Model Boat Mayhem

The Shipyard ( Dry Dock ): Builds & Questions => Steam => Topic started by: flashtwo on August 19, 2014, 10:04:52 am

Title: Stuart D10 forward/reverse RPM
Post by: flashtwo on August 19, 2014, 10:04:52 am

Hi Mayhemers,

Having replaced the con-rods and cross heads and done some tests (see the "Good Vibrations..." thread below), I recorded much higher revs in reverse (astern) than forward (ahead) - 790 RPM reverse as opposed to 590 RPM forward for the same steam conditions.

I've checked the timing of the steam valve openings and it appears that in forward the valves start to open slightly after top/bottom dead centres, but in reverse starts to open at dead centres.

Then perhaps its also has something to do with the load imparted by the 5 inch prop (from Prop Shop). Does it impart less load in reverse because of the blade profile and allow higher revs?

Does anyone have any thoughts on this?

Ian

Title: Re: Stuart D10 forward/reverse RPM
Post by: Big Ada on August 19, 2014, 06:50:06 pm

Would changing the Hand of the prop help?.
 
Len.

Title: Re: Stuart D10 forward/reverse RPM
Post by: boneash on August 19, 2014, 07:26:54 pm

I think you have just set yourself a research project..... cast an equal pitch and area 3 blade prop and prove the possibility in the test lake!
Or  dry run the engine each way with a 'rope' around the shaft x times connected to a spring balance. An Absorbtion Dynamometer I think they were called.
Or the DC motor generator dyno, if you want to be modern!!
And then there is the grid tie possibility.....

cheers
R

Title: Re: Stuart D10 forward/reverse RPM
Post by: rhavrane on August 21, 2014, 09:12:40 pm

Bonjour flashtwo,


I have several steam machines including  D10 / Reeves Warrior MK3 among them. None of my steam machines runs equally on both sides, this is why I buy my propellers (Propshop generally) AFTER having tested the machine to determine its best side. 


I have discussed with professionals, this is normal, even if everything is supposed to be perfectly machined.


For my D10, I have choosen their  STD/4550/4/LH (http://www.prop-shop.co.uk/index.php?section=store&sub_section=productDetail&id=947&product_group=37) or RH /BR reference as you can see it HERE (http://www.youtube.com/watch?v=6SLqSuZjE94)  at 4'45" or THERE  (http://www.youtube.com/watch?v=utYZJDJPBVg)at 1'30".

Hope this will help you, best regards,

Title: Re: Stuart D10 forward/reverse RPM
Post by: TurboTyne on August 23, 2014, 09:06:32 am

Jim Bamford, in one of his brilliant articles in Model Engineer, (Oct 18th 1951, page 507) described a simple water brake dynamometer made from a syrup tin.  I'm half-way through building a more adaptable (I hope) version of something similar. (If we were not 300 miles apart you'd be welcome to use it).

Let me know if you want a scan of the article.

Regards  Mike

Title: Re: Stuart D10 forward/reverse RPM
Post by: flashtwo on August 23, 2014, 09:44:15 am

Hi,

Thanks for your replies.

Boneash reminded me that I had built my own simple prop that was the original one fitted to the engine. The prop is symmetrical and has flat blades and I'll make some tests with it to see how it affects the forward and reverse performance.

When I was developing the monotube boiler control system, I coupled the D10 engine up to a D.C. electric motor to act as a crude generator and load for the engine - I had considered an hydraulic brake at the time, but wanted a variable load as given by a rheostat in series with the "generator".

I have recently made a camera attachment for the steam launch and shall be taking some video down at Herne Bay tomorrow and put it on Youtube.

Thanks Rhavrane for the videos (with engine sounds) of your arrangements, it makes a very useful comparison.

Ian