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Old Mar 29, 2011, 09:50 AM
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James Frolik's Avatar
Cologne, Germany
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Cessna 421 ARF from ZD-FLY

I took a gamble at the Karlsruhe Modeling Fair and bought this model: Cessna 421 ARF from ZD-FLY of Shenzhen Xingyaohua Industrial Co., Ltd. I paid too much for it, but that's not the point: I took a gamble. Good or bad?

DOES ANYONE KNOW ANYTHING ABOUT THIS PLANE'S FLYING CHARACTERISTICS?

I know nothing about it. I haven't seen any reviews nor any posts or references about it...anywhere. I rarely make a purchase like this into the unknown. But I bought it because (1) it looks cool and I admire civilian aviation models, (2) its EPP bead (or EPP grade) appears consistent with the fine quality of Hype-RC kits (Germany's Kyosho subsidiary) of which I am very familiar, (3) the design and fit of all molded parts appears quite good, and most of all (4) it has retracts; this is my first retractable gear model.

Specifications:
Wing span: 1600 mm
Length: 1377 mm
Wing area: 30.4 dm2
All-up-weight: 2400 g
Wing loading: 79 g/dm2
2 x 1100kv outrunners
2 x 30A ESCs
2 x 10x5E props
1 x 3s LiPo min. 20C
5 x 9 g servos
3 x 30 g servos (for retracts)

The wing loading is high for a foamy and I will change the 2-blade props to 3-blade 9.7" VarioPROPs, probably set at 4-inches pitch.

But I'd like to hear from anyone who has this model, seen this model fly or crash, or knows someone who has this model.

Thanks.
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Old Mar 31, 2011, 10:12 PM
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James Frolik's Avatar
Cologne, Germany
Joined Dec 1996
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Well from the limited views and zero responses, it seems I'm the first, or one of the first few, who has taken a chance with this model. So far, bad chance.

After further inspection at home, I can say is that yes, the EPP foam and model's molding is good. The motors are nicely built outrunners. It will fly.

But the landing gear is absolute garbage. It's hard to describe this clearly, but the retracts are just a dumb and weak design.

The mostly ABS plastic retract structures are soft and weaken with every up & down. A thick metal strut supporting the first third inside each plastic main strut eventually loosens and begins to swivel—not unlike the nose wheel. The plastic strut that covers this metal strut also begins to loosen and swivel. There is a set screw for each of the three struts, but tightening it is only a temporary stop for the swivel on the mains. The nose wheel's swivel will simply develop more and more play until something gives.

Each landing strut's heavy-duty servo is appropriately slow and exerts plenty of torque, but the long thick wire pushrod that reaches to each strut is simply inefficient. Each servo arm is too short to keep the wheel fully up or down. The block mechanism inside each strut's rotational core that secures it either up or down is that soft ABS plastic—and it keeps developing more slack.

The power setup should have a UBEC, but the schematic calls for both ESCs to supply the receiver (BEC) power. This is stupid. There are 8 servos and sharing thier power load between the two ESC/BECs leaves no redundancy. Both BECs could theoretically overload; should one BEC go bad, the other would immediately overload and shut down if it didn't burn out first. And you can't do much with a dead receiver. I will use a UBEC.

Otherwise, the model still looks cool. I've got 4 months to sort it out before trying to fly it. Nonetheless, regardless how it eventually flies, I would advise anyone to stay away from this model if you want to spare the landing gear trouble.
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Old Apr 01, 2011, 10:31 AM
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United States, SD, Sioux Falls
Joined May 2010
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I too have one of these (I think). I bought mine at the Arizona Electric FlyIn. Mine is marked as a CerMark kit. It looked OK at the desk, and I have not really dug into it yet (too many other projects going) but I suspect any mechanical retracts from PRC, and will usually replace them with servoless anyway..

I have a paint scheme picked out and will get to it this summer.
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Old Apr 01, 2011, 11:17 AM
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Cologne, Germany
Joined Dec 1996
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Singpilot,

Thank you for the attention. I googled Cermark Cessna 421 and came to Palos R/C Flying Club's newsletter from April 2011.

Within the newsletter is a picture of the same model I bought, and there is also a small text that reads "Mike Sula also brought his Cessna 421 by Cermark...". And yes, on the wing is the decal ZD-421. Mine has the same decal; your model is the same as mine.

But the Cermark Website currently does not have this model listed.

