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Friday, November 18, 2011

E-Flite Ultimate 20-300 10 ARF - Build & Flight Review

Update:  Out of curiosity I swapped out the Super Tigre for a Power 10.  Results: little T:W difference and very nose heavy.  Recommend an ST .10 with GWS 11x7HD for sweet spot performance.

Even with the lighter .10 this plane is difficult to balance far enough aft, so keep the nose as light as possible while locating components during construction.  The best aerobatic CG is at the rear-most top wing bolt, or about 4.5" from the center top leading edge.

Finally I had a chance to complete my latest aerobat.  It's been a while since I tested and flew a bipe, so I was extra excited to get the Ultimate up.  The winds mostly cooperated for the flight review, with only about 2-3 knots on the surface and 10 knots steady at about 200 feet.


First I'll finish my kit build and "on the ground" remarks, then get to how the plane flies and grading.

E-Flite's Specifications


F-Flite stock photo
Wing Span: 38 in (960mm)
Overall Length: 41 in (1045mm)
Wing Area: 473.5 sq in (30.5 sq dm)
Flying Weight: w/ battery: 39–41 oz (1105–1160 g) -- mine weighs 36.7 with 1300 mAh 3S, 40-50A Hobby King opto ESC, Common Sense RC 6V BEC, and Super Tigre .10 motor, ready to fly
Motor Size: 10 size brushless motor
Radio: 4+ channels
Servos: Spectrum DS75 (with programmer)
Prop Size: APC 12x6E
Spinner Size: Included
Hardware Included: Yes
Speed Control: 40 amp brushless
Recommended Battery: 3S 11.1V 2100mAh Li-Po
Setting up the power system first ...given E-Flite's propensity to miss the mark on power system design (ref their Champ 15e's recommended Power 15 and 3200mAh battery which was a disastrous choice!), I am deciding between using a Power 15, the recommended Power 10, or a Super Tigre .10 motor and corresponding battery weight for 6/10 minutes of aggressive/sport flying.

The rough numbers look something like this:


Power 15
Power 10
Super Tigre .10
OEM Fly Weight
41.0
41.0
41.0
OEM Motor Weight
4.3
4.3
4.3
OEM Battery Weight
6.4
6.4
6.4
OEM Empty Weight
30.3
30.3
30.3
New Motor Weight
5.5
4.3
2.4
New Batt
6.8
6.4
5.0
New Fly Weight
42.6
41.0
37.7
Wing Area
473.5
473.5
473.5
Wing Loading
12.96
12.47
11.47
Wing Cube Loading
7.1
6.9
6.3
Est. Thrust
55.0
50.0
45.0
Est. Thrust:Weight
1.29
1.22
1.19

I'm a little concerned that weight creep and battery fade could knock the ST .10 solution off a 1:1 T:W, which I think is a critical threshold for a 3D aerobatic plane. Since the Power 15 and Power 10 are pretty close in Wing Loading, I'm going to accommodate a 15 size motor with the internals.  That way the light weight .10 is an easy switch later.

For guts I choose a Hitec Optima 6 Lite Rx for a bulletproof link and real time responsiveness tied to the feature-packed Aurora 9 Tx.  I picked up four 13.5g .10 sec Turnigy metal gear micro servos for $5 each, to add strong fast control throws.  I have a stash of Hobbyking 40-50A SS series ESCs that were about $12 each, those need a BEC so I got a Common Sense RC 6V switching model for about $20 delivered.  I have a supply of 69g $18 Super Tigre 10s and I added a $28 152g Turnigy G15 as my preferred motor.

Total outlay, about $125 for the motor and guts.

 
 
 

Bare airframe = 16.4 oz. This thing is looking more and more like a perfect match for the light, ultra-high thrust-to-weight ratio Super Tigre .10.
16.4 oz includes motor mount, landing gear, 
wheels and pants (no tail wheel)
This wide angle lens photo doesn't do 
justice to the squat, stubby fuselage
Over-engine-ing, thus spiking weight and killing flying performance, is becoming a disturbing trend with E-Flite's crop of toy makers. They desperately need to hire someone with aircraft design experience.

Making matters worse, note that the Power XX line of brushless motors have a below average thrust-to-weight ratio with middle pitch prop gearing, in the range of 10:1 (55oz/5.5oz).  The Super Tiger .10 approaches a 19:1 motor thrust-to-weight ratio (45oz/2.4oz) with the same 6 to 7 pitch.  That actually includes the aluminum X mounting bracket for the ST .10 ratio, but no mounting hardware on the Power 15.

