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SkyMaster MB339 Build Thread

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Old 02-10-2013, 02:44 PM
  #351  
wojtek
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Default RE: SkyMaster MB339 Build Thread

The original is fine, but its only OK .. without front support, there is always some play. with quick disconnects, a less than solid joint can cause problems there to such as air leaks when there is play. I would not flt any more aggressive maneuvers without it. I always like to make things built as solid as possible within the realm of whats possible on any airplane if it can be done easily, and without much weight gain. better safe than sorry Also, some wings/fuses may have better fits than others.

speaking of reinforcing, there are some spots under tha main gear in the wing that desperately need some more internal support. There is not much torsion strength between the retract rail mounts .. I'll snap some pics of a simple solution when i'm in my shop and post here .. I know some guys have had the hear pop through the top skin. I have not had a single problem, and thats mostly flying on grass ..




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Old 02-10-2013, 04:36 PM
  #352  
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Default RE: SkyMaster MB339 Build Thread

Some photos would be good , i was going to add a brace to the front also .
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Old 02-10-2013, 07:02 PM
  #353  
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Default RE: SkyMaster MB339 Build Thread

I hope these two photos of a new wing give an idea the way i marked them up ... sorry, but i have no visio here, so it was a manual drawing on them in PS, lol ..

The gear load will act like a pry bar on the mounts, one pulling out the other pushing up ( looking from the bottom of wing) . Because the ribs do not esist at the inboard and outboard section of the gear rails, this area is weak and has no support for this torsion pry load. You have to do all you can to reinforce this . There is a lot of room on niner side of the wing inboard from the retract mount. Its tight to get to, but worth the effort as this area will take the most load. Anyone that has seen gear push up has seen the upper skin crash here where there is no rib/former. Simalar to the outboard area of the rails. THe one mount could also use being supported with some triangle cut ply for structural strength. I have had tons of flights on grass, and the gear is not an issue at all with this set up. With all 3 tanks full, and around 50oz of smoke fluid on top of that with a P200 for power, my plane definitely was a pig hog on the gear, lol . ..

as for the wing mounts, i have done snaps and spins ( within the realm of what would be scale I guess ) , and never had any separation issues.. I would not trust a single small bolt per wing, and also i would not trust the aluminum tabs either without gluing these in myself. I have seen these pull out of the glue in the wing quite easily actually. I ended up pulling them out( by just heating them) and replacing with my own ..

I really need to get going on my 2nd MB339 after the 1st one went in running out of fuel :\

Wojtek
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Old 02-10-2013, 11:42 PM
  #354  
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Default RE: SkyMaster MB339 Build Thread

Great observation Wojtek and while tidying up the gear doors on my MB I noticed that the ply mount for the mains flexed. On one side the ply was beginning to split. I cut some more ply and inserted them vertically between the wing skin and mount and its definitley better. Do you fly off tarmac/asphalt or grass? If the former I would be interested to hear if you had problems with bouncing on landing and how you setup the mains. How much oil? How much air pressure?

I'm working on one other mod for this year - putting electronically ignited smoke flares in the wing tips

Thanks - Dom







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Old 02-11-2013, 01:26 AM
  #355  
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Default RE: SkyMaster MB339 Build Thread

hi Dom
i found, same issue with gear blocks, have had to strengthen them, with carbon cloth and plywoof vertical braces, seems ok now.
I normally, just fill oil up to , air valve, then just pump them, with air via supllied air bottle.
bounce on landing, could lower expos not help you, just a thought

I have a questions
how much flap deflection do u have for landing flap
i notice these supplied tyres, are not inflatable, unless im not seeing the valve
overall a super model
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Old 02-11-2013, 03:03 AM
  #356  
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Default RE: SkyMaster MB339 Build Thread

Wojtek:

Great pictures. I did similar reinforcements when I received mine. I also added a couple of carbon fiber strips to the front part of the fuselage in order to avoid any bending (fuselage is really long and in some maneuvers it could bend a little bit...).

Dominic:

From the Skymaster website...

Use an injector filling oil in strut (see Mpeg files). Because oil is incompressible, so the volume of oil in the strut will determine the bottom end of strut when the aircraft subjects heavy landing situation.
 
@ Using the gas tank filling air in strut (see Mpeg files) when they are not loaded by the weight of aircraft (The gas pressure in main gear can reach 25 Kg/cm2 when loaded). The pressure for main gear is about 6-10 kg/cm2(90-150 psi) and 2-6Kg/cm2(30-90psi) for nose gear. The air pressure will determine spring rate and static ride height of strut. The typical static ride height for main gear is about 16mm from filling valve center to seal and 14 mm for nose gear from M3 bolt center of fork to seal.
 
@ Always filling gas in main (or nose) strut when they are unloaded and filling valve on the top to minimize amount of damping oil leaking from the valve.
 
