TOPMODEL CZ GRAFAS glider - Page 9 - RC Groups
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Sep 22, 2012, 04:01 PM
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Stan Rose's Avatar

Thank you for your prompt respose.

The Grafas that I am currently assembling does not suffer from poorly fitting tail halves. On the contrary, it's as if the manufacture has now corrected the problem. So much so that they are actually very tight and as a result somewhat awkward to assemble and I doubt very much whether they will come adrift in the air.

In the past when I have had the problem of loose fitting tail halves on other models I have solved the problem quickly and easily by taking each tail half in turn, turninig it upside down and laying it on a flat surface then getting a small, sharp screwdriver and holding the screwdriver vertically above the tube about a third of the way along, give it a sharp tap so that the tube within the tail half is slightly crimped. BEWARE- don't hit the tube too hard or you will have trouble getting the swivel rod back inside it.

Once reassembled the crimped tube is usually sufficient to prevent any further unwanted movement.

Of course this only works for metal tubes and not carbon ones.
Last edited by Stan Rose; Sep 22, 2012 at 04:18 PM.
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Sep 22, 2012, 04:39 PM
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Stan Rose's Avatar
Thinking a bit more about this problem it occurs to me that there is a solution for carbon tubes if you are happy to keep the fuselage and tailplane permanently assembled. (This assumes that you have suitable transport to accommodate this arrangement)

You could turn each tail half upside down and lay it on a flat surface, then carefully drill a small hole in the underside of the carbon tube. Re - assemble fus. and tailplane and when happy about final position put a small drop of thin Cyno down the hole, this will spread along the wire and bond to the carbon tube. Then it will never come off again!!
Sep 22, 2012, 05:05 PM
Full Scale Piper Cub Driver
Piper J3's Avatar
Why not just rub a little "glue stick" on the rods once in a while? Or put the slightest bend in one of the rods?

A lot less destructive...
Sep 23, 2012, 09:05 AM
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mikmerl's Avatar
Stan, because I have a lot of models that take up a lot of space I would be hesitant to make the stabs non removable. It’s not such a big deal really but I did have a high adrenaline incident (see post #103)

Piper I like your suggestion of the glue stick.
I will give it a go.
Some time I ago I poured thin CA on the rods and allowed it to dry. It was an improvement so I believe that the glue stick may be worth trying.

Carbon rods cannot be bent. They are either straight (as molded) or broken, there is no in-between state.

Sep 26, 2012, 01:29 AM
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gerryw's Avatar

just got a Grafas

Hello from Victoria BC.
I just got a Grafas and am assembling it. I have been reading this thread since I placed the order and waited patiently for delivery two days ago. I have put several balsa planes together, this one is an ARF with somewhat more than average work to complete. This will be my first high performance glider. I have a foamie Diamond 2500 which has served me well, but I want better thermal ability. I think the Grafas will deliver that.
The wings are done except for the connection between the inner and outer wing sections. Working on the fuze now.

I have 2 questions for people who have already built one:

1) In mounting the firewall, I noticed that the front of the fuze is cut at an angle of a few degrees to the right, like for a regular plane. There is no down angle, just right. I thought gliders did not need this as the motor is on for such a short time. The Diamond has no angle and does not need one. Should I file the front of the fuze flat and mount the f/w square, or continue with the current angle? In either case, I have to file a bevel into the f/w to fit as it is has no bevel now and stops about 5-10 mm from the front. The instructions indicate it should be mounted about 1 mm back from the cut end of the nose.

2) Mikmerl, in post #6 you used the regular servo connectors for the wing. Did you epoxy them in, or just leave them loose?

Thank you.
Sep 26, 2012, 04:15 AM
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Stan Rose's Avatar

Pleased to hear that you are also buiding a Grafas, I hope you enjoy the build as much as I am doing.

My advice is to leave the angles of the nose exactly as produced by the manufacturer because you will find that without right sidethrust most models will tend to vere to the left as a result of the torque produced by the motor. The amount of torque will vary depending on what powertrain you decide to use, as a general rule the more potent the powertrain the more torque produced.

As for downthrust, if after initial flights you find that the model climbs too rapidly and tends to loop with the motor on, you can appply down elevator to counter this initially and then it is a simple matter with modern computerised radios of mixing in some down elevator with the motor until you get the sort of climb that suits you, as the permanant solution.

I also sanded a bevel to allow the firewall to move forwards to the correct position and produce a snug fit in the tapered nose.

Hope this helps.
Sep 26, 2012, 09:09 AM
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mikmerl's Avatar
Stan described it well.

The right thrust seems to be adequate for the P factor in our case.

The manufacturer cannot know how powerful a motor you will install so he cannot have the appropriate down thrust built into the fuselage. This is a high lift airfoil so the faster you fly it the more down you will need during powered climb out. If you need to hold in let’s say 10 degrees of down elevator under full power with one motor then it will make little or no difference holding in 15 degrees with a more powerful motor.

It is easy to program your radio to introduce down elevator during powered climb, I prefer to do so manually every time I go to full throttle.

As for the servo plugs I have glued both male and female plugs in the respective slots so that when the wing panels are joined the servos are automatically connected. If you like, have a look at another of my assembly threads post #18). I did the same on my 4m mouldie.

Sep 26, 2012, 03:12 PM
-Flight enthusiast_
gpeden's Avatar
HI Jerry,

I used the suggested multiplex connectors for the wing joints and it worked out well. This was one area where I didn't strive to save weight at all cost because I figured the connector would be more resilient and reliable. In fact they help keep the wing together If you go that route, I found it to be useful to glue in thin balsa strips in the bottom of one side's connector to hold it in place during the setting of epoxy, because the pre-milled hole is a little deep on one side of the connections.

Oct 12, 2012, 11:48 AM
Registered User
Originally Posted by Mathelo
Every time I see one of these I wonder about the torsional rigidity of the wing given the lack of D-box and the round spar. Has this ever been an issue?

Hello fellow modellers,
I like to lift this question again.

Is there any problem with torsional stiffness?
How is ribs attached to carbon spar, Ca glue?

Like to know before ordering a Gracia.

Oct 12, 2012, 12:54 PM
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mikmerl's Avatar
A few days ago while flying the Grafas I was distracted by the sound of a helicopter in the vicinity. I looked behind me towards the direction that the sound of the helicopter was coming from to assure that there was no danger potential.

When I looked back to where the glider was last I could not find it. Seconds past (felt like minutes) while I was franticly scanning the specific space to no avail. I was about to give up when I saw a movement, shifting my attention there I caught the glider in a near vertical dive very close to the ground.

There was no time/height for a gentle recovery so I just yanked up elevator expecting to hear the wings fold or flutter. To my relief the wings took the crazy load and the glider traded off the speed