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Sunday, January 29, 2012

Dynam A-10 EDF RTF - Flight Review

I picked up this cool 42" Dynam 72 MHz Hog for less than $120, a few bucks cheaper than the PnP version.  Nothing my 2.4 GHz Rx spares drawer can't fix in 15 seconds or less.

Some of these photos look flat, but the finish is a moderate gloss.  It is depicted most accurately in the first shot:
Hmmm... no packing material.  The tail surfaces 
in the smaller boxes are also free floating.
The 72Mhz transmitter carries negative value.  Yay!
Dynam provided a high level of completion out of the box, the
model is sold as an RTF.  The paint could be a bit less mottled,
in places, but overall the finish looks very good for the price.
Paint chip from sliding around during shipping.
Minor crash damage in the box due to no packing material.
The business end looks good. 


At $119 for a 42.5" wingspan, twin 64mm (including a nice 72 MHz Tx and Rx), this jet seems well priced relative to competition.  Banana Hobby sells a 1 inch smaller twin 64mm A-10 for $165 including retracts and a right-size 2500 mAh 3S battery.  In more mainstream models, the old Parkzone Habu 15 size foam EDF jet with a single 69mm fan used to have a street price around $240 as a PnP. 

The electronics kit includes two 40A ESCs, pre-soldered to work as a unit from a single battery.  Both ESCs provide power to your choice of Rx via a custom reverse-Y connector, doubling your BEC Amps and presumably reliability.  The ailerons are each powered by individual servos and come attached to the receiver through a Y-connector by default.  The elevator push rod has to be attached to a pre-installed servo in the tail, same with the nosewheel steering to a pre-installed rudder servo.  There is no rudder control surface attached to the rudder servo, leaving room for improvement.

The fans were well balanced from the factory, so nothing special had to be done to get the jet in the air.  Thrust to weight ratio is high for an EDF jet, barely above 1:1 with the included 3S 2200 mAh 20C, but the smallish battery gets very hot supplying both of the fans at full stroke.  Flights with a 3000 mAh 40C resulted in a noticeably faster higher top end speed and a cool battery bay after landing.

I did my usual foam improvement mods to the jet before taxing out.  

The only non-standard mod I recommend is to open up some battery bay cooling airflow, especially when running the over-taxed included battery.  It might be smart to embed a carbon fiber main spar into the strong but very flexible wing.  The aft half of the fuselage seems like it could be a weak point, the foam fuse thins where the motors attach, so I used Gorilla Glue to glue the entire plane up even where only screws were specified.   No worries, this way.

Another possible mod is to mix differential thrust for rudder.  But that would require more prep time that I wanted to spend on a calm wind day.

One required tweak is to bend each landing gear outward about 10 degrees like a tripod, otherwise the plane is uncontrollable on the ground due to each flexing in different directions as speed builds.  

In the air:

Once the gear was pre-stressed, the jet had no problem jumping into the air after a shorter than usual EDF take off roll.  It's a little bit odd using the rudder stick for NWS only, I need to subtract a few points for that.  With the addition of larger wheels, the high engines would make this an ideal Forward Operating Base RC airplane, just like the real thing.

The jet climbed out strong and trimmed up quickly.  Once in trim, the A-10 makes for a simple hands-off flyer and a surprisingly capable glider.    CG tests were spot-on with the battery velco'd about an inch back from full forward position, leaving plenty of room for larger batteries positioned more aft.  Nice.

Even without a rudder, the jet was very controllable and quite maneuverable.  The small elevator surface made me wonder on the ground, but it became immediately apparent that the elevator is very effective in this jet.  It might be picking up a little thrust vectoring.  Aileron rolls were quick and positive at 125% throw.

The jet slows down nicely, and the straight wing stall characteristic are benign for a jet.  On the other end of the thrust curve, the plane is suprisingly fast for its somewhat stubby profile, once a larger 40C battery is under the cockpit.  It looks great in the air.

All in all, this A-10 would make a great first jet, while supplying plenty of fun for any skill level.  EDFs aren't as responsive as props, so although this airframe is docile and stable enough to serve as an great aileron trainer, the thrust curve is a little too flat to pull (push) beginners out of corners.  Additionally, the lack of an aerodynamic rudder can get a little tricky on take off, plus complicates and delays spin recovery.

Great price, great fun.  Time for grades:

Appearance: B-
Great presence.  Minor paint pitting. Two shipping dings.  Dainty gear.

Airframe:  B+
Maneuverable when pushed, otherwise trainer-like.  No aerodynamic rudder.

Power System: A-
Great push.  Good speed.  Fans aren't super responsive.   Stressed stock battery.

Build Quality/Durability:
B
Nice EPO foam with some flex, needs carbon.  Big battery bay and positive hatch. 

Value:  A
Low price makes up for a few finishing flaws and dainty landing gear.

Overall Grade:
B+
Flight characteristics and value help overlook imperfect finish & weak battery.


Friday, January 27, 2012

Z8RC UMX Beast 3DS

Powered by a custom 3-cell battery instead of the stock 2-cell, this Z8RC mod gives this old bird a much needed kick in the pants. 

The Model 12 Pitts goes vertical like never before.  CG is slightly improved with the larger battery pushed all the way back; the plane glides nose up and stable.

