Seagull DH-98 Mosquito engine choice

[Danny Fenton]

Mmmmm I seem to have one of these now as well....... I blame gavin Mack

[Martin Harris - Moderator]

Posted by Martin_H on 20/11/2017 23:12:07:

Posted by Jon Harper - Laser Engines on 16/11/2017 14:58:34:

It sounds like you covered the bases as well as is reasonable to expect so it would seem that the model itself is just very flicky. Tweaking the ailerons will help a bit but you may also need to change your landing technique and use throttle instead of elevator to control your decent. I have to use this method with my Sea Fury as it will slow up and stall easily if a 'normal' approach is used. I run in with a fair bit of power and only use the elevator to tease to nose up to horizontal before wheeling in. 3 point landings are a nono and i suspect the mossie will be the same.

Interesting...I thought it was common practice to use throttle to control rate of descent and elevator to control approach speed - just as full size... I suggest all modellers read 'Stick and Rudder: An explanation of the Art of Flying' by Wolfgang Langewiesche. If you cannot get a copy of this book then it is available on digital download from Amazon, and at a quite reasonable price, considering what I paid for my hardback copy! I learnt to do flapless sideslip landings with my 1/4 scale Cub using the techniques in this book.

How spooky to read this from another Martin H - apart from the book reference I could have written his post almost word for word - including the Cub landing technique - I'm often to be found doing circuits and bumps with mine trying to get some consistent upwind wheel touchdowns!

When you get properly hooked up with a throttle controlled approach, there's an almost surreal connection between the throttle lever and the descent rate while you're coming over the hedge.

[Gavin Mack]

Can someone who has built this advise on which horn goes where as the manual does not make it clear

[Denis Watkins]

Gavin, horn installation in the manual looks pretty straight forward in pre cut slots

Are there different sizes in the packet?

[Danny Fenton]

Looks like there are a few sizes. I would guess the one on its own or the ones you have three off are the rudder and two for the elevator. The longer reach ones are for the ailerons. Convention is that the hole in the horn is perpendicular to the hingeline. That might give a clue? I can open my kit if it would help?
Cheers
Danny

[Paul C.]

Come on chaps we need more photographs in this thread 😆😆 😊

[Gavin Mack]

rcuniverse link below

**LINK**

If the rc universe review is correct then I have mixed up the horns, but they might be wrong. I found the aileron slot thickness was to shallow for the aileron horns shown in RCU review (may not be case in other mosquito kits. I used the 3 smaller horns for ailerons (lined up over the hinge line) and rudder, and then found which remaining horns lined up over the elevator hinge line which them left the flaps. too late now they are glued in.

 

 

Edited By Gavin Mack on 10/01/2018 22:53:25

[Gavin Mack]

 Just added 3 photos to mosquito album. I didn't like the motor mounting method, Instead of measuring and glueing the movable wooden block I have fixed the block as far back as it can go. using 4mm all thread allows easy adjustment of motor to fit in cowl. I'm planning on using (as I had them already) Turnigy G46 670kv motors with 14 x 7 3 blade master airscrew propeller I have both tractor and pusher props. haven't decided yet whether to use both tractor or 1 tractor and 1 pusher. Number of cells not decided yet 

 

Edited By Gavin Mack on 10/01/2018 23:32:20

[Chris Walby]

Hi,

I have tried both tractor/tractor and tractor/pusher on my BH Mossie and prefer the latter, just helps prevent a bit of swing on take off and adverse yaw if the throttle snapped open in flight (looks non scale!)

If you are calm and all is going well its not an issue, but swing/yaw becomes a problem if your workload is high like aborted landing due to running out of runway (pushing a poor decision to land long - been there done that!). So if you can fit tractor/pusher I would. Its a bit like fitting 3 blade props, I do as they look nice, but they are not very efficient (another can of worms).

[Danny Fenton]

My Mossie is just about ready to test. Only trouble is we now have snow on the ground!! Anyway cannot test until after next clubnight as the thing needs weighing as it is close to the club limit.

on 2 x 5S 5000mAh packs in parallel, I get 1300 Watts, 66Amps, from two Turnigy 4250 350kV motors. Through a pair of 55A ESC's. the motors are swinging 17 x 10 but I am going to go for 17 x 12 just to give me some more airspeed in case I need it.

Not that it is relevant at all, and really isn't useful, but is reassuring, I have 13lbs of static thrust. And throttle steer configured on OpenTX. It really yaws nicely with it enabled. This should be great for take-off, but doubt it will help much on landing. Assuming the swing is torque then I should be okay.

I have extended the power leads and fitted 220uF caps to stabilse the surges.

I have used SBUS decoders in the nacelles to reduce number of wing leads.

ESC under the nacelle

seperate UBECs for Rx and each retract servo. Only 2 channels on R6 used, rudder elevator + SBUS. Channels on the SBUS decoders are used for all wing functions. Two decoders, one in each nacelle.

Cheers

Danny

[Rob Cawsey]

Guys if you went down the IC route have you still got the electric motor boxes going spare I'm looking for a replacement set?

[Danny Fenton]

Did someone ask for pictures?

Mine flew last weekend, and although a touch hairy, possibly c of g issue, I got the model down safely.

Really looks the part in the air

Cheers

Danny

[Jon H]

Looks great Danny.

When you look at c/g i would also recommend looking at the control throws. If you have more than about 10 or 12mm i would suggest you have more elevator throw than you really need.

