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CMP Pro Marathon 20~24cc AEROBATIC AIRPLANE

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Old 03-22-2010, 01:29 PM
  #1
opjose
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Default CMP Pro Marathon 20~24cc AEROBATIC AIRPLANE

This weekend I got the opportunity to thresh out my CMP Marathon sold by Nitroplanes:

[link=http://www.nitroplanes.com/ma20aeairera.html]Click me![/link]

I have an XY 26cc gas engine in it, flying with an 18x8 Wooden prop.

I used SG5010 ( Hextronics / Tower Pro ) servos all around, and used all of the included hardware except for the Tail Wheel and main wheels.

I elected to install larger 3..5" wheels which I had on-hand for better grass handling.

Visible in the shots is the Futaba Servo Syncronizer, and the Spektrum receiver.
I'm powering the electronics with a Venom 6v 3800mAh pack and a 2200mAh 6V Hydramax pack for the ignition.

Both battery packs are mounted UNDER the gas tank, and protected by foam over a plastic barrier.


As you can see the plane is impeccable... it came out of the box without a single wrinkle.

In the air it is a dream. It will not drop a wing at full elevator deflection, nor does it stall out.

It merely enters into an "Elevator" type decent at full stall with no wing rock... very nice!





Tail Wheel



Main Gear

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Old 03-22-2010, 01:31 PM
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Default RE: CMP Pro Marathon 20~24cc AEROBATIC AIRPLANE

More shots







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Old 03-22-2010, 01:51 PM
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Default RE: CMP Pro Marathon 20~24cc AEROBATIC AIRPLANE

As can be seen, the .26cc engine is almost completely enclosed within the cowl.

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Old 03-24-2010, 01:47 PM
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Default RE: CMP Pro Marathon 20~24cc AEROBATIC AIRPLANE

Very Nice OPJOSE !!! I've got one, was planning on putting a DLE 30 in it. I fly at 3700 feet ASL. Haven't figured out the weight issues yet, me being somewhat of a newbie. Looking forward to flying this one.
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Old 03-24-2010, 01:55 PM
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Default RE: CMP Pro Marathon 20~24cc AEROBATIC AIRPLANE

A DLE 30 will be an incredible match for this plane.

You will not have any weight issues with this engine. It is lighter than the engine I used!

If you look in the fuselage shots, you'll see that on either side ( front and back ) of the gear mounts I epoxied in wide triangular stock to add forward-backward gear mount strength.

There is some tri-stock already there as it comes, but I believe in trying to spread out the load forces as much as possible.

In prepping the plane I also made a 30 min epoxy mix adding about 10-15% by content of alchohol to thin it out.

I spread this LIBERALLY over all of the internal wood structures to help strengthen and seal the wood joining areas.

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Old 03-25-2010, 07:23 AM
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Default RE: CMP Pro Marathon 20~24cc AEROBATIC AIRPLANE

Thanks for the info !! That helps a lot.
Rod
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Old 03-25-2010, 10:47 PM
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Default RE: CMP Pro Marathon 20~24cc AEROBATIC AIRPLANE

Hey Opjose, based on your experience, would that plane do well with a Supertigre G3250 glow engine? Your bird flies nicely; looks light on the sticks.
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Old 03-26-2010, 10:46 AM
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Default RE: CMP Pro Marathon 20~24cc AEROBATIC AIRPLANE

The engine I'm running is rated at 2.5 HP, the SuperTigre at 3.2.

I would imagine it would do GREAT with this engine, but remember I have not flown it this way.

I'll bet it could be either side or inverted mounted w/o problems as the cowl is fairly spacious.

The intakes also offer great engine ventilation too.



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Old 03-31-2010, 05:03 PM
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Default RE: CMP Pro Marathon 20~24cc AEROBATIC AIRPLANE

Do you have video of this plane in action yet? The only one I saw was a really crappy video in high winds. I just crashed my big Taylorcraft and need something to put my Zenoah G26 in and have thought about this one. The thing is, I am not a 3D pilot at all. Mostly sport aerobatics. Havent been able to find out much about it. Thanks,
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Old 03-31-2010, 05:17 PM
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Default RE: CMP Pro Marathon 20~24cc AEROBATIC AIRPLANE

I'm a bit too busy flying to film it at the same time... heh...

I don't have a video, but I may try to enlist a friend to do some filming while I fly it.

