ,once bonded with araldite and riveted it will be very stiff and rigid enought
( I did by the past large bunch of those wings for Le mans and didn 't have any issue at all with this thickness
Hope this helps
keep our good progress !!
 
Thanks for your input Michel. I’m going with the 1.2mm thickness as I have 5/32 countersunk solid rivets that I intend to use as much as possible(bucking bar limited). A universal head rivet would work great with 0.8mm sheet, but the countersunk cut would go through to the rib, which I take it is not ideal.
Andrew
 
There is a flush rivet method that uses the thin 0.8mm cover sheet by dimpling the outer sheet and countersink cutting the rib tab to accommodate that dimple and then rivet, but I'll stick with what I'm doing.
 
Still waiting for the airfoils to get folded, so onto other jobs.
Made the helmet head rest.
Moved the chassis further back on the build table. The front clip needs widening to sit better over the wheels and lengthened. The doors also require some surgery.
Going to add removable front air splitters and mold in some short tunnels. Maybe some side cannards. The M8F seemed to suffer from understeer so a bit more downforce at the front cant hurt.

One thing I'm still getting my head around is the front airfoil. The first few races of the 1972 season the M20 front wing was just the foil shape, after Denny headed for the moon, McLaren added front edge scrapers to the front airfoil and clip. In the next few years other teams moved the M20 front wing to different positions.
So what works best?
The tub is flat bottomed with a bit of rake with a subtle defuser to be added at the rear.
Andrew.
 

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Hi Andy
one of the most effective front wing ( to my humble opinion is the one used on chassis 3 ( see some pics at donington some year ago ) Provided you fit under each sides some spoiler with a lip down about half inch ; remember with such a wide underfloor ( even you think to install a little diffusor is very very hudge and you need to get minimal flow at speed over 90 km/h
Any "akerman" on top of that front wing is welcome to get the wing working properly at low speed on tight curves
Hope this helps !!
If needed can draw for you some CAD "squetches" to help understanding how the "spoiler lip" can work ( made in composite in order to be consumable stuff to survey )
 

Howard Jones

Supporter
Here's the M20 #3 front wing. I have to wonder if a full-width full splitter would not have worked better. Especially with a couple of diffusers in front of the tires like most modern prototypes. It would of course not look correct and for that reason alone I wouldn't recommend changing it.
 

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