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Friday, July 20, 2012

BlitzRCWorks Mini F-22 Raptor

Update 8/30/2012:  See for a great fan upgrade (and noise reduction) that combines the trust of 4S with the lighter battery weight and balance of 3S. 

Update 7/20/2012:  4S testing is complete with exceptionally strong EDF thrust, even when capped by computer at 20 Amps.  I flew two 1000 mAh batteries.  The first lasted 5:00 mins-even, with plenty left for landing.  The second I flew to exhaustion at 6:35 minutes after a lot of relatively low power setting, high alpha envelope exploration. 

Given the great wing loading, industry standard low cost 4S 1000 mAh batteries (only 20C required for 20A current flow), chimp friendly construction and 4S accommodating stock motor and ESC, this little jet is a super package. 

$78 including a battery?  Awesome.

First flight on 4S:

The only real draw backs to the Mini Raptor are the inherent simplicity of a two servo elevon set-up and a CG that is still a bit forward with a solid battery pushed all the way back.  I wound up adding 50% up-subtrim and 125% up-elevator travel while in the air.  That flew about perfect, but the jet still ran out of flare on landing.  It would probably be perfect with a little foam trimmed-out to slide the battery even farther back.  Consider adjusting your neutral elevon position to a nose-up bias during construction.

An 850 mAh 4S might be no-mod answer, but I think the flight times and T:W are just right with a 4S 1000 mAh limited to 20 Amps current. 

It is a pretty small jet, but priced aggressively. 

For the F-22’s awesome flight character and the Mini’s low WCL and huge T:W, it wins Z8RC’s Most PNP Fun Under $100!

Overall:  A


Update 7/19/2012:  The Raptette functions perfectly with a 4S 1000 mAh (4 ESC beeps), and the slightly slimmer form factor of the $8 Sky LiPo battery allows a more aft position and gives a little better balance than the 3S 1300 mAh.

Rather than chance blowing the 20A ESC, I tested the 4S battery with the throttle in End Point Adjustment mode.  Starting at 50% upper half stick travel set, I put the throttle up to the firewall and slowly incremented the EPA to 69%, where the Amp draw showed 20.5 Amps and 307 Watts.

Running up the plane to the new full throttle (69% EPA) revealed a Thrust:Weight ratio well above 1:1 (400W per pound).   At 15A average throttle, a 1000 mAh 4S gives 4 minutes of flight time, so the numbers look great. 

Flight test tomorrow, winds permitting.

Original review follows:


$69.  What more is there?

bh F-22Banana Hobby’s Baby Raptor

- Wingspan: 510mm (20 in)
- Length: 740mm (29 in)
- Flying Weight: 330g (11.6 oz)
- Drive System: Ducted Fan 50mm, 5-blades
- Servo: 2X 8g high speed micro servos
- Speed Controller: 20 Amp Brushless Speed Control

- Linked elevons
- Construction: EPO foam
- Motor: Brushless EDF
- Servos: Two as elevons
- Landing Gear: None
- 5 minute assembly time
- Magnetic battery hatch (canopy)

- Radio: 3 Channel
- Battery: 11.1V 850mAh LiPo


The quality of this kit is very high for the money. 
The packaging looks like Sky Angel.  So does the fan, ESC, and EPO foam.
Unlike models that need one, this jet actually has a complete manual with decent pictures.  I flipped through it after I built most of the jet.

The baby Raptor goes together in less than 5 minutes. 
I haven’t seen EPO this smooth and strong and thin.  Very nicely done!  Puts other micros to shame at 1/3rd to 1/2 the price of some.

Airframe quality is superb at this price point.  The little bugger appears to be very tough indeed.


Servos are the usual junk, but other Sky Angel models have proven to be very reliable in the electronic component department.

The fan is a good size for a micro/mini at 50mm with a 5-blade impeller, and the ESC is surprisingly chunky at 20 Amps.  All in all, a gorgeous little midget.


The mini F-22 is a lot more airplane for the money than traditional micros.   Like all F-22’s, the plane has copious wing area.




A great little flier without enough push on 3S.  4S trials soon.   Maiden:

With no landing gear, the only way to launch the mini Raptor is by hand.  I didn’t feel a lot of push on run-up, so I decided to use the discus method, where you hold the bird by its wingtip and start spinning like an Olympic athlete about to launch a solid iron frisbee. 
It was a good thing I did, because even with my best heave, the Raptor settled back down like a apple seeking Newtown’s gargantuan cranium.  Once I coaxed it to a mostly skyward vector, I was able to get enough altitude to trim out the elevons.  I made the possible mistake of using a 1300 mAh 3S, because I knew from the similar Sky Angel MiG-15 that flight time would be an issue using the recommended 850 mAh, and even a 1000 mAh is worth maybe 4 minutes. 

