CESSNA 337 SKYMASTER by NITRO MODELS

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In writing this review my aim was to give some information about the construction of the Nitro Models' Cessna 337 Skymaster as I could hardly find anything concerning the tips about this RC plane over the internet. I hope my descriptions may be helpful for those who intend to build one of these models.

In this review I will try to give some tips and talk a little bit on the pros and cons about Nitro Models' Cessna 337 Skymaster.

SHORT HISTORY:

The first Skymaster, model 336, had fixed landing gear and first flew on February 28, 1961. In February 1965 Cessna introduced the model 337 Super Skymaster. The model was larger, and had more powerful engines, retractable landing gear, and a dorsal air scoop for the rear engine ("Super" was subsequently dropped from the name). The main advantage of the inline twin engine was that in case of an engine failure during take off or landing or in flight, the plane would not yaw towards the opposite site as the twins on the wings thus increasing flight safety (This is completely true for the RC model as well).

THE RC MODEL:

I purchased this model from "General Hobby" in USA, however the model is produced in China by Nitro Models. The pakage arrived in good condition all the way from USA to Turkey and I was lucky about that.



[Sadece Kay ([Sadece Kay)

GIVEN SPECS:

Wing span: 81"/2060mm.
Wing Area: 1085 sq.in/70 sq.dm
Flying Weight: 10 Lb/4540 gr.
Fusulage Length: 62"/1570mm.
Engines: 2c 0.46 ci x 2 (Two engines) (I used .91 ci 4c Os SII for the front and Saito .82 4c for the rear)
Radio Req.: 5 Ch
Servos: 9

When I opened the box, everything was packed well with foamy covers for enhanced protection.


[Sadece Kay ([Sadece Kay)

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To start with, I must say that the manual given with the model is completely rubbish and unreliable. You must know the language named "Chinglish" but still the manual is inadequate. That was the main reason for me to look for information over the internet which did not turn out to be sufficient.

So I decided to start with my own experience and first of all I commenced with putting the fusulage on the wheels. When I took the fusulage out of the box I noticed that the covering was as not tight as it had to be. I recommend to do the ironing for restretching the covering before starting to build the model.

First I cut out the covering over the landing gear casing and placed the main landing gear to the fusulage with the wheels. The wheels supplied with the model , to my experience, are too small and poor ones for this model so I used 3.5" diameter aluminum alloy cased wheels for the main gear. This brings an advantage if you have grass or stabilized runways for flight.

[Sadece Kay ([Sadece Kay)


[Sadece Kay ([Sadece Kay)


[Sadece Kay ([Sadece Kay)

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[Sadece Kay ([Sadece Kay)


[Sadece Kay ([Sadece Kay)


[Sadece Kay ([Sadece Kay)

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Having finished the installation of the main landing gear and putting the model over the wheels I had to move on with the installation of the front gear. However before starting to do so I felt that I had to reinforce some parts of the firewalls both in the front and at the back of the plane so I cut small pieces of triangular balsa wood and used cyano adhesive for attaching the reinforcments as seen in the pictures below. Believe me the Chinese producers are very reluctunt in using adhesives in the models so it is always better to double check the joints with them.

[Sadece Kay ([Sadece Kay)

[Sadece Kay ([Sadece Kay)

[Sadece Kay ([Sadece Kay)

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The centerline of the firewall was not indicated so I had to do the measurements and drill the holes for the front wheel assembly. One of the most challenging parts during the build up was the placement of the blind nuts to the back of the front firewall for the attachment of the front wheel assembly. This should have been given ready by the factory as I had to spend quite a lot time on this application.

I passed a push rod through the holes into the plane and slided the blind nuts to their places. Using some medium cyano will help for the permanent placement of the nuts.

[Sadece Kay ([Sadece Kay)

[Sadece Kay ([Sadece Kay)

Then I had to drill the push rod hole as well according to the length of the wheel arm and placed the push rod as seen in the picture below.

[Sadece Kay ([Sadece Kay)

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After the completion of the the front wheel assembly, the fusulage was on its wheels ready for the placement of the front wheel control servo.

TECHNICAL NOTE: This model does not include a rudder so the front wheel servo controls only the front wheel. If rudders are to be formed use of a different servo working synchronously with the front wheel servo (Mixed) is recommended.

Before the installation of the front wheel servo I designed the electric equipment and checked it working before putting it into the model. One of the things I could have found over the net was that this model ended up with a tail heavy balance and putting the electronics towards the front was recommended. Keeping this suggestion in mind I placed the LIPO battery and the UBEC into the cockpit. For this model I used a RHINO 11.1V 20 C LIPO battery together with a TURNIGY 8-15 A UBEC for downgrading the voltage to 6V. The connection sequence was as follows: LIPO to Switch, Switch to UBEC input and from UBEC output to receiver.


[Sadece Kay ([Sadece Kay)

[Sadece Kay ([Sadece Kay)

[Sadece Kay ([Sadece Kay)

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Doing this, the system became receiver ready and I could center the servos before final adjustments.

I preffered a Hitec HS325HB carbonite gear servo for the front wheel.

