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Potensky Cobra and Eagle

The two Potensky models proved to be very robust and enjoyable to fly. The choice of picking one over the other would have to lie in the type of flying that you prefer and your piloting skills.

Splash

 




Wingspan 30.7"
Length 26.4"
Motor POT 03B (Speed 300 geared 5:1)
Speed controller 8amp (14amp burst)
Batteries 7-cell 720mAh NiMH or 2-cell, 2100mAh LiPoly
Prop 10x4.7 Folding
Servos Hitec HS 55 (4)
Receiver Hitec 555
Weight 10-12oz.
Available from Hobby-Lobby
Manufacturer Potensky

Introduction

The Potensky Cobra is a small 4 or 5 channel, full-house acrobatic 3D parkflyer, made from almost unbreakable EPP foam. The output thrust of the geared Speed 300 motor is greater than the weight of the plane. The fuselage and wings are made from black EPP foam which is a characteristic of its European design. The fins and control surfaces are made from a Depron-like foam called "Potpron". This is a fully acrobatic, symmetrical wing model with a wide range of speeds which is developed for outdoor flying in small fields. The model plane flies for about 10 minutes using a 7-cell 720mAh NiMH battery pack. Optionally, a 2-cell, 2100mAh Lithium Polymer (LiPoly) pack can be used to reduce weight and increase flight time. Static pull is 1.75oz (50g) higher than the mass which allows the model plane "to hang" by the propeller. The plane's 3D dynamics and flight characteristics are exciting to fly, or even just watch.

The kit includes a complete power system and all the parts needed to finish the model. The Cobra design also allows for easy attachment of an optional float set to convert your land flyer into a water acrobat. A custom plastic canopy, long carbon fiber rods, and a steerable tailwheel assembly are also included.

The Hitec 555 micro receiver and HS-55 servos are a great fit for the Cobra To complete the model, you need a 4-channel radio system, 4 micro servos Optionally, a 2-cell, 900-2100mAh, LiPoly pack will reduce weight and add duration.

Assembly

The basic Cobra parts are all foam (left) and include decals, manual, and a complete power system (right). When I first realized that the kit was made in the Czech Republic, my initial concern was for the building complexity and clarity of instructions. I was relieved to find both a full size drawing with all the components in place, and a manual that consisted entirely of pictures; the universal language. Potensky Microsystems did a great job on both the design and the documentation. After seeing the on-line video of the Cobra performing 3D maneuvers and hovering in place, I was excited to get started! I thought, perhaps this model could be used at my local indoor events for some wild aerobatics in the gym.
The manual is divided into distinct sections and steps, so I have decided to exactly follow the manual with my comments and hints. I hope that you will consider them a helpful aid to the manual.
Step 1
Cut the 3 circuit board formers free and sandwich them together with the supplied toothpicks. I used CA to glue the assembly together which will be used to support the landing gear. I roughed up the inner side with the supplied sandpaper before gluing.
 
Step 2
Cut off the toothpick ends and sand the nubs off the assembly.
 
Step 3
A 5th hole (2mm) is drilled near the middle of the assembly for additional support. Again, I used CA to glue the toothpick in place. Do not cut off the toothpick since this will be glued into a slot cut in the fuselage.
 
Step 4
To ease the pushing of the landing gear assembly into the pre-cut slot in the fuselage, I rounded the top two corners with sandpaper. I then cut the foam lengthwise at the slot in the fuselage to facilitate the center toothpick. I also sanded the outer sides of the assembly and applied a small amount of white glue before pressing it in place into the fuselage slot. Be sure that the openings for the metal gear rods face the outside.
 
Step 5
Rough up the circuit board firewall piece, and glue it to the foam fuselage nose so that the top of the circle on the firewall board is flush with the top of the circle in the foam fuselage nose. I used white glue on this step. The smaller hole in the nose routes through to the top receiver compartment.
 
