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Seagull Extra 300L, help needed


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Hi Guys
Just bought a Seagull Extra 300L (1.4 mtr), and I need some advice.
Pleased with the purchase so far, but a closer inspection reveals some oddities.
First of all, I assume the model comes without servos, yes?
Mine has a 3001 on rudder and a 311 on elevator. Seems to be working fine, so no issues there, but the aileron servos are ParkZone PKZ 1081. Can't find any specs on these, apart from discontinued and replaced by Spektrum SPMSA 382.
Can't find any specs on these either, but they look pretty weedy so might replace with Emax ones.
Now comes the real question, regards c/g and overall weight.
Manual says c/g should be 75mm from LE. The model had a mark on the wing but this was 100mm back. Also the previous owner had epoxied a load of weight to the front of the cowl.
Anyway, put it on my balancer, and even with the heaviest battery I could find, 2 x 3s 5000 in series, I could only get the model to balance on the rear 100mm mark.
Also with the big battery, took the all up weight to a whopping 7lb 9 oz, or 3450g.
Certainly won't have any issues with turbulence at that weight but it does seem awfully heavy to me.
Am I missing something?
Jeff

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Jeff, I have one of these models, and fly it but it has a glow motor, not electric.

It is 1lb 3oz lighter than yours at 6lb 6oz

The C of G is bang on the Wing Tube at 75mm

And I never add weight to the cowl, as it can break through or pull the cowl off.

There is a small weight at the front of the engine mount but our set ups are different.

I have regular JR servos in the wings

Hope this helps

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Hi Denis, thanks for the quick reply
Not sure if it answers any questions, or brings up a whole set of new ones.
First things first, you say yours balances at 75 mm, bang on the wing tube. My wing tube is 100mm from the LE, not 75.
I did catch a post on RCUniverse from way back, where someone flew his at 100mm, so I might give that a try.
However, a c/g too far back, and an overweight model is a recipe for a re-kit.
Not sure what glow motor you have in yours, but I have a spare Irvine 53 over here, and that weighs in at 524g,
On my electric set up I have a motor at 275g, two batteries at 362g each, or 724g and the weight in the cowl at 289g. That's a grand total of 1288g or getting on for 3lb in real money.
Bear in mind this only gets it to balance at the 100mm point.
Just to make it more interesting still, I downloaded the manual, and that recommends a 35 size motor at 830Kv on 4 cell.
Whether that would have enough power to get out of the way of its own shadow, I'm not sure, but it would never balance anywhere near that way.
Agree with you about attaching weight to the cowl. That wouldn't have been my choice either. The previous owner had epoxied a strip of lead, and 15 two pence pieces in there. The loose change alone would be 107g by itself.
That of itself poses a problem. If I manage to find a way round this balance issue, won't be able to remove the weights without destroying the cowl.
Might change thinking on aileron servos. Was going to use a pair of Emax ES09's, but I have a spare pair of midi size I might use instead, we'll see.
Still can't help thinking I'm missing something obvious, any ideas?
Jeff

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The OP states they have the manual and it gives CG as 75mm from LE of wing at root. Denis Watkins also posted a screen shot of a manual showing the same thing. It looks to be taken from the manual of the Seagull model with the part number SEA-199N as per the attachment. I wonder if the OP actually has this model as they seem to have bought it used (references to servos already fitted..). Either it's not the model in the manual or something else is amiss...

7645719.pdf

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Hi Guys, appreciate the help.
Alan, you might well be right. I have the two seater, which makes it an L, despite having 300S on the tail.
However more important is the 300S is a much bigger aircraft overall.
Span is 63" compared to 55" for mine. Overall weight for the S is 6.6 to 7.5lb, S is max 6.6lb.
Power requirement is .61 to .75 2str for the S, where the L is .46. In short, the L and the S are completely different aircraft, over and above number of seats.
Caveman
Thanks for the link, but that's not the model I have.
First page describes gluing the wing halves together with a ply joiner. Mine are in two pieces, plugging to each side on an aluminium tube joiner.
No doubt it is for a Seagull Extra 300S, but not the model I have. Either an earlier or a later version. Right at the end of the manual it describes fixing a 35mh aerial, so I would suggest earlier.
Still have no idea why, despite having a bigger motor and heavier battery than recommended I still need some weight in the cowl just to get it to balance some 25mm further back that the manual recommends.
Just one silly thought.
Manual suggests marking the c/g on the top of the wing and balancing the model upside down. I did mine on a proper balancer right way up.
Can't possibly make a difference, can it?
Jeff

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Yes Alan, I've just looked at my manual and it's the same as the one you posted, although mines a poor black and white version, not the coloured one. HOwever, the cog instructions are the same.

 

I have to say that when balanced at 75mm back from the wing root I found the model to be very nose heavy. I checked the cog using an on-line calculator which suggested a position further back.

 

I was in the process of moving the cog further back in small increments in order to find a good position when a close encounter with another model caused mine to impact the ground at high speed, ending any further experimenting. ☹️

 

I still have the wings in the loft somewhere!

 

GDB

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Jeff, my model was the smaller 300L with a 2-piece wing and an aluminium wing spar, exactly as per the manual Alan has posted 3 posts back. Mine had a Irvine 46 MKIV and standard Futaba 3003 servos throughout.

 

GDB

 

PS I've just realised that you saw my erroneous post which I edited. Please ignore my original post!!

