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Saturday, August 25, 2012

Banana Hobby/LX Models Super F-16–Build and Flight Review

DoubleViperAviano

ABOVE: A typical Lead/Wingman combat config.  This pair has already dropped 4 x 2000 pound Laser Guided Bombs, as evidenced by the set of empty MAUs on each jet and the laser designating targeting pod on the leader’s right chin mount.  Targeting pods are rarely photographed in the open position—note the glass eyeball has rotated out from its normal hiding place in the stowed, protective ground position.  The leader is using it to find and track the heat signature of the Tanker taking the photo (refueling doors on the spine are open).  These two F-16’s are heading north.  You can tell because the wingman’s jet has an IR Nav pod used at night and all the MAUs on stations 3 and 7 are spent; so the sun is rising post-mission, not setting pre-mission.


BELOW: Loaded Blk 40 with 4 x AIM-120s on stations 1, 2, 8, and 9;  marking rockets and TER mounted Mk-82s/GBU-12s on station 3 and 7; external fuel tanks on stations 4 and 6; ECM pod on station 5 (centerline), with a Targeting Pod on the right chin and Nav pod on the left.  Takeoff weight: 46,000 pounds, about the same as a combat loaded World War II B-17, but with longer range, many times the speed, and few foot bombing accuracy—not to mention it is still one of the best Fighters the world has ever known.  Yeah, the F-22 is better in an air-to-air role, although you have to compare one F-22 @ $350M to seven F-16s @ $50M.  Air-to-air is rare; air-to-ground is the USAF’s daily bread and butter.Off we go


With a lot of 1:1-scale flying time in the Viper, I’ve been waiting for the right Blk 40 F-16CG model to come along.

Loaded Loaded: 2 x AMRAAM, 2 x Sindwinder, 2 x JDAM, 2 x Drop Tanks, Targeting Pod (right chin), Nav Pod (left chin), ECM Pod (centerline)

F-16The LX version looks pretty darn good, so I pulled the trigger.  Sure, it has a few errors, like 6 hard-points instead of 9, and there are no chin mounts for pods.  It appears to be modeled after a Blk 50, as evidenced by GE motor cues, the IFF interrogator antennas, and the too chubby HARM load-out.  Close enough for RC land.

RC thrust vectoring isn’t exactly scale to the F-16 either, although TV was extensively tested as an incredibly cheap performance enhancement on F-16s.  Thrust vectoring was eventually canned because let’s face it, GE powered Vipers already make the F-35 look pretty shabby in a knife fight.  Even though dog fighting isn’t a high probability event anymore, the F-35 is vastly inferior to a Blk 40/50 F-16 in the phone both, and since government officials generally aren’t sophisticated enough to understand that dogfighting prowess isn’t paramount today, a TV Viper would’ve probably posed an unwelcome threat to the F-35 program.   So, no dice on full scale TV.

It’s interesting how political a life the venerable F-16 had from the outset: first the F-15C mafia tried to squash BVR enhancements for fear of emphasizing obvious Eagle obsolescence.  Then the Viper’s F-35 replacement rolled in at three times the cost and not nearly as maneuverable, so the Viper couldn’t be upgraded further even when it would’ve amounted to an incredible deal for the taxpayer.  Gotta keep the Gucci Suits in business, I guess.  …but I digress.

The LX model looks something like a GE powered, Big Mouth Viper. 

The easiest way to tell the difference between a Pratt & Whitney F-100 and a GE F110 powered Viper is the nozzle.  The silhouette of a Pratt nozzle is straight edged, and it is made up of a lot of turkey feathers:

PWNozzle

GE nozzles are rounded, with fewer, larger feathers, and the feathers zag towards the end.  The silhouette is not quite as rounded as the squadron litho below portrays. 

GENozzle

The model has a decent rendition of a GE nozzle with fewer feathers that zag properly, and it looks reasonably rounded.  F-16 savvy dudes will home right in on that:

Nozzle 
The intake isn’t quite right for any F-16 variant, but it extends the full width of the fuselage section above it, so I guess it has big lips which is true to the Blk 40 and 50.

