TJIRC Carbon Magnus Build (Konrad)

[Konrad]

I have a soft spot for the 60" class of slope ship. So much so that I bought a carbon Magnus. The value is great that I even got the Yellow one for fear that the market will wake up and realize that they are worth 1.5 time what we currently have to pay for them. (I don't like yellow as I loose that color in the "brown" hills)?

This thread will document my build, issues and solutions. I'll be asking the Aloft Hive mind for their take on the how and whys.

First the model kit is on par or above the European 60" kits I currently have (20 year old designs) when just looking at the airframe. If looking at a value statement they are out of this world. I know many folks wished they had bought a dozen Sunbirds when they first came out at their introduction price. I'm here to say that if you made the wise choose to avoid having too much inventory in the RCRCM Sunbird. But it would now be wise to stock up on the TJIRC Magnus. They are this nice, you will be wanting one in your arsenal for a long long time.

Now down to details. My kit from 7/2020 has some real neat tear dropped servo covers. These should give more than enough servo arm clearance if using 8mm thick servos. I'm not sure how much servo arm clearance they will provide with 10mm thick servos. (The 10mm servo brings the servo output shaft 1mm closer to the servo cover, effectively shortening the servo arm if you want to keep it under the cover).

I plane to use KST servos and IDS for my wings. I think this will allow me to use flat servo covers.

Staying with the servo mounting is there a reason the fuselage servo tray doesn't span the whole canopy opening? I like to install full length servo trays to offer some much needed lateral support to the nose.

Also I've notice that the stabilizer on my Magnus does not appear to be as stiff as one would expect after seeing how stiff the wings are. (They are more than stiff enough, but compared to the wings they appear to be a weak point that may not allow the airframe to reach its full potential) Anybody have a feel for this? Is this a problem? And if so how might one address it?

All the best,
Konrad

 

[Tahoed]

A couple of us have built different servo trays. The tail stiffens up quite a bit after you install and bolt it in.

 

[Konrad]

I've been seeing a lot of fuselage servo trays that look little more than a small plywood rectangle.

Good point about the stiffening of the stab when glued in.

 

[Jonathan Wells]

I should have specified a servo tray, I used the supplied tray for a quick build, was keen to get the prototype flying.
Later today I will draw up a full length tray design and send it over to them.

 

[Konrad]

THANK YOU!

A pre-cut blank that fits the perimeter of the opening.

I'd like to ask that the opening for the servos and battery be left off the drawing. We all have our own Ideas as to what and how we like to mount the servos. If opening are provided can their size be put in the sale data to help the customer with their purchase of equipment?

 

[Konrad]

I have some concerns with the laser cut parts. It appears that the laser cutting vendor is having some issues with the thick plywood. My concern isn't so much about the quality of the parts but rather the life of the laser. I hate to see this kind of laser char as it will cut down on the life of the laser's lens. The smoke will deposit (condense) on the mirrors and focusing lens. These deposits will absorb the laser's power and heat up. This will burn the mirrors. And worse over heat the lens cracking it. These lenses cost $300+ for the lasers I've used.

The issue isn't just one of focus but one of beam angle (think of this as depth of field with a camera). Most lasers will allow the selection of different lens housing to select the proper beam angles. The narrower the angle the longer the depth of field, but the more power is needed cut.

I have to ask what servos were these tray cut to fit? The closest servo I have are the KST X0-8 but the the opening is still 0.75mm too wide. and the screw holes don't align. The Blue Birds BMS-A10V aren't even close. Maybe there needs to be an adjustment to the cut files?

All the best,
Konrad

 

[Jonathan Wells]

No idea, nothing to do with me, I did design the control horns though.

"I have to ask what servos were these tray
cut to fit?"

 

[Konrad]

Is there a way to ask TJIRC?

 

[Jonathan Wells]

I'll ask them... I'm sure you could contact them through their website or Facebook.

 

[Konrad]

Facebook, never!

 

[Tahoed]

 

[Konrad]

Found a minor quality escape. The stab hinge becomes rather distorted when flexed. This was traced to a long blob of epoxy from the manufacture of the wipers having fallen across the hinge line. This was easy enough to fix by grinding away the epoxy ahead of the hinge line. Well it would have been super easy if I hadn't slipped with the grinder!

All the best,
Konrad

 

[Konrad]

Since it looks like I'll be repairing my slip I thought I'd try to add some carbon reinforcement the trailing edge spar. I really don't think this is needed but some folks are making note that the stab isn't as stiff as they would like.

