(CAD) 28 Cyl P&W R-4360

[Rayanth]

... right, I'll just order the darn Offy book. ;D

Chances are it'll make me want to make an Offy. I've already got a few others on my potential list...

Damn you guys for giving me the bug! Now I'll be making little putt-putts until the end of my days... which is a long way off.

In other news, re-made the Edwards 5 Radial in CAD today. Needed to remember how I made the cams, so I figured I'd just do it again! Law of Sines gave me some pause for a while, but I'm back in business.


- Ryan

 

[steamer]

Damn you guys for giving me the bug! Now I'll be making little putt-putts until the end of my days... which is a long way off.


Well I certainly hope so!


Good night Ryan

Dave

 

[gmac]

Ryan;
I'll add my +1 for the purchase of Ron's Offy book, particularly for understanding the machining methodology. Another book I'd recommend, particularly for the radial is L.K. Blackmore's "Bentley BR2 World War 1 Rotary Aero Engine" which covers the plans and fabrication of a scale engine. One of these;
[ame]http://www.youtube.com/watch?v=P_-HhEfH1XQ[/ame]
Ron did one in 1/8th scale with glow system;
[ame]http://www.youtube.com/watch?v=R3bcrfC1Pz8[/ame]
I'll be following this thread - never mind the nay-sayers (just teasing, the support around here is phenomenal), why build something you're not passionate about?!
Cheers
Garry

 

[Rayanth]

I was at the museum today, working on the YO-3A, but took some time off to grab a few measurements of the 4360 we have sitting in a corner gathering dust.

These measurements aren't exactly precise, but they are close enough for my purposes. Combined with the drawings I have from the patents and Graham White's book, they should enable me to derive quite a lot of other dimensions.

Cylinder base to intake port (low point of 'top' of cylinder): 11.5 inches
Half width of cylinder: 4 inches at base (because the cylinders are split between casings, this derives other info)
Front of row 2 cylinder to front of row 1 cylinder: 10" at base
edge of cylinder to bevel over case bolt: 1"
base of cooling fins to cooling fins at intake 'top' of cylinder is 10 inches, with 66 fins

initial derivatives of this information:
half a cylinder base is 4 inches, thus a cylinder base is 8 inches. front to front is 10 inches between rows, so there's 2 inches of 'space' at the case's face between rows. Additionally, as a cylinder is also 8 inches wide, and there is 1 inch to the bolt bevel, this leaves about 10" to each face of the heptagon that forms the perimeter of the case.

Depth of the cylinder, to the top of the cooling fins, combined with drawings from the book and patents, will allow me to set a scale to those drawings, and thus derive other dimensions; those dimensions combined with compression ratio and stroke will let me back-calculate the length of the master rod and link rods!

Hey, it's a long way to go around to get there, but since I can't take our engine apart, it's what I've got

- Ryan

 

[gadabout]

hey there is one on Ebay at the moment (Well was yesterday) starting price of $25k

http://cgi.ebay.com/ebaymotors/Prat...490484QQ_trksidZp3286Q2em7QQitemZ120715766222

cheers
Mark

 

[Rayanth]

Yeah, i've seen them for as little as 5k in the past. Still trying to pay off 17k on my car, which is actually doing me some good at the moment ;D

 

[Rayanth]

Piston, Revision 0

Just worked 13 days straight, so I apologize for the lack of updates on this front. Today is a rare day off, before I go into another 12 days straight, and I'll have enough consecutive weekends to tell the company they can't designate me on the weekend of the 9th and 10th, so I can go to the (very nearby) Arlington Fly-In.

Today I'll try and get some of those dimensions I posted earlier, into some semblance of working dimensions to derive other stuff from. I would like to get the master rod started, but I need other things first.

Using the dimensions I recorded from the 'real thing' a couple weeks ago, combined with existing knowledge of bore, stroke, and compression ratio, I can figure out the dimensions of the cylinder. This will theoretically help me figure out the master rod length, and I can work from there.

So one of my measurements taken was the cylinder's height, which I placed at 11.5 inches to the top of the 'intake port' (This is the point on top where the intake is bolted in. The 4360's Intake is on top of the cylinder, and exhaust on the side). The following picture shows what that measurement actually means, highlighted in yellow. I can use this to figure out the scale of the shown drawing, then work out such things as valve sizes, the height of the cylinder sleeve, etc.

