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Member postings for Dave Cooper 3

Here is a list of all the postings Dave Cooper 3 has made in our forums. Click on a thread name to jump to the thread.

Thread: Which Set Should I buy
01/11/2018 11:48:53

Hello Eric

I'm in a similar position to you. If budget comes into it, then I think Taranis (FrSky) is worth a look. Good range of Tx and Rx and you could still go with Hitec servos, hence, a minimal mix.

Not sure about service though - with 2.4 GHz gear most components are 'surface mount' ie non-serviceable (at least for me). So, it's straight-forward replacement if it goes wrong I suspect. Probably best to check on warranty for the Tx though.

Most of the flyers at my club use Taranis and report no known problems....I guess time will tell ! You can use something called "OpenTx" (firmware) which is fairly easy to set-up on your PC with a little familiarity. Plenty of help available on-line also.

Good luck

Dave

Thread: EDF efficiency
30/10/2018 21:06:59

I wonder if anyone has investigated the number of fan blades and the rigidity of the fan housing as key variables to efficiency ?

I'm looking at installing one in a Jet Provost model next year (about 46" span), and, one supplier suggests that a twelve-bladed fan in a metal housing would be best. I think the recommended O/D was 80mm. On asking about the cheaper plastic Chinese fans, the advice was to walk away...

On reflection though, if the fan housing is tightly constrained by the duct walls - would it actually 'flex' that much ?

Dave

Thread: Flying a Turbine
29/10/2018 19:56:56

I wonder if a possible approach for clubs would be to operate a 'risk-assessment /planned progression' approach :-

1. A new member wanting to fly turbines would first have to demonstrate safe, competent flying on a fast(ish) EDF model. Either their own, or, possibly owned and operated by the club.

Main benefit - no (or little) fire risk. Failsafe(s), installation checks etc to be regularly carried out by a competent club examiner. 'B' cert to be encouraged, but, let 'A' cert's progress to this on EDF first.

2. Existing members will be known to others. If they are 'top-notch' fliers then let them go the turbine route if they want to but with compulsory technical checks as above. If they refuse - what are they hiding ? 'Progressing' members - EDF first.

It only needs one bad accident to lose a site (or, heaven forbid, a life)....

My own planned progression here for your comments :-

Year 1 Airfix kit /scale drawings of a jet provost

Year 2 PSS model jet slope soarer

Year 3 EDF Jet Provost or similar 'straight-wing' jet

Year 4 Professional turbine flying lessons / Jet build

Year 5 Maiden jet with professional / v.experienced club member on buddy box

Overkill ?

Dave

Thread: Reduction Drive Design
28/10/2018 21:47:28

cymaz - I only have very limited theory on this but I did look into it last year for a turbine-powered LMA Westland Wyvern (reduction gearbox with contra-rotation props). Hardly an SE5 I know, but if using a simple 'toothed belt' drive we calculated a power-consumption loss of about 10-15% of quoted 'driveshaft' bhp. Whereas the full 'planetary' gearbox was soaking up some 25% with spur gears (noisy, but efficient !) and anything up to 35% for helical gears.

Prop's also vary enormously in efficiency (we were planning on variable pitch to help with this), so, I would advocate the simple test rig approach - perhaps 2 or 3 props of the same diameter but with sensible pitch spacing. Take thrust measurements at a set rpm (spring extension /Hooke's law). Repeat test with different tooth ratios on the belt set-up (driven over driver gives the gearing ratio....)

You may find you need a different engine or a change to a more efficient prop design. I think I would stay with two-blader's as 3's and 4's add complexity (as well as cost !). BTW those are BIG prop's so take care near the test rig ! Also, have a close look at torque /bmep figures /curves when choosing an engine - these may be more critical than quoted bhp figures especially if going the bigger pitch route.

Good luck

Dave

Thread: EDF efficiency
28/10/2018 09:21:27

Just a thought :- When designing the radiators on my Le-Mans style sportscar, I went for a 'tight fit' between the radiator edges and the duct wall thinking that this would give the best result (it's a ram-air duct design). However, one day in the model wind-tunnel (10% scale), one of the radiators detached on one side and suddenly we were getting better mass-flow figures from the duct exit.

Next experiment was to fit smaller radiators with a small air gap between the rad's and the duct walls - result even better mass flow. No heat input to the rad's as all measurements were cold. This could, of course, just be reduced drag. Maybe a simple experiment with an EDF fan in a larger duct O/D to I/D could yield an optimal gap between the fan casing and the duct wall ?

Dave

Thread: Hi From Bristol!
27/10/2018 00:02:47

Woodspring might be worth a look (nr Gordano). They do fabulous display days as well.

