Strictly.... “ Hot Air “

[Jasonb]

It's coming along well Jo, will this one be considered safe enough you you to play with alone?

Spent a bit more time on mine this evening and got a couple of 10min runs on the blow torch before things got a bit too warm. Also started working on a gas burner, it's still a bit too orange a flame which makes a bit of soot so will make a few alterations to get a bluer flame. The burner is much quieter than the blow torch and the engine itself makes very little noise which is nice. The Jumping about was only because it was not sitting firmly on the fire bricks.

<a href="https://www.youtube.com/watch?v=wdpskBAPUHE" target="_blank">http://www.youtube.com/watch?v=wdpskBAPUHE</a>

[Jo]

I thought those little engine ran on night light power 

It's coming along well Jo, will this one be considered safe enough for you to play with alone?

Actually any engine running is going to have to be re-evaluated as my running crew has come up with a new excuse to save his thumbs in that he can't visit any more    I think this engine might be safe enough for even my thumb to be allowed near and it needs to be running before 24th November 

Jo

[Jasonb]

I did try a tea light, you can just see it on the left at the start of the video but my alternative base does not allow enough air in so it goes out or burns very weakly. I've ordered some Mamod fuel tabs to try, that is what Dave was using on his at Bristol, Might also try some meths

The gas is clean and practical and uses the same small camping gas bottle and hose that I use for CHUKY

[Bertie_Bassett]

looks like a nice runner Jason 

once iv got my workshop rebuilt something similar is on my 'to do' list

[Alyn Foundry]

Good morning.

I had one customer that informed me of a successful run using a night/tea light candle. He was a master at model engineering.

Every moving part had been hardened then mirror polished. He had turned several grooves into the piston to reduce drag.

The major difference was that he had reduced the thickness of the hot pot bottom to thousandths of an inch.

A handy burner for this engine can be made by using either the Primus 8842 or the 8719 as a perfect gas mixer. The chamber can be made from any piece of off cut metal you have around 40 mm diameter.

Cut it deep enough so that the burner can be press fitted into a hole drilled into the side. Bore out a cavity to around 36 mm diameter leaving a couple of mm left at the bottom. Counterbore the opening to 38 mm at 1 to 2 mm deep. The gas ring is made from metal that fits the counterbore. I used to use my Gardner chimney top turned upside down for this. The upturned edge provided a barrier to wind that would otherwise blow the flames out.

I often wondered if the matrix from one of those portable gas heaters cemented in would work. Never tried it myself. With Diamond hole saws now readily available it might be worth a try?

Cheers Graham.

[Jo]

Bluechip and I have just had a little fondle of the hot pot for my engine and Dave agreed with me that as drawn it is going to take a fair while to get the pot anywhere near hot enough to run so it is probably worth reducing the thickness of the bottom a tad.

I also noticed that I fitted the cylinder for the displacer before I ate the contents and the displacer tins seem to have expanded now that they have had their caps removed 


I have not yet got as far as thinking about the gas ring I have enough problems that I have found I have plenty of 3/16 Whit taps but the only dies I have in that size are blunt 

Jo

[Jasonb]

Single point them

I was wondering if one of the small cheap camping gas rings would do for these larger engines, just take the legs off and you have a burner about 40mm across, I have one you can try when the engine is made.

https://www.ebay.co.uk/itm/Super-Mini-Portable-Camping-Gas-Powered-Butane-Propa-Stove-Burner-Cookout-Picnic/132482835729?hash=item1ed897a511:g:gYsAAOSwokJaalOc

[Alyn Foundry]

Hi Jo.

Regarding the hot pot base thickness.

You have three options really. The first is to leave it as thick as possible. This makes the heating time the longest but the advantage is that on a windy rally field it won't stop running.

Reduce the thickness a little and have an engine that starts and runs reasonably quickly.

Or go wafer thin for almost instant start and stop.

The choice is ultimately yours.

Cheers Graham.

[Jo]

I was going to give it a try as it is then look to go thinner later

Jo

[Jasonb]

Last night I was sent a couple of extracts from an original No5 drawing, it shows the power piston with a number of grooves along it's sides and I think the curved bottom of the pot is given as 3/8" but it's a bit hard to read but looks to be that compared with other dimensions so would equate to 3/16" on the half scale model

[Alyn Foundry]

Hi Jason.

The grooves in the piston will reduce the friction to a degree but we found that our engine ran just as well without them.

Regarding the curved hot pot bottom I naturally assumed it was done that way to increase the heating surface area. We didn't try to copy this but the thickness of our casting would allow the builder to put a slight radius into the bottom of the outside, you could even round off the bottom corner too.

Cheers Graham.

[Ian S C]

The groves on the piston form a labyrinth seal, and i supposed to increase performance, but I'm not too sure. Only disadvantage 'v found was when I thinned the skirt of a piston a little too much, and the skirt fell off. Skirt thickness I was aiming for was about 1 mm, the groove about .25 mm, well it was a bit of old window weight after all.
Ian S C

[Chipmaster]

Yesterday I was talking to Graham about castings and heating Robinson Hot Air engines. Graham suggested I added some pictures of the propane burner I made for my engine on MEM as they are cheaper than buying Primus / Sievert 8842 burners.
A few years ago having bought a commercially manufactured ceramic burner to suit a Stuart 504 boiler I thought I could save money by making my own. At the time I found it difficult to obtain the honeycomb ceramic material for a reasonable price. However, it now it is widely available particularly on ebay. I have also used the ceramic honeycomb material salvaged from Super Ser portable gas heaters but it is difficult to remove the material in one piece.
The pictures of the burner I made for my Robinson Hot Air engine show how simple it was to make. The brass body is held together with silver solder and the ceramic material is sealed round it's edges with fire cement. the optimum flame is obtained by adjusting the gas / air mix by moving the jet in or out of the Bunsen type mixer tube.

Gas jets threaded 1BA are available in a range of sizes from several suppliers including,
Chuffed2Bits http://www.chuffed2bits.com/page9.html
Forest Classics https://www.forest-classics.co.uk/ceramic-burners/round-burners/bix-001-2-diameter-x-1-deep-round-burner


Andy

[Alyn Foundry]

Good morning Andy.

Many thanks for posting your pictures.

I suggested the use of Primus/Sievert burners as all the " headache " of getting the air to gas ratio correct has been done by the manufacturer. They aren't cheap however and your solution is far less expensive.

Viewing the flame sees perfect combustion.

I take it the tank is refillable? Butane?

Cheers Graham.

[Jasonb]

Andy, what dia is the burner? if about 40-50mm the little camping stoves I posted a link to above would do similar

There is a drawing for a burner to go with Sandy's 3" vertical boiler which is almost identical to your burner should anyone need a drawing, it's in the plans and drawing section.