Look what happens to the power system trade space when you lower the overall weight and normalize flight time.  Wing Loading and Cube Loading is of special note.  A bigger motor buys you nothing in thrust improvement, and reduces maneuverability by 16%. 


Power 15
Power 10
Super Tigre 10
OEM Empty Weight
22.0
22.0
22.0
New Motor Weight
5.5
4.3
2.4
New Batt
6.4
5.4
4.0
New Fly Weight
33.9
31.7
28.4
WA
473.5
473.5
473.5
WL
10.31
9.64
8.64
WCL
5.7
5.3
4.8
Thrust
55.0
50.0
45.0
Thrust:Weight
1.62
1.58
1.58

This Ulitmate Bipe displays very light construction, kudos to the Chinese workers who executed the build for unfair pay. The final quality is not on par with Great Planes balsa and ply ARFs. Horizon's aggressive band of insane religious zealots will cry foul - but they have no idea what they are talking about - anyone actually examining the models will note a clear quality difference. For example, the covering is so thin to be cut or damaged too easily, and the wrap displays poor attention to detail.  Quite a few crinkles can't be fully cured with heat, and the edges of the applied color scheme are peeling. The wing(s) leading edge has no balsa sheeting, only a dainty leading edge spar.  General fit and finish are average to good, with slight but noticeable asymmetries.

This ARF is priced with serious aerobats at $150.  I'd prefer to see it selling in the $110 range, based on the outrageously capable Great Planes Edge 540 (41") and Yak 54 (41").  The Z8RC all time best Great Planes Yak-55M (51") is only $20 more.  At $150, the Ultimate has its work cut out.

The motor is in:
2.2 oz Super Tigre .10 with Hobbyking 40A ESC and Common Sense 
6V XBEC for quick servo response.  Prop is an 11x3.8, geared for 3D.
I decided to go for handling over raw thrust.  The ST .10 motor provides about 44 oz of static thrust with an 11x3.8.  Unfortunately, weight porked out significantly with the large ESC and 1 oz BEC, finished weight is projected at 32.5 oz.  I had these power system items sitting on the shelf, but I might replace them to lighten up the plane by an oz or two.

My motor mount consists of 4x1" #4 bolts (you can use the imbedded blind nuts with any #4 bolt) through .75 inch aluminum tube spacers--very simple, light and strong.  The added aluminum provides an excellent heat sink to help keep the motor cool, made more important by the tight spinner to cowl fit.  I am also going to add an Ultimate-profile aluminum spinner for direct drive shaft cooling.

The cowl is a good fit with plenty of room to pass over the wide firewall as it is installed and removed.  It is vented nicely at the bottom, but the exit hole also serves as the battery bay; that is great for battery cooling, but not as good for motor cooling air flow.  Since the large cowl size and tapered fuse generates a little play at the back edge, I inserted 1/8" spacers under the four screw-down points, allowing even more cooling air flow to pass between through the cowl and fuselage sidewalls.

For now, T:W is a measly 1.2:1 with battery.  Good enough for 3D, and the lighter wing loading should be top notch.  The thrust line is straight.
The tail servos go in next, before the bottom wing seals the cabin.  All of the pre-cut servo bays were a perfect match for my choice of inexpensive Turnigy MG90 metal gear analog servos (these turned out to be just ok; they are a tad imprecise).  I pre-drilled the screws to avoid splitting the balsa and ply.

The wings were easy to install and a nice ARF fit. The bottom wing bolts on with #4 hex head screws and washers for a snug fit.  The top wing bolts to the two stage truss in front of the canopy, then the side force generators slide between the tips and screw-in with two fine thread 1/16th inch diameter bolts through each wing.  The method is fine, but the arc of the SFGs was a bit off, and the wings twisted (as evidence by directional ripples in the wing covering) once everything was tightened down.  I used a heat gun to drum it all up--I'm glad I didn't reheat the bare components before assembly.

Lastly, the tail wheel slides in then the tail surface control horns slide through pre-drilled holes and cap on the other side using CA. The control horns are some of the easiest I've ever installed, but they don't have much of a push rod  leverage adjustment, as far as where to accept the clevis.

I am not a fan of E-Flite's servo attachment system for this bipe, they use carbon fiber rods glued to clevises then though small plastic servo pins secured with set screws.  The thing is that the servo arm's plane of motion is well below the push rod, leaving room for the plastic arm to bend or twist under load, causing less than true actuator motion, or worse, fatigue and possible breakage of the servo arm pins.  I will replace these as I have time.  For now, I dotted it all with CA to keep it as strong as possible.