As there are two engines, two individual servos are required for throttle. I used two Hitech HS475HB servos for each throttle and joined them on the 3rd channel with a Y cable.

[Sadece Kay ([Sadece Kay)

[Sadece Kay ([Sadece Kay)

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This brought me to the installation of the motor mounts to the firewalls.

TECHNICAL NOTE: Two identical engines with identical propellers are recommended for multi engine aircrafts. Due to some economic reasons and because I had the engines at hand I decided not to purchase another engine to make them identical but as the engines are placed on the same axis (INLINE) I preferred to use two close sized engines (Saito 82 as the rear engine and OS 91 SII as the front engine) on my model. I cannot take any responsibility for those who would prefer to do so on their own models.

I started with the front engine mount. The holes are not ready and you have to calculate and drill the holes according to the engine mounts and the engine that is going to be used which I believe is another handicap during construction. I also drilled the push rod hole on the firewall as well.

Reverse installment of the engines is recommended in the instruction guide so be sure to adjust your mounts accordingly.

[Sadece Kay ([Sadece Kay)

[Sadece Kay ([Sadece Kay)

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The front engine (OS 91 SII) was placed as the front engine to its place in the known reverse fashion and the front fuel tank with its silicone tubing was installed.

TECHNICAL NOTE: The recommended engines by the producer for this model is .46 ci 2c engines ( which I believe will hardly fly this plane) so the given fuel tanks are very small. I used higher capacity tanks both for the front (500 cc) and the rear (480 cc) engines.

This almost completed the front engine installation.

[Sadece Kay ([Sadece Kay)

[Sadece Kay ([Sadece Kay)

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All the procedure was repeated for the rear angine mounting again. Drilling, placement of blind nuts, installment of the engine mount and installment of the engine (Saito 82 4c) was done in the similar fashion with the front engine.

[Sadece Kay ([Sadece Kay)

[Sadece Kay ([Sadece Kay)

[Sadece Kay ([Sadece Kay)

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After installing the rear engine I placed the rear engine's fuel tank to its place which almost completed the installment of the engines.

TECHNICAL NOTE (IMPORTANT): The rear tank is prepared in the usual fashion however the front of the tank should look towards the front of the plane not to the rear as to ensure the clunk inside remains in the fuel during climbs. This knowledge was not mentioned in the construction manual at all. This is a must have knowledge for someone who is going to use a pusher system for the first time.

[Sadece Kay ([Sadece Kay)

[Sadece Kay ([Sadece Kay)

[Sadece Kay ([Sadece Kay)

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Coming up this far made the fusulage look like from this

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to this.

[Sadece Kay ([Sadece Kay)

[Sadece Kay ([Sadece Kay)

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The soldering machine in the last picture above was used for cutting the cover over the windows. Hot soldering machine is a better and more precise tool for cutting the cover instead of a knife.

Having done this the windows were placed and the fusulage construction was almost completed with only the cowlings being not attached. The reason for this was that the multiengine planes need to undergo an engine synchronization before flight and it could have been done more easily without the cowlings. The cowlings were installed after the synchronization of the two engines.:rolleyes:

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The most challenging part of construction was the construction of the wings. The manual described the wings' to be fixed permanently however it would be impossible for me to carry the wings with my sedan car so I had to find out another solution.

One of the truly annoying things about the model was that the aluminum wing joiners ripped the paper joiner guides within the the wings and prevented the wing to sit its place snugly. This gave me the idea that I had to reinforce the joiner guides within the wings so I had to cut of the covering and the balsa. Having done this I wrapped the joiner guides with fiber cloth and reinforced them by using epoxy glue. I further put reinforcments over the top and bottom of the wings from plywood and drilled them with 5mm bit by drilling also the aluminum joiners. The aluminum joiners were fixed with epoxy to one side of the main wing Then I used 5mm hex screws for joining the wings. The wings ended up as detachable wings and easy to carry in a sedan car.

[Sadece Kay ([Sadece Kay)


[Sadece Kay ([Sadece Kay)


[Sadece Kay ([Sadece Kay)

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[Sadece Kay ([Sadece Kay)

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Doing the same procedures on the other wing half the plane was almost ready for flight. First I took the fusulage to the field and did the engine synchronization. Once this was completed I put two on board glow igniters one for the front and one for the rear engines. The rear engine especially is almost fully covered with the cowling so it will be wiser to use an on board glow igniter.

[Sadece Kay ([Sadece Kay)


[Sadece Kay ([Sadece Kay)



Following this both cowlings were placed in the known fashion.

[Sadece Kay ([Sadece Kay)

The propellers I preffered for this model were a JXF 14x7 wood two blade in the front and a Master Airscrew 12x6 pusher glass filled nylon three blade at the rear.

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The placement of the cowlings and the cockpit finished the construction of the plane and it became ready for the CG measurement. The recommended CG for this model is given to be 120 mm. from the leading edge of the wing.


[Sadece Kay ([Sadece Kay)


[Sadece Kay ([Sadece Kay)

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This ends my evaluation on this model. I hope my experience helps to others in building a new beautiful rc plane like this.

Barlas N. Aytacoglu