Seagull's big PC9

[Ian Jones]

Kozmyk, I've sent you a PM. Thanks for reproducing that message - reading it again I see I didn't properly answer the question Tim asked.

 

AUW = 12.25lbs, the SC180 FS will be contributing to some of that as well as the other items I listed.

[Tim Mackey]

So your bird is 12.25 lbs Ian - a tad heavier, but as you say, quite a lump you have in her there. Nice to know she flies at that weight though

Not wanting to pre-empt the results, I quietly confess to being slightly concerned that the powertrain will not be up to the spirited flight performance I want, she is a heavy big thing -but as I said, it was a case of utilizing a motor I already had looking for a home.

I had hoped to fit my onboard sound system too, but that just adds more weight so its a no go for now. IF she proves underpowered, then my likely action will be to just bite the bullet and either ( switches to hushed tones....buy a nice big smelly 2 stroke ) or a new lower Kv motor, and up the cell count to 8.

Off to wash my mouth out now

 

[Tim Mackey]

Just did a few tests with a larger ( 15 x 8 ) prop, and the results are below. Did my usual 30 seconds of WOT and low throttle mixed, then 90 seconds of mixed, and finally 30 seconds at 1 kw just to assess likely duration.

Picture 1 shows the 14 x 7 versus the 15 x 8, and as can be seen....

Power has jumped to over 2kw ( + 33% )

Current is now a rather hefty 90A peaking at 96A ( + 35% )

And RPM is 8928 ( - 4% )

 

It certainly has some oomph now, but I am running my 80A speedo very close to maximum, and duration may be a problem.

Of course, there should be some unloading in the air.

 

However, a 90 second burst of mixed throttle consumed 1364 ma, so by that reckoning, I might get around 5 minutes which would be fine.

This is the data of that run.

 

Then I did 1 x minute with the throttle set to give 1 kw which would fly it easily, and this consumed 737 ma - based on that particular data, a 5000mahr pack should be good for around 6.5 minutes.

Recharging after all the tests ( 3 minutes+ in total ) put back 2700 ma, so just over half was consumed. Allowing for not running the pack too low, this suggests that 5 minutes may be achievable.

If I decide to use this larger 15 x 8 prop, the extra power should mean I could possibly use 2 x 5000 packs in parallel, but how much effect the extra weight will have is a worry, especially as I am at 12+ lbs now.

Decisions

[Ian Jones]

Make it a proper turbo prop Tim

[Tim Mackey]

Now theres an idea.....just need a way of convincing the accountant

[Tim Mackey]

Almost finished, the fuselage IS finished now, and the decals have finished it off an absolute treat. The tail is also finished, and sits,complete with servos and wiring loom, fully independent of the main fus. I settled on a simple yet purposeful solution to the wing joining. Obviously the loads are taken through the substantial aluminium main joiner, and alignment is taken care of by a rear incidence peg.

 

First I cut two oblong access holes through the lower wing skin sheeting, near to existing lightening holes.

I then cut a hardwood block which is screwed and glued onto the inside of the revealed main root rib - this will take a 6mm threaded steel screwed insert. The existing lightening holes allowed me access for a clamp to hold the block whilst the epoxy set.

A 1/8th ply joining "strap" was then cut to fit the hole, and is permanently fixed to the main wing centre section - "bridging" across the joint, whilst slightly flexing to fit the small dihedral angle.

 

Heres the threaded insert screwed into the hardwood block.

 

 

 

 

This is fixed to the outer panel with a single 6mm nylon wing bolt and washer.

 

 

 

After its all finished, I will cover with matching film and paint as required.

[Richard Wood]

Interesting motor run data - that's a potent setup.

96A is a lot of current but the motor's rated at 100A so

you're getting the max out of it.

Hard decision to make on the battery though.

 

Do you get any screeching & oscillating if you run up slowly

from low throttle with your Scorpion?

I often bang the throttle straight up to about third so the motor

starts correctly & then back off a bit.

I don't know if this is an ESC timing thing or my imagination but

Scorpion motors seem to be prone to doing this.

 

 

[Tim Mackey]

Sounds like a timing issue yes. I am using a turnigy plush series ESC and have set the timing to MID, and it seems to throttle nicely even from standstill.

I have found in the past, that altering other factors such as PWM and start up options etc, can also affect the "stutters" - sometimes you need to play with different combos until you hit the sweet spot, and sometimes, it just never gets completely right - some ESC simply cannot handle the motor chosen. This is the only Scorpion motor I have, so not sure if its a known issue with them.