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Old 03-31-2010, 07:10 PM
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Default RE: CMP Pro Marathon 20~24cc AEROBATIC AIRPLANE

Yeah, I hear ya.... I rarely film my own either. So tell me about it, I am sure it can be wild, but can it tame down too? I am a little shell shocked right now of losing the Taylorcraft. [link=http://www.rcgroups.com/forums/showthread.php?t=1184727]Post 15 shows the carnage[/link] I am a pretty experienced flyer, but like I said, I dont do 3D. I dont mind a little wild in the air, but I like the landings to be mild
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Old 04-01-2010, 01:06 PM
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Default RE: CMP Pro Marathon 20~24cc AEROBATIC AIRPLANE

The plane glides very well, so as long as you tone down the throws and dial up the expo it can be a fairly docile flyer.

Just be sure to completely wring out the engine before your first flight.

I also recommend doing what I did with the epoxy mix and tri-stock.

The extra hour of work this caused me ( at most ) was well worth it.

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Old 05-09-2010, 09:14 PM
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Default RE: CMP Pro Marathon 20~24cc AEROBATIC AIRPLANE

Hi Opjose
my CMPro marathon is arriving this week. I got a few questions that hope you can help me on. (I'm fairly new to gas planes). I'm planning to use four Hitec 645MG servos for aileron, and elevator.then a Hitec 985MG for the rudder. My radio is going to be a spectrum DX5e TX with an AR500 full range receiver. So here comes my questions:
(1).  I'm wondering if the AR500 receiver is able to power up the above servos I mentioned?
(2). Do these servos have enough torque to turn the control surfaces.
(3). What servo should I choose to control the gas engine? (I'm getting a SPE 26cc)
(4). Did you put the servo on the engine mount (like the picture from nitroplanes did?) would the vibration from engine kill that servo?
It'll be great if anyone can comment on these.
Thanks
Mark
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Old 05-10-2010, 11:44 AM
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Default RE: CMP Pro Marathon 20~24cc AEROBATIC AIRPLANE


Quote:
ORIGINAL: mark wang

I'm wondering if the AR500 receiver is able to power up the above servos I mentioned?
I don't understand the question. The receiver does not "power up" the servo.

Power is supplied by your receiver's battery pack, so you should choose something adecuate for the load.

I installed a 3200mAh 6v battery pack to power my Specktrum AR7000 receiver and servos and a 2200mAh 6v pack for the ignition.


Quote:
ORIGINAL: mark wang

Do these servos have enough torque to turn the control surfaces.
Yes.

Quote:
ORIGINAL: mark wang

What servo should I choose to control the gas engine? (I'm getting a SPE 26cc)
A standard servo would be fine, just disable the spring on the carb so there is no force exerted on the servo.

Also don't forget you'll need to do something about a choke as well!

Quote:
ORIGINAL: mark wang

Did you put the servo on the engine mount (like the picture from nitroplanes did?) would the vibration from engine kill that servo?
Yes I put it on the mount as pictured.

Re: Vibration

There is no real difference.

If you put the servo behind the firewall it still will pick up some engine vibration.

I've never lost a servo ( yet ) that was mounted on an engine box.
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Old 05-10-2010, 12:17 PM
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Default RE: CMP Pro Marathon 20~24cc AEROBATIC AIRPLANE

Hi Opjose

Thanks for answering all my questions. It's been very helpful. Just one more question.

What servo should I choose to control the gas engine? (I'm getting a SPE 26cc)
[/quote]

A standard servo would be fine, just disable the spring on the carb so there is no force exerted on the servo.

Also don't forget you'll need to do something about a choke as well!

What do you mean by "do something about a choke"? can you eleborate on this a little bit?

Thanks
Mark


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Old 05-10-2010, 12:20 PM
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Default RE: CMP Pro Marathon 20~24cc AEROBATIC AIRPLANE

You need to be able to choke the engine ( i.e. hole in cowl to put finger over inlet venturi, linkage to choke, etc.) Otherwise starting may not work very well.
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Old 05-10-2010, 12:23 PM
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Default RE: CMP Pro Marathon 20~24cc AEROBATIC AIRPLANE

Oh I see. thanks. great help
Mark
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Old 05-10-2010, 12:42 PM
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Default RE: CMP Pro Marathon 20~24cc AEROBATIC AIRPLANE

Gas engines are choked via a choke valve.

You can hook a servo to it ( preferred ) so that you can choke or kill the engine from your TX.

On smaller engines a manual choke wire is sometimes used, but I find that this can "walk" accidentally closing the choke valve in flight, so I recommend a servo instead.