Step 6
Stick four of the toothpicks into the outer holes and glue in place with white glue. This provides additional support for the firewall.

Step 7
Let dry and then cut the toothpicks off close to the firewall.
 
Step 8
This step made me laugh when I saw the need for a hot wire gun because few of us own one. Fortunately, the foam holes needs only to be cut about 1/4" deep to fit the backend of the motor so a sharp razor knife works very well in this step. Trace the firewall circle with your razor knife about 1/4" to 3/8" deep and remove the foam See the "Motor" steps 1-4 for how the motor will eventually be placed.
 
Step 9
A 5mm hole is drilled into the side of the fuselage so that the ESC battery connection can be later routed from the inner tunnel to the outside. The hole size here is not critical.
Step 10
Cut the middle section away from the foam cowl as shown in the manual diagram using a sharp razor knife. I cut my cowl from the back and angled the knife so that the walls became thicker as it approached the nose.
 
Steps 11, 12
I decided to skip mounting the foam cowl until after the motor was mounted. If the cowl needed more trimming, It would be easier done while still removed from the fuselage.
 
Step 13
Cut two pieces of carbon rod about 260mm (10.25") long. Cut each 10" piece from different rods.

Step 14
Slice a slot into each side of the fuselage rear and glue the carbon rods in place with white glue. I filled the long slice in the foam with glue first and then pressed the carbon rod in place with pliers. After the glue dried, the side-to-side movement of the fuselage tail section was much firmer.
 
Step 15
Cut a slot into the bottom tail of the fuselage for the tailwheel assembly.
 
Step 16
The pre-assembled tailwheel was excellent quality. I sanded the sides of the assembly and then glued it in place with white glue.
 
Step 17
Like the tailwheel assembly, the landing gear wheels and custom hubs were very nice quality. They simply pressed into place onto the gear rod and inserted into the fuselage bottom assembly.
 
Step 18
Hold the plastic canopy in place and press the 3 plastic nails into the proper position in the foam. Remove the canopy and nails. Rough up the nail shafts with sandpaper and press into place with white glue.Keep the back two nail heads close to the foam and leave the front nail head
up about 1/16" at an angle. Wipe off any excess glue.

 
Elevator Assembly:
 
Step 1
Find the 4 pieces needed to assemble the elevator and stabilizer. The elevator joiner is a piece of the fiberglass circuit board about 1 3/4" long and 3/16" wide.
 
Step 2
Cut slots in the leading edge of the elevator halves and glue them together with the joiner using 5-minute epoxy. Use the stabilizer to help you align the elevator and hold it in place with some light weights until the epoxy dries.
 

Step 3
Attach the elevator to the stabilizer. The kit comes with some iron-on tape for hinging but I used my own 3M Blenderm tape that has a nice stretchable property to it. I found that the iron-on tape worked best on the EPP foam wing.
 
 
 
Step 4
Round the leading edge of the horizontal stabilizer with the supplied fine grit sandpaper.
 
Step 5, 6
Before gluing the elevator assembly to the tail, I decided to first build the rudder assembly and then test fit everything before gluing.
 
 
Rudder Assembly:
 
Step 1
Round the leading edge of the vertical stabilizer with the supplied fine grit sandpaper. The leading edge has the curve in it.
 
Step 2
After sanding the leading edge round, I studied the tail assembly again. The toothpicks from the horizontal stabilizer assembly were needed to help mount the vertical stabilizer.First, I re-inserted the horizontal stabilizer assembly into the tail all the way. For the elevator to swing properly, I needed to trim the back of the tail slot a bit. Next, I used a ruler to measure equal distances along the leading edge from tips to fuselage. I then centered the elevator joiner at the rear and double-checked the leading edge again. Lastly, once I was satisfied with the alignment, I stuck two toothpicks down through the top of the fuselage into the stabilizer, locking it in place. It was now easy to pull the assembly apart and then use white glue to secure it back in place permanently.The vertical stabilizer pressed down on the toothpicks so that the trailing edge was flush with the rear of the fuselage. I taped the front down until the glue dried. Be sure to also check for a right angle between the two stabilizers.
 
