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Member postings for David P Williams

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

Thread: DH89a Dragon Rapide
31/03/2020 16:03:40

I am contemplating starting the build of a 1/6 scale 96inch span DH89a Dragon Rapide.

I have two plans - the Jerry Bates one (which is actually the Bob Sweitzer one from 1982 that Jerry bought the rights to), and the Martin Tuck one from the old Nexus Plans. I also have the canopy and fibreglass cowls from Jerry Bates.

The Bates/Sweitzer plan is very detailed and quite complex - the Tuck one much less detailed and much simpler, although missing quite a bit of vital information. The Bates one has one piece wings (tricky to transport 8ft wings even in my large-ish estate and the Tuck one has wings that detach outboard of the nacelles (still a tight fit in the car !). I thought I might be able to use a combination of the two. I'm not aiming for a super scale competition model - just a good standard club scale one.

I've built quite a few kits, and a handful of builds from plan only, but they have been smaller and less complex than this, so this is a nice daunting challenge. Any online build blogs I can find (all of them a few years old) seem to end in unfinished models, which is a bit worrying.

I have one main question for you more experienced builders and designers and that relates to the wing aerofoil profile. Both plans show this to be undercambered, but all photos and info I can find about the full size aircraft appear to show a flat-bottomed section, albeit with a hint of reflex toward the trailing edge.

Somewhere online I found a set of Pilot's Notes, which stated that the aerofoil section is RAF34(Modified).

Below are ribs/section from both plans, a rib drawing from the full size servicing and repair manual, RAF34, and photos of a full size during restoration.

The Jerry Bates plan -

jerry bates plan rib.jpg

The Martin Tuck plan -

martin tuck plan rib.jpg

Rib from Maintenance and repair manual -

rib.jpg

RAF34 -

raf34.jpg

Full size restoration -

dh-89 2012-16.jpg

wing section2.jpg

Some of the historical builds from the Bates plan that I found online stuck to the plan profiles, others filled in the undercamber to give a flat bottom. So few of these made it to flying models with flight reports that it's unclear which version worked.

What would you do?

Thread: Tufcote / Furniglass
13/03/2020 11:41:21

I've used Deluxe Materials Aerokote with success. Does what it says on the packet. You can get a matting agent for it, so you can mix gloss to matt through varying degrees of satin.

Thread: Geoff's Jet Provost - Build Log
27/02/2020 17:27:53

Looks great Geoff. Yes I'm working on tip tanks - I think it looks so much better with them. I fired up Fusion360 and the 3D printer and made these. They weigh about 10g each without paint, just need to make sure not to add too much weight when I paint them. Need to decide whether to glue them on or use magnets.

img_1658.jpg

img_1659.jpg

Thread: Pushrod connectors
16/02/2020 19:37:17

I'm not insisting on using them Martin, I merely said that if you want to use them I think the SLEC ones with hardened grubscrews are the best bet. I usually only use them on the throttle lever of 4 stroke I/C engines as it sometimes makes the linkage in the engine bay easier, especially if the lever is close to the firewall.. I have used them, usually on ARTFs to replace the knacky ones supplied, for control surfaces and in all cases I've never had one go loose or fail, but YMMV.

16/02/2020 12:40:49

Denis beat me to it - yep, Modelfixings M3 grubscrews.

16/02/2020 11:48:38

Won't do any harm, but cup-point hex grub screws do bite into piano wire.

16/02/2020 10:49:06

If I have to use them, I use these from SLEC. I replace the screws with hex head grub screws and use loctite too. A tube or small socket used to press the starlock on gives a snug, pretty slop-free fit on the servo arm. They won't come off in a hurry - they take a lot of prising to remove if you have to.

Thread: How wings generate lift
13/02/2020 22:38:18

@Nigel - thanks, I was being over-sensitive, apologies from me too.