Maybe once yours is actually flying and windmilling, it will solve your problem?

[Richard Wood]

Cheers Tim.

It's a Scorpion ESC so should be a good match.

I think it's set to high timing & normal startup, but I'll play

around with settings & see what happens - it's all good fun.

 

Not recommended to do what I tried once on a bench run

with a stutterer - try to set it off in the right direction with a

finger.

Ouch - they bite!

 

[Tim Mackey]

Ouch

[Tim Mackey]

Shes finished and awaits her maiden flight.

[Ian Jones]

Looks good Tim.

 

What have you used to stick the "optional parts" on ?

 

 

[Tim Mackey]

Ah yes, those mysterious optional parts LOL - took me a while to figure those out

I didnt bother with the wing bolt cover plate, as I just couldn't see how this was do-able unless you drilled two holes in it first? Whats that all about ??

The radar dome, air-intake scoop and sharks fin I just cyano'd in place, after first cutting the fin down to around half size otherwise it just fouls on the ground.

[David Ashby - Moderator]

Looks grand Tim. When's the maiden?

[Tim Mackey]

As soon as I can get JB down to the field - and of course arrange some dry weather

[Ian Jones]

I used cyano for those parts Tim but they are back on my bench now - they came off when I was checking if they had stuck. I'd stuck them on after the maiden and put the rest of the decals on too.

 

I didn't fit the cover plate for the same reasons as you, so I presume you may have made the same mistake as me. It's not a wing bolt cover plate. It's a fairing to blend in the shape of the nose into the the underside leading edge of the wing. Of course my presumptions could be wrong because of your custom two peice wing arrangement. I still don't know how I'm going to get it to stick on though.

 

What about canaopy glue, could that do the job?

Edited By Ian Jones on 14/02/2011 16:49:02

[Tim Mackey]

Ah, nice one Ian - Ill go and have another look at that bit then!

I normally use a good quality clear silicon sealant - the type used on fish tanks.

[Danny Fenton]

I have one in my Chippie that stutters never manged to cure it. Once its spinning it doesn't have a problem in the air. If you let it stop when taxiing back in though it will stammer again so keep it scale, keep it running

 

Good luck with the maiden Tim, i am sure it will go well

 

Cheers

Danny

[Richard Wood]

Looks very good Tim .

The Tx in the pics gives it some scale - it's a big model.

 

I cured that stuttering Scorpion by setting whats called a

'Motor Start Booster' in the ESC from 'soft' to 'strong'.

Starts up smoothly now.

 

Cheers

 

 

[Tim Mackey]

Thanks Richard.... yes its quite large - the canopy especially makes it looks quite an imposing model.

As I say...I have found no issue with the motor and ESC combo I am using, I am on medium timing, primarily because I wanted to reduce the power a bit !

[Bob Cotsford]

for the underwing fairing, could you attach it with a bit of velcro to allow access to the wing bolts?

[Tim Mackey]

I think we have established that it doesnt actually fit at that part of the wing Bob - its just the lousy pictures (and no text) in the manual that had me thinking that

[Vecchio Austriaco]

Looks really nice - I wish I would be at this stage with my Bonanza...

Good luck - looking forward to your maiden report.

[Tim Mackey]

Thanks VA - your Bonanza will look terrific when done I am sure.

Weather here is very cold and raining in-between the grey skies - not my favourite time for flying down the field - the slope beckons me thinks.....if the wind swings westerly

[Tim Mackey]

Ian, if your still following this - I sorted the wing fairing out as follows.

First, cut out the final shape from the rough moulded plastic piece, and trace around it onto the covering film once positioned. Then rough up a small area just inside the markings on the wing.

 

Next, UHU por a small fillet of dense foam, carved and sanded to the right profile, into the front edge section of the fairing.

 

UHU por the front edge in place on the wing, and then run thin cyano all around the curved section. The cyano sticks it very well, but will leave a white bloom, so then trace and cut out a semicircular band of matching film, and apply to cover the glue line.

 

Once applied, it blends in well enough, and does finish the job off nicely TBH.

 

some more views....

Here, you can also see the finished job I did on the wing retaining straps.

 

 

 

 

 

Edited By Tim Mackey - Administrator on 15/02/2011 12:20:42