Step 3
Cut a half circle into the rudder so that it clears the elevator joiner. Attach the rudder to the vertical stabilizer using either the supplied iron-on film (it does not shrink with heat) or your own preferred method. I used aileron tape for attaching the rudder to the vertical stabilizer and a Kavan white hinge to solidly mount the rudder bottom to the fuselage.
 
 
Step 6
Use either a small piece of carbon rod or a toothpick to attach the steerable tailwheel bar to the rudder. I CAed two short pieces of toothpick into the rudder.
 
Step 7
Slice a line between each servo bay and the receiver bay inside the cockpit.
 
Step 8
Install the rudder and elevator servo and route the servo wires into the receiver bay. Hold the servos in place by using the black plastic pins with some white glue.
 
 
Step 9, 10
Slice a straight line on each side of the turtle deck and bury the white snake tubing so that it aligns with the outer side of each servo. The bent end of the metal rods should end up about 1/4" above the horizontal stabilizer. Rough up the outside of the white snake tubing and glue in place with white glue.
 
Step 11
Cut the white snake tube to the proper length, if needed.
 
Step 12
Cut a small slot into the rudder and the elevator to mount the control horns. The left side control rod connects to the rudder and the right side control rod connects to the elevator. I used foam safe CA to glue the control horns but 5-min epoxy would work equally as well.
 
Note:
Whenever you are attaching a control horn to Depron-like foam, be sure to properly spread the glue over a broad area to add strength to the joint. Alternatively, a small piece of balsa can be used around the control horn for adding strength.
 
 
Wing Assembly:
Step 1, 2
Do step 2 first, which is to round the leading edge with sandpaper to remove the molded corners. Then use the iron-on tape to attach the ailerons, one to each wing half. The iron-on tape works well on EPS foam. The EPP foam sanded very well using the supplied sandpaper.
Note:
Since my ailerons warped after mounting the wing halves to the fuselage, I would recommend waiting to attach the ailerons until later.
 
Step 3, 4
Slice lines into the top of one wing half and bury the carbon rods after first filling the slots with white glue. The rods are slightly angled as a "V" from the wing tip.
 
Note:
The proper wing alignment and incidence checking are left up to the builder. Please use proper measuring tools to ensure your success. A right angled "builder's triangle" and 36" ruler work well. I felt that this part of the design was rather ambiguous and could benefit from pre-positioned holes in the fuselage and slots in the wing for alignment.
 
Step 5
Holes must be poked through the fuselage to fit the carbon rods through. After studying the pictures for a while, I decided to align the center of the aileron servo opening with the center of the black EPS wing (excluding the aileron). This allowed me to hold the wing with the carbon rods adjacent to the fuselage for exact placement to poke holes in the fuselage. The top surface of the wing also aligns with the bottom of the aileron servo opening. I used a spare metal control rod from another kit to poke holes through the fuselage.
 
Note:
After I had finished the Cobra, I was given a tip when building the Eagle that helped with the initial placement of the wing halves. Copy the supplied full size plan and place it directly against the fuselage to mark the correct wing position. For more details, see the Eagle Wing Assembly section.
 
 
Step 6, 7
I used 5-minute epoxy to glue the wing half on and held it tight against the fuselage until it dried. I believe that this is how I warped my ailerons since the wing ends may not have fit flush against the fuselage wall. Be sure to epoxy the carbon rod sections that will reside inside the fuselage. I also epoxied the rear toothpick and wing end that pressed against the fuselage. Double-check the wing incidence with the horizontal stabilizer.
 
