Seagull DH-98 Mosquito engine choice

[Chris Walby]

Ian,

Did you back right off at the top of the loop or carry a fair bit of speed through the upper apex? I was thinking that if there is any difference in the motors across the speed range and its at a low airspeed you'll get a lot of yaw coupled with a rolling effect as you power back up.

Any information and experiences welcomed before I take the plunge

[Ian Moody]

Chris, I just kept even full power on and it didn't seem to slow down a large amount. I will get my mate to film it next time I am flying it (at a decent height of course) It sort of flicks but is easy enough to control. Its hard to explain it.

I didn't power up so I don't think it was an offset power concern.

After seeing everyone else's Mossies with the sensitive elevator I was expecting the same and was amazed it flew so smooth.

[Danny Fenton]

Hi Ian, thanks for the info on your flight, and darn you! I have had to source a 2nd hand airframe as I felt I was robbed of mine, before I had a chance to sort it out. And now that yours flew so well.....

At this rate the review will be in three parts! Not sure I will volunteer to do another.....

Signal loss and rearward C of G I reckon killed it....

So I am going to bring the c of g well forward, what about throws and expo?

Did you use the flaps at all?

Cheers

Danny

[Jon H]

flicking off the top of a loop is likely a tip still situation. As you get to the top of the loop let off a little elevator to keep angle of attack down as relative angle of attack will have increased due to a drop in airspeed. Given that gravity is assisting lift at that point you wont have any trouble pulling it over with the reduced elevator pull. Just remember not to yank too hard on recovery or it may stall again.

Danny while i have not flown this model i would recommend the smallest movements you think you can get away with and no expo. I was assisting a friend with a 75 inch P51 at the weekend and we settled on only 8mm up/down elevator for normal flying rates and as the initial 15 high and 10 low were both considered too sensitive. With rates as low as they are expo made it feel mushy so out it came. The model is now responsive and smooth without being sensitive. She looks great too!

[David P Williams]

Signal loss Danny? Was that the Taranis or the Jeti?

[Danny Fenton]

Hi David on Taranis, i bound the model to a friends X10 not sure why the signal loss. May have been poor aerial placement on my part.
Cheers
Danny

[Biggles' Elder Brother - Moderator]

Danny, did you get a "RSSI Low" or "RSSI Critical" verbal alarm? If not, and it was signal loss, I don't know whay not?

BEB

[David P Williams]

Sorry Danny, being a bit naughty probing. I'm a long time Spektrum user (with never a glitch) and I get a bit tired of the seemingly constant 'only get signal loss with Spektrum, and everything else is bombproof' posts. Whilst commiserating with you for your misfortune, it is a little comforting that it does happen with other radios.

[Danny Fenton]

BEB I cannot really say what we got, the model flew fine with no issues on my Mode 2 X7 then two weeks later on the mode 1 X10 we had RSSi messages, in the heat of the moment I couldn't tell you whether they were low or critical. The model went in and the props were not running with much energy, one prop unbroken and both spinners intact. Whether Chris pulled the throttles back or whether the failsafe had cut in and that's why it spun in we will never know. Unfortunately in my haste to bind to the X10 I neglected to enable logging, wish I had.

My Jeti is 5 today, and has never missed a beat. If I could have sorted out the SBUS equivalent on the Jeti then I would have. But then my friends would not have been able to bind to it, and I valued their flying opinion.

I think the problem was my error and down to poor Rx aerial placement, nothing to do with the radio equipment choice.

So David please let's not go there.

Cheers

Danny

[Jon H]

For those who contacted me about fitting Laser 70's to this model i have some good news.

Chris popped into the factory today with his wing/nacelle and we were able to look at the installation. Long story short its pretty simple and requires no major mods mods other than lowering the tank as shown in the photo. A small scallop should be created around the carb inlet and the mounting box needs to be beefed up (its a bit wimpy for any ic motor imo) but other than that its plain sailing.

