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Monday, June 4, 2012

P-51D Big Beautiful Doll 1600mm EPO w/Electric Retracts, Flaps, Lights (PNF)


Update 6/20/12:  Rimfire .60 and video.


Update 6/4/12:  I really enjoy the scale 4-blade prop included with this warbird, and the sound is tremendous (for e-power).  On 5S, the speed is surprisingly good for the size of the prop and the blade count (video below).  But as I broke-in the motor (or maybe just plain "broke" it), it started to choke on 5S during static runs, and more problematically on takeoff.  It continued to run fine once unloaded in the air.

My Soft throttle solution might have fixed the stock motor problem entirely, as might ESC timing changes, but I didn't start experimenting in earnest until my replacement motor, a Power 46, was already installed and it too balked right off the bat wien using 5S.

With the Power 46 installed, I was forced to abandon the gorgeous Starmax 4-blade as the motor was too weak to turn it with it's 700 kV gearing.  The stock motor is 400 kV.  So reluctantly and given that the 46 was already installed, I decided to try a 4" aluminum spinner with a higher RPM 2-blade solution.

Unfortunately, the Power 46 turned out to be disappointing, even with 2-blades hauling the plane on 5S.  Using Soft Throttle, I was able to achieve pretty good RPM with a 13x6.5.  But in the air the Mustang didn't seem much faster than stock running on 5S, and I had to give up the scale prop and much better audio.  I was ready to get back to troubleshooting that big beautiful prop spinning on 5S with the stock motor.

Then I saw a new Rimfire .60 on an LHS shelf for 50% off it's $99.99 marking, so I jumped on it.  The Rimfire .61 (50mm-55mm 650kV) fills out the motor bay very nicely, and at 2200W it is more than twice as strong as the 900W Power 46 with almost identical motor weight.

I videoed my first test flight on 5S then on 4S using a 14x7 (the Rimfire .60 has no advertised 4S option, but it runs just fine on 4S).   On 5S the plane is reaching new top speeds with spectacular vertical capability.  Even on 4S, the Rimfire gives the Mustang zip the Power 46 lacked on 5S.
Today, I flew the P-51D on 6S with flawless performance from the stock ESC and big Rimfire motor.  The big Mustang is finally getting close to matching my sweet imagination.  I hope all it needs now is the  optimum prop.  More soon...



Update 5/9/12:  Added video of a 5S pass and final grades.
Update: Although they held up fine, to be safe I changed the main retracts for these "super expensive" $14/gear reatracts.  These 2 meter wingspan gear are more substantial and have no play in the down position so ground handling is improved.  They do not come with gear struts and the stock struts are thin gauge for the bore of the heavier duty mechanism.  I added an inner diameter = outer diameter brass tube to the top of each strut for a snug fit.  
Other than drilling 4 holes to match the smaller, stock gear's bolt pattern, mounting is plug n play after trimming 1/8" around the frame of plywood anchors.  Not difficult.  I did like the slower speed of the original gear, but the new ones are not too fast.  The tail gear retract remains stock but for my upgraded pull-pull wires, see discussion below.

This P-51D continues to perform extremely well and out of the 10-15 plane variety pack I typical bring to the fly it always gets the most, if not all, spectator requests to watch it fly.  
The stock prop is gorgeous and it generates monster thrust and adds realism through the sounds it makes in the air, but top speed plane would benefit from a steeper pitch 2-blade.   But I like the stock 4-blade so much I hope I don't have to replace it for a long time (wishful thinking?).
Another interesting thing is how you find yourself treat genuine value vs. an obvious rip off so differently.  I enjoyed putting $28 upgraded retracts into this plane $175 plane and am already looking for other upgrades.  I would throw away one a same-price Ultra Micro before replacing a $30 part, and take the discount on a new semi-disposable POS instead.