LX decided to recreate an ANG 188 Fighter Wing Arkansas Razorback F-16 with a 1986 tail number.  Oddly, the 188 FW doesn’t fly GE Vipers.  In fact, they don’t fly F-16s at all.  They fly A-10s.  The unit converted to Hogs a long time ago, and A-10s are perfect for the Arkansas ANG mascot.  Back when they flew F-16’s, they had older, Small Mouth Blk 32s with F100 Pratt power, unlike this LX model. 

All that said, the BlitzRCWorks model is a great, affordable starting point for what I want to do.  It definitely seems good enough in stock form for RC fun, and it’ll be great fun if it turns out anything like I imagine.

This won’t be a typical build.  I decided to start with the airframe only kit, and upgrade the plane from top to bottom as I put it together.  The price was right at $136:

SPECS
- Wingspan: 860mm (34 in)
- Length: 1300mm (51.2 in)
- Drive System: 2400KV Outrunner Brushless motor
- EDF Diameter: 70mm

FEATURES
- Construction: EPS
- 2-axis (360 degree) Thrust Vectoring

REQUIRES
- Radio:  6-9 channel 

PAID
-
$136

The first upgraded component to go in is a ChangeSun 10 blade 70mm EDF and 70A 2-6S ESC: 

CS 10 Fan Insert
The ChangeSun 10-blade fan has a reputation for great jet sound, big thrust, and even bigger Amp drain. 


ON THE GROUND                                                                   
 
UNBOXING

The airframe only kit shipped in a much more complete form than I expected.  Yikes, some of the assembly could be a little tricky…

boxkit
sideside2
intakeguts

Although there are a few pieces in the airframe kit, building the LX Models F-16 is turning out to be pretty straight forward.  There are some steps that cannot be undone, so assembly order is important.  The basic idea is to start with the lower fuselage as a base platform, then build the fuse from the bottom up. 

Motorin 
Just enough finished for motor testing.  Nozzle painted.
The landing gear goes in first, the ChangeSun 10 blade unit went in next. 
I’ll be using a channel for each of the 9 servos (3 gear retraction, 1 nosewheel steering, 2 elevon, 1 rudder, 2 thrust vectoring) so that I can sequence the landing gear, control the amount of thrust vectoring, employ flaperons/spoilerons and even tune the amount of nosewheel steering resulting from rudder movement.

The CS 10 fan seems pretty quiet during initial ground testing.  I took my time balancing the fan impeller and also the included CS 10 spinner using the drill bit technique, and it turned out that both pieces were shipped way out of balance.  That exercise paid off, the first CS 10 motor run was smooth as silk.

With the fuselage together, test power is above 1:1 Thrust:Weight on 5S, but the wings still need to be added as do all 9 servos.  I’m optimistic on this build, it is shaping up nicely.

wiring

The internal wiring is as complex as it is permanently sealed inside.  The loose wire is for the tail mounted rudder servo. The landing gear, as usual, is going to be a clear weak point.

Complete

42.0 oz RTF without battery



IN THE AIR
 
BLUF

Incredible high alpha slow flier that needs more power than a single 70mm EDF typically delivers.

START/TAXI/TAKEOFF

The completed plane looks fantastic.  I’m flying it clean for the maiden.

rtftailrtfquarter 
rtf 
The Super F-16’s maiden went very well – for losing the motor.  Seems I made a slight miscalculation thinking the 2850-2200kV motor I installed had enough punch for the ChangeSun 10-blade fan.  Luckily I stayed close to home for a decent forced landing.
 


The two second streak of white smoke emphasizes the high power consumption of the CS 10 fan.  Thrust was not spectacular pre-failure, either.  The sound was ok, but nothing to write a blog about, either.  It makes sense that if a motor isn’t up to the job, it might not generate enough rpm, thrust, noise, etc, to break into an semi efficient operating envelop. 
 