The tank in the photo is a radio active 8oz and it just squeezes in with the nacelle over the top.

[Danny Fenton]

Very dispondant with mine. I am on a second airframe. I reduced the weight at the tail by ditching the heavy shock absorbing tailwheel, and solid rubber wheel. two 5000 5S cells stuffed right into the nose cone, and some church roof to get it at 130mm with wheels up. Unfortunately that has pushed the weight up to 16.5lbs!!!!

Not sure I want to even try it at that weight

Ian did you weigh yours?

Cheers

Danny

[Chris Walby]

Danny, wow that's 1.1 Kg over Sea Gull's max weight, although it will just mean that you will need to fly it a bit faster.

Odd as there is nothing in the RC Universe article saying they needed to an a load of lead and their AUW was very close to 6.4 Kg at actual 6.46 Kg.

Just how much lead did you need to add to get C of G?

Teaching you to sick eggs, but is there anything else to could more forwards like ESC's, RX + anything else....

Let us know how you get on and thanks for posting.

[Danny Fenton]

Hi Chris, the RC universe article really didn't make sense. He was putting the batts on the c of g.... that is definitely not going to work.... I wrote a comment to that effect but strangely the comment has been removed.

Seagull suggest the c of g at 150, and the model will sit at 150mm with a single 5S5000 in the nose, and I mean right in the nose! With no additional lead. That model was around 6.5kg.

However to shift the c of g to the 130mm mark recomended by Ian has meant adding a lot of weight, a second 5S5000 and probably 300g of lead!!! But as they say tail heavy fly once, (or once and a half in my case) So if the c of g has to come forward to 130mm to fly controllably, then thats what it needs.

The ESC's are in the front of the nacelles, the motor and batt wires are also in front of the c of g. The tail wheel has been replaced by a lighter unit. This model is shiny, no idea why. But that means a coat of flat clear kote is also missing, saving more weight. the servo and std mechanical retracts weigh less than electric units.

Others have used 2 x 6S5000 and I guess that is why. My 5S5000 weigh in at 600g a 6S high current will weigh around 840g

But at this weight i am nervous of both low speed AND high speed flicks. As the weight now stands I cannot fly it at Greenacres so another venue will have to be found.

Cheers

Danny

[Chris Walby]

Danny, thanks for your frank comments as its really useful for the rest of us and I agree with all of what you have said. I have a couple BH Mossie 's which have a 4S5000 as far forwards as possible which is a lot for a 2.5kg model and one with an additional 270g of lead to get C of G.

I feel your pain as its really hard with the mossie getting weight forwards, but what about ali spinners (ail does not weigh much, but the steel nut is a far forward as you can go Could get a heavy version!).

Unfortunately I learnt the hard way trying to land slow (3 blades and full flap had very high drag) so IMHO quicker and at worse a go around rather than tip stall at 25ft with gear down is a better option.

I am sure you have been through this, but if C of G is at 130 mm where does it end up with gear down, just gives options knowing that C of G is at "x" with gear up and "Y" gear down should things start to get a handful in the air and you need to revert to different setup.

All the best and keep posting

[Piers Bowlan]

Danny, the Elevator and Rudder servos appear to be well aft, behind the C of G. I wondered if you had considered siting them just behind the LiPos? Perhaps not a huge difference to the nose weight required but it might at least help a bit.

[Ian Moody]

My Mossie weighs 15lbs with two 6s 5000s right up against F1 and as I have said before I have a receiver pack under the lipo's as well. I have also changed the retracts for electric retracts from Hobbyking. What worries me is the undercarriage because of the lever effect of the long undercarriage legs if you don't come in straight with no side slip whatsoever the sideways lever effect could easily bend the legs or wrench the retracts out causing damage to the nachelles. I hope to fly mine again today so will try a few slow flying stall experiments at height and the loop concern I had before to try to pin down exactly what happens at what speed. The knees are knocking already just thinking about it. I may not have a Mosquito by the end of today, we will see.

