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Old Jan 20, 2008, 07:03 PM
Electric Coolhunter
Thomas B's Avatar
United States, TX, Fort Worth
Joined Jun 2000
14,213 Posts
Mini-Review
L-39 from Freewing Models

Freewing Models recently announced a nice little foamy RTF L-39 Albatross EDF model in the blue and yellow Bretling color scheme. The model has been discussed here:

http://www.rcgroups.com/forums/showthread.php?t=789373

Factory website here:

http://www.sz-freewing.com/

The model spans 31.5" and is about 38" long. (the web site measurements are backwards) and is molded in EPS foam. It has a 64mm fan.

I was recently able to procure a slightly blemmed kit from a dealer overseas. While normally supplied as a RTF with TX, RX, 3S lipo and charger, my kit had these items deleted by the dealer and the price discounted, plus a blemish discount. It came with a mystery inrunner motor of 4300 Kv with a nice heat sink, a 30 amp ESC (Looks like a Welguard) and a set of four 9 gram class servos (transparent red cases) pre-installed. The needed y-harness is also included. The L-39 has a steerable nose gear, which is nice

Mine came repacked by the overseas dealer without the normal shipping insert, in order to save weight and postage costs. The L-39 sustained some minor damage at the aft top end of the exhaust duct, where the rear of the horizontal tail mounts. No problem to fix with a little 5 min epoxy.

Mine did not come with a manual, but as simple as it is, this was not an issue.

Assembly is quite easy. The horizontal tail bolts on, the vertical tail plugs in and epoxies on top of the fuse and horizontal tail and the two wing panels plug in on a plastic spar and socket system, with the root edge attached with 5 min epoxy. The nose cap is thin vac formed plastic and is easy to epoxy on. Mine was not trimmed all that well and left an uneven gap.

The main gear plugs into a receptical on the bottom of each wing panel.

There is a long tunnel on the bottom of the model that is the run for the ESC power wires and ESC servo wire. Near the wing spar, the area opens up a good bit and RX location goes here. There is a nice plastic cover that hides the wires after the RX is installed. I did have to add another short extension to the ESC lead to get the connector up to the RX location.

The bottom of the nose has the fairly typical Asian lipo hatch and latches. The compartment is fine for a 1350-1700 pack, but not large enough for a 3 cell 2100-2200 pack. There is a plastic cage to support the battery all the way around, so it will take some chopping and changing to be able to get the larger packs in there.

I chose to replace the elevator pushrod, as it sported a really excessive Z-bend measuring about 1/2" across. It allows far too much elevator slop. I substituted a 1/32 music wire pushrod. It still had to arc over to meet the elevator horn, but works much better with no Z-bend needed.

The rudder and elevator servos can be easily accessed if you carefully remove the small plastic fairing on the fuse behind the canopy.

I was about to forget the bolt on tail and glue everything, but realized that the bolt on tail allows some decent access to the ESC through the upper part of the exhaust duct. I ended up epoxying the aft part of the vertical tail to the horizontal tail and used two small drops of epoxy to retain the forward part of the fin and its tab into the fuse. This will allow fairly easy removal of ther entire tail assembly, if needed.

There were some moderate fit issues between the wing panels and root areas of the wing on the fuse. Both wings wanted to fit with the upper surface at the wing panel root slightly above the other root surface. It looks like the wing spar sockets were mounted a bit too high. It was not too bad, so I made things fit as well as possible and held the panels in place until the 5 min epoxy was set. If you are not careful, you could end up with slightly different wing incidence from one side to the other, so be careful!

My horizontal tail was tilted to one side when viewed in comparison with the wing from the front of the model. I shimmed up one side of the tail mount area to fix this.

I installed a nice new hot off the hobby shop shelf Spektrum 6200 full range micro RX with a satellite RX (like the AR7000).

I charged up a Dualsky 1700 3S pack, installed it, bound the RX and checked the balance. It looked a bit tailheavy, so I added a 3 medium sized screws to the nose. I left the CG at about 28% MAC. I set the throws using the TLAR method. The daylight was getting away, so I ran the fan up and the thrust felt pretty decent. We can measure the draw later!

I ran over to the local upcoming subdivision with streets built, but no houses iinstalled yet. Powered up the model, put it in the street and taxied out.

Throttle up and after a short roll in the blustery afternoon wind (10-15mph), the model was off and flying. Speed was pretty good, considering the fixed gear. Needed some up trim, which means I need to take a closer look at the overall decalage. Inverted, it took no down stick and actually needed a little bit of up to stay level.

Pitch was a little sensitive, but I had no expo loaded yet.

Easy to roll, but does something a little odd in the latter half of the roll: The aft fuse starts coning around the axis of the roll. The nose does not do this, it pretty much stays on the line picked...odd. Could be some odd differential in the ailerons...need to check that. The slower the roll, the less this effect shows up.

