Office of Steam Forum for Model & Toy Steam Gas & Hot Air Engines

Question: is it truly a stability issue due to the CG being too high, or could it be just that the CG is slightly off the centerline to starboard?

On another note, I'm guessing you'll be installing a larger diameter exhaust line next to eliminate the back pressure you seem to be experiencing. Perhaps also tightening the cylinder pivot a bit as well, to allow for higher pressure operation?

Hi Daniel,

Question: is it truly a stability issue due to the CG being too high, or could it be just that the CG is slightly off the centre line to starboard?

I think a bit of both. The boiler has two water tubes under it so making it about 12mm (1/2") higher than it might be, the hull has a beam of 105mm (4.1/4") and the boiler casing with the boiler is the same height, and when the boiler has water in it, it is quite a weight.
Yes, the centre line of the CG is off, mostly due to the burner having no fixed position under the boiler, this now has been fixed.

On another note, I'm guessing you'll be installing a larger diameter exhaust line next to eliminate the back pressure you seem to be experiencing.

Yes, a short, larger diameter stub exhaust pointing over the side has been fitted. There aren't many photographs of a Henley available but several show the exhaust going straight from the engine to the side.  There isn't a lot of space between the boiler and its casing for an exhaust pipe of any diameter, the pipe also has to be fairly long and has several tight curves in it.

Perhaps also tightening the cylinder pivot a bit as well, to allow for higher pressure operation?

The spring is set to its optimum; regarding pressure against friction, I have had similar problems before. Too much steam and engine at terminal velocity, fitting a regulator would fix it, but why take the easy way, but I might end up fitting one.  Henley's weren't fitted with regulators.  My thoughts at the moment is to partially cover the burner to reduce the heat and/or fitting a smaller diameter steam pipe to the engine. With the burner fixed and ballast to keep the hull vertical fitted another steam test could be made, but with the temperature down to -5C there will be serious ice in the test take and the domestic authorities are not keen on steam in the bathroom unless it comes from bath or shower; thought, I might think of taking a long shower?

Take care Tony.

Hi Raphael,

Other question, would your steam machine need an oil lubricator as I don't see anyone?

The Stuart Turner Henley weren't fitted with either regulators or lubricators, and at least for the start I am not going to fit them. But who knows later maybe.

I know that wet team is self-lubricating but perhaps would that help a little for steam sealing?

Yes, I think using steam oil might improve the sealing at the engine port face.

Concern, you should have to install an oil separator to the exhaust to prevent oil going on the water...

Again yes, but given the lack of room between the boiler and engine, along with having to be able to remove the burner fitting a oil separator and its reservoir isn't really practical.

Other possibility, add a sheet of Teflon on the cylinder faces like this.

I haven't heard of using Teflon for port faces, how is it held in place and does it wear well, alas I have no French so didn't understand the cometary. I have used PTFE instead of 'O-rings' which works quite well

After yesterdays -5C temperature it is a balmy +3C today, so if I manage to finish the modification on the Henley perhaps another steam test will take place.

Take care Tony. 

Hi Raphael,

Thank you for posting your video, it is very interesting, alas the port faces of the ST engine are very small and are totally covered by the port face of the cylinder, so there is nowhere to use screws to hold the PTFE.

The temperature here has risen to 10C today, yesterday it was 5C, the ice in my test box was 12/15mm thick and had to be broken up and replaced with warm water for me to test the modification's made to the Henley.  These modifications consisting of a brass weight screwed to one of the longerons of the hull to improve the hull's stability, it now sits vertically in the water but is still a little tender being slow to recover when displaced. A new fore deck was made from tin plate to replace the thicker aluminium one made, I should have thought there wasn't much weight difference as aluminium is about a third of the weight of steel, if thinner aluminium becomes available I will make another deck. A lighter funnel has been made and fitted. The burner now sits on a carrier which holds it in one place centrally under the boiler. The burner is now covered for a third of its length to reduce its heat output.

What difference did these modifications make? Well the engine maintained what seemed about the same speed for ten minutes before the flames died back, I had though it might have run longer because of the shorter length of the flame. The engine leaked considerably less steam. Using less steam was reflected in the fact that when the boiler drained they was 25ml more water removed, so some progress?

Alas my camera ran out of battery before I could take all the photographs I wanted which might be a relief to some.  I think an open water test next when it can be arranged. I live very close to a large lake which isn't very suitable for model boats which aren't radio controlled, but maybe a length of string tied to the rudder post?

Take care Tony.

Bonjour,
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