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Monday, June 18, 2012

Banana Hobby F-22 Raptor (41" Wingspan) - Build and Flight Review





Update 6/18/12:  Already, a flap/slat servo has stripped and both elevon servos have started to behave very erratically as a result of normal use.

Plan on replacing the two elevon servos (minimum) with metal gear servos.    I'm not sure if I pinned the internal elevon servo wires when I initially glued the wings on, but when I decided to change them out the internal wiring was so tight I had to cut them off at the base of the servos, then carefully solder extensions onto the existing internal wiring.  Not the easiest way to swap out servos.

I recommend pulling out the elevon servos as soon as you open the box to see if you can get them out far enough for easy replacement, right away.  If not, expect  a pretty delicate operation in the not too distant future.

Back to a B overall for high risk flight control components.

Update 6/5/12:  FPV using two 4000mAH 3-cells in series.  These batts are well matched and have been mated together since birth but have less grunt and only last about half as long as one of my 6S 4000s:



Update 5/19/12:  Another video.  With youtube viewer shortcuts:
Shortcuts
0:02 Flaps/Slats Extend
0:20 Max Power Takeoff
0:40 Glide #1
1:30 High Speed Pass #1
2:22 High Speed Pass #2
2:27 Max Aileron Roll
3:26 Glide #2
3:55 Min Radius Loop
4:30 Low Speed Maneuvering



Update 5/16/12:  This flight video will have to work until I take a better one:
Also, I'm upgrading the plane from a B to a B+ overall.  The build has held up a little better than I thought it would to date.  I have done extensive taping and foam crash proofing.  The F-22 is a terrific flier.

Original review follows:


INTRODUCTION
One thing is certain about the Banana Hobby (LX Models) F-22 Raptor, it looks the part.

SPECS
- Wingspan: 1046mm (41.2 in)
- Length: 1513mm (60 in)
- Flying Weight: 2100g (74 oz)

FEATURES
- Construction:  Dense Styrofoam (not EPO)
- Motor: Twin 2100kV Brushless 70mm EDF units (measures 67mm rotor diameter)
- Servos: 10X 9g high speed micro servos
- ESC: 2x 50A Brushless speed controller w/ 5A BEC
- Landing Gear : Threaded rotary shaft driven servoless retracts
- Nose gear Landing Light which also functions as a (nose) gear down indicator
- Painted pilot figure (white helmet, USAF Vietnam era)
- Electable canopy module with parachute
- Smoke system with two colored smoke canisters (fireworks)

INCLUDES
- Four foam JDAMs and associated MAUs
- Two drop tanks (which also house the smoke canisters) and associated MAUs
- Instruction Manual* 

REQUIRES
- Radio: 6 to 12 Channels**
- Battery: 22.2V 6S 3600mAh 25C Li-Polymer
- Battery Charger
* Not exactly. It includes a small picture book, none of which answer the questions one is likely to have.
** 12 Channels is an exaggeration. Included channels (8 in total) are: 1 aileron channel that links one aileron, one horizontal stabilizer, and one thrust-vectored nozzle to act as the right elevon (Channel 1), 1 elevator channel linking one horizontal stabilizer, one aileron and one thrust-vectored nozzle to work as the left elevon (Ch 2), throttle on an internal Y harness (Ch 3), rudder and nose wheel steering (Ch 4), servoless retracts (Ch 5), 2 x flap servos which also operate the leading edge slats (Ch 6), smoke ignition (Ch 7), pilot ejection (Ch 8).


ON THE GROUND

UNBOXING
The plane ships as a box full of major components, each requiring some assembly.  Those used to foam ARFs requiring very little build time are likely to be disappointed.  The F-22 needs quite a bit of glue (included, but no thanks, I'll use my own), four servos need to be installed, and all the pushrods and belcranks need to be decoded.

The wiring also needs to be decoded.  The servo leads are tucked into the main fuselage where the forward fuselage needs to be glued in place.  To LX's credit, each lead is tagged with a label.  Once you figure out how simple the scheme is--each side's elevator, aileron and nozzle are all Y connected together for a total of 2 channels--it is easy to hook up your choice of receiver.  The only mildly confusing part of the servo connections is the servo lead coming out of the forward fuse labeled "Direction," which I eventually figured out meant "I am from the nose-wheel steering servo, please connect me to the open Y connection on the rudder channel."
We learn quite a few things from the box.  First, LX stands for Lanxiang China.  One side of the box shows some or all of their other models for sale.   On the box ends, we learn the plane has "color smoke" and cockpit ejection.    And in fact, the model comes with a smoke detonation system and two pyrotechnics that slide into the back of the included drop tanks.  There is a servo pre-installed in the cockpit for the sole purpose of knocking the canopy off of it's magnetic latch--I guess the the included parachute does the rest.  Hilarious, only a Chinese designer could get excited about pilots ejecting from an F-22.
The other box end seems to show an F-22 in the process of being shot down.  But it is hard to say what LX was thinking given that the box also clearly states the model is "Ready to Fly."  I don't know, that might be a bit of an exaggeration.  Mine was built and ready to go in about a day.  Much of that time was spent figuring out the Rube Goldberg, but somehow fiendishly simple, elevon/thrust vectoring scheme.

