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Just for fun. Ground up engine build.

Just for fun. Ground up engine build.

(OP)
Howdy all,

I'm a mechanical that lives at a machine shop all day. If I really wanted to I could make literally anything in that shop.
I've set my sights on an engine. What better to say I'm a mechanical engineer than design and build a ground up engine... only problem... Engines have a lot of chemistry in them too.

So this is what I have my sights on... a 150-200 hp @ 2400 rpm 7 cylinder NA SI radial. Yes, I would like to some day put it on an airplane (so weight is of concern), but if it never gets that far, it's okay. I just need something to keep me busy for the next year or so as the lady and I save up for a house.

I dug up my Norton and Mott Machine design books, purchased Heywood and Taylor ICE books, and a VW engine shop maintenance book... even found a very cool radial engine balancing paper from the 30's that's apparently still gospel. That being said and reading all this theory has left me a little interested in real world problems:

1)From what I can tell octane rating is at best a rough comparative estimate (seasonal blends, atmospheric changes temp, dry bulb, wet bulb, humidity, dew point blah blah a million other variables it seems) as to what pressure will cause the fuel to detonate. Obviously since hydrocarbons only have so much energy, obviously the higher the chamber pressure before ignition the better. So... Is there a table somewhere that has a rough estimate of octane numbers to ignition pressures? Or... Since other engines that seem to work well for my application run an 8:1 compression ratio running 100LL (av gas) and 93 octane mogas... should I just leave it at that and hope it works?

1.2) Secondary to that... I'm having a hard time trying to figure out what Aluminum alloy aside from A242... which no one I know can get in billet let alone cast... I've been thinking about using by FEA skills to thin-wall some other material in hopes to keep heat rejection at acceptable levels, possibly get rid of multiple thermal expansion values... Steel would be ideal if I can get it to work, brass would look awesome... not so great endurance limit, great thermal props... but that's beside the point. How thin I can make it is up to max cylinder pressure (p3). Which I'm not sure how to nail down not having a better understanding of how to deal with octane ratings.

So I plugged the numbers for naturally aspirated, isooctane, at 8:1... I ended up with about 230 psi at P2, and P3 was right about 1030 psi. Does that sound safe? I'm still playing with safety factor, but I think I'm okay with a SF of 1.2x for a good bit of ground testing. Anyone at Lycoming care to speak up? lol.


2) Leaded fuel... aside from it's octane enhancing characteristics which hopefully will be contained to my first question... Okay so really all I can seem to find is that with no lead = harder valve seal material. Is that it? The go to reference is apparently from 1954 "Iron or steel similar to the valve". Older Radials I've personally made replacements for had bearing bronze guides and seats. I'm guessing I can still run 100LL (Low Lead) in an engine with these "harder" seats?

3: Head design. The engine is going to be a pushrod, 2 valve per cylinder. It's just lighter that way. I'm thinking a domed head. Parallel valves would be nice, but I'm using a cam ring so its not like I'm going to get to entirely mitigate valve guide side loads anyway. That's all possibly useless information, but it might mean something to someone smarter than I. That being said... What's the deal with dual ignition (two spark plugs)? When I do a magneto check when flying I loose 50 rpm killing one of the plugs. Is it simply allowing the combustion process to happen faster...thus I gain more RPM... or is there a P2 pressure increase I need to be aware of over my calculation in 1.2?

Thanks ahead of time! Sorry if some of the questions are simple... this isn't my area of training. Yet.

Bonus: After reading the other thread about forced induction basically eliminating concerns about manifold design... that's pretty tempting.. especially seeing as how I think Rotec (only current mfg's of radials) do it for that reason. I'm not wanting to turbo, or for that matter turbo-normalize my system, I would rather have any % reliability over performance, but lets say I ran a straight vane impeller directly of the crank inside of the induction housing (its round on a radial) how much boost are we talking to get rid of worrying about geometry?

RE: Just for fun. Ground up engine build.

Re: Bonus question: A centrifugal supercharger running at 2400 rpm is not going to produce any useful boost.

My friend Wayne spent WW2 rebuilding gearboxes for superchargers for, I think B29s. He had to do selective fits, i.e. start with a large number of gears, in order to make the speed increaser gearbox live long enough to even test. He didn't have many used gears to use, because a failure usually fragged the housing and all the gears.

The McCulloch supercharger sold for cars in the fifties was much simpler and more reliable, or less unreliable. It used what amounted to a big ball bearing set up as a planetary gearbox, with about a 1:5 ratio. You'll need double that, and gearboxes get real expensive real fast at that ratio.

