Seagull Mosquito Laser build

[Chris Walby]

Thanks Richard, that's got me thinking as the Laser prop range is 12×7-8 13×6-7 14×4-5 so depending on ground clearance (and yours is okay on 14's) I could go 14x4 if it looks okay.

I have a pair of ali spinners as I seem to get prop creep with the plastic ones and I could hide a couple of chunky spinner adaptor nuts if C of G is rearward.

I was looking at the tail wheel, very nice, but must pull the C of G back Has everyone used theirs?

[Danny Fenton]

I ditched the tailwheel on my second one, too heavy and at the wrong end of the model!

Both of mine came in under 7kg around 14.5 lbs with cells.

I used the supplied spinners and 17 x 12 apc props

Cheers

Danny

[Jon H]

Posted by Chris Walby on 07/08/2018 06:45:30:

Thanks Richard, that's got me thinking as the Laser prop range is 12×7-8 13×6-7 14×4-5 so depending on ground clearance (and yours is okay on 14's) I could go 14x4 if it looks okay.

I wouldnt drop to 4'' pitch. Your pitch speed will be very low and the model will feel like it has no power. 13x6 is the best start point for the engines. After an hour or so you can try a 14x6. It wont rev as fast as the 80 will spin them but it might be ok.

[Chris Walby]

Thanks Jon, I was only going by the Laser website and thought you might chip in with your experience, cheers.

13x6 or 14x6 will probably work well when it comes to the noise test. I don't think the 12x8 suit the Dual Ace but it got it through the noise test (noisy nacelle covers and low ground clearance) so it is what it is. Once the 70's are in the Mossie I'll noise proof the nacelle covers and extend the U/C and try the noise test again with something less pitchy.

On the subject I weighed the tail wheel and it comes out at 51g which is worth considering its omission as its so rearward.

Edited By Chris Walby on 07/08/2018 09:23:18

[Jon H]

13x7 should be quiet as well

[Richard Wills 2]

I am going to try higher pitch props next, have a pair of 14x8's I can test. Feels like it's a bit 'low geared' on the 6's.

Edited By Richard Wills 2 on 07/08/2018 12:57:11

[Chris Walby]

Richard, Only personal feeling, but I find high pitch props hard work at low speed (landing). It seems a bit of all or nothing, like harder to deal with just when my workload is at a maximum.

Just me but I like a larger diameter less pitch setup, not sure about other peoples views with more experience?

Jon, I'll buy a pair of 13x7 for starters

[Denis Watkins]

Posted by Chris Walby on 07/08/2018 13:46:01:

Richard, Only personal feeling, but I find high pitch props hard work at low speed (landing). It seems a bit of all or nothing, like harder to deal with just when my workload is at a maximum.

Just me but I like a larger diameter less pitch setup, not sure about other peoples views with more experience?

Jon, I'll buy a pair of 13x7 for starters

Agree Chris

As a rule of thumb for choices, go to pitch being approx half the diameter

E.g, 10 x 5, 11 x 6, 12 x 6, 13 x 7 do feel less agressive

[Jon H]

i tend to work on the basis that 50-70 engines like 5-7 inch pitch. 80-100 tend to be better on 6-8 and anything over 120 is 8 inch as a starter. Really big engines go up to 10 inch easily.

In general it runs hand in hand with rpm. Small engines rev faster so lower pitches give the same pitch speed when all is said and done.

For warbirds i aim for 50-60 mph pitch speed as this seems to give a realistic performance.

[Richard Wills 2]

Chris I do find that pitch can affect landing considerably, depends on the airframe to a large extent whether it has flaps or is otherwise draggy. The Mossie has fairly generous flap and needs a significant amount of power on on the approach, so shouldn't be really affected too badly. Best compromise for the whole flight I suppose.

[Chris Walby]

Update time

But first the disclaimer... I am measuring up and seeing what goes where, so bracing screws, fixings and elastic bands will not be used in the finished article!

Tank position relative to carb.. that will do nicely

So this leaves me with a question, do I cut a hole in the cowl for the cylinder head, exhaust and carb to poke out of (red option) or cut from the underside of the cowl exhaust stubs to just in front of the rad intake and then make a removable panel (with a hole in that) (green option)

Am I making any sense?

PS glued the horizontal stabiliser on the fuselage, just to show a bit of progress!

[Jon H]

Green option is more work but will look neater all told. Its also likely to make fitting the nacelle covers and general maintenance a great deal easier long term.

[Danny Fenton]

Keep in mind the nacelles will get a bit floppy if you cut them too much There is no structure to support them.

[Chris Walby]

Red option

• Retains maximum strength
• Should looks better as just bits that need to be cut out will be showing
• Can be nibbled stage by stage to get required size
• Once done, can't do green option so would need to make new panel

Green option

• Cut panel out with easier access to engine
• Removed panel can be nibbled for required size + scoop/deflector if more cooling is required
• More work, but less fiddling
• Only visible cut lines will be the vertical ones
• Might end up all floppy!

