Cermark MB-339 - RC Groups
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Nov 04, 2012, 10:24 PM
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Double E's Avatar
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Cermark MB-339

Alright here goes. I recently upgraded my Wren 44 turbine to the new Wren 75 Jubilee. Ron at Wren USA gave me a great trade in on my 44. With the new 75 putting out about 18lbs of thrust I figured it's time to step up to a larger aircraft. I've been flying 80-90mm EDF's for a couple of years but as I continue to progress in the hobby I've been sucked in by the smell of Kerosene and that awesome turbine sound. My buddy Frank was selling an old unbuilt Cermark (DL Aeromodels) MB-339 for a great price so I figured I'd go for it rather than dropping a couple thousand dollars on a new airframe of a more popular aircraft. I haven't been able to find very much information on builds for this kit so I figured I start my own build thread.

One of the first questions I have to answer is how much fuel I'll need and where will I position the fuel tanks? If anyone has any information to share about this plane, I'd be very greatful for the help. The Wren 75 burns about 9oz of fuel a minute at full throttle so I figure I need close to 50oz to get between 5 and 10 minutes of flight, depending on throttle management.
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Nov 05, 2012, 09:06 AM
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Double E's Avatar
First decision made. I have ordered a set of custom molded Jet Tech tanks that will carry 60oz of fuel.

Now let's start talking about servos. I assume full size all around and I'm not looking to break the bank so I might look at Savox digitals but I need to check out the specs to make sure they are powerful enough.
Nov 06, 2012, 07:47 AM
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Dr Honda's Avatar
Welcome to the turbine world.

First... I like RC Groups... but for turbines... most of the guys are over on RCU, and you will get all the info you want.

OK... 60 oz of fuel on an 18# thrust engine will realistically get you 5 minutes. With a turbine... you don't want to have a flame out. Not only is it hard on the engine... most jet's are heavy, so they don't glide well. (not all, but most) So, always land with fuel.

Since the Jubilee is a new engine... I would set your timer for 4 minutes, for your first few flights... then adjust as needed. Wren's fuel consumption numbers are normally very close... but who knows. I have a JC Falcon, and it THIRSTY !!! It burns WAY more fuel than advertised.

Also... as you already said... throttle management is a big factor. Just for an FYI... I'm not a speed nut... so I fly around half power most of the time. On my 18# thrust jet... I have the timer set to 5 minutes... and I will land with about 1/4 tank of fuel. If you find yourself holding the throttle open... then you will want to use a taxi tank so you will have a "Full" tank on take-off. Some engines burn a lot of fuel at idle, since they aren't in their efficiency range.

Servos are up to you. There are no hard set rules. There are a lot of people who will tell you that you have to use corless, mega-torque, digital, titanium gear servos.... and that's just not true. There is nothing wrong with a quality "Standard" servo. So... just look at the model... what it weighs... how big the surfaces are... and how fast it will fly. Yes... jet's are fast... but the surfaces are small, and normally don't "Deflect" very far. On my little T-45... the ailerons only move about 9mm!! Because of that... it really only needed 20 oz-in servos.

With that said... I do like metal gears. They are just more durable. BUT... you don't have to get crazy with metal servo arms until you get into some larger/heavier air-frames.

Just an FYI... I've been using Power HD servos for a few years now, and have had great luck with them. They are very nice servos... and are cheap compared to the big names. Oh... and I HATE Hi-Tech servos. I've had a bunch of failures, and 2 caused losses of the model. OEM serovs (JR, Futaba, etc) are normally good, but since a lot of them are coming out of China now... there is no reason to pay the prices they ask.
Last edited by Dr Honda; Nov 06, 2012 at 08:01 AM.
Feb 24, 2013, 09:58 PM
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JPHen's Avatar
Picking up one of these also. Any updates?
Jun 10, 2013, 08:11 AM
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Im looking for a cermark mb339 they are a very good flying planes. If anybody know anything please let me know.

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