Use a turbo or run n/a.

Mike Halloran
Pembroke Pines, FL, USA

RE: Just for fun. Ground up engine build.

Re: Dual ignition. It does speed combustion but the big plus is reliability. The engine keeps running if you loose one magneto.

----------------------------------------

The Help for this program was created in Windows Help format, which depends on a feature that isn't included in this version of Windows.

RE: Just for fun. Ground up engine build.

"I just need something to keep me busy for the next year or so as the lady and I save up for a house. "

I'd expect an engine building project to be a seriously big drain on the house fund.

RE: Just for fun. Ground up engine build.

quote "1)From what I can tell octane rating is at best a rough comparative estimate (seasonal blends, atmospheric changes temp, dry bulb, wet bulb, humidity, dew point blah blah a million other variables it seems) as to what pressure will cause the fuel to detonate."unquote".

there is no direct relation between the octane rating of a fuel and the pressure that can be allowed within the combustion chamber. apart from the parameters you already mention the dimension and shape of the combustion chamber plays a major role in determining how far you can go. what you want in the end is a compression ratio that with the given fuel will just not detonate by itself but only starts to burn in a controlled way after the sparkplug(s) have ignited the mixture. maybe you can find out what the original fuel requirement was for the engine and from the specs of the fuel get a idea what octane rating is required. be aware that 100 LL AVGAS and 93 motor octane may be quite different, both in octane rating and lead content. and if you want to use the engine in a aircraft you are only allowed to use the fuel type that was originally specified.

quote "2) Leaded fuel... aside from it's octane enhancing characteristics which hopefully will be contained to my first question... Okay so really all I can seem to find is that with no lead = harder valve seal material. Is that it? The go to reference is apparently from 1954 "Iron or steel similar to the valve". Older Radials I've personally made replacements for had bearing bronze guides and seats. I'm guessing I can still run 100LL (Low Lead) in an engine with these "harder" seats?"unquote".

lead , apart from its octane rating boosting capacity had a number of side effects. one was that too much lead could lead to sparkplug fouling because under certain circumstances bonds between Pb and Si (from airborne dust) could build deposits that lead to short circuit the sparkplug. a other, favorable, side effect was that it acted as a kind of lubricant by forming a Pb deposit on the valve seats reducing wear substantially. geenrally speaking all alloy engines use steel valve seat inserts and life of them usually is enhanced by using leaded fuel. in modern engines running on lead free fuel nowadays seats are made of tougher material that can do without lead and also their operating temperature has been brought down a bit to preserve their strength.

"quote".3: Head design. The engine is going to be a pushrod, 2 valve per cylinder. It's just lighter that way. I'm thinking a domed head. Parallel valves would be nice, but I'm using a cam ring so its not like I'm going to get to entirely mitigate valve guide side loads anyway. That's all possibly useless information, but it might mean something to someone smarter than I. That being said... What's the deal with dual ignition (two spark plugs)? When I do a magneto check when flying I loose 50 rpm killing one of the plugs. Is it simply allowing the combustion process to happen faster...thus I gain more RPM... or is there a P2 pressure increase I need to be aware of over my calculation in 1.2?"unquote".

two sparkplugs are used to prevent detonation. generally speaking aircraft engines are short stroke/large bore engines and when using only one sparkplug the chances for detonation are larger because the flame front originating from the sparkplug needs to travel over a longer distance to reach the wall of the combustion chamber. when using only one sparkplug the moving flamefront may cause extra compression of the not yet ignited fuel/air mixture so much that spontaneous combustion (better known as "knocking") will occur. when using two sparkplugs (and thus two flamefronts) chances are the flamefront reaches the far away air/fuel mixture in time before the mixture has been heated to the extend that it ignites spontaneously.

RE: Just for fun. Ground up engine build.

(OP)
Thanks for the reply folks! Still looking for more info and verification of that estimated pressure.