@ If it is difficult to charge air through filling valve, using a screw-driver loosen valve 1/4 turn and the pressurize process will be easier. (Don't forget to tighten it again!)
 
@ When pressurize process is complete, then place aircraft on the ground and press main wing up and down until bubbles purge from damping oil and strut generates steady damping force.
 
@ Usually, you don¡¦t fill oil in strut frequently, because consumption of damping oil is very low.
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Old 02-11-2013, 05:11 AM
  #357  
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Default RE: SkyMaster MB339 Build Thread

OK so the normal way of holding the wings is fine but how is this done ?any pictures?

not keen on a insert and bolt in the front seems like a accident waiting to happen
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Old 02-11-2013, 06:30 AM
  #358  
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Default RE: SkyMaster MB339 Build Thread

Hi all,

I looked at the assembly instructions on the Skymaster web page where the control surface deflections are described (see pictures). I cant get more than 15 mm down on the elevator, at that point the stabilizer root surface parts (stabilizer - elevator control surfaces) touches each other. The figures in the picture, 25 - 30 mm, does it mean total up - down throw, or 25 30 up 25 - 30 down, similar as (I suppose) it is meant in the aileron picture figures? Is 15 mm down sufficient when flying inverted? Which control surface deflections do you folks have on your MB-339 birds?
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Old 02-12-2013, 12:28 AM
  #359  
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Default RE: SkyMaster MB339 Build Thread

Pics of my wing and fuselage attachment taken while I was doing some very unexciting gear door maintenance over a continually rainy weekend. I'll look at control throws tonight.



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Old 02-13-2013, 03:36 PM
  #360  
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Default RE: SkyMaster MB339 Build Thread


ORIGINAL: DominicM

Great observation Wojtek and while tidying up the gear doors on my MB I noticed that the ply mount for the mains flexed. On one side the ply was beginning to split. I cut some more ply and inserted them vertically between the wing skin and mount and its definitley better. Do you fly off tarmac/asphalt or grass? If the former I would be interested to hear if you had problems with bouncing on landing and how you setup the mains. How much oil? How much air pressure?

I'm working on one other mod for this year - putting electronically ignited smoke flares in the wing tips

Thanks - Dom


Dom,

I fly mostly on grass, but it handles the same on Tarmac for me .. If its bouncing, it means there is still speed that needs to bleed off before touchdown. . I use all the flap throw I can get so it acts more as an air brake and I use 1/4" crow on the ailerons . The plane can land at a more scale looking speed this way with a little more speed, without the kangaroo hop


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Old 02-13-2013, 03:53 PM
  #361  
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Default RE: SkyMaster MB339 Build Thread


Hi,
I just want to highlight my post (#357)...
Someone here who can help with advice?

Regards,
Robert

ORIGINAL: Helirupert

Hi all,

I looked at the assembly instructions on the Skymaster web page where the control surface deflections are described (see pictures). I cant get more than 15 mm down on the elevator, at that point the stabilizer root surface parts (stabilizer - elevator control surfaces) touches each other. The figures in the picture, 25 - 30 mm, does it mean total up - down throw, or 25 30 up 25 - 30 down, similar as (I suppose) it is meant in the aileron picture figures? Is 15 mm down sufficient when flying inverted? Which control surface deflections do you folks have on your MB-339 birds?
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Old 02-14-2013, 02:54 AM
  #362  
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Default RE: SkyMaster MB339 Build Thread

Today I should be going to the club so I will try to measure mine and report back.
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Old 02-14-2013, 04:04 AM
  #363  
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Default RE: SkyMaster MB339 Build Thread

Thanks Wojtek. I'm using full flap but not crow with the ailerons. I'll have to see how to do that with the DX18. Cheers.

Got my paint from Skymaster yesterday. Quite a lot for the $30 paid. Should get my MB back to pristine condition after it got a little crispy with my P160SX letting go 3 minutes into a flight.
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Old 02-14-2013, 04:18 AM
  #364  
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Default RE: SkyMaster MB339 Build Thread

hi guys

im installing a p160 and was wondering what tank combo people are using ?is there enough fuel onboard with the standard 3 tanks fittment ?
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Old 02-14-2013, 04:34 AM
  #365  
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Default RE: SkyMaster MB339 Build Thread


ORIGINAL: smillinollie

hi guys

im installing a p160 and was wondering what tank combo people are using ?is there enough fuel onboard with the standard 3 tanks fittment ?
I have a Jetcentral Rhino on mine and I usually fly between 7 to 8 minutes with the stock fuel tanks.
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Old 02-14-2013, 05:45 AM
  #366  
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Default RE: SkyMaster MB339 Build Thread

I run a P160SX with those tanks and time for 8 minutes flight time using mixed throttle. I have most of one of the small tanks left on landing. I have found CG does shift rearwards a bit during the flight but not a great problem.
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Old 02-14-2013, 08:24 PM
  #367  
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Default RE: SkyMaster MB339 Build Thread

I fly a P200, and use throttle quite a bit ( it is however speed limited to 150 - 160mph ) I get 12min no problem .. but that's without junk under the wings ! ( just 2 tip tanks)


When I added 4 drop tanks ( 2 per wing ) this reduced my flight time to under 10min based on the drag alone ( turbine had to push harder to maintain speed on the limiter ) ... This caused me to run out of fuel on my gear pass [&o] ..


