Seagull Super Chipmunk ARTF

[David Rayner]

I was very luck to receive this as a crimbo gift from my wife. As I have an SC 70 FS looking for a new home it should fit the bill well.

Here are my observations, now that I have a first radio connection and control surface operation.

Content - Overall I think everything promised is in the box, except for the Spinner. As i usually source these separately this is not a loss - but color matching may be an issues.

Quality - The hardware seems to be good so far. The covering is a bit rough in places. Still loads better than I could do though.

Fit and build

The wing joining Tube is too long - I have cut 5mm off.

The tail wheel should be fitted before the horizontal stabilizer is glued in. Otherwise you will need to make extra clearance hole - guess how i know

The under carriage mounting holes needed to be re-drilled and the grooves trimmed.

The substantial sprung Oleo legs seem to be back to front. I have to dismantle them and see if they are easy to put right. I also had to correct the bends so they sat flat on the wing.

The flaps hit the ailerons - however they are hinged.

Most of the problems have been resolved - but the instructions are basic relying on pictures that are just about good enough. So this is really for people who have built an ARTF and are not concerned about getting the tools out. None of these issues are show stoppers.

This looks like It will be a great looking plane when completed - and I will update this thread with my progress.

[Biggles' Elder Brother - Moderator]

Sounds interesting David - any photos?

BEB

[David Rayner]

Here are some pictures of the oleo legs.

It looks ok untill you realise the wheel is on the inside of the leg

These are the legs out of the box

The look good and seem strong and well made. After a bit thought i stripped them down and re-assembled the rights way round.

And here is the assembled model on my very cluttered bench - next job the cowl. Gulp.

[David Rayner]

Just made my last post and had a reply from Seagull about the C of G. I was a bit confused as the manual says 88mm back from the LE in the text - in bold but repeated many times.The picture - of the actual model - shows 110mm back from the LE. Hmmm

 

A quick mail to the support team and they confirmed is was actualy 110mm, Very quick support - but a basic error!

Edited By David Rayner on 27/01/2014 14:31:32

[Mowerman]

This model is reviewed in latest RCMW. Also noted that CG needed to be 20mm back from suggested position.

Other than that looks very nice and reported to be good flyer.

[David Rayner]

Thanks for pointing that out Mowerman, i have just seen the digital copy. I was also suprised about the flap throws in the manual , so the reviewers comment about 85 deg being "fun" will be worth a try.

Edited By David Rayner on 28/01/2014 11:30:45

[MikeS]

This is good thread. I am planning on getting one from Wings n Wheels if I can find one there. I also read the review in RCMW and felt it would be a good model to go with my Grob Tutor.

[David Rayner]

Maiden Flight!

Sunday was a wonderful day to fly, so set for the maiden flight. The SC70FS fired up first go and was soon on song. So... Deep Breath.....

With the very able Andy standing by on trims I opened the power up and... No nasty tracking and in the air at a walking pace and away she went.

Now

Earlier in the post I mentioned the two C of G positions. I was careful to set the 110mm recommended but was aware this was the most rearward so was a bit concerned.

Pitch sensitive? New Pants!

Andy took over and tried to trim it then brought it down for a look. I added 60g of weight to the inside of the firewall and now she fly’s well and i2 perhaps a bit nose heavy. I will carefully recheck the c of g and post again on this but wonder if 88mm is the correc tmeasurement.

Once that scare was dealt with, I was able to make some initial impressions.

This is an airframe that want to fly, it lift of quickly and floats in to land. The Flaps are not needed, so a great first Flap model to learn with.

I have the Flaps set for 2s slow open and close and they does not seem to make a pitch change that I have seen yet.

Control throws are sporty and expo and rates make for a smoother and more scale presentation. (at least under my thumbs)

A hard pull on the up elevator produced a flick - so something to watch out for.

The undercarriage appears robust and has just the right amount of bounce.

The 70FS engine (the recommended size) gives scale flying but not unlimited verticals. it feels comfortable at half power and so ok. I can understand that some pilots may prefer a larger 90 size engine though.

Overall first impressions are good and I am looking forward to getting more flying.