Something else I've noticed is that the TE of the wing and stab are about 3 times thicker than the comprable 60" Mibo Dart III. I'm not sure what constraints there may be between the two manufacturs but I see a lot of epoxy filler between the carbon skins of the Magnus. A razor sharp TE was to be one of the benefits of a molded ship.

 

[Konrad]

I'm not sure why I'm doing this. I don't recall reading of any failed stabs, and surely not from any front side flying. So it appears I'm acting like a lemming. Now the 5 of you that are following me know I don't like carbon tubes used as a spar. I feel that the use of the carbon in a tube shape isn't using the carbon to its fullest potential. This might explain why I'm using 60K roving (30k@2). I'm trying to bond most of this in the vertical plane to offer the greatest stiffness from the added carbon. I do have some carbon bonding to the top skin to add some more support to the hinge. After this cures I will then repair the damage I did to the elevator wiper.

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All the best,
Konrad

 

[Konrad]

The epoxy cured. With me this is always a concern.

I'm happy to report that the elevator still moves freely. With all the epoxy being thrown around the area, I was concerned that the elevator might have bound up solid. The key to this success was cleaning up as much of the "over flow" as possible with IPA and a Q-tip. You might have noticed that I masked the wiper. This was done to be a release layer should the wiper get bound to the stabilizer skins. after cleaning up things I then preloaded the elevator in the down position.

Just on the off chance that there was epoxy in the hinge, I will flex the hinge before full cure. I waited until the epoxy has set but not really cured. This is usually at the time point of about times 5 the pot life. With the epoxy in this state I then flex the hinge. I cleaned up any epoxy that might appear to bind the hinge and stabilizer with IPA. As the epoxy is close to being cured it will take some effort to clean it up. (As this model looks to be using a foam skin don't use acetone). I then unmask the wiper and again clean up any epoxy mess. I make sure everything is moving freely and that nothing is picking up epoxy. I then set (hold) the elevator at a setting away from neutral. This is in case there are some issues, it isn't likely to cause double centering.

Now did the carbon do what I expected? Yes, the stabilizer and elevator appear to be much stiffer. And this is even more pronounced at the hinge line.

I'd like to see TJIRC add some carbon cording to the vertical surface of the rear stabilizer spar on their next carbon Magnus production run. I don't know how the stab is laid up up but if some of this carbon can go over the top wing skin to support the hinge line so much the better.

All the best,
Konrad

 

[Konrad]

I forgot to weigh my stab before making the mod. Mine is now at 52 grams. I'd like to ask someone to weigh theirs for a before weight. I'd also like to learn what the carbon tube mod weighs.

All the best,
Konrad

 

[Konrad]

Yikes! I just unwrapped the right wing and was stunned at what I found. The layup of this wing half is drastically different than the left wing. There are gross surface discontinuities that are at least 0.15mm deep. These span the whole length of the flap. There is also a lot of weave showing indicating a dry lay up. Also one can see (feel) the sub structure in the surface. This is not what I'd expect to see in a quality molded model. I fear I'm going to have to retract my comment about the quality of the the TJIRC products being on par with some of the European manufactures.

I'm also showing what looks to be pry marks from a screw driver that may have been used to lift the stabilizer out of the mold. At first I thought this mark might have been shipping damage but now I'm sure this happened at the time of manufacturing.

Add these issue to the way too thick trailing edge and TJIRC is not the quality OEM I had hoped them to be. I still think they are generally a good value but one needs to inspect each model closely before purchase.

All the best,
Konrad

 

[Hank GB Z]

You need to stick with balsa models where you have more control over these things.

Hank

 

[Tahoed]

When I pay for a Chevy, I don't expect a Ferrari... The plane looks great if I take off my glasses and stand 2 feet away and instantly removes the Massive Discontinuity issue.

 

[Diceman]

Wow! You got servo frames with yours? I didn't even know they came with them! I did not get any (not that I would have used them anyway for what I put in)....Bonus!!!

I agree with what Ed said, you are not paying super top dollar for this plane, but your are getting a fantastic plane for the price even though it might same some small imperfections (they tend to all do in one way or another). This plane is right now my favorite 60" ship. I do not fly the Sunbird or even the Prodij much any more. The Prodij not so much because of now its rarity and one piece wing. The Magnus has become one I must take with me every where I go flying, that and my Mini Vision!