@MikeHalloran The Rotec (Australian radial engine mfg who designed their own engines from experience gained from Radio Control engines) has an engine driven fan I guess they call it. Looks like a centrifugal compressor. I didn't figure it did too much, but was intrigued with the idea of not stressing about the induction ducting quite as much as I have been. Thought that may have been their idea. Maybe it's just there to help with mixing the fuel air charge... That looks like about the only thing that it could be doing. I pulled out my turbo-machinery design book to check... go figure designing a jet engine is easier... anyway looking at the equations for a centrifugal flow compressor... even if it was well designed nice fancy twisted vanes and such, an 8 inch compressor at 2400 rpm at standard conditions gave me a pressure ratio of 1.006! LOL yeah that does nothing. Looks like getting 5 psi boost out of that thing would require at least 20,000 rpm...215m/s tip speed which is doable at least its not choked at mach1... but that's a 10:1 ratio hey look at that right on Mike... YEAH I want NOTHING to do with that. I'm already going to have enough spinny things to balance lol!

Naturally aspirated it is.

Tmoose. Designing something is cheap fun. If it never comes out of Solidworks so be it. Building it... well I probably have a big advantage. I have a HUGE scrap pile with traceable rems, and more regrind endmills than I can shake a stick at. I imagine the little things like rings, valves, pistons, a carb... and other off the shelf things along with Gas and medical fees will be the truly expensive things.

Romke: Awesome post. Few things. I'm designing the thing from ground up (I guess I should have said that instead of building), nothing currently exists... okay except a few lines in solidworks covering linkage design... I was quite happy with myself when I figured out the geometry for the master rod that results in equal TDC in all cylinders... that was a trick and a half. Also If this thing does get stuffed in the front of a plane the engine will be listed as an experimental. Per 14 CFR 65.103 If it's installed in my experimental aircraft, its up to me to decide what grade(s) gas goes it it... if I get that far. Anyway back to the fun stuff.

"there is no direct relation between the octane rating of a fuel and the pressure that can be allowed within the combustion chamber. " Then you were talking about the combustion chamber shape. So from a practical standpoint that boils down to empirical testing to figure it out!? I mean I plan to go with a fairly conventional hemispherical head design... I would think someone would have at least published a "Here is a standard engine we tested with different octanes, here are the conditions, this is what happened." So what is it proprietary info? I get if it's empirical as you suggest, that's a lot of R&D $ to figure it out. But from my end... there appears to be no set method to say this engine design will work with X octane rating fuel. That's a tad frustrating. Am I missing something?

I've heard of certified (as opposed to experimental like my engine) 100LL engines getting certified to run on 93 octane mogas with a STC (supplemental type certificate) basically just adding a placard and paperwork to the aircraft with no engine modification, but they recommend running a tank (about gallons) of leaded fuel every 50 hours or so to help with the seals. I'm assuming there would be a loss in efficiency between the two fuels, and thought it would have been fun to try to calculate it out to understand the difference.

I certainly know about fouled plugs in a leaded engine. An R22 with a fouled plug will make you hop from side to side in a hover... not a comfortable feeling... in an airplane ya just blast it clear with a minute of high power. And for that matter well aware of the redundancy factor of dual ignition.

So... as far as flame front propagation, having two ignition sources just allows for quicker combustion, so the pressure build from the flame front advance in a large cylinder causes detonations. That's cool. Is it still a safe bet that the pressure doesn't go higher than my constant volume simulation of about 1000psi? I figured it's a "perfect" worst case anyway.


OH yeah! I almost forgot... Tougher valve seat material. Like what? I had bronze in mind when I started this. Steel... I've heard of welding stellite to valves but surely not that tough on the valve seats? Since lead is great with seals, instead of a fuel with lead, how about metal with lead in it? What about 12L14? Its a mild steel with ~.2% lead in it to help it cut REALLY well. Or is that too soft?

RE: Just for fun. Ground up engine build.

Old radials had induction system 'fans' to help with fuel distribution around the ring. Sequential port injection would be a simpler route today.

A242 is an old 'piston' alloy still used in heads owing to heat resistance. A couple percent Nickel really helps and it is the best at retaining pressed in valve seats. You'll need to get it from an aluminum foundry that casts cylinder heads. I have used 4032 for billet pistons but have no experience with it as a cylinder head. It has some high temperature virtues and you might want to review it.

Your max pressure estimate is close enough. Your 1.2 SF is too low for most engine components. Figuring the stress accurately in a cylinder head with all of the thermal gradients/stresses is not feasible.

FAA regs require dual ignition "or equivalent" (what ever equivalent is). Also an engine driven fuel pump. Two plugs will speed up the combustion process a bit especially in large diameter cylinders.

You seemed to have picked a max speed, now you need to pick a reasonable brake mean effective pressure in order to determine the displacement of your seven cylinders. (perhaps about 140 psi).

The large diameter and air cooling temperatures put a lot of stress on aircraft engine valves. (check out Winsert and a sturdy diesel exhaust valve.)

