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Old Jan 11, 2014, 01:08 PM
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Tucson
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Seagull Super Chipmunk 55

I was looking for a sport aerobatic plane, not too big, and so am trying a Super Chipmunk. A few sources have the Seagull model, and the size was right. I will keep notes on what I encounter. Purchase price is about $250.

Basic stats:
Super Chipmunk Seagull 7.9lbs 63 wingspan, fuselags 53, rated for .55 glow, 643 sq. inches, 29 ounces loading.

Power system:
ASP .90 4-stroke glow engine, from Taiwan, via eBay. I am hoping for at least 7.5 pounds of thrust at Tucson elevation. I chose ASP, as an exploration of the cheaper Asian 4-stroke glow engines. I have a .52 on a Smith Miniplane, and it runs smoother the more that I run it, and is not too finicky on tank placement.
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Old Jan 11, 2014, 01:30 PM
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Tucson
Joined Nov 2009
1,108 Posts
Initial observations...

Shipping is a double shipping box, with the kit box inside. advantagehobby sent this, and it arrived with no damage.

Covering is high quality. You can blow it smooth, but watch the heat. The white covering will shrink, but much of this model has multiple layers of covering, and a hair dryer can burn the outside layer.... I air blew it until it was acceptable, but not perfect.
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Old Jan 11, 2014, 01:52 PM
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Tucson
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Build notes...

Wings are removable, and the low tech plastic bolts are reliable (10-32 twist?). Wings screw on to "gull wing" wing roots. Looks cool, but doesn't leave much room for the screws (being plastic, the can be cut down with a wire cutter). Wing connection is strong. I epoxied a fiberglass tube inside the aluminum wing tube, almost full length. The FG tube is just about 5/8" outer diameter, and I buy them from a kite shop online (goodwinds) and they are about 16mm (or just under). With this epoxied inside the wing tube, you will not bend the tube with strong aerobatics, but you add a number of ounces to the build.

Included gear is fixed, with a strong shock absorber. Carefully drill out the laser cut hole for the gear into the wing, until the gear fits exactly. There is a good wood foundation in the wing, for the gear. It seems very sturdy, and does not twist (tracking should be good on the ground). I relieved the fiberglass gear covering a bit by the wing with a Dremel, to allow the covering to lay flat to the bottom of the wing. I may leave spats off.

Fuselage is all sheeted, and strong. I like this.

Tail feathers are glued on a pretty thin foundation, but should work. Watch out when installing the tail feathers. You can epoxy on the horizontal tail first. You must thread the tail wheel wire through the horizontal tail, before you attach the wheel assembly to the body, or epoxy on the vertical tail, or connect the rudder to the vertical tail. A bushing on the tail wheel wire holds the weight of the plane off the CA rudder hinges (good). You may want to put a thin plywood plate under the tail wheel plastic mount, to slightly strengthen this area.

To call the model a "55 size" plane is a misnomer. 7.9 lbs needs 7.9 x 150 watts = 1185 watts to the prop = 1.6 horse power for full aerobatic flight. So a .90 2-stroke would probably fly it with power vertical aerobatics. Hopefully, a .90 4-stroke will also. But a .55 2-stroke would only fly it like a trainer, and not fast enough.

Power system:

.91 ASP 4-stroke ordered from eBay in Taiwan. About $160. I am trying this, because I am exploring the cheap Asian 4-stroke glow engines. An ASP .52 FS that I have on a Smith Miniplane is running smoother, the more I run it, and putting out almost 5 lbs of thrust. With an electric starter, it starts in 2 short zaps, running a 11 x 5" prop for low air speed on the biplane.

I strenghened the Chipmunk firebox (it is 3-sided) by epoxying 1/8" plywood on the 3 sides of the box, and screwing through them into the firewall. I may epoxy some 1/8" plywood strips on the inside of the firewall box back almost to the wing tube, to strengthen this connection to the firewall.

I am using an Aeroworks 24 oz tank. This fits into the firebox, and will probably give a good 15 minutes of flying time. If I need more nose weight, I can fill the tank more.... I am using the Aeroworks $13 fiber engine mount, as this is strong, and includes hex head bolts for the engine mounting and attaching the mounts to the firewall, and the dead bolts.

The ASP .91 FS fits on the Chipmunk best with the piston horizontal coming out the left side of the plane (viewed from back). Carb is very near to the middle of the tank. There is a tank pressurization line with this .91 ASP. I used one pre-installed dead bolt (upper left) but installed 3 new dead bolts to fit the Aeroworks fiber mounts. The pre-installed dead bolt is a slightly smaller size than the supplied Aeroworks bolts. So, I did not take out any of the pre-installed dead bolts.

The throttle arm will need a pushrod outside the firewall box (but within the fuselage). The large tank covers the built-in servo tray, but it should be simple to build another right around the wing tube at the right height.

I will check for prop clearance (12 - 13 inch prop) when I get the tail wheel mounted.
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Old Jan 11, 2014, 02:26 PM
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Tucson
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On the CG: (KEEP ALL WEIGHT FORWARD -- SEE LATER COMMENT ON CG)

The initial CG test, without pushrods and servos, with .91 ASP mounted and empty gas tank and wing gear installed, was about 25-30% wing cord. This is close enough to make me believe that I can install the elevator servos, rudder servo, and throttle servo as is convenient, and will be able to balance the plane properly.

