Strictly.... “ Hot Air “

[Alyn Foundry]

" Graham
Not strictly from rejects, but definitely Robinson related. A few weeks ago I managed to acquire an unmolested set of castings for the Robinson hot air engine, still I think, in the original packaging. There is one drawing, is that all? I don't quite understand how the displacer piston goes together, what material did you use. I was thinking of thin wall brass tube with sheet brass end pieces, made to be a slack (maybe 30 thou) fit in the hot end cylinder. How hot does that get? Can I use soft solder on that displacer piston?
The other bit I don't understand is what seems to be a governor valve in the end of the cold cylinder. How does that work?

Regards

Richard "

Hello Richard.

We'd love to see some pictures of your acquisition, I'm hoping they look better than with my now famous " Special coating " ?   

Yes, only one drawing. This was an emulation of how Gardner did theirs back in the day.

The displacer is best made from a ready made lightweight Steel tin, the process and utilisation of same has been covered in previous pages.

Yes it's a governor and it works by air trying to pass the disc and drawing the disc onto a shoulder that then closes the transfer port. A couple of small holes drilled through the disc prevent the engine from stopping dead.

Please use this thread to detail your build progress and feel free to ask any questions that may arise.

Cheers Graham. 

[Mcgyver]

As this is an open thread please post any “ Hot Air Engine “ related builds or pictures of your engines here.

Lots of hot air here, just ask my wife.

I didn't see any Rider Ericsson models, so thought I'd put some up of one I made, probably 10 years ago now.  Its great runner, pumps water well.  A few deviations from the drawings, the power cylinder I machined and then lapped the bore.  For the piston I shrunk some bronze rings on the AL piston and turned them in situ.  My thinking was to get good performance it needed minimal clearance, minimal contact area between the cylinder and piston (rings) and both should be very round, straight and smooth

[Perry]

Hello Mcgyver, what a beauty you have there. Very attractive in that green paint.   

[Alyn Foundry]

Hello Mcgyver.

Many, many thanks for posting the pictures of your Rider Ericsson hot air engine. It looks lovely, what scale is it?

I have a set of un started castings, well apart from the finished flywheel.... Mine has the 11” diameter one.

Cheers Graham.

[Jasonb]

Watch out Graham Jo will be after those

[Jo]

Watch out Graham Jo will be after those

We are still waiting for pictures of his Welsh  Casting Gold Mine 

Jo

[Mcgyver]

It looks lovely, what scale is it?

I have a set of un started castings, well apart from the finished flywheel.... Mine has the 11” diameter one.

Thank you, its 1/4 scale irrc.   11" sounds about right for the flywheel.   

The full size were made in different sizes - I couldn't tell you what size the model is of.  A while ago I visited a chap in the Muskoka area who had a great collection of full sized mechanical things including two Rider Ericsson engines.  Here's some snaps I took.  Digging them out reminds me of the of a few finishing bits I haven't gotten around to yet on mine.

[b.lindsey]

That is a lovely R.E Mcgyver. Still one of my favorite engine!! I agree it looks good in the green also.

Bill

[Alyn Foundry]

Hello All.

Finally, the weather has improved here and I ventured out to the workshop.

Geof of the Anson engine museum asked me to make him a Robinson for the upcoming 150th anniversary of L Gardner and sons engine business.

Pictures of the start on a rejected platform with very poor lettering.

Cheers Graham.

[Chipmaster]

Here are some pictures of my crab meat tin displacer. To avoid tangling the drill with the stainless steel scouring pads when drilling the central hole, I soldered a small tube inside the tin to keep the scouring pads away from the drill.
P1070307 by Andy, on Flickr
P1070311 by Andy, on Flickr

and here are three pictures of the governor with small holes to avoid bringing the engine to an abrupt halt.
P1070400 by Andy, on Flickr
P1070399 by Andy, on Flickr
P1070401 by Andy, on Flickr

The shaft is peened over the disc to retain it and the disc is sucked against the flange that can be seen in these pictures
P1070394 by Andy, on Flickr
P1070396 by Andy, on Flickr

This part of the engine gets very rusty. what are your governors like Graham? 

Andy

 

[Alyn Foundry]

Hi Andy.

Poke, poke....

Ahem, I didn’t fit one to mine!

However, your excellent photos should help with Richard’s recent enquiries immensely.

Whilst supping my mug of “ roseylee “ I was thinking about a couple of other hot air engines that you rarely see like Hayward Tyler and Bailey. Has any member here built or scratch built any models ?

Cheers Graham.

[Alyn Foundry]

Anson " commission " update.

Overall time 2 hours give or take.

Cheers Graham.

[Perry]

Hello Graham and all. Since my first try on stirling engine  http://www.modelenginemaker.com/index.php/topic,6504.0.html   I found great interest on this topic and would definetly like to build more hot air engines in future.
I’d like to take advantage of this hot-air dedicated thread and ask few questions :


1.   Lubrication

Beautiful, above pictured Rider Ericsson may be a perfect example and I would like to understand what is the lubrication practice for power piston and displacer piston rod and how to ensure that oil will not get to the bottom of the hot cap after some time.

In my experience with my brave little stirling is that after some running time (hours) tiny amounts of light oil, that I use to lubricate displacer piston rod, will leak trough gland and find its way down to hotcap bottom, this resulting in oil burning/smoking inside and affecting engines performance. ( I dont lubricate power piston at all)

Is this not an issue with full size hotair engines and larger models?

2.   Regenerative displacer piston

Grahan, watching your progress with Robinson engine made me thing about this topic, I’d like to understand, if in this scale, does the regenerator actualy add anything to the  performance of engine.
Specificly,if the enlarged „dead volume“ introduced by the regenerator does not take away the bebefit of the regeneration. Fully enclosed displacer piston would not create this additional dead volume.

And sub. question to this topic: why is stainless steel wool/mesh a good choice for regenerative purposes? I undrstood that SS is good for displacer piston due to low thermal conductivity.Isnt good / high thermal conductivity a property that is desired for good regenerative function? Would cooper mesh be usable / better / poorer option ?


Many thanks for all answers

Perry

[Alyn Foundry]

Good morning Perry.

You have raised some interesting questions.

Re. Lubrication.

As we all know the smaller you get in size with a hot air engine the less power you have, even the lubricant can cause drag. Luckily the half scale Robinson is large enough to cope with ordinary engine oil.

Over a long period of time oil does get into the hot end and “ cook “ but never really caused any problems as we ran them at outdoor rallies.

Re. Regenerative displacer piston.

You raise a good point about the use of Stainless Steel as opposed to a Cuprous material. The thermal efficiency of say Copper would be far superior but according to record Robinson’s used perforated Iron sheets.

Whether or not the use improves performance, I cannot answer with any confidence, but....

We tried both a sealed empty tin and a fully stuffed open tin displacer in the same engine. We found with the sealed tin the engine wouldn’t exceed a certain RPM no matter what the heat intensity was. With the stuffed and open tin the engine would accelerate with higher heat.

Our conclusion was that the air in the closed system had to get around the small space of the sealed piston causing drag whereas with the stuffed piston the air could move much more freely.

Cheers Graham.

[Ian S C]

For the regenerator you do not want the heat to be conducted from one end to the other. Andy Ross in his experiments with regenerators found that the best he could come up with was stainless steel foil with dimples on it to separate the rolled sheets. Stainless wire and mesh have been used, you have to be careful with some engines if you use stainless(or non)steel wool as it can break up and the bits get in the wrong places.
Ian S C