With all that said and done, this is a fine looking aerobat.   And the seemingly bland color scheme looked nicer than I anticipated in the low morning Sun:
The only major kit defects included a very noticeably warped rudder and some wing warping during final assembly and lock down.  I might be able to straighten the rudder out with a heat gun (update: done).  Other than a slightly twisted  frame and a generally flimsy, but light build, I give E-Flite's slaves reasonably high marks for their ARF execution.

The plane's hardware kit was ok, but less than confidence inspiring.  But in general, the hw kit is not nearly as bad as the F-Flite Aeronca Champ 15e, but it is not on par with Great Planes products in the same price class, either.  Durability, hardware, jig use, and fit and finish all suffer by comparison.  The hardware includes everything you need to finish.  I love that the wheels and pants are pre-installed on their respective landing gear struts.  I added carbon fiber winglet skids to help protect the low hanging, bottom wing aileron servo mechanisms from wing tip scrapes.  A slice of tacky foam rubber keeps the battery from slipping on the wooden firewall mount.

The plane looks great both on the ground and in the air.  The Ultimate's proportions are unique and unmistakable; reasonably well accented by the sweeping blue and yellow color scheme.  The clear bottom covering works fine for inverted orientation, but a contrasting color and pattern would be better.

As always, my maiden videos are of the actual maiden flight.  This one started on high rates, I thought I had downshifted to low before takeoff.  Ooops - discipline is the key to model longevity.

In the Air:

I elected to fly with a 2100 mAh battery for my initial circling of the flagpole.    I thought it would be both safe (nose heavy) and large enough capacity for a lengthy test hop.  Both were good calls--the plane needed a lot of trim and would have been more of a handful with an aft CG.

The wide stance of the Ultimate makes for ultimate ground handling.  Even under full power, the plane tracks straight throughout the takeoff roll.  Even with the heavy battery, the plane's nose still rose sharply on my first takeoff, with a light stick feel.  Wing loading felt reasonably light, right away.  The Ultimate's WCL is 6.2.

Poor alignment of the wing box caused major trim adjustments in both rudder and aileron trim, even through all the control surfaces were perfectly aligned with their visually neutral position.

Once dicing air, I realized I had also rushed the prop under the long, included Ultimate-profile plastic spinner.  Between the spinner's own fussiness and the bag fresh APC 11x3.8. the engine noise from the mighty feather weight Super Tigre .10 was high; clearly out of balance.  My fault.

Flight review bottom line upfront:  The Ultimate is a worthy flyer, and the small .10 motor provided plenty of pull with a correspondingly light feel and agreeable wing loading.

The 20-300 is sharp in the air.  Manners are good but not impeccable, as we've been spoiled to expect from several varsity level Russian designs in their RC incarnations.  The main issue with my first day out was the CG.  The plane balanced according to plan, but the result was solidly nose heavy behavior in the sky.

A nose heavy orientation persisted even after I switched to a 1300 mAh LiPo under the hood.  The Ultimate seeks dirt when inverted hands-off, requiring more than a little nose down stick for level flight.  It also slides off of a hover more easily than it should.  While I am not looking forward to disassembling the complex wing box and push rods, some of the internals need to shift aft as their is no fore/aft battery adjustment possible with the stock setup.
E-Flite recommends a sport CG of 3" behind the middle 
chord leading edge, and an aerobatic CG 3.5" back.  By trial 
and error, the proper aerobatic CG is at least 4 1/8th".back
which is just in front of the rear wing brace.  This is exactly 50% 
of the cumulative center wing chord line, but only 30% of the 
average cumulative chord line after accounting for wing sweep. 
The proper aerobatic CG for this plane is likely even farther back.
So here again, we have an inexplicable E-Flite offering that is a pretty nice model, but without so much as a clue as to basic weight and balance.  It is almost like E-Flite's cludo staff received the plane from China without any instructions or guidance, then drew-up all-wrong power system recommendations and CG instructions.  Amazing that an RC plane company can get away with knowing so little about flying.

Control throws appear to be a bit limited, but in the air the plane rolls very rapidly with plenty of rudder authority to knife loop.  The elevator could stand to deflect more in both directions--hop up your throw as much as possible for 3D style maneuvers.

The E-Flite 20-300 is a joy to fly, but it has a few shortcomings.  It also has some solid advantages as a precision aerobat:

First, post stall behavior is a bit unruly.  It could be my rudder warp, or it could be that this Ultimate needed lateral balancing before hitting the air (update: lateral balance was fine), but a fully developed falling leaf stall consistently rocked hard and dug-in to the right.  Wing rock was more pronounced than expected from an extreme machine, eventually causing the plane to flop the nose-over and out of the stall as power is added.