Measured installed thrust is up 50% to 5.4 oz
No modifications to the existing UMX Beast 3D are necessary.  
The mini bipe is 3-cell ready right out of the box.
It takes three Zippy 2S batteries to make two 3S batteries, but the cost still demolishes E-Flight's overpriced and under performing offerings, at about $2.85 per 3S 180 mAh battery.  Weight is the same as E-Flight's 200 mAh 2S.

Back Left: A single unwrapped cell before re-wiring.
Back Right: Normal 2-Cell before unwrapping.
Front: Fabricated 3S Battery.
Fabricating two 180 mAh 3S batteries from three Zippy 2S 
batteries took about 30 minutes. It is a simple matter of wiring 
the cells in series, then adding a 3-cell balance connector 
to tap the progressive voltage increase at each wire node.

The plane hauls noticeably more mail on 3S Meth, but the draggy airframe keeps it from getting darty.  The plane benefits most from the dramatically improved static pull.

Flight time was a little disappointing from a 180 mAh 3S at 3:40, but there was a whole lot of vertical packed into that flight.  The cells were well balanced.

Unfortunately, my HD video was set to macro focus.  I'll post a video next time.

See also:  http://z8rc.blogspot.com/2011/12/umx-beast-3d-flight-review.html

Thursday, January 26, 2012

Blade mCP X Tail Blow Out - 100% Fix

Update 2:  The wind was blowing hard but I managed to get enough flying in to repeatedly juice the tail under full power.  The P-51 motor absorbs everything the engine room can dish out, which isn't  exactly explosive power.  Still, my Blade 400's tail fades a little more than the Z8RC mCP X at full bog.  

A Z8RC boom truss is a critical piece of the puzzle.  I banged one end of the truss lose on a hard landing/crash and didn't notice it disconnected until the heli got airborne.  The AS3X-amplified boom resonance was even worse than stock with more rotor power and end mass.

It is a shame E-flite decided to go the rip off route and package a known defective tail motor with the mCP X.  Now that it is common knowledge, it is even more of a shame they refuse to recall and fix their bad helicopters or refund everyone to date.  A 3 cents wholesale more expensive motor from China shows what the electronics can actually do.  

The electric tail is still a bit of a bumble bee as the motor spool up time falls short of belt-driven response, but fixing the manufacturer's defective base design with a larger motor and superior boom design makes this helicopter shine.


-----

Update:  The UM P-51 motor is even stronger and a slightly easier mod.   Same idea, mod the entire gearbox to slide onto the tail section.  It feels heavier with the extended boom which is probably no longer necessary, but it flies great!  The heli is as about as stable in yaw as my Blade 400.

This is a simple mod that involves a little Dremel'ing of the motor casing and soldering two tail rotor wires.  Takes about 10 minutes start-to-finish.  

Again, the hardest thing is squeezing the tail rotor on the slightly larger diameter shaft; a vice, some padding on the back side of the motor housing and on the prop hub, and a little patience works fine.
The green notch is actually in the other side of my modded
motor case flange, but you get the idea.  Crush the brass 
motor pinion with a vice to remove it.
Original article follows:

See also: http://z8rc.blogspot.com/2012/01/fixing-blade-mcp-x.html

Those trying to flip an mCP X know that the stock tail motor is too weak.  The helicopter loses most of its tail authority during high torque maneuvers and motor punches, spinning uncontrollably until the torque lets up or the ground helps stabilize the tail boom.

So the Z8RC fix is on.

The Flyzone UM Fokker Dr.1 motor is slightly larger than the diminutive mCX main motor included in the mCP X tail boom, so it seemed like a perfect upgrade. Replacement mCP X tail booms with an integral motor run $13, so mod risk is low.
The Flyzone Dr.1 motor is a pretty good fit.  The mCP X 
boom needs to be stepped thinner into a tongue that 
wedges between the motor and its plastic casing.  The 
casing was cleaned up but not structurally altered. 
I left the Fokker motor in its original gear box casing and removed the reduction gear and airplane shaft.  After a few Dremel mods, the case fit like butter over the mCP X motor mount after the stock motor was sliced off at the base of the motor case.  The weight difference is negligible.
Result:  100% blow out fix.

The tail is so solid with the larger motor that when combined with the Z8RC truss mod the mCP X rivals or exceeds my Blade 400 in directional stability.  It is unbelievable how steady the tail can be made during full power punches once the mCP X tail boom is completely redesigned.

The most difficult part of this mod is carefully squeezing the tail rotor blades onto a slightly larger diameter motor shaft.  You have to use wide pliers or a vice that squeezes both ends, the motor backing and rotor blade center hub, at the same time or the shaft will push off the plastic back of the motor casing under the required force (fixable :).

Foam Improvement

When all roads lead to foam, crash-proofing foam planes before entropy sets in is key.  Although I've never crashed a foam plane, I can only imagine how these tips might help:

 #1.  Don't pay too much

The first key to realizing the value of foam is not to pay too much for a foam plane.  While it is tempting to buy the colorful marketing on the box, remember that the plane won't look like the picture after a month or two of hard use.  If you can picture the plane worn, scuffed and patched up, and you still think it is a good deal, that's the right price for a foamie.