I rushed the 5 minute mini build and didn’t install a telemetry wire from the ESC power lines to a Hitec 6 Lite Receiver, so I only had servo voltage on the telemetry readout.  Bummer, cause I wound up tagging the LVC, not expecting a 1300 to quit so soon.  I figured the worst that could happen was a grass landing—which was the best that can happen too.

The Banana Hobby website needs to re-write the standard “10 minute flight times” bullet on their 50mm EDF series.  My old, decrepit E-Flight (=crap battery) 1300 lasted 4:50 to LVC dead stick.  A good 850 mAh 3S (the recommended battery) doesn’t stand a chance of lasting 5 mins, let alone 10.

I’m going to try a 4S 1000mAh next, I hope takeoff is a lot less exciting. 

With the 1300 mAh 3S, the tiny spawn of Raptor flew solidly nose heavy.  I knew it was on the nose heavy side, but I couldn’t shove the battery back any farther without melting some foam.  I wish I had balanced the plane a little better in retrospect.
The plane flew great once dialed-in.
The mini Raptor is fairly quick flat out, which was a little it surprising given its wimpy static push.
Other than the need for one or two more clicks of up-elevator trim than the radio had to give, and maybe 10-15 aileron clicks to level the wings, the Raptor flew very nicely.  The out of trim setup was likely my fault for trying to get the Raptor up quickly today.  Be sure to level all the aileron and elevator surfaces perfectly, and maybe add a touch of symmetrical up-elevator at the neutral trim setting.
There was plenty of throw.  I was happy I actually glanced at the manual to determine if the aileron or the elevator should take the far hole in each elevon servo’s control horn.  This is the only real question (other than CG point) I had during the build.  The manual is silent on the decision, but in the back it shows the elevator requiring more movement than the ailerons, so I gave the far hole on the servo arm to the elevator pushrods.  That was the right choice.
Rolls were coupled in typical elevon fashion, and the plane was too weak to loop.  Overall aerobatic prowess is low on 3S; limited to fast rolls on high rates.
Thrust – unmeasured on the static stand, but clearly weak on 3S. 

The fan came nicely balanced. 

A good 1300 mAh 3S should last about 6 minutes. The E-Flite 1300 I used for the maiden was old and low end of the performance spectrum even when it was new. 

If I had trimmed a little foam to get the battery far enough back for a proper CG, I think the jet would have climbed better, instead of staining to lift the nose at half speed or less. 

I set up my rates like this for the maiden:

     High – 100% Aileron/Elevator, 55% Expo
     Medium – 80%
Aileron/Elevator, 55% Expo
     Low – 60%
Aileron/Elevator, 55% Expo

I felt the jet was still a little touchy in roll on Low, but without enough Elevator to flare out the landing given the forward CG.

Not much to see here.  My forward CG precluded solid high alpha, but the plane seemed eager and stable to jack the nose up, like a good F-22 should. 
I think a 1000 mAh 4S (I need to order one), placed far enough back, will be the ticket.
No rudder is a high alpha handicap.   I will probably add mix like I my rudder-less MiG-15, where the rudder stick only lifts the inboard aileron (in this case, elevon) to create little drag differential to synthetically replicate a rudder’s yaw control.

The “approach” was an SFO pattern with a rapidly dying battery.  Once the motor sagged, I switched to a straight-ahead grasser.  No damage, easy enough, and will be better once I get the throws and balance iterated.

CG: heavy nose.

F-22s seem to fly very well at RC scales, all the way down to micro.  High alpha is very stable, as is the entire flight envelope for that matter. The stealthy rake of the vertical stabs effectively adds dihedral.  “Needs a computer to fly” …Not!  

The Banana Hobby product page says:
  • Perfect for first time flying EDF jets
  • It may be easier to fly than propeller planes

    Even given the inherent stability of F-22 EDFs, I beg to differ.  The small scale of the airplane makes it harder to trim out, even though it is very stable as far as micros go.  The lack of Thrust:Weight on 3S is fairly challenging to coax along, especially upon launch. 

    While it is true that the F-22 is a terrific high alpha jet, the big wing can create a drag hole that is tough to power-out of unless you carefully trade AOA for kinetic while lots of battery is available, or sacrifice altitude.  Get it wrong and the jet will settle lower and lower even with the nose up high, and become even harder to recover until it feels for Earth or stalls completely.


    Appearance: A+
    Beautiful Micro.  EPO, so the looks might last a while.

    Aerodynamics: B+
    Very stable + lots of throw = fun.  F-22 quality flight.  Small.

    Power System: D+ on 3S, A on 4S
    Low T:W. Few-minute flight times w/recommended battery.

    Build Quality/Durability: A-
    Super simple.  EPO.  Yay!  

    Value:  B- on 3S, A+ on 4S
    60% less than junk Styrofoam micros.  Most fun you can have under $100.
    Overall Grade:  A
    Excellent power, wing loading and high alpha on 4S (only).  Limited by simple elevons and slightly forward batt position.

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