Have fun designing.

RE: Just for fun. Ground up engine build.

The design and analysis work required for this engine is far more complicated than you seem to appreciate. And unless you have extensive knowledge of metallurgy, heat transfer, kinematics, fatigue, dynamics, fluid mechanics, combustion, tribology, etc., your engine project will likely be unsuccessful.

Save your money for the house payments. And if you want to make use of your machine tools and skills, find something that you can make that people are willing to pay good money for.

RE: Just for fun. Ground up engine build.

(OP)
Ehudson Thanks! I feel like I have at least skimmed over all of my reference books... I will look a little harder in my Taylor book re safety factor.

Induction fan for fuel distribution. I can deal with that. Just for mixing, or is my uncle not as crazy as I thought when he said that having the induction system below some of the pistons was a bad idea, said the bottom cylinders had gravity working for them and the top ones wouldn't get as much. That being said just about every WWII era and beyond radial was forced induction of some sort... maybe there's something to it with a NA radial.

Sequential port injection... hmmm. I know nothing about that just yet but sounds light weight. I will have to learn more. Is there a mechanical control or are we talking about bolting computers onto my engine? I'm not against anything that would take away some of the heavy accessory.

I will look more into your 4032. About a year ago I was flying a little LSA with a Rotax in it that had liquid cooled heads...but everything else was air cooled. I cant say I'm completely against that idea as it would probably make head material selection A LOT easier. Maybe even 6061 or A356. But I would really rather not do that. Another system to design , be heavy, and fail.

140 psi huh. Pretty close. I was looking at 146... At least I know I'm in the ballpark THANKS!. I'm still playing with the numbers but that's sneaking up on 500 in^3. Seems high...

I would really like to hang this thing off of a Great Lakes like I have been flying recently that currently uses an IO-360 180hp @ 2400rpm. If not that, there is another kit plane with a bit of a minor cult following called the "Flitzer", much smaller... after talking with the designer, he would like to see about 100 hp on it, and that get's into the range of using VW parts which is actually pretty typical for experimental aircraft. (thus my VW mechanic book)

For your viewing pleasure: https://youtu.be/SyRJeZ6s8uM <-that's some inspiration right there. after seeing that I thought, I can do at least that good.



RE: Just for fun. Ground up engine build.

"So from a practical standpoint that boils down to empirical testing to figure it out!?"

Yes, indeed it does unfortunately. Each engine design comes with it's own octane requirement. And engine designers make sure that the final design can run knockfree on the recommended commercially available fuel. The compression ratio and the shape of the combustion chamber are the most important parameters. A hemispherical head is superior to a classic flat head with side valves as used in older lawnmowers. From a practical point of view you could start with a 1 cylinder testengine with a compression ratio of say 8:1 and see if it works. If so you might be able to increase the CR in small steps. You will then come to a point where the fuel used will no longer burn smoothly and the engine starts "pinking". There are two circumstances that are critical: low speed knock (that is usually quite audible) and high speed knock (which is much more difficult to detect because the noise generated is less audible because other noise sources may "hide" the knocking sounds). High speed knock can ruin the engine within a few minutes, usually by burning a small hole in the piston....

"So... as far as flame front propagation, having two ignition sources just allows for quicker combustion, so the pressure build from the flame front advance in a large cylinder causes detonations. That's cool. Is it still a safe bet that the pressure doesn't go higher than my constant volume simulation of about 1000psi? I figured it's a "perfect" worst case anyway."

That may be. But you should realize that ignition means "igniting the fuel air mixture immediately around the sparkplug". the flamefront then starts to ignite the air fuel mixture radially from the sparkplug. if you have a dome shaped small cylinder head with the sparkplug in the middle the distances to the air fuel mixture to the farthest points that need to be reached (the edge of the piston that more or less "touches" the cylinder) will be reached in a few milliseconds (before the air fuel mixture there has been compressed by the already burning fuel to a degree that makes it ignite by itself due to the raised temperature). When you use a relatively large dome head or a head with a design with some areas that are distinctly "further away" the flame front will be too late reaching those areas. it is thus not "quicker combustion" that is needed, what you want is to get the timing right by starting the combustion everywhere by means of the flame front within the combustion chamber before the air fuel mixture goes off due to autoignition.

