I got interested in hot air engines earlier this year and wound up building the popular Moriya model designed by Dr. James Senft. I got lots of help and encouragement from the guys on the Home Machinist forum. There's a pretty lively discussion of the entire build here, including a link to a copy of Dr. Senft's original plans.
Sometime later I got interested in the Manson-style hot air engine, mostly due to its simplicity. Surprisingly, I wasn't able to find a complete set of drawings for a Manson engine, so I tried to come up with an original design. My first attempt was similar in a lot of ways to the Moriya engine, but it didn't run very well. The next effort was kind of a cross between the partially complete plans found here and the build log for yet another example found here. It ran much better than the first attempt, but still wasn't great. But once again, the guys on the Home Machinist forum came through with some great hints for improvement, and with them, a third engine very similar to the second one ran like a champ. There's even a video:
This file contains a Fusion 360 model for the third version, 2D drawings based on that model, photos of most of the parts, and a few miscellaneous notes. If you have any questions or comments about these plans, I'd love to hear them, either here or in a comment attached to the video mentioned above.
15 comments:
Hello, I am a high school student in Japan and my team is planing to make a manson engine. I came across your plans and showed then to the group and we think it's absolutely brilliant!
However, all of the machines and tools we have are based on the metric system.Therefore we were wondering how precise the measurements have to be.
We are planing on converting the measurements into millimeter and rounding up to a hundredth and adjusting a little to the tools we have at school.
Do you think these calculations will mess anywhere up?
Please hit us back if you get the chance. Thank you very much!
Thank you for your interest in my plans. You should be just fine if your parts are within 0.01 mm of the dimensions given in the drawings. There are only a couple of things that you really need to worry about:
1) The piston must move freely within the cylinder, but with a nearly airtight fit. Here you will probably lap the two parts together to get the required fit, and that process won't care about your units of measurement.
2) The port in the piston must line up with the ports in the cylinder at both ends of the piston stroke. But since these ports are nearly 1 mm wide, it won't matter if they are off by a hundredth here and there.
Besides doing the conversion to metric, you may have to make some actual changes to the dimensions to match the test tubes, O-rings, bearings, and fasteners that you have available. The file READ_THIS_FIRST.txt in the plans package has some hints on all this. Be sure to read it!
Good luck with your project. If you post the results online someday, I would love to hear about it.
-- Russ
Thank you very much for such a swift response! We started recalculating right away.
We'd read the file READ_THIS_FIRST.txt and we maneged to get our hands on 25mm test tubes. However, we didn't have any 21mm test tubes around, so we have adjusted some of the measurements accordingly. As for the bearings, o-rings and fasteners we had no problem at all.
Thank you very much for the input!we'll be sure to tell you how the project goes!
Great! That all sounds good except for the test tube problem.
You want to keep the gap between the two test tubes qutie small, so that almost all the air inside the engine is forced from one end of the cylinder to the other as the piston moves back and forth. Also, extra air inside the engine means you will need more heat to make it expand and more cooling power from the fins to make it contract.
For the same reason (to minimize the air inside the engine), you want the end of the smaller test tube to almost touch the larger one when the piston is all the way out. The dimensions given in the plans are a good place to start, but you may need to adjust the test tube lengths after the engine is built to get this just right.
So, how big is the gap between the test tubes that you have available? If it is too big, can you find a pair that match more closely?
Sorry, I miss spoke(or miss wrote in this case). We didn't manage to get "20mm" test tubes, and maneged to get "21mm" test tubes.
We're hoping that this 1mm difference won't mess too much up, but I would love to know what you think about this.
I'm confused now. What are the sizes of the two test tubes that you have?
In particular, what is the actual, measured inside diameter of the larger test tube that you have? And what is the actual, measured inside diameter of the smaller test tube that you have?
-- Russ
I'm sorry for the very late reply.
The test tubes are still on there way, so we aren't able to actually measure the inside, but the diameter of the two test tubes are 25mm and 21mm on the outside.
Thanks for the update. I understand now. So your smaller test tubes (for the displacer) are just slightly bigger than the ones I used. Let's assume the larger 25 mm test tube has a wall thickness of 1 mm. That means its inside diameter will be 23 mm, which will leave a 1 mm gap between it and the smaller (21 mm outside diameter) displacer. That should be a little better than the slightly larger gap that I have on my engine, as long as the tubes don't actually touch each other. Any rubbing between the two test tubes would almost certainly create enough friction to keep the engine from running.
The test tubes arrived just today, and the inside diameter of the bigger one was 22.35mm and for the smaller one was 18.40mm. So it turns out that the inside diameters of the two are almost exactly the same to yours.
Our guess is that we might need to make the smaller test tube shorter to adjust.
You are right that getting the correct length for the displacer test tube (the smaller one) can be tricky ... partly because the curvatures of the round ends of the two test tubes may not match perfectly.
If you build the engine according to the drawings, the joint between the Piston and the Clevis will line up exactly with the end of the power cylinder when the flywheel is rotated so that the piston is as far into the power cylinder as it will go. Sometimes this position is called "top dead center". When the engine in this position, the end of the smaller test tube should extend to within 1-2 mm of the end of the larger test tube. Here's how to make that happen:
1. Intentionally make the smaller test tube too long by 5-6 mm.
2. Assemble the engine, but don't install the smaller test tube.
3. Verify that the joint between the Piston and the Clevis lines up with the end of the power cylinder as described above. If it does, proceed to Step 4. But if it doesn't, you should figure out why and fix whatever is wrong. If you don't, it's likely that the ports in the piston and cylinders won't line up properly either and the engine won't run for sure.
4. Remove the large test tube, install the small one (that's still too long) and replace the large one.
5. Rotate the flywheel until the end of the small test tube touches the inside of the large one. Then measure the distance from the end of the power cylinder to the seam between the Piston and the Clevis. Call this "X".
6. Trim the length of the smaller test tube by the distance "X" plus 1 mm. Then reassemble the engine. Now now the end of the smaller test tube should be about 1 mm from the end of the larger test tube when at the top dead center position.
-- Russ
Alex, can you join the forum at this URL:
https://www.chaski.org/homemachinist/
If you can, it might be better to start a thread so we can have this conversation there. For one thing, you may benefit from the wisdom of other people who happen to read and comment. Some of them are very smart and very helpful.
Also, it would be possible to include pictures to help explain some of the things we are talking about and maybe show your progress as you build your engine.
Thank you very much! I'll open a forum with the name "Manson engine" and post a few pictures of the progress so far.
However, due to some exams coming up next week, we won't have time to work on the project. I imagine we'd be able to restart in about two weeks.
We have finished our exams and have started a thread on the website with the name "seeking advice on manson engine". We weren't sure whether you'd be ok with us putting pictures of your blueprints on so we've only posted pictures of the parts we have made so far.
If you could check it out that would be great!
Thanks for starting the thread on the other website. We can continue this conversation there.
I don't mind if you post pictures of the plans, but it is probably not necessary because anybody on the other website who was interested has probably downloaded them already.
-- Russ
PS: I hope you saw my message here on May 13 at 8:03 PM about the test tube lengths.
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