#2.  Get the good foam

Not all foam is created equal.  EPO foam is much stronger than EPP beer cooler or packaging foam, and it can be more effectively painted.  EPO foam is specific to steam molded model airplanes, AFAIK there is no other use for this particular cocktail of chemical reactions but permanently contaminating the Chinese mainland:


There are a variety of other types of RC airplane foam.

#3.  Price required upgrades into the deal up front

Some foam planes are so inexpensive that upgrades make sense right off the bat.  Cartwheeling a plane because the stock retracts are junk might cost more than $20 for a good set of servo-less retracts that are more fun to use.  Good motors are cheap and can make all the difference when flying a model.  A more appropriate battery or prop can make a big difference.

An RTF or ARF that bundles components that won't fly well or break quickly has an phantom price tag.

#4 Crash proof before flying

Non-negotiable lifesavers on foamies heavier than 10 oz:
  • Glossy clear mailing tape along the main wing(s) leading edges 
  • Glossy Scotch tape control surface hinges
  • Glossy Scotch tape leading edges of horizontal/vertical stabilizers
  • Add under-wing tip skids, e.g.:
    • Slice-in small thin sheet CF slats, parallel to tips
    • Slice-in small metal washers
    • Strip of glossy mailing tape
    • CA flat nylon zip tie
    • Add thin aluminum sheet or soda can material, cut to shape and attached using outdoor double-sided mounting tape
  • Add thin carbon fiber spars to fix structural vulnerabilities or  excessive aerodynamic flex
  • Add thin foam weather stripping along wing attach points to take up play 
  • Check/Secure cheapo plastic clevises or replace before flying
  • Check/Secure check all servos
  • Check/Secure any surface-glued control horns
  • Check/Secure the firewall and motor mounting points
Negotiable:
  • Add carbon fiber tail and wing wires to fly more squarely
  • Light acrylic gloss or dull spray coat to help seal painted, or especially unpainted foam
  • Glossy clear mailing tape to preserve common handling points
  • Add wider nylon or metal washers under all screw heads and wing attach bolts
  • "Glass" the inside of the plastic cowling and pants with smeared-thin Gorilla Glue
  • Add air vents to keep motor, ESC, and battery cool (exit area = 2x entry)
  • If motor is tightly insulated, add aluminum prop adapter and aluminum spinner as heatsinks
  • Glue entire plane as a single piece to avoid future play and to minimize flex
I say "glossy" tapes because the dull or magic/invisible clear tapes never seem to adhere well to EPO.


#5 Consider buying the airframe only

This can be a good build strategy to keep costs low and component quality high.

#6 Consider buying critical extra parts

Sometimes more expensive is cheaper.  Aside from discontinuation insurance, this can guard against isolated shipping charges for stuff easily worn out or damaged - battery hatch, canopy, landing gear, etc.    It is always a good practice to check if the store stocks spare parts for any plane.

Tuesday, January 24, 2012

Z8RC UM 3-Stryker vs. Carbon Z Scimitar

Can Z8RC's mad scientists double the speed of the Carbon Z Scimitar with a UM Stryker 180 hopped up on a 3S crack adrenalin rush?
Results coming soon!

Saturday, January 21, 2012

Sky Angel MiG-15 Build and Flight Review

UPDATE 5:  Added landing gear with a steerable nose.  See Z8RC Mods, below.

UPDATE 4:  Added a rudder and thrust vectoring.  See Z8RC Mods, below.

UPDATE 3:  Uploaded the HD version of the maiden video, linked below.

UPDATE 2:  Flight grading complete.

UPDATE 1:  While the wind blows, I added a segment on fan balancing.

I couldn't think of a reason not to buy this cool $64 Sky Angel MiG-15, so here it is!  According to their website, Sky Angel is part of J-Power Group maker of the Z8RC favorite foam parkflier warbird, the P-38 Lightning featured in the sidebar.

I was going to do a build thread followed by a flight review, but the plane was finished before I knew it.  Great job Sky Angel!  The level of ARF subsystem completion actually make it "almost ready" to go.  Refreshing.
I like that the nose is not painted, it is 
wrapped in a form-fit red plastic ring.

- Wingspan: 25.6 in
- Length: 25.6 in
- Wing Aea: 171 sq in
- Wing Loading: 10.8 oz/sqft
- Wing Cube Loading: 9.9
- Flying Weight: 12.4 oz w/800 mAh 3S
- 50 mm Ducted Fan w/Brushless Outrunner
- 20 Amp Brushless Speed Control
    The EPO airframe ships in six large foam pieces, but all the electronics are factory installed. Required assembly consists of gluing the foam building blocks together, running two push rods through pre-installed tubing, then tightening down two elevator control arm adjustment screws.  If you subtract think time, it's a 5 minute build with a few shots of CA accelerator.
    The cockpit doubles as a battery hatch.  It is solid 
    and looks great. The magnets needed a bit of depth 
    adjustment for maximum click.  I changed the ESC battery 
    connector to match my 800 mAh 3S battery collection.
    I only tweaked the jet with two, minor airframe mods:

    First, the mini MiG has a traditional flat-bottom airfoil cross-section.   Like a trainer, the wing should generate  a lot of lift, but also sharp stall behavior once Critical Angle of Attack is exceeded.  I dialed-in about an 1/8th inch of permanent spoileron (up aileron x 2) to keep stall development as wings-level and gradual as possible, by forcing the wing root section to reach Critical AOA sightly before the wing tips.
    A little cranked-in spoileron approximates washout.  
    Both push rods are for elevator.  There is no rudder control 
    as shipped.  The jet has independent aileron servos which 
    add some yaw control options given a computer radio.
    Next I added three carbon fiber landing skids from a thin woven sheet of amazingly light and tough carbon fiber, shown in the pic below.  The aerodynamic effect of the skids should roughly cancel each other, as there is as much nose skid area in front of the Center of Lift (roughly the weighted geometric centroid of the lifting surfaces) as the two wing skids behind it.
    Although there is plenty of power to push the plane on the skids, the jet has no rudder channel so its probably still best to hand-launch.  At least landing on pavement is an option.