Notes

• Cowl will have to come off to adjust the slow running, so once in a blue moon
• Main needle is accessible with either option

I think I need a pole on this

PS what's the best way of cutting straight lines with a Dremel?

[Jon H]

Posted by Danny Fenton on 07/08/2018 23:17:47:

Keep in mind the nacelles will get a bit floppy if you cut them too much There is no structure to support them.

 

When Chris brought his in i noted they were about 1/8 thick fibreglass! They were really solid, im pretty sure cutting them wont matter in this case.

As for straight lines just use a fine dremel cutting wheel and go easy on it. OIf it all ends up a bit sloppy you can glue thin strips of ali sheet onto the hatch that extend to cover the cut lines. Paint them grey and noone will ever know the horror that lies beneath 

Edited By Jon - Laser Engines on 08/08/2018 08:29:14

[Danny Fenton]

Blimey Jon, I have 5 cowls in total and they are all flimsy. The scoop underneath is fairly solid but still not that thick!

Maybe I just got lucky/unlucky

Cheers

Danny

[Bob Cotsford]

If there are thin areas in the moilding then slap on a layer or two of 1oz glass cloth before cutting. My cowl cutting method is to drill pilot holes in the corners (1.5mm works well) then join the dots with a Dremel cutting disk.

[Chris Walby]

Still thinking about the cowl cutting.... yes, yes I know I'll have to do it at some point, but not just yet, while I have other things to do!

• Vertical stabiliser epoxied in
• Pilot first undercoat
• Retract servo installed and tested I intend on having these on different channels so I can endpoint trim them
• Controls rods put in

Fuselage is going to look empty with just a RX battery, UBEC, RX and a couple of servos

[Chris Walby]

Progress update.

Managed to avoid cowl cutting by:

• Installing the tail wheel
• Throttle linkage
• Fuel tank bung, clunk, vent and drain lines
• Other retract servo
• Go up the flying field as its stopped raining

Need to hunt the Dremel out for the tail cowl and while its out I suppose I could cut the cowls

or I could start on beefing up the bulkhead and motor box

[Chris Walby]

More progress and still avoiding the cowl cutting by finishing off the tail wheel cover. Cut with the Dremel (once I found it) and located it with four screws (can't say I like gluing access panels) and then moved my attention back to the fuselage to connect control rods.

That's when I found the tail wheel would lock in one direction and very stiff in the other! I do remember someone else having this issue so it was in the back of my mind to check the full movement. So off with the cover, quick trim of the tail wheel bracket and ply/balsa hole and the nut doesn't override/lock anymore.

Picked up the 13x7 props and found one of the spinner adaptor nuts hasn't been threaded, wondered why the screw would not go in , A quick job on the lathe while I am making the spinner to engine prop shaft spacers (It might not be the best, but there is something really nice using a 1940's lathe...perhaps because its older than me!). Or perhaps its all the unguarded belts and no safety features...Treat it with the respect it deserves and it rewards with the smell of cutting fluid...nearly as good a smell as methanol/Castro

...cowl cutting next

[Ronos]

Hi Chris, I am following this thread with interest, but could you tell me something? Are you planning on connecting the two servo's for the throttle and retracts via a Y harness to the RX?

[Chris Walby]

Hi Rono and welcome.

I have disscussed the throttle with Jon and the conclusion is that with a matched pair of Lasers and correct start up procedure it is not necessary to have them on different channels (it's the mid throttle rpm that needs to be the same) + bigger problem for me is I can't get my DX8 gen1 to do throttle cut on the aux channel, so a no no for me. My retracts are standard servos (heavy duty) and are on different channels so I can set individual end points. I have had lots of grief in the past with mach retracts so this seems the best solution. Apologies as send on my phone. PS I like to keep it as simple as possible as hopefully it's less things to go wrong.

Edited By Chris Walby on 12/08/2018 09:45:13

[Ronos]

Thanks Chris, the reason I ask is that I might get on of these sometime, and interested in how the two servo's for the throttle and retracts are set up. I have looked on the link for the wiring diagram on the other page,but says page not available. hope you can post some photo's when you get to that stage.

[Chris Walby]

Ronos, I'll PM you.

Progress... I went for Jon's option as it leaves me with a panel that can be used to infill the sides if I need to.

Ooorrr that's a nice fit

The cowl is still ridged which brings me on to my next problem!

Problem, with the cowl sitting against the LE of the wing the TE of the cowl sites up (gap) and if I push it against the wing the U/C hole closes and it seem rather stressed.

What options do I have?

• Cut the cowl (slot) at front of U/C opening to allow it to close up
• Infill the gap (about 10mm at the TE) with a strip of balsa

I am tending towards the infill and it leave the cowl intact and less stressed

 

 

 

 

Edited By Chris Walby on 12/08/2018 16:34:37

[Jon H]

if you heat the fibreglass with a heat gun you might be able to soften the resin slightly and allow a flexibility. Once the resin cools it will go hard again.

Go easy with the heat to begin with until you find the spot at which is starts to go soft.