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Old 03-06-2008, 01:53 PM   #1
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Default Hobby-Lobby Skymaster build

Last august, I was given a Hobby-Lobby skymaster 337 when they went on clearence for $50. I've finally got the guts to fly this thing (it's got a bad rap for needing a skilled pilot) so I'm going to start a "build" thread on it. (it won't take much building.

So far I've replaced the stock geared 380 burshed motors with two BP2217/9 brushless motor, and pulled the servos out of the elevator so i can move them up into the main wing to get better balance. I will post pictures when I get home from work.

I moved the servos because I plan on running linkages to the back control surfaces instead of having 20 grams of weight hanging 8 inches behind the COG.

I'm also contemplating going from the stock red/white paint scheme to the military O-2 grey / black.

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Old 03-06-2008, 03:05 PM   #2
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As I have the same plane, and have it sitting dormant on my shelf, I will keep an eye on this build.

Do me proud, CC.....Do me proud!

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Old 03-06-2008, 05:32 PM   #3
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it should scoot along pretty well. looking forward to the pics!


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Old 03-10-2008, 03:32 PM   #4
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Couple of quick questions:

1) To get to the servos I need to remove the bottom wing panels, which will require me to glue them back on, I'm looking for the same type of glue as was originally used. It's clear and kind of rubbery. Feels like silicone caulk. Isn't there a UHU glue like this or GWS glue?

2) I hate the rudder and elevator servo layout, especially since there are perfect places for them on the underside of the main wing just inside the booms. I'm moving them there, but need to know what kind of pushrod to use:

Will this do: (already have some)
http://www3.towerhobbies.com/cgi-bin...&I=LXJGT6&P=SM
or do i need this:
http://www3.towerhobbies.com/cgi-bin...?&I=LXFU92&P=M

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Old 03-11-2008, 04:21 PM   #5
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Default Build delayed

I've decided that since this plane has some sentimental value to it, I'm going to do it up right. That means replacing all the servos and painting it along with re-doing how the control surfaces work.

This means I need to buy more stuff and right now I don't have the budget for it. so the build is going on hold.

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Old 04-27-2008, 03:54 PM   #6
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My build has started back up, yesterday, I put the alierons back on using Dubro metal pin hinges (look like door hinges) But I think i screwed up, I used foam safe CA to glue them in and I got some on the hinge itself. now they are very stiff to move. Is there a way to free them up without damaging the foam around them (other than just moving them back and forth alot) Also any tips on how not to do this to the rest of the surfaces?

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Old 04-29-2008, 01:44 AM   #7
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Question Removing sticker goo?

I still haven't solved my aileron "problem", but I'm going to progress the build anyway. I'm getting it ready for paint tomorrow, and to do so required removing all the stickers. The majority of the stickers left a sticky goo on the plane. Does anybody have a suggestion to get it off without damaging the foam?

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Old 04-30-2008, 04:46 PM   #8
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Default Second guessing my servo choices

Hopefully this question will see some views and get an answer.

i was going to replace the stock servos with HS-55's but i'm second guessing if they will have enough torque for this plane. The ailerons and elevator are fairly large so maybe I'd be better off with HS-65's or something else?

suggestions?

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Old 06-08-2008, 06:09 PM   #9
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Default Ready for maiden

After many delays I have finally got the Cessna ready for maiden.

Changes I've made:
1) 2.5" dubro sport wheels for landing on grass.
2) Carbon fiber rod through center wing section that slides into the outer wing section support struts.
3) Replaced stock brushed motors with BP brushless 2217-9 motors
4) BP 30A brushless speed controllers.
5) move rudder and elevator servos from being on the tail to under the main wing using pushrods.
5a) This required fabiricating a new tail wing and rudders out of foam board.
6) Linked rudders using 1mm carbon fiber rod.
7) moved battery to under the windscreen. (used magnets to hold it on).
8) BP switching BEC
9) AR6200 receiver mounted on the wing inside the cabin.
10) painted with Model Masters yellow.
11) replaced all but nose wheel servos with E-flite DS75H servos (out of my blade 400)
11a) this required removing the foam bottoms of the wings, which required me to fabricate new bottom covers out of 2mm depron.

