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Sport Planes (Formerly I/C & Gas Conversion) Discuss I/C or Gas Conversions, Aerobatic Planes and Sport Aircraft

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Old 01-08-2011, 04:32 PM   #1
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Default HobbyKing Pitts Model 12

Here's my youngest holding the Pitts Model 12 I've just put together.

It's the HobbyKing 42" ARF: http://www.hobbyking.com/hobbyking/s...idProduct=8785

I had to do a lot of work to get it into flyable order. The original fuselage was very badly twisted, HobbyKing replaced it which was good as I stripped the covering off the original, straightened it, and recovered, so I now have a spare fus.
There were a few other quite serious issues with the kit;
The worst one is the method of connecting the top and bottom ailerons just doesn't work at all. Fixing it properly meant stripping the covering off all four ailerons and building in anchor points near the aileron trailing edges for struts to join the ailerons. You can see that the aileron colour is slight different to the wing due to the new covering not being quite a perfect match. it might be possible to botch up a solution that did the job without re-covering the ailerons but better do the job right IMHO.
The plywood motor mount also needed beefing up. As standard it could barely support it's own weight and was already falling apart when it came out of the box. The reviews on-line mention motors falling out mid flight and I'm not surprised. The only surprise is that the motor stayed attached long enough to get airborn! The other weak areas that I beefed up were the cabane strut mounting to the fuselage and the lower wing where it bolts into the fus.. These may have been strong enough for gentle use but pulling a few 'g's would have ripped the wings off I'm pretty sure.

One thing I wished I had changed but haven't yet is the control surface hinges. The kit came with cheap flexible sheet hinges which are fine for the tail surfaces but they are quite stiff and with 4 on each aileron there is a lot of stiffness in the movement of the ailerons. I may yet have to cut them free and put 'proper' hinges in. I'm going to get some higher torque servos for the ailerons and see if that does the trick, if not it's time to chop the old hinges out which may be a tricky job.

All I'm waiting for for the maiden is a tailwheel assembly (the kit one is horrible and far too heavy) and the new high torque metal gear aileron servos.

Would I recommend this kit?.. Well even with it's issues it was good value for the price I paid and if you are happy to do quite a few modifications and aren't too concerned that the instructions supplied are worthless, then it builds into a nice looking model which I think should go rather well.
If you want a quick and easy to assemble model that goes together right out of the box then probably look elsewhere.

Hope you like it....


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Old 01-08-2011, 05:29 PM   #2
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Nice! I've got one that is quite a bit larger (27%) but I'm sure that one will fly a lot like it.

hands on the sticks all the time!!! These planes go exactly where you point them... whether you want them to or not!

2012 SEFF Night Bowling Champion!
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Old 01-08-2011, 05:45 PM   #3
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Originally Posted by firemanbill View Post
hands on the sticks all the time!!! These planes go exactly where you point them... whether you want them to or not!
Yep.. that's what I thought.. i just hope i dont inadvertently point it vertically into the ground
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Old 01-08-2011, 05:56 PM   #4
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Originally Posted by JetPlaneFlyer View Post
Yep.. that's what I thought.. i just hope i dont inadvertently point it vertically into the ground
LOL, Yeah I worry a little about that every time I fly mine too!

It sure does get your adrenaline pumping!

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Old 01-21-2011, 10:03 AM   #5
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Bill,

Curious to know where the CG was set on your Pitts? The joke of a manual supplied with the kit doesn’t cover it and while I'm pretty happy that I've calculated the required position accurately (at or just slightly behind the lower wing LE) it's always good to hear what others are using. It will need a little noseweight to get the CG right, If I'd have known I'd have gone for a larger battery.. If all goes well with the maiden I might just invest in a bigger battery or two anyway.

Weather permitting it should fly this weekend. I got my new servos (Bluebird BM-380MAX) these appear to have adequate torque and with their metal gears are tough enough to move the horribly stiff ailerons but there is a lot of buzzing at full travel due to the resistance put up by the cheapo hinges.... Might get around to replacing the hinges eventually but it will have to do for now.

Most of my flying over recent years has been freeflight, micro RC, or gliders.. So slightly out of my comfort zone with this one....Wish me luck!

Steve
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Old 02-05-2011, 12:44 PM   #6
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I maidened the Pitts and I'm pleased to report it went pretty well. I was concerned that the little wheels might struggle on grass but she took off fine, tracked straight and lifted off on about 3/4 power.

Full throttle gives startling acceleration but for mild aerobatics 3/4 throttle is plenty and for stooging around half throttle is fine. Trim wise it was pretty close, no aileron trim required and just a few clicks of up elevator which is to be expected given the symmetrical airfoil and zero-zero rigging angles. Needs a bit more downthrust as full throttle pulls the nose up into a vertical climb pretty quickly.

