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Monday, April 16, 2012

Great Planes F-86 Micro EDF TxR - Flight Review

Update 2:
Video with a 3S 180 mAh 25C:

Pretty fast little jet!



Update 1:  In early December, 2011 Z8RC began exclusively designing and testing 3S batteries and ultimately far more powerful 3S-pure Piggyback power systems for E-Flite 2S Ultra Micros and micro helicopters.  Z8RC innovation spread like wild fire through the RC community.  Within weeks, RC forums went nuts flying our exclusive Z8RC 3S and Z8RC 3S Piggyback system ultra micros.  There was much rejoicing!

No surprise - Z8RC now has the world's only F-86 micro jet running on clean, pure 3S power.  Here are the rad numbers:
 
Power
Fly oz
Thrust oz
Load V
A
W
T:W
2S 250 mAh
2.46
2.11
7.36
4.03
29.7
0.86
3S 180 mAh
2.65
3.18
11.37
7.14
81.3
1.20

Z8RC's hopped up 3S-abre pumps a cheek-stretching +40% boost.

Although the stock Electrifly Ammo 10-15-11500kV Inrunner has no listed manufacturer spec, Z8RC's 3S power system seems to fall within burst limits using other small Ammo Inrunners advertised burst capacities between +70% and +100% of their constant Amp rating.  An IR shot straight up the tail following a 10 sec 3S full grunt burst displayed 91.8 degrees F.

Flight video here soon.  Original blog article follows:


Great  Planes new line of universal "Anylink" models is off and running.  These planes are similar to BNFs but they can bind with Futaba, Hitec, Spektrum, and JR transmitters.  The magic happens through a small transmitter module that plugs into your radios' buddy box port.

The little F-86 is advertised as the world's first transmitter ready micro EDF, even though Chinese no-name brands have been doing Micro EDFs for a long time, and as such it was quite expensive at $120 after my standing Towerhobbies club discount.  That price includes free shipping and a free "Anylink" transmitter module.

It is time to see if the little foam jet stands up to its crazy price tag.

Great Planes F-86 Sabre Micro Jet Specs:
- Wingspan:  15 in (381 mm)
- Wing Area: 53.1 in² (3.4 dm²)
- Weight:  2.35 oz (67 g)
- Wing Loading: 6.4 oz/ft² (20 g/dm²)
- Wing Cube Loading: 10.5
- Length:  14.4 in (366 mm)
- Requires: AnyLink and compatible 4-channel transmitter or Tactic 2.4GHz radio
- 11,500kV brushless inrunner motor
- 30 mm HyperFlow™ ducted fan unit
- 6A brushless ESC
- 4-channel 2.4GHz SLT™ micro receiver
- (3) digital ultra-micro servos
- 7.4V 250 mAh 25C LiPo flight battery
- Balancing DC LiPo battery charger
- Cigarette lighter DC power adapter
- Unpainted pilot figure 
- Airfoil xsection - undercambered
- Foam type - very smooth, painted Styrofoam

Target Wing Cube Loading
Glider - 1 to 4
Trainer - 5 to 7
Aerobatic - 8 to 11  << The F-86 Micro jet flies here
Scale - 12 to 15

Racer - 16+  


Upon box opening, the Sabre looks scale with a high level of finishing detail for a micro.  But more importantly, component quality is much higher than Horizon Hobby Ultra Micros.  Great Planes includes a standalone 6A ESC, 3 industry standard digital servos (no delicate and fussy linear servos) and a high quality motor and fan.  The parts represent higher end fare for better long term reliability, but each piece is also replaceable, upgradable and aircraft transferable, unlike Horizon's expensive all-in-one micro boards.

One obvious inconvenience is the odd battery connector--just what I need, another standard. I'll be replacing the connector with a 2S standard, red thingamajig.

 Another minor deficiency is non-steerable, but removable landing gear.
The diagram on the box is marketing material, but it's nice to have a basic blueprint of your model's interior.
Perhaps most impressively, the free TxR "Anylink" finally gives DSM/Spektrum users access to a strong, high quality link on a frequency hopping 2.4Ghz standard with an affordable line of receivers.  Anylink has 9 channel potential!  6 channel Tactic receivers sell for less than $30, or about half the price of Spektrum receivers which have become infamous for being crash prone.  The included Tx module is currently limited to controlling parkflyers, as it only draws 20 mA of power from the host transmitter.