Problems encountered during build:
1) could NOT get all the sticker goo off the plane I don't know what they used, but goo gone, isoproponal and denatured alcohol would not remove it.
2) the paint I used refused to stick or cover the red parts. I ended up wiping all the yellow off with denatured alcohol after painting everything else. I will go back and re-paint them red.

It still needs the finishing touches, but it is ready for maiden. Planning on doing that tonight once the other guys in the area are available to document

It weighs 36.7 oz without battery and 40.7 oz with battery.
With the stock 9x8 props it draws 19.25 amps at full throttle

Pictures attached.


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Old 06-08-2008, 07:13 PM   #10
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Good luck CC looking forward to a flight report.

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Old 06-08-2008, 07:19 PM   #11
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Same here.....mine still sits on a shelf, waiting for it to be given life......

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Old 06-08-2008, 10:02 PM   #12
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Default Maiden report

It's still in one piece, that's always a good thing .

It was a little windy ( < 5mph), and there is a storm coming so my plan was to only take it out for taxi trials and range check. Range checked to 31 paces. Taxi trials showed a tendancy to pull left so needed right rudder. Also the nose wheel likes to come loose whenever it hits a big bump. I had already dremeled a flat spot in the wire to try and prevent that, but the screw that is used doesn't let you get the most torqe on it so it still twists.

Other than the nose wheel everhing seemed fine, and the wind was comming from the correct direction so I decided to maiden it after all.

Taxied to the end of the gravel parking lot, smoothly increased the throttle and once it got speed gave a little up elevator and she took off nicely. A nice right hand turn away from the powerlines and over the field and down wind to line up for landing. (I do not do any trimming out on maidens. I take it off, see what the problems are and then land it.) Lined up for landing pointed the nose at the runway and started reducing throttle. Flaired just before touchdown and greased it in.

Greased the second takeoff/landing, and then bounced on the 3rd 4th, 5th landings.

Rudder is very affective for their size. She requires about 3/4 throttle to cruse and needs up elevator to fly steady. I've got it set up to be nose heavy (COG is 1/4" in front of wing spar). You also have to keep the power on until the wheels are on the ground. It glides like a brick.

I'm going to replace the front wheel screw with a alen head one to get more torqe on it and some 10x8 E-flite props should help with more thrust.

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Old 06-11-2008, 02:25 AM   #13
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Default 2 "crashes"

Well, Since I figured out how to get rudder -> gear mixed in the DX6i I was able to re-program this plane so it has flapperons.

During the process of re-programming I bumped the throttle and the plane crashed off the TV tray onto the floor. The prop cut the bottom of one of the wing panels and a few holes got poked into the other panel. No other damage and both damaged panels can be replaced once I get some more 3mm depron. Also dented the body in various places. This thing picks up hanger rash like nobody's business.

Today I took it out for flights at the RC club. The grass was long and the field is bumpy, It took full throttle to get the plane rolling and once it was rolling it was hard to control. I did manage to get it airborn (almost tipstalled) and few a few laps. A few clicks left aileron and she was trimmed out. flaps resulted in a minor pitch down that was corrected with elevator.

A few test approches proved that the flaps do indeed help slow the plane down without loss of control (running 60% flaps) First landing resulted in a nose over with no damage.

Second takeoff was attempted with flaps on to try and shorten the takeoff run BAD IDEA. When the plane finally did get airborn it immediatly tip stalled. I managed to get it's nose down and level in time to hit the ground, but the long grass and bumpy field made it kartwheel and I busted a wing tip off. Nothing foam safe CA can't fix.

At 40oz this thing is a tank in the air. You have to keep the speed up, and the turns shallow and quardinated with rudder. My setup probably has enough power to do a loop, but I would not risk it with the way the wing is held on. Although the majority of the weight is probably transfered through the struts to the bottom of the plane.