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Old 06-07-2010, 07:45 AM
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Default RE: CMP Pro Marathon 20~24cc AEROBATIC AIRPLANE

Hi Opjose
I finally got my zenoah 26ei engine a few days ago that I planed to put onto this plane. I just did a rough measure and the zenoah engine is actually pretty long. It's just about to fit if I mount it directly to the engine box of the plane. there is no space for standoffs or any anti-vibration mechanism. So would it be ok to just mount like this? Would I have any weight issues? (the engine is about 1.5kg over all).
Another question is that the gap between my control surfaces and the main wing is about 3mm. And I've already applied apoxy to it. Can I seal the gap with hinge tape and make sure there is no air leakage? why would people say it's a hacker solution? To my understanding, as long as there is no air leakage, it should fly well. correct me if I'm wrong.
Thanks
Mark
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Old 06-07-2010, 11:03 AM
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Default RE: CMP Pro Marathon 20~24cc AEROBATIC AIRPLANE

Yes you can mount it directly to the engine box. Many planes do this...

I added a hardwood "doubler" behind the existing front face of the box to add additional strength. You could do the same.

Re: 3mm

For-get-about it, go fly!

3mm is so small that air will NOT get through the gap at all.

I've pushed this plane fairly fast in the air, using fairly high pitch props, and I have yet to see any flutter what-so-ever.

All too often people tend to overstate the gap as being the primary cause of flutter ( IT IS NOT! ).

All SEALING a gap does is it provides added strength to the control surface itself.

This helps limit any bending of the control surface laterally which can arise at high speeds if harmonic vibrations occur.

However the surfaces on the Marathon are thick and strong, so this is not a problem.

Up-down flutter is the only worry, and you can take care of that by eliminating slop, setting up your linkages for maximum mechanical advantage, and using a decently strong servo ( I'm using 130+ oz/in servos all around ).

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Old 06-07-2010, 12:42 PM
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Default RE: CMP Pro Marathon 20~24cc AEROBATIC AIRPLANE

Hi Objose
Thanks for your help. Yeah, I'll use a doubler to add some strenth. for the gap, I'll just seal it. I'm useing hitech 645 servos (metal gear), they are about a bit over 80oz at 4.8V (I'm using 4.8V system, don't want too much load on my AR500 receiver).
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Old 06-07-2010, 01:03 PM
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Default RE: CMP Pro Marathon 20~24cc AEROBATIC AIRPLANE

Don't bother sealing it, the plane simply doesn't need it.

I've been flying the heck out of it, and my gaps are around 4-5mm... no problems what-so-ever.

I'd invest in a set of 6.0v packs though.

My 26cc uses a 6v pack for the ignition ( 2000mAh ) and I use a 3800mAh 6V pack for the electronics.

This gives me enough current for a full day of LONG flights... e.g. 8-10 15-18 minute flights, without recharging.

BTW: Both of my batteries are mounted UNDER the fuel tank as far forward as possible.

When you install the engine, the best incidence occurs when the prop hub is centered on the existing cowl prop hub opening, when the cowl screws are in place.

I also put in washers under the cowl screw openings on the interior of the cowl, and fiberglassed them in with small 1" fiberglass squares and epoxy.

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Old 06-17-2010, 12:44 AM
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Default RE: CMP Pro Marathon 20~24cc AEROBATIC AIRPLANE

Hi Opjose
I think I'm running into problems again. In the manual, it says flying weight is 5.2-5.4kg, but I just measured my plane weights around 6kg, I'm using a zanoah 26cc engine and I think that;s where the extra weight is comming from. Would that be a problem or is it just gonna land at a higher speed?
Thanks
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Old 06-17-2010, 12:51 PM
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Default RE: CMP Pro Marathon 20~24cc AEROBATIC AIRPLANE

Heh... that's all?

Don't worry about it... you'll see NO effects on this plane with that small of a weight difference. I've loaded it down with far more.

I'd put my AUW closer to 7.8kg as I run the plane with big heavy battery packs.... and it sill does not drop a wing when slow!

Normally the manufacturers understate plane weights anyway.

The Zenoah is not a light engine though, so just be sure your C.G. is OK. But always err on the side of a nose heavy plane.

I'm awaiting a new engine for mine as well.

I found the XY engine I used to be a anemic compared to even other inexpensive Chinese gassers.

I calculated that it was producing about 1.8HP at most, and I know I can substitute other 26cc engines that produce well over 2.5HP.

From an aerobatic standpoint the plane was fine, but I want more vertical pull.

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Old 10-23-2010, 08:12 AM
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Default RE: CMP Pro Marathon 20~24cc AEROBATIC AIRPLANE

hi there i need help with my marathon i bought it second hand with a roto 25 in it but i have no idea of the cg position
please help someone
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