APPEARANCE / FIT N FINISH
The plane mostly goes together ok, but the wings are a tight fit and need to be patiently wiggle together with quite a bit of force.  Dry fitting first means doing that twice, which is no fun.  Worse, one of my vertical stabs (err, I guess I mean 45 degrees off from vertical) wouldn't go in its slot without significant trimming of the foam base.

Once together, there is no denying that the LX F-22 is one gorgeous bird.  It actually looks better in person than the photos portray.  The only minor detractor from the final impression is the artificial glue seam between the forward fuselage and the main fuselage.  I taped and painted that.

Unfortunately, the surface finish is dense Styrofoam,so it is extremely easy to scratch, dent, or otherwise mar the beautifully painted surface.  That said, the F-22's paint is more forgiving than industry standard Z-foam, as tape application and careful removal is possible without removing the paint.  But make no mistake about it, this is no EPO bird.  It is delicate indeed.

BUILD QUALITY/SETUP
Build quality is my first big beef with the plane.  It isn't a lack of care, but poor materials that let the Raptor downThat wouldn't be as big a deal if it were not for the premium price tag.  For $379 pre-battery, I have a hard time accepting a Styrofoam jet. 

Perhaps worse, the parts of the plane that have been assembled are glued up around the electronics, so replacing a servo could be impossible without clipping the lead and grafting the new lead into the existing internal wiring.   The fans are accessible via a screw-on hatch, but getting to the ESCs requires foampen heart surgery.

The landing gear is pre-installed and extremely clever, but all plastic.  I've already knocked off the nose gear by a simple pavement to grass overrun landing.  The gear is lightly glued in place, probably on purpose to save the plastic struts in the event of an impact.  But I screwed up--during the re-glue I used some Gorilla Glue which expanded into the back of the base and almost ruined the gear.  I wound up cutting the glue out, but only after the lack of movement over-stressed the motor's plastic gear-locking arm, cracking it.  The only way to fix it was to glue the servo arm attach screw in place along with a glued metal washer for added strength.  It seems to be working fine now, but all plastic gear? Really?

You'll also notice a main gear door stuck open in the video.
Ok with that out of the way, now for the good stuff about the gear:  It is quite strong.  It has built in shocks.  And out of the box, the plane taxis better than any plane I've ever driven.  It makes you want to find a slalom course.


ISSUES 
  • Left rudder too tight to fit
  • Soft foam surfaces
  • One Bel crank broke in half while inserting push rods (resorted to pre-drilling the holes).  Fixed by using an inner-half hole on both connected bell cranks.
  • Lower level of completion than other foam ARFs
  • Right nozzle's control horn was fractured at the foam base by the QC technician; neither caught nor corrected.  Root cause: vectoring nozzle binding with surrounding structure, needed 1/16th inch of foam trimmed from one side.
IN THE AIR

BLUF
OMG!  This plane flies fantastic.  Don't get me wrong, this F-22 is anything but aerobatically pure, but the combination of stability, agility, and slow speed float is unmatched. 
START/TAXI/TAKEOFF
Uneventful.  The Raptor's chunky plastic landing gear taxies perfectly with an excellent turn radius.  Takeoff roll is a brief 25/50 feet using half/zero flaps, followed by a strong, near vertical climbout. 

FLIGHT CONTROLS
I visually aligned all control surfaces and the plane required no trim for straight and level cruise--an RC first for me.    The Raptor is amazingly stable and well balanced at the recommended CG.  Elevons are never quite pure, but the airplane rolled very quickly on high rates with minor to moderate pitch/roll coupling. 

Pitch authority with assistance from thrust vectoring, is even more impressive than a real Raptor's full public disclosure. Rudder authority is excellent even at slow speeds, and you often need for post stall maneuvering.

Yaw control is impressive but actually the weak link as it can't match the strong vectored pitch and roll control at zero airspeed.

BALANCE & AEROBATICS
From full blower to idle, the Raptor tracks perfectly in all three axises.  The plane's pure stability and balanced feel is surprising, as is its low speed/float capability.  The 45 degree cant on the (sort of) vertical stabilizers seems to add a strong dihedral-like effect on upright stability.

