# The rise of FrankenEngine - An engine for the VP-21

### Help Support Homebuilt Aircraft & Kit Plane Forum:

#### Aviacs

##### Well-Known Member
The weight is almost entirely immaterial.

Around here roads go down and up besides miles of long sort of level stretches

We can Google and use the standard formulii to get close:
This document gives a Cd for a semi-upright motorcyclist (60 deg leg angle) and motorcycle as 0.78, and the approximate frontal area as 0.68 M^2.
Fd = Cd 1/2 ρ v^2 A
Given standard conditions and your specified 75 MPH (121 km/hr)
Fd = 0.78 1/2 (1.2 kg/m3) ((121 km/h) (1000 m/km) / (3600 s/h))2 ( 0..68 m2)
So, our drag force = 360 Newtons
To get the power required to achieve this:
Power = 360 N (121 k/h) (1000 m/km) (1/3600 h/s)
- 12,100 watts, or 16.3 HP.

BINGO!

500cc can do that "all day", so could a Honda 305. You are arguing theory against experience
2 x 16.3HP = 32.6 HP, well toward the upper end for cruise (75% power) of the OP "30 to 40 HP" engine requirement.
2 x 500cc = 1000 cc = 61 in^3.
So geared 60 cu in vs 100 cu in direct drive?
Once gearing is chosen, there can often be great efficiency gains over direct HP if even longer props can be used than the competitive HP direct drive unit in a given flight application. E.g. a 175HP GO300 with 84" prop has performance advantage over 180HP O360 with 76" prop in same 172 airfame.

(long straw argument)........Yes, we can add fin area and more effective baffling, etc. But there are diminishing returns. The issue is the finite heat flux ability of aluminum (or any solid). In our engine, heat is being added to the inner surface of the combustion chamber and piston. That heat needs to flow out to the fins where it can be exchanged. This flow occurs at a rate that depends on the cross sectional area of the aluminum and the temperature gradient. Extra fin area helps, but the physical limits of the cross sectional area of the aluminum eventually imposes a limit. When the temps inside reach about 500F, your head will live a very short life.
A thought experiment: We buy a roll of aluminum foil and unroll the whole thing. We set up a fan to blow air over this tremendous expanse of foil. If that foil was at 300F, we could easily shed thousands of watts/hr to the passing air and the foil would never get hotter. But what will happen if we put a little flame (500 watts?) on a corner of that foil? It will rapidly exceed the melting point of aluminum. Sure, the expanse of foil was capable of shedding thousands of watts of heat, but the aluminum in the immediate vicinity of the local heat application couldn't move it away as fast as it was being added, so it got hotter until it melted. We count on this same thing if we are sweating a connection on a long pipe: we add heat with the torch faster than the copper pipe can carry it away, and eventually it gets hot enough to melt solder. The long pipe easily has enough surface area to dissipate the heat from our torch to the surrounding air, but because the copper can't transport it away fast enough, our connection gets very hot. And copper moves heat much better than our aluminum head does.

If an engine can run for an hour in a given regime, the cylinder head is not going to melt after 2 hours.
What you seem to be arguing is that you have not experienced it and you don't understand it, so it can't be!
But examples of the engines you say can't exist are out there running steadily.

Airplane engine designers are smart. If they could add more fins to their air cooled creations and thus reliably make .75hp/cu inch, they would do it. Gearing/PSRUs can let us turn a more efficient prop for a given HP output, but it does nothing to improve the thermal transfer issues that fundamentally constrain air cooled heads and cylinders. Where are all these geared air cooled airplane engines?

Pobjoy did it in the 30's and the engines were fairly widely used, for the time.
AFA as the rest of your Q: Most of the engines used in WW2 were geared; as were the transport/commercial piston engines that followed. All turbo props are. There were plenty of successful small GA geared engines built after the war. PSRU's are somewhat analagous to turbo charging - works great. but economically only suits a really small percentage of operators.

Your concerns about heat issues are correct, but you are not recognizing that powerplants that exceed your personal imagination or calculation limits exist and have existed for most of a century. To try to make the points you want to make you set up straw arguments and tiptoe around the concept that an efficient engine by definition converts more fuel into torque and less into heat. OHV vs flathead, as a very early evolution. Compression ignition vs spark ignition going further. Other types & combustion chamber configurations somewhere in between.

I'm done, though.
You keep trying to argue that things that exist or existed don't, or taking things in directions that i have not necessarily argued against as specific cases.
To repeat, since aviation with IC engines began, design consideration has been whether to go simplicity & design a large enough displacement to provide the necessary HP at a specified relatively low direct rpm for propellor efficiency; or whether to decrease physical size and often weight by designing a "high" rpm engine and getting the propellor rpm through PSRU.