Edited by Caveman
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14 minutes ago, Jeffrey Cottrell 2 said:

Hi Guys, appreciate the help.
Alan, you might well be right. I have the two seater, which makes it an L, despite having 300S on the tail.
However more important is the 300S is a much bigger aircraft overall.
Span is 63" compared to 55" for mine. Overall weight for the S is 6.6 to 7.5lb, S is max 6.6lb.
Power requirement is .61 to .75 2str for the S, where the L is .46. In short, the L and the S are completely different aircraft, over and above number of seats.
Caveman
Thanks for the link, but that's not the model I have.
First page describes gluing the wing halves together with a ply joiner. Mine are in two pieces, plugging to each side on an aluminium tube joiner.
No doubt it is for a Seagull Extra 300S, but not the model I have. Either an earlier or a later version. Right at the end of the manual it describes fixing a 35mh aerial, so I would suggest earlier.
Still have no idea why, despite having a bigger motor and heavier battery than recommended I still need some weight in the cowl just to get it to balance some 25mm further back that the manual recommends.
Just one silly thought.
Manual suggests marking the c/g on the top of the wing and balancing the model upside down. I did mine on a proper balancer right way up.
Can't possibly make a difference, can it?
Jeff

But then it sounds like the manual YOU refer to in your original post (CG 75mm back you quoted) is NOT the correct manual for the model you have. It would perhaps help others to answer your query on where the CG should be if you post a photo of your actual model so that we can locate the correct manual with the correct CG position or else we are all guessing!

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Hi Alan

Been right through the manual I have, even found the pictures Denis posted.
Everything I looked at convinces me this is the model I have. Servo layout, three bolt fitting for the u/c, glue in fiberglass control horns, the list in endless.
Only thing different is the colour scheme, and we all know how often these are changed.
I do really think the manual I have is the correct one.
Anyway, took some pictures as requested.

Caveman
Apart from the colour scheme, that's the one I have. Front page of the manual is identical, and the dimensions match with my aircraft.
Thanks also for posting a pic of the back page. Clearly says c/g 75mm back from le at wing root.
I rest my case, m'lud.

DSCN0001.JPG

DSCN0002.JPG

DSCN0003.JPG

DSCN0004.JPG

DSCN0005.JPG

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1 hour ago, Caveman said:

I have to say that when balanced at 75mm back from the wing root I found the model to be very nose heavy. I checked the cog using an on-line calculator which suggested a position further back.

 

 

 

 

Hi Caveman

Just done the same operation, and the results are interesting. By my calculation I could have the c/g at 109mm. However it does show the distance from le to ac (aerodynamic centre) as 75mm
Could it be that Seagull just chose the wrong number to put in the manual?
Anyway, I seem to be heading to the model being safe to fly at 100mm.
Still not sure about all up weight, but only flight testing will tell me that
Must remember spare underwear for the maiden.
Be a little while yet.
Decided to swap the wing servos as well, might need a bit of lateral thinking.
Work in progress
Jeff

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Hi Guys, the plot thickens.

Had the Extra out for its maiden this afternoon. First flight, and very nearly its last.

Model was almost uncontrollable. So called level flight had the tail hanging down at 30 degrees or so, and over sensitive on the primary controls. All signs of a too rearward c/g.

Nowhere near enough power either, but I think I have sorted that. Did a re-calibrate of the esc, Now showing 36.71a and 859w on a 14 x 7 prop. Got a 15 x 7 on order, hope to get above 900w.

Main thing, though, is the c/g. Not sure what to do about that.

It has a massive metal tailwheel set up, and that could be swapped for a simple skid. Lose a bit of weight at the extreme tail end. Also the esc could be moved to right behind the motor which would help a bit, but can't help feeling that won't be enough.

Any ideas?

Jeff

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Have tried to stay out of this Jeff, as we all know, rearward C of G is a nightmare.

That tiny iddy biddy tailwheel is not going to make a near 8lb model unflyable, so leave that where it is for groundhandling.

Could you get a wings off side pic so I can compare to mine, like this, and see the builds are similar.

My C of G is just online with the front of the wing tube.

IMG_20220802_114834.jpg

Edited by Denis Watkins
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  • 2 weeks later...

Hi Denis
Sorry its taken so long to get back to you, other projects keep getting in the way.
Anyway, to horse:
As requested attached is a side view of my model. Apart from the colour scheme looks identical to yours. Measured on the wing, distance from le to front of wing tube is 90mm. That puts centre of the wing tube at 100mm.
I see internet posts of flying at 100mm, and my c/g finding program says could be 109mm.
Anyway, added some more nose weight to bring it to the 75mm from the manual. Clubmates pronounced it very nose heavy, and after a test fly, I would have to agree.
For the test flight, as well as the nose weight, I re-calibrated the esc to produce more power, and cut down the control throws to avoid the overcontrolling from the first flight.
Anyway, test was encouraging, if only a little.
Took a while to get off the ground, as expected, and control responses were sluggish, also as expected, but it flew and landed in one piece, so that's progress.
Main thing is I flipped it to inverted and it took full forward stick to fly level. Seems my clubmates were right, too forward c/g.
So, I made the extra noseweight removable so can pull it off bit by bit, see how it goes. The weight fitted by the original builder is glued in, so will require surgery to remove it. Not sure whether to go that route. Depends if it could use the c/g going even further back once I remove my weight.
So, work in progress, slowly.
Any thoughts would be appreciated.
Jeff
P.S. Came across a guy in York, who was flying his with fpv gear at the rear pilot position. This plus even more noseweight pushed the overall weight to over 8 lb. He said it flew fine at that weight, but landing speeds were pretty high.
There's hope for mine yet.
J

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