HobbyKing Pitts Model 12...Longest ARF build ever? - RC Groups
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Jan 08, 2011, 12:19 PM
Grumpy old git.. Who me?
JetPlaneFlyer's Avatar

HobbyKing Pitts Model 12...Longest ARF build ever?

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

On and off (mainly off) I've been putting this together for nearly a year!

I had to do a lot of work to get it into flyable order. The original fuselage was very badly twisted, HobbyKing replaced it FOC which was I cant quibble with. I stripped the covering off the original fus, straightened it, and recovered, so I now have a spare

There were a few other quite serious issues with the kit which belayed the build;
The worst one is the method of connecting the top and bottom ailerons just doesn't work at all, the linkages are all wrong. 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 top and bottom 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 fully 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. Reviews on HobbyKing mention motors falling out mid flight and I'm not at all 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 TE 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 cheapo 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 resistance to 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 IMHO 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 with no fuss then look elsewhere.

Hope you like it....
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Feb 05, 2011, 05:35 PM
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reacher10's Avatar
I have three batteries thru mine and it is one nice flying plane. I'm just waiting for the snow on the runways to melt for some more flights.

It's a thinking mans ARF for sure. On mine the wings were built PERFECTLY WRONG!!! the struts should slant out from the bottom wing. When I dry fit them they slanted in from the bottom wing...hmmm. I dry fit them in the upper wing and they slanted out...that ain't right. Those rib sections on both wings were transposed. Otherwise the fit was perfect. This required very tedious dremmel work to correct.

More info to come and I'll post some pics.
Feb 11, 2011, 02:15 PM
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reacher10's Avatar
Here are some pictures of the modifications to the cabane struts.

I also made a sliding battery tray to get it as far forward as possible.

I reversed the landing gear to attach to the bottom of the plane and used 3mm nylon screws to attach them so if it does tear out it won't rip the fuselage apart with it. I got the carbon fiber gear from HK (130mm).

I shortened the motor box so I could use the prop adapter end of the motor. After I cut out 2" from the center on a chop saw I grafted it back together. By cutting out 2" the box lines up perfectly for grafting and used 1/2" threaded standoffs.

I CA'd a 3/16" piece of ply to the fuse where the tail wheel bracket attaches.

I Just checked the AUW and it is 1635g = 57.67 oz. = 3.60 lbs.

Exceed RC 3548 950 kv (Monster power 15)
60 Amp ESC (no name) and CC 10 amp BEC.
12 x 6 APC prop. I have a APC 12 X 8 on it that I'll use on the next flight...cause I can.
4S 3000 mah 20C turnigy and blue lipos.
500 watts...can't remember the amp draw.
Plenty of power, unlimited vertical.

2" aluminum spinner http://www.jrhobbyhardware.com/shop/...products_id=27

CG is the leading edge of the lower wing. I didn't do any modifications to the lower wing attachment but I will. It's a little suspect as it's designed.

It's out of stock right now but I ordered mine from the HK USA warehouse and got in 9 days for $100.00 shipped.

All in all it does not fall out of the box and go together, you really need to think this one out but for the price it is a really really nice flying plane. Perfect rolls.

Here is the discussion I found on the HK forum and found out what the CG was and how to strengthen the cabane struts. http://www.hobbyking.com/hobbycity/f...24419za4f51497
Last edited by reacher10; Mar 27, 2011 at 12:09 AM.
Feb 12, 2011, 01:26 PM
Grumpy old git.. Who me?
JetPlaneFlyer's Avatar
Maidened mine last weekend, she went great

Only issue i came accross was the soft standard landing gear legs that bend outward and back on anything other then a perfect 3-pointer. The gear bending caused a prop strike which snapped to puny 4mm shaft on the Turnigy motor. The shaft has a groove for a circlip and snapped right across the groove. I can see that this is a weak point on the motor so i splashed out on a Scorpion SII 3020 1110kv. This adds 50% more power, i'm now pulling 60A on the 3 cell battery for about 750W.. should be fun

Also replaced the landing gear with carbon legs.

Feb 13, 2011, 10:12 AM
Grumpy old git.. Who me?
JetPlaneFlyer's Avatar

I like some of your modifications, looks like we did much the same mods but in slightly different ways.

On the aileron linkage, your solution should work ok because you put the horns right on the TE.. the instructions showed them on the LE of the ailerons which wouldn't have worked at all. i want for the 'Rolls Royce' solution, stripped the covering and built in mounting points for the pushrods flush with the aileron surface (see photo)

For the battery i chopped a hole through the firewall and slid the battery in as far forward as it would go to get the CG right. the battery is mounted on a glass fibre plate which slots into a socket fitted to the front of the motor housing structure.

I also put a sliding latch in to hold down the canopy, the standard magnet retention was a joke.
Feb 13, 2011, 01:13 PM
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Nice plane, I have always been tempted to put one together. Though I've got you beat... I spent over 2 years building my Super Sportster EP and it didn't even need modifications.
Feb 27, 2011, 10:54 PM
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reacher10's Avatar
I flew mine on the other day...just a really nice flying plane. However I did roll off the runway a little hot and with our field being craggy, one of landing gear struts pulled out.

I had modified them to attach to the bottom of the mounting plate with 3mm nylon screws and there was zero damage. It worked great but I felt the 3mm screws snapped a little too easy so I picked up some 8-32 nylon screws at the WRAM show.