"OH yeah! I almost forgot... Tougher valve seat material. Like what? I had bronze in mind when I started this. Steel... I've heard of welding stellite to valves but surely not that tough on the valve seats? Since lead is great with seals, instead of a fuel with lead, how about metal with lead in it? What about 12L14? Its a mild steel with ~.2% lead in it to help it cut REALLY well. Or is that too soft?"

Stellite om the (exhaust) valves is used because the valves may get very hot and other steels may not be able to withstand the temperatures that are caused by the passing exhaust gases - the valves may get "soft" and distort under the constant "hammering" from the closing process. Sometimes hollow valve stems are used filled with NaCl to better disperse the heat load over the whole valve and not just the end that gets heated up. The seats are usually alloy steel that has sufficient hardness. i have never come across bronze or lead alloys used for valve seats - both will lack sufficient hardness and also will not be capable to withstand the temperatures encountered. Seat inserts are made by special firms that supply them to engine rebuilding workshops. Maybe you should contact a local engine rebuilder to find out how they handle it, it might be possible that you can fit valves and seats that are made for other engines.




RE: Just for fun. Ground up engine build.

The project is complicated. However, the best way to learn about engine design is to begin laying one out.

RE: Just for fun. Ground up engine build.

It would be a good idea to perform a torsional vibration study based on the number of cylinders your engine has, the firing order of your engine, the dynamic balance condition of your crank/conrods/pistons, the operating speed range of the engine, and the characteristics of the propellor you intend to use. Torsional vibration was always a big problem with radial aircraft engines.

As for what material to use for your heads/cylinders and how thin you can make the parts, the primary concern is fatigue life at operating temps. In terms of fatigue life at operating temps, the allowable stress levels for most non-ferrous materials are much lower than you might imagine. For example, A356 aluminum casting alloy or 6061 wrought aluminum alloy should probably be designed for a max fatigue stress of around 12-14ksi at engine operating temps.

RE: Just for fun. Ground up engine build.

(OP)
@EHudson Thanks. I like to learn new things. That's why I'm here. Only so much they teach BS Aerospace engineers these days, trying to fill in the gaps.

tbuelna My cash crop is making thousands of wheel spacers and various other military related fast spinning things. I have a lot of big round chunks of aluminum with x certs going out as scrap that I dream about being an engine case.

See what you think of the attached paper... as far as I can tell its public domain. It's the go to reference for balancing radials from what I can find. Everyone references it. I haven't jumped into it too hard, because I haven't even really sized up my overall engine parameters. But figured when I get into it a little more I will give excel a workout. from what I can tell P&W still maintains some patents for their balancing methods on radials, but the patents are the only information I can find about it which isn't too much help because its for double and triple stack 1000+hp engines. On top of that, it appears for my simple single row, and if I dont let it get too big, it wont be any worse than any of the prewar radials. that lacked any of the geared counterweight systems. Taylor appears to have made fairly short work of it in his vibration chapter.

As for material strength reaching fatigue limit at temp. well aware. Try arguing with a Sikorsky structures guy for two years about mounting an aluminum welded weapons mount to their precious helicopter.

My FEA kung fu is strong. If I do anything radical with this... that's going to be it. I've made a good bit of money making stuff lighter and prove it works the same. I would like to figure out a good thermal load, and see if I can get the required cooling, all that stuff out of a steel head that matches the barrel would be awesome in my book.

If that doesn't work I like A242 because it has an operating temp around 550°f and elevated temp s-n curves are floating around that I can play with to make a good estimate of life limit and stay a long way away from it. I have been playing with 242 for a while now http://www.eng-tips.com/viewthread.cfm?qid=342154 . The great part about the really old engines, and possibly my new experimental is that they didn't have life limited parts. fly it till it cracks then weld it back up. I've seen some Warners that look like they were repaired with welds that I wouldn't hang my coat on. But A242 means casting. I would like to look at alternatives because casting is an outside process to me. that means $.

Romke I'm 100% about buying parts that are beyond my scope to build/or spec metallurgy. NaCl... Really? straigt up table salt. I know some of GM's LS monsters and the Merlin had sodium filled valves. Even saw a video of them making them a while back. but is it really just salt? I thought it was super scary sodium metal. Even read something else about disposing of them, you're supposed to break them and put them in water to convert to sodium hydroxide, fix the hair clog in the drain, and toss the bad valves out.

I'm also not opposed to making a single cylinder test engine. My Taylor book has some pretty specific geometry specifications for hemispheric heads and valve sizes that I bet would get me pretty close. Also, a single cylinder could rack up a good bit of hours. Might even run a go cart with it! 70 cubic inch...1100 cc single piston engine! haha. It's late... early. I'll be back tomorrow afternoon if the Friday evening doesn't get too out of hand.

