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A FrankenFour Inline?

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Tiger Tim

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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?
 

Victor Bravo

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That is exactly the rabbit hole Pete Plumb went into on his project.

(For those of you old enough to remember, imagine Mickey Rooney and Judy Garland standing there, in glorious black and white...) "We can use 90% of the Continental engine, all we have to do is cut the case in half and make sure the oil goes through the right holes... and then just bolt it back together!"

And then reality, physics, and the configuration gremlins show up :)
 

Tiger Tim

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That is exactly the rabbit hole Pete Plumb went into on his project.
Yeah, that was in the back of my mind when I was typing BUT there’s also a history of a couple engines produced in the thirties that were air cooled but used as many Ford internal parts as possible.
 

Niels

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For noise reasons tip speed have better be 220m/sec or less.
What prop diameter is relevant for the aircrafts that will benefit from such an animal?
Or asked another way how many rev per second?
 

blane.c

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D-Motor has the right idea.

A 50hp-ish flathead direct drive would be the least parts count. Going for displacement instead of rpm to create torque the overhead valve contraptions are just extra weight.
 

blane.c

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I think if you need to make $5,000 an engine to keep the lights on then a $20,000 engine that costs you $15,000 to make is feasible but a $10,000 dollar engine that costs you $5,000 to make is not marketable.
 

Vigilant1

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I think if you need to make $5,000 an engine to keep the lights on then a $20,000 engine that costs you $15,000 to make is feasible but a $10,000 dollar engine that costs you $5,000 to make is not marketable.
Why? You're making the same $5k per engine either way, but you've got considerably lower up-front labor costs and lower inventory "drag" for the cheaper engine. All things being equal, volume can be expected to be higher at a lower price point, and that leads to efficiencies.
 

Riggerrob

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A few people have tried to make radial engines with Harley-Davidson cylinders, but none of those projects seem to be flying any more.

On a related note, one guy did bolt an almost-stock, air-cooled, V-twin, Harley-Davidson, motorcycle engine to the front of his Zenith 601. The only significant modification was a PSRU. As soon as the Harley-Davidson factory heard about the project, they threatened to sue the independent engine "hacker" out of business.
 

blane.c

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I ain't saying it can't be done, just saying that is what you are up against.

You are up against it all the way. Liability. Warehousing. Manufacturing. Sales.

I think you'd have to have deep pockets to chew all of that sandwich and a benevolent mind towards small aviation.
 

Hot Wings

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all we have to do is cut the case in half and make sure the oil goes through the right holes... and then just bolt it back together
Seems simple. But it can get complicated pretty fast - as he found out with the crank on the O-100. Not quite as simple as lopping off 2 throws of an O-200 crank.
<< >>
A few people have tried to make radial engines with Harley-Davidson cylinders, but none of those projects seem to be flying any more.
I did a LOT of work back about the time I joined this group on building a new aircraft opposed 2 cylinder engine using a lot of OTS parts. It was going to be about 40 Hp and 65#. I was at the point to start making casting molds and time to spend some money, just not my time. As much as it hurt I had pretty much decided to write the whole thing off as sunk costs because I didn't see enough of a market to make the biz model work. Pete introduced his O-100 at almost the same time..........Last nail in that project's coffin.

I still have the CAD - still can't make the biz model work. I might build one for my personal use some day.
I have a pretty good idea of what is needed for this kind of project. It isn't as easy as it sounds but it is possible.
<< >>
Regarding the HD top end: I still have the Harley parts I bought to measure for my project to see if they might be adaptable. IMHO they aren't even close to being usable on an aircraft engine project. The heads are just too heavy and massive. Aftermarket Harley cylinders on the other hand are a pretty cheap source of large diameter air-cooled cylinders.
 

TFF

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There are plenty of machinist hobbyist that make engines just for fun. The issue is they just want a display engine to run on a stand. It’s how Rotec started; a personal display engine. Making an engine is easy. Making an engine you trust your life to and can be light enough is a whole level they are not working on.

If there was an engine I would copy for an airplane build, a double sized Alfa Romeo 4 cylinder engine is perfect. It’s about as simple and modular as an engine gets. The 2l is too small. Needs to be 4l. An Offy is 270 but much more complex.
 

Topaz

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Why? You're making the same $5k per engine either way, but you've got considerably lower up-front labor costs and lower inventory "drag" for the cheaper engine. All things being equal, volume can be expected to be higher at a lower price point, and that leads to efficiencies.
Because the other overhead items remain roughly the same, regardless of how much you charge for your engine and how many you make. It's not all about parts and material costs; it's not even mostly about parts and material costs. At the end of the day, you personally will be making "x" dollars a year as your salary, just turning on the lights costs "y", paying the salaries of any employees or outside vendors helping you build engines costs "z", and on down the line, including building rent, insurance (liability and worker's comp), tools, taxes, waste disposal fees, advertising costs, your share of your employee's medical insurance and Social Security taxes, ad nauseum. Every penny of all of that comes out of what people pay you for your engines, less material and parts costs.

