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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: Aircraft General Discussion
14/08/2021 21:13:29

A DH Rapide has been flying around south of Bedford most of the afternoon. I suspect that it has been visiting Old Warden, possibly to give pleasure flights.

dh rapide.jpeg

03/08/2021 09:55:13

There was an air show at Old Warden on Sunday afternoon. Possibly aircraft from there. There was (I think) a Spitfire holding north of the airfield mid-afternoon that you might have seen/heard.

08/07/2021 17:45:41

The first scheduled flight that I took was on a Dakota. Every time I see one flying, it makes me feel old…

Thread: Self-Lock threads
26/06/2021 09:01:40

An interesting concept. Thanks for highlighting it.

Thread: Aircraft General Discussion
06/06/2021 15:46:21
Posted by Andrew Johnston on 06/06/2021 15:41:05:
Posted by Mike Poole on 05/06/2021 22:08:32:

You might get another look tomorrow.

Yep, she flew over my mum's house in north Bedford about 2 hours ago, heading SW.

Andrew

And she’s just gone over us (south of Bedford) on her way home.

Dave

Thread: Tokamak is still on the go
11/05/2021 11:17:34

ITER is aiming for 150 million degrees. JET is probably similar (it is over 25 years since I worked there...). The point of ITER is to scale up the JET reactor to get closer to a power reactor, i.e. one that can run for months and produce significantly more power than it uses. I am not sure how making a smaller tokamak fits in with that progression.

Thread: Multico high speed drill info
28/04/2021 18:40:09
Posted by Michael Gilligan on 16/04/2021 10:02:57:

Dr. Dave had a similar enquiry **LINK**

https://www.model-engineer.co.uk/forums/postings.asp?th=139922&p=11

... but apparently drew a blank with the links that I provided.

It looks a mighty useful machine [deep throat], so I hope you have more joy.

MichaelG.

Blimey, you have a good memory, Michael! I never did manage to find any info on my drill...

Dave

Thread: Have You considered getting a 3D printer
16/04/2021 19:59:12

Spurred on by this thread, and an Amazon voucher from my employer for Christmas, I finally bit the bullet & invested in a Sovol SV01 printer. It only took a matter of days for Mrs Dave to go from "and what are you going to use that for?" to "magic has entered the house!".

After printing a few tool and collet holders from Thingiverse, I tried a dial gauge holder: not only is it too big for my dial gauge, but it didn't fit the QC tool post either... So, out with the CAD, measure up a standard Myford tool holder and a few hours later, this appeared:

dial gauge holder.jpg

The gauge is a nice push fit and it fits the tool post as-is. It just needs the screw for height adjustment (I printer an M5 thread to see how effective this would be.

Chuffed with the result!

Dave

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...

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