Loops were best with a large throttle reduction at the top. Otherwise, it wants to level out inverted and fly away. With the throttle reduced, it comes around nicely.

My L-39 shows some tendancy to want to snap roll as you come level after the loop if the loop is a little too tight. I did some abrupt turns with lots of elevator and it also wanted to snap, always to the left. I will check out the lateral balance and take a closer look for any warps or weirdness in the wings.

Lands very nicely, like any easy to fly low wing aircraft with trike gear.

Only had time for the one flight, but I do like the way it looks in the air and I think it will be a real pleasure to fly after a few tweaks.

It feels like it wants a CG change to about 25% of MAC and perhaps a thrustline tweak to improve the overall flight characteristics.

I will run it up on the wattmeter later tonight and post some photos and power draw data as well.....right now it is time for dinner...

The model weighs 24.8 oz ready to fly, with the 3S 1700 pack installed. (4.8 oz battery pack)
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Last edited by Thomas B; Jan 20, 2008 at 09:33 PM.
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Old Jan 20, 2008, 07:49 PM
EDF rules... :)
AirX's Avatar
Joined Nov 1999
13,454 Posts
Hi Thomas,

Sounds like a fun model.
What sized fan does it have?

Eric B.
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Old Jan 20, 2008, 09:28 PM
Electric Coolhunter
Thomas B's Avatar
United States, TX, Fort Worth
Joined Jun 2000
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It is a 64mm fan.

The web site says the inrunner has a Kv of 4300.
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Old Jan 20, 2008, 11:43 PM
Electric Coolhunter
Thomas B's Avatar
United States, TX, Fort Worth
Joined Jun 2000
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I ran it up on the wattmeter and saw about 225 watts and 22 amps on the 1700 Dualsky 3S pack, a little into the run with the top of the charge off the battery.

This gives nearly 150 watts per lb (call it 145) on the stock motor and fan and ESC setup, which is a decent sport EDF setup.
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Old Jan 21, 2008, 07:41 AM
Will fly for food
Maryland
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That coning in the fast rolls could be due to the amount of wieght in the rear. The full scale T-38 could suffer from that, but worse, in that if could cone enough to go flat, which would then have the wings fold up.

There are some things with the dynamic roll stability with weight concentrated to the front and/or rear, even though the Cog is correct.
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Old Jan 21, 2008, 08:10 AM
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Quote:
Originally Posted by Thomas B
I ran it up on the wattmeter and saw about 225 watts and 22 amps on the 1700 Dualsky 3S pack, a little into the run with the top of the charge off the battery.

This gives nearly 150 watts per lb (call it 145) on the stock motor and fan and ESC setup, which is a decent sport EDF setup.
I am getting 28A on 3s 2250 20C longmax pack, plane is extremely nose heavy with this pack.
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Old Jan 21, 2008, 10:41 AM
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How long do you guys think that little 2040 inrunner will last pushing 250-300 watts? On one of these L-39 threads, someone said they were getting 450g of thrust with the stock setup. Does this figure seem correct? Will the stock EDF unit accept a larger diameter motor like 24 or 28mm?
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Old Jan 21, 2008, 11:15 AM
Electric Coolhunter
Thomas B's Avatar
United States, TX, Fort Worth
Joined Jun 2000
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Quote:
Originally Posted by darmar
I am getting 28A on 3s 2250 20C longmax pack, plane is extremely nose heavy with this pack.
I am going to a larger pack, for sure. I was planning on opening up the aft end of the battery compartment to gain some space to keep the heavy battery further back to minimize the nose heavy effect.

Where exactly did you put the larger battery?
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Old Jan 21, 2008, 11:16 AM
Electric Coolhunter
Thomas B's Avatar
United States, TX, Fort Worth
Joined Jun 2000
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Quote:
Originally Posted by bhatch21
How long do you guys think that little 2040 inrunner will last pushing 250-300 watts? On one of these L-39 threads, someone said they were getting 450g of thrust with the stock setup. Does this figure seem correct? Will the stock EDF unit accept a larger diameter motor like 24 or 28mm?
The stock 20mm motor does have a nice large heat sink on it to help dissipate the heat.
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Old Jan 21, 2008, 12:00 PM
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Quote:
Originally Posted by Thomas B
I am going to a larger pack, for sure. I was planning on opening up the aft end of the battery compartment to gain some space to keep the heavy battery further back to minimize the nose heavy effect.

Where exactly did you put the larger battery?
I did open up room in battery bay in the aft end as you plan to do. It's still tight with all the wires and balance plug.
Got also clear plastic tube in the exhaust that helps counter the extra weight of 2250 pack. Made some mods to inlet tunnels too, as those are oversized for 64mm fan, but forgot I will need some matching paint to touch up original paint and to paint white depron parts.