For those using strong, frequency agile 2.4GHz links with affordable receivers already, the free Anylink value isn't as strong but at least you can bind to TxR models without additional investment.
Yellow wingtip stripes provide the only top/bottom color scheme contrast.
Bell-cranks protect the servo electronics, especially with the optional tricycle gear attached.
Another weird connector.  Great.

On the Ground:

The micro F-86 really looks great for its size.  Molded panel lines and a gorgeous little magnetic canopy make the miniature Sabre convincing.  It's the price I'm worried about.  Sure, this micro is an incredible value compared to Horizon's UM line, but let's not compare to the wrong people.  There are a few more convincing values already established in RC land:
Banana Hobby's EPO nano F-86 sells under $70 without a receiver.
Pete's receiver ready 4-cell 44" wingspan EPO 8 ch Sabre includes flaps, servoless retracts and airbrakes for about $180.  Hmmm.... 
Nitroplanes 37" SkyAngel EPO PnP 3-4 cell MiG-15 also has a $140 tag.
Hobby King's $60 SkyAngel EPO Sabre.
I would hate to see Great Planes set their prices in relation to ridiculous rip-off Horizon Hobby competition only to lose the big picture.  There are much better values out there, even in the micro-nano scale and parkflyer genre.

It is tempting to believe that the cheaper Chinese models are somehow of lesser quality than more established Made-In-China brands like Hobbico/Great Planes and Horizon, but that simply isn't the case.   All of these foamies are a bit wanting in the quality department, but none offer a clear quality advantage over the other when compared at similar scale.

That said, much cheaper Chinese EPO foam lines from Airfield, Durafly, Dynam, Exceed, J-Power, SkyAngel, Starmax and Art-Tech, sport a MASSIVE quality advantage over Hobbico and Horizon Hobby models when compared at the same price point.  So much so, that factually Horizon Hobby and Hobico, while popular among convenience shoppers and beginners are not remotely competitive Chinese makes at this point in time.  That said, Hobbico is priced more acceptably than Horizon Hobby. Horizon trails the pack with absolutely punishing value deficiency per dollar spent. 

Anylink

The included transmitter module velcros onto the back of your existing transmitter.   It tucks under most Tx handles with the antenna poking through, so it doesn't really require any space and it is unnoticeable in operation.

A Spektrum installation plugs-into both the buddy box port and the battery charging jack to provide Anylink its trivial 20 mA of electrical power.   The tranmitter's power switch stays off.  Spektrum users need to switch Anylink into its "alternate mode" by holding the rudder stick to one side for one powerup cycle.  After that channels map properly.  I needed to reverse all my model setting channels except the throttle channel.   Anylink inherits any computer radio settings like D/R, expo and mixes, just like any buddy box radio mode, it is as basic or advanced as the non-transmitting 2.4GHz or 72MHz host radio.

Anylink was up and running a minute or two after reading a short paragraph of instructions.  It seems to work perfectly.  Nice!

While there is a bind button, I did not have to bind my F-86 to the Tx module.  That seemed strange since my Anylink Tx module and my F-86 model arrived in discrete shipments.

The Anylink instruction manual mentions that almost any transmitter with a buddy box port will work.  When I read that, I remembered buying my Dynam A-10 as a 72MHz RTF bird because it was actually a few dollars cheaper than buying it as an ARF without a radio.  With that it mind, Anylink has to be one of the cheapest ways to get into 2.4GHz RC, it is darn near free, all you need is an 72MHz transmitter with a buddy box port plus a TxR airplane or a very inexpensive Tactic receiver.  It is a wonderfully cost effective device for flyers on a tight toy budget. 

In the Air:

I was encouraged by the Sabre's measured installed static thrust with the stock 250 mAh 25C 2-cell, which produces 1.8 ounces of thrust in a 2.35 oz jet.  This little motor really blows.

But there is more to exciting flying than static thrust.  Speed, for example.  A jet airplane can only go as fast as it's exhaust velocity, no matter how much thrust it generates.  The fact that this fan is tiny with high measured static thrust is very encouraging for top speed, because a small diameter means a small m (mass flow of the air), and that implies a high delta V (velocity change of the air) in the following general Thrust equation derivation:

F = mA

 ...therefore...

