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Member postings for Allan Bennett

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

Thread: Carbon u/c for Lysander
23/11/2009 20:04:36
I'm planning on landing lights, and have already got a bunch of 3mm while leds which I was going to make into 7-light arrays.  But your idea of a Poundland torch sounds like it's worth looking into.  I've got a home-made switch which operates off an Rx channel -- maybe I'll link it to the flaps channel in my trannie, rather than using a separate switch.
 
Our local model shop is having a 20%-off night for club members tomorrow, with EFlite reps on hand I believe, so I'll order the Beaver radial then.
22/11/2009 20:37:52
Thanks, Terry, sounds like a simple scheme to do
 
But I'll still be going there with my camera within the next couple of weeks -- it's only about 12 miles from me -- just to check out some detailing.  I'm not a fanatical detailer, but I do like to see the full-size so that I can make some small improvements.
22/11/2009 11:33:27
I see, so you pull the whole "guts" out to change or charge the battery.
 
I like your idea for the undercarriage.  I've never silver-soldered before; doesn't it heat up the piano wire when you're soldering to the brass tube, and risk detempering it?  Presumably you then use standard nylon clamps to attach it to the ply plate in the model?
 
I'll keep this in mind in case my cf version suffers the same fate as yours
21/11/2009 21:20:30
Interesting feedback, Terry
 
I don't charge the battery in the model, since I do all my charging at home and take about 4 packs per model to the field.  Access will simply be via a hatch cut into the top of the plastic cowl.   The only problem with taking off the whole cowl, or just the front of it, is that you need to remove the prop to do so, don't you?
 
My AXI 2826/12 setup gives me 600 watts with the 5S A123 and a 12x6 APC E prop.  In doing that it's right on the 60-second maximum amps rating, but I never use full throttle for more than about 15-seonds at a time and that setup has given me no problems in two other models over the past couple of years.
 
My ESC will be mounted outside my motor "box", as will my BEC if I need one -- Jeti Spin 66 should be able to handle six HS-81s okay I think, but I'll check the spec before I commit.
 
I've gone for Goldenrod flexible pushrods for elevator and rudder.  I use about 3" of rigid metal rod at the end of them so that the plastic inner doesn't extend beyond the outer.  I would have liked to have mounted the servos (HS-81MGs) at the tail, but I'm mindful of the need to keep weight forward.
 
I installed the access hatch this afternoon, and hinged it one side with Solartex.  I haven't really planned that far ahead, but I'm presuming that my receiver and two servos will be mounted beneath B03 at that location.
 
You're right, with a glow model I would expect it to balance on the c of g with no fuel, and then to be nose-down when fully fuelled.  With my electric conversions I'm usually happy if they're slightly nose-down with the battery in.  I'm afraid it will be some while before I can report how it balances with my A123s where they are.
 
I'll be using Solarfilm for most of the covering, but Solite on the tail surfaces.  I'll be over to Old Warden shortly to see exacly where the different colours go, and to check out a few details such as what exactly does the glazed access hatch near the tail look like, and what can be seen through it.
Thread: Law - am I breaking bylaws?
20/11/2009 19:35:38
Posted by Bruce Richards - Moderator on 20/11/2009 12:17:12:
Allan, what makes you think it is illegal to fly model aircraft anywhere. As far as I know (and I think what others are saying above) it is legal to fly anywhere as long as it is safe and not specifically forbidden.
 
 
 
Perhaps I've put the wrong emphasis on it -- it's not the flying in the air that I'm saying is illegal, it's the use of land as a flying field that I was meaning.  You need to have permission to be on the land and to use it.
 
Taking it a little further, you may even need Planning Permission if you regularly use the land (with owner's permission) as a model-flying field.
20/11/2009 12:07:43
Going back to the original question (a bit late, I know), so far as I know it is illegal to fly model aircraft anywhere -- never mind whether it's National Trust land, or who's it is -- without the owner's permission.  Most insurance will probably have a get-out clause if you're not flying legally.
Thread: Letchworth (North Herts) club
20/11/2009 11:59:57
We are a non-BMFA club flying in Letchworth, Hertfordshire.  Our site can accomodate glow and electric models up to about 1.20 2-stroke or equivalent.  Check out our web site www.lmas.org.uk for more details if you're interested.