[Ian Moody]

Well. I had a flight today and the take off and circuits were smooth so I took it up to about 400 feet and slowed it right down and fed in up elevator until i got a stall with the port wing dipping and a spin developing. The stall was not vicious and it was easy to get out of the spin using just elevator and ailerons. The next thing I tried was the loop again and it screwed out vertically at the top of the loop and it was because of the lack of airspeed because I tried another at full power and it didn't screw out. I tried putting large inputs of elevator in at speed and it didn't like that at all with it trying to flick out out of the manouver in a very similar fashion to a model that is tail heavy. I believe the only way to fly this model is with minimal movement of elevator or its dead. Anyone else flown theirs?

[Danny Fenton]

Thats great information Ian. I sat my Mossie back on Vannesa this morning, quite despondant. And guess what the c of g had moved to 110. I do not know what happened. Perhaps the pendulum pointer was not hanging vertically i dont know. But anyway, a little lead and 1 x 5s 5000 pack and i am on the 130mm so good to try again. Maybe tomorrow. Maybe during the week. Under 7kg again now.
Cheers
Danny

Edited By Danny Fenton on 19/05/2018 20:54:16

[Jon H]

Posted by Ian Moody on 19/05/2018 20:21:18:

I believe the only way to fly this model is with minimal movement of elevator or its dead.

This is not uncommon behaviour with warbirds and its the reason many a spitfire has bitten the dust. Anything with a sharp taper is likely to suffer more than something like a P47 with a larger wing. I know both are semi elliptical but the P47 wing comes to less of a taper at the tip.

A mixture of model setup and a slight change in your flying will see you safe. I recommend the lowest rates you can get away with (as you already noted) and when doing something like a loop don't be afraid to power through it. Once on top just let off the elevator a touch and let gravity do the rest. You could also adjust the aileron linkages to move both ailerons up slightly. This will give a slight increase in the washout (if there is any) in the wing and may help hold off a tip stall. Don't go mad, even 1 or 2mm will help a bit.

Edited By Jon - Laser Engines on 19/05/2018 23:09:36

[Ian Moody]

I have been flying warbirds (twins and singles) for the last 35 years so am quite aware of tapered wings characteristics and model set up and how to do a loop with power but there is something about this particular model that I am not sure about. It seems to me that the elevator is extremely sensitive, more so than any model I have ever flown and it is really annoying because it looks great in the air. I like to throw my aircraft around a bit and do low passes at about 2 foot but don't feel confident with this one. Maybe if someone else can fly theirs and report back we would gather more info and narrow down what the concern is.

[Denis Watkins]

Look at the Mossie in Plan Ian, as if for the 1st time

Massive twin nacelles, well forward, huge centre chord, with a relalitively small tail

But a long thin elevator, right smack dab in the middle of the propwash from the twin power.

Just instinct suggests that elevator authority will alter with prop speed

Edited By Denis Watkins on 20/05/2018 10:18:40

[Denis Watkins]

[Jon H]

Posted by Ian Moody on 20/05/2018 10:06:06:

I have been flying warbirds (twins and singles) for the last 35 years

ahh fair enough. didn't mean to tell you how to suck eggs.

I have not been able to fly one of these yet, I might see if I can wrestle the controls off the chap at my club when he finally gets his in the air

[Danny Fenton]

Ian pop over to RCGroups there is a thread over there that may be of interest?
Not many of us have flown these. I heard Andy Johnson has been wrestling with one too....
Cheers
Danny

[Ian Moody]

Jon, No worries mate just sort of pointing out that I am not new to flying warbird twins etc that was all.

Denis, Two other members of my club have different Mossies and they don't have differences in their elevator authority at different speeds.

One of my mates seems to recall a full size Mosquito skewing out of the top of a loop but cannot remember where he saw it.