If you're thinking of going EDF / turbines in the future then they have that covered too.

Last I heard Beaufort have a waiting list (at least for their Badminton site)...

Regarding your Tx, I'm currently building up some RC test equipment - mainly for Futaba 35 MHz kit, so if the problem persists, I may be able to help. Got the builders in next week laying a new workshop floor etc. so, not for a while yet though.

As a first step, you could do a continuity /resistance check between the battery connector and the main RF board. If the Tx has been stored for quite some time with the battery in and connected, there is the possibility of some 'black-wire' corrosion. NiMh's don't normally suffer with memory problems but they do lose storage efficiency after a certain age.

Dave

Thread: Grumpy old git returning
26/10/2018 23:12:09

Hi Don /Nigel

I also fly full-size gliders - it's amazing how much they vary with different designs of airbrake / flap combinations.

Our club's strip is orientated more or less east-west and we often have a 90 degree x-wind, and, being on a hill-top has significant turbulence in north-westerlies. If using a model here it would be difficult to get a 'compromise' flap /elevator mix for all conditions.

For this reason, I'd have a basic mix available but have it 'switchable' as well. I know this is one more thing to fret over on a busy approach, but, maybe just use the mix on calm days to start with.

Having said that, I probably will use just the sticks most of the time !

Dave

Thread: Which part of building a new traditional balsa model plane do you enjoy the most?
26/10/2018 17:19:29

Three things :-

1. The smell of cellulose dope just before covering /repairing.

2. When things line-up exactly like dowels and screw holes etc. - doesn't happen very often for me but when it does it's magic !

3. Wings rocking gently as the vintage model taxies slowly over freshly-mown grass.

Simple things eh...

Dave

Thread: Grumpy old git returning
26/10/2018 16:55:50

Hi Nigel

Yes, a pitch-change with flaps is quite common. If you have a 'computer' Tx though you could mix in some down elevator to alleviate. this. Otherwise, it's a case of getting ready for it with the old thumbs !

I now do my 'aerial experiments' at about 300-400' giving me a bit of thinking and recovering time...

Dave

ps Some models will need different elevator trim with flaps depending on how the centre-of-lift moves about

Thread: Matador 60
25/10/2018 12:28:31

By Googling "Making the Matador 60 glow engine" - will bring up quite a few useful links (sorry was not able to post here).

There is one very good one from the "Model Engineers Workshop" site giving any build 'problem' areas - eg valve seats, left-hand crank threads etc. (These should not be a problem to experienced machinists but an amateur, such as me, may need to seek help !)

There is also some useful info' on expected performance figures for various prop sizes - 0.44 bhp for one build which should help with matching to a suitable size model.

There doesn't appear to be any 'exotic' materials or heat-treatment mentioned although one builder did report making the crankshaft out of a large HT bolt.

Dave

25/10/2018 10:15:02

Just a word of warning to others contemplating this build :

The gears that are used to drive the camshaft are no longer available from the supplier listed on the plan.

This info' came from another forum. The supplier listed, is, I believe "Moffats" and the gear wheel pairing is I think simple "spur" type. Someone else mentioned "APC" as an alternative supplier, but, I'd have thought that a trawl through Model Engineer magazine would produce something...

You could, of course, machine your own gears if all else fails but this would need some fairly sophisticated workshop tooling.

Dave

Thread: Grumpy old git returning
24/10/2018 23:08:51

Hello Nigel

Talking of STOL, I am just finishing a KK "Achilles" with some leading edge 'slats' of my own design. I converted it to RC and electric some time ago. I added a couple of extra wing bays to cope with the weight gain over rubber etc. It has lightweight Rx and servos working both the elevator and rudder via closed-loop 40 lb fishing line.

The tiny Rx is a signal-processor type and can 'memorise' the last command in the event of Tx signal failure....a friend maiden'd it for me and it needed a 2p piece on the nose to get the CG right. (Why do I always build heavy tails !!!).

The hope is that the slats will permit slower, high-alpha flight, although without the added benefit of flaps as well it probably won't rival a Feisler Storch. Still it's fun to experiment even though the parts for the conversion are really now too small and fiddley for my ageing fingers.

Dave

Thread: RC Test Equipment
24/10/2018 19:09:42

Thanks for the info' Pete - I'll get checking !

I'll dig out my old magnifying glass to check the PCB - have already tested the plug-in Xtal but will now check the fixed one too.

I got a X10 probe with the 'scope and I found an instruction manual on the internet.

Will call for a chat soon (I'm bound to miss something important !).

