Seagull DH-98 Mosquito engine choice

[Geoff Parkes]

Bill, you will get contra props for electric from a company called 4 max in the U.K. as I posted I have a Brian Taylor Mosquito, electric powered and use 2 x 14 x 6 contra. props, he used to sell 3 blade contra.props as well, but not certain if he sells them now, a visit to his site will tell you.

[Bill Walter]

Geoff , Jon and Cmaz

Thank you Gentleman for the answers to my questions about the mosquito.

I'm still in the "thinking about it" stage because I've had such poor luck with twin engine planes

I will probably do it though

Bill

[Jon H]

Posted by Bill Walter on 08/11/2017 13:14:53:

Geoff , Jon and Cmaz

Thank you Gentleman for the answers to my questions about the mosquito.

I'm still in the "thinking about it" stage because I've had such poor luck with twin engine planes

I will probably do it though

Bill

Without knowing your history with twins Bill its hard to comment but there is definitely a learning curve with them as even on electric they can still give trouble. I have seen esc's give up, identical setups run a different rpm and (very spectacularly) one esc go into low voltage shut down when the throttle was slammed open on a go around. With the instant torque of the other motor it didnt end well for the model.

All that said, they are well worth the effort and the various ic multi engine models i have flown have all been really enjoyable and well worth the time spent learning the way they wanted to be handled.

[Richard Wills 2]

Maidened the Mossie this afternoon, unfortunately it did not make it home in one piece! Damage isn't too bad, one broken nacelle box and one broken wing seat. Engines performed faultlessly, plenty of power. Ground handling is not good, even at double the book throws the rudder is very ineffective. Once up climb out was uneventful, and my god it looks good in the sky. Got it trimmed out, and flew some circuits. Pitch sensitive even on low rates, not too bad though. Rudder just doesn't do anything, not even enough to correct the adverse yaw. Did some faster flying and it took it all in it's stride, really fun. Time to land, brought it in on full flap, settled nicely into slightly nose down descent kept the throttle open a 1/3 ish, plenty of speed, but no rudder response to speak of so decide to let it direct itself into wind, plenty of space on the beach. Then the crunch. Fed in a little elevator at about 4 feet to level the descent, and bang, violent wing drop to the right and cartwheel. Ended up on it's wheels left engine hanging from the fuel pipes, right engine still ticking over nicely....

So repair time, enjoyed flying it, so hopefully be back soon.

[Sabre Flyer]

Hi Richard, congrats on your maiden and sorry to hear of the prang on landing. Hopefully it is not so big a repair job though. Was it the sensitive elevator that caused the tip on landing or did you get a sense of it being prone to tip stall? Did the c of g feel good?

[Chris Walby]

Sorry to hear the bad news and hope its repairable without too much work.

Where you using flaps (half or full) as my BH mossie is very draggy at full flaps (lesson learnt the hard way from 10ft and the wrong side of the hedge!), but normally okay either no flap of 1/2 flap.

Surprised about he rudder response as the BH one seems okay 63" wingspan and rudder 15mm each way if that's any help.

Keep posting as its good to hear how you get on.

[Jon H]

Most unfortunate Richard. The lack of rudder authority on takeoff is likely down to not having any prop wash over it like a single engine model. A slower throttle up should help this. Dont forget that full size mossies suffered from takeoff swing as well and needed careful throttle application.

A tip stall right is unusual and could suggest the left engine was running faster than the right at that point. I also agree with chris about the flaps. My Sea Fury in particular needs loads of power to keep it motoring along with the flaps down, and that has a 360v up front!

[Richard Wills 2]

No the sensitive pitch didn't cause the crash, I accounted for it and only really put pressure on the stick to level off. I did wonder if the cg was too far back, but 45 degree inverted climb suggested it was actually slightly nose heavy. This was as the manual suggested which I don't think is too far off. The only warning to speak of is the ailerons go mushy, which unless in a turn you won't notice, and then a violent drop to the right. Unless you turn gently it will snap out of a turn at normal flying speed if you pull too much elevator, so it is going to need respect.

Bigger concern at the moment it the rudder, felt like the servo wasn't working, even at speed. checked on the ground and it is.  Was at half flap on the landing, dummy approaches it felt better at half than full.

Edited By Richard Wills 2 on 15/11/2017 16:59:33

[Jon H]

Double check the rudder rod isnt bending once there is airflow over it. The rudder is a fair size so im a little shocked its that ineffective.

The snap behaviour you mention suggests a lack of washout in the wings. If you have an incidence meter it might be worth checking both wings are the same. Even if they are, lengthen the rod on the ailerons slightly to raise them both a smidge. 2 turns of the clevis is likely to be more than enough and will hardly show on the ground.

what is the rudder deflection by the way? i would look for a good 45 degrees if it was mine. 

Edited By Jon Harper - Laser Engines on 15/11/2017 17:13:53

[Richard Wills 2]

I am going to do some work on the rudder, the hinge methos used means it's a bit sloppy, not too bad but may as well look at it, and the linkage. There is something amiss as like you say it's not small! I have about 35 deg at the minute, will increase this.

Good tip on the ailerons up to create washout, it needs it.

Decided it is going in the naughty corner for a bit while I finish putting my 109 together.

[Ray Charnock]

Hi Richard

Sorry to hear about your maiden crash mine is not quite ready yet i have to get the cg set and the control throws set weather not so good a quick question did you have to add any weight to get recommended cg.

Regards Ray.

[Richard Wills 2]

Posted by Ray Charnock on 16/11/2017 08:43:24:

Hi Richard

Sorry to hear about your maiden crash mine is not quite ready yet i have to get the cg set and the control throws set weather not so good a quick question did you have to add any weight to get recommended cg.

