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Old Feb 07, 2011, 11:50 AM
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Mini-Review
HobbyKing Monster 1.55m P-51 REVIEW

P-51 Monster Mustang 1.55m 5Ch XL-EPO (61inch) ARF




http://www.hobbyking.com/hobbyking/s...dProduct=12166

Introduction
This is a relatively large size foam plane. It is made from EPO which is more durable then EPS. The quality of this particular EPO foam is on par with many other "EPO" types out there from various manufacturers.
This plane comes in three variant color schemes. for this review, I have the "Big Beautiful Doll" version.
The other two can be located here:
Green: http://www.hobbyking.com/hobbyking/s...dProduct=12163
Black: http://www.hobbyking.com/hobbyking/s...dProduct=12167
All three versions can be purchased directly from www.hobbyking.com or through their German, Australian, and USA warehouses. They are listed at varying prices depending on the warehouse you decide to order from since customs charges and handling, etc may already be included. The Hong Kong warehouse listed price is $199.63. This is the main warehouse and ships world wide. Shipping price to the US at zipcode 80524 comes out to be $62.54 for a total of $262.17
At the USA warehouse at the time of this review, the price is $222.38 with shipping of only $0.1. Yes thats correct, 1 cent. So, a real good buy right now.
http://www.hobbyking.com/hobbyking/s...dProduct=14906

Specifications
  • Wingspan: 1550mm
  • Length: 1350mm
  • Propeller: 4 blade (included)
  • Weight: 2300g
  • Motor: C4250 Brushless outrunner 600kv (included)
  • ESC: 45A (included)
  • Battery: 14.8v 2600-3000mAh 4S1P (not included)
  • Servos: 8 units (included)
  • Retracts: 3 x Electric Retracts (included)

Needed for Completion
  • 6 channel radio
  • 4s 2600 or larger lipo battery

For this review, I was sent two Turnigy 4s 3000mah Nanotech batteries from Hobbyking. These are pretty slim and I was surprised how small they are. They are rated at 25-50c discharge and can be charged at a 5c rate. Pretty impressive charge rate. Some of these new Nanotech batteries can be charged up to a 15c. Price of this battery is $32.44
http://www.hobbyking.com/hobbyking/s...dProduct=11920


Packing and Contents

Since the plane is decent size at 61 inch wingspan, it is shipped in a pretty good size box.

Removing the wing halves, this is how the rest is packaged:


The walls of the foam container are pretty thick and there was no damage to the box itself. Internally, there are several compartments with various items located within. Please be very careful removing each item as I found some were wedged in pretty tight. One note, the tail assembly which includes the vertical stablizer and rudder as well as the elevator and rudder servos/tail wheel retract had a minor bend/crease at the very top of the rudder itself. This seems to be due from the person packing the box at the factory as there was no evidence of distortion or damage to anything else or to the interior of the shipping box compartments.
Now for the complete contents of the box as it arrived:


The decals are sticky back types and adhere quite well to the foam.

Building and Constrution Notes
The main fuselage is a nice large piece with plenty of room for electronics. The included 600kv motor is already installed on a plywood firewall that forms a sandwich of the firewall, foam and a backplate of ply. This is a very secure setup and the firewall will not pull out of the airframe. The included esc is only a 45amp and is already hooked up with a Deans male connector. As you can see, there is ample room for various size batteries.


While the esc is ok, I believe it is at the very limit of capability for this size motor and propellor size. I highly advise replacing it with at least a 60 amp, but it will get you up in the air quickly. Just dont hold full throttle long. When I initially tested the motor, with the 4 blade included prop, the amp draw was pretty close to 42 amps at 650 watts on a 4s 20c 4900 Rhino battery. The 3000mah nanotech 4s batteries I was sent have a higher discharge rate and thus can up the power a little, so the 45 amp included esc was at the extreme max at full throttle. You never want to push an esc to max limits for long, so replace it when possible. As a note, the included 4 blade prop is about a 14x7. This basically equates to a 16x5 2 blade prop, so don't expect stellar speed from the stock setup. More on this later.