Step 8
This is probably the toughest step of the entire assembly. The manufacturer did not provide a good technique for aligning the wing. Be sure to check the position of the leading edge of both wing halves and the incidence with each other. First, I positioned the free wing half under the carbon rods and marked their positions on the wing after verifying the leading edge alignment.Next, I sliced the slots for the carbon rods and positioned the wing in place. When I was satisfied with the alignment, I marked the trailing edge position on the fuselage and then inserted the toothpick about an inch forward into the fuselage.I then drilled a larger hole than the toothpick width into the mating position in the wing and cut the carbon rod channels a little wider from the wing center to about 1" away from the center. This allowed me some slop to slide the wing half around the exact alignment position.Using 5-minute epoxy, I glued the toothpick area and the entire wing side against the fuselage and held it in place while I triple-checked the leading edge alignment and incidence.The result, although not easy, was not bad! My alignment was sufficiently good for this relatively slow speed aerobatic design.Lastly, I buried the rest of the carbon rods into the wing with white glue.
 
Step 9
The HS-55 servos fit very snug without any cutting and really don't require the additional black plastic pins to help hold it in place. This can optionally be added later, if needed.
 
 
Step 10, 11, 12
I connected the entire aileron linkage assembly and centered the servos before finding the exact position for the control horns. The control horns ended up right near the leading edge of the aileron which allowed for maximum throw range.
 
 
Motor Assembly:
Note:
The power connector on the ESC is not a mate for the Dean's 2-pin polarized connector <u>and</u> it is not wired to the US convention. On my battery packs, the male pin is wired to the (+) positive terminal of the battery pack. Check your polarity before connecting the ESC to a battery pack!
 
 
Step 1, 2, 3
After roughing the motor case with sandpaper, I glued the mounting bracket into position with 5-minute epoxy. My gearbox, prop, and ESC came pre-assembled so steps 1 and 3 required no work. This was a nice touch!
 
 
Step 4
Feed the controller wire out to the receiver compartment and route the power connector out the hole on the left side of the plane near the wing leading edge. Screw the motor assembly in place with the two provided screws. All the wires were pressed down into the opening in the cockpit and then the receiver was placed inverted on top.
 
 
Final Steps:
Appling the decals was straightforward and easy. The yellow and black decals enhanced the overall color scheme.After checking the motor for proper operation and setting all the control throws, I glued on my foam nose cowl with white glue and then applied all the decals. To get the decals to properly stick to the EPP foam, I spread a thin layer of white glue on the foam first.

The finished Cobra was RTF at 11.7oz with a 7-cell, 720mAh, NiMH pack. The 7-cell pack was moved just under the CG line for a proper balance The model balanced perfectly with my 3.3oz, 7-cell, 720mAh, NiMH pack from Hobby Lobby after carving the foam out forward of the stock opening.




The CG is 2 - 11/16" from the wing leading edge at the fuselage.My empty plane weighed 8.4oz. The 7-cell, 720mAh, NiMH pack weighed 3.3oz. I was RTF (ready-to-fly) at 11.7oz with my 7-cell NiMH pack installed. I measured 4700 RPMs at 6.2amps with this setup.A better performance choice for the POT 03B power system on the Cobra (and the Eagle) is the Lithium Polymer 2100 Block from Radical RC. This is a 2s1p (2-cells in series and 1 cell in parallel) block of  2100mAh cells that weighs only 3.4oz. It can deliver 7 amps continuous and up to 14.7 amps in short term bursts. My Cobra was RTF at only 11.8oz. The 2100mAh cells would provide me with 30 minutes of flying time; very impressive! Alternatively, a 2s2p pack of Kokam 1020mAh cells will also work equally well.Cobra with 3.4oz, 2-cell, 2100 Block from Radical RC For really high end performance, the 2-cell, 900mAh, high-current LiPoly pack from Bishop Power Products weighs only 2oz and can deliver up to 15amps in short bursts! This is the lightest and most powerful pack that I have seen to date. It is very impressive! My Cobra was RTF at only 10.4oz.