In comparison, my Great Planes Yak-54 (41") exhibits only slight wing rock in an 70-80 degree AOA, nose on the horizon, idle stall.  My Great Planes Yak-55M (51") is stable in the same condition.  My Great Planes Edge 540 (41") stays rock-solid, no wing rock at all with the wings level in an 85 degree AOA, nose up to the horizon, idle stall.  The 41" Edge 540 is actually the best of the bunch in this particular post-stall maneuver, and it also has the most elevator up and down throw, a full 70 degrees of travel.

My second flight vid shows stall behavior under various degrees of power, starting around 3:50:

Second, knife edge flight couples unwantedly with elevator when banked left, and is sharply coupled to both elevator and aileron when banked right.  This makes the maneuver more difficult to coordinate than a typical, extreme-aero monoplane.

The plane's speed and energy are a little lackluster, probably due to my choice of motor and prop.   The APC 11x3.8 Slo Fly generates enough thrust for solid 3D, but couldn't generate enough pitch speed to deliver an exciting amount of energy.  With a 2200 mAh battery, the prop struggled to hover.    The GWS 11x7 is a lighter and more powerful prop, it goes on as soon as I order a few.  (Update: the GWS 11x4.7 Slo Fly pulls harder than the APC 11x3.8--ahhh, much better)

Hovering is pleasantly stable, but likely lacked a far enough aft CG to obtain best results on this initial outing.  Hammerheads were also a standout maneuver, as the rudder has no problem wrestling the plane either left or right, regardless of one's airspeed.  Hopefully, fixing Horizon Hobby's bereft understanding of basic aerodynamics will make the airplane behave better in the air, especially in the post-stall environment.

Landings were some of the easiest I've experienced with an aerobat of this caliber, again, aided by a too conservative CG as laid out by the manufacturer.  Ground handling is second only the GPY55M, mentioned above. 

The Super Tigre .10 was a good choice for this plane, given all heavier options.  The plane is too nose heavy and the wing loading would be nothing special when running a heavier 10 or 15 with a bigger battery behind the cowling.  Shades of the E-Flight Aeronca Champ 15e taint the Ultimate's recommended power system.  Again, E-Flite seems to have totally missed the mark, the factory's selections would be way too heavy and CG forward for this Ultimate bipe's airy personality.
This was my original layout which proved nose heavy even 
with a 1300 mAh battery.  I mistakenly trusted E-flite's clueless 
CG recommendations.  My new layout moves everything 
except the battery into the cabin as far aft as possible.
I think the ST .10 with a GWS 11x7 or 11x4.7 will be very well matched to the plane with a high C rate 1600-1800 mAh 3S.  I'm going to relocate and lighten up the ESC and BEC as well.  More optimization to come.

Here's how the plane stacks up on my Yak vs. Yak scale, followed by a traditional Z8RC grading system:

Assembly Hours
8

Price as tested (no battery)
$260

Component Quality
7
10%
Value
7
15%
Photo

Span
38.0

Length
41.0

Span/Length
0.93

Motor
ST. 10  1200 Kv

Prop
GWS 11x7

Installed Thrust
44.5

Wing Area
473.5

Flying Weight w/Batt
36.8

Wing Loading
11.2

T:W Ratio
1.21

Take Off Roll
10.00
2%
Tracking
8.00
6%
Wall
8.00
2%
Fast Aileron Roll
10.00
4%
Slow Aileron/4 Point Roll
8.00
4%
Rolling Turns
9.00
3%
Loop
10.00
2%
Outside Loop
10.00
3%
Knife Loop
8.00
3%
Knife Edge
7.00
3%
C8
9.00
2%
Hammer Head
10.00
4%
Inverted Flight
8.00
4%
Snap Roll
10.00
4%
Lomcevek
9.00
3%
Spin
9.00
4%
Inverted Spin
9.00
4%
Harrier
8.00
3%
Torque Roll
9.00
3%
Hover
9.00
5%
Pattern/Landing
10.00
2%
Speed and Energy
7.00
5%
Grand Total
85.20
100%

Appearance: A-
Lines echo Pitts M12.  Color scheme looks better in the air. 

Airframe: B+
Highly predictable.  Toss-able.  Some coupling.  Post-stall wing rock.

Power System: n/a
Flaw: needs lighter motor/ESC/batt for both CG and wing loading.

Build Quality/Durability: C-
Light weight.  Flimsy construction.  Warping.  Weak covering.

Value:  C-
US distributor design flaws mar an expensive but nice Chinese model.

Overall Grade: C+
Above average flyer with less refined nuances.  A few quality misses. 
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