The manual direct you to begin with the wings. Pictures in the manual are quite small and some are hard to see what the text is specifying, but it does get the job done. Now, the biggest issue with this plane is it is not setup to have removable wings. For a plane this size, that's a problem. I will detail the modifications I did later, so don't fear, it can be overcome.
All the servos are already installed, so it really is a pretty fast build, although it will take a fair bit more time then simply 1 hour as listed on Hobbyking's website. You must install the main retracts in the wings including putting the struts into the retract units themselves. The struts are held on by two grub screws. They seem to hold the strut ok, but seemed a little soft to me. Time will tell if they hold ok. The retract units are screwed down onto plywood plates. Make sure the painted silver plates are glued down all the way as a precaution. One of them was slightly pulling away on mine. No big deal, just check it.


The wings are held in place by two aluminum rods that pass through the central fuselage. There is no direct hole location on the wings that you can see, but there are carbonfiber tubes imbedded in the wings for these rods to slide into. The best way to locate them is simply place the rods in the fuse(they also come with black plastic sleaves that rest in the fuselage) only part way and place a wing half up against the fuse side. One the wing half is butted up against the fuse, push both rods against the wing half to mark the foam with a depression. No need to press too hard, you only want to make a mark so you can then use a drill bit or other tool to relieve the foam there to allow access to the imbedded reinforcement tubes in the wings.


Once you complete this for both sides, make sure all the servos in both wings work first before doing anything else. All of them worked fine on mine, but it's prudent to check because at this point, the manual wants you to glue the wing halves to the fuselage making them permanent. I used a slight bit of epoxy on the black sleaves that sit in the fuselage portion to keep them from moving. I suggest you do this also. On mine, since I made the wings removable, I did not glue both alumuinum rods to both wing halves. What I did was glued the portion of the front aluminum rod that sits within the right winghalf and did the same to the portion of the rear aluminum rod that sits within the left wing half. This way, both wings can be slid out and the rods themselves aren't lost while transporting the plane. One is permanently attached to one wing half and the other permanently glued to the opposite wing half while both will slide into the opposing wing half for structural support when the plane is assembled.

Tail section

The tail area is a nice complete unit by itself. It is simply glued to the main fuselage and all the wires are routed through the middle. My main complaint about this area is that the servo controlling the tail wheel steering is not at all accessible. There is no way to remove it without doing surgery on the tail unit. This ended up being a problem on mine. Yes the servo worked, however, it was for some reason functioning opposite to the rudder servo when hooked up. The kit comes with several y-harnesses labeled with the appropriate channels theya re to be used with, so you are supposed to have both the tail wheel steering servo and the rudder servo connected to the same channel. Using that specific y-harness, the two servos operated in opposite directions. Now, I cannot comment on whether this was a mistake, such as someone in the manufactoring process gluing one of the two servos in backwards or not or whether the pull-pull cables may have been installed incorrectly by the factory or neither. I simply don't know.
There are a few remedies for this if it does happen with yours.
  • Use a 7 channel radio and receiver and simply mix the two to the rudder channel and reverse one or the other to make them work together
  • Use a servo reversing y-harness instead of the included y-harness
  • Remove the pull-pull cables and switch them at the steering arm on the tail retract unit.

I decided on the last option since I was planning on using a 6 channel receiver. I could have easily used a mix as the radio I use is a 9-channel JR 9303 2.4g spektrum, however, not everyone has the extra channels so I wanted to use a fix that anyone could do.
Here is a pic showing the cables criss-crossed after I changed them. When the plane arrived, they were straight back from the steer arm to the servo arm. To do this, you need to unscrew the retract unit and remove the cables carefully and replace to the opposite side from which they originally were hooked up on the steer arm only.


Before I swapped the pull-cables around, the tailwheel steering was functional, but notat all precise by any means. It would have been very hard to keep the plane straight even if the steering servo was workign in the same direction as the rudder servo out of the box. If you look again at the above photo, you can see the pull-pull cables have springs in them, but one of them is stretched out significantly more then the other. This is where the slop comes from. Now, added to this problem, once I swapped the cables over, the slop became really pronounced to the point I couldn't get the tail wheel back to center deflecting the radio's rudder stick all the way even at 125% travel adjustment. So, an additonal fix needed to happen and the only way to do this was to remove the steering servo to get at the pull-pull cables to either replace them with crimp style with no spring or to cut and modify the current cables to remove the spring section.


