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Old Oct 13, 2012, 04:21 PM
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HK Mini P-51, Taking the Scenic Route, Part 1

I could probably better title this "More Money and Time than Brains", or "I Can't Believe my Wife Didn't Stop me From Buying Another Plane."

Either way, with limited flying experience, a semi-limited budget, and limitless understanding from the Minister of Finance (my wife) I ordered the Mini P-51 from HobbyKing.

To be honest with myself, I'm not ready for it, and I'd wager that if I were to fly it right now it'd be scrap within minutes. But this isn't a plane I purchased to fly RIGHT NOW. It's more of a "wait until Spring" project, where I've allowed myself time to build the plane and develop the skills. Plus it gives me something to tinker with in the meantime.

The hangar currently houses:
1. Hobby Zone Super Cub, modified with a flattened wing with ailerons and an upgraded ESC and RX. Otherwise it's pretty much stock. It's been crashed and repaired a number of times, but still flies great (now that the electronics are upgraded). It's currently 20% epoxy by volume. When it hits 40% I'll buy a new fuselage and wing and re-build it completely.
2. Park Zone Ultra Micro T-28, which is a blast to fly. Considering how fragile it is, it's still in great shape and is my go-to plane when I have only a limited amount of time/space to fly. There is a small-ish park near our house, too small for other planes, but the UM is perfectly at home there.
3. HK Atom Mini Glider. This one is actually my son's plane, but I bought it for him so I'm considering it part of MY hangar! Bone stock, and it'll probably stay that way.
4. Black Horse balsa ARF Piper Cub, 60" span. The plane that started it all for me, a gift from the estate of my dad's friend. It's never flown, and it's got some sentimental value so it may never fly. But it looks good hanging in my office.
5 thru 8. Four differnt scratch-built foamies. Three are from the Flite Test website; a NutBall, an FT Flyer, and the FT Delta. These use the same swappable fuselage and the wing is just changed depending on how I feel like flying/crashing. Plane #8 is a FunBat modified to fit on the FT fuselage. These planes are in various states of build. I think I like building them more than flying them at times. Or I like the smell of glue and paint...?

Back to the P-51, my plan is to take my time, go through the plane and fix/alter/change things to make it ready for me, when I'm ready for it. Since I haven't used this blog feature on RC Groups in the past I'll save this now and start my review and build information later.
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Old Oct 13, 2012, 04:28 PM
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HK Mini P-51, Taking the Scenic Route, Part 2

The P-51 arrived yesterday afternoon, at exactly the same time my daughter called and asked me to pick her up at school. It's like she planned this with UPS to make me cry... New toys for dad, and they have to wait.

The box arrived in very good shape, delivered from the HK US warehouse. Everything was wrapped well enough, and the only damage I could find was a small bend at the bottom edge of the tail and a few small scratches. As I unboxed it I went through a mental inventory of parts - wing, fuselage, extra prop & spinner, tools, misc hardware, manual... Um, manual? Is it under the foam? Manual? Nope. Evidently trees are so scarce in China that they can't provide a frickin' manual. Even one page with a few details, such as the Center of Gravity. Naaah, people will buy it anyway, so why bother?

I flipped the fuselage over and found what I expected for the ESC, a 10A unit which fits in along with the aileron servo and pushrods. Not a whole lot of room in that bottom cavity!
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Old Oct 13, 2012, 05:05 PM
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HK Mini P-51, Taking the Scenic Route, Part 3

So all is looking good, except for the lack of instructions. It's time to plug in the RX and battery to make sure everything works. In goes the Orange RX and a charged 2S I had on-hand. Control surfaces check out, so I give the motor some juice. The motor fires to life, but it doesn't sound quite right. After a little digging I find that the spinner is rubbing against the cowl. Not a huge issue, but it still shouldn't happen.

The spinner pops off without much effort, which makes me wonder if it could have come off during flight that easily. With the spinner off I find that the nut holding the prop on is about 4 turns loose. Yeah, that's a slightly bigger issue than the spinner. In my limited time flying I've found that in 90% of cases or more, having a prop attached to the airplane helps the airplane achieve forward momentum. Again, a quality issue.

As mentioned previously, the stock ESC is a 10A. There are numerous posts from people who have used this ESC for many flights without incident. Others claim it's not sufficient, even in stock trim when running a 3S. This is a project plane for me, so I figured I may as well swap out the 10A with an 18-20A (ordered from HK, and currently somewhere between China and Wisconsin). Before pulling the stock gear out I hooked it up to the Watt Meter and a 3S and found it's pulling about 9.6A on the bench. I'm no engineer, and that may be just fine, but I'd rather err on the side of caution and just swap it out. The 10A will be re-used on a different project. The battery planned (and purchased) for this plane is the Turnigy 3S1000mAh 25-35. It's bigger than some people use, but I've heard of people using larger batteries so it's a good compromise for me. I know I'll need to work to make it fit, but I shouldn't have to work THAT hard!

