57" MX-2 from General Hobby

[joeycoates]

So I have a little Evolution 10gx that has been in need of a new home after my Phoenix Decathlon met it's untimely death due to a dead stick landing into a barbed wire fence (12 more inches and she would have made it :facepalm: ) So I have been looking and finally came up with this little guy.

http://www.generalhobby.com/skyline-aerobatic-electricnitro-airplane-green-p-359.html

It is a 57" MX-2 with 654 sq/in of wing area. It is advertised to come in at 4.6-5.3 lbs ready to fly. Now I do not know if this weight is fuel or electric, but my original goal was to try to come in at 6lbs or less dry. The 10gx that I have seems to be an unusually strong one for whatever reason, it swings an APC 13x6 at 10,500 with the stock muffler, and it turns 11,000 with the Bisson pitts muffler which really surprised me. This is an easy 500 rpm's more than what most other are getting. According to the thrust calculators this should make about 10.75 lbs of thrust. Now in my experience this is nowhere near accurate, but if I get 8-9 lbs then I think it should be pretty good.

I ordered the airframe on 2/15 and it shipped 2/16 which is good. However, I paid extra for 2 day shipping and it was sent normal mail, something to be taken up with them later. I ended up receiving the airframe yesterday 2/24.

Upon initial inspection I am really I pressed with it, especially for $140. The covering is very good as is the paint. The construction looks to be very clean but I did of course go over every glue joint that I could get to with mostly thin but also some thick ca in certain places.

Here are some initial pictures and the start of the build process. I also took pics of pieces as I was weighing them to estimate all up weight. So far it looks like I will be under 6 lbs which should be pretty good, maybe not crazy electric power, but using a 6.5 oz fuel tank I will be getting 15-18 minute flight times which is nice.

Total right now is coming in at 5.83 lbs which looks to be ok.

 

[3dNater]

Following

 

[joeycoates]

So I am continuing work this evening. One little item that I found a little different is that the airplane comes with a small DVD instead of an instruction manual, and it is kind of generic covering several different airframes. Really not a big deal to me, the only things you should really need it for is the firewall to thrust washer measurement, and the recommended cg. Otherwise if you have assembled an arf or two it really just kind of falls together.

With that being said, the DVD calls for you to install the horizontal stab, elevators and rudder right off the bat. I do not like assembling in that order as I think it is much easier to get the engine lined up and mounted while tail feathers are not in the way. This allows you to stand the fuselage straight up while getting everything set. One thing I did notice is the recommended distance of 115mm from firewall to the thrust washer seems to be 3-5mm too short. I followed the recommendation and the pattern on top of the cowl going to the turtle deck is a bit off. I am not going to worry about it as with the heavier engine up front I do not mind having it set back a bit, but it is worth mentioning.

I now have the engine, throttle servo, fuel tank and rudder servo mounted. I have also fitted the cowl and trimmed it to the muffler and spark plug boot as well. The cowl came withing 1/8" of clearing the plug boot, but I did have to make a small hole to clear it, kind of looks like an igniter hole for glow. I still need to block off the hole opposite of the cylinder head in the cowl, and I am going to cover the open structure of the F2 former to prevent the fuselage from being pressurized by airflow, and to prevent exhaust gasses from going into the lower fuselage. I will probably cover the top, bottom and sides of the engine box while at it. Lord knows I have more than enough scrap white covering.

Once that is done I will move to the tail feathers and landing gear. The ignition box for the 10gx comes with quite a long spark plug lead so I will have some flexibility in where I mount it while making sure it is not too close to the receiver. This should help however with getting the cg right without having to add any weight. So far I am very impressed overall with the airframe, especially for the price. If it flies as well as I hope it does then I will be pretty pleased.

Some pics...

 

[joeycoates]

Ok, it is now complete and ready to fly. Everything went really well, it is a very easy building airplane. I really did not run into any noteworthy issues, but as is to be expected a little bit of the hardware was not up to par. Some of the ball links in my particular kit were just way too tight and no amount of exercising them would loosen them up. But that was really it.

I did cover the motor box and the F2 former, it looks clean and a ton of air will not be going through the fuselage. Since it is not electric I do not need the airflow, and I would not have anywhere for it to escape to. I ended up using a small clear plastic cup to block off the non-cylinder side of the cowl. I cut a small opening in it to deflect air onto the bottom of the case, but mainly it is there to block air from going in that side and right back out causing the engine to possibly overheat.

So once all.was said and done it came in at 92.5 oz (5.75 lbs) which is 1.3 oz less than my initial estimate, and about 4 oz less than my initial.goal. I do not know exactly how much thrust an APC 13X6 spinning at 11.5k makes, but I do know that it is over 7 lbs which should give it a better than 1:1 ratio even with 6.5 oz of fuel on board. If I really wanted to I know I could cut another 2-4 oz off by ditching the wheel pants and spinner, but it looks good so I will hold off on that. I really hope it flies as well as it looks!