I wanted to use the included cables to make this happen in case someone else ran into this and didnt have any pull-pull cable stuff lying around. So, once you cutout the servo as shown, you can remove the cables. But, be warned, you can't simply cut the spring section off as the cables would then be too short. What you need to do is straigten the spring section out. Do this using two pairs of pliers and pulling one set along the spring section to smooth it out as best you can. There is no way you will get it completely straight, but that isn't necessary. Now, test fit one cable and measure about how long you need once the servo would be back in its original position. Don't glue this back in yet, just test fit and measure the length required. Give yourself extra room length on the cable by about 2 inches. Put a cable on the servo arm with about 1 inch poking through the other side. Bend the cable towards the direction the stearing arm is and twist that 1inch portion around the cable to secure it from coming off. Do this for both sides. Now, replace the servo unit back in position(still dont glue in yet) and put the other ends of the cables through the corresponding holes for the stearing arm of the retract unit. Make sure the stearing arm is close to straight side to side so you get good deflection both directions. Pass the cables through the hole and bend them in a backwards loop making the cable length itself as tight as possible. Do not wrap or twist the the excess around the stearing arm or the wire cable wont slide through when the tail wheel is retracted, but do bend the excess around in a half loop so they dont come off. Another idea would be to use crimps on these ends when the tail wheel is fully down and locked, not retracted.
Here is a pic of the tailwheel servo once glued back in place. You can see the cutout lines.
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Old Feb 07, 2011, 11:52 AM
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Canopy

The battery hatch is a nice large piece, but you still need to glue in the pilot and glue the canopy on.


The black foam pieces for the exhaust are somewhat delicate so please be careful. I manged to crunch one unknowingly.

The elevator halves are simply glued in place. There is no joiner rod or internal aluminum/fiberglass support rod.

Installing the spinner is rather easy. But, the stock prop comes in 6 pieces. 4 blades and two part hub which is screwed together. I recommend epoxing the entire assembly.
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Old Feb 07, 2011, 11:57 AM
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Battery placement

There is a lot of room for battery location to get the CG right. What i did was cut out a piece of the foam box the plane was shipped in to make a block so the battery cant move forward. I cut two pieces of balsa stock and glued them in place to wedge the foam block in place. This makes it removable in case I ever use a longer battery.


The battery pictured is a 5s 5000 turnigy 25c pack. With the pack where it sits, the CG comes out slightly nose heavy from the manual. This is a good thing
Behind the battery, you can see another foam block sitting there to prevent that battery from moving rearward. This spacing was done in case a different weight battery was used and needed to be positioned more aft for proper CG.
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Old Feb 07, 2011, 12:05 PM
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Balancing

I have to admit, this plane is pretty easy to balance since the battery area is so large. I used several different battery setups and the CG didnt really move much. I used a 4s 4900 rhino, a 5s 5000 turnigy, and two 4s 3000 nanotech batteries in parallel to test CG and all of then came out really close without moving anything forward.
Here is a pic of the plane balanced with the nose slightly down with the two 4s 3000 nanotech batteries in parallel. This gave me a comfortable 6000mah capacity.
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Old Feb 07, 2011, 12:08 PM
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Transportation

Since this plane was not designed for removable wings, I decided to take the plane to the field as one piece to show how much room it takes up in a standard SUV. This is a Jeep grand Cherokee.


I could fit one other smaller plane in the vehicle, but that's it. I will detail the removable wings in just a moment.
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Old Feb 07, 2011, 12:11 PM
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Flight Report

The winds were pretty bad the day I had available to do the test flight. They were around 20mph, but, mostly straight down the runway. So, this would be a good test of the power available on the stock setup as well as test the rigidity of the wing mods for making them removable. If the plane can take 20mph winds, then its going to be just fine during better flying conditions.

As a note, because of what I did to the tailwheel steering and removing the springs and such, I had absolutely positive steering control. This was essential given the amount of wind i was delaing with. Since the winds were that high, i used both 4s 3000 nanotech batteries to give as much weight as possible for the plane.

I was able to keep the plane straight on the roll-out, but, because there was somewhat of a crosswind, once the plane left the runway, it was blown fiercely to the left and right rudder deflection kept it from being blown into the next county.
Trimming the plane was not too bad. i didnt need any aileron trim, only some down trim to keep the plane from climbing. this was both a result of the wind and maybe a little up in the neutral position of the elevators.
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Old Feb 07, 2011, 12:17 PM
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Ok...here's the test flight video. Winds were horrible at 20mph, but, in the middle of winter, well, at least it was 40 degrees instead of 20 with snow everywhere.
At the end of the video, you'll see the plane drift quite a bit. Since the plane is so light, even the rudder had a hard time keeping the plane from drifting A LOT as the speed was decreased on approach. I didn't want to risk trying to go around that time since the winds just seemed brutal, but I should have started the decent further out away from the runway. I had anticipated it drifting sideways some, but it was more then I was expecting as it got slower.

