1/18 Scale Blue Box F4U-1A Corsair Modification

[JayW]

4 hours ago, RLWP said:

I'm off to google Vought F4U tyre inflation pressures... 

 

Richard, I have this from the Erection  & Maintenance Manual for F4U:

 

 

Not sure if the F4U-4 specified the same tire pressure.  Probably was about the same.  I agree with you that an underinflated tire uses up precious energy.  However when it comes to an aircraft tire, there would be a number of considerations that don't necessarily apply to a car.  For instance, keep the tire size to a minimum - landing gear bays are big open inefficient structures, the smaller the better.  Longevity would not be much of a consideration.  Landing loads (sudden loading and rotation) would be a big deal.  Take-off weights that are very much more than landing weights.  Excessive tire pressures present challenges like requiring beefed up surround structure that can withstand a blow-out, which adds weight.  Etc.  So trade-offs galore.  Balance that all out, and perhaps you get something the layman might not expect.  

 

That pic of a F4U-4 is, like you noticed, probably a just landed aircraft at near minimum weight (as opposed to a full load-out).  And it will have the deck operations 112 PSI pressure or something like it.  I agree it doesn't show a very large contact patch at all.  The only thing I can think of that might cause an error in my calculating is the capability of an unpressurized tire to carry weight on its own.  But that just has to be a small number measured in the tens or hundreds of pounds, versus aircraft weight measured in the thousands of pounds.  That aside - physics is physics.  The only way a tire like that can have a really small patch with a Corsair airframe is to inflate it to unbelievable pressure.  

 

We need an ex-Goodyear engineer to chime in! 

 

[Timmy!]

When I CAD tires I use charts like these.

 

Goodyear Tire Dimensions

 

Sorry but I don’t know what size tire a Corsair has but you probably get at good guess here.  Each tire listed has a maximum and minimum tire width.  You could find something close do a little math and find a percentage difference.  Personally, I’d figure the percentage of the difference between the  maximum and minimum width of a tire that’s close to the Corsair tire, half that number and adjust the CAD.  Ort be Close enough.

 

Good luck,

 

Also loving the build! 
 

Timmy!

[RLWP]

I think I know what it is that is bothering me. I've gone a bit lateral and found a heavily loaded aircraft tyre:

 

http://silverhawkauthor.com/images/site_graphics/Aircraft/Aircraft---Canada/Avro-Lancaster-Ruhr-Express-prep-for-its-1st-Op-over-Germany---MIKAN-No--4542803.jpg

 

Http, so you'll have to click that one in Chrome

 

That Lanc tyre is definitely loaded and deflected. What it doesn't have is a pronounced bulge at the bottom - the whole sidewall is bowed out

 

I'm going to have to drop this, I'm getting a little obsessed with it. You're definitely on the right lines in what you are doing

 

Richard

[Landrotten Highlander]

1 hour ago, RLWP said:

That Lanc tyre is definitely loaded and deflected. What it doesn't have is a pronounced bulge at the bottom - the whole sidewall is bowed out

I was just thinking about that this morning.  I think it is the shallow bulge that makes a tire  look flat versus loaded.  When you think about it in 3 dimensions it makes no sense for a rubber wall to remain vertical until it hits the floor - there should be a bent along the whole length of the wall.

 

Hence the bulge is spread out along the area between the rim and the floor.  As such things are difficult to quantify in mathematics without knowing the stiffness of the rubber and the complete makeup of the tire I think it is safe to leave the bulge away, just stick with a flat area as per your calculations.

[RLWP]

1 hour ago, Landrotten Highlander said:

I was just thinking about that this morning.  I think it is the shallow bulge that makes a tire  look flat versus loaded.  When you think about it in 3 dimensions it makes no sense for a rubber wall to remain vertical until it hits the floor - there should be a bent along the whole length of the wall.

 

Hence the bulge is spread out along the area between the rim and the floor.  As such things are difficult to quantify in mathematics without knowing the stiffness of the rubber and the complete makeup of the tire I think it is safe to leave the bulge away, just stick with a flat area as per your calculations.

 

Having rubbed shoulders with chassis engineers for years, you soon learn that tyres are incredibly complicated. What with sizes, rolling radii and rolling circumferences

 

Richard

[JayW]

Geez Jay - what happened to the cockpit work?  Good question.  I have been kinda fixated on digital modelling of the landing gear components, trying (unsuccessfully?) to limit the modelling to items that cannot be scratch built in a convincing manner, or are just too hard to do (like my infamous outer wheel half machined part).

 

I showed you the digital models for the tire, inner wheel and outer wheel.  I await 3D prints of the tire and inner wheel - test parts to see how the process works with the level of detail I am providing.  Can't wait!  Thank s Peter and Tim for your help so far.

 

Since then I have modelled the brake housing, lower strut, and axle cap.  Here are some renderings of them:

 

 

 

 

It is my understanding 3D printed parts, due to the process of layering slices of material on top of one another, that the final part is a bit brittle and not very structurally stout.  So - would a 3D print part work for the "elbow" of the lower strut?  Good god - it would be so hard to scratch build and have it look good.  My concerns:

 

  

 

I also want to 3D print the scissor links, the upper cylinder (either the lugs only, or the entire part), the drag links, and parts of the actuator.  All are complex shapes.