[calum burgess]

How did you get on with the c of g. And how does it fly after the adjustment. I still have to build mine and have been watching this thread with interest, I am going to put an ASP91fs in mine but running on petrol.

[Keith Miles 2]

Five years on from this original post (!) and I have one of these and would be interested to get an update or hear from any other owners, or previous owners!

I bought mine a few months back to replace the (much prettier, in my opinion) World Models Art Scholl/Penzoil version which suffered a terminal mid-air collision after only a couple of flights! It WAS flying beautifully! Immediately tried to source another but without success, it apparently having been discontinued. The only option left was this Seagull version.

Shortly after buying it, I discovered that another member had one, electric powered. He had bought it from another member when it had apparently crashed immediately after take-off. Apparently, it had gone immediately nose high, before rolling hard left before hitting the green stuff. Keep that in mind and read on!

Said purchaser subsequently repaired it (very nicely, I should add) and made a number of neat, and some necessary, improvements along the way. Apparently, the original power set up was, he informed me, barely capable of a fast taxy until both the cell count and prop size were increased. Oleos were modified because he felt (and I can agree) that the springs (contrary to the originator’s view) would be good for a Range Rover or for use as chest expanders! (He is an aircraft engineer with more skill, enthusiasm and patience than I, so mine have been left alone for now!).

So, to that CG issue/inconsistency and other matters....

It does seem that 110mm is way off! He has it at about 90mm now, I’m told, and it flies pretty well at that. He has found however (and on looking at mine, he seems to be correct) that there is wash IN at the wingtips and that the model has a tendency to viciously drop the port wing at the stall which, if not quickly corrected with rudder, results in a very rapid spin! Handy to know! Apparently, the real life standard Chipmunks have this tendency as well so make what you will of all this and, also, the earlier mentioned take-off incident!

So, to my model.....

I can concur with ALL that was listed by the original poster and would add, loose trim; wheel spat holes not aligning with bracket holes requiring filing of the spats to correct it (see photograph); flimsy leg fairings attached with small self tappers into balsa; the usual “dodgy” instructions and pictures requiring some experienced interpretation and the biggest pain of all, an aluminium wing tube which (as previously noted by the originator) was too long. Not only that but mine was too tight in the wing recesses requiring several hours of careful (and tedious) rubbing down with various grades of silicon carbide paper. At this point, despite several “rub downs” of both the tube and the recesses with tissue and rags, I’m still getting black hands. Not ideal when the model is predominately white! Hopefully that will cease at some point!

I was also not happy, on this particular model, with the single servo/two-into one pushrod arrangement for the elevator. I like as much free movement as possible to keep servo loads to a minimum so opted to modify the servo tray in order add a servo and reposition the one for the rudder (see photograph).

So, that’s where I am at the moment. Cowl is cut and shaped and ready to fit. Prop and spinner can then go on and balance can be checked. A quick check suggests that this one is also tail heavy at present and may well need a fair bit of nose weight adding. Oh, and then the final decorations of course. After that, it will be brown trouser time.

Oh, forgot to mention that it is also fitted with one of those old fashioned smelly, greasy and noisy glo-powered four strokes, an OS 81 for those interested and who haven’t totally moved on to the world of a five minute flight interspersed with an hour sitting down and chatting while a battery charges. Not that I’m against chatting, you understand (as you may have noticed?).

😊

[Denis Watkins]

Is this the 63" span Keith? We have two at my patch, and one of them, may as well be mine, as my best friend had me assemble most of the model, and I fly it more than he does, but he has my Wot 4.

I set up the 2 into 1 elevator on one servo, as near as humanly possible accurately,

Then added 6 very small washers to the front and rear of each pushrod, then soldered them into an impregnable assembly,

This would need a dremel cutting disc in the future, if this ever needs removal

 

Edited By Denis Watkins on 15/08/2019 20:27:31

[Keith Miles 2]

Yep, that be the one, indeed, it’s now the only one around, it seems. I couldn’t even find a standard un-Superised Chipmunk in that size!