Regards Ray.

yes, 13 oz on the nose bulkhead. ended up at 15.2 lbs dry.

[Ray Charnock]

Hi Richard. thanks for the information what engines are you using 2 stroke or 4 stroke.

Ray.

[Richard Wills 2]

4 stroke, Saito 82's

[Jon H]

Posted by Richard Wills 2 on 16/11/2017 09:44:27:

4 stroke, Saito 82's

boooo

[Chris Walby]

Jon,

What's the difference in weight between a Saito 82's and a Laser offering to save on the 13 oz of lead and to buy British + increased reliability?

 

PS - I am a member of the anti lead freedom fighters! our motto "down with lead"

 

PPS sorry to go metric, but Seagull say AUW 6.2 to 6.4kg Richard's was 6.895 dry so that's somewhere (best case) between 7 and 10% overweight (no fault of Richard as you need CofG in the right place) and I have had this with the BH Mossie (adding lead to get correct CofG)

Would the + 10% weight have an effect on low speed flight characteristics, more abrupt tip stall?  

Edited By Chris Walby on 16/11/2017 11:01:13

[Jon H]

At the size of model we are looking at the weight is not an issue i wouldnt think. My 80'' fighters are 19-23lbs so 15 or so is plenty light enough.

In terms of engines our 80 is 190g heavier than the saito effort and our 70 only 80g heavier. I am sure twin 70's would be plenty but the 80's would turn a larger prop which might be quite nice.

As for the ALFF i will pass on membership as adding lead has never worried me. Its got to balance at the end of the day. I do agree though that lead can be minimised by careful placement of parts. No need to add 2 lbs when 1 will do.

The spin was likely due to a number of factors all related to it being a new model. Very low experience with said model, imperfect rates/balance, imperfect approach and perhaps slightly mismatched engines.

I dont know if you tested the stall at high altitude Richard? for me this is a key point of any test flight as it gives me a clue what will happen at the stall. some say its pointless and give numerous reasons for it, but for me knowing that a model will flip on its back is important information and will encourage me to be gentle on approach.

[Richard Wills 2]

Don't think the weight of the model is an issue, in fact comparing it to my 60 sized Mustang at 11 lbs, it is quite light. Had a quick check over the model last night, and the rudder linkage does have a bounce in it under load so maybe that explains the soft rudder. I'll sort that and increase the throw.

The engines are almost as far forward as the position of the lead, so 2 80's would balance better. The model was more than adequately powered, so the 70's would be great. In fact it took off at about 2/3 throttle without elevator on a nice long run so lots more than necessary. I have 14x6 2 blades on it they look just right.

I spent quite a while matching the engines with a curve on one channel through the rev range by ear, didn't resort to a tach but I have spent a lot of time balancing twin 2 barrel webers so I know they sounded close.

Jon I did do a stall test, which was vicious, but didn't seem to be at a speed/AOA that seemed dangerous, and also noticed it's tendency to want to fall into a spin if you bulied it in a bank so did keep up the approach speed.This was my first proper twin, not counting the foamy 110 have, so John is right on the low experience thing. I spent some time last night working out what I was doing, and I think I made a big mistake in coming in about 30 deg to the wind because there was a longer run of clear sand on the beach in that direction, not thinking about the trouble I was having with the rudder. At the moment of doom I was just starting to think about a flare, doing my final heading correction with you guessed it, a bit of left aileron just as I started to feed in elevator and also without thinking reducing power. Lesson learned, and I can't wait to get it back in the air and have another go.

[Jon H]

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.

[Ray Charnock]

Hi all

Last year i was flying the Freewing Mosquito and when i was flying it i always thought about the opening scenes in the movie 633 squadron were the aircraft are coming in to land as you can see they always approach at speed and put the aircraft down on two wheels same on take off its slow opening of the throttle then raise the tail to get rudder authority this is how i flew my mosquito and that is the way i will fly this one.

Ray.

PS i am not trying to tell people how to fly their mosquito thats just my way of doing it.

[Martin_H]

Fitted my Saito FG11's to the ply nacelle mount - perfect fit! Was worried I'd have to redo the mount holes to suit the Saito engine mount but no problem!

[Ian Moody]

Posted by Martin_H on 19/11/2017 11:23:27:

Fitted my Saito FG11's to the ply nacelle mount - perfect fit! Was worried I'd have to redo the mount holes to suit the Saito engine mount but no problem!

Do you have any photos of the installation and of the inside of the nacelles also of the inside of the fuselage please Martin. There is very little to be found on the web about this model yet except for someone flying it like a pylon racer in Vietnam and I would love to see some more detailed pictures of the parts. I quite fancy one of these.

Thanks Ian

[Martin_H]

Posted by Ian Moody on 19/11/2017 15:38:55:

Posted by Martin_H on 19/11/2017 11:23:27:

Fitted my Saito FG11's to the ply nacelle mount - perfect fit! Was worried I'd have to redo the mount holes to suit the Saito engine mount but no problem!

Do you have any photos of the installation and of the inside of the nacelles also of the inside of the fuselage please Martin. There is very little to be found on the web about this model yet except for someone flying it like a pylon racer in Vietnam and I would love to see some more detailed pictures of the parts. I quite fancy one of these.

Thanks Ian

Hello Ian,

Check your inbox, I can send a copy of the Seagull Manual in glorious technicolour!

[Martin_H]

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.

[Gavin Mack]

Link to manual

http://www.skysharkrc.com/Downloads/Mosquito_Instructions.pdf

 

 

Edited By Gavin Mack on 05/12/2017 21:31:25