 

I will return to the cockpit shortly (I keep telling myself).  Stay with me friends!

 

 

[brahman104]

Fantastic work on the CAD stuff Jay..... it is quite addictive isn't it?

 

I see your concerns about the structural integrity of the print. Yes 3D printing can be great at giving extremely hard to fabricate parts with relative ease, this is always a potential problem.

 

I actually think the easiest way around this is to continue with your 3D printed parts, then get some silicone that can withstand low temperature alloys such as white metal, and cast copies of your printed parts. You might need to do a bit of tweaking, such as having the axle integral with the printed leg so you don't have a weak spot at the hole, but I'd say that's you best shot?

 

Just my thoughts, but I'm renowned for devising the hardest way to do things

 

Craig

[JayW]

15 hours ago, brahman104 said:

alloys such as white metal, and cast copies of your printed parts.

Hi Craig.  I used white metal aftermarket landing gear on past builds of a P-51B, and a P-47D.  Both began to deform and sag with time, and I've heard of this issue from other modelers.  I wonder if there is a material out there that doesn't do that, and can be cast as you describe.  I believe my plan B is going to be good old fashion whittling and filing, and use printed parts in the less stressed areas (like the scissor link lugs).

[airscale]

fabulous work Jay - I can't believe how far you have come in such a short time

 

..it is easy to think of 3D as opening a new world where complex becomes simply an investment in time, and for some uses it has no equal. However, it is quite brittle (unless you have it done in PLA but that holds no detail) and personally I wouldn't trust it for an UC mount, or anything structural that does not have a lot of material involved

 

you could try it and have Shapeways run you up a copy just as a test as I would love to be proven wrong, but it gets me all twitchy thinking of your big beautiful F4U sitting on these

 

Peter

[JayW]

3 hours ago, airscale said:

you could try it and have Shapeways run you up a copy just as a test as I would love to be proven wrong, but it gets me all twitchy thinking of your big beautiful F4U sitting on these

 

If other materials is not something Tim can provide, I need to look into this.  Do you think Shapeways is a competitive outfit in which to explore?  I am getting a feeling cost might be the biggest factor!  OMG if each of these parts is going to be up to $25 to $50 each, why that will put a huge damper on my indiscriminate 3D modelling!  

[airscale]

20 hours ago, JayW said:

 

If other materials is not something Tim can provide, I need to look into this.  Do you think Shapeways is a competitive outfit in which to explore?  I am getting a feeling cost might be the biggest factor!  OMG if each of these parts is going to be up to $25 to $50 each, why that will put a huge damper on my indiscriminate 3D modelling!  

 

Tim can do PLA, but it is very coarse in print resolution - I only say shapeways as the interface is easy to use and they have lots of options around materials / resolution etc. But then with that comes cost - I had my P51 spinner printed in metal & it cost 140 euros & turned out to be a bit of a waste of time as the finish was like a diamond grinding burr..

 

Peter

[spartacus2000]

hi Jay. My solution is to divide the leg lengthwise in order to have 2 L-shaped parts, with a groove in the center in which you can insert a metal rod. This will be the supporting structure and the shells that enclose it will be the ornamental element. I suggest you print the pieces in resin for a better definition of the details. If you want we can see how to do it, if you pass me the Rhino files, I will prepare the pieces ready for printing then you see where to have them printed.

P.M. me if you want

Cheers

[RLWP]

@JayW  - you seem to have got yourself a bit lost at the moment.

 

It's true you can construct wonderful things in CAD, I used to do that for a living. Will you see most of that detail? And if you are going to have to pay to get it printed it's going out of your control, and it's going to cost

 

So far in this thread you've demonstrated that you are good at making parts - excellent in fact. Can I suggest you take a break and decided what it is you want to do? To me, you are more than capable of finishing this 'plane with the tools you already have.

 

Richard (who is quite familiar with losing himself down fascinating rabbit holes)

[Thunnus]

Amazing work as always, Jay!  The integration of "traditional" plastic modeling, your mastery of fashioning parts from scratch and now CAD modeling is awesome!

[JayW]

2 hours ago, spartacus2000 said:

hi Jay. My solution is to divide the leg lengthwise in order to have 2 L-shaped parts, with a groove in the center in which you can insert a metal rod. This will be the supporting structure and the shells that enclose it will be the ornamental element. I suggest you print the pieces in resin for a better definition of the details. If you want we can see how to do it, if you pass me the Rhino files, I will prepare the pieces ready for printing then you see where to have them printed.

P.M. me if you want

Cheers

Thanks!  I am very early into this process and am still not at all sure how far I am going to go.  I have begun to work with a fellow in the UK who is sending me a couple of test parts.  We'll see where we go from there.  I like your idea, alot.  Never thought of it!  I'll get back to you if it comes to that.  Again thanks.