A FrankenFour Inline?

[Topaz]

I wasn't talking about sales tax. Income tax. Which comes out of my pocket as an expense, just like any other, since I'm a sole proprietor. CA taxes income tax on a somewhat modified version of adjusted gross income.

I was giving a very simplified example of a real-world situation, not tax advice, meant to illustrate how even simple business transactions have "hidden" costs that can sap cash flow and wreck a business in the long run. Nit-picking the tax numbers isn't to the point. Too many people completely neglect things like overhead and taxes in their "profit" calculations and, among other things, that's why fully 95% of new small businesses don't survive to see their fifth year.

 

[BBerson]

I am looking at an inline engine on its side, no height issues. Similar to model airplanes.
I would put it on the right hand side because I can lean over to the left side for a clear forward view.

 

[scramjetter]

Can we get this as an inverted inline, or inverted V? Pretty please?

Hi all, this is just me brainstorming here but in another thread Matt (CluttonFRED) brought up the idea of a cheap kit for an air cooled four cylinder direct drive inline engine of 50-ish horsepower and it has me wondering what the minimum number of bespoke components would be for such an engine. For example, cylinders/pistons/valves/rockers could be sourced from a small industrial engine, crank and cam (plus lifters, main bearings and caps, etc.) from the automotive world, hardware is universal, and so on. Could it be as simple as just needing a crankcase and accessory cover to tie all the catalogue parts together? Has it been done in recent times?

 

[blane.c]

I still think flathead cylinders for the O-100 would be cool.

And would make it less wide.

 

[WonderousMountain]

Certainly,

No need to do it the way I am. Case is all that really HAS to be new.
You need to be a stringent and creative project manager. Absolutely,
secure in your vision and performance requisites. There are many areas
to absorb benefits, and all of them opportunities to falter.

Suzuki, Subaru and VolksWagon seem to be the leaders in conversions.
The Suzuki has 75mm Pistons. Suitable for a stroke of 60-90mm. Likely,
you could source part sets from 8-12 cylinder engines cheaper than 4's.

 

[Topaz]

...ETA: Ahh, I think I see the issue. If we interpret "keep the lights on" to mean "pay all fixed expenses and overhead", then Topaz's response is the logical one. If " keep the lights on" means " keep this business up and running (as the best use of my time and talents)", then my response makes sense.
" No more pizza from Tony's down the street. Looks like they've turned off the lights and rolled up the carpet.'

Perhaps I'm misunderstanding you - and apologies in advance if that's the case - but from my point of view, if you don't "pay all the fixed costs and overhead" every month, you're going to be "turning off the lights and rolling up the carpet" in exactly the amount of months it takes to drain down your reserve fund. I don't see the two as being different animals.

 

[Hot Wings]

I still think flathead cylinders for the O-100 would be cool.

And would make it less wide.

It would make it less wide but it would also remove 90% of what makes that project possible/practical - using OTS O-200 parts.

 

[cluttonfred]

I would be very interested to discuss what would be involved in taking, say, off-the-shelf air-cooled VW cylinders and heads and marrying them up with a custom case and crank and appropriate fuel, oil, and ignition systems in an inverted inline engine. Modest performance, direct drive, maximum use of existing components right down to bearings and the rest. Even 40-45 hp would be enough to make it worthwhile for Golden Age-style single-seaters.

 

[blane.c]

Continental A40 - Wikipedia

en.wikipedia.org

 

[TFF]

From an old sport aviation

 

[billyvray]

What we need is a person like Allen Millyard to conjur up unusual engines on a whim. I do not care if you aren't into motorcycles, you will probably enjoy his Youtube videos. The man build unique engines from parts of others for no other reason than he can. In a shed. With a manual lathe and mill. And hammers.

This vid is of using some Wright radial cylinders to build a vtwin. That would swing a mighty prop.

 

[TFF]

A place to dive in is historical Hot Rodding of the 50s where to hot rod something meant you had to make it. Sometimes crude sometimes art. It takes initiative. Some of the most interesting engineering were the people trying to get in the bubble for the Indy 500. Creative backyard building having to compete with people who could afford the best.

 

[pictsidhe]

There have a been a few crankcases fabricated from welded sheet. They can be very light. They have not been a hit in series production as they take too much labour. For the man in his shed with limited tooling and resources, they are a very attractive option.
Cranks are difficult. There have been a few built up cranks in production, but they have dropped from favour due to costs. This is something else for a Shedi to take a long, hard look at. I'd be looking at a jig to offset bore crankwheels for crankpins.

 

[Hot Wings]

I would be very interested to discuss what would be involved in taking, say, off-the-shelf air-cooled VW cylinders and heads and marrying them up with a custom case and crank and

As Pictsidhe noted "cranks are difficult" - Pete found this out with the O-100.
There have been plenty of inline 4's made over the years that could be donors for the crank. You have to decide at the start if this is going to be a direct drive or reduction engine. If DD then you probably should be thinking about an auxiliary prop hub/bearing. This can be integral to the new crankcase. While looking at cranks also look at matching in block camshafts as a source of that part. Best to keep the cam/crank with the same bore spacing. Look for a cam that is originally used with roller lifters. Rollers don't work well on soft cams.
VW cylinders are attractive, but the heads? Not very adaptable to an inline engine. Look for individual heads like found on the 2CV/BMW motorcycle etc.

The Honda GX-690 head/cylinders might be a good starting point - if you can figure out how to package the exhaust system. If you want a small radial these would be my first choice.

Edit:
If you thing designing an airplane is a massive collection of compromises ... it comes in a close second to trying to design an aircraft engine using a significant portion of OTS parts to reduce cost.