Now I can replace the screws at the field by using hex nuts instead of the blind nuts and the struts should take a bit more force without snapping and I have my fingers crossed with no structural damage to fuse.

Also the reason for not using blind nuts is that they are on the inside of the fuse and when/if they push in and come loose it's a pain in the arse to get the screws caught again. I use socket head cap screws and ground down a hex key so it's a tight fit and it holds the screw well so I can easily giude it thru the hole from the inside and simply thread a regular hex nut on the bottom/outside.

At the WRAM show there was the exact same plane in the swap meet area and sure as sheet the area where the struts attach was trashed. The person did try and make it fight worthy again but there was significant damage to the fuse when it tore out.

So anyone who reads this thread and is putting this plane together, do yourself a HUGE favor, DO NOT attach the LG struts according to the design and attach them from the bottom with nylon screws.

I Hope this helps.
Mar 23, 2011, 08:56 AM
Registered User
very cool!,.. I live about 20minutes away from where the real ones are built! and actually designed their logo in the early 2000's,.. gorgeous plane and powerful
Mar 27, 2011, 06:10 PM
Grumpy old git.. Who me?
JetPlaneFlyer's Avatar
Originally Posted by reacher10
So anyone who reads this thread and is putting this plane together, do yourself a HUGE favor, DO NOT attach the LG struts according to the design and attach them from the bottom with nylon screws.

I Hope this helps.
This is a weak point on the hobbyking Pitts 12.. I pulled the landing gear off after reasonably ok landing when the gear hit a lump of earth. It did quite a bit of damage so I beefed up the undercarrage mounting plate. The original was a rather weak design at best but made much worse by the glue joints being partly dry on my model.

As for bolting from the bottom.. Not sure how you would do that because there is no access from the bottom?.. Also if the gear is designed to come away in a heavy landing it would likely do a lot of damage as it departed. On mine the wheel pant punched a hole in the wing as it folded up, plus the damage to the fus as the gear came away and I bust a prop and bent the motor shaft as the nose hit the dirt... All in all I'm inclined to think it better to keep the gear attached rather then designing it to come off.

Mine is all fixed now, much stronger and no heavier, better than new!

Anyone with this model i'd advise to check the undercarrage mounting structure regularly and if you can get access running some more CA into the mounting plate to former joints would do no harm.. The full fix i did requires a bit of surgery, afraid i didnt take any photos of the modification but i could describe if anyone is interested.

Flying today and practicing inverted.. this is the first model I've had that doesnt need any down elevator to fly inverted, not even a touch. Guess i must have the CG set quite near the aft limit but it flies fine.
Mar 27, 2011, 07:50 PM
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reacher10's Avatar
You can see in this picture that I cut the covering away and replaced it with repair sticky back monocoat: https://www.rcgroups.com/forums/atta...mentid=3795303

When one strut did come out all it did was break the stringers. I don't use the wheel pants so no damage was done plus the carbon fiber LG is two seperate pieces so if it did have the wheel pants it might not pucture the wing...but it might.

After I reattached the LG strut I just left the bottom open. You don't really see it plus it provide a place for the air rhat come thru the cowl to escape.

Below is the LG strut after I fixed it.

I also bought some of the water slide inkjet decal paper. They came out pretty good.
Mar 28, 2011, 02:14 AM
Grumpy old git.. Who me?
JetPlaneFlyer's Avatar
I REALLY like your decals!.. donít suppose you have copies of the images you used to make them have you?... please

I'm actually slightly relieved to hear than most people appear to be having issues with the UC mounting.. I thought it might just have been my poor landings to blame!.. But the design of the mounting is really bad. The mounting plate fixes to the firewall at the front, which would have been ok if it had been glued properly. But at the back the plate fixes to a half former that itself is only fixed to a 1/32" ply lattice box structure, which unsurprisingly fails on anything less than a perfect 3 point landing onto a billiard table smooth surface.

I put a larger plate in that spans between the firewall and the main fuselage former into which the lower wing dowels locate. I removed the half former completely, also added a couple of ply stiffening webs to stop the plate flexing.

Mar 28, 2011, 07:09 AM
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reacher10's Avatar
I found them here: https://www.rcgroups.com/forums/show...1#post10740986

The Yellow APC doesn't work with clear decal paper. I would get the black one from the above thread as well as change the text on the Phillips 77 to black.
Mar 28, 2011, 07:39 AM
Grumpy old git.. Who me?
JetPlaneFlyer's Avatar
Brilliant!.. thanks.

I'll print them off tonight.

Apr 08, 2011, 07:16 PM
Grumpy old git.. Who me?
JetPlaneFlyer's Avatar
Went flying today and shot a video with a cheapo micro cam:

Pitts Model 12 (4 min 43 sec)
Apr 08, 2011, 11:35 PM
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reacher10's Avatar
Very nice! I have about 10 or 12 flights on it now and I love it. It's a sweet flying plane and prolly my favorite.

I'm still testing the flight envelope and I'm flying it just about the same as you other then I have a lot of power. One of the guys at the field chuckled when I told him I'm taking it easy with it. He thought I flew the crap out of it...LOL.

Tomorrow is supposed to be really nice. We've had 2 1/2 weeks of really windy days....20-30 mph, so tomorrow will be a real treat and the Pitts will be the go to plane.


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