The same cant detracts from inverted flight, which isn't nearly as friendly as upright, hands-off cruising, but very few warbirds exhibit pure aerobatic symmetry. 
Rolls are very fast in the warbird/sport category, and above average even for an aerobat.

Differential thrust vectoring and the use of elevons render each roll a micro barrel roll. Loops track perfectly through the full 360 and radius ranges from huge to less than the length of the jet.  Spins can be perfectly flat to nearly aligned with the vertical due to thrust vectored pitch control.  I have yet to explore the full capability of +/- thrust vectoring.

The Raptor feels perfectly balanced as the power comes off--the nose stays put until airspeed dwindles to almost nothing. As the airplane runs out of airspeed entirely, the tail settles slightly before the nose and slowly develops an almost elevator-like, nose high sink rate. With a touch of power the airplane will hold altitude in a high alpha pseudo stall.

POWER
Thrust - unmeasured, but slightly above 1:1 static
Amps/Watts -
Speed -
Flight Time - 5-6 minutes on 4000mAh 6S

ADVANCED HANDLING CHARACTERISTICS
AHC is where the Raptor earns its money.  The combination of uncanny lift from the clamped slats and flaps, double-surface elevons, and vectored nozzles adds up to a lot of more ooohs and aaaahs per maneuver than most EDF jets manage in an entire flight.  

My flaps are set to a 3 second servo travel speed, for smooth transitions during extensions.  I experimented with mixing 25% slow flaps to pitch control, and it seems to work beautifully.  High speed G gets slapped on hard, then as the plane slows the flaps and slats dig in.  The plane maneuvers well down to almost  zero airspeed.

The plane can perform a tight back-flip at any starting airspeed, down to zero.  The slower the start, the tighter the "loop" and the Raptor can essentially loop in place with almost no altitude delta required.  Truly impressive, high quality fast-to-no speed maneuverability.

Top speed is slighter better than I expected, but not outrageous.  I left the bombs and tanks off to maintain stealth.  The pure volume of rushing air out the back add a jet-like "whoosh," underpinning the typical whine of the twin EDF motors.  The resulting sound is a lot meaner than most EDFs.  The units ran  smooth and seemed well balanced right from the manufacturer.

Floating into a landing is a little unnerving, only because the Raptor gets so slow without much tendency to seek its previous airspeed via a natural pitch change.  It stays slippery and maintains energy well even with slats and flaps half to full down.

Ultimately, the nose needs to rise to maintain glide path as more AOA is required for lift generation, and at that point a slightly nose high sink rate develops.  The sink can be managed with power with the nose held high.

The plane never tried to tip stall/roll on me while slow, but it will start a manageable, uncommanded turn in a full stall unless opposite rudder is stomped on.

The Raptor is a joy to land with the nose jacked up with a touch of power.  Landing no flap/slat might get the nose up even higher--more practice required.  The reluctance to bleed energy requires quite a bit of runway even with full slats and flaps.

Speaking of slats, the inclusion of leading edge slats is not something you see everyday on an RC model.  Execution is as simple as it is flawless, the slats work perfectly and slow speed lift generation is stunning.  I hope more airplanes use this pull-pull flap-slat concept in the future.


IN FLIGHT ISSUES
  • Occasional hiccups out of one (or both?) of the fans near full power.  I initially thought it might be the plastic fans breaking in since it first occured right after the maiden takeoff, but the issue continues beyond a normal break-in peroid.  Doesn't seem to burp on the ground.  Strange, but so far harmless.  
  • The bottom-mounted thrust vectoring control horns are directly exposed to well flared off, high Angle of Attack landings--need to be protected with homemade covers
  • Main gear door stuck open once.  Seems easy enough to adjust the string door pull.

GRADES
Appearance: A+ 
Stunning airplane!  Did the Raptor always look this good or is it growing on me? 

Flight Characteristics: A+ 
Uncanny stability mixed with bizarre thrust vector agility.  A high rate G monster coupled with amazing slow speed finesse.  Wonderful balance and float. 

Power System: A- 
Couldn't ask for much more push.  Top speed is very good.  Nice fan smoothness, power and sound.  6S is not especially cost effective.  Reliability could be suspect. 

Build Quality/Durability: D  
Here lies the catch.  Overstressed servos.  Very soft foam.    Inaccessible wiring.  Slop in  flight control connections.  Fragile foam gear doors and nozzles.  Plastic gear struts and delicate mechanisms.  Nice fan units, ESCs and motors. 

Value: C- 
Very expensive for the cheap airframe build quality.  Nice power train components.  Weak servos.  Flight quality is superb even for the high price point. 

Overall Grade: B  
If you think jets are built to fly, A+.  If you think they are built to last, C-.  I'm going to reluctantly recommend it because it is such a hoot to fly.
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