Indoor "Easybox II" from NQRC
Flying a bit of indoor recently has made me keen to try and find new and interesting aircraft which can fly slowly and predictably. Although I've had some limited success with flying a Stevens Aero 'lil squirt I was always concerned she was a bit heavy for the duty, and thought to myself something with a little more wing area, and attention paid to keeping her light might work out okay.Enter the Easybox II, designed by Paul Daniels from North Queensland Radio Control. At first glance this neat build yourself balsa parkflyer looked like it might be just the ticket. And the price - $50 bucks for the whole kit including *all* hardware and covering. Combined with some cheap electronics from UnitedHobbies.com (including a tiny 16g outrunner) the inkling of an idea for a new slowflyer for indoor was taking shape.
So, I ordered the EBII from Paul, and some bits from UH. The total parts list in the end was:
- EBII (from NQRC)
- 16g Hextronics Outrunner (from UH)
- EM 3.7g Servo x 2 (from UH)
- Towerpro 12A ESC 9g (from UH)
- Hitec HFS05MS RX (from Nitrodude)
- 2s 850 LiPo (from NQRC - not stocked anymore unfortunately)
Construction was breeze. Even with only a plan sheet (rather than instructions) this plane went together very quickly. As per the name, the fuse is a box with two the two fuselage sides running the length of the aircraft with shorter pieces used to brace top and bottom to allow for the various bends.
I was using my flash bulbs and being a miser with thin CA to keep the weight down as much as possible. Even for a slow builder like me the main fuse only took about an hour to put together.
The wings were a straight forward affairs with a smart approach by Paul to the main wing spar. Rather than one solid continuous main spar (the more standard approach) two thinner pieces locked the ribs in - one from above and one from below. A third and fourth piece was then CAed across the "front" and "back" of the two wing spars making a "box" configuration which would be extremely strong for weight. Given I was after every weight saving I could achieve, after consulting with the designer (yes Paul is one of those guys that answers your emails and does his best to help you out) rather than building the spar up to the full box I only glued one of the braces in place between each set of ribs, alternating between bracing the front, and bracing the back of the spars. Hopefully the photo explains what I'm on about.
One tip I would say for the wing is sand the trailing edge pieces to shape before you glue them to the ribs. Once installed, it is a tiresome job to delicately sand the trailing edge without catching/splintering/breaking the wing ribs.
To try and reduce weight even more the whole model was given a really good sand. I think everyone detests one part of building models. For a lot of guys it's covering. For me it's sanding. Nevertheless, I carefully hand sanded her back, and managed to achieve a saving of around 4g through sanding the fuse - not bad when the fuse weighted in at about 32g before the sanding.
The wing was sanded to shape - not without some cursing I might note. Check my tip above about shaping the TE before glueing it in place. After that came the covering. I had contemplated covering only the top of the wing (to create an under camber affect, and to reduce the weight of covering). However, after discussion with the designer by email the decision to fully skin the wing was made because: 1) The laminate covering is an important part of the strength of the wing, 2) The airfoil isn't designed to be an undercamber wing and 3) the main spare arrangement would likely disrupt good airflow.
The laminate is easy to work with, and with the EBII wing being a constant chord wing covering is a breeze. The whole wing was covered in two pieces, doing one wing half at a time, and getting a nice smooth finish was easy. If you haven't worked with laminate for covering before, Paul has some notes on his site. By and large, very similar to other covering. Only thing from my perspective is that a heat gun is essential - the hair dryer wont cut it.
In the end, covering the whole wing probably added about 4g over covering just the top half of the wing. The weight of the wing and the airframe was coming to around 70g at this stage (I made a note at the time - do you think I can find it now).
Avionics and Power System
I started by installing the 16g outrunner to the front firewall. Paul's original design has a brushed can motor sitting behind the firewall direct driving a prop. However, I was worried about weight being to far back, and the outrunner was really only made to base mount.
The ESC was installed, and a 2s450mAh (which I was to later find out was dead) was used to check the balance, and give me positions for the RX and servos which live under the wing. The whole fuse (but without the wing) was test balanced like this to help me determine the right spots for the RX and the servos so that I was within cooee of getting the Centre of Gravity.
Just quickly on power system - I had calculated I should easily be able to get 40watts out of this system, giving her a power loading of about 100w/lb - more than adequate for what I had in mind.
The included control linkages and horns (yes - *all* hardware included) were installed into the fuse and tail feathers without fuss. I used double sided tape to secure my servos in place (they live in the space under the wing). Just a word of caution here - make sure the inner wall of the fuse is free from balsa dust so that the double sided tape gets a good hold on the wall of the
aircraft. The control surfaces on the tail were hinged using magic tape. Also, because the aircraft was going to be operating at slow speeds I set her up for maximum control throw (furthest hole at the servo, closest hole at the control surface).With all the gear in I tried powering up the motor, and found out the 2s450 I planned to use was dead. Switch of plan - rifled through the battery box and found a 2s850 - a little heavier than I would have liked, but had the advantage of being available, and without needing to give an explanation to Mrs Oz about why more parts were needed.