    Speaking of the lack of rudder, I decided to partially simulate rudder by making the rudder stick lift a single aileron on the inside of the desired turn direction.  Should be simple, right?  Wrong!  Unfortunately, I used an old $8 OrangeRx receiver as a suitable match for the low price of this MiG, and that decision forced me onto a Spectrum radio standard.

    Spektrum's crude way of issuing control commands made the required mix difficult to implement and near impossible to conceptualize, because Spectrum mixes "flight control" channels, not simple servo channels, this often generates major logic problems.  This desired mix is but one problematic example: with a dual aileron setup, the flap channel always moves both aileron servos in the same direction so it's impossible to control only the servo plugged into the selected flap channel. 

    A proper radio standard logically controls each servo as a discrete, unlabeled channel which keep mixes pure, simple, and powerful.  This fundamental Spektrum design flaw causes endless empirical trial and error gyrations to find the just right anti-kludge to counter the baked-in faulty logic.  Just awful!

    After about an hour of thinking it through, combined with a methodical process of isolating variables and empirically determining input effects, I finally stumbled upon an effective anti-kludge.  It makes no apparent sense, but it works (almost):

    WINGTYPE: Dual Aileron
    MIX 1:  Rudder > Aileron ACT L +100% , R +100%
    MIX 2: Rudder > Flap ACT D +100% , U -100%

    Miraculously, this enables the aileron stick to work as pure aileron control while the rudder stick lifts only the inside aileron while leaving the other motionless, presumably to induce some yaw.  It also mixes the two concepts when the sticks are used together.  Interestingly, when ever the two sticks are moved opposite one another with the same deflection, you always get pure spoilerons (both ailerons up) of the degree of stick deflection, regardless of which direction the sticks are deflected.

    Unfortunately, because Spectrum's flight control logic is fundamentally flawed, this complex kludge makes rudder trim impossible so it must be deactivated.  Because the rudder is mixed to the "flap channel" instead of to a servo-as-a-channel concept, the rudder trim rocker always moves both ailerons in the same direction.  This is poor control logic, nothing more than inferior intellect permanently embedded in the DSM-X standard. Uhg.

    A proper radio, like my Hitec Aurora 9, simply requires mixing left rudder to +100% of Servo 1 (= the left aileron servo) and another mix to map right rudder to +100% of Servo 5 (= the right aileron servo).  How friggin hard is that?

    The MiG's power is good for a basic ducted fan model with a measured Thrust:Weight ratio of [9.5 oz / 12.4 oz], or about 0.77 running on a fresh 800 mAh 20C 3S.

    When completed with a battery laid into the bay, the MiG-15 balanced exactly at the 95mm point from the root leading edge, as outlined in the decent instructions.  The spot is coincident with the rear edge of the painted black wing walkways.  Nice.

    Overall, I'm very impressed with the quality of this simple and tough EPO foam model.  Even with a battery installed it feels light when handled, which is usually a good sign.  It is such a quick and easy build, it makes you wonder why it even costs $64.  In my view, that is goodness.

    I hope the flights go as well as well as the ground assembly!

    -----

    Since the winds are out of limits for the time being, and Sky Angel bought me some time with their high level of completion, I decided to do a few upgrades that I sometimes don't have time to do or forget to do.
    Over time, I've found these upgrades well worth the time, some are obviously just for foamies:
    1. Taped the wing leading edge with clear glossy mailing tape for wing strength and foam protection.  The MiG's top side wing fences and leading edge antennas required a trim-around.  There is no problem a new xacto blade can't solve.
    2. Taped the bottom center fuse, gun, and wing tanks in front of the skids.
    3. Taped the square fuse panel under the rear canopy to preserve the finish while popping open the canopy at the magnet. 
    4. Taped the wings roots inside the first wing fence for a place to grab the plane.
    5. Embedded two plastic servo arms in the vertical stabilizer to serve as push rod wire guides.  The push rods are thin and bow under pressure.  This should help lock elevator response to stick position.  After cutting each servo arm and installing it separately, I realized I could have embedded the entire uncut servo arm through the rudder and it would have been stronger.
    6. (Not shown) Embedded two carbon fiber reinforcing rods in each side, where the wing tank mates to the wing.
    7. (Not shown) Embedded a carbon fiber rod down the barrel of the gun.
    8. (Not shown) Cut a thin air duct running from the front of the battery bay down into the nose intake, to get some cool air around the battery and ESC.  The back of the bay is already vented down to the motor.
    9. Balanced the fan.
     