POT 03B Performance Summary:


 Pack Type Weight 

Current Draw 

RPM 
 7-cell, 720mAh, AAA, NiMH  3.3 oz    4700
 8-cell, 720mAh, AAA, NiMH  3.7 oz  7.9 amps  5400
 Radical RC 2100 Block  3.4 oz  7.5 amps  5600
 Bishop Power Products  2.0oz    

Control throw setup:
I don't use exponential settings on my initial control throw setup. I look for proper direction of movement and that my dual rate control surfaces move about 40 degrees on high throws and about 20 degrees on low throws.


Some Pre-Flight Fun:


The geared Speed 300 power system can hover the Cobra at 3/4 throttle. After reading the manufacturers promotions about the Cobra's hovering capability on a geared Speed 300 motor, I couldn't resist trying it out for myself before even test flying the plane. Due to the soft new snowfall, I realized that I could do no damage to my new model so it allowed me to "play" until I reached a 20 second hover. It was my personal best hover time and not a limitation of the plane's power system. Although I would not yet attempt this feat over a harder surface, I had a blast pushing my flying skills to new limits!


Indoor Flight Testing:
In the Winter season, patience is indeed a virtue! Before I had proper conditions to test fly the Cobra outdoors, a local indoor event came along so I took my new untested model to give it a try indoors.


 
 
Although a bit hot, the Cobra flew indoors My only trimming of the control surfaces was with a good eye, so I was a bit apprehensive to fly the maiden voyage indoors. The Cobra took off with plenty of power and circled the gym with great agility. After several highly skilled pilots gave it a try, the consensus was that it was a little to hot for flying in a gym size area. Even though the Cobra took a few hits onto the hardwood floor, it came away from the event unmarked. I was happy with the test results.
 
 
 
Outdoor Flight Testing:
 
 
 
The Cobra is a blast! In stock form, it has fantastic performance! Although it is too hot for a gym-sized indoor flying area, it would work just fine in a larger domed arena. When outdoors, it becomes an extremely fun flyer with a wide dynamic range of flight performance. It can be slowed down for gentle loops around a small field or go straight up on full throttle!


The optional float set was tested by my friend, Paul Weigand. He reported that it is a perfect match for the Cobra. Whether flying off of water or snow, the floats are a great deal of fun and detract very little from the overall performance.  The stock power system works very well on a 7-cell, AAA, 720mAh, NiMH pack. You can also triple your duration using a 2-cell, 2100mAh, Lithium Polymer pack.


I have found the Cobra to be incredibly tough! I am very impressed with the overall design and performance of this geared Speed 300 EPP foamie.
 

Potensky  Eagle

 

Wingspan 35.4"
Length 28.3"
Motor POT 03B (Speed 300 geared 5:1)
Speed controller 8amp (14amp burst)
Batteries 7-cell 720mAh NiMH or 2-cell  LiPoly pack
Prop 10x4.7 Folding
Receiver Hitec 555
Servos Hitec HS 55 (4)
Weight 14oz
Available from Hobby-Lobby
Manufacturer Potensky

Introduction:

The Potensky Eagle is the Cobra's bigger brother. It has a 4.7 longer wingspan that incorporates a thicker, more aggressive airfoil than the Cobra. This allows the Eagle to fly much slower than the Cobra at the cost of high end performance. Many R/Cers may prefer this more docile flyer because it can be more easily flown in a small field or even indoors. The Eagle fuselage and wing are made from white EPP foam. The ailerons and tail fins are white Depron-like foam. The POT 03B power system is identical to the one used in the Cobra. The large control surfaces allow the Eagle to exhibit great maneuverability even when flying very slowly.Since the construction of the Eagle is almost identical to the Cobra, I will only highlight the specific steps that differ

Assembly:

Fuselage Assembly:
Since the Eagle's fuselage tail is bigger than the Cobra and the plane flies slower with the larger, thicker airfoil, Potensky did not require adding carbon rods for reinforcement.
Step 5
Align the firewall bottom of the circle to the bottom of the circle in the foam fuselage nose.
 
