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Seagull Mosquito Laser build

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Chris Walby31/07/2018 22:31:08
979 forum posts
230 photos

Well the time has come...and I must start with a thank you to Jon at Laser Engines for his assistance and all of the other Seagull Mosquito owners for their build threads which have been most helpful.. If the Dual Ace is anything to go by and I really hope it is a pair of 70's should fit without too much lead to get the C of G.

So alas poor Speed Air as I need a engine template and I am having too much fun with the Dual Ace to spare a couple of 70's although they will migrate there in the end!

Quick taster and then I am off to do lots of measuring.


Chris Walby03/08/2018 22:38:48
979 forum posts
230 photos

Its all starting to come back to me regarding Jon's comments having re-read my notes. The positioning of the 70 is quite tight against the engine box and I need to decide if I need to nibble the odd corner off to make enough room or not.

A spot of drilling new holes for the engine mounts against the bulkhead and measuring to ensure the spinner will clear the cowling and its looking like a plan

Jon suggested some additional bracing and during the general handling a couple of the existing joints came loose so there will need to be a through dribbling of the Deluxe glue to make sure it all stays together.



Cowl trimming should be interesting for maintenance although it looks like it could nearly hide in there!


I'll add the rest of the spec in once I get a bit more done.

Any questions or comments then please post.

Biggles' Elder Brother - Moderator04/08/2018 09:29:48
15748 forum posts
1460 photos

Wow, that is very tight to the firewall isn't it. Looking at the cowl it appears from the photo that it's going to be quite a tight fit too. Are you anticipating any cooling issues? I know Lasers tend to run cool-ish and cope well with enclosed spaces, but that is a fairly extreme example!

Also, I know Danny Fenton had a lot of issues balancing this model, are going to end up with a 'church roof' stuck in the nose do you think? As I see it, from an aerodynamics perspective, the main problem is not just the weight - its the fact that with extra weight goes the need to fly faster and then when you have to slow for landing you end up at a higher angle of attack much sooner than usual and those pointy ended wings sure won't like that!


Ian Moody04/08/2018 09:50:40
78 forum posts
10 photos

Another problem I have had with mine is the round bar between the retract and the undercarriage cross bar (sorry don't know the correct term for it) snapped on both retracts on a landing that wasn't heavy in the slightest. I have converted my retracts to a set of servoless metal jobs from Hobbyking and a mate has turned a set of decent steel bars for me. He says the supplied bars are made from special Vietnamese goats cheeselaugh

I will be interested as to how much lead you will need to add with ic engines as I am considering putting two SC 70 Fourstrokes in mine.

Jon - Laser Engines04/08/2018 11:45:40
4786 forum posts
179 photos
Posted by Biggles' Elder Brother - Moderator on 04/08/2018 09:29:48:

. Are you anticipating any cooling issues?

When Chris came to the factory with the model we looked at that. We talked about adding some vents behind the engine to get the hot air out but in general it looks like it will be ok as the whole area behind the engine is open.

Its worth noting though that as it is open any oil from any engine will splatter all around inside the wing so its worth getting the fuel proofer out and giving the inside of the nacelle a regular clean to prevent oil collecting.

Ace04/08/2018 12:36:03
265 forum posts
15 photos

Following with a keen interest as twins have always fascinated me.

Question - looks as though engines are inverted which puts the tank very high in relation to the carb, are you anticipating any siphoning issues or mixture richening on closing the throttle with such a head of fuel?

Chris Walby04/08/2018 12:36:20
979 forum posts
230 photos


My long post just auto deleted crying

Plenty of room and will have to extend the exhaust to get it out of the cowl. Exhaust air will exit via U/C aperture or I'll see it I can make something on the back of the rad cowl (to stop oil blowing about).

The cowl will need to be cut to get it into place and that will allow a section in front of the cylinder head to provide inlet cooling.

Jon suggested a scallop or two in the bulkhead to allow the carb inlet/linkage which is no issue as the tank won't be in the box. That will allow some useful bracing to be put in to make sure the bulkhead is secure.


Thanks for the heads up, I'll look to turn something up, cheers.

This is only my opinion, but I think Seagull are making IC models that can be converted to electric at this size which gives the electric guys a challenge getting enough weight forwards. My Seagull Dual Ace is on twin 70 comes out just light compared with the 2 stroke/electric guys who have to add lead to get C of G, so win win!

I might need to put the RX lipo further back (like the Dual Ace) to get C of G but its way better if slightly nose heavy on the 130mm C of G point compared with getting everything forwards frown

I like the convenience of electric, but its just not the same for me when you roll into a low pass with a pair of 4 strokes sounding so nice.....

I'll keep up dated on the build and see where things work out.

Chris Walby04/08/2018 13:08:39
979 forum posts
230 photos

Ace, I tried all kinds of engine positions and how I was going to hack the cowl etc... Jon just said to put the tank under the nacelle box... I find simple solutions the best...even if I have to be told the obvious ! blush

PS The Dual Ace is a reasonable cost kit and flies very nicely (well I think so) so that's what I am cutting my teeth on (see my build log and importantly other peoples comments). Go on you know you want a twin!