    Perfect fan (or prop) balancing:

    A fan is as easy to balance as a prop, and this one needed it badly producing a loud harsh vibration at full throttle.  All you need is a set of drill bits, a vice that can open a few inches, and two strong magnets capable of suspending the drill bit between them.  Any magnetic prop balancer can also work, but most are too big for a small fan, so you'll need to adjust the distance between the magnets to accommodate the length of a small drill bit. 

    Removing this fan is simple. Stand the jet on its tail to avoid losing the washers between the fan and the motor.  Remove the bottom access panel.  Hold the fan still with an index finger while rotating the rear motor bell counter clockwise (looking into the jet exhaust tube).  The fan will unscrew forward then fall off without applying any force.  Make sure the washers stay on the shaft behind it.  I had to trim away a small bit of foam to get the bullet nose of the fan through the access panel.  The other option is to let it fall out the nose intake, but there are washers still on the motor shaft and I didn't want the fan to get stuck.

    With the fan free, insert the right size drill bit as a substitute motor shaft.  It needs to be a sharp drill bit and a snug shaft fit (shrink tubing can be your friend).

    Suspend the fan on the drill bit between two magnets stuck to the jaws of the vice.  Open the vice wide, so the drill bit is barely suspended in the magnetic field.  Place the drill bit so the sharp end is the one touching its magnet.  Slowly close the vice.  The fatter metal on the flat end of the drill bit will become more attractive to its magnet as the vice closes, eventually the flat end of the drill bit will pop over to its magnet.  Back the vice open a little, and put the sharp end of the drill bit back on its magnet.  You want the vice open just the right amount so the sharp end of the drill bit barely dances on it's magnet, at that point you'll get a virtually friction-free fan balance.

    Apply bits of tape or dots of glue inside the hub of the fan to balance it, until a light nudge spins it for a long time without wobbling.  Don't mess with the fan blades.   Now you'll have a smooth running fan as long as the motor bell is balanced, and most are.

    Good thing the wind is blowing, I probably should have done all this before flying anyway!

    In the Air:

    Finally today dawned with a beautiful calm morning, I definitely need more of those.  I don't even know where to start with this MiG, what fun.  Fun like a wooden rollercaoster is fun, because you aren't quite sure if it is going to fly off the tracks.  This was, without a doubt, my craziest maiden flight ever.

    The adrenalin rush was mostly my fault.  I dialed in some spoileron to keep the MiG from tip stalling.  That was a good thing.  To my credit, I even pre-positioned 5 down-elevator clicks from what looked like neutral.  That was, of course, assuming the balance was good.  I used a 1000 mAh battery, thinking it'd be a little nose heavy and all good.

    Bzzzzt.  Not so much.  To my discredit, I heaved this baby with way too many variables dialed in and out and up and down. The net result was a strong tendency to climb, coupled with decent right roll..  That's no big deal (well, it is a bigger deal with a ducted fan that isn't as responsive as a prop), the real problem was that it ate all of my DX6i's down elevator trim without so much as a burp.  Now what?

    After managing to get some altitude (pretty easy with too much up elevator), I decided it would be better to try to sub-trim down with the airplane up high, than to try to land holding the nose-down with the airplane down low.   So I clicked my DX6i over to the subtrim page.

    I didn't remember if I reversed the elevator servo or not, so I wasn't sure which way to trim.  I tried trimming in the arrow down direction first.  Oops, that just popped the nose way up and the MiG entered a fast spin (2:40 mark).  I threw all the power, down elevator and outside spoiler that I could muster at it, and the plane recovered without a rudder.  Whew!

    Now holding the stick even farther forward, I realized the flaw in the DX6i's right-side roller, making it very hard to fly and modify settings.  The DX8 fixed the problem by making a lot of the menus inaccessible unless you turn the radio off, so you have no choice but to crash right away.  With some thumb switching while doing the lobster eye, I slowly beat back the wrong radio design and reversed the sub-trim, and then...  .....ahhhhhhhhhhhhhhhhhhhhhhhhhhhhhhh...

    Hey, I thought, this thing really flies great, it's me that sux!

    The MiG definitely flies like a 1st gen jet fighter, and I love RC planes that fly like the airplane they attempt to model.  What fun!  The nose track is soft and the usable pitch range is expansive, just as one would expect.  That enables a broad airspeed envelope.

    At high speeds that plane is totally under control and the flight control response feels well tailored.  The scale size of the small surfaces prefer airflow.  High speed passes are point and shoot, and the and the small elevator allows a lot of trim resolution (a place the DX6i normally falls short).  The swept wings are stable in a scream.  The small ailerons keep a lid on over-controlling the delta on the longitudinal axis.  

    Like all early-gen MiGs, this airplane also makes a surprisingly capable low speed adversary.  The plane demands careful attention at slow speeds, both the pitch and the roll axis become mushy.  But there is plenty of room to slow down while ratcheting the nose higher and higher, as long as you project your flight path far enough forward and so you can limit the big changes to pitch.

    I didn't want to flirt too deep into the stall on the maiden and spin the jet, but I managed a few low and slow passes before the battery gave out.  On one or two occasions I felt a few light, pre-stall pitch oscillations.  The plane stayed well composed and seemed to porpoise mildly on the pitch axis only.   Promising.

    The built-in flight timer surprised me, not because of the number of minutes coaxed out of the 1000mAh as revealed by the video counter, but because the first 3.5 minutes of my airborne buffoonery must have passed like 30 seconds.