So for the “re-maiden” I’ve decided to put two motors on deck:
 
     1.  Turnigy 4S-6S L 2855 2100kV ($12)
     2.  E-Flight 4S-6S BL32 2852 2150kV ($75)
 

L2855-2100EFLM3032DFA-250

Turnigy 2855-2100Kv               E-Flight 2852-2150Kv

 
Since the Turnigy is larger and only costs $12 (a $2 discount popped-up after staring at the page for a minute or two), it’s up first.  It is reported to work well with the CS 10.  If it turns into a smeak of white smoke, I’ll install the E-Flite BL 32.  If that one fires, I’ll throw out the CS 10 idea and go back to the Super F-16’s included 6-blade EDF unit.  I purchased an extra Turnigy L2855-2100 to accommodate that possibility.
 
The F-16 handled well in the 2 minutes it was airborne.  The CS 10 was clearly shackling the motor; thrust was adequate at best.  I will reserve judgment, good or bad, until I get the power system right.
Re-maiden, soon…

The Turnigy 2855-2100 is installed and seems to be turning the CS 10 pretty strongly.  With a 3300 mAh 5S, T:W is about 0.9:1.  With a 2800 mAh 6S T:W is about 1.1:1.  That’s a lot of push from a single 70mm.  With the stock 6-blade fan, T:W was in the gutter at 2100 kV, but realistically a higher kV motor could be used with fewer fan blades.

More soon…


I got a chance to fly the jet this morning with the CS 10 fan and Turnigy 2855-2100 in perfectly calm winds.  I flew with both 6S and 5S.  6S was definitely the preferred setup given the low gearing of the motor and strong fan.  The batteries were only warm upon landing and the power system seemed fine spinning the 10-blade.

Here is a “re-maiden” video double feature.  The first half shows 6S, the second half shows 5S.

Check out the High Alpha passes in the first and second sortie.    The slow pass at the 9:00 minute mark (handicapped by 5S) got a little too nose high for the thrust output, at maybe +70 degrees or so, but it shows the F-16’s incredible high AOA slow flight potential.  The forward and ventral strakes help the Viper remain stable at crazy AOAs.

GENERAL CONTROL

The F-16 is an iconic jet for a reason, handling is first class and this RC version is true to scale in that respect.

At high speeds and low Angles of Attack (AOA), the frontal area of the F-16 is skinny, allowing the plane to penetrate like a motor with fins. 

At high AOA, the “Lawn Dart’s” long, needle-nose strakes energize airflow rolling over up and over the lifting body.  The forward strakes redirect kinetic energy into lift, and the nose continues to track up hard while minimizing energy bleed.  But the blended fuselage contributes a lot of wing area, creating a platform with solid turning and hauling fundamentals, it’s not all about Jedi Mind Tricks played on the airflow.   The recent Flanker-E review had a similar long strake config (not a coincidence) and similar outrageous pitchability and control, but lacked the wing area required to fly as slow on the wing.  It was more geared to sustaining high speeds than high turn rates at mid to lower speeds.

Make no mistake about it, the venerable Viper is at the top of its game in a 2-circle rate fight—force a close high speed pass beak to beak, watch your opponent turn first then turn opposite direction to prolong the turning engagement.  Let the awesome power of the GE motor combined with the light weight and low drag of the single engine design, all pile on top of the F-16’s killer aerodynamics and you’ll blow the doors off the other guy’s turn rate.  Result: by forcing both fighters to take the long way around, you’ll be looking down his tailpipe in no time.  Best rate fighter ever. 

You better be in the best shape of your life when this over-powered rumbling spawn of satan crushes you with it’s all-axis acceleration, then never lightens up.  Better have your heavy noggin squared-up over your shoulders when you start, or your giant nugget will fall back, hopelessly pinned to the side of the headrest for the duration of that turn.