Original review follows:
-----
The Starmax Big Beautiful Doll P-51 is quite a sight.  For $175, I had to give it a try.  The plane is much larger than your typical foamie with a 63" wingspan; it's a mega chunk of EPO foam.
Same price as an E-Flite Ultra Micro, really?
The kit comes with the electronics installed for you, requiring assembly of the big chunks.  Overall, the plane goes together pretty quickly and gives a very high quality first impression.
Picture taken at 12:27.
Picture taken at 12:50.
On the Ground:
The two pictures above were taken 23 minutes apart, and I took my time dry fitting the parts.  The plane goes together easily and everything fits well.
The main wing remains removable for transpo.
I glued my wing halves together by smearing the plywood main spar and joining faces lightly with Gorilla Glue.  The completed wing attaches to the fuselage with a pressure fit above the radiator and two bolts at the CG.  The wing could be removed for transportation, but there are 8 connections and not a whole lot of extra wire length on some of them.  Probably best to buy some servo extensions so you can leave the wires connected in a long bundle if you need to break the plane down to transport it.
Big prop; big motor.  
45mm x 58mm 4-5S with 80A ESC
The motor is listed as a 4558 400 kV brushless.  The ESC is 70 Amps as evidenced by the shrink wrap printing, though some retailers list it as 80A.
16 x 6 x 4-blade.
The 16x6x4-blade prop is gorgeously detailed and very hefty.  Mine was pre-assembled and well balanced.  Each blade is replaceable, assuming you can find them or buy an extra prop or two with the plane.  Initial ground runs show tremendous thrust, but little speed.   Using a 5-cell looks to be within limits and provides theoretically unlimited vertical, but I suppose it should because it still tops out with only 40 mph pitch speed.
Prop
Battery
Amps
Watts
Thrust
T:W
16x6x44S-4000mAh-20C58.566790.40.92
16x6x4
5S-3300mAh-25C
68.2
1148
127.8
1.26
The prop could use a lot more bite to convert some of that static thrust to top end speed.  To be sure, a honkin' 16" 4-blade was an aggressive target for an electric plane at this price, so it isn't surprising that it had to be geared low.  We'll see what the plane looks like in the air before a prop or motor re-attack.
The powered LEDs are bright.
The wing tip LEDs are very bright but have spot lenses that focus thin beams straight outward instead of flood lenses.  Diffusing them might help during low light flying.
The retracts are nice and slow, and seem reasonable for the size of the plane, if not a little rickety.  The doors aren't quite flush, and might be designed that way to help hold the gear up or maybe to help them down, but more likely it is a slight miss.  Slicing an 1/8th inch off the three gear door support points is an obvious and simple fix.
The tail wheel retracts too.  Steering is made possible with a pull-pull cable system that attaches to the full size rudder servo with removable and adjustable ball links; the cables fold in the gear up position.  It is straight forward and works well but adds about 30 minutes of assembly time to figure out, install and adjust, as the scant manual doesn't even include a photo.
Full-size servos move the rudder and elevator.  The rudder servo steers the tail wheel separately via the two ball links shown in the photo.  This was slight shipping damage to the wing root corners.
Nice paint and cockpit details.  The canopy mold needs to be trimmed and attached to the magnetic cockpit hatch (sharp scissors did the job cleanly).
Overall, this plane has an awesome presence.  While I think it is priced about right with it's .46 size motor, 70A ESC, three retracts, flaps and lights for $175 from HK, it is shocking that some flimsy, relatively featureless micros cost about the same.
HK will throw in a DSM compatible receiver for a few extra dollars, but I went with a $70 Hitec Optima 9 ch for voltage telemetry and to make each control surface independent per side, mixable and adjustable.  2 x ail, 2 x flap, 1 x elev, 1 x rudder, 1 x gear, ESC = 8 channels before tunable gyros or bombs--which might be forthcoming.
My final flying weight without modification measured 101 oz with a 17.6 oz 4S 4000 mAh inside.  The listed flying weight is 2800 grams, or 95 oz--sounds like ball park number, I don't think so.
Overall, value is through the roof.
In the Air:
The first flight couldn't have gone better. Well, unless you count the landing roll as part of the flight.  The right main gear set screw wasn't very tight and twisted in it's retract anchor upon touchdown--immediately seeking the only three ton vehicle within one mile.
No damage, yay!  Tighten those set screws!
A slight mod I performed as a fix was to Dremel both main gear struts so that each of the two set screws has a flat spot on the metal to hold.  As shipped, the flat spot machined into the strut is only wide enough to catch one of the two screws--of course, the one that wasn't very tight.