    Zzzzzz z z z zzz z zz     z z z      z     z       zt.   No motor.  No good runway options.  The MiG-15 glided like a champ and set down softly in the grass.  +1 for the Soviets.


    All things considered, this jet might be the most fun I've had RC'ing for under $70 (OrangeRx included).  No, it definitely is. 

    As much fun as this MiG is, I might alter  a few things.  One, landing gear would be useful, imagine that.  The tin can w/motor design isn't the best hand-launcher, but now that it is trimmed up it might be easier. I'm going to look at some gear options.  Two, my simulated-rudder mix worked great.  It effectively provided a way to trim out yaw and might have saved the jet from the spin.  But if I add landing gear, I'll probably need a rudder for nosewheel steering too.

    Updates to follow.  Or... maybe... this was so much fun it's already time for the bigger Sky Angel MiG-15?  Either way, more to come...

    Z8RC Mods:

    Landing Gear with a Steerable Nose 

    After learning that hand launching is better way to test the durability of Sky Angel's EPO foam (outstanding) than to get airborne, I decided it was time to add landing gear.

    What could be easier than drilling a 5/16" hole in the bottom of the nose to insert a Parkzone Bf-109 steerable tailwheel?  Running a pushrod from the rudder servo (see mod below) through a hole in the cockpit to the tail (nose) wheel's reversible control arm was a piece of cake.  The curvature of the fuselage perfectly matches the curvature of the mounting plate.  The steering works perfectly.
     
    Maybe I'll add some gear doors?
    The mains were almost as easy - 0.25" aluminum tubing with a hole drilled in the bottom to accept a screw to act as an axle.  I drilled a hole halfway into the foam wing to accept the aluminum strut and covered with a square of balsa with a matching hole.  Gorilla Glued it all in place.   I poked a few holes in different directions into the foam so the glue has place to expand and form roots.
    Maybe I'll add some gear doors to finish it off.

    Rudder Mod with thrust Vectoring

    This was an easier mod than I expected.  Installing a rudder is as simple as sliding a second servo into the empty holder next to the elevator servo, then threading a piano wire push rod through the existing hole for the motor wires into the exhaust tube.  I sliced the foam rudder off on the scale lines, in two parts above and below the elevator, then ran a carbon fiber rod along that same line to act as a hinge.  I continued the CF hinge rod all the way down through the exhaust tube and anchored it in the bottom of the aircraft.  That made it easy to add a control horn inside the jet exhaust.  I also added a thin carbon fiber flap to the hinge rod, at the back of the jet exhaust for thrust vectoring.  Incorporating thrust vectoring in a jet is a good thing since there is no prop to blow the tail surfaces (= thrust vectoring).  Pix and flight test to follow when the touch up paint dries.
    A carbon fiber rod forms the new rudder hinge. 
    The control horn is inside the exhaust tube, as 
    is a carbon fiber deflector for thrust vectoring.

    Z8RC Grades for the Sky Angel MiG-15:


    Appearance: A+
    A big red star on a smoking tin can.  Awesome.

    Airframe:  B
    Wide flight envelope. Built for speed.  No rudder or gear.

    Power System: C-
    Decent power.  Fans aren't responsive.  Needed a balance.  Loud. 

    Build Quality/Durability:
    A+
    Super tough EPO foam!  Smooth finish.  Nice canopy/hatch.

    Value:  A+
    Jet around in style on any budget.

    Overall Grade:
    A
    Looks fab.  Flies fab.  Tough to get airborne.  Huge fun for the money.

    Friday, January 20, 2012

    Fixing the Flyzone Fokker Dr.1 Micro

    Update:  Shortening the front 2 of 4 landing gear struts by slicing off the existing anchors, making them shorter by an 1/8th inch when reinserted and thereby increasing the Angle of Attack of the fourth wing, fixed the plane's tendency to tuck-under (unwanted, increasing nose down).  It also allows the plane to fly a smidge slower.

    Also see: http://z8rc.blogspot.com/2011/12/flyzone-fokker-dr1-micro-ep-rtf-flight.html

    It is a shame to lose the cool factor of the Flyzone Dr.1 because of Hobbico/Flyzone's crappy micro gearboxes, so I had to fix the Triplane.  The Z8RC brushless Parkzone Corsair conversion was so quick and easy, I decided to transfer an old Hobbyzone Champ's internals into the Fokker.  This project wasn't quite as easy, but only because I had to figure it out as I went along.
    If you follow this tutorial, it should take about an hour for a full Flyzone Dr.1 to Spektrum DSM conversion, perhaps as little as 30 minutes for a motor and gearbox only conversion.  Both are easy.

    Since I had the plane open, I opted to do a full conversion so I could lose the additional transmitter when I fly the Triplane.  Plus, a full conversion allows computer control.

    There is another possible fix, but I haven't confirmed it. On Tower's site it shows the Flyzone Playmate replacement motor with a metal pinion.  This motor should fit.  It seems like it would be a pretty similar level of effort to the gearbox-only change-out, as far as opening the airplane and cutting out the gearbox (I don't think you could change the motor without pulling the gearbox but it might be possible).  But it wouldn't power up the plane any more or allow the use of a better radio.

