Carbon u/c for Lysander

[Allan Bennett]

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

[Doug Ireland]

That is very impressive Allan and it looks just the dogs do-dads! Careful though, or you'll get a heap of guys asking you to make one for them; starting with me

 

I'm surprised that a factory manufactured part wasn't included as an option with the CNC pack?

Edited By Doug Ireland on 18/11/2009 23:02:37

[Peter 'Ivanna Crashalot' Savage]

make one for me please! nah j/k do you think glass fibre would be sufficient?

[Doug Ireland]

Probably wouldn't be as strong as carbon fibre though Peter.

[Former Member]

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[Allan Bennett]

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.

[Former Member]

[This posting has been removed]

[Allan Bennett]

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?

[Allan Bennett]

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

[Peter 'Ivanna Crashalot' Savage]

Looking nice, It is confusing as to how high up the forward fuse sheeting goes

[Allan Bennett]

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.

[Terry Whiting]

Allan,

Yes I'm going the electric route but completely different to your's.

 Your method I presume will be recharging with batteries whilst in the model.

As I use Lipos I wanted easy access to my batteries to change between flights. My answer to the problem was for the cowl to be made in two parts, the forwad section unplugs from the other.

With wings, tailplane, and stabilizer built, I have now turned my attention to the fuselage.

I have a secondary firewall which the motor and battery tray is mounted to. F1 also has a square opening.

The whole power train slides in and out of the fuselage, which only requires one locking screw under the cowl,  unplug a BEC extention lead, and the whole train is free.

There will be no servo access hatch under the fuselage, as both servos will be forward  just under a removable . cockpit floor. Both will be 'close loop' (pull pull).

 The hatch position I will make a exit air vent 

 

My motor is a T4130/6   510kv     1kw, purchased  from RCMDirect,  using  4s made up by  2s x2 in series, this set up gives 600W which  I used in my 1 & 1/2 Strutter.

The reason I went for that size motor was the requirement of nose weight, it is the same weight as a 52 fs.

 

Allan you stated your battery is 13.5 oz the same as a tank of fuel, but remember you do not balance a model with a full tank, so you may not need nose weight.

 

I know Tony Nijhuis shows a flight pack in the cowl, but that without fuel onboard for balance. 

Edited By Terry Whiting on 21/11/2009 09:06:08

[Allan Bennett]

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.

[Doug Ireland]

I've thought about this glazed access hatch too Allan and have decided not to bother with it.

[Terry Whiting]

Hi Allan, sorry I didn't read your thread right through, it threw me when you mentioned fuel tank and batteries. I know understand where your batteries are situated which is a good idea when using that type of cell.

No I do not have to remove the prop, the whole (90mm) forward cowl section with the motor mounted to the secondary firewall and battery tray can slide out.

My fuselage F1 has also square hole, and 3 keyhole locking slots, one  at 10 o'clock, one at 2 o'clock and one at 6 o'clock , all keyholes are backed with 2mm glass fibre sheet to give a smooth action 

The secondary firewall has three  4mm panhead bolts  which are adjustable, the heads  pass through the the keyholes of F1, once home a slight downward pressure give a reassuring 'Click', I then screw in my locking screw from under the cowl

Both firewalls are of 4mm birch ply, but as both have sq holes the weight penalty is just 21g

 

I did not like the idea of the aluminium U/C, and in the past I have made carbon fibre U/C. I hope you do not have the same trouble with your  CF U/C, as  mine delaminated in use at the position of my second lay up. I wondered if it was due to a miniscule difference in the epoxy mix, on the other hand I might not have keyed the first lay up sufficiently.

Since then I have used piano wire, brass tube and  2mm X  20mm brass strip.

In this case the wire will be of 8 gauge.

 

 I cut an accurate flat cardboard template giving all the angles, and a side view template. I select some brass tube with an inside diameter about 2mm greater than that of the piano wire, of this I will cut 8  20mm pieces .

 

To the wire the first bends I make are those which will make the fuselage saddle, on each leg I slip on a piece of brass tube, these are taped to stop sliding off, I can now make the second bends.

From my side view template I cut  2 pieces of the brass strip which fits the position of the wing strut, and 2 for the axel positions. The wing strut positions are are silver soldered to the tubes first, now the remaining 4 pieces of tube are postioned at the axel position and brass strip s/ soldered.

I now clamp the U/C to flat board as it will be in the fuselage , and the loose tube are postioned carefully  and  epoxied, I use 24 hour  JB Weld, which is a fantastic product 

 

 I use this method as you do not detemper the piano wire I have made many U/C with this method, and none have so far failed.  

 

  

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Edited By Terry Whiting on 22/11/2009 10:51:21

[Allan Bennett]

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

[Terry Whiting]

No the piano wire does not reach that sort of temperature. That is one of the reasons of using brass tube 2mm over wire size, if the tube and wire was a precision fit it would take much longer for the S/solder to flow 

Using Easy Flow  silver solder has I believe one of the lowest melting points of all silver solders but make a very strong joint . 

[Terry Whiting]

Allan,

The Old Warden Lysander is all 'satin black'. with brick red lettering. 

I'm an  O W  regular visitor, just love it. I  based the following models on their fullsize.

The  Pup, SE5, Tomtit, Hurricane, and now the Lysander. 

[Allan Bennett]

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.

[Terry Whiting]

I never  go the whole hog with scale, but  I just like adding certain features which take it out of run of the mill look alikes.

The cowl I have fitted one of PodiumRC's Dhc Beaver radial engines, it's only an ABS press out but quite good, the price was too, £4.39 + postage Other than cutting out from the waste material, it needed no other trimming.

 

Those wheel spats are crying out for working landing lights.....answer

A  'Y' lead on the flaps, 3g servo, miniture microswitch, LED's and reflectors taken out of a couple of 'Poundland torches plus alkaline button cells for power, total 22g. ,

 

A  balsa  made exhaust , and cylinder head blisters finishes off the cowl.

 

The canopy needs some furnishings, otherwise it will look like a 'greenhouse'  but have never seen a picture of it's interior, but still looking. 

[Allan Bennett]

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.

[Allan Bennett]

Posted by Doug Ireland on 22/11/2009 01:43:46:

I've thought about this glazed access hatch too Allan and have decided not to bother with it.

  I visited Old Warden this afternoon, and here's what the glazed panels look like on their Lysander -- identical each side, and you can see straight through from one side to the other.

 

[Doug Ireland]

What are they for Allan, to check the linkages perhaps?

[Terry Whiting]

Doug, when I was at OW looking over the plane, I thought then were for visual check, and the glazing panel could be removed giving access.

The whole tailplane is capable of being trimmed, and I have notice when the pilot does his walk round check, he does peer into these glazed panels for quite a few seconds.

 

A feature I will give a miss.

 

[Allan Bennett]

Posted by Doug Ireland on 28/11/2009 22:26:02:

What are they for Allan, to check the linkages perhaps?

 

That's all I can assume.  Anyway, I think I'm going to incorporate them into my model since they look quite simple to do.

 

As Terry Whiting has observed, the panel they're in looks like its removable, so a rectangular piece of clear cellulose painted black, with the windows left clear, could be recessed into the structure.  I've already filled in between the stringers at that location, so I don't think that cutting a small hole where the clear window is should adversely affect the structural integrity.

 

Having seen the real thing, I'm also going to put the blisters on the engine cowl, as well as what looks like a single exhaust pipe (?) on the lower right side of the cowl.  It's difficult to see in the cockpit at OW, but at least I need to include something to represent the pilot's seat and instrument panel.

Edited By Allan Bennett on 29/11/2009 08:50:16