I also think I have a problem with the angle of attack while on the ground causing the plane to stick to the ground and then pop into the air.

She will fly again.

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Old 06-11-2008, 02:31 AM   #14
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Great reports, This is just the kind of info our members need.

Thanks, Kosh

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Old 06-11-2008, 03:33 AM   #15
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Bummer CC...I'm sure it can be good plane once you get the bugs worked out. Looks good anyhow.

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Old 07-03-2008, 02:54 PM   #16
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Default Should call it the White Elephant

It took about an hour to fix the repairs from the last flight, and then I went out for the re-maiden again last night. First flight takeoff was scary, it didn't want to rise and when I pulled back on the stick it popped up and almost crashed. Once it was in the air it flew alright. It's fast, heavy, and slow to respond. I found that it's better to use the rudders to turn and anti-aileron to keep the plane flat (otherwise it banks hard and starts to fall) 5 minute flight took about 50% out of a 2200mah 3 cell. The landing was rough but no damage done. This plane Really should be flown from some kind of smooth runway, not 3" tall grass on a beat up soccer field.

The second "flight" didn't go so well. I figured it was the grass that was causing it to not rise right, but I'm doubting that now. I tried to take off and it was refusing to raise the nose ended up on it's side with no damage, Second attempt ended in a popup, stall, and slam into the ground which bent the nose gear, loosened the nose gear holder, and broke the wing where it meets the body on both sides. It hit the ground nose wheel first with quite a lot of force, and the carbon fiber rod i put in it causes the wing to be pre-stressed in the middle because the rod is trying to straighten the wing, and the struts are designed to give it dihedral.

Anyway, I think a major part of the problem is that I didn't have the nose gear long enough and the plane must have been sitting with a slight nose down attitude. Secondly I think the front motor might have started coming loose on the first flight causing IT to have more down thrust which would exacerbate the problem. I also think I'm going to find a way to restore the dihedral that the Carbon fiber rod tries to take out. Best way I think would be to cut the carbon fiber rod and use a joiner with a bend.

Anyway, So far 2 successful flights, 2 failed takeoffs resulting in crashes.

Also I changed the props from the stock GWS knockoff 9x8 to a pair of master airscrew fiberglass 10 x 7.5 I'm now drawing 26.7 amps at full throttle with ~260-280 watts. The new props really helped get the plane moving.

I

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Old 07-17-2008, 03:59 AM   #17
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Default The white elephant flys..... AGAIN

Seriously, this thing is a white elephent, but I think I'm getting the hang of it.

The wing repair wasn't as bad as I thought it would be, A little medium foam safe CA and kicker and she wing break was fixed in 15 minutes. I didn't stop there though. After that last crash I new it was a bad idea to have the wing pre-stressed from the straight carbon fiber rod, so I wanted to cut the rod and have it angle in the middle.

After unsuccessfully trying to find a piece of aluminum tube that fit around the carbon fiber I figured out that I had some fiberglass rod that fit IN the tube. So I cut the carbon fiber rod in half and epoxied the fiberglass rod in side with some nylon soaked in epoxy around the outside.

If anybody else is building this plane This is the number one Must do mod as it allows you to keep the dihedral and have carbon fiber main spar.

From there I went on to strengthen the main wing bolt holes in the front of the wing I did this by first putting coffee stir straws through the holes where the screw goes and then filling the outside of the hole around the straws with gorilla glue till it was about half full. I then put a metal washer on top of the gorilla glue so that when you screw the wing on the screws are tightening against metal embedded in gorilla glue that is gluing the carbon fiber spar in along with the foam. (I should have taken more pictures sorry)

I also lenthened the nose wheel wire by half an inch.

It now balances about 1/4-1/2 inch in front of the silver wing brace.

I few it off a baseball field tonight, the hard ground made takeoffs easy. It was in the air before it passed first base from home plate. Otherwise it flew the same as before.

It still has a tendency to pull the nose way up if you hit the throttle and if you let off the throttle it won't stall because it noses down fast so I think I've got it fairly nose heavy.