    I was tempted to add ailerons, that would be an easy mod, but the Dr.1 airframe is so light I decided to keep it as much of a slow flier as possible.  The final, full conversion weighs 35 grams in RTF form, a whopping 1 gram lighter than stock.    Thrust to weight ratio came in right at 1:1, a monster improvement!

    1. Remove the white cowling, it was glued in place with two dots at the bottom sides and another dot or two at the top middle.  Slice the glued spots with a sharp knife.  Take your time and it'll work loose.

    2.  Cut along the green line, below, just behind the landing gear to remove the entire motor section with the gear attached.
    The Champ motor is way bigger than Flyzone's motor.  But the biggest difference is the motor pinion is brass instead of plastic.  Flyzone's plastic motor pinion will strip within a few flights, guaranteed.  They are selling known defective products to save 0.0004 cents per copy.
    3. Glue the black dummy radial motor between the four spikes sticking out of the nylon Champ gearbox frame.  You'll need to trim a little bit of foam out of the center of the dummy radial to make it fit snuggy.  It is important for the radial to be snug and glued securely, because the back of the dummy radial will help glue the Champ gearbox to the Dr.1's firewall in the next step.
    4.  Glue the back of the dummy radial to the Dr.1's firewall.  The motor axis should be aligned with the existing shelf where the old gear box sat.  You'll need to trim away some of the foam underneath the original gearbox to make room for the larger motor.  You'll also need to trim a bit off the two highest cylinders since the dummy radial will be a touch lower inside the white cowling.

    The back edge of the nylon frame of the new gearbox should be aligned with the front face of the Dr.1 firewall to make sure the motor shaft sticks out far enough to clear the Champ prop.
    5.  If you are doing a motor-only conversion, solder the two pins of the Champ motor's male connector to the male connector of the Flyzone's motherboard's motor connection (shown in the picture below Step 2, above).  Keep the red wires in the same orientation to make sure the motor spins the right direction, it won't hurt the motor if you get the polarity wrong, but you'll have to do it again.  Wrap the connections with a small piece of electrical tape.  Button up and you are done!

    6.  If you are doing a full conversion as shown above, cut the foam below the Flyzone servo motherboard to remove it.  Insert the Champ's all-in-one motherboard in the nose.  I moved it back a little to help with the CG.  It needs to be oriented just like it sits in the Champ, with servos on the top side of the board as it sits in the plane (with both the plane and the board sitting right side up), otherwise the rudder and elevator servos will be swapped.

    7.  With the rudder and elevator control surfaces centered, bend a 90 degree angle in the control rods and insert them into the Champ servos.

    8. Plug in the motor.

    Button up and you are done!

    E-Flite Ascent BL 450 PNP - Fight Review

    UPDATE:   After pretty light use, the E-Flite 370 in the Ascent failed without warning between two flights.  It landed fine, only to never run again.  Seems like a simple quality failure, attaching another motor to the plane works fine.  My Ascent only weighs 14 oz with a 7x3 folding prop drawing 8.5A flat out, well within the motor's limits.  E-Flite 370 moved to AVOID.

    UPDATE:  Avoid the Ascent until you read: http://z8rc.blogspot.com/2011/12/fixing-e-flite-ascent-450-bl.html

    UPDATE:  With little effort, I have been able to substantially improve the Ascent.  I substituted an E-Flite 370 motor and a lightweight 18A ESC (make sure any substitute ESC can brake (not break) the prop).  I removed the plastic casing of my Optima 6 and wrapped it for 6L like mass.  The Ascent's new base weight is 13.9 oz.  The new thrust-to-weight ratio with a 1000 mAh 3S and 10" Radian folding prop is a somewhat astonishing and improved 1.2 to 1.  

    I crammed everything as far forward as possible to keep CG under control, and with a 1000 mAh 3S it looks pretty good at just behind the main wing spar, but hasn't been flight tested due to 20G40 mph winds!

    Soaring weight and WCL is down 14% and T:W is up. I'm hoping for about double the flight time per mAh, due to the improved ratio of [power off:power on] and much improved performance of both.  

    As they say in aviation, the rich get richer.  As it turns out I could have gone lighter still on the power system to get T:W under control, but might have had to slide the wing aft (easy adjustment - drill two new holes).  Using a 2S battery could be another easy adjustment.  

    All that said, I think the 370 was a sensible choice if for no other reason than it is a simple drop-in replacement.  It takes about 5 mins to install, only because you have to tap-out the shaft and reverse it.

    -----

    UPDATE:  Substituting a slightly modified 10" Radian folding prop gets the Amp draw down to 12.58 at full throttle, allowing a smaller battery and saving weight.  Since a 1300 mAh battery lasted 30-40 mins, I'm going to try an 800 mAh in the hopes of getting significantly longer flight times.  Going 2S saves another 5%.  Lightening the longer sail portion should be worth a lot more flight time than losing unused power on the margin.  

    Battery options and weight, pending flight testing:   
     
    Battery
    Ascent oz
    Batt oz
    Soaring oz
    Batt % Base
    Turnigy 1300 mAh 3S
    15.3
    4.1
    19.4
    26.8%
    E-Flite 1250 mAh 3S
    15.3
    4.3
    19.6
    28.1%
    E-Flite 1000 mAh 3S
    15.3
    2.9
    18.2
    19.0%
    E-Flite 800 mAh 3S
    15.3
    2.2
    17.5
    14.4%
    E-Flite 800 mAh 2S
    15.3
    1.5
    16.8
    9.8%

    Also fixed: the 450 run very hot with the stock 11" prop.  I also added a slot for the front of the cannopy and velcro on the back, to eliminate the inconvenient and dangerous screws (mandates work inside a live prop arc).