@Jon - Airbus, Boeing, etc are excellent at applying the effect, but it seems no-one has the definitive physics/mathematical explanation of exactly what's happening.

@others - I know it's a lengthy article, but if you read through to the end it explains the questions you are raising.

I knew that the Bernoulli’s theorem explanation had been discredited, and that an explanation based on Newton's Laws was the accepted version now, but there are things going on that are still not properly explained or accounted for.

13/02/2020 18:09:27

Have you guys read the whole article, or did you just see the Bernoulli’s theorem debunking bit and think "I know that" and come back on here to point out how stupid I was not to know that (I did). It's the stuff further on towards the end of the lengthy article that I found interesting.

13/02/2020 16:31:37

Came across this article the other day and found it very interesting.

Seems that all the stuff I was taught about how wings generate lift was wrong, or at least incomplete, but there still is no absolute definitive explanation.

Thread: On a lighter note
31/01/2020 16:21:13

Had a 105E estate (Deluxe!) in the early 70's. Used to thrash it from Manchester to Newcastle and back every weekend to see my girlfriend who was at Uni up there. Foot to the floor all the way, speedo needle pointing at the main beam warning light. Great car!

My mate had the van version. We used to roll both of them on their sides onto old tyres to weld up the floors.

Thread: SLEC Chipmunk build blog
31/12/2019 15:38:02

That's fantastic Tim, and quick too. I spent about 2 years on and off to finish mine. I tried to take a couple of pics of my u/c fairings for info. Didn't have space to get the wing down from racking but you may be able to see marks where it's hit the wing surface. They're unsupported litho plate, just attached to the oleos at the front, so they bend easily. The good news is that these models fly so nicely that they make even my landings into greasers.

img_20191231_143928768_hdr.jpg

img_20191231_143908114.jpg

30/12/2019 16:47:48

Tim - The fairings look great. I cut mine away at an angle where they meet the wing, as the legs do spring backwards on landing even with the oleos, and the fairings punch into the wing surface (assuming you have kept the rest of the torsion spring setup of the wire undercarriage)

Thread: ESM Tigercat - powered by Laser engines
05/12/2019 13:15:48

Yep - years ago a friend transported his Pitts that way too..

img_0254.jpg

Thread: New EDF Mini Jets- Jet Provost & Folland Gnat
04/12/2019 11:24:38

Good tip with the pipe insulation Tim. Bit of a three-handed job isn't it?

27/11/2019 16:04:23

Thnks chaps - I'll carry on pondering.

26/11/2019 17:05:26

Hi all, still busy assembling my JP.

How did you do the elevator linkage(s) - did you follow the plan? Seems a bit tight and fiddly to use wire and soldered on threaded adaptors with normal clevises.

Did you do the 'Y' linkage to both elevators? Was thinking of modifying to link the elevators with a joiner and run a single snake/wire.

What do you think?

Thread: Full size aircraft displays
23/11/2019 17:53:40

Also many years ago, 1977, I was an Officer under Training at Dartmouth Royal Naval College. One quiet afternoon I was involved in an inter-divisional cricket match on the sports field above the college when a pair of Buccaneers came reefing round over the Dart, rolled inverted and blasted above us at less than 100ft, waving through the canopies. Magic.

Thread: Laser Engines - Technical questions
22/11/2019 11:40:19

Bert - if you want to sell the 7-77 I have a Flair Stearman kit waiting for itsmiley

21/11/2019 12:42:53

Yes please Jon. I have an unbuilt Top Flite Giant Scale 1/5 Mustang kit in the loft waiting for exactly this engine.

Glow for me - the smell of petrol in the car and workshop makes me feel sick, so I would have to run a petrol engine on Aspen which would negate any fuel cost savings. I don't fly that much anyway, more of a builder than flyer, so fuel costs don't bother me. Never have a problem with any of my glow engines, including the cheap ones, as they're all tuned correctly. Can't remember the last time I had a deadstick, including the twins.

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