Here is a photo taken from the above-mentioned newsletter.
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Old Apr 02, 2011, 04:55 PM
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tigerbug's Avatar
Loveland, Oh
Joined Aug 2004
151 Posts
I'm In on the Cessna 421

I just returned from the Weak Signals show in Toledo Ohio with the same plane. Purchased from Cermark booth after lengthy discussion. I think the guy was very honest and I asked alot of questions. He flys it and loves it.
I just got home and dry fit most of the pieces so far so good.
Let's keep this thread going. I can only build on the weekends so it will take me some time.
Please share any paint schemes and more importantly what type/brand of paint that will be bright in color and hold well to the foam.
I will try to post more as I get to building the plane. He did say check all screws/bolts and add loctite. I would do anyways but he said it can be an issue if you don't.
That's all I know for now.
Tigerbug
Cincinnati Ohio
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Old Apr 02, 2011, 06:14 PM
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James Frolik's Avatar
Cologne, Germany
Joined Dec 1996
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Hey Tigerbug, thanks for joining the thread. I guess you, Singpilot and myself are a few of the earliest users of this modelóalbeit I'm on another continent. But mine will fly first in Oregon this summer vacation. (I always stock up on my stuff at the German modeling fairs and bring it stateside with me for a modeling holiday.)

I don't doubt the model flies okay. But how is the landing gear on others' model? This is part of a model that really suffers sudden stress. If the landing gear gives on a model this size, there will be damage.

I am seriously considering replacing the retract mechanism with something of better quality: HobbyKing, perhaps? (Ironic, isn't it? Better quality. HobbyKing.) The one pictured in my third post can now swivel about 120-degress; and I feel that I'm going to have to cut into the retract rotation block to see what's wearing down. It would be nice if any new gear's metal strut shaft would fit into the kit's scale-looking plastic strut.

As for paint, Multiplex has started selling a special spray paint for EPP and I intend to try someóbut it isn't cheap. As for paint schemes, I'm not sure whether to use the decals minus the registration call numbers, of create my own. Here are a few pictures I'm considering. I'm kind of leaning toward the light tan instead of white surface.
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Old Apr 04, 2011, 03:53 PM
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Loveland, Oh
Joined Aug 2004
151 Posts
Multiplex Paint for EPP

I sent Multiplex Customer Service an email asking about the paint you referred to in your last post as being especially for EPP although you said it was expensive. Here is what they sent to me:

Hello Matt,
Thank you for choosing Hitec products. We use standard over the counter Krylon spray enamel. Keep in mind that you are spraying foam, and that it is real easy to scratch and get to a new layer of foam. We do not make a foam specific spray paint for the Elapor foam.

Thank you,

Billy Tompkins
Customer Service Rep.
Hitec RCD, LLC
Multiplex USA
Phone (858) 748- 8440
Fax (858) 859-2618
12115 Paine St.
Poway CA, 92064

Any more information regarding the pain that you have. Maybe it is something not sold in the United States??

I want to paint my plane (airbrush) rather than decals. Not sure I will try and follow any actual Cessna scheme. I think I will simply paint the nacelles blue, and go blue on the top half of the fuselage and also on the bottom. I will most likely run a strip of painters tape right down the middle of the fuse nose to tail and peel off after painting blue to make the white stripe. Will probably add some numbers.
I was disappointed that my windshield is already glued in place. The cockpit is huge and calls out for a pilot and passenger to be placed in there. I tried to peel it back but it is glued very tightly. I may simply spray the window glass area black but that would really be a travesty.
Have you considered lights at all for you Cessna?
Keep us posted.
Tigerbug
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Old Apr 04, 2011, 06:44 PM
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James Frolik's Avatar
Cologne, Germany
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Quote:
Originally Posted by tigerbug
I sent Multiplex Customer Service an email asking about the paint [and] Here is what they sent to me:

Hello Matt,
[...]We do not make a foam specific spray paint for the Elapor foam.
I will say that Multiplex USA is behind their Mother Ship's curve. Just look at the attached product release from the German model aviation magazine FMT. This product, Multiplex ELAPOR COLOR was first available here late last year. I recall seeing it in a hobby shop—or maybe it was at the Jet Power event.

Any way, perhaps in the past few years Multiplex U.S.A. has tried getting their act more coordinated with Germany. I hope they have. But their reply to you indicates that maybe they have not.