All of my warbirds are very elevator sensitive and i have very low rates set on all me elevators. I dont use any expo but the rates are well down.

[Danny Fenton]

Hi Jon, yes you are quite right, the amount of elevator in the last shot, as I am touching down shows that very little is needed. I have probably too much throw set. In my defence I usually find a fair bit is needed to keep the tail down. The model behaved better when the power was eased, I think part of the problem is the massive propwash from the twin 18" props, perhaps a throttle to rates or expo mix will be needed. But it is still early days.

The manual doesn't state c of g wheels up or down, Brian Taylor usually states with gear down. The wheels on this model are very light, the c of g doesn't shift much when the wheels go up. I need to also check to see if the elevator contol outers are flexing.

I had positioned the rates on a different switch, and couldn't find it in the heat of the moment, that would almost certainly have helped!!

Looking forward to the next flight

Cheers

Danny

[Jon H]

Its possible that it was a bit lively with the engines powered up because the thrust line was slightly wrong. A friend had this issue with the black horse he111 and it was only when he asked me to have a go with it that i realised the problem he was having. If you find the model climbs under power and drops its nose with power off then it needs a little downthrust.

Of course it could just be a function of the speed and slightly excessive rate.

I will find out soon enough as another friend has one that is almost done and should be flying soon.

When it comes to c/g i always balance with gear up and empty fuel tanks on the basis that this is likely to be the most tail heavy condition the model will see and anything else is leaning towards nose heavy. Also, the model will spend 90% of its time with its wheels up, and the first thing i do with a new warbird is get the bloomin wheels up! It tidies up the airflow and removes a large amount of drag. It also means that if it hits the fan and i have to put it down i am ready to go. Landing off the runway with retracts down is likely to end up with something broken

[Danny Fenton]

Hi Jon, thanks for your thoughts. The design of the model makes it very possible to get the thrust lines wrong! But I had thought I had it fairly accurate eventually. The mk1 eyeball has them pretty much straight/vertical from the sides. A bit of right thrust on each motor. The model doesn't alter in pitch with throttle, it alters in sensitivity which leads me more and more to the conclusion that the controls are to coarse. next flight with reduced travel, some expo and a clear understanding where the three position rates switch is!!!

Anyway the forecast for the weekend is very poor so I guess that is it for now....

Cheers

Danny

Edited By Danny Fenton on 29/03/2018 17:45:05

[Jon H]

Yea my friend didn't get his thrust lines wrong either, you can thank black horse for that!

[Danny Fenton]

You miss my point Jon I set the thrust lines not Seagull. The bulkheads are in slots and free to move in all directions, including fore and aft to allow for different motor lengths. Once you have them where you want you glue them.
As I say the model does not alter in pitch with different power setting it alters in sensitivity, ie more prop-wash perhaps....
Cheers
Danny

[Jon H]

Yea I just realised I misread your earlier post. I still wouldn't rule put thrust lines though as my own design twin needed more downthrust after doing some test flights. I still suspect the rates are the main issue. I'm very interested in the model though as I have always fancied a mossie

[Ian Moody]

Gents,

I think your assumptions are correct because if you look at the behaviour of the aircraft in the original Youtube clip in Vietnam or wherever it is, the traits are there of a sensitive elevator and with the speed the pilot is flying it the sensitivity is enhanced even more. I am waiting for some bits to complete mine but will be wary of how much movement I have on the elevator before flying. I am setting it up as electric but may convert to two 70 four strokes later.

[Christopher Wilkinson 1]

Hi,i have just maddened mine this evening, im running twin Saito 82s I set the elevator at the lower rate stated in the manual with 20% expo and it felt about right def doesn't need any more. I have the the cg at 145mm wheels up and it flew really nicely landing was uneventful slowed up really nicely with about 40 degrees of flap into a westerly 2-3 straight down the runway.Think it would fly great on 70 four strokes the 82s have ample power without being too much.If you go with four strokes you need to seriously beef up the engine boxes far to much vibration I glassed the outside with 2 layers of west system epoxy and cloth.

[Jon H]

A friend recently bought one and i was able to have a look at it. I was generally impressed and there is loads of space for tanks so i could easily fit some laser 70's. Its another model on my looooong list of models i want!

[Ian Moody]

I have test flown my Mossie today and have no concerns at all with the twitchy elevator. I have a 6v 3300 battery in the nose cone that I run all the servo's from which adds a slight forward c of g so perhaps this is all that is required to tame it. I also have two 6s 5000mh battery packs fitted for the motors with the battery's hard up against F1. It flew beautifully with a smooth take off and landing. I am very happy with it

[Danny Fenton]

Nice one Ian, can you give the c of g when you get a chance? Mine went in big time, but I might know of another that I am tempted to get.... dont want it to beat me and as you have proven that it flew okay. What props and motors?
Cheers
Danny

[Ian Moody]

Danny, The c of g is at 130mm from the LE with empty tanks and the undercarriage retracted. The motors and props are the same as you suggested in the part one build you did. One disconcerting flight characteristic I experienced was when I tried to perform a loop the aircraft got to the top of the loop and then did a sort of corkscrew manouver that was quite scarey. One of my flying buddies recons the full size did this on a loop?? Anyway, I don't think I will be doing any loops in the future. It rolls lovely, dead axial. And it looks great in the air.

May I ask how yours bit the dust if you don't mind?

Cheers Ian