Dave

Thread: Matador 60
23/10/2018 22:22:22

Hi All,

Has anyone made a "Matador 60" four-stroke glow engine from plans ?

I have the plan(s) for one plus a box of raw materials. I'm currently looking for a small lathe with milling attachments to do the machining work on.

As the plan dimensions are all imperial, a friend has advised me to convert everything to metric...(thread forms as well ?).

I think a spreadsheet could do the conversion maths quite easily. Any tips on type of lathe etc.? Also, it would be good to know if there is a recommended order of work /special finishing requirements etc.

Thanks for any assistance,

Dave

Thread: RC Test Equipment
23/10/2018 21:50:53

All, just been reading up on some RC theory - especially, Superhet Tx and Rx, AM and FM material. Many of the diagrams were a mixture of 'black box' IC's and discrete components, and, I was able to follow most of it.

However, in the concluding section on superhet Rx's it stated that the tuneable coils (Inductors) are quite fragile. The circuit diagram outside of the main IC 'block' contained an RF amp, Mixer transformer and an IF amp all with tuneable coils. It occurred to me that as my non-working Rx came out of a crashed fuselage (it hit a road in a vertical dive), one or more of these coils could be u/s resulting in no signal output ?

Now to the test.....would a simple continuity check across the coils' contacts on the pcb suffice to say if it is ok or not ? Would further tests be necessary eg a 455kHz IF injection at an appropriate point. What about the second IF stage (the Rx is dual conversion), or, perhaps, a check on the fixed Xtal maybe (I don't know how fragile these are) ?

Bit of a teaser for me - thanks for any pointers.

Dave

ps Got my 'scope working now. It would be good to use it to help solve this one !

20/10/2018 20:11:46

Thanks for your reply Gangster - I like simple solutions /methods, so there is definitely some food for thought here ! However, I suspect my current faults (dual conversion, 35MHz) may lie in the two IF stages ie signal in but no signal out. The hope here is that I can use the 'scope to trace where the signal path is lost.

BTW is your picture an actual Ripmax Gangster of certain vintage ?

Dave

20/10/2018 16:43:30

Hi Chris, Yes I already have a 'pocket' multi-meter that will do ohms, ac and dc voltage, light current etc. But one that would do RMS values, temp's and frequency etc. sounds very useful...we have a Lidl and an Aldi opening up in our area shortly so, will pop along and see what's on offer.

Dave

20/10/2018 10:34:33

Thanks for the info' folks. Will follow up all leads as suggested.

Denis : Yes, I remember diagrams and photos of the Rx's suspended in a sort of cruxiform from each corner in the "radio compartment".

Robert: Thanks, looks like a first class link - I have some 35MHz fault-tracing on the go now.

Geoff : My 'scope came free within the family, so if the CRT goes....Yes, at Rediffusion years ago I remember our Avo's being replaced with more modern one's. I should have grabbed one then before it went into the skip !!! The 'scope is a bench top model and not too heavy to move about. I think I spotted a manual for it on ebay....will have to investigate.

Dave

Thread: Single Channel Radio Control - RH Warring
19/10/2018 23:06:19

I remember the adverts for the MacGregor sets from my school days and was very tempted. I then went to our local flying site at Llandow, in South Wales, and saw a British Remcon set (nearly) in action. I think the Tx case was red and the owner said it was home-constructed from a kit. I was very impressed. Would this have been a reed set ?

Also around at this time was the RCM&E plan /kit for full proportional (35MHz FM ?). Again I was tempted but lacked the necessary electronics knowledge to 'have-a-go'.

In the war, my uncle was a Radar expert and, around the early fifties, he built a RC set with a powerful ground-based Tx. I know I tried lifting it once ! The model was a high-winger like a Junior 60 or Trenton Terror (I have a plan for that). A possible dream one day would be to fly the Trenton Terror with a home-constructed radio and four-stroke engine. (I have a plan for the "Matador" FS motor). Lots of plans - not much execution !

Need some more electronic test equipment and a small lathe...plus a fair dollop of experience.

Dave

Thread: RC Test Equipment
19/10/2018 20:21:35

First oscilloscope arrived today - a Tektronix T912. Quite an old CRT model but with dual trace, storage and 10MHz bandwidth.

Next on the shopping list will be some good meters eg AVO 8 (analogue) plus a quality digital one. To follow, a spectrum analyser and frequency counter if anyone is 'unloading' ? These may have to come via kit construction if I can't afford a ready-made commercial unit.

As a first RC project, I quite fancy a single-channel valve Tx /Rx pairing. If anyone has a suitable circuit diagram, valves, pcb, instructions etc to assist with this I would be interested to hear from them...

Dave

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