You might prefer a given configuration,and me another.
You can't argue that the choices don't exist nor that both historically have provided solutions.

smt

Last edited:

#### Geraldc

##### Well-Known Member
That wasn't the case with Ford flatheads, they had a bad tendency to overheat because of the long time/distance that the exhaust stream stayed in the head (adding heat to it).
Fords problem was the valves were in the center and the exhaust had to go past the cylinders to the manifold.
Putting exhaust on top and inlet on sides would fix that.

#### Geraldc

##### Well-Known Member
Between plane work }I have been working on a 100 year old Douglas motorcycle.
The main difference between that motor and all the 4 cylinder boxer motors is that the cases are split sideways not lengthways.

This makes manufacturing cases easier because there are only 2 main bearings that can be off the shelf ball bearing unit to handle thrust as well.
Any suitable crankshaft with 2 cranks between the main bearings can be cut to suit.
Cylinders and heads can be off the shelf.

#### cluttonfred

##### Well-Known Member
Supporting Member
A Harley Davidson 1200 puts out about 45 hp at 3600 rpm. A couple of those HD cylinders, pistons and heads on a custom or cut-down crank and a custom opposed case like Geraldc described would be a hoot and have a great sound. You could drop it to 40 hp at 3200 rpm if you wanted to swing a bigger prop.

#### Hot Wings

##### Grumpy Cynic
Supporting Member
A couple of those HD cylinders, pistons and heads on a custom or cut-down crank
And Harley pistons and cylinders with bores up to 4.25" are pretty common. They need larger spigot holes in the case but if you are already machining from scratch it isn't much more work.
The Harley heads would make a nice bolt together OTS solution - if you can handle the weight. Stock Harley heads are H E A V Y.

#### Hot Wings

##### Grumpy Cynic
Supporting Member
What is the continiuos([email protected]) power output of a hardlygoingson?
Maybe the proper question to ask would be "What is the continuous power of a HardlyLeakingson* with aircraft style cooling shrouds?"?
I don't think anyone really knows?

*My father was the first Harley dealer in my state and I spent summers working off my new Schwinns back in the shop. I actually have pretty neutral opinions of Harleys other than being quit intimidated by their weight when I had to move one, back when I was 10. The Laverda wasn't quite as bad but I was a little older then as well.

Edit: This presumes that the limit is due to heat dissipation. It could be the volume of the oil tank !?!

#### blane.c

##### Well-Known Member
Supporting Member
Objectives:
Gather ideas, in the spirit of the VP-21 and Motorcycle Of The Air threads, to design an engine suitable for this class of EABs. Project is to be open source so individuals can build from scratch, use cottage industry parts or buy complete FWF packages.

Controlling parameters:
Opposed 2 cylinder.
4 stroke direct drive
Maximum RPM = 3600 ………… less is better.
30+ Horse power. 40 would be better. This means 60 cubic inches (1.0L), or more, if we use 0.5 Hp/cu/ in. as a base line.
80 pounds maximum weight ready to bolt to the engine mount, minus prop and exhaust.
Should run on 85 octane E10 or low Sulfur Diesel (not both – pick one)
As many off the shelf (OTS) parts as possible. Minor modifications acceptable. This means those that can be done with hand tools or at ANY machine shop.
The OTS parts should be sourced from current production or past vehicles that have been produced in million+ quantities.
Simple. No dual OHC, VVT, variable compression, 12 valves per cylinder or antimatter containment fields.
Unless someone comes up with another option it will be presumed that this will mean a clean sheet engine case/block is needed along with either clean sheet heads or those built in the fashion of the ½ VW or ½ Corvair.
Past engines to use as templates:
Onan
1/2 VW
1/2 Corvair
Aeronca E-113
Conteniental A-40
O-100
Franklin 2 cylinders

The thing I question most is the first constraint "opposed". A inline on its side 80lbs and under would be as good? The blank side of the engine could be a space for the battery and miscellaneous to fill a cowl proportionately and if a inline weighs slightly more on its own maybe the way everything associated is arranged could turn out to be even or moot.