On flaps and ailerons:
I am using Solar 109 (analog) servos on everything (2 for the elevator halves). Wing servo mounts are decently made and fit well. I relieved the servo arm exit holes a bit for the ailerons, for range. I have the same complaint about the flap servo mounts as for many other ARFS -- the covers are asymmetrical, which is very scale, but means that you can't run both flaps off the same channel, or must find a pair of opposed direction servos. I solved this by reversing one servo mount cover, and placing one flap control horn at an offset on the flap to match the reversed orientation servo. Works fine.

The flaps are big, barn door flaps. They may be scale, but I will have to test their effect, before using them. The hinges work something like Fowler flaps -- interesting. I doubt if the flaps will work with a full 90 degree down deflection (they are so large). I work the flaps with channel 6 on the Futaba radio, which is a twist knob. I will just wind down the flaps a bit, for landing.
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Old Jan 12, 2014, 07:24 AM
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Tucson
Joined Nov 2009
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On tail control hookups:
I have an ongoing complaint with Seagull ARFs, because control rods are sometimes too light, plastic tubes for the control rods are sometimes badly placed and preglued into the fuselage, and split elevators with separate control rods are assumed by Seagull to be run with one servo. And, Seagull control tubes are often epoxied to braces behind the cockpit, that are not in line with servo tray that is also preglued in place. The Chipmunk is much better than the average Seagull ARF, but...

I cut free the 2 inner supports for the 2 elevator control tubes, back from the cockpit, and also the rudder control tube. And broke apart the 3 plastic tubes. This allowed me to position servos anywhere in the cockpit, and on any level, and use 2 elevator servos. I used 2 Solar 109 servos for the elevator halves, in the preinstalled servo tray.

I installed a "flying servo" for the rudder pushrod (I used a salvaged aileron servo hatch mount, stripping off the plastic outer covering, and epoxying the outside hatch surface to the side of the cockpit. This allowed me to install the rudder servo above the elevator servos, and a bit offset toward the front of the plane (for access). This rearrangement of the tail servos and pushrods is a stronger installation, and has almost no binding.

With these modification, I could use the pushrods and pushrod plastic tubes that Seagull supplied. They are good quality, as well as the metal clevises, and the alignment of the tail pushrods coming out of the body lines up perfectly with the control horns on the elevators and rudder. GOOD JOB SEAGULL, ON GETTING THE REAR ALIGNMENT PERFECT!
I like the fiberglass control horns that Seagull supplied.

On throttle servo placement:
I mounted a throttle servo on top of the wing tube, up against the back of the nitro tank box, on the left side of the cockpit. I will run the throttle pushrod inside the left cabin wall, until it gets back to the servo. ASP engines have a throttle lever that takes very little pressure to move (WAY TO GO , ASP!).
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Old Jan 12, 2014, 07:36 AM
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Tucson
Joined Nov 2009
1,108 Posts
This Seagull ARF is coming together much better than the Silence Twister. The tail control rod placement and their servo placement is the only major modification that I have made. I have spent a week of putter work getting it all together.

It will take just as long to run in the APS .91 FS with 13x6" prop, that I have installed. Then we will see what the Super Chipmunk will do in the air. I don't want to rush the breaking in of the engine, as the engine has a lot of power, and I will need a slow idle speed to control the model on the ground.

The supplied pilot is painted in a complementary stars and stripes helmet. Nice. The whole plane looks very sharp. I may change bottom colors a bit, to make the up-down orientation a bit easier. These exact scale colors can make for difficult orientation detection!

Hope that these notes were helpful.
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Old Jan 13, 2014, 02:05 PM
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Tucson
Joined Nov 2009
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Update on CG:
WARNING!
Seagull says to fix CG at 88mm back from leading edge, at root of wing. This is a long way in front of the wing tube! Also, this is about 30% of the wing, minus the flaps! So Seagull made this plane to fly much more nose heavy than 20-25% total wing chord.

Using the range 80-88mm, and with an 1800 3-cell Lipo installed just behind the nitro tank, and tail servos in rear of cockpit, it took 16 x AA batteries (in front of the box behind the firewall) to make this CG (without the cowl, or pilot figure). This weight will probably fit on the outside of the firewall box, under the cowl, and a little right behind the firewall.

The initial high wing loading (29 oz) and this added weight to make recommended CG will cause the Super Chipmunk to fly like a heavy warbird.

You may want to dispense with all this added weight, and see if you can fit a 1.20 glow 4-stroke on the firewall!