My printed copy of the image the above is excerpted from, has that dimension at approx 1.65 inches, giving me a scale of 1.65/11.5 or 14.3 %. Any dimensions taken from this drawing, divided by 0.143 should give me an approximate fullscale dimension, then divided by 6 gives me my scale dimension. To confirm this, I take a measurement of the piston, which we know has a bore of 5.75 inches, measures 0.82 in the drawing printout, which is 5.734 inches using my math - close enough for government work! And I'm former Air Force, I would know ;D

I will probably use this value to go back and work out some of my other dimensions that I was sort of guessing on, like the crankshaft. This drawing shows that as .43 inches, or 3 inches full scale, so half an inch at my 1/6 scale, and... I used .435 inches, so I have some work to do. (this was for the master rod journal) And of course a change here changes my master rod, so I'm glad I checked this now.

Moving back, I have decided to do a revision 0 mockup of the piston. Knowing the piston is 5.75 inch bore, I can correlate the two drawings I have that show the piston, to glean information on the wrist pin, and one view even shows a very clear outline of the master rod, which will help me later. The piston on the R4360 is hemispherical and has 4 rings, with one additional ring at the very bottom. The image shown gives a piston height of 0.59 on paper, or 4.125 at full scale, so .6875 (11/16) at my 1/6 scale. I can't quite make out the detail on the grooves for the piston rings, so I will just use an arbitrary for now, and call it 1/32x1/32, and space them roughly where they look in the drawing. I can blow it up later and get a slightly more accurate idea if I wish. Lastly, the hemispherical part appears to extend about .06 inches, or .4195, or .07 inches at scale, I'll go with the nearby .0625, 1/16th of an inch.

One minor deviation, the 1/6th scale puts the bore at a strange 0.9583 inches. I like to work with even numbers, so I would round this either to the nearest thousandth, or nearest fractional equivalent, which lets me choose between 0.958, or a fraction of either 15/16 or 61/64 (0.9375 or 0.953125 respectively) - 15/16 sounds nice and easy even though it's further from true scale, so I will use it for now. I understand machining is easier in decimals, but for now, it's easier for me to track the numbers if they equate nicely to fractions. This is being done in CAD, so they can always be changed later

So, without much further rambling, we have a piston of 0.9375 bore, that has a base height of .6875, plus a hemispherical addition of .0625. This piston has (4) 1/32" grooves for the rings, plus an additional one near the bottom. (Some math would normally be required to figure out how to make that hemisphere, but CAD lets me just do an arc consistent with three points, and then rotate that arc about an axis to get the 3d solid (I can then go back and get the radius of the arc if I need it - in this case it works out to 1.7890625 inch radius)

iso view:

side view to show hemispherical surface:

That will wrap up this post, but I'm obviously not done with the piston. It's all I can do from the one view in the patent that I was working from. Another view will give me the dimensions for the cutout for the wristpin, and the wristpin itself... and that will be my next post. perhaps later today, we shall see ;D

As always, comments are highly welcomed, as I don't have the machining experience to know if my decisions are wise! Would you have done something differently? Did I forget something important? Note this is Revision 0, or not-for-production; it's intended to get the basics down, and will not be made as-is. Rev0's are expected to be changed as other parts of the engine are designed and force changes in existing parts.

- Ryan

(edited to correct typos. who needs proofreading when there's a 'modify'?)

 

[steamer]

Ryan,

A logical progression. Seems like a plan to me!

The elephant goes down one bite at a time.

Dave

 

[Rayanth]

One small addition to the piston.

The patent picture that shows the cutaway view of the piston is to an odd scale. as the cutaway isn't of the same piston as the other view i was working from, which was the cylinder that points directly up. The cutaway is at an angle, so the piston is 'squashed' and that was going to lead me to inaccurate dimensions.

Upon closer inspection of the piston's cutaway, I determined that all four of the upper rings are compression rings. There's simply no cutout deep enough for oil to reach them, so the only oil ring must be the one at the bottom. Part of me wonders if this is to help combat the oil-pooling issue with the lower cylinders of radials. Either way, I opted to just fashion my own cutout for this area.

The 'walls' at the bottom were kept at 1/16" thickness to ensure stability for machining. the wrist pin was settled upon as 3/16" thickness based on what i could estimate from the cutaway drawing, so the hole for the wristpin is 3/16".

The only thing left is the holes for the oil to pass into the oil ring. I held off on this because I'm concerned of the size. the oil ring slot is 1/32" as currently designed. This limits the oil holes as a maximum of 1/32" diameter... and this seems rather small to me. I know at that scale liquids behave differently, so I ask the group - should I enlarge the slot so the holes can be bigger, or is 1/32" (0.03125) sufficient with, say, 8 holes ?