This did affect the CoG unfortunately, and I ended up having to put a small amount of plasticine on the tail to get her to balance. Not much. This was just attached with sticky tape (it's very important you don't over engineer on indoor models ;-).
AUW with flight pack - 172g (6.14oz). Works out to a wing loading of 4.4oz/sq ft. That was a little higher than I was hoping, and having to change the flight pack at the last moment probably robbed me of my target of sub 4oz/sq ft.
Maiden
I maidened the EBII (or EBIII as I was calling her by now after my customisations ;-) down at my local oval on a pretty calm day (maybe 2-3 km/hr winds). From the hand she took just one click of trim to fly level. She felt solid in the air and easy to fly. I slowed her down quite a lot and before I knew it was tooling around at 1-2 metres - the sort of altitude is not the way I normally approach maidens. However, the plane felt solid, and I was happy with her there.
I did some loops and stuff, and had an easy landing to finish - all up a very satisfactory maiden.
The next flight gave me an unscheduled chance to test the robustness of the aircraft courtesy of a receiver failure (or maybe it was the double sided tape slipping of the balsa - I think RX though - the one before the Hitec). So here's the situation. From about 5 metres up running I started her into a turn to the left which she continued after I released the stick. She turned over and went into a stall turn. I gave her power and tried to pull up but she didn't answer elevator and I cut the power a moment before she nosed in.
Fearing the worst I walked over. Damage - broken firewall, and just a little glue needed around the nose. Back at home I cut a square of balsa to replace the firewall, and CAed the nose back up - took about 20 minutes including time to reinstall the motor. From nose in to flight ready in 20 minutes. The aircraft had inadvertently passed another of the indoor flying criteria - robustness, and ease of repair (you don't take precious models to indoor - you just don't).
Her next flight was out at Murrumbateman with my mate, The Mongrel. On this day I really started to make an effort to see what was required to fly her low and slow, and we got some video (first plane in this youtube vid so take a look). Although not on the vid, as I pushed myself for lower and slower I had another "incident" with this plane. She stalled while in a banked turn, went in touching a wing tip onto gravel. I closed the throttle before impact - no damage.
After a bit of practice in the wide opens I was happy this plane could give indoor a go. One thing I had learnt from flying her low and slow outside was that although she was steady, and relatively easy to fly slow, I just needed a little more finesse on the throttle than I was used to. More power was required for turns to stop her stalling, which needed to be throttle back in straight level flight to stop too much speed being gathered. Thinking back to how aircraft fly there is nothing too surprising here, except that many of us probably don't build this into our flying when we are on the wing because we are so far above stall speed.
The Indoor Night
Well, the big night finally came, and with my past record of fixed wing at Indoor (it isn't exactly confidence inspiring) it was with some trepidation that I launched the EBIII off.
She completed her first circuit quite easily. Although I was in a bit of hurry (you always are with indoor) nothing was happening to fast for me to keep up. I was throttling up for corners, and back for straights. In the straights a little bit of up elevator was giving me a slight positive angle of attack and letting me fly just a little bit slower.
However - the table they had stuck out on the floor for landing helis on earlier, which had been looking at me evilly all night, did finally strike. I tried to enter a turn a bit slow and a bit too close to the ground - it was all okay with extra power, if the table hadn't jumped in front of my aircraft. Realising things were perilous I went full noise to try and get over the table - bang - into the table I went, and the floor a moment after. A few gasps from the crowd.
I went out, grabbed the model. One minute with the thin CA, and a borrowed rubber band, and she was flying again (almost no damage).
On her second flight of the night my landing was just a little rough and partially cracked the sheeting of the forward lower nose - CA - fixed. Otherwise a good flight.
On her third flight of the night, everything went just perfectly. Although there were some moments when she almost seemed to be in formation with other models (3 models, seemingly flying in formation, indoors - it is crazier than it might even seem).
Conclusion
About the EasyBox II - a great fun little plane. Easy to build, cheap, durable. If you've never built with balsa before, it's a nice place to start. I think she would even make a half decent trainer, particularly if the beginner has someone to help them over those first few flights so you don't end every flight with repairs.
About the EasyBox II as an indoor model - it was a lot of fun getting her to this point, and I will keep on flying her at indoor. Her airfoil means she has to fly a little quick compared to her contemporaries, but she has a grace of her own. She is very robust and repairable (critical for indoor).
What we really need is an EBIII, using 1.5mm balsa for the fuse to save weight, and a more appropriate airfoil with undercamber wing - what about it Paul? ;-)
Other Weight Saving Ideas to Pursue Your EBIII (Indoor Easybox)
Here's some ideas that Paul and I came up with that didn't make it into this model, but seem like decent ideas:
- Use Carbon Fibre rods rather than dowl for wing retainers.
- Drill some holes in the airframe - this very strong airframe can lose some rigidity and not really suffer.
- Use lighter batteries - this build showed, surprisingly enough, that this model comes out pretty neutral even when built with ultralight components. Mounting the outrunner in front of the firewall is clearly a critical step here, but it should be possible to step down to a 2s350mAh and still get the model to balance.
posted by Oz RC Boy @ 8:40 AM
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