#### Hot Wings

##### Grumpy Cynic
Supporting Member
A inline on its side 80lbs and under would be as good?
There is nothing magical about the opposed restraint. It is just what shook out of the tree. Here is part of the path to the choice:
A small 4 cylinder is just too many parts and machining operations - especially for the custom bits. A 1L 4 cylinder uses some pretty small bores or strokes and peak torque is gong to be about half of a 2 cylinder of the same displacement. To make Hp at low rpm we need good low rpm torque. Kind of a bad analogy - you can beat on a 4# rock all day with a tack hammer and it won't move. One good hit with an 8#..............
This limits the options to 2 cylinders.
As many OTS parts as possible. The crank, being the base of the engine, is where I started.
There are plenty of inline 4 cyl cranks available that could be cut down. With an in line you are limited in bore size by bore spacing. This also makes the crankshafts longer, and generally less stiff.
There are also a lot of traditional V8 and V6 cranks that could be cut down. Those kind of force us to a "V" engine of some configuration or an uneven fire. The "V configuration complicates the machining process for cottage industry level shops.
A similar big V4 based on one of these cranks might be an interesting project for the 80 Hp range?
What was left? Boxer engines for crank sources. Since the VW has a long history, and is likely to be available, for a long time that Is what I picked.

There may be a better option?
If the little Suzuki 1.0L 3 cyl, or a similar SIMPLE engine was still available I'd probably have developed that path - even before the B+S 810.

#### sotaro

##### Well-Known Member
Hot Wings,
This has been an entertaining read. I appreciate that you have thought a lot about this idea. So many suggestions, some conforming to your original post and some not. What I haven't understood is what is your scope. How much time, money, years do you plan on putting into this engine? Pete Plumb took years to develop the O-100 to the state it is in now, with a significantly less ambitious development plan than your OP indicates. What can you do? Are you actually planning on producing a working engine that can be produced and sold? It can be difficult, despite reading the entire thread three times, to keep track of what you are posting and that of others less focused on your OP. I laud your ambition. I appreciate your conception, pragmatism and tenacity. What is realistic? I am certain Pete thought he could get the O-100 to market by now. Do you have a partner in crime (besides the brilliant participants on this thread)?

I like the scope, 30-40 hp, opposed, air cooled, 4 stroke, direct drive, carbureted twin at under 80 pounds without alternator nor electric starter. I don't see much of a non experimental aviation market for this design. Do you? If you could make the half VW lose 12% of its weight and perform better would you have satisfied your ambition?

From your posts, I assume you are willing to cast/machine the cases, the intake and exhaust manifolds, the baffles. Other parts would be off the shelf or modified production parts, especially the crankshaft. What of the head? Are you willing to have cast or machined the head with OTS valve train? What kind of volume production do you imagine? Price?

Thank you for sharing your thinking. I especially appreciated the lifter conundrum with diagram and OHV vs flathead. My thought is that with this small an engine, the width of OHV is not going to alarm anyone. The loss of volumetric efficiency and combustion efficiency with the decreased compression ratio and expansion ratio is not to cheer anyone.

#### rv7charlie

##### Well-Known Member
Supporting Member
A 1L 4 cylinder uses some pretty small bores or strokes and peak torque is gong to be about half of a 2 cylinder of the same displacement. To make Hp at low rpm we need good low rpm torque. Kind of a bad analogy - you can beat on a 4# rock all day with a tack hammer and it won't move. One good hit with an 8#
Lower parts count obviously keeps costs lower (usually), and I can see how an 8# hammer can do more damage (at the same speed), but we're not breaking rocks, and hopefully, we're not breaking cranks or props, either. Does your logic mean that a Lyc 360 is superior in operation to a Continental 360? Would a 2 cyl 360 cu in Acme Special be superior to both?

It seems to me that the closer peak torque is to average torque, the less 'meat' is needed in all the related components to survive, and average torque (times rpm) is how we determine how much work is getting done. More cylinders just means more steady torque with lower peaks.

#### Hot Wings

##### Grumpy Cynic
Supporting Member
What is realistic? I am certain Pete thought he could get the O-100 to market by now.
If Pete had lived a bit longer I'm sure he would have had the O-100 on the market, if not by now, then soon.

At one time I seriously considered this as a for profit business. Unless some very fortunate set of circumstances come together I'll never again be in a position to do that. I - might - still be able to build one for myself.

If some one else gets some ideas from this thread, are in a position to develop something that is real world workable and does it, then this thread has met it's objective.

There have been a lot of good ideas presented here along with some very interesting old engines that I had never seen before. I appreciate all of the input and hope there is more to come.

#### Vigilant1

##### Well-Known Member
Supporting Member
It seems to me that the closer peak torque is to average torque, the less 'meat' is needed in all the related components to survive, and average torque (times rpm) is how we determine how much work is getting done. More cylinders just means more steady torque with lower peaks.
This makes sense to me. A 4 cyl and 2 cyl of equal average torque will turn same prop at the same speed. The 4 cyl will be smoother with lower peak loads.
OTOH, a 2 cyl can be lighter.
-- The cylinders, head, and pistons will have a lower total weight for the same displacement.
-- The case will be shorter.
-- The crank will be shorter (so stiffer at the same dia).