Elevator Assembly:
The elevator assembly steps for the Eagle are the same as for the Cobra
Rudder Assembly:
Step 5,6
Attach the rudder to the vertical stabilizer using either the supplied iron-on film (it does not shrink with heat) or your own preferred method. I used aileron tape for attaching the rudder to the vertical stabilizer and a Kavan white hinge to solidly mount the rudder bottom to the fuselage.
 
Wing Assembly:
When assembling the Eagle wing, I decided to skip mounting the ailerons until after the wing was attached to the fuselage. This would eliminate the warping that I had on my Cobra ailerons due to uneven surfaces between the fuselage wall and the inner wing end.
 
After telling my friend, Paul Weigand, about my difficulty in aligning the Cobra wing halves, he suggested that I copy the full size plans that came with the kit and lay it directly on the fuselage to mark the correct wing position. This technique worked very well, and, perhaps, it was what the manufacturer had intended.
Copy the full size plan and cut out the wing area
Position the plan against the fuselage wall
 
Trace the wing cutout with a felt tip marker
After poking holes through the fuselage, the wing easily aligns in place and glues with 5-minute epoxy
Cut the ailerons to a perfect length for each wing half

Final Steps

Note:
Whenever you are attaching a control horn to Depron-like foam, be sure to properly spread the glue over a broad area to add strength to the joint. Alternatively, a small piece of balsa can be used around the control horn for adding strength.

Balancing the Eagle

The Eagle CG is 3 1/4" from the wing leading edge at the fuselage. It appeared to be a bit tail heavy when trying to use the stock battery slot. My 7-cell, 720mAh, NiMH pack wanted to balance under the landing gear and my 2-cell, 2100 LiPoly block balanced as shown above. Since I wasn't thrilled about either choice, I decided to use my 8-cell, 720mAh, NiMH pack below in a stick configuration
I cut a slot into the top of the fuselage and my 8-cell stick pack had a nice force fit to keep it in place. The model balanced perfectly and I could get to the connectors easy and swap packs easy from this position. My empty plane weighed 10.3oz and I was RTF at 14.0oz with my 8-cell, 720mAh, AAA, NiMH pack. The 8-cell pack gave me 5400 RPMs at 7.9amps.

Indoor Flight Testing:

Like the Cobra, the Eagle had plenty of power and agility when flying indoors but it was still a bit too hot for a basketball court sized gym. E-Zoner, Matt Kirsh (mkirsh1) test flew the Eagle indoors for me. This testing was mainly performed to show the excellent power and agility of the stock design. The model was not meant to fly indoors, but, in a larger domed arena, it certainly could!
 

Outdoor Flight Testing:

As you can see from the characteristic orange prop, I managed to damage the gearbox on my Eagle when flying it indoors also. Since the Eagle's cowl is rectangular, and, it is larger than the Cobra's cowl, I decided to try using a GWS EPS 300C (CS) power system with a GWS 11x8 prop. This is a similar power level to the stock POT 03B power system but with a larger and higher pitch prop. It fit perfectly using only one screw and bolt into the existing firewall.
We had several a very nice Winter days to test fly the Eagle. It was only 25 degrees outside but it was sunny and there was no wind. The Eagle performed very well. As expected, it flew slower and more stabile than the Cobra. It trimmed out easily and could be flown in a very relaxed manner. The Eagle flew inverted just as well as it did upright and only a small amount of up stick was needed for level flight.
The Eagle is a slightly larger and heavier model than the Cobra. The thicker airfoil and longer wingspan provide the Eagle with a more stable character that might be favored by some folks for more relaxed flying. The heavier weight and additional drag both limit the upper end performance with the stock POT 03B power system but it is still very capable and a great deal of fun to fly! My Eagle flew well on an 8-cell NiMH pack.
The white EPP foam and contrasting red decals made the Eagle very easy to track in the sky. Takeoffs and landings from a paved surface worked very well. We needed only 10' of runway before the Eagle was airborne.