To get the stock ESC out you have to pull the motor & motor mount out and the ESC then can then be unplugged and removed from the fuselage. Easier said than done. To get the motor out you need to remove the yellow cowling which then gives you access to the firewall screws. The cowling is super thin plastic and held on by double-sided tape. I snuck an Xacto blade in all the way around it to loosen it up, and finally it came off. The three screws for the motor mount are easily accessable now with the supplied screwdriver. Once they're out, pull the whole assembly forward and the ESC bullet plugs are now barely accessable so you can unplug it.

The stock motor mount is made from two layers of plastic sandwiching some foam from the fuselage. The front plastic on mine was loose, so I pulled it out and epoxied it back into place (hopefully not screwing up the alignment in the process). As I was checking out the naked fuselage I noticed an open cavity above the battery compartment. I don't know if this is mainly a cooling duct or just open to save weight, but it might be a good location for the ESC. Moving it from the bottom would help prevent it from fouling the aileron servo. At the same time it would move weight UP, which may not be the best plan. Time will tell.

So the cowl, motor, motror mount, and ESC are removed, and it's time to find a way to make my battery fit. It's too wide to fit past all the "ribs" inside. Others have cut out the floor or done semi-major surgery to get a battery in the plane. From what I can see it looks like I only need to widen the existing slot. A sharp blade, some good lighting, and about 20 minutes of work later and the 1000mAh slips right in and has a nice friction-fit. Since the plane is currently in many pieces I don't know if it goes far enough forward for a good CoG, but if needed I'll cut on it some more. I think I can get another 1/4" or so.
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Old Oct 13, 2012, 06:09 PM
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HK Mini P-51, Taking the Scenic Route, Part 4

Before I forget to mention it, the lack of manual or pictures or diagrams of any manner annoyed me. Almost as much as trying to work on a plane with no landing gear and an oddly shaped bottom.

It would have been helpful if the manufacturer included some kind of stand to hold the plane stable while it's worked on.

Oh, wait a second, they did. It was a block of foam taped into the original shipping box. It wasn't labeled or marked, just taped into the box like a big wedge. Had I not seen a picture of somebody else's planes sitting on it I would probably have thrown it away.

It works quite well, by the way.

So the motor and ESC are out and I'm waiting for the 18-20A ESC to arrive on the slow-boat. The original ESC was connected via some decent quality bullet plugs. I had thought about just cutting the wires and soldering in the new ESC, but then it dawned on me that I could just de-solder the old plugs and re-use them. Out comes the soldering gun and a few minutes later I've got the plugs off and ready for the new ESC. I like these plugs and would use them on other builds in the future. They fit very tightly and don't feel like they're going to accidently come loose any time soon.

On to another area of the plane, I had read a few stories about the canopy blowing off at high-speed. Most of these were from people who modified their birds to get extra speed while mine will be left stock. However, I haven't found any replacement canopies for sale yet so I decided to take a little extra caution and add an extra magnet at the front of the canopy. A small hole was drilled and the rare earth magnet was epoxied in place. While I was at it I re-glued the other three magnets since they appear to have been installed with some pretty rubbery adhesive - two of them came loose while I was removing the canopy.
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Old Oct 13, 2012, 06:21 PM
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HK Mini P-51, Taking the Scenic Route, Part 5

So I've got a few hours into the build (re-build?) so far and I have some comments about the plane.

Overall, it seems like a decent deal at $60 USD. Right out of the box it could have been flown as-is. There are a few quality issues that should either be noted or acted upon by anybody buying this plane.

- The ESC is maxed out in the stock configuration. If you re-prop or create more power you'll probably want to replace it.
- Replacing the ESC is a pain.
- Check the prop nut and secure the spinner.
- Check spinner clearance to the cowl.
- Find the instruction manual online and print it. It's not great, but it's better than nothing.
- It would be really nice if spare parts were available from HK. Props? Replacement spinners? Fuselage or wing? Don't tell me they wouldn't make some good coin selling these parts!
- The finish/design of the plane is pretty good. This would make a good (and expensive) display model.
- The foam is about as fragile as an eggshell. I swear I could see my fingerprints embedded in the foam!
- The stand is a nice touch, it would have been nice to know it was a stand and not just a chunk of foam though.
- A bigger battery box would be a plus, but the foam is easy to cut so it's not hard to customize it to fit your needs.