RE: Just for fun. Ground up engine build.

@tbuelna

''The design and analysis work required for this engine is far more complicated than you seem to appreciate. And unless you have extensive knowledge of metallurgy, heat transfer, kinematics, fatigue, dynamics, fluid mechanics, combustion, tribology, etc., your engine project will likely be unsuccessful.''

@OP take heed of the above - 7yrs ago I set out to design and cast 'just' a cylinder head. Approx 3hrs reading per night since and Ive only just got there now.

Keep in mind your engine design is approx 1/4 of the total design work. There is machining planning, jig design, tooling, parts moving on table when machined, what size billet/casting to start out with for balancing machining stresses, tolerances, material choice, and a thousand other things.

These statements alone makes me wonder if you are indeed ten yrs off it yet - ''I'm having a hard time trying to figure out what Aluminum alloy aside from A242''

''OH yeah! I almost forgot... Tougher valve seat material. Like what?''

Its a HUGE undertaking - coming from someone that designs stuff daily with a full machine shop behind them + foundry.

I'm the last person in the world to shoot something down, and I'm just saying, be prepared.

Brian,

RE: Just for fun. Ground up engine build.

Perhaps someone will suggest an investment casting house that will take the model of your head from a 3D printer and turn it into a casting in 242.

Check out Winsert for seat materials. Diesel exhaust valves are going to be pretty tough.

tbuelna's suggestion regarding performing a torsional analysis is good advise for any multi-cylinder engine. Good reads are: 'Mechanical Vibrations' - by Den Hartog and 'A Torsional Vibration Handbook' by the British Internal Combustion Engine Research Assn. The later has just recently been reprinted, by Cambridge, in paperback form (Although the neat fold out sheet with a lot of pendulum damper formulas was omitted).

You might want to check "Aircraft Engine Design" by Joseph Liston out of the library.

The VW video was interesting. Aluminum connecting rods scare me, owing to the tendency to overage and fatigue. Sure the top fuel guys use 7075 aluminum rods but they don't run them long.

Look up mega-squirt for ideas on home made sequential fuel injection and ignition control.

RE: Just for fun. Ground up engine build.

(OP)
BrianGar and tbuelna, I said this was for fun. If all I get out of this is a cool solidworks render so be it. I'm here to learn stuff.
Like tribology... never heard that word before and I have an aerospace degree too.

Check this out about TV. Looks like it might be a thing.
http://www.enginehistory.org/NoShortDays/TV.pdf That's a pretty cool little gizmo. Thankfully with only 1 throw, It looks like it's going to be a fairly easy thing to overcome. Some of the gizmos I've seen for the multi row radials are ridiculous.

@Ehudson, looks like between my Taylor books and your Hartog fella we might be able to figure this up. I'm going to order Hartog's book. I'll see if I cant get into tanaka this weekend also and see what he really has to say.

As for winsert... oh yeah. I'm all over that. $20 John Deere valve seats that sounds cool. That being said my A&P just so happened to be ripping apart a an IO-360 last night for a piper. I was astounded. FAA-PMA SL75838A valve guide. Came with inspection tags, dimensions to ream too, and a metallurgy cert... Iron with Nickel and Chrome. Amazing. It works for them, probably would work better than what I could come up with right?


Also! I have in fact done the 3D print to investment casting on a 17-4 part. Even did a small batch production run. I had asked the foundary once upon a time to do an a242 head about the time of my last thread and they had 2 things to say... No and No. Apparently A242 which is what lycoming still has listed on TC's is a bear to cast and my place wasn't confident they could pull it off. Second they said the 3d print process that they use was in no way going to get used for a flight critical part... on something at the time we were talking about pursuing PMA. Maybe I could just melt down some lawnmower engines, and pour that over some ABS makerbot models buried in the sand. LOL! but seriously I've cast some ant hills, I was really surprised at how well it turned out. I might try it just for fun on my 1 cylinder test engine... bigglasses

@BrianGar, so what did you end up doing? If nothing else what did you read?

I'm not a metallurgist. I dont want to be one. It's a radial engine... we've been making these things for over 100 years now. Someone has to know a good material to machine an air cooled head out of. Once I know that... s-n high temp, slap a big SF on it, throw some forces at it at 10^6 cycles strength and call it good.

RE: Just for fun. Ground up engine build.