- Ryan

Postscript:
I may consider deepening the cutout for the master rod. I would have to look into it as a possible 'later' thing. If I cut out more material there, then I'm lightening the piston's overall weight, and thus forcing less work on the engine, and getting more power in the end. As it is right now, the cutout goes to the edge of the bottom compression ring, and it might not be that huge of a difference.

(edit to Postscript: I probably will have to go at least a little bit deeper. I forgot to account for clearance for the top of the master rod. doh!)

 

[steamer]

Hi Ryan,

Make sure you have enough wall thickness between that lower oil control ring and the counter bore.

1/32 doesn't sound too far out. I would use Ron's Offy piston oil ring drains as a guide as his engine runs far faster than this will. So should be big enough

Dave

 

[Rayanth]

thanks for the heads up, Dave, I'll take a look and compare to the offy's thickness when I get a chance... possibly sunday. Work just exploded into an angry hornet's nest, so I haven't had a great deal of time to sit and think on this.

- Ryan

 

[Admiral_dk]

Hi Ryan

I wouldn't use so many rings - to much friction on such a small engine - max. two compression rings and one oilring.

Of cause - if your goal is to make it as accurate as possible instead of a good runner (witch is rather tuff with this many cylinders in such a small scale) go ahead otherwise reduce the number of rings, surface area of the piston to cylinder interface and all other points of contact. If you make an exact copy of the original - I'll expect that you lose more than 70% of the generated power to friction.

 

[gbritnell]

On a model engine I don't know how much lubrication is provided by an oil ring.
As was stated, for model engine use 2 rings should be more than adequate for sealing and they can both be of the compression type.
gbritnell

 

[gbravo]

In my actual design of Wright J5, also I am considering 3 compression rings and one oil ring in the botton of the pistor, but if you estimate loose of 70%, is very high, I will recheck.
The oil ring in the piston botton I think is necessary because the oil splashed from the main connecting rod bearing and crankshaft bearings, drop directly to the bottom cylinders.

 

[Rayanth]

So I grabbed the offy book on the way out the door and am examining it again. I can't compute the thickness of the wall at the oil ring off hand, i'll draw it up in cad and run the calculator on it there, but of note is the oil passage holes, which I had questioned my size on. I had arrived at 1/32" at scale, and the Offy is 3/64, or 1.5/32, which means I am probably fine at 1/32, but I will just adapt it to meet the Offy's size.

Calculating the wall thickness at the minimum point will require some basic trigonometry, and better calculator functions than my phone has handy, so I will do it later ;D

- Ryan

 

[Admiral_dk]

An oilrings function isn't to lubricate the piston / cylinder, but to remove the excess oil from the cylinderwall in order to keep it in the crankcase. So for that reason it could be argumented that you should keep it, although it alone isn't going to keep you out of trouble with "hydro locks" in bottom cylinders if it's stationary for longer times between runs.

I'm most certainly no expert on motors with hanging cylinders, but I do know that one of the ways to prevent some of the problems is simply to let the "cylinder sleeve" reach higher into the crankcase than the oil level.

I'm not sure, but the P&W engines might be dry sump systems, witch will help quite a bit too.

 

[steamer]

Well we can all discuss the function of the oil ring in this case. I have NOT built a radial.

However, I think Ryan stated at one point that he spoke to Ageless regarding their 7 and 14 engines and maybe he has gleaned some information from that....


Just a thought....

Dave

 

[Rayanth]

I hadn't really gone into great detail about the designs with Ageless, but I am about to place an order for the 14cyl plans, on payday. Probly get the casting too, just to put it on the 'to do' list for when I do get the shop set up ;D

(Current plans there are for a 1 cyl engine first project, then the 5 cyl Edwards radial, then the 14 Ageless while using the skills gleaned, to tweak the 28 design. The 4360 will be built in stages, with a single cylinder test bed to run each cylinder on to ensure they all work before mounting them all on the same engine. Might do a 7 cyl test bed as well, just because ;D)

As for oil rings...well i'm not the expert there. Discuss away!

- Ryan

 

[steamer]

Just looking for data...Data is very helpful.

Dave

 

[Rayanth]

Speaking with an A&P mechanic at work who has rebuilt a few 4360's, the purpose of the oil ring is indeed to drain excess oil from between the cylinder wall and piston. However, this then raises the question- why use a ring, and not just a channel in the piston and the holes through it? What purpose does the physical ring add, that pays off for the added friction and complexity?

If you forgo the ring, and use channel/holes, you could ensure that they drain beyond the base of the liner, and thus are effective on the gravitationally bottom cylinders...with a ring you have to make sure the ring stays in the liner, and lose that effect.

- Ryan