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Member postings for Bob Cotsford

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

Thread: Holding screws in
22/04/2019 13:32:27

I try to replace screw retention on hatches with a spring latch, either a single central latch or one each side mounted in the fuselage side mounted so that the sprung pin locates into a notch in the edge of the hatch tab. As I'm all electric now I want quick access to the battery so screwed on hatches are out.

Thread: Anyone for a Tiffie?
20/04/2019 13:54:16

Let battle commence!teeth 2

20/04/2019 11:05:38

I think the red bomb racks on the wing underside tie it down, it's BEB's. Warrington is only a couple of hours up the M6 so as a life member of the RB396 restoration group I feel obliged to put in a bid.

Thread: Galaxy Models Mystic plans
19/04/2019 18:18:40

Mine had a hatch in the underside of the nose between the front formers, it also had another hatch under the tail so I guess that a previous owner hads found it needed tail weight when running a petrol motor in it. I used an OS 120 Surpass and it went quite nicely, not overpowered by any means.

The tailplane was sheeted too iirc.

Thread: for fast electic is supreme
18/04/2019 14:08:08
Posted by Dickw on 18/04/2019 10:54:54:
Posted by Bob Cotsford on 18/04/2019 10:39:03:

What amazes me is that a folding prop can hold up under such high rpm!

They are mostly handmade specials, but some commercial options are available.

Have a look at what I pay for a folding 18" prop that will take up to 8kW (done it) at a mere 8,500 rpm for my F5B planes.

Dick

Eeeeek! disgust

18/04/2019 10:39:03

What amazes me is that a folding prop can hold up under such high rpm!

Thread: Free seaplane plan from the 80s
13/04/2019 10:09:11

I still have a pair of wings and a tailplane from mine, maybe even the fuselage somewhere. It's possible that the floats are up in the loft too. Mine was PAW19 powered, but I always thought it would have flown better with less washout and more power. I don't recall seeing the plan the last time I went through the pile unfortunately.

Thread: Have batteries - what plane
10/04/2019 16:44:44

My WotsWot (uses the same battery mounting system) will happily accommodate a 6S4500 pack. OK, happily might be stretching things but it fits. Just use a slightly lower kv than the recommended motor, or a smaller prop for 6s. IIRC my WW has a 4258 size motor rated at 500kv with a 13" prop - 13*8 rings a bell or it might be 13*6.5 .

Thread: Burn Crispy Aviators
10/04/2019 12:04:46

How oddly appropriate, my home address starts 'pilots.x.x'!

Thread: Who Else Wants a 63" Lavochkin La7 kit?
10/04/2019 11:56:23

One lesson learned on the Taifun is that metal motor standoffs get in the way when you need to move the battery forward. Admittedly the Taifun has got quite a long tail moment compared to it's nose length but having to add 10oz of lead is still a bit of a pain. That's one model that really could have benefitted from a top hatch and wooden box engine mount!

Back to the La7 - I can leave final battery positioning until after painting and fitting out. Someone has even thoughtfully provided an air channel in the side of the cowl that's perfectly sized to take an escsmiley.

First the scrap-box cutting guide to help getting a straight square cut with a standard razor saw.

cutting gude.jpg

the ply crutch coss member needed relieving in order to get bigger 6S packs through, servos will go in the cutout at the rear.

la7 leccy ready.jpg

Big 'ole in the front bulkhead where there used to be a moulded IC engine mount. I aught to tidy it up by cutting out the redundant throttle cable outer.

another view.jpg

10/04/2019 11:20:48

Having got bored with wheezing my way through winter I finished off the Graupner Me Bf108 Taifun and now it's the La7's turn. First I needed to get rid of the oily-based bits and replace them with electricity compatible parts. If I'd gone electric from the start I'd probably have made the veneered top a hatch from F2 back to the rear of the cockpit, as it is a top hatch has to end about an inch in front of the canopy. To lift out the rear face needs to be angled, a quick geometry job on the side view gives the rquired angle. The scrap box provided materials to knock up a guide that clamps to the fuselage sides and, as it's name implies, guides a saw to cut the required angle into the top deck. I took out a slice 9/32" thick to allow for 1/16" ply facings and a coat of paint. Another slice out at the front of the top running down the rear of F2 meant that sliding a blade between the ply crutch and the 1/2" square either side feed off a top hatch. Ply facings, drillings through F2 and the front facing gives locations for two dowels and a balsa platform let into the centre rear will provide a mount for a spring latch.

