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Old Aug 16, 2015, 03:44 PM
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Sabre slot-Jet.. 3rd time lucky maiden

I've had this idea kicking around the grey matter for a while now..

Finally got going! Using an old-school projector and a 3-view i matched the fuse size to a Zaggy wing i had lying around. The fuse is 20mm isoboard insulation foam and tail feathers is 6mm depron.

Wingspan is 900mm.. so she's a nice size.

Lectrics is a 2218 2500kv motor matched to a 6x4 prop for now. Rest to be determined once o got some amp/watt readings...

Flight control will be ail/el only.. bank & yank! Just the way i like it!

The distinctive swept-up horisontal stab is a bit bit of a contol nightmare.. just gonna use 2 servos.

I want to fettle/carve some shape onto that slab-fuse before fitting electronics..
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Old Aug 17, 2015, 10:18 AM
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That's pretty cool. One of my favorite planes. Definitely following.
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Old Aug 17, 2015, 02:02 PM
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Fitting an undercarriage, or landing on the prop ?, as the locations seems very vulnerable to prop breaks.

Sorry, otherwise a nice shape.
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Old Aug 17, 2015, 02:22 PM
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I did a similar lay-out on a Hawk-ish sport jet before and had no prop breaks.. bit of scuffing but never anything serious... I hope my luck will not change

With the hi kv motors the props are relatively short and stubby so maybe my luck will hold.

Even with the SportJet i considered gear but my fav flying spot is not gear friendly. But is sure will be fun running off ground!!
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Old Aug 24, 2015, 12:10 AM
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Sabre electrified and ready for maiden...

Got bored with the cr@p weather here so started to put some make-up on this girl.. (not finished yet)

Forgotten what a big job it is to hand-paint models... next time i'll just cover it in rattle-can silver

I ended up with a 3550KV heli motor and 5x5 APC. 38A at W.O.T

Howling like a banshee... sweet music!!
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Old Aug 24, 2015, 04:58 AM
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Great Idea !!!
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Old Aug 26, 2015, 01:10 AM
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Tried to maiden yesterday... had an un-controllable looping effect despite full down.

Question is: does the fact that the bottom half of the prop have unrestricted flow have this effect? Compared to the top half in fuse which is fairly restricted..

I didn't notice this when spinning up, but i wasnt paying attention to that sort of thing..

Also, do you think my tail surface is too small compared to the wing? (judging by the pics above)
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Old Aug 26, 2015, 06:16 AM
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George , we always vote for larger tail surfaces , especially if you scaled it up from a 3 view ...
Or you can try launching at less than full power ...
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Old Aug 26, 2015, 09:24 AM
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Quote:
Originally Posted by gpw View Post
George , we always vote for larger tail surfaces , especially if you scaled it up from a 3 view ...
Or you can try launching at less than full power ...
I did enlarge the h/stab significantly.. problem is in relation to the wing (which is actually a Zaggy wing) it may be small as i just scaled the wing-span. The actual plan-form of the zaggy wing is a fair bit wider than the lenght-scaled Sabre wing.

As for full power... I wanted to get her up quick and then trim. Full power was applied as i had the idea she's just a little chubby! The instant loop got me! Pilot "brown-out".... freeze.. or all of the above...

Got some rebuilding to do as the maiden ended abruptly after the attempted loop recovery ending 45-degrees into the deck

She WILL fly!
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Old Aug 26, 2015, 09:55 AM
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Try a hand launch glide test, if you do it over some long grass it reduces the risk, or climb on power, cut the throttle and see what the glide is like.
If the glide is very stally, porpoising, then it's either the balance or trim set-up.

Did you use one of the CG calculators, such as -- http://adamone.rchomepage.com/cg_calc.htm

Also what sort of incidence angle have you built in.
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Old Aug 26, 2015, 12:53 PM
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Ray,

Tall grass is at a premium this time of the year.. end of winter.

That CG calc is exactly the one i used. I like that one as it does not expose my lack of knowledge re technical terms

My aim was to get a zero-zero incidence. It may be a half a degree negative on the h/stab (stab leading edge down, if anything)

Does a pronounced dihideral on the stab have any adverse influance?
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Old Aug 26, 2015, 01:49 PM
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I don't see why any dihedral on the stab should have an affect, plenty of models fly with 'V' tails.

I would still say try the CG calculator. It can look rather complex, but actually it's fairly simple.

Just take a few dimensions of your model, see the picture below for a guide.

Well worth trying even just to prove you got it right first time, or .......
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Old Aug 26, 2015, 03:03 PM
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Sorry if my blabbeling created the wrong impression..

I DID use that very CG calculator. I used 5/10/15% safety margin to get 3 values to see the range. I ended up setting up on the 10% v alue of 176mm.

Interestingly, the CG value when totally ignoring the H/stab, and including it as a "low efficiency" stab is only a couple of tenths of a millimeter...

I ran the plane again tonight and there's a distinct nose-up pull. The trust line is set 0-0 as i've allways done on all my slot jets... I syill think the abnormally thick fuse section behind the prop is disturbing the airflow sufficiantly to create the nose-up pull...

After repairs i will fiddle with the thrust-line to see what it does...
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Old Aug 27, 2015, 04:50 AM
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What does it glide like ?
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Old Aug 27, 2015, 05:13 AM
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Didn't try the glide thing.. will now when fixed.
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