Ah, good old Wot4. I’ve crashed five of those over the years but am a much better pilot now and No.6 has been with me for some time now and gets LOTS of airtime, on an Irvine two-stroke of, course. Hoping to do my “B” with it before too long, once I get past the fear of attempting a bunt. The model is probably willing, however.....!

I am assuming, from your post, that the Chippie flies okay, then? No scary moments? Have you tried flaps? Just wondering what your overall impressions are compared to that of certain parties. Similar build issues, maybe? Oh, and more importantly, that CG issue?

Not quite with you on the washers thing. Any chance of a picture because I’m a bit dim?

😊

[Denis Watkins]

Washers and bound copper wire, semipermanent fixing

Edited By Denis Watkins on 16/08/2019 08:22:50

[Braddock, VC]

I wonder if one of you kind gents could advise the diameter of the torsion wire for the undercarriage please.

[Denis Watkins]

Posted by Braddock, VC on 16/08/2019 10:11:52:

I wonder if one of you kind gents could advise the diameter of the torsion wire for the undercarriage please.

Ours is a joint build Chipmunk Braddock, but I rebuilt this U/C with 4mm metric wire

That is near enough 8 swg

Reason being, it is flexible, yet rigid enough, and my bender can handle this size

More on the C of G, our instructions state 88mm 

And as we are intermediate flyers, no claim to being expert

The flaps were set from off, to 10° takeoff, and just 25° landing

This worked best, as most models, when deployed during finals throttle already decreased

So no lolloping nose up, or mixes needed, just a solid increase in lift at lower speed

As always, the model is under some power until the wheels touch down, so none of this gliding in at the end of the approach

Edited By Denis Watkins on 16/08/2019 10:52:13

[Braddock, VC]

Thanks for that, I have a scratch built model that needs torsion wires like that, regrettably it needs 5mm otherwise I would have ordered up spares from seagull, just my luck, eh?

[Keith Miles 2]

Denis, thanks for the picture. Er, yes, I would say that looks pretty robust!

Mind you, in the end, for peace of mind, I not only went with two servos but both of them, and that for the rudder, are Hitec 645MG Ultra Torque!. Probably overkill, but, hey-ho!

So, sounds like you’ve had no flying issues. Not knowing how long you’ve been flying it caution might perhaps be advisable regarding the aforementioned stall characteristic and also, as I forgot to mention, and as experienced by both my friend and the post originator, it also seems to have a tendency to flick with hard application of “up” elevator. I’m told that tapered wings can produce some “interesting” aerodynamic effects!

As usual, I have my control surface settings as per book figures to begin with, on full rates, and I then downrate from there plus, usually adding about 20-30% expo on elevator and aileron (Mode 2). Flap sounds about right. Would equate to the 20-30 mm recommended, I assume. My deceased Chippie was my first flapped model and I was in the process of fine tuning them when disaster struck so never got to try them for either take-off or landing! Bah!

After the scare stories (and the assembly issues!) my faith in this model is slowly being restored, so thanks for your input.

Stand by for updates!

[Keith Miles 2]

Denis, I forgot to ask how the two Seagull Super Chipmunks, at your field, are powered? Just curious, that’s all .

[Denis Watkins]

Both IC 4 stroke Keith,

Ours on the 72 and another on the 81

We are predominantly IC at my place, presently, but approaching 50/50 with electric power

[Keith Miles 2]

OS 81 in mine. Made a lid for the top of the tank bay to keep any spits of fuel out of it. Also added a ply plate inside the tank bay to move the tank back slightly in order to allow sufficient clearance behind the engine for plumbing. Also forgot to mention that I had to ignore the figure of 110 mm given for the distance between bulkhead and rear of prop driver due to the OS engine dimensions. It also seemed, later, that with a different engine, and the cowl positioned where it should be, that the prop driver, using that figure, would probably not have cleared the front of the cowl! My engine is as far back as I can practically allow and the cowl fits as far back as it will go. Prop driver just neatly clears the cowl but at a distance of 125mm. Another possible “gotcha” for the unwary! I also usually pressure feed the tanks on my models but after discussions with my regular guru, and a successful experiment with my Wots Wot with the pressure line removed, I’m going to try that with this one. Tubes are in place for an easy change over if required. I have also fitted a sintered bronze clunk filter as recently fitted to the Wots Wot to cure an air in the fuel line issue, the subject of another recent thread!