If the parts and materials cost for each engine is $5,000, then I have a very hard time imagining that you can pay for all these other things with another $5,000 per engine, at any reasonable dream of production rates for aviation engines. If you sell 100 engines a year, that's $500,000 a year to pay for everything and everyone associated with making those engines, on top of material and parts costs. Everything and everyone, including yourself.

Example: I occasionally broker printing on the graphics projects I do. When I first started out, I was aghast that I was being told, as a general rule, to mark up my costs for printing "about 20%" and have the customer pay the marked-up price. 20% seemed awfully greedy! Then I started wondering why the more printing jobs I brokered, the worse my business seemed to do. I sat down and figured out the math on this very simple case. Let's say I'm charged "$1000" for a print job. I give the vendor $1,000, and they give me the printed pieces. I then charge the customer $1,000 for the print job. They give me $1,000. I'm charged income tax on the $1,000 that customer paid me by both the feds and my glorious state of California. Let's say my federal tax bracket is 15%. California lovingly charges me another 8% for the privilege of living here. So that's $230 out the door, just in taxes. The printing cost me $1,000, the client gave me $1,000, and the federal and state governments took $230 of that for themselves. Charging my client even-money on the printing (no mark-up) means I lose $230 every time it happens. No profit - I'm taking a loss. I have to charge $1,230 to the client just to break even (actually, slightly more, but let's keep this simple). A 23% mark-up doesn't make me any profit at all - it just stops me from losing money on the deal. And that's just to cover taxes - the gasoline I burn to go pick up the print job and take it to the client, or delivery fees if I pay someone else to do it, come in on top of that. My real markup on things like print jobs is 30%, and it's not even remotely some kind of "profit center" for me. I still come very close to breaking even or losing money on brokering, which is why I don't like doing it very much.

Now carry that across to everything else needed to build a widget or an engine. Running a business is way more expensive than most people understand. It's a wonder the manufacturer can make them so inexpensively without losing their shirt.

This is Business 101. And it's why so many new companies go under in their first year. Or their fifth year. I'm on my 13th year of being in business, and I'm still learning how to do it, I think.

Rant over. Carry on.
 
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Derswede

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Topaz, that is about the most succinct explanation I have heard in awhile of being practical in a business sense. All those folks that tell me "you must be making a fortune" running a small business either have never run a small business or were selling (or using) drugs. At 14 years in business by myself, I calculate every deal every which way I can, too easy to break yourself with just one bad deal. And yet people think you are stiffing everyone.

After this Covid mess, I am 8 months without a paycheck. Wife is out a job, and I am selling my stuff to make ends meet! No magic wands in business. If there is not a market (profitable) for a product, unless you have VERY rich and generous family, or are working for the Gov't, leave it. As cheap as I am, I would hate it if my customer base was as cheap as me......! One reason the Hawk has not flown yet. Years ago, a person asked my dad how he could afford to rebuild so many airplanes! He pointed to me and by two brothers and jokingly said, "I have slaves......!" I am the chief cook, bottlewasher, financial planner and attorny/CEO/CFO/janitor at my company. My title is "JOATMOS". Stands for jack of all trades, master of some.

Derswede
 

BBerson

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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.
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.
 

Vigilant1

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I think if you need to make $5,000 an engine to keep the lights on then a $20,000 engine that costs you $15,000 to make is feasible but a $10,000 dollar engine that costs you $5,000 to make is not marketable.
As I read it this, I have the choice of two products.
1) A product that has a retail market value (price) of $20k, and all my costs to manufacture and market this product (amortized fixed overhead, etc) would be $15k per unit.
2) A product that has a retail market value (price) of $10k, and all my costs (as above) would be $5k per unit.

I don't understand why 25% margin per unit above my expected costs is better than 50%. More margin gives me more safety if my costs go up, and room to reduce prices and remain in the black if demand declines at my present price.

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.'
 
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rv7charlie

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Topaz, I feel I should point out that there seem to be serious tax accounting questions in your $1K expense/sale example. Yes, someone will have to eventually pay the sales tax on the item/service, and you'd have 'overhead' in ordering and picking up the item/service. Unless CA has instituted a value added tax, the transactions shouldn't get taxed twice. Not collecting sales tax from the end user shouldn't be part of the equation; it should be a given that it would be collected. And I can't imagine that CA makes you pay income tax based on your gross income, which is what the example implies. If you purchase goods/services for x dollars and simply recover those x dollars from your customer, then there is no income on that amount, and therefore, no income tax on that amount.

Having owned a business for quite a few years, and having a short stint as a Revenue Officer with the IRS about 45 years ago, I'm pretty confident about the above. Having said that, I agree that many new business persons are naive about margins needed to actually make a living.

Tim,

Even if the idea was physically (and economically) possible with OTS components, you'd have to deal with the extra weight of both the crankshaft and the block, beyond what a 'flat' engine would weigh. Then you'd have to deal with the operational and configuration issues tied to the inline format aircooled engine. Cooling will be trickier, and the crank would have the potential to have torsional/stiffness issues beyond what you'd have with a flat engine. And as BPearson mentioned, few existing airframes would easily accept an inline four, due to length and probably height issues.

FWIW,

Charlie
 
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