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Hi! First post on this forum!

I've been on a hot air engine hype recently and have now decided to finally build one, but instead of making a toy, I've been thinking of making something semi-useful, so I've decided to take my aim at a hot air engine outboard for my boat! Been thinking about heating the engine with wood just for the coolness of it, but if that doesn't work I would fire it with propane. After some research, it seems that somewhere between 100 and 300 watts are needed to power the boat. Because of my toolset not being that expansive, simplesness is the way to go, and a simple engine I like the design of is the manson engine!

Now, I've been trying to find someone, anywhere, that have done a Manson engine build that have done something useful, but the supply of instructions and/or images has been limited.

So my question is, has anyone measured the power output of the manson design? Has anyone calculated watts/cc of this engine type? Can it generate 100-300 watts, especially when it's wood fired?

Thanks in advance!

//NordicTinkerer

nordictinkerer wrote: ↑Thu Feb 08, 2024 7:52 am Hi! First post on this forum!

I've been on a hot air engine hype recently and have now decided to finally build one, but instead of making a toy, I've been thinking of making something semi-useful, so I've decided to take my aim at a hot air engine outboard for my boat! Been thinking about heating the engine with wood just for the coolness of it, but if that doesn't work I would fire it with propane. After some research, it seems that somewhere between 100 and 300 watts are needed to power the boat. Because of my toolset not being that expansive, simplesness is the way to go, and a simple engine I like the design of is the manson engine!

Now, I've been trying to find someone, anywhere, that have done a Manson engine build that have done something useful, but the supply of instructions and/or images has been limited.

So my question is, has anyone measured the power output of the manson design? Has anyone calculated watts/cc of this engine type? Can it generate 100-300 watts, especially when it's wood fired?

Thanks in advance!

//NordicTinkerer

I don't want to be discouraging, but I haven't known Manson type heat engines to have a reputation for high power output or ease of construction. There may be exceptions but none come to mind.

This is a long involved video but illustrates what has been my general impression. For this and other reasons, I haven't personally had much interest, and as a consequence, have, admittedly no personal or first hand experience with the Manson type engine.


https://youtu.be/KLNQ9WaE_ss?si=bktkfOcFOl-whj5q


Now, the fault may be some flaw in design choice by this builder in this particular instance, but AFAIK this case is not atypical.

It could be a challenging project.

Tom Booth wrote: ↑Fri Feb 09, 2024 3:25 am
I don't want to be discouraging, but I haven't known Manson type heat engines to have a reputation for high power output or ease of construction. There may be exceptions but none come to mind.

This is a long involved video but illustrates what has been my general impression. For this and other reasons, I haven't personally had much interest, and as a consequence, have, admittedly no personal or first hand experience with the Manson type engine.


https://youtu.be/KLNQ9WaE_ss?si=bktkfOcFOl-whj5q


Now, the fault may be some flaw in design choice by this builder in this particular instance, but AFAIK this case is not atypical.

It could be a challenging project.

Gonna look at that video later, thanks for the tip!

What would, in your humble opinion, be a more suitable engine-arrangement for an outboard engine, an alpha-type stirling engine seems to have a higher power to volume ratio, but the beta engine seems mechanically simpler to my untrained eye.

//NordicTinkerer

I doubt you could do better than the advice of Andrew Hall, who literally "wrote the book" on Stirling engine powered boats.


http://stirlingengineboats.com/Stirling ... age00.html


See in particular the chapter "Don't Reinvent the Wheel"

Hall, and apparently the whole, active Stirling boat building "community" associated with him, with decades of dedicated trial and error, collective experience and know how have settle on the Beta type engine.

Now, personally, I've never considered a Beta particularly attractive or easy to build and therefore have, until recently written them off as beyond my skill level as a wannabe machinist trying to figure out how to setup and use my first small, old antique second hand metal lathe.

Recently however, I've seen the light and consider the Beta as having the most potential for high power output, aside from, perhaps some untried, untested, theoretical designs.

Anyway, I did not know Andrew Hall's opinion until looking it up just now in response to your question. Thanks! I can now add Andrew Hall's authority and lifetime of experience to my recent theoretical argument in favor of the Beta:

If you want to consider my theoretical musings on the Beta and it's potential here:

viewtopic.php?f=1&t=5598

Now, not to say Hall agrees with my opinion that cooling is not required or beneficial in a Stirling engine. I'm quite sure all his and other members of the Stirling Engine Society boat engines use water cooling and why not? Floating on cold water, but that is really a separate issue.

Disclaimer, as yet I have never built or even owned a Beta, afaik nobody of sound mind agrees with my unconventional opinions that run contrary to "established science", so proceed at your own risk and don't blame me if you decide to follow my advice. Better to listen to someone with real experience like Andrew Hall.

Personally, I'd probably ignore Halls advice and build a high temperature Gamma, simply because in my personal experience, I've had the most success and the best power output from small Gamma model engines. They are uncomplicated, straightforward and really easy to build, but, I'm making, at the moment, a gamma powered phone charger. No chance whatsoever that will ever propel a boat across a lake.

IMO it may be that Hall and friends would achieve higher output by NOT using water cooling. I could be wrong of course, and likely I am wrong, but having water available, I doubt anyone would even consider NOT utilizing it

But, if heat is your fuel, does it really make a lot of sense to deliberately dump all the fuel into the lake as one putt putts along on the water?

With such a disadvantage or enormous "fuel leakage" or heat wasted to unnecessary IMHO water cooling, heat continually flushed out of the engine, the Beta stands out as capable of producing useable power output under what may be IMO the worst possible circumstances: virtually unlimited drain of the heat/fuel supply.

Well, been researching for a while, and thoroughly read through Andrew Halls page, there were a lot of things I haven't considered (like the killtap, need for reverse, so on and so forth) but there are some parts that I've read on his page that I will humbly disagree on, not because I believe I'm smarter, don't gte me wrong, but because the stirling engine boat society has contradicted a bunch of what he had said himself. Like needing to use a boat without a transom, as they've shown many boats on their page that do have one, and the need for it to be pressurised, when Peter Lynn have made on that's an athmopsheric engine with a displacement roughly 2500 cc that is able to move 3 people at the speed of 5 knots.

So, I'm actually going to be going with the athmospheric route, as well as making the engine a gamma configuration, as I've found that that would be the simplest one to make with my available tools. I've been thinking about having it air cooled for ease, but water cooling with a thermosiphoning system is also on my mind. Once I get my CAD software up and running on my laptop I will check which of those 2 ideas would be the simpler to make.

I also found, a single source that quoted a real number for w/cc for a manson engine, according to Ken Boak, a manson engine as a power output of around 1/5 w/cc, which is very small compared to other athmospheric engines that I could design, I'm not giving up on it yet, but I'll probably use it as a stationary toy engine (or maybe build a fan as the guy in the video you posted) rather that trying to achieve any real power from it. Have an idea for an ethanol powered bike, but it'll probably never come into fruition, or I'll just modify my already existing bicycle with a gas engine.

//Nordic Tinkerer