 

[3dNater]

Do you have any other props to try? I bet a 14x4 will give you a bunch more thrust.

 

[3dmike]

Great build thread [MENTION=3746]joeycoates[/MENTION]! Don't ditch the pants! I have always thought how weird a plane looks without it's pants. Maybe it's just me.

 

[joeycoates]

I agree, it just looks better with the pants, same thing with spinners. I have seen people ditch them for a bit of weight savings and it just does not look right.

I do not have a 14x4 yet, but have already planned on trying one. For whatever reason (not that I am complaining) my little 10gx runs very stong so I am really looking forward to getting it up.

 

[SnowDog]

I don't use pants because I fly on a grass field and the pants will be worn out and shredded within 10 flights.

 

[3dmike]

Wow how high is that grass?

 

[joeycoates]

Ok, so we FINALLY had some nice days to fly in the North Texas/Dallas area! For the last two weeks it has either been snowing, sleeting or raining. Our area lakes have been low for years now and I think that most of them are finally back up to a fairly normal level which is good.

Anyway, I was able to go out and fly the little MX-2, and this is one very, very nice flying airplane. I cannot imagine a way to beat it for a 3D type full airframe for $130, I have not even found anything CLOSE. The knife edge is great with just a very slight tuck (which might be fixed with CG, the 45 degree inverted test seems to show it can come back a bit) and the flat spins are just fantastic. I have not had a chance to fly it just a whole lot yet as I am still working on getting the 10gx engine sorted. I am getting close though, one of the main issues has been that it keeps on spitting the pressure line off of the muffler. The Viton fuel tubing that the engine came with keeps on splitting at the pressure nipple, and Tygon melts... I just put the Viton back on with a piece of Tygon over it, I have read where the Viton they ship with the engines has this issue but if you order it direct it does not. Either way I now know that:

1. It will recover from a flat spin while deadstick
2. It has a pretty darn good glideslope
3. No bad habits while slow (does not fall off in either direction hard)
4. It slows down very nicely without an undue propensity to balloon

To be perfectly honest, I have only landed it under power I think three times out of ten or so flights! Like I said though, I am pretty confident that the needles are sorted if I can keep the dang pressure line on, I have never had so many issues with something so simple. As far as flight characteristics, from what I can tell it has a little bit of wing rock which CG might help, but I have not really put enough trust in the engine yet to get too low and slow. It does hover well though and the 10gx has plenty to pull it out. Maybe not ballistic, but comfortable. Once the engine is completely sorted I might stick a 14x4W on it to see how that does, I am pretty sure it will turn it. The rolling harriers are pretty good as long as I am careful not to let it start to wrap up too fast, smaller airplanes seem to get going pretty fast as compared to a 30cc or larger due to the weight and momentum. All control surfaces seem to have more than enough authority to get out of whatever I seem to get myself into. The snaps both positive and negative are simply violent. One thing I did note however was that I needed to wrap just a little bit of tape around the locating dowels for the wings otherwise they were able to shift up/down maybe 1/2 degree. Once I wrapped tape around each of the rear locating dowels it was all tight.

As far as the hardware, most all of it was good. The only pieces that I replaced were some of the ball link as they were too tight for my liking and did not seem to want to loosen up. Some of them were ok, but others were just too tight. Also, if you do choose to build it gas, the fuel tubing to be used in the tank is reportedly gas friendly, and maybe it is if you do not mind the tubing swelling to twice its normal diameter! I found that out the hard way.... I had already put a Dubro gas stopper in it, but the instructions specifically stated that the tubing was good for gas applications. Other than that the supplied hardware was actually pretty decent.

With all of that being said this little airplane is the real deal. It flies better that my old Funtana X50 (which was a favorite) and better than my old Reactor 50 (which for whatever reason I did not like as much as the Funtana). And the MX-2 is cheaper than either. I think the Funtana might have come out a bit lighter, but I was also running a 55ax in it and not the gas engine which is heavier. Either way the MX-2 has more wing area. One of the best things about the airplane is that it is fairly cheap. While I do not ever want to put one in, I just do not have as much fear of something bad happening when the airframe is only $130. Sure it would hurt, but not as bad as it could be! Due to that I think I can do a lot of learning with this airplane, and it is really sharp on top of it all. Today at the field people first commented on how good it looked, and then after a few flights I had a lot of people come over to comment on how well it flew. Like a bunch of guys with 30-60cc airplanes were asking questions, when I told them the plane sells for $130 they were asking where from? So it gets a thumbs up to the point where if I do stuff it I will be ordering another one, it would be worth replacing.