Harley heads are 242. The only lawn mower part in 242 that I know of was the lost foam head on the small Tecumseh OHV vertical shaft mower. I think if a lost foam part and sand castings are possible then an investment casting should be possible.

As regards Greg's question about torsional analysis, For a single cylinder engine or a twin with a stubby crank it is probably not necessary. So for a short stubby radial engine crank intuitively we'd say, no.

But, just ask yourself if you've ever seen a pendulum damper inside one of them? Have you ever heard of one having a 'critical speed'? While I confess that I have not laid out a radial, I can answer yes to both of those questions, so I'd be curious about the natural frequency.

RE: Just for fun. Ground up engine build.

Re TV analysis, you would want to estimate dynamic deflections of the crankpin to keep the bearings alive.
Re head alloy, you may not find a foundry that will use anything but 356 for small runs.

If you can find a billet of the alloy you want, you can CNC it to nearly any arbitrary shape. ... including cutting fins with a power hacksaw, which has some precedent.

Mike Halloran
Pembroke Pines, FL, USA

RE: Just for fun. Ground up engine build.

I cut my finns with a 9"angle grinder on prototype 4 yamaha500 with my head on it
the ducati prototype was sand cast with core boxes.

A tidy mind not intelligent as it ignors the random opportunities of total chaos. Thats my excuse anyway
Malbeare
www.sixstroke.com

RE: Just for fun. Ground up engine build.

Quote (GregLocock)

Is a TV analysis necessary for a crankshaft that is one throw only?

A single throw crank for a 7 cylinder radial is still a rotating structural component subjected to input forces of varying magnitude and frequency. This crank has structural modes that can couple with input forces just like any other crank. Obviously a short single throw crank has higher torsional stiffness than a longer crank with multiple throws would have, but that does not mean there are not any TV issues with it.

@RoarkS- If you have good machine skills, I would recommend machining your A/C heads/cylinders from 2219 aluminum bar. 2219 has excellent high temp strength and is readily available.

RE: Just for fun. Ground up engine build.

(OP)
Well, I have managed to collect a good bit of reference information on the subject. I'm thinking that the range of horsepower that I am wanting to play 150-200 may be in a range that would not justify much concern past a 1st order vibrations. Even found one source quoting that engines smaller than large 2800 cu double row engines, a good set of motor mounts should make most 2nd order vibrations "unobjectionable." I can't see myself using a constant speed prop just yet, So I think I will design around a fixed pitch wooden or composite prop so as to help keep down things wanting to fool with the TV of my crank. Besides a good CV prop is nearly $5k!

However. After going thru Hartog... I'm entertained at the complexity of the methods they went through to approximate the various mass properties required. I think this is where solidworks is going to shine.
I should be able to at the least use solidworks to investigate the true MOI properties of my designed system along with torsional stiffness of the crank... much like this fella:
http://thebloughs.net/understanding-crankshaft-cou...

but... I'm confident I can at least take a stab at some dynamic motion also, and hopefuly forego the separation of the rods into concentrated masses about the pins.

The only thing that I think may be stretching my ability would be input of firing pressures on the pistons. It appears that there are fairly well known models for cylinder pressure that are scale-able that would make good approximations. It would just be a matter of timing them in solidworks to see what I end up with. I know if I could do that, I could do a pretty good job of "emprically" changing the model to achieve the best "perfectly rigid" balance possible... It's after that, I'm not sure how powerful the simulation software is going to be dealing with a dynamic torsional analysis of the crank. I may have to do some learning there.

But even still... Looking at older (smaller) engines such as the Warner, Ranger, Wasp Jr., and Kinner I'm not yet convinced that it's an issue. Even the famed ABC Dragonfly was nearly 1400 cubic inches. (I'm thinking 500 cubic inches is going to be my upper limit.) This seems to be written by someone pretty smart... and those engines did not have any TV equipment as far as I know-> http://thebloughs.net/work/wp-content/uploads/2014...
Ahh... even better As I've been in the blueprints of this thing... didn't know there were engineering reports I could get my hands on...->http://thebloughs.net/work/wp-content/uploads/2014...

I'm very interested in the Chilton style damper and definitely play with it. The mechanism appears to be fairly simple, but I will have to figure out if it's added complexity is of value.

More to come!


RE: Just for fun. Ground up engine build.

RE: ABC Dragonfly and crank torsional resonance -

FWIW one of the very first Google hits was this dedicated thread on one forum -
http://www.theaerodrome.com/forum/showthread.php?t...

