Thorp Air Command - T18.net

You may want to use 6061 though.

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Lee Walton
Houston, TX
N51863,N118LW
KEFD

For what it's worth, both of my spinner bulkheads are 0.062

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Bruce Finney
N18JF T-18C #262
Yelm, WA USA

Matt,

All of the above are excellent techniques. My simple technique for cutting the hole tried and true is using solder. I unroll about 8" and wrap it around the base of the prop where it will meet the spinner. I shape the solder to the airfoil exactly, then slide it off the end of the blade. I then trace the solder "template" onto cardboard and cut out a jig for marking the spinner.
Your cut will be much closer the first try than with anything else I have tried...

V/R
Smokey

Last night I received a spinner bulkhead from Chuck and it looks like it is going to work very well. Thanks Chuck.

So onto the cuttouts for the prop. I have read all the posts and referenced articles. In Tony B. article it mentions making one of the cuttouts and then making sure to cut the other one exactly 180 degrees from the first one. This is my concern. How do I make sure the second cuttout is exactly 180 degrees from the first one. I am thinking I need to use the rear bulkhead as a guide.

Smokey, I did not have any solder handy so I tried your technique with some .041 safety wire and think that worked OK. But with your technique how did you get the correct angle when transfering to the cardboard? I ended up cutting and taping together a constrution paper jig for marking the spinner, but I am conserned that when transfering it to the slightly bigger diamiter spinner that one side will give more than the other and my cuttouts will be slightly off. Am I concerned about nothing?

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Matt Smith
Des Moines, IA
55RC

Matt - I (given my age on my draughting table with a slide rule and a HP 41C as backup) would use a compass and make a circle on construction paper the diameter of the spinner - a line anywhere on the paper and intersecting the center point will give you the opposite points to measure off for the blade openings.

This web site will not let you load answers at the same time.......................
Place the spinner on a flat surface. Use a thin wire #22, place a mark on the spinner at the base. Using several sets of hands, wrap the wire around the base for the circum. Cut the wire in half, using the wire place a mark from the original mark going in both directions, you will now have two marks opposite from the original mark , draw a third mark between these marks will give the opposite side. We were fortuate to have an old spinner and used it to make a template,using the marks transfer the template to the spinner. Drill #40 holes and cleco the spinner to the base. Remove spinner and measure and mark the front bulkhead on the spinner, drill #40 holes if you choose to use screws. I would use PL5200 from Home Depot and glue it.
I will try and submit this now so all you guys hold off with an answer as this web site won't let two people answer the questionat the same time it blocks it and looses it.

This works too ...

Bill are you having trouble loading files?

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Lee Walton
Houston, TX
N51863,N118LW
KEFD

Hi Lee, I found that article but it did not have the pictures. Thanks. His article mentions measuring around the base but doesn't say how. I was thinking it wouldn't be hard to get off a 1/16 of an inch and then the cuttouts would be off. Bill's wire trick should work by measuring both ways and then splitting the difference. Fraser's compass method would work if I had a bigger compass. I guess I could use a nail and a 6.25 length of fine wire to make a circle also.

Bill what are you suggesting I glue? I am not planning on using any screws in the front bulkhead. Just a tight fit. Wouldn't be able to glue it or I wouldn't be able to take the spinner of to retorq wood prop???

Thanks everyone.

Lee I think Bill was saying that when he tried to post his message the first time Fraser was posting at the same time and Bill lost his post and had to retype it.

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Matt Smith
Des Moines, IA
55RC

Roger that Matt!

Don't sweat the 180 deg thing so much ... You're not making exact cutouts on the first cut. Leave yourself some breathing room and then fine tune the cutouts against the prop.

You can use tracing method by the way ...

Place the spinner on a flat surface over a piece of cardboard or something you can mark on, trace the spinner on the surface. Find the center of the circle using a compass (think back to geometry 101 ..or HS) .. then draw a line through the center crossing the spinner tracing. Place the spinner back on the surface, mark the spinner at the opposing sides. That's 180 deg, guaranteed!

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Lee Walton
Houston, TX
N51863,N118LW
KEFD

Matt, I hope you're not like me.... I usually screw up the first time. Lately I've been getting a little smarter, though; now I do the second one first. ;-)

But seriously..... here's a thought.
Consider making a thin paper mache mold of the dome first, and work with that. If anything, it will at least give you a 3D feel for how it will all fit together before you start cutting for real.

I think it was explained well above, but if not.. the key to the templates (I think) is to index them to the line that goes through the center of the circle.

d

(Take my advice with a grain of salt... I haven't done this job yet.)

I think we may be scaring Matt ... it's really not that tough of a job, just follow the Tony B instructions and it's EASY!

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Lee Walton
Houston, TX
N51863,N118LW
KEFD

I understand about starting with under sized cuttouts but still slightly concerned. I am sure I am making a mountain out of a mole hill but, when placing the spinner back on the prop to see where to trim the cuttouts more how do you make sure that you are holding the spinner exactly in the center? I got it, if I have the assembly on my bench I can use a square to make sure that it is centered. I was working on the template with the prop on the plane and thinking if I am 1/4 inch high or low when trimming then I am going to be off when it engages the rear bulkhead.

Again thanks everyone, and wish me luck tonight.

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Matt Smith
Des Moines, IA
55RC

Hi Matt,

I'll try to confuse the issue even more!

Lay the backplate on a flat surface. Using prop bolts assemble prop on top of backplate just as it would be installed on plane (may need to drill holes in surface below backplate to allow bolts to go through backplate enough to get tight fit of backplate on bolt shanks). Now take a small square and lay on table vertically and slide up against leading edge of prop and mark directly below on backplate. Do the same for trailing edge of prop. Repeat for other blade.

Now make a mark on the centerline of the leading edge and trailing edge of the prop (just above the outer edge of the backplate). Now measure from table up to the mark on leading and trailing edges and make note of heights. Repeat for other blade.

Now remove prop and put spinner shell on backplate. Transfer marks to spinner. This will define the width of the cutout to match the prop exactly. Using square, mark vertical lines on spinner straight up from the marks that define the leading edge and trailing edge prop. Now using the measurements for the LE and TE of prop you just took, mark the height on the spinner shell. Now you know the shape of the cutout from center of blade down to table. Now grab the prop again and make a paper template for the top of the blade. Make marks on the template to reference it to the earlier marks you made on the leading and trailing edges of the prop. Make sure template fits blade just above outer edge of backplate. Now take template and tape it to spinner lining up the marks for the height of the LE and TE of prop. Now you should have the shape of the cutout.
Make sure to cut undersize and trial fit about 50 times while cutting!

Bernie
N18XS

Matt, go get some aspirin.......Dan

Bernie...you the man !