As you arrive for the kill, all your opponent sees is the underside of your jet.  The design allows you to pull plenty of lead to shoot while maintaining energy.  With time you’ll learn when to tug hard on the electric side stick and finally bleed enough speed to slow the jet to your match a struggling opponent without overtaking him.  Stitch any pattern you want with the gun spewing 100 rounds per second of 20mm high explosive in a tight shotgun pattern.  

Does my build of the Banana/LX scale Block 50 faithfully re-create that experience?  No. 

The airframe seems capable and scale enough; the missing ingredient is Thomas Edison's GE motor and its avalanche of thrust when you contemplate throttle movement.   The model just doesn’t have the kind of horsepower that shoves the chair into your back or crushes your spine in pain.  EDFs have a long way to go. 

BALANCE & AEROBATICS

Instruction manual CG is perfect. 

Unfortunately the battery location is well forward of the CG point, making trim calibration difficult with all the LiPo variables still in play.

POWER SYSTEM 

Too weak to capture the personality of the modern big mouth F-16.

In fairness, I wanted to put the ChangeSun 10-blade in a model as a sub-objective to this build.  There might be better optimized power systems out there. 

I kind of doubt the thrust deficiency is all my choice of 6S 10-blade EDF.  I tested the stock 6-blade fan with a 2100 kV motor on 6S, a reasonable approximation of the stock motor’s 2400 kV motor on 5S and it was not as thrusty.

I think the root problem is a 70mm throat diameter in a fairly large model.  Using CS 10 seems like a decent way to address that issue, but maybe an 8-blade on a little higher kV motor would be optimum.

Before I leave the Power System section, a note on exhaust note: 

One reason I picked the CS 10-blade was its reputation for high fidelity jet noise.  I found that claim to be a little overblown (ha ha).  It is definitely a quiet EDF as far as EDF’s go. I think the “whoosh component” of the sound has a better chance of burning through
the overall racket produced by lower blade count EDFs.  But that doesn’t really make the whoosh sound louder.  Close passes are the key to hearing high quality air rush. 

ADVANCED HANDLING CHARACTERISTICS

King Kong.  Enough said.

APPROACH & LANDING

Approaches were very well controlled.

I wondered if the F-16 would need flaps and/or slats to land slowly/gently enough.  The answer is: sort of. 

The plane has such bad a$$ high AOA control that you can slow way down, under complete control, and drag the nozzle all the way down the runway.  The question is, how do you get the wheels on the ground before the nozzles and ventral fins are ground into stubble?  In that sense flaps or flaperons (the elevon setup removes that possibility barring inserting more servos) would help.

I’m still working on this one. 

IN-FLIGHT ISSUES 

- Servo-driven main landing gear are too weak to overcome the airflow during retract. 
- Landing gear piano wire is too thin gauge for the weight of the jet; needs a complete servoless re-design.

OVERALL

In general, this model is a fantastic flier.  The lingering questions are:

1. How to best power it with today’s 70mm EDF technology?
2. Is there better way to get it on the ground than smushing a jumble of servos and toy landing gear after each sortie?

A puzzle worth solving.  I’m going to iron this one out some more and update.

Update:  Just tooling around:

  GRADES                                                                         

Appearance: A+
One of the best renditions of a desirable F-16 Block 50.

Aerodynamics: A+
Unmatched handling and high alpha control, just like the real thing.

Power System:  N/A
Not included.  Scale of jet is difficult to power sufficiently though the 70mm form factor.  The ChangeSun 10-blade has plenty of static push on 6S, but not dazzling top speed. Maybe a 3200 kV 6-blade on 5S, or a 2500 kV 8-blade on 6S would do a little better.  Limited to 6S due to battery bay/scale constraints.  10-blade fan eats batteries and ups weight. Slippery jet helps conserve fuel between blasts.  

Build Quality/Durability: D+
I purchased the airframe only.  Soft foam needs edges taped and inlet reinforced.  Stock landing gear is awful.

Value:  B-
@ $136 for the airframe there is $ enough left to populate with quality components, even to re-design the landing gear. 

Overall Grade: B
Iconic handling is worth the hassle.  My mistakes are your gain.

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