This was posted before i think , .. the end of this video you can hear it die and watch my MB go in ..


so please learn from my mistakes and remember that ordinance adds A LOT of drag, which can mean higher fuel usage !


[youtube]http://www.youtube.com/watch?v=LKTG1LZisG0[/youtube]

this was the original maiden, landing was stalled out a little too early on this flight ...
[youtube]http://www.youtube.com/watch?v=_N-i8hrzgKQ[/youtube]


I have another MB on the way in the shop . Miss this plane too much not to always have one !

~V~
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Old 02-14-2013, 11:20 PM
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Default RE: SkyMaster MB339 Build Thread

You really do mix the sticks around on that second vid. [X(] Good to see the airframe can take those high G pull backs on the elevator.
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Old 02-15-2013, 03:47 PM
  #369  
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Default RE: SkyMaster MB339 Build Thread

ORIGINAL: Helirupert

Hi all,

I looked at the assembly instructions on the Skymaster web page where the control surface deflections are described (see pictures). I cant get more than 15 mm down on the elevator, at that point the stabilizer root surface parts (stabilizer - elevator control surfaces) touches each other. The figures in the picture, 25 - 30 mm, does it mean total up - down throw, or 25 30 up 25 - 30 down, similar as (I suppose) it is meant in the aileron picture figures? Is 15 mm down sufficient when flying inverted? Which control surface deflections do you folks have on your MB-339 birds?

I measured mine today.

Flaps: 30 mm
Ailerons: 18 mm
Elevator: 20 mm
Rudder: 50 mm
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Old 02-18-2013, 05:40 AM
  #370  
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Default RE: SkyMaster MB339 Build Thread


Thanks, Gonzalo!

ORIGINAL: Gonzalo38

ORIGINAL: Helirupert

Hi all,

I looked at the assembly instructions on the Skymaster web page where the control surface deflections are described (see pictures). I cant get more than 15 mm down on the elevator, at that point the stabilizer root surface parts (stabilizer - elevator control surfaces) touches each other. The figures in the picture, 25 - 30 mm, does it mean total up - down throw, or 25 30 up 25 - 30 down, similar as (I suppose) it is meant in the aileron picture figures? Is 15 mm down sufficient when flying inverted? Which control surface deflections do you folks have on your MB-339 birds?

I measured mine today.

Flaps: 30 mm
Ailerons: 18 mm
Elevator: 20 mm
Rudder: 50 mm
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Old 04-05-2013, 09:50 PM
  #371  
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Default RE: SkyMaster MB339 Build Thread

Does anyone have any landing gear for this plane they would sell ?
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Old 04-20-2013, 11:08 PM
  #372  
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Default RE: SkyMaster MB339 Build Thread

First proper weekend of Spring in the UK so made the most of it. Building up confidence to fly this thing lower.

Thanks to Rich for waving the vid camera vaguely in the direction of the model...

[youtube]http://www.youtube.com/watch?v=vfvKREWGuxo[/youtube]
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Old 06-22-2013, 11:33 AM
  #373  
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Default RE: SkyMaster MB339 Build Thread

Do any of you guys haVe problems with the ducting, ie do you have a shroud over turbine to keep air directly feeding into turbine inlet.
Im suspecting, that i am having flameouts due to air flow restrictions
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Old 06-22-2013, 05:15 PM
  #374  
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Default RE: SkyMaster MB339 Build Thread

Never had problems with flame outs in mine. The only time I had one was because one of my fuel tanks was sucking air.

Have you checked everything else in you plane in order to discard other possible causes ?
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Old 06-22-2013, 07:31 PM
  #375  
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Default RE: SkyMaster MB339 Build Thread


ORIGINAL: savasn

Do any of you guys haVe problems with the ducting, ie do you have a shroud over turbine to keep air directly feeding into turbine inlet.
Im suspecting, that i am having flameouts due to air flow restrictions

as long as the overall intake area is adequate ( and it is on this plane for even big block blowers ) , the engine will be able to suck all the air it needs, no matter if its directed right at it or not. I would suggest looking elsewhere in the system first for flame out issues.

Like Gonzalo38 mentioned, the fuel system will usually be at fault somewhere ..



Voy
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