In practice, true efficiencies and saved weights between these two options likely come down to which OTS parts are available.
A little flat 4 would be something to see.
(Inverted V Twin, 30+ HP, low risk, collaborate with Tipi, 3 months tops to first engine start, 77 lbs with starter and electric)

#### Hot Wings

##### Grumpy Cynic
Supporting Member
Would a 2 cyl 360 cu in Acme Special be superior to both?
If I were building a pile driver - Yes.

I said it was a "kind of bad analogy" and I'd rather avoid the nuances of this particular physics problem on this thread.

#### GeeZee

##### Well-Known Member
DIY lost foam casting of finned cylinders. Seems like a crankcase would be doable as well.

#### rotax618

##### Well-Known Member
The costs of producing a reliable small engine is enormous, I recon that the “Franken” parts should be confined to ancillary parts added to a reliable bullet proof ‘core’ to make it more suitable for aviation purposes.
I know from my experience working with the Suzuki G10 that the basic engine weighs about the same as a Rotax 582, and I’m sure that it is not the only 3 cyl auto engine that is that light. Naturally it would only produce about 40hp direct drive, but add a small turbo and you would have 55-60hp ( the turbo conversion weight is reduced by the fact that you don’t need a muffler). The Suzuki runs reliably tilted over at 70deg exhaust down and can be tilted at 90deg if a large enough oil return pipe is fitted between the valve cover and the sump. The crank being 120deg they are easy to hand start. All 3 cyl engines exhibit an odd ‘wobble’ at idle but are absolutely vibration free at revs.

#### blane.c

##### Well-Known Member
Supporting Member
The costs of producing a reliable small engine is enormous, I recon that the “Franken” parts should be confined to ancillary parts added to a reliable bullet proof ‘core’ to make it more suitable for aviation purposes.
I know from my experience working with the Suzuki G10 that the basic engine weighs about the same as a Rotax 582, and I’m sure that it is not the only 3 cyl auto engine that is that light. Naturally it would only produce about 40hp direct drive, but add a small turbo and you would have 55-60hp ( the turbo conversion weight is reduced by the fact that you don’t need a muffler). The Suzuki runs reliably tilted over at 70deg exhaust down and can be tilted at 90deg if a large enough oil return pipe is fitted between the valve cover and the sump. The crank being 120deg they are easy to hand start. All 3 cyl engines exhibit an odd ‘wobble’ at idle but are absolutely vibration free at revs.

I am such a fan of three engines maybe three cylinders is just a natural progression? So are three cylinders pop, wheeze, pop, wheeze, pop, wheeze?

#### Hot Wings

##### Grumpy Cynic
Supporting Member

Nice find!!
I was kind of disappointed that he makes each core individually. I tried molding cores using raw Styrofoam beads and steaming them in a master. I couldn't get it to work reliably for thin fins.
I did pick up a couple of tips to try.

Thanks for the input!

#### Tiger Tim

##### Well-Known Member
I know, not a two cylinder, but IIRC there was an engine in the 1930s called a Douglas Bearcat(?) which was a new case, air cooled cylinders, and heads for Ford Model A internals.

Perhaps an air cooled conversion of a liquid cooled industrial four cylinder would be worth exploring. Something designed to turn at low-ish revs and last forever without major service.

#### Kiwi303

##### Well-Known Member
I know from my experience working with the Suzuki G10 that the basic engine weighs about the same as a Rotax 582, and I’m sure that it is not the only 3 cyl auto engine that is that light.

There are lots of small japanese Kei car engines around the 660cc mark that are 3 cylinder, often with 1L big brother engines to run the same core in the next tax bracket up. They just don't appear in the USA because you LOVE your big gas guzzling V8s and monster trucks.

I've looked at the subaru EN07 4 cyl which has several 64hp supercharged options as an engine option for a Jodel D.11. 4cyl 660cc, it's older tech now, and heavier, but at the time I was investigating (2010, 2011) is was still being made new (until 2012) that with a MB C180 Kompressor supercharger rather than it's own 660cc supercharger, and cam reground for more torque at lower revs.

The later KF engine is becoming more available from japanese parts sources, Daihatsu K-series engine - Wikipedia which is what I'd be looking at now... 2012 onwards. 3 cyl.

Any import shop that brings in engines for the ricer boys will be happy enough to take your money and add any japanese engine to their next container of imports.