Edited By Allan Bennett on 20/11/2009 12:01:17

Thread: Carbon u/c for Lysander
19/11/2009 21:09:19
The forward fuse sheeting in the photo, aft of former F2, is currently higher than it need be.  I plan to  trim it back to the correct size using the cockpit canopy as a guide.
19/11/2009 19:33:58
I've also read in the Lysander threads that some people are planning and/or doing electric conversions, but I've not seen many details:  I'm planning to put an AXI 2826/12 in mine with a 5S A123 pack, a setup I've used successfully in a couple of other models.
 
I extended the main spine box BO1, BO3, BO5 forward by 50mm, through F1, and then created a new small bulkhead at the front to mount the motor to.  The battery pack sits nicely inside BO1 etc. supported on a sloping piece of liteply and restrained by Velcro ties which are epoxied to the bulkheads.  Access will be via a hatch in the engine cowl.  I suspect that, unfortunately, some lead may be needed in the cowl, since the AXI motor is lighter than a .48 4-stroke and the battery is 13.5 ounces -- about the same as a fuel tank full of fuel.  Maybe I'll be okay, since the battery's weight is forward of where the fuel tank would be.
 

Edited By Allan Bennett on 19/11/2009 19:36:10

Edited By Allan Bennett on 19/11/2009 19:36:40

19/11/2009 12:04:18
Posted by Phil Wood - Moderator on 19/11/2009 09:38:29:
It may be viable for them to make them but they'd have to sell hundreds or thousands of the same size & shape to make it profitable...........

... Who's going to pay that for a U/C if they can make their own?
 
Don't I know how to pee on a bonfire?
Pollysorry
 
 Well, Carbon Copy sell a similar-size carbon undercarriage for £22.99 + postage, so there must be some demand since they're still in business after several years.  I don't know how many they sell to break even, but I doubt if it's into the thousands.
 
Anyone done the aluminium u/c yet, so they can tell us the material cost, and the weight of the finished article?
19/11/2009 08:47:22
You've identified the downside, Phil -- I used about 0.75 square metres of cloth for that which, depending where you source it, costs about £15.  Plus the resin cost.
 
I'm certainly not compentent enough to make carbon undercarriages for others, because I don't even know yet if it's strong enough to take the stress of landings (I'm reasonably confident because I've compared its thickness with a similar-sized commercial carbon u/c that I have on another model), or if my construction technique is correct.
 
But Carbon Copy, who are just down the road from me, will make custom carbon u/c at cost.  I wonder if there would be enough interest to make it viable to have them do some professionally.
18/11/2009 20:07:16




I've been reading the couple of Lysander blogs on this site, and thus far haven't seen any mention of the undercarriage, so I thought I would post my experience in case it's useful to anyone.
 
Having had experience of aluminium undercarriages gradually bending out of shape, plus the fact that (a) I don't have a vice or any way of neatly folding 3mm aluminium and (b) my local model shop doesn't stock anything that thick or large enough, I decided to make myself a carbon-fibre undercarriage.
 
I made a mould out of balsa, 4" wide, smoothed out the internal corners a little with fillets of lightweight filler, sealed it all with sanding sealer, sanded it lightly, and then covered it with Solarfilm.  All materials were to hand, so the cost was practically nothing.
 
After waxing the mould and applying release agent, I then laid up about 18 layers of 200 gramme carbon fibre cloth with epoxy finishing resin.  I made the centre and sloping parts thicker by interspersing shorter pieces of cloth with full-length ones, and I did the job in three separate sessions, letting it harden between each session (don't know if that's good practice or not, but six or so layers was all I could lay up before the epoxy began to go off).
 
The finished article slipped out of the mould without much persuasion.  I then stuck a copy of the undercarriage plan onto it as my guide for cutting and for hole-drilling.  I'm really chuffed with the end result.  Although weight reduction wasn't my primary aim, it weighs 125 grammes compared with my calculation that a 3mm aluminium one would be about 230 grammes (perhaps someone with an aluminium u/c could check that for me?).
 
I'll insert some photos of the mould, and of the undercarriage in various stages as soon as I figure out how to get pictures off my PC into an "album"
 
Edit:  I've cracked it ... images are now attached.

Edited By Allan Bennett on 18/11/2009 20:13:15

Thread: First Heli.
17/11/2009 20:06:27
My personal experience, which I'm happy to recommend to anybody, is that after 20+ years of fixed-wing flying I bought a Twister Bell 47 (now replaced by Twister Bell Medevac) contra-rotating heli.  After about two years with that -- hopefully a youngster will be quicker to master it -- I bought a T-Rex 500 and am practicing the hover with that.
 