[Keith Miles 2]

Update, update. 110 or 88?

Model balances level, as it is, at the 110 mmm position.

BUT, with fingers at 88mm position, 12oz of nose weight (a lump of old lead gas pipe) had to be taped to the cowl, at the engine position to achieve balance!

AND the model is also already 8oz above design weight, although I suspect that design weight of 7.9lbs is optimistic.

The three high torque servos (my mod) for rudder and elevator only account for a less than 3oz difference above fitting two standard ones and, also, offsetting that, are about a couple of ounces of added ply and fuel proofing at the front end.

So, as others have experienced, CG and balance seems to be a bit of an issue with this model, especially in view of conflicting supplied CG information from the manufacturer!

So, I would be interested to know, if at all possible, of those models already flying successfully, where your ACTUAL balance points are (lipos fitted or fuel tanks empty, of course!).

Need to have a little think about mine, at this point, but I definitely won’t be adding 12oz!

[Denis Watkins]

In this smaller scale size class, Keith; warbirds included, and even as we move up to 10lb, 15lb, 20lb yipes!!!

We have no choice with C of G, where weight has to added, the model then needs that weight, you know that

We all don't want to add weight as speed goes up.

I maiden most models at my patch, and if the C of G comes out On or just in front of the wing tube, then I go for it.

In this size class, I can compare the Super Chipmunk to a Corsair we fly, a Kyosho 50 Hurricane, and the Seagull P51.

All need flying with care, should be kept moving, no loitering, and have planned flights without ad lib stick inputs that allow them to bite you.

When you know the model better, then explore the envelope.I

This Super Chipmunk with the OS70fs Balances at 90mm, upright or inverted.

There looks to be 4oz noseweight across the front of the engine mount

We cast weights to bolt under motors

Don't stick weight in a cowl, as an heavy arrival will break the cowl

[Keith Miles 2]

Denis,

Thanks for your CG info. Will check again later but not happy adding 12oz even if there was room to get it in. It would put the model way over design weight and that ain’t good either.

What was interesting was that the thread originator first balanced at 110 mm then just added 60g. He never came back with his new CG position, hence my question.

I note that your models, apparently, have only relatively small weight added as well.

Whether my servo mod has made mine especially tail heavy remains to be seen. May have to change that to avoid adding too much balancing weight. No other reason for it that I can see, other than a flawed design.

And I have never had to add more than 3 or 4 ounces for balance on any model thus far, the worst case being my Wots Wot.

[Denis Watkins]

To add Keith, after having a look

Our flight battery is alongside the tank on the front bulkhead

And the OS motor is way up front on the engine mount

[Keith Miles 2]

Hi, Denis, thanks for info.

No, I would never add weight to a thin cowl, attached by self-tappers, especially 12oz!

As for engine position, moving mine forward would be unlikely to shift the balance significantly (see previous photo). Moving the lipo flight battery forward would make it difficult to remove for charging and, similarly, I doubt that it would make a significant difference either in terms of achieving 88-90mm CG (see photo below).

in case you have not seen one, I also include a photo of my deceased World Models version. You will immediately notice significant visual differences. There are quite a few more, including the one-piece wing! That said, overall dimensions are pretty identical but the WM version is a recommended pound lighter (that comparatively heavy Seagull u/c having much to do with it, I reckon!). Stated CG of the WM model is 105mm and it balanced at that with no adjustment and flew fine with just a touch of aileron trim.

Noting that David Rayner added only 60g after balancing at 110mm, and noting your recent comments, I’m minded to do similarly and then just test fly it, or get one of our far superior pilots to do it! I’m reasonably confident that it won’t be uncontrollable. Touch wood!

And, yes, that is a Corsair in the background! Bought second hand. Flown once. Had to repair one of the retracts. Subsequently noted side slop at one of the hinge positions, so rudder may have to come off. One day, I’ll get around to figuring how best to go about fixing it. It’s a closed loop system and access is a little tricky!