Btw I used 3mm depron for intakes mod, see pictures.
Template included too if anyone wishes to do the same. After testing thrust and amps no significant change so far at least in static test.
Looks more scale this way.
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Old Jan 22, 2008, 07:15 AM
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Perth, Western Australia
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Hi,
Just received my L39 today & began building it an hour ago. Must say am dissapointed, as thomas pointed out the wing fitting isnt that good. Mine was Horrible! big gaps etc etc and i didnt realise until i had pressed it on, epoxy was already setting. So i was left with a ~1-2.5mm gap on both wings. Really pissed to say the least & now have to bodge up the gap = extra weight. Build quality is cheap, tape is used instead of hinges for example.

Nowhere near the build quality of my parkzones planes.

Paint is nice though. Dont like the hard style foam, dents/scratches to easy. much prefer elapor.

Should of got a multiplex twister as i intended, but i couldnt justify $300Aus for a plane and motor, but think i might buy one anyway down the track.

I'll she how she flies..... (if it flies assuming i have my wings straight because there now level with the fuse as thomas pointed out).

Sorry to rant a little but hte manufacturer needs to fine tune it a bit. Place i bought it from had 1st class customer service & fitted a few extras (best part of the plane).

mike
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Old Jan 22, 2008, 11:53 AM
Electric Coolhunter
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United States, TX, Fort Worth
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Damar, nice job oin the inlet redo...makes it look a lot more scale.

Mimne will eventually get a blue agressor scheme, like the pic below that also shows the real diverter on the inlet.

Yep, the wing fit could certainly be better.

I was able to close the wing to fuse gap almost fully closed by pushing very hard on the wing panel. I did have a couple of spots left with very thin gaps that were closed when the wing was epoxied on.

I would advise future builders to try to trim the end of the wing spar 1/16 to 3/32 of an inch to perhaps allow the wing to seat more easily with the root surfaces flush.

Another small but slightly annoying flaw was that the molded foam hatch in the bottom of the fuse that gets glued in at the factory after the fan is installed was protruding about 3/32" from the bottom of the fuse, causing some fit issues with the battery hears and the long plastic tunnel cover. The ARF versions might not have this issue., or can easily fix it.

I ended up deepening the wire groove in the foam here so that the tunnel cover would fit better.

The horizontal tail screw bracket was loose on mine and I re-epoxied it to the stab for security. Make sure you rough up that very smooth plastic before doing so.

Overall, I do like the model a lot and am looking forward to getting it nicely dialed in.

I am going to cut some access to the nose gear bay so that it can be removed to fly the model with no landing gear....will look much better that way, in the air.

I do plan to eventually loose the decals, spackle the wing joint and a few other spots and repaint the model to that cool blue agressor scheme. The one in the pic could be replicated and use the exisiting overall blue as one of the camo colors, if the scheme was worked around the problem areas like the wing joints and the decal removed areas.

The model BADLY needs some pilot figures in that large front office as well...
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Old Jan 22, 2008, 12:23 PM
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Regarding wing fit, you should always do a dry fit, on any part first then glue it if it's correct.
This is why I like GWS models, otherwise even if you pay $250 for RTF let's say from HL you will be disappointed with mass production assembly job, wanted to admit it or not.

Thomas, excellent paint scheme choice. I am waiting for nicer weather to maiden mine then play with mods.
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Old Jan 23, 2008, 07:06 AM
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Fitted the rear stabalizer/rubber assembly. This time i trial fitted first. I trial fitted the main wings a little but since they were becoming a little tight i thought theyd line up, then used the epoxy. But i learnt my lesson....

I bought mine as a ARF. Ducted unit was installed in the fuse.

Rear stabalizer sits in nice and firm, but added a little silicon on the edges for security. The stabalizer flaps didnt line up with each other, actually way off. Kind of did a little bending with the rear wire connecting the two then used some epoxy. at the rear of the flaps i linked them 2gether with some servo wire. Heated each end up and melted it into the back ends, then epoxied over the top. Lessened the flex between the two dramatically.

My rudder sits in nice after some sanding but the actual part that moves is on an angle and cant seem to do anything about it without cutting it off.

I also reinforced all the tape style hinges.

I must say after putting it all 2gether (minus rx and servos cause am waiting on a rx in the mail) sure is a good looking plane.

Am fitting the wheels and have already replaced the small front with a larger wheel for grass takeoffs but agreed she does look better without them.

Cant wait to power it up and get her airbourne.
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Old Jan 26, 2008, 07:09 PM
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Thomas, I think I got pretty good idea why you getting that odd coning in the fast rolls.
ESC is basically just hanging on the wires in the exhaust tube and is flapping up and down with any plane movement. You should try to make it stop moving by supporting it with let's say thin balsa strip or depron plate.
I mounted depron plate vertically under the esc, just light tack with silicone. sanded it to basic airfoil to reduce drag in the pipe.
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