Elevator range:
The Solar 109 servos don't have much throw. I used the outside location on the servo arm, and the inside location of the FG elevator control horns. Then I had to change the Futaba 7C radio elevator range to +140 for down and +110 for up (so the rudder still clears the full up elevator). Note the limited up elevator movement. This gets me about all the elevator range that the design will allow.
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Old Jan 13, 2014, 02:24 PM
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Tucson
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With a 13 inch prop and engine location (above), the Chipmunk still has good prop clearance when the tail comes up to flying position, and the main wheels are still on the ground. Even with some mediocre landings that compress the shock absorbers, I should not be breaking props when landing.
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Old Jan 13, 2014, 02:25 PM
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Tucson
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Next step: running in the .91 ASP FS glow engine.
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Old Jan 23, 2014, 02:47 PM
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Kent,UK
Joined Jul 2010
10 Posts
hi
Did you ever fly this plane. I have been flying 25 years and fly aerobatics etc. But I built one of these last year and it flew badly. Mine had a 71 os surpass and came in under the mauals auw. It was one of the best looking planes i have built. Unfortunately it flew bad. It would tip stall into a spiral dive. It would snap out of the bottom of manouvres and scew out of loops etc, it was a scary plane to fly or land. it crashed so i re built it. then it span in again. It was recently given a good review in RC MODEL WORLD. But i would like to hear from someone else before I suspect the servos or something else.
If i saw a video of this flying ok I would gladly buy another.
ED
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Old Jan 28, 2014, 07:56 PM
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Tucson
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Today I tried a maiden flight with the Super Chipmunk. The ASP 90 FS had a 13 x 6 prop, but the plane really needs a 13 x 10. The plane flies lighter than the almost 8 lbs full up weight, but it needs a lot more air speed than the 35 mph that the 13 x 6" prop gave.

For trim, I needed only 4 clicks UP elevator.

Caveat: I put a big roll of pennies behind the fire wall, and filled the 24 oz tank almost full. So the plane was a bit nose heavy. My CG was probably a bit behind the suggested CG (the manual says that the CG is quite a bit forward of the wing tube, but this is maybe 15% chord. That seemed a bit too far forward. I flew the CG a bit forward of the wing tube.

The plane is interesting! The tail will lift off at about 1/3 throttle. I kept the plane on the runway a bit longer, then gave it a bit UP elevator. It lifts off easily.

I used 50% expo on the ailerons and elevator. The rudder I dampened so that I could stear it easily on the ground. Ground handling is good, using a bit of UP elevator to keep the tail wheel on the ground.

With a 13 x 10" prop, this should be a nice aerobatic plane. I don't think that it will have the responsiveness of a 3D plane, but it should do IMAC aerobatics. I can write more later, when I get a bigger bite prop and more air speed. I did not use flaps on the first flight. The plane slows down for landing, without having to use flaps.
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Old Feb 06, 2014, 10:35 AM
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Tucson
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Update:
I tried a 12 x 10" prop with the ASP .90 4-stroke, and while this kept the plane in the air, it did not give the airspeed that I needed.
I tried a 13 x 10" prop, and lost the plane on the first turn after takeoff (started a tail slide, I countered with some right rudder, but speed was slow enough that the tail started a big stalling tail sweep, and I could not keep the plane in the air).

Final conclusions:
1. this ARF has much too high a wing loading
2. the CG in the manual is very far forward -- this is not an ARF engineered to have a 25% CG
3. this ARF will only fly with higher speeds (40+ mph). Any slower than this risks loss of tail grip with maneuvering.
4. Landings are fine, if you don't try to maneuver at slower speeds.
5. takeoffs need speed, and I could not get a .90 glow 4-stroke and prop combination that would develop safe speeds for takeoffs.
6. this is a scale, "look-good" plane, not an aerobatic plane.
7. if you're going to try to fly this plane, quit the subtle approach, and put a 20cc gas engine on it and fly it like a WWII flying brick warbird.

I'm sorry that I spent the $250 on the ARF.
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Old Feb 28, 2014, 10:05 AM
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Kent,UK
Joined Jul 2010
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Exactly as I found. Thank goodness for this thread. I could not believe mine flew so bad. Then RC Model World, go and give it a rave review. But the truth is here to see.
Crying shame, such a nice model.
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Old Sep 01, 2014, 10:47 AM
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United States, MA, Burlington
Joined Apr 2012
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chipmuink

Has anyone else had any luck with this plane. I just bought one. I have a Saito 100 I can put in it. Or I might look for an OS 75ax. It seem like the CG is an issue from what I was reading.
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Old Sep 07, 2014, 11:41 AM
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United Kingdom, Wales, Swansea
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Quote:
Originally Posted by lfd47 View Post
Has anyone else had any luck with this plane. I just bought one. I have a Saito 100 I can put in it. Or I might look for an OS 75ax. It seem like the CG is an issue from what I was reading.
Interesting read. I can't see this plane listed as a current model, although I'm sure I saw it somewhere recently? Anyway, I have a Seagull plane similar in wingspan and weight - the Seagull Sparrowhawk. I bought it 2nd hand in electric form, and I was thinking to convert it to glow 4 stroke. I haven't flown it at all yet, but I've seen a video of it flying OK.

I note the the Chippie was fitted with an ASP FS 91, and this is what I was thinking for the Sparrowhawk, maybe upping it to the 1.20. The spec says for 4 stroke '1.0 - 1.10', but I don't know of any such animal. Question is, though - was the 91 too underpowered for the Chipmunk?
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