The big Mustang was sensational in the air--poised and reasonably powerful on 4S.  Unbelievably quiet.  it flew beautifully, no doubt due to its size and sleek scale design.   As you'll see in the FPV, it required a lot of down elevator trim, creating a slight but visually noticeable downward elevator deflection once on the ground.  But the CG felt good, well balanced in the air with no elevator correction needed in idle on final.  Darn it, the elevator incidence angle was adjustable as shipped.  It is held in place with two long screws, I knew I shouldn't have glued the stab in place.
A second mistake was to anticipate and pre-mix 10% down elevator with flaps.  None was required so the nose pointed down slightly with flap extension due to my mix.  Nice!
What a gorgeous and rock solid platform in the air.  This slippery Stang is faster than I anticipated on 4S, based on the calculated prop pitch speed.  That draggy four banger prop disk must unload considerably once airborne.
First impressions:  What a bargain!  Laser tracking.  Faster roll rate than expected.  Faster passes than I expected.  Sensitive elevator needs to be detuned.   4-blade pull is very strong, and it sounds terrific and realistic from the ground.  Flaps were perfectly symmetrical and very helpful, a first in my RC experience.  Stage presence is unreal for the money.
Takeoff - 1:35  Feeding copious down elevator trim.  The Aurora 9's trim resolution is so fine, it probably took 25 clicks to level out
1:40 First full throttle pass followed by a second
2:32 Low alt loop - the plane's handling was definitely confidence inspiring
2:51 Looking for railroad cars to strafe, the plane looks fantastic rushing by
3:20 Max roll demo.  125% aileron travel.  One hole from maximum travel on both the servo arm and the aileron horns
4:50 Beginning of flap extension testing
6:06  Half flaps down
6:18  Full flaps down
6:22 Right main gear twists
Next flight: 5S.
My second flight couldn't have gone worse.  Winds were dead calm all morning and forecast variable at 2-3 mph all day.  As soon as the wheels lifted off, winds started to gust, then quickly jumped to 10G15 mph.  By the time I landed winds were 20G30 mph in a quartering crosswind.  This was strong and gusty wind for 1:1 scale flight.  As you can see, the 6.5 lb Mustang was battered in the wind, especially on final, but there isn't another plane in my stable that could have survived even half this whipping wind storm.
This flight was on a 5S 3300 mAh 30C battery, which I slid forward thinking this battery is 1.9 oz lighter than my last flight on a 4S 4000.  The new CG measured slightly farther forward than my first flight.  I didn't retrim, thinking the CG move was not substantial and I was probably trimmed a bit nose-up for the last landing.  Immediately upon take off, the plane had a strong desire to dive, but I'm glad I had a more forward CG for this flight.
Fortunately, I was still able to perform my standard durability test, where I set up for landing then a 25 mph crosswind gust grabs the plane like it's a one oz micro and hurls it directly into a 3" diameter tree branch--whack!!  On one of my many attempts to get the plane down in one piece, the plane cartwheels hard right yaw after banging into a 50' tree, almost stopping it midair.  The Mustang's uncanny slow speed control allows me to power right out of the tree with little further drama.  No serious damage, partly thanks to crash proofing my leading edges.  Holy *^&$%!!
Extent of the damage from a 50' tree strike
I've posted some horrible flights, but this one has to be the worst.  I'd prefer to delete it, but what else could show the amazingly forgiving flight characteristics, slow speed control, and wind resistance of this sensational P-51D Mustang.  It is gut wrenching that some terribly made, poor flying toy planes are selling at the same price or more.  What a sad reflection on the clueless state of the broader RC market.
Takeoff   Calm wind
0:36 Too much left over down trim for new CG
2:40 Decent 5S pass in buffeting wind
4:40 Hands off inverted, nice CG
6:20 Tree strike nearly stops the plane midair
Landing 20G30 mph wind.  Gawd! 
While the eventual touchdown in the video above wasn't that crazy, it revealed a weakness in the Starmax tail wheel's pull-pull system.  The supplied string is plenty strong, but it apparently stretched under load.  This introduced some play into tail wheel steering.  Note, the pullrod distance decreases by a couple of inches as the tail wheel retracts.  I decided to try copper strand wire as my fix.  It seems a lot more solid:
Wires taught = tail wheel down
After a two relatively minor fixes, one to the tail wheel pull/pull cables and a second to main retracts, the BBD flies and taxis as good as it looks.
The sound of the big motor through high speed passes on 5S is a treat for the senses, in additiona to being one of the best looking and flying P-51Ds on the market, it is also the best sounding electric Mustang that I've heard:
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