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CMP Beaver conversion

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Old 12-16-2012, 03:41 PM
  #1  
tomd-RCU
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Default CMP Beaver conversion

The Beaver was ordered from HobbyKing. I received it in top condition. Everything was well packaged and I was surprised at the quality of the plane. It is a balsa built and covered with shrink plastic.

I am thinking of using an OS 32SX engine with a Pitt's style muffler.

The work involves removing the already built electric engine mount and replace it with a suitable mount for glow.

Of course a pushrod and an extra servo will have to be added for the engine as also a fuel tank.



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Old 12-16-2012, 03:52 PM
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Default RE: CMP Beaver conversion

The front of the firewall needs to be flush with the front of the fuselage. Since I will be using 1/4 inch plywood to build it, I cut the original firewall 1/4 of an inch inside the front of the fuselage.

To keep the new firewall in place, I glued inside the remaining firewall four pieces of 1/8 inch plywood. Tabs were cut on these pieces to hold the firewall in place.
Triangle stock was used to reinforce the whole structure.
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Old 12-16-2012, 04:11 PM
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Default RE: CMP Beaver conversion

This is a picture of the original electric motor mount.

You can clearly see where I made the cuts.
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Old 12-17-2012, 06:34 AM
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Default RE: CMP Beaver conversion

Considering you only using a .32, do you really need to use 1/4" ply for the new firewall? Save some weight and use 1/8".

just a thought.

Bill S.
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Old 12-17-2012, 04:14 PM
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Default RE: CMP Beaver conversion

Here is a picture of the firewall installed.

I made sure I gave it about 3 degrres of downthrust and close to two degrees of right thrust.

Twin Flyer, yes 1/4 inch plywood might be overkill bit it is my first conversion. Is there a rule of thumb when choosing plywood thickness vs engine displacement ?

My calculations tell me I might need some extra weight in the front because of the short nose moment of this plane. If this turns out to be the case then the extra weight of the plywood will pay off.
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Old 12-17-2012, 04:18 PM
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Default RE: CMP Beaver conversion

The open space was closed off using 1/16 plywood.

I used high temperature gasket material to seal the joint betwwen the firewall and the rest of the enclosure.

Because this enclosure covers the cowling supports, I made sure I drilled holes in the enclosure to access the T-nuts installed by the manufacturer.
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Old 12-18-2012, 06:31 PM
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Default RE: CMP Beaver conversion

Judgeing from past experience 3 degrees of down and 2 degrees of right sounds like way too much. Every conversion I have done to date needs some thrust taken out compared to what the electric setup had built in (and I use engines on the larger size for the plane). I would rather start either flush or with 1 and 1 and add washers as needed.
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Old 12-20-2012, 03:11 AM
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Default RE: CMP Beaver conversion

ckreef,

Thank you for your input.


What you say does make sense. When the throttle is activated, an electric motor develops it's torque more rapidly than a glow motor.
I will need to try the airplane and, if need be, I will reduce the thrust incidence.
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Old 12-20-2012, 05:27 PM
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Default RE: CMP Beaver conversion

This picture showas the engine support in place. The engine will be an OS 32SX and it will installed rotated 90 degrees to the right.
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Old 12-20-2012, 05:29 PM
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Default RE: CMP Beaver conversion

This picture shows the engine installed with it's Pitts style muffler.

The throttle arm had to be extended to clear the muffler.
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Old 01-29-2013, 10:53 PM
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Default RE: CMP Beaver conversion

You're doing an awesome job!
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Old 01-30-2013, 04:17 PM
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Default RE: CMP Beaver conversion

Thank you Kmot.

Since glow fuel is used, I need to install a support for the fuel tank at the right height.
This picture shows my work.
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Old 01-30-2013, 04:22 PM
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Default RE: CMP Beaver conversion

This picture shows the servos installed.

Notice I had to add a third servo for the throttle.
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Old 02-01-2013, 12:29 AM
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Default RE: CMP Beaver conversion

Hello Tomd,

nice conversion. I bought the Beaver from CMP(The Military version) and for a week ago i did start the conversion to glow and used your "knowledge" for the firewall.
This is almost ready and i'm thinking now about the engine. First i thought the .60 4 stroke is the egine i like for the sound, but a 4 stroke is somewhere an attack on thefuselage of the aircraft and a 2 strokeis not so nice for his sound.
What do you think?
Rgds
Theo(From the Netherlands)

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Old 02-03-2013, 05:39 AM
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Default RE: CMP Beaver conversion

Hello TKO,

I naturally prefer the sound of a 4 cycle to that of a 2 cycle especially on this type of airplane.

I recently checked the balance of the airplane and with my 32 SX the airplane is a little rear heavy. This tells me that the use of a heavier engine would not need additional front weight. However, I would think that a 60 would be too heavy up front. I think a 46 size engine would be best.

As for 2 or 4 cycles, here is my thinking. Around the circunference of the cowling are three tabs whose holes have to align on T-nuts on the firewall.
If you use a 4 cycle there is a good possibility that 2 of these tabs (the holes) will be blocked by the head of the engine. You will then need to add tabs at different places on the rear circumference of the cowling to keep it in place. Believe me, adding two tabs is not an easy matter. I had to do it for the 32 SX, I imagine it would be more difficult with a bigger engine. Check my picture below and you can see the two extra tabs I had to add. Of course, forget about the fake radial when you add these extra tabs. There is no way you can align the tabs with the T-nuts with the fake radial in place.