Then, 5 hits down was this -
http://www.realclassic.co.uk/books/granvillebradsh...
" The worst problem was crankshaft resonance and failure, which in those days was not well understood or easily corrected, and was somewhat unexpected on a short, single row radial. "

RE: Just for fun. Ground up engine build.

(OP)
EHudson... WOW! I just got a copy of "Aircraft Engine Design" by Liston... What a wealth of knowledge I'm just getting into it... but the information in the appendix alone! I can actually draw an SAE #10,20,30,40,50 prop hub! sill looking for a #1 flange but that may even be too old for this book. The material selection... AMAZING book so far.

My particular copy is a 1942 copy from the Chrysler Engineering library. Just check out how amazing the library tag is! (see attached)

Anyways...

A few things of interest I was reading about how the R2800 crank is assembled with a thru bolt and face splines. A few things... what is used to safety that bolt? I can't imagine just a lock nut. Then anyone have a good bit of knowledge of why I might go out of my way to make it an involute spline profile? With modern machinery wouldn't it be just as easy to do a filleted 45° design or perhaps just put dimples in both sides that would hold ball bearings?

Thanks!

Oh one last edit for the evening... So the mention of the ABC Dragonfly... It was nearly 1600 cubic inches but made just over 300 horsepower. My guess is the engine I'm wanting to make will have a much higher power density. It goes without saying that I will look at the various vibration sources throughout. but I think it would be a safe bet that TV is probably has a higher correlation to power than cubic inches than I had assumed in an earlier post.

RE: Just for fun. Ground up engine build.

(OP)
Radials slave rods have fairly different crank pin paths... thus accelerations for each cylinder would be different...

Does the rate at which a fuel air charge is compressed have any bearing on its combustion?
The lady already turned out the light for the evening, so I guess I won't be reading any books about it until tomorrow.

For reference...
Here is an older set up I drew up a while ago... this is the one that sent me down the rabbit hole. It has an evenly spaced slave pins on the master rod at a constant radius about the main. It is far more along than my current set up, but I was just curious what I could do with it as a baseline until the other is ready.

I have it being driven at design max RPM. 5 and 7 fire in sequence so I was curious to look at them... 1.25X higher acceleration with a bit longer dwell time at TDC... scary. 650g's vs 520g's that's pretty snappy, but they are only going about 51 ft per second max that's not as fast as I thought it was going to be... I was half expecting supersonic velocities.

Look at that double peak in #5! I cant wait to see what happens when I add them all together to see what's happening. No wonder these things are not made anymore... but ya sure can't beat the sound.

I wonder how much fun could be had with a programmable ignition...

RE: Just for fun. Ground up engine build.

You want some fun, you might want to try building a
Marchetti (8 cylinder radial 4-stroke) engine or a
Fairchild-Caminez (4 cylinder radial 4-stroke) engine.

Both use conjugate cams and massive bellcranks instead of a crank and master rod, and have good primary balance because of symmetry.

I don't think a radial will benefit particularly from a programmable ignition, but they need a strong spark to fire the lower plugs, typically fouled by drained oil.


Mike Halloran
Pembroke Pines, FL, USA

RE: Just for fun. Ground up engine build.

Those 'splined' crankshaft couplings might be just a bit more involved than you might guess.

Tonights homework is to check out curvic and Hirth couplings. The old American radials were curvic couplings.

RE: Just for fun. Ground up engine build.

(OP)
Check this out! http://www.geartechnology.com/issues/1186x/Back-to... geez... what hasn't been made in Rochester NY!?

It's all about knowing the name of what to look up! The Hirth couplings are much like the M14 rear sight adjustment knobs. The lead machinist and I were talking that maybe if we put a fillet on the form tool that we might like that idea the best. But... The curvic coupling looks pretty interesting. I will have to read all of the link to figure out what's so great about it. Thanks again!

Edits as I'm reading: Curvic claims that they can make interchangeable parts even on turbo-machinery! Again, the lead machinist fella and I were discussing if we would have to send the unit out to be precision ground once it's assembled... looks like maybe not.

RE: Just for fun. Ground up engine build.

What hasn't been made in Rochester for a while is money.
... at least not like in the days when Kodak was printing it.

Mike Halloran
Pembroke Pines, FL, USA

RE: Just for fun. Ground up engine build.

(OP)
Lol! I worked with a bunch of RIT guys who were happy to get away. Never been there. Too cold. I wouldn't make money there either.

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