2011-02-05 19.06.40 HK 1.5 P-51.avi (4 min 28 sec)


Now...at the end of the vid..you'll see the factory didnt use much glue on the main retract hard points. I have since reglued this area with a lot of epoxy.
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Old Feb 07, 2011, 12:20 PM
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So...now I will describe the removable wing mods I did to the plane.

There are tabs on each wing half that get inserted into the fuse. On those, I hollowed out some foam and glued in some plywood. These are bases for glueing in place some blind nuts(or T-nuts as they are called at Home Depot).

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Old Feb 07, 2011, 12:25 PM
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Once the ply plates were set in place, the wing halves were re-inserted into the fuse of the plane. Then, I marked and drilled two holes per side and stopped once I got to the plywood. This marked where the holes needed to be.

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Old Feb 07, 2011, 12:30 PM
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Now that the plywood plates were marked, I could drill them out once they were removed from the wing halves and then place the blind nuts securely under them. Then, the wood plates are glued on making sure they line back up with the holes on the bottom of the fuse.
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Old Feb 07, 2011, 12:34 PM
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Two more wood plates were cut and are used on the bottom of the fuse for the hex head bolts and washers to press down on. These were of course drilled for holes to match the plates used on the wing halves

Now, I applied epoxy to the wood plates that will sit on the bottom fo the plane, then inserting the wing halves back in the fuse and pressing the wing hard against the fuse, insert the hex head bolts through the bottom wood plates, through the foam of the fuse into the wing tabs where the blind nuts are. Now.....hold the wing half in place as the epoxy on the wood plate on the bottom of the fuse dries to give as close fit as possible. Repeat for the other side. I also painted the wood plates silver prior to glueing them in place.


Once both sides are done, you have this:
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Old Feb 07, 2011, 12:39 PM
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At the front of each wing half along the fuse, I also glued on rare earth magnets and metal strips to help keep the wing from trying to pull away from the fuse. These weren't necessary and in the end, didnt do much, but hey, it was worth try.

With the two bolts per wing half, the wings are quite stable and strong since they have the aluminum rods and carbon fiber tubes for strength.

Now please keep in mind, you will need some additional servo extension wires if you want to make the wing removable to have easy access to the wires, but in the end its really worth the trouble to do all this since it can now be transported in a much smaller space.
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Old Feb 07, 2011, 12:46 PM
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Conclusion

This really is a decent plane, even with some minor issues you might have to deal with. What arf doesnt require you to think a little, honestly. For the price and getting full house controls, including electric retracts all the way around, motor, an esc usable in probably something smaller, and servos already installed that seem to wrok just fine....it's not a bad buy at all.
Its larger then an FMS and only marginally smaller then the new 63" Starmax.
It flies well, even on the stock power setup, although many ppl have decided to use a 14x10 2 blade prop on the stock setup or simply change the motor to something else.
The stock motor can take a 5s battery using the stock prop, but you MUST change the esc for this. It is unclear how long the motor might last on 5s though.

Pros:Nice size
Decent motor
Scale looking prop
Electric retracts
Not really expensive and uses a 4s batteries that most ppl can afford and have chargers for.
Lots of room for batteries and the plane can carry the weight easily of large capacity or higher cell count

Cons:
Wings were not designed to be removable
Tailwheel steering was quite sloppy, but fixable
Tailwheel steering and rudder servo didnt act in unison on my sample
Included ESC is too small for the job

I would like to note though that hobbyking DID send me a 60amp esc to use as a replacement. I wanted to use the stock esc for one flight for this review just to see if it would work ok. I have seen reports, however, that the stock esc doesnt hold up long, so please change it to at least a 60
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Old Feb 07, 2011, 03:42 PM
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Nice. How did you get them to send you a 60A esc, as follow up on this review?
They can send me anything they want, I'll give them my honest opinion on it
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Old Feb 07, 2011, 04:22 PM
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As part of the review yes. I have already installed the 60 amp esc along with a separate BEC to use the next time weather permits getting the plane to the field. At that time, I will test out the stock motor on 5s to gauge speed difference. Probably also bring a different 4 blade prop to test on 4s.

Winds were just too much to try and swap out the stock esc at the field and then try another flight.
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