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Member postings for DrDave

Here is a list of all the postings DrDave has made in our forums. Click on a thread name to jump to the thread.

Thread: Recommended suppliers and services
07/04/2021 12:44:17

My go to company for most milling cutters is Cutwell. And MSC can have tools at a respectable price in their monthy “Flyer”.

Dave

Thread: Model Turbines
22/03/2021 20:30:51

Byron,

If you removed bearing R2' and increased the shaft diameter between the remaining two bearings, that would give you a small increase in stiffness. The biggest increase in stiffness would come from adding a bearing in the left hand housing, on the opposite side of the turbine from the existing bearings: is there a reason that you cannot do that?

And keep up the good work. It is fascinating watching your development process.

Dave

Thread: A Marine Condensing Engine
14/03/2021 20:01:50

That is impressive: thank you for showing us how you assembled the raw parts to make the "castings". I have learned a lot of the Black Art of cast iron & JB Weld!

Dave

03/03/2021 12:46:19

It is very impressive, the detail that can be created from bar stock & JB Weld! I must try harder...

25/02/2021 09:16:15

Tug & Jason: thank you for your replies (regarding the angle between the cranks). There is also the relatively large pipe joining the HP cylinder to the LP cylinder which will help, too. My mind has been put at rest!

In my own defence, I had just been watching a video of Ilmor’s 5-stroke IC engine, where the phasing of the exhaust from HP to inlet of LP cylinders is critical.

Dave

24/02/2021 19:40:47

For a compound steam engine, does the angle between the cranks have a significant effect on how well the engine runs? I.e. is there an optimum angle where the exhaust valve for the HP cylinder and the inlet valve for the LP cylinder work together and give more power than a more random timing?

Or am I over-thinking this?

Thread: Design of boilers
24/02/2021 19:20:20
Posted by Bob Worsley on 24/02/2021 17:49:26:

Stefan-Boltzmann is THERMAL transfer of energy, and as such does not cover all wavelengths of electromagnetic radiation for the simple reason that only around the infra red is heat transmitted. Perhaps you need to read a few books and then apologise.

That's an interesting statement! I dug out one of my old text books, "Heat Transfer" by JP Holman to see what he might have to say. "When the energy density is integrated over all wavelengths, the total energy emitted is proportional to absolute temperature to the fourth power.

Eb = (alpha) x T^4

This equation is called the Stefan-Boltzmann law."

There then follows more than 20 pages of theory before the equations for heat transfer are derived. These are a function of (T1^4 - T2^4), but also include emissivity factors and shape functions. Note that this difference in temperature to the fourth power is for heat transfer: it is not Stefan-Boltzmann's law.

I recall from my Heat Transfer course many years ago that calculating the shape functions is fiendishly difficult, except for trivial examples. Even the finite element program that I was using last year, and which has a thermal analysis capability, is not brave enough to attempt it!

Dave

Thread: Engineering / Modelling Books for Winter Evenings?
10/02/2021 18:35:05

“A View from the Hover” by John Farley gives a good insight into the development of the Harrier and the life of a Test Pilot. It is also a good read.

You might struggle to find a copy, but “A General Account of the Development of Using Atomic Energy for Military Purposes under the Auspices of the US Government” is fascinating! Published in 1945, shortly before the first atomic weapon test, it details the physics, chemistry and industry required to go from a pin-head sized piece of fissile material to the amount required for a bomb. Before you ask, I inherited it from my dad who got it back in 1947, according to his entry on the cover.

Thread: A Marine Condensing Engine
07/02/2021 20:55:28

Hi Tug,

You lost me at “slip jointed”, I am afraid. Could you explain that in a little more detail, please?

It looks like it will be an interesting engine when finished. I will be following your progress keenly.

Regards

Dave

Thread: General Aeromodelling Discussion
03/02/2021 20:42:26

For some reason, I have very few pictures from my aero modelling days. This is not me, or anybody that I know. However, I was impressed that anybody would dare to fly a free flight model that size!

This was at a Shuttleworth Aeromodelling day some years ago.

shuttleworth free flight.jpeg

Thread: 3D Printed CNC soft jaws for work holding
03/02/2021 12:29:19

That looks to be a really useful method of holding delicate work: why didn’t I think of it? A 3D printer is rapidly moving from my “desirement” phase to my “must have” phase.

Thanks for sharing this.

Thread: General Aeromodelling Discussion
29/01/2021 13:33:57

The smelly old diesels did have one beneficial side effect. The shot of amyl nitrate in the blood when they back-fired and the prop bit you finger...

Thread: What Did You Do Today 2021
28/01/2021 21:45:59

I have been following Turbine Guy's 3D printing in metal with interest. This looks like an ideal solution for the cam covers on an engine that I am building. There is a lot of detail that is really not suitable for machining, such as lettering.

I finally got round to uploading a file tonight to get an instant quote for aluminium printed parts. One company wants £480 for two, the other $400 for two. Plus import duties and all the other taxes. They are only 133 mm long, for goodness sake.

Time for Plan B.

Thread: General Aeromodelling Discussion
27/01/2021 18:25:16

There seems to be a pattern here. My first model ‘plane was (I forget the maker) a plastic control line Hurricane with a Wen Mac engine. It didn’t end well. As a thirteen year old, I seem to be a late starter, I knew that an aeroplane had to take off into wind. I broke the model before I learnt that, with CL, you take off down wind...

We then moved to SA and a school friend introduced me to proper model aircraft. A Golden Bee on the front of a balsa and nylon cloth CL combat aircraft. That was magic and the seed was sown!

In contrast to most people, I did have a couple of goes at changing to RC flying. I got so bored with flying too and fro in straight lines that I didn’t last longer than a couple of flights. Not for me.

Edited By DrDave on 27/01/2021 18:26:04

25/01/2021 19:36:36

I was in SA many years ago, but no longer, Joe. I used to fly speed in the mid-seventies, when Basil Mengies was the King of Speed.

Then university got in the way...

25/01/2021 17:09:10

kandb speed aeroplane.jpeg

As a lad, I used to fly this speed aeroplane at the Rand Model Aeroplane Club. It was powered by a 6.5 cc K&B Torpedo engine. Great fun, even if it go home as "pieces of eighth" at times...

As an aside, some years later, I was having dinner with a friend. Conversation eventually got round to aero modelling, at which stage his son gave me a sideways look and asked whether I used to fly a 40 speed 'plane at RMAC. I did. To which he replied that he and his friends used to hide behind the car when I flew!

Thread: Tether car
25/01/2021 10:59:54
Posted by Old School on 25/01/2021 10:44:39:

8126ea6d-c7ae-468b-b23e-a15caf3f58a8.jpeg

Hi Old School. Is the arm that pokes out the top a fuel cutoff? I have never seen tether cars “live”, only on YouTube, but they are most impressive.

I used to fly control line speed. I keep getting the draw to go around in circles again, but I have managed to beat it off so far!

Thread: Model Turbines
03/01/2021 20:59:30

That is really useful feedback on Shapeways. Their customer support & turn-around time are impressive, especially over the feastive season. I am intending to try their 3d printing in aluminium shortly, based on the input from Werner & yourself.

Dave

Thread: Unusual Project
11/09/2020 19:30:03

Speed model

You don't need a symmetric aeroplane for it to be able to fly...

Thread: Make your own Tokamak
02/08/2020 20:41:31
https://youtu.be/vYvhxqTjAsg
I think that I need a 3D printer...
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