Another consideration... a bigger engine means bigger servos. There is no problem in the fuselage. However, It is a diffrent story for the wings. I upgraded my servos to Spektrum's A5030 (these are minis)and I am having a hard time fitting them in the wings. I am almost there.

You are right a 60 size engine would be too much for the firewall. A 40 size 2 cycle would be a better choice even if the sound that we want to hear is not there.
Good luck and post pictures of your work.
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Old 02-10-2013, 02:45 AM
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Default RE: CMP Beaver conversion

Thanks Tomd for all the information. I have to wait for the delivery of some items from Hong Kong and than i hope to finish this Beaver.
As soon as i start to build the engine on the fuselage i make some pictures.
Last year i was a couple of weeks in Canada to make a roundtrip and visit family of my wife in Edmonton. We started in Calgary and via Jasper,Edmonton to Vancouver Islands and than back to Vancouver for our flight back to the Netherlands. What a beautiful country is Canada
Rgds
Theo

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Old 06-02-2013, 06:25 PM
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Anymore updates on this? I'm looking to get this plane and go glow on it. Wouldn't mind seeing some pics of the finished plane.


Matt
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Old 04-08-2014, 07:08 AM
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I'm converting mine to use a 4 stroke Magnum 52. I think with the high aspect ratio wing and light wing loading it should be plenty of power.

I have to say that I'm fairly impressed with the overall quality of this ARF. Especially, since it only cost $129 from NitroPlanes. Although, I've seen some better, but a whole lot more ARF's that were way worse quality. During the build, the only thing I wasn't real pleased with was the flap/servo linkage. They went out of their way to conceal the flap pushrod and servo which causes the installation and setup to be a real pain. Since the aileron servos are exposed anyway, you might as well go with a more conventional pushrod and servo arrangement for the flaps.

As far as the firewall and engine mount goes, I cut off that whole protruding electric motor mount. Then installed the firewall in two pieces split down the middle (1/8" aircraft ply. Those two were epoxied directly to the front bulkhead. Then, I epoxied a 1/16" piece of aircraft ply in the rear of those two plates in the center of the bulkhead. The whole thing is very rigid and the motor won't be going anywhere without the airplane.

I wanted to retain the original cowl mounts but since I was side mounting my engine I moved the rights side cowl mounting lugs to bottom. This is one of the thickest sturdiest cowls I've seen in a while. The mounting arrangement is also very sturdy. The whole inside of the cowl and firewall are now ready to fuel proof with black Top Flite LusterKote Paint.

Once I get the engine installed, I'll post some more pictures.
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Old 04-08-2014, 03:59 PM
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Hello Phalco,

With the 32sx engine and no extra weight , the Beaver was tail heavy.

I changed the engine to an OS 55AX with a Pitts style muffler and also had to add extra weight.

However, there is now a problem... the blind nuts on the firewall are now hidden by the motor and the muffler.

I imagine you must heve the same problem ?
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Old 04-08-2014, 04:23 PM
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Tomd, Did you have to add weight to the nose? If you did, I will have to, as well. Since the 55AX is heavier than the Magnum 52. All the blind nuts and bolts are easily accessible on mine.

Never mind, I see all the lead.

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Old 04-10-2014, 09:23 AM
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Tomd, is the CG given in the instructions (68-72mm) accurate or did you have trouble with the CG in the air?

Thanks
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Old 04-11-2014, 01:47 AM
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Hello Phalco,

The CG on my Beaver is at 70 mm. When it flew with the OS 32 SX I realized it was tail heavy because I din't balanced it properly.

When I changed to the OS 55 AX I made sure that the nose pointed slightly down when I balanced it,

I did not fly the plane in this configuration yet as winter here in Montréal is not over yet..
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Old 04-16-2014, 06:59 PM
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Tomd, when you flew it with the OS 32SX was the CG at 70mm or is it at 70mm now that you've got the heavier OS 55AX on it?

I've got the engine mounted. Only as few days to completion and maiden flight. The winds have been pretty high here in Texas with fronts moving through the area. Hoping for some good flying weather soon.

Is there still snow on the ground in Montreal? Ever considered putting the plane on skis? I think floats would work pretty good as skis, too.
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Old 04-19-2014, 01:36 AM
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Hello Phalco,

With the 32 SX I thought I had balanced the plane properly at 70 mm. However, I now realize that the plane was not pitching slighltly forward as is required when i held it on my two fingers.
The airplane was almost horizontal with a slight pitch to the back. I guess in my head I did not want to add weight. When I flew the airplane, on takeoff it pitched up and in the air it wanted to gain altitude.
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Old 04-19-2014, 04:28 AM
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Tomd, okay...I think I understand what happened. I'll go ahead and balance mine at 70mm so that it is level. That should put me in the ballpark as far as CG is concerned. Do you have any experience with electronic flight stabilizers (gyros)? I bought a couple from Nitro Planes. They were only $19. I thought I would try them out. I've been flying for many years and most of my planes are nitro fueled. But I'm not sure if these little stabilizers will work with nitro engines since they tend to vibrate more than electric motors. I guess I could try one out on one of my older planes first. Just wondering if you had any experience with them...
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