 

[Tiger Tim]

I would be very interested to discuss what would be involved in taking, say, off-the-shelf air-cooled VW cylinders and heads and marrying them up with a custom case and crank

The trouble I see with a VW in-line four is you’d need a loooong centre main bearing since the #2 and #3 exhausts would have to tee together between heads. Not insurmountable but it then requires a custom crank. By going with cylinders that have the intake on one side and exhaust on the other the cylinders can all be equally spaced to match an existing crank. Inline four cylinders are pretty ubiquitous in the automotive world so there’s no point in reinventing the wheel or modifying something when there could be an off the shelf example already out there. Plus the automotive crank will have had more R&D money spent on it than all of our airplane projects combined, will probably be forged, and thanks to there already being millions of them in service they’d be cheap-as-borscht compared to aviation or custom parts.

 

[Tiger Tim]

There have been plenty of inline 4's made over the years that could be donors for the crank. You have to decide at the start if this is going to be a direct drive or reduction engine. If DD then you probably should be thinking about an auxiliary prop hub/bearing. This can be integral to the new crankcase. While looking at cranks also look at matching in block camshafts as a source of that part.

That’s exactly what I had in mind.

 

[Topaz]

I would be very interested to discuss what would be involved in taking, say, off-the-shelf air-cooled VW cylinders and heads and marrying them up with a custom case and crank and appropriate fuel, oil, and ignition systems in an inverted inline engine. Modest performance, direct drive, maximum use of existing components right down to bearings and the rest. Even 40-45 hp would be enough to make it worthwhile for Golden Age-style single-seaters.

As others have said, ask Pete Plumb. That's essentially what he did with the O-100. What I learned from talking with him, in person, standing over his engines and parts for his engines, is that this is not as simple as it sounds. To get everything working together properly, efficiently, and producibly, you end up designing a new airplane engine that's based on - not built of - existing engine parts. I know the dream is to "just" take as many existing parts as possible and hook them together with a new case, but it just doesn't work that way. Now, I think Pete has gone overboard in making his engine "perfect" (and yes, I've told him this directly), but even without that perfectionism, it's clear that the job is more than just bolting together stock components. The crankshaft alone turns out to be a major design and production problem.

 

[Vigilant1]

VW cylinders are attractive, but the heads? Not very adaptable to an inline engine. Look for individual heads like found on the 2CV/BMW motorcycle etc.

Could the stock VW heads be cut, as is done for the 1/2 VWs?
Someone I know (Hot Wings) was looking at designing single VW heads optimized with porting and cooling fins most appropriate for aircraft use. Just sayin... He's always looking for another project to add to his collection.
Using VW bits would presumably allow use of the available Nikasil cylinders. Pricey, sometimes problematic in some applications, but light.
I don't think I'd be a customer for a small-batch inline air cooled 4cyl of 75 hp, but I could see that some folks might like one. It would probably be a niche product.

 

[Victor Bravo]

There are way too many existing inline engines, upright and inverted, that would be a better starting point than a clean sheet. Business or personal issues aside, the Raven Redrive engines apparently worked well based on a cheap and plentiful light automotive engine (I even napkin-sketched out an airplane for it, halfway between the Chilton monoplane and the Miles Sparrowhawk). The only advantage of what is being discussed here is using air cooled cylinders to create a Gipsy or Menasco looking thing without a radiator. That's all well and good, and a hearty Mazeltov for anyone who wants to do that, but the development time on that will keep whatever dream airplane from flying for a long time.

 

[wsimpso1]

I think the number of components could be zero if complete single cylinder engines are bolted together end to end.
A two cylinder or three cylinder is no problem. Four inline gets a bit long but might be doable.

If this were easily done, we would have already seen it, right? So why do we not see it?

Let's talk four stroke singles. Firing frequency is 1/2 per rev, with pistons going up and down at 1 per rev. Crank natural frequency must be at least 1.5x max rotational speed in revs/sec to put resonance out of range. Given the size needed on the power end for carrying pulley and belt loads, crank natural frequency is probably pretty high...

Now couple three together and stick a prop on one end. The crankshaft torsional stiffness just became one-third as stiff, and both prime frequencies just tripled. Only one flywheel is needed and it can be lower mass because you have the prop serving as flywheel. With crank resonant frequency dropping to somewhere around SQRT(1/3) = 58% of what it was while primary and secondary frequencies tripled, you very well could have all kinds of resonance issues walk right down into the operating range. Then the crankcases also have to keep their resonant frequencies safely above firing frequencies, and yet they have the same problems with stiffness dropping to a third and input freq tripling.

Then there is the whole issue of coupling one end of the existing crank to the other end of another crank. Coupling methods for the cranks and for the cases would each be pretty tough to solve.

In total, UGH.

This is why when engine builders talk about using more cylinders, they build shorter thicker cranks and shorter crankcases and shove the cylinders as close to each other as they can. For instance, the Porsche 917 engine, a 4.5l flat 12 is not just two 2.25l flat 6's. The Porsche 6's are boxers, each cylinder has its own crank throw with each opposed pair of pistons going out and in together. The 917 dispensed with that, with six throws to make the crank stiffer. These efforts make the crank natural frequency high enough to avoid resonance without it getting really beefy and heavy. What about yaw axis vibe from each pair of pistons both going the same direction that way? Well, the crankshaft front and back halves are mirror images of each other, so the cases have to stand the moments, but those forces are all internal to the crank case.

In multi-engine helos, they do not couple the engines together, they run an input to the gear box for each engine with a one-way clutch, among other things.

Now none of this is to say you could not do it, but there are a peck of challenges to making it all work.

Billski