The Twister Bell is distributed by Perkins, so parts are easy to come by and simple to install.  The only downside, as with all contra-rotating helis of this size, is that it can't fly in anything more than a very slight breeze.  I do most of my hovering practice in the garage, but I have flown outdoors in the calm we sometimes get a dusk.
Thread: Lysander F7 error?
03/11/2009 19:29:31
Posted by Tony Nijhuis on 03/11/2009 13:13:31:
Alan,
 
the 82mm is a bit misleading as F7 dosen't extend past stringer 7....I think F7 may be a couple of mm short because I have measured 77mm from top of stringer 1 to the centre tangent of stringer 7 at the rake back angle.....the bottom line is F7 should be about 79mm (top to bottom edge) to fit  perfectly
 
OK, I was measuring on the front face of F7, so my 82mm results in the back edge of F7 extending down beyond stringer 7 a bit.  Checking my plan again, this is exactly what is shown on the side elevation -- the front face of F7 extends 4mm below the centreline of stringer 7 (i.e. 1 or 2mm beyond the bottom edge of stringer 7), and the back face about 6mm.  Contradicting that, I see that the size of the notch for stringer 7 in F7 is 4.5mm, which prevents the bottom of F7 dropping below the bottom of stringer 7 which, I think, is why I my replacement F7, made to my 82mm measurement, was too tall.
 
Anyway, it's not a big deal, so thanks for responding in such detail.
03/11/2009 08:41:40
Hi Tony, thanks for the great design.  I've just about finished the fuse, and it's one of the easiest plan-builds I've done so far.
 
Anyway, about F7:  If I draw a line across the bottom of it on the plan, and then measure top to bottom, I get just short of 76mm; if I then go to the fuselage side elevation on the other sheet, and measure the top-to-bottom slope height of F7 in position, I get 82mm.  So, it still seems to me that F7 is 6mm too short, and this is exactly how it was in my build  before I realised where the problem was ... the top stringer already sitting in its notches in F8, 9, and 10 flew over the top of F7 without touching it when F7 was sitting properly on the two side stringers #7, at the correct slope.
 
Comparing F7 with F8 is not valid because F8 (according to my measurment off the fuselage side elevation) should be about 4mm shorter in elevation than F7 because of the slope of the top stringer.  That's discounting the fact that F7 should also be taller and wider overall because the stringers are notched full-depth into it instead of by only 2mm or so.  So, if F7 matches the top part of F8, then it's too short.
30/10/2009 19:14:31
Posted by Peter Savage on 30/10/2009 14:38:48:
Oh it wasn't F7 that i didn't put the stringers fully in, they go all the way in, its the front one that only goes through the top stringers

 The one that's leaning backwards, and forms the back of the cockpit?  That's F7 on the plans

30/10/2009 08:59:35
Did you make yours from plan, or did you have the CNC set?
 
On the plan, I'm convinced the F7 they've drawn is a true elevation of the former (as if it were vertical) which hasn't allowed for the extra height required because of the slope.
 
Before I realised what the error was, I was filing away at the bottoms of the notches in F8 so that the stringers could drop fully into F7 without me having to bend them down.  If you didn't push the stringers fully in, you're going to have to infill between them before you start covering, to give a smooth end to the covered section, and a smooth seating for the canopy.
Thread: the local model shop...long may it live..
29/10/2009 20:51:57
I rely 100% on my local store (about 3 miles away) for almost everything from glues and wood to radios and glow engines.  I certainly wouldn't want to have to rely on the internet for basic building materials.
 
In the past I've used the internet for things like electric motors, speed controllers, and spares for my T-Rex.  But my local shop can get most things for me within a few days -- usually from main distributors, rather than from other internet sources -- and their prices with my club discount compare favourably with the internet sources I've used, so I'm now getting my T-Rex spares there and I'll be getting my next motors too.
Thread: Lysander F7 error?
21/10/2009 13:56:27
Oops!  I've just fitted my new F7, and it's too big! 
 
Seems like 5% stretch might have been enough, but at least with the too-big version I've been able to file out the slots to fit the stringers nicely, and then sand down the external profile to the correct curve.
20/10/2009 21:20:18
I'm just getting around to attaching the 4.5mm stringers to the main frame of my Lysander and I've found that former F7 is about 8mm too short.  I'm working from the plan, not with the CNC set, so I don't know if this affects those who've bought the set.
 
Anyway, I've copied F7 off the plan and then stretched it heightwise by 10.5% to make it the right height (width is okay) so I can cut a new one.
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 Yes - for the first time
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