Repairing the POT 03B Gear Drive

My second indoor flying tests proved to be a battering experience for the Cobra, and later the Eagle. After several direct nose hits on the hardwood gym floor, I managed to strip a tooth from the nylon spur gear.
At the time, I was not able to get a replacement geardrive for my POT 03B power system so I decided to try replacing it with an MP Jet ball-bearing gearbox.
Here are the parts I used:
The POT 03B gearbox separates from the motor by removing two screws. To remove the prop, if desired for further inspection, simply unscrew the large black spur gear. Even though the MP Jet gearbox simply presses onto the stock pinion gear that comes with the POT 03B motor (as shown above), the teeth are too thick and broke after only one flight. It is easy to remove the stock pinion gear by prying it off with one or two flat blade screwdrivers. The metal pinion gear that comes with the MP Jet gearbox simply taps on with a hammer. Be sure to support the back end of the motor shaft on something solid before tapping the pinion gear in place. Tap the pinion gear almost flush with the motor shaft. Since the MP Jet gearbox is planetary, you will need to reverse the wires going to the motor so it runs in a forward direction.
The motor needs to be screwed onto the firewall first, and then the MP Jet gearbox can be pressed on. Once you are satisfied with the depth of the gearbox on the motor, you can add some black electrical tape for added security across the motor/gearbox seam. I ended up cutting off the 3 mounting tabs on the MP Jet gearbox so that it recessed better under the foam cowl.
The APC 10x4.7 SF prop is more efficient than the stock folding prop. I measured 8.5amps with the 10x4.7 prop and 11amps with the 10x7 prop. I went with the latter size since I use throttle management during flights.
The Cobra is re-fitted with an MP Jet Speed 300 5:1 BB gearbox and APC prop.
The Eagle was repaired with a GWS EPS-300C (CS) 5.33:1 geared Speed 300 motor and an 11x8 prop.

Overall Summary

My overall impression of these two designs is that they are both excellent! The two Potensky models proved to be very robust and enjoyable to fly. The choice of picking one over the other would have to lie in the type of flying that you prefer and your piloting skills. The other obvious difference is the color of the EPP foam. The black European-style EPP foam is less often seen in the US and makes an interesting attraction.
The Cobra requires a higher flying skill set since it has a smaller, thinner wing and flies faster. The Cobra also offers a higher performance level that works very well with the stock Speed 300 power system. A 2-cell Lithium pack provides incredible duration and power without any modifications. You are less likely to want a power system upgrade with the Cobra.
The Eagle allows for a more relaxed type of flying. The higher drag and increased weight reduce the top end performance

Discussion

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Old Jan 03, 2004, 03:24 PM
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BeechSkipperDude's Avatar
Manchester NH
Joined Mar 2001
264 Posts
i'm pissed, my potensky eagle did not come with plans. so i have no idea where to mount the wing. the intruction manual only says how far back from the nose to mount the carbon spar. ahhhh. someone help
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Old Feb 29, 2004, 10:28 PM
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Xnaron's Avatar
Joined Feb 2003
3,759 Posts
Great review Greg! I noticed that you put the carbon fiber wire on the top of the wing. The instructions call for it on the bottom and the top. This would give the wing the most rigidity. By putting them on the top of the wing you gain some rigidity but not as much as by following the plans. Was this a mistake on your part or did you have a reason for doing it this way. I just got my Cobra. I bought it without the motor and am putting in a pjs550 with a TP1900 pack. Performance should be great. Are you still flying your cobra?