P.S.—Yes, I have considered lights for my Cessna. But if the weak landing gear cannot be rectified appropriately, I will not invest much more than a nice paint scheme. Also, I have thought about cutting out the pilots' side windows and replacing the EPP with clear plastic in order to give the cockpit more image—like a place for your pilot(s). The passenger windows can remain dark decals.
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Old Apr 05, 2011, 12:42 PM
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Loveland, Oh
Joined Aug 2004
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Other paint options

James-Thanks for sending the Elapor Color announcement. Very interesting that USA is so behind. I did a search for this paint and can locate all over Europe but they will not ship to US. So I searched for other options and thought I would share them here:

http://www.wattflyer.com/forums/showthread.php?t=21666

I have been reading a number of other threads on RC Groups and Watt Flyer and they are all pretty much the same. I did read something I had not seen before about prepping this foam for paint. It was suggested to either wash the foam with a light dish detergent with degreaser or wipe down carefully with alchohol. Both methods clean of the "Releasing Agent" used to get the foam out of the mold easily. When removed paint will stick easier and last longer. Makes sense but I have never tried it. I tend to like water based acryllics and I do use WBPU (Polycrylic) quite a bit on planes I make from scratch with Depron and EPP.
I think I will most likely clean first with one of the methods noted above, then lightly sand when it is dry. Then will lay down a base coat of WBPU. Once dry I will then paint over the WBPU. After paint colors are dry I go over again with a light protective coat of WBPU all the while trying to keep down the added wight.
I am very anxious to get started on this bird but now having to pay my dues for having been out of town for an entire weekend with guys from my club attending the Weak Signals RC Convention where I bought the plane. It will be a couple of weeks before I get into building and painting mode.
Tigerbug
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Old Apr 06, 2011, 07:03 AM
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Good ole Smithsburg, MD
Joined Mar 2007
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My Venom C-47 Skytrain (thread) has ZD-Fly stamped into the center wing section - guess it is the same company making these. Good luck with your build(s)

Cheers,
Steve
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Old Apr 08, 2011, 07:22 PM
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James Frolik's Avatar
Cologne, Germany
Joined Dec 1996
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Here's a temporary fix to the landing gear's swivel.

The new retaining screw will eventually loosen in the ABS plastic and the thread will start stripping with every subsequent tightening. Perhaps a slight drop of CA in the hole will harden the threads. I don't know. But this is what I've done for now until I find some scale-like retract replacements.

Next step is to build some main gear doors...that work.
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Old Apr 09, 2011, 03:56 PM
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Cologne, Germany
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Here's a video I made of the motor's acceleration and deceleration. Fortunately the ESC provides relatively smooth steps. The power source was a constant 11.5 volts.

Of course this is a no-load test. It doesn't sound real fast when spinning at full throttle, but if you add a 10-inch prop then two of these motors should provide ample thrust for a 2.4kg model.


ZD-FLY 1100kv Motor-ESC (0 min 47 sec)
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Old Apr 09, 2011, 07:20 PM
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Cologne, Germany
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Here's yet another video I made of the main retract mechanism.

The left wing's retract servo doesn't have a long enough servo arm, the right wing's servo does. My radio's retract channel is set to 150% end-point-adjustment for both up and down, and it's clear that without the longer servo arm the wheel strut would be loose and not secure. With the longer servo arm the gear retracts just enough and feels secure. But that doesn't mean it really is. There's always humming in the servos regardless whether there is tension or not; it has to do with the end-point-adjustment.

Bad Quality Retacts in Motion.m4v (0 min 54 sec)
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Old Apr 11, 2011, 01:05 PM
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Loveland, Oh
Joined Aug 2004
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Painted now to start the build

I went ahead and painted the Cessna. I only need to finish the elevator fin as my airbrush kept clogging up on me. I lightly sanded the entire airframe. I then laid down a very light coat of Polycyllic with a foam brush. I went with a Royal Blue color similar to the color used here on RC Groups in the header / info bars. I think it came out pretty good. Only problem was a bit of overspray ( I should have taped off more area than I did. It's hard to see this happening becase you are paying close attention to the area that is receiving paint and just don't realize that even with an airbrsuh there is always some paint floating in the air. I just used some alchohol to rub this off and it came off fairly decent. I then sprayed some acryllic over all painted surfaces to seal and provide a bit of low level gloss.

Nacelles are glued in place after testing the motors etc.

James thanks for your continuing updates regarding the gear issues. I will look into that next. I use a JR 9303 so I will be able to slow down the retracts making them more scale.

After I get the tail fin finished being painted I am hoping she goes together pretty fast. I am at work or I would upload pictures which I will do sometime soon.
Guys-Keep the info coming.
Tigerbug
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