That's about it for a little while. I'm tired of working on it, and it's time to eat. Here's hoping I don't crash and burn this baby on it's maiden!
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Old Oct 26, 2012, 10:00 PM
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The new ESC finally arrived, and then I realized I didn't order the JST connectors for the battery connection... They're currently on the way from Hobby King, along with a bunch of other bits and pieces for the P-51 and other projects.

Quality shrink tube is always nice to have. I've had thick and stiff shrink tube in the past and plenty of shrink tube that didn't work worth a damn, but I really like this stuff pictured from Summit Racing. I bought this full kit years ago for my automotive work and it includes small enough tube to cover a single wire as well as the really big stuff that is large enough to shrink wrap an Orange RX 6 channel receiver when removed from the case.

Back to the ESC, it's a little bigger than stock but there is plenty of room inside the P-51's belly. When test-fitting it I noticed that it kept getting in the way of the wing attaching bolts. To keep this from happening I simply hot-glued the ESC in place directly between the bolts. I did have to fiddle around with removing the motor while doing this to help get the wires tucked up nice and neat inside. Kind of annoying, but that's life.

I also got around to working on the magnets that hold the cowl in place. It looks like it'll work well enough. I still need to add the small pins to keep it straight, but that'll be a quick/easy addition.
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Old Dec 17, 2012, 07:52 AM
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I just got this plane for my B-Day and had to do some of the same mods. I haven't widened the battery bay yet but I did put a 30amp esc in it (a spare from a decommissioned plane). I'm going to start with a 800mah battery and see if I can balance it just before the 8.5" CG so it's a little nose heavy. Seen some people recommend this in a couple youtube videos. Eventually I'll be adding the rudder. All in all it looks like a blast to fly; fast, stable, and responsive.
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Old Dec 17, 2012, 03:01 PM
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Just wanted to send you a FYI. Maidened the plane today with a 30amp ESC, 1500mah 30c 3cell lipo, and stock motor. I had to melt some area in the fuselage with a flat attachment to my soldering iron to get the room for the battery. I was able to push the 1500mah lipo up under the hood until only the back end was in line with the fake instrument panel. It balanced out right around 8.5" from the top of the spinner, right where the instructions called for. 13oz all up weight, a little heavy but a 1000 or 800mah lipo would only save 2oz. Tossed it into the sky on about 1/3 to 1/2 throttle, hung in the air plenty of time to get my throwing hands on the sticks then I throttle up to over half throttle. She hummed around a soccer filed size are super smooth and very nice turns. Had to keep the nose pointed up a little in the turns in order to get level turns or she would tend to dive down a little and loose a couple feet of altitude. No crazy tricks because it was the maiden and small area. Little windy which caused the plane to 'bob' up and down in the air at times however she cut through the wind like hot knife through butter! I'm more of a scratch build guy and this is my first 'scale' ART plane. Very impressed with the flight characteristics; smooth, fast, predictable, and fun. Would highly recommend.

One issue, I set the timing and frequency on the ESC to high out put (22-30 degree timing and 16kHz frequency) and locked my engine up. I've never fried an engine but pretty sure this one is toast. Found a replacement on HeadsUpRc dot com; HURC 2712-17 Outrunner Brushless Electric Motor. It's a 300 class engine with a firewall mount, 1700 kv, puts out 15oz thrust with a 7x3.4 prop ("GWS EP 7035 prop produces about 15 ounces of thrust at 7.5 amps with a pitch speed of 46 mph. Excellent prop for this motor.") or you can use an APC 7x5E prop ("produces about 15 ounces of thrust at 11 amps with a pitch speed of 49 mph. Avoid constant wide open throttle.") I'll re-post with my thoughts on the new engine after the New Year.

2712-17 Specifications:
Weight (motor only) = 0.9 ounces (25 grams)
Diameter = 1.1 inch (28mm)
Total Length = 1.7 inch (43mm)
Shaft Length = 0.4 inch (10mm)
Shaft Diameter = 3mm
Voltage = 7 to 13
KV = 1700
Current = 10 amp max.
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Old Dec 17, 2012, 03:10 PM
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Found another replacement engine on HeadsUpRC, however this one is 1/2oz heavier:
Emax CF2812 Outrunner Brushless Motor
"The EMAX CF2812 is a 1.4 ounce, 1600 KV, direct drive outrunner brushless motor that works well on small, high speed parkflyers, and on models that require the use of a small prop (such as pusher models). It will produce about 23 ounces of thrust using a 3 cell Lipo battery and a 7 inch prop."
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Old Dec 18, 2012, 06:12 AM
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Thanks for the information, I'm looking forward to getting my P-51 in the air (eventually). It'll be Spring before that happens though...
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