Oh, and I also attached a pic of my re-organized shop and new "hanger"


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Old 07-17-2008, 04:26 PM   #18
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Now that I have the plane flying mostly decent, It's going to be handed over to the Fiance to make it look nice. I'm going to give her free rein over it so we'll see what she comes up with.

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Old 07-17-2008, 11:48 PM   #19
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Great to hear it flys! Its a unique looking plane and it perks my interest.

Will it fall out of the sky with just one motor?
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Old 07-18-2008, 03:14 AM   #20
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With my motors, I think it could stay in the air on just one motor. I forgot to mention that it cruses just below half throttle

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Old 07-18-2008, 12:25 PM   #21
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Sounds like you got it going good CC. Any chance at a video?

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Old 07-18-2008, 01:44 PM   #22
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I don't have a video camera unfortunately.

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Old 04-06-2009, 03:23 PM   #23
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Wow - 40oz - what a beast.

I think you are probably right - you could fly that with just one of those large motors.... which actually doesn't sound like a bad idea considering your AUW.

I still have mine, NIB, the same original red version that comes with brushed motors. I'm still waiting to start it until my flying skills are a bit better - especially for such a high wing-loading.

I was thinking of using a pair of cheap eMax cf2822 motors with SuperSimple 18A ESCs and GWS 8060HD props... good for about 22oz of thrust per motor and almost 50mph speeds. They weigh about half as much as yours. I added it up: your BP motor/ESC combos weighs 6.7oz total, and the 2822's with ESCs will weigh 3.8oz total.... that almost 3oz of weight savings, which ought to help some.

I think for the size of wing, this plane really shouldn't exceed 30oz AUW -- unless you want to fly it like a jet, fast and heavy. Assuming a lipo weighs 4-5oz, and my motor/ESC combo weighs about 4oz, plus 4 servos at 1.2oz -- that's about 10oz of weight for the electronics alone. So I need to try to keep the empty airframe under 20oz to hit my 30oz AUW. I haven't weighed just the airframe by itself, but a plane that size shouldn't weigh more than a pound empty.... so I'm not sure where all the weight is coming from. I'll have to get out the kitchen scale and measure each piece to see where I can trim some fat.
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Old 04-06-2009, 03:36 PM   #24
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At 40oz it fly's very scale like. You have to keep some speed on it, but landings are really neat because it doesn't float on the ground effect like most of my other planes, It's fairly easy to do 3 point landings with it and the rollouts are very long and scale like.

the first thing you should do is the carbon fiber wing spar. The pictures in this thread should be fairly explanatory. my epoxy spar connector is working very well and I don't have to worry about the wings folding and they are held on much better than stock.

I originally looked at that e-max motor which i think is the same as:
http://www.hobbycity.com/hobbycity/s...runner__1534kv

I went with the BP's because I could get them easier.

I wanna be a pirate. Arrrrr

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Old 04-06-2009, 04:23 PM   #25
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That's a different motor... that's the higher kv 2812 - about a 7x4 prop max - great for sub-16oz parkflyers. The 2822 is about 1200KV and works great with a 9x5 or 8x6 GWS "HD" prop -- I actually have one with the 8x6 prop on a 30oz seaplane and can ROW no problem and cruise at under 2/3 throttle: http://www.rcgroups.com/forums/showthread.php?t=755688. They are $6 at HobbyKing. One cavaet: the bearings need lubed -- they aren't pre-lubed from the factory.

I appreciate scale-like flight - but this thing really is a brick with wings. Considering that my flying field is a baseball diamond, I'll need to build mine lighter so it can more easily ROG and land on the short infield grass.

But, as heavy as yours is, it's not as heavy as GTfreeflyer's... a whopping 48oz!!! AUW: http://www.rcgroups.com/forums/showt...=670195&page=3

Note that he mounted his front motor to a piece of ply glued to the foam face - same as you - and he discovered that the built-in thrust angle was way too much at about 10deg right-thrust - so he shimmed it back to about 2deg right-thrust for better results.
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