Disclaimer. Other models and engines are available... but where's the help and advice if you need it.

Ace04/08/2018 14:58:12
265 forum posts
15 photos

Cheers Chris, Arr so the tanks are not in their final position. Like you I will be cutting my teeth on a ASP 61 fs powered Dual Ace.

Chris Walby04/08/2018 18:46:25
979 forum posts
230 photos

One cup of tea, another of coffee and the decision confirmed at the flying field between bouts of flying is to move the bulkhead.

I tried the exhaust and carb at all kinds of angles with the exhaust pointing up and the slow running screw only possible from the other side of the nacelle. Nice try but the more I looked at it the messing later on to get everything to work.

Engine stays where it is and move the engine mounts back 25mm (including bulkhead) + the benefit the bulkhead does not look like a tea bag and the carb linkage lines up nicely + the exhaust points directly down now smiley

Slightly worryingly was the ease it all came apart.



Bulkheads are on the to do list tomorrow.. plus a bit of gluing.

Biggles' Elder Brother - Moderator04/08/2018 19:01:27
15748 forum posts
1460 photos

Yeap, I think that is a necessity Chris.

We all do it don't we, there's a problem, in our heart of hearts we know the solution but its a lot of work and carries some risk that we might mess things up. So we convince ourselves that there are ways around it. Only after reality gives us good slapping around the ears do we accept what we really, secretly, knew from the begining! I do it all the time!


Jon - Laser Engines04/08/2018 20:31:43
4786 forum posts
179 photos

its only wood!

trebor05/08/2018 08:00:14
1906 forum posts
214 photos

How low will the carb be to the centre of your fuel tank position ? Watching with interest as your using nice motors.

Chris Walby05/08/2018 22:34:09
979 forum posts
230 photos

Trebor, I'll have a look once the glue has set on the bulkheads, but if I remember rightly Jon suggest it would be okay. if it needs modifying apparently "its only wood" and the main thing is there is plenty of room in the nacelle anyway.

Progress today was painfully slow although I have the new bulkheads in place (25mm further back) and made a start on the instructions

Aileron and Flap horns epoxied in and aileron servos fitted.



Hopefully install aileron and flap push rods tomorrow with wingtip covers (hoping UHU-Por will be okay for this).

I'll try the engine in the wing with the cowl to see how it line up and then if its okay get on and brace the boxes up.

Thanks for following and any questions/suggestions please chip in, ttfn

Martin Harris05/08/2018 22:50:04
8790 forum posts
215 photos

Hi Chris, I think I would have preferred to see some tabs on the sides of the new firewalls. Do you have any plans to add some reinforcement or are you relying on the glue joints to resist the flight loads and vibrations?

Danny Fenton05/08/2018 23:38:28
9103 forum posts
3944 photos

Chris, C of G 120 - 130mm just to be safe

Looking good, the Seagull joints on those nacelles are very dubious, I would go over them all. I had an "arrival" and the nacelles completely fell apart, not one bit attached to another, but no bits broken amazingly!



trebor06/08/2018 06:24:36
1906 forum posts
214 photos

Is the top going to stay open or does it get boxed in ?

Ron Gray06/08/2018 07:29:02
1441 forum posts
363 photos

Having fell foul of the poor construction design of a Seagull P40’s engine bulkhead, I would brace them back to the next bulkhead plus glass cloth the internal surfaces.

Chris Walby06/08/2018 13:15:08
979 forum posts
230 photos


Martin, I have left enough in front of the bulkhead for a strip + the majority will be in the back with 4 triangular ply braces, as the tanks aren't in there I have plenty of room to play with. so two top and bottom on each side.

Danny, 120 to 130mm it is and that suits having a pair of Laser 70 in there... at this rate Jon could have sold me a pair of 80's..wink

Trebor, I need access for the nacelle to wing bolts (having said once the box is epoxied it isn't coming out!), but access for throttle linkage might be handy, I'll have a think about a removable one. The wing is pretty solid so once glued in its not going far.

Ron, I watched your thread with interest and I think I would have needed a change of underpants with an engine that size breaking loose. Someone mentioned a Deluxe glue that has very good capillary action so I'll use that everywhere I haven't glued bracing in. At least access is not an issue for me (had to wait until the nose wheel bulkhead failed on the Dual Ace before beefing it up!).

Thanks for all of the comments, much appreciated

Controversy next....

Chris Walby06/08/2018 13:41:32
979 forum posts
230 photos

Thinking of the electrical bits and bobs and servos are going in.This might stir things up but my opinion is to keep it simple as in my book the longer the chain the more likely a link will fail (if its all single points of failure).

My BH mossie used 15 pin connectors (VGA connectors) which seem to do the job, but with increased vibration and current carrying capacity I am going for 7 pin JST-XH (balance lead connectors) and solder all other connections. My son had a very hairy flight caused by an in wing servo extension joint causing the servo (big aileron with big throw) to oscillate between full deflection. Once unplugged and plugged back in a it hasn't done it again, but it would have beaten me!

Anyway he is the first pass.

seagull mosquito wiring diagrams.jpg

PS Gear on different channels so I can set up end points etc so they are nice and slick !

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