Thrust = m[(Vexit - Vinlet)/delta-t]

So I was hoping for great things.  But the reality is...

Top speed is very good, but not great.  Even with the landing gear left at home, the F-86 Micro Jet starts strong but fizzles after a minute or so of flying time--not unlike larger scale EDFs.  During the first minute, get-up-and-go is sufficiently engaging.  After the edge falls off the battery, slow flight becomes more interesting than diluted full throttle passes.  

Speaking of slow flight, the mini F-86 can definitely slow down.  I ran out of flight time while exploring the low side of the airspeed envelope on the maiden, but what I was able to probe impressed me.  A few slow flight characteristics and handling anomalies emerged during my first short flight:

First, the plane never tried to tip stall all the way into a spin, even with the nose jacked way up from a too hard hand launch, the tips take turns stalling while the nose continues to rise.  Loops were consistently tight, with no tendency to roll off into an turning accelerated stall.

Slowed down, the Sabre was able to hold altitude at 30% throttle.  When the battery gave out, the plane established an easy glide on the wing.  In fact, I flared out my first flame-out landing way too early, there was a lot of lift potential left even at very slow speed; when the nose rose easily, it surprised me.  All of these clues lead me to believe the micro Sabre will be a very rewarding airframe to slow down, as long as you keep that Sabre from Dancing:
An F-100 does the infamous Sabre Dance
Here is my maiden flight video, the fist 30 seconds were pretty scary due to three compounding errors:  (1) too much up-elevator set by the factory.  (2) Classic F-86 flight characteristics coupled with a nice light nose/battery and copious lift potential.  The plane wanted to Sabre Dance right away, and at first it felt tail-heavy/nose-light to me.  But after flying out the whole battery, I think the balance is between good and perfect.  This is the way the all Sabres misbehave in a fully developed stall; you just have to break it hard before it breaks you harder.  (3) Too strong a toss.  I didn't realize how easily the nose would float up at slower speeds, the plane looped right away, I pulled it through on faith--phew!
What better way to begin an F-86 maiden 
flight than with a full stall Sabre Dance 
at the 0:28 second mark?
That covers fast and slow.  The middle of the envelope is a great place to relax.  The plane flies casually and under complete control.

Sport-quality loops (eggs) and rolls (with some barrel coupling) were cooperative, even though my chosen rates were a bit less than ideal.  Based on visual inspection of the surface throws, I decided to go with 125% aileron on high rates, and 70% on low.  The high rate setting was pretty good with a solid roll rate for a scale model.  The low roll rate could have been relaxed to about 55% (of 125% travel) to squash any bank overshoot while retaining enough roll authority.  A sedate low rate, while perhaps a tad sluggish, would keep the strong wing sweep from introducing minor oscillations to roll axis stability during casual maneuvering.

All in all, I really enjoy flying the Great Planes F-86 Micro Jet.  I hadn't replaced the odd battery connector for my first flight, so having only one usable battery left me wanting to fly the plane again, mostly to fully explore the promising low side of the airspeed envelop.  That is obviously good, and bad since the battery connector is rare and inconvenient.

That said, it was probably worth taking a little time to stop before testing alternate batteries that may have lightened the Sabre's nose too much.  I was thinking about adapting my 180-200 mAh micro 2S batteries, but I think that might have resulted in a tail heavy config.   Balance with the included 250 mAh 2S is near perfect, and given the little F-86's tendency to Sabre Dance coupled with pretty short flying times, it is probably better to go with a same-weight or larger alternate battery. 

Grades:



Appearance: A  
Fighter looks.  Smooth finish Styrofoam.  Nice paint scheme and decals.

Airframe: B-
 
Good handling.  Sweep requires roll discipline.  "Sabre Dances" in full stall.

Power System: B

Adequate push.  Very good speed.  Quick power fade.  4.5 min flights.
 

Build Quality/Durability: A-
High quality electronic components.  Cheap foam.  Nice canopy/hatch.

 
Value: B+
 
Lags larger scale competition.  15% discounts common.  "Anylink" a plus.
 
Overall Grade: B+
A lot of fun with a nagging opportunity cost. 
TxR w/Anylink is better than BNF.
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