At the front a 1/8" ply box provides a stand-off to suit a 5055 motor and if needed can accept the front of 6S LiPo pack. A Ripmax -Wot style battery mounting plate and I think that's the woodwork complete.

Photos to follow!

Thread: Have batteries - what plane
10/04/2019 10:52:38

Parallel two of the 1850s to give a 6S 3700mAh pack, that gives you a large range of models that will perform well on the available power - WotsWot, Acrowot, Bollero for a start.

Thread: Hawker Typhoon
09/04/2019 18:02:41

Crowdfunding page - every little bit helps!

Thread: Disposing of modelling goods?
06/04/2019 17:15:28
Posted by cymaz on 06/04/2019 16:45:51:

That’s the models in the skip, not me

Sure? Skip ~ £250, funeral ~ £4000.devil

Thread: What's your do everything model, or do you have one of everything?
03/04/2019 16:19:10

I tend to have a favourite of the month and then I try to rotate the second and third models that I take so that they all get a regular airing. It doesn't do much for getting really familiar with the flying characteristics but it does keep me on my toes and interested.

Favourites usually rotate between various Wots though the ARTF WotsWot and Wot4 dominated last year, closely followed by a Flair SE5a. Much depends on the weather on the day.

Thread: A sticky glassing problem!
31/03/2019 13:26:20

My problem with Poly-C is that it needs so many coats to fill the weave of even lightweight glasscloths. PolyC/glass gives a more resilient finish than epoxy in that it flexes more, but it does appear to peel off more easily as I found out when examining the remains of my Poly-C/glass covered Joker. I wouldn't call it's adhesion poor, just not as good as epoxy, but if it's bonding to balsa either will be stronger than the wood itself and will pull away the outer wood fibres rather than peel away cleanly.

Use it for glass mouldings - I've not tried it but I'd guess you would be painting on dozens of coats to fill the weave on heavier cloths and I suspect shrinkage would be a major problem. Epoxy would be both quicker and stronger in my opinion.

Sorry Don but I too believe it to be re-packaged Ronseal industrial wooden flooring sealant/varnish. I also believe it gives off something in addition to water when drying, as a COPD sufferer I can detect airborne chemicals down to parts per million levels!wink

Thread: What's your rate limiting step?
26/03/2019 11:15:15

Nah, ribs don't need to be accurate, that's what long sanding blocks are made for face 1. My pet hate of late is covering and finishing - all those nasty fiddly bits like trimming a canopy to a neat fit and getting it to stick on, finding somewhere accessible for the rx and it's battery(ies), tidying/hiding all the spaghetti and then finding that somehow the model is now tail heavy so you need brackets to attach half a yard of roof flashing up front inside a paper-thin ARTF cowl.

Thread: FrSky ACCESS - New improved protocol
26/03/2019 10:57:24

Andy, as I read it the multi rx functionality is changing to allow full telemetry from all receivers. The last time I bound a second receiver using the X12 as it is I had to bind one rx without telemetry.

It states that the powermeter and spectrum (Spektrum?surprise) analyser needs the rf module from the latest transmitters such as the Pro version - is that using something different to the iXJT modules in the Taranis and Horus X12?

Thread: Fuse
25/03/2019 16:32:11

Sam35 looks to be the place for olde-worlde models and freeflight, iirc there is a growing trend towards 'radio assist' which just allows RC control of a small rudder for emergency use just to keep the model within bounds, otherwise the models are trimmed and flown as pure freeflight.

25/03/2019 09:18:22

We used to use the auto rudder to keep the model circling, as you say, which with luck on a calm day would keep the model somewhere near the launch site give or take 1/2 a mile. If the model gets into a good thermal it can vanish upwards to several thousand feet surprisingly quickly, any wind at all and it could travel miles. Even if it comes down within that half mile it can take binoculars to keep track of it. If you want the model back invest in a dethermaliser, the clue is in the name!

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