    Every once in a while I buy a plane on a whim, then wonder if I might regret it.  I was looking for something new, and cool and most likely aerobatic.  Maybe something with a gyro or two or three, or maybe a newer, bigger helicopter that technology and the economic depression magically made more affordable.  But all I found in two excellent hobby stores was the same old tired selection of RC models fashioned by Chinese slaves working endless 24 hour shifts in overcrowded factories, knee deep in filthy festering bacteria and squaller.  If only it was less expensive, I thought...

    But then, stashed in a corner I found this handsome little Ascent, sans pricetag.  It wasn't the coolest gryro-driven mega-bat on the planet, but it had a certain uniqueness to it and it wasn't injection molded in a poison Chinese Styrofoam commune; so it might even fly decent.
    After a brief myocardial infarction caused by a sticker shock induced arterial coronary embolism at the checkout counter, I took the bugger home.  I was mildly comforted the the included 450 motor, temporarily ignoring my stash of lighter, more powerful Super Tiger .10s motors.  At least it is all put together, I thought.  It is labeled "PNP" afterall...

    Well, uhm, sort of.  The fuselage is PNP, but the wing and tail assembly are traditional ARF.  So we have a minor manufacturer integrity issue, but still, the kit isn't overly complex as far as ARFs go:
    The fiberglass fuselage is sleek and gorgeous in gloss 
    white.  I added an aluminum skid to the bottom (not shown).
    The build took about an hour, maybe a little longer.  It's what all ARFs should be--almost ready.  The finished product looks sensational from the top, but is a bit too plain from the bottom--solid white trim, minus the wing tip art shown in the first photo.
    The final product weighs 15.5 oz, with the only variable being your choice of receiver.  I was out of Hitec Optima 6 Lites, so I installed a straight Optima 6 for now.  That cost me 0.2 oz.  Still, the manual recommends an E-Flight 1250 mAh 3-cell, which weigh exactly 4.3 oz.  That makes the best case flying weight 19.6 oz.  The plane is advertised at 18-19 oz flying weight, which is only possible if you use a 1000 mAh battery or less.

    The Ascent can maintain level flight with 15% throttle set.  As sold, max flight time is in the 30-40 minute range with mixed aerobatics and pure soaring.

    With a Wing Cube Loading of 5.7, the Ascent is too heavy for a sailplane of it's size.  The problem is 100% due to E-Flite's botched choice of power system - a very disturbing, and very consistent trend - E-flite blew another one big time.  Let me be clear, E-Flite's choice of power systems are the absolute worst in the business - there is no more clueless company in popular RC design today. 

    The Ascent has way too much power, and is way too heavy as a result.  With glide trim set, bringing in half throttle stands the motor-glider on its tail, 90 degrees nose-high.  Half the reason is massive motor overkill, the other half is a very heavy motor in the nose, demanding substantial up-elevator to establish best glide.  Uhg.

    Build quality is very typical for Horizon ARFs: fair overall quality marred by an occasional potentially fatal lack of attention to detail.  On my second sortie's pre-flight control check, I noticed a near full deflection elevator that wasn't moving.  The thin ply control arm had worked it's way loose, or was possibly never glued in.  A drop of CA prevented certain catastrophic failure.

    My wing-set was warped slightly out of the box.  It took a flight to notice, because the rudder came back trimmed well deflected.  I also noticed positive right roll in a dive, or low angles attack, which generally makes aileron more effective and rudder less effective.   Twisting the left wing under a heat gun relived some factory baked-in right aileron--all fixed.  Speaking of aileron, there are none, so check the wing incidence for true, or perhaps add aileron trim tabs.

    This sailplane should really come with proper ailerons considering the nearly $200 price tag. An additional quality issue is one of my prop blades always hangs half open instead of folding back. 

    The Ascent could be sooo much more if E-flight knew what they are doing, but it is still a ton of fun!  The heavy flying weight and silly power make the sailplane a good wind penetrater.   Soaring time is shortened by the fast glide speed, but the slippery fuse and wing look great slicing through the air at high speed in total silence.  The Ascent's high speed and lack of noise look a bit uncanny in the air.  Very cool.
    First 10 minutes of a 30 minute maiden (HD camera limited).
    Overall, I didn't expect to enjoy flying this sailplane plane half as much as I do.  Those who don't mind overpaying for a nice flying ARF will want to replace/halve the power system weight and battery size, though CG might be an issue.

    Appearance: A+
    Gorgeous top view; bland bottom view.  Sexy fiberglass  fuselage.

    Airframe: A+
    Sleek.  Occasional nasty stalls aggravated by heavy weight. 

    Power System: D
    Very heavy.  Very overpowered.  Rocket-like vertical hand launches.

    Build Quality/Durability: F
    Wrinkled, warped covering.  Elevator control horn loose.  Cheap prop.

    Value:  D+
    Pricey at $190.  No ailerons.  Heavy and small scale for the wingspan.

    Overall Grade:  C- (stock), A (w/Z8RC fixes)
    Unstoppable fun with mostly easy to fix quality gaffs.
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