Brendin
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Old Sep 06, 2004, 03:33 PM
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Joined Aug 2004
66 Posts
Well I've taken my Potensky Eagle with PJS550R Outrunner Motor and Thunder Power 7.4v 1320mah High Output LiPoly Battery out a few times. I am not impressed yet though. The 9x3.8 that Hobby Lobby recommended was terrible!! After two flights I changed to a 9x6 pitched APC prop and speed and manuverability increased greatly, although it still doesn't want to climb straight up so I can't see how it would ever hover!! I have a GWC 10x4.7 prop mounted and ready so I will be trying that out this afternoon to see if its any better. My previous plane (Alfa P51 Marie Mustang) was twice as fast air speed wise, rolled twice as fast and much smoother, as well as would climb straight upwards forever using a 11.1v 1320mah Lipoly/MPJET 20202 setup.
Maybe I need to upgrade this Eagle to an 11.1v setup, I'll play with the prop first and maybe somehow engineer a way to mount the 3 cell lipoly underneith so that I don't have to hurt the current 2 cell battery hole that is dug out of the plane already for a test run.
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Old Sep 10, 2005, 07:39 AM
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Good 'oll MA.
Joined Jun 2004
227 Posts
Does the eps300c work well with the cobra and mp jet gearbox? Would I have to change the pinion on the 300c?
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Old Dec 25, 2005, 06:18 PM
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Joined Dec 2005
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Building & Maiden Voyage Advice Sought

Hello Potensky Eagle & Cobra pilots,

I have skim read some of the forums and review articles on the Potensky models, but need some more pointed advice...

I have purchased the Potensky Eagle ($89 with motor/speed control) as my second RC plane. I currently fly a Graupner Mini Piper and fly it very confidently and now am ready to move on and learn aerobatics. I use a Hitec Flash 5 radio system. I will be flying stock (at least to start).

This will be my second build and second plane to fly; hence I could really use your advice.

If you were to do it all over again from opening the box through landing from your first flight, what are the steps you would take?

- - - - What I know - - - -

I know it is important to:
a) Break in the motor / set brushes
b) Am I safe using the CG (center of gravity) in the instructions?
c) Trim everything out at zero
d) Do a frequency test before each flight

- - - - ADVICE NEEDED - - - -

1) What would you reinforce during build?

2) Use vinyl tape for hinges for control surfaces?

3) Motor break-in - is water break in or running all out for 2 minutes best? How do you do a water break in with this motor?

4) What is best way to mount decals?

5) Are there any unsuspecting challenges I should be aware when assembling? If so, how do I handle them?

6) What is the best way to set my radio computer up (mixing?) for learning aerobatics as a newbie to sport flying?

7) For first flight is a rolling take off or a throw best?

8) When taking off what should I expect (for example with the Mini Piper you throw / set throttle at 75% / let go of sticks and it makes a gentle left circle ascent)? What should I be doing?

9) What's the best way to install the wires in the wings? Xacto blade the shape and the CA or Epoxy gule them in?

Any building and first flight advice you can provide me with be much appreciated. I have a lot to learn and would like to make my maiden voyage both educated and prepared to increase my chances for success.

Happy Holidays,

Jeremy
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Old Feb 11, 2006, 08:54 PM
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Potensky Eagle building question . . .

Hello pilots, I am currently building a Potensky Eagle and have a few questions:

**** Based on Greg Covey's "The E Zone" review, I have purchased: ****

1) Du-Bro hinge tape (aka 3M Blenderm) - will this stick to the EPP for the ailerons?

2) Great Planes' Medium Nylon Pinned Hinges - are these too heavy? Will using one alter the CG? Should I use "Small" as opposed to "Medium" sized hinges?

Would a CA hinge be preferred (my local hobby store says the weight is equal for both will not effect the plane's performance)?

**** CG Question ****

3) I am using Hitec HS-55 for the rudder/elevator, but the lighter / higher torque HS-50s for the ailerons. How much will this weight shift effect my CG and flight performance?

**** Build Question: ****

4) When you lay the metal wires through the wings (for support) how do you lay the wires? The plan says one on top of the other, but Greg Covey's review shows the wires horizontally placed as opposed to vertically stacked.

5) Can I use 5-minute Epoxy on the Depron and EPP?

Any guidance would greatly be appreciated?

Jeremy
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