The U/C legs are a bit soft and anything other than a perfect 3-point landing bends the legs out and the prop strikes dirt.. so some carbon fibre U/C legs will be the next purchase.

I'm very happy

Steve
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Old 02-07-2011, 05:47 AM   #7
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Thanks Steve,
I've almost ordered that one about 4 times, and i know I will buy it someday.

I have a a Pitts about 30" ws that is fully ready to go, I am forcing my self to get back to my old flying ability, before I start flying some of my nicer planes, for now I just stick to foamies.

Dave R, Proud PGR rider.
When you have flying skills like mine,
You become a master at repair.
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Old 02-07-2011, 07:15 AM   #8
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Wildflyer,

I'm sure that your flying skills are more than up to it. I actually found the Pitts pretty easy to fly and I'm far from the best flyer on the field. The light wing loading helps, throttle back and everything happens nice and slow, almost trainer like. The trickiest thing I found was down to my lack of recent experience with biplanes.. Throttle right back and it loses speed very quickly due to all the drag. This caught me out on a couple of landings where I came in shorter and harder than intended.. For best results you need to keep a bit of power on during the finals.

I see Hobbyking are out of stock again anyway

Steve
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Old 02-07-2011, 08:13 PM   #9
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Thanks for the encouragement, but right now I seem to be simply doing dumb things that cause crashes. I've got to put in more stick time with expendable/repairable planes before I bring out my built up planes. I haven't been able to fly much, as I am building a new kitchen from scratch. I used to be a home designer/builder so the kitchen is not to hard for me, but I am now disabled by a nerve disease in my legs, I can't stand up more than 2-4 hours, before I am done for the day.

In 1985 my mother had terminal cancer, I took out my frustrations on my airplanes, I flew the out of them, until they were destroyed, and then started flying a better one. I went through at least 6 planes that summer, because I flew from dawn to dusk every weekend, my last plane was a full house plane that I put 200+ flights on it with no crashes, except for takeoff and landing it didn't go 20 feet in a straight line, before I was trying some other stunt, my friends started calling me Wildflyer back then, and it has stuck with me since. Now I should be called Weird-flyer because of some of the stupid things I have done that caused crashes.

But now I am in forced retirement, kitchen is almost done, and summer is coming, so I am going to start a lot of flying. Things are getting better as I flown something every day, this year except 5 days when I just couldn't squeeze it in.

Dave R, Proud PGR rider.
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Old 02-08-2011, 10:29 PM   #10
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The motor I was running in the Pitts was the recommended (and cheap) Turnigy SK3542. this motor seemed a pretty good match. on 3 cells spinning a 12x6 prop it pulled over 40 amps and over 500 watts.. not too shabby.

The problem i discovered with the Turnigy moto is the fragile shaft. After just clipping the prop on the deck during landing the shaft sheared. The shaft itself is only 4mm diameter and it has a groove for a retaining circlip, not too surprising that the shaft sheared across the circlip groove.

I decided to upgrade the motor. I went for a Scorpion SII 3020 1110kv. This has a much beefier 5mm shaft with no circlip groove, so hopefully no more bust shafts. Despite being only a few grams heavier the Scorpion motor is rated for a constant 60 amps rather than the Turnigy's 40A. Running a 12x7 prop on fresh battery I'm actually pulling a little over 60a static and a whopping 780 watts... so that's a 50% increase over the old motor

Might need top be carefull with the throttle as my ESC is only rated for 60a but I'm sure in flight it will unload, so should be ok.. expect fun
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Old 03-28-2011, 12:30 PM   #11
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I've got about 25 flights under my belt on the Pitts now and i'm really starting to get the feel for the model. It goes best when flown aggressivly, it will slow down and cruise around like a trainer but it just doesnt feel right flown that way, the handling gets a bit vague at slow speed although never dangerous and the stall when it comes is a non-event.

Only problem i've discovered is the landing gear fixing. It's very weak and if you fly from a rough field it will almost certainly fail. The left hand undercarrage leg ripped right of the fuselage on mine doing a fair bit of damage in the process. The ply mounting plate that the legs bolt to is not well designed and the glue joints were part dry, an accident waiting to happen!

I've beefed mine up and repaired all the damage, it's better than new and should stand up to a few bouncy landings now.

One thing i found with this model is with CG 95mm from the LE of the top wing it flies inverted without any down elevator at all, which is very nice. First model I've owned that did this.

This is the first larger size electric model I've owned (previous have all been micro) and I'm bowled over by just how much power this thing has, vertical performance is only limited by my eyesight and acceleration is startling. I've used both 3000mAh and 2200mAh (3 cell) batteries and get 8 minutes on the big ones and 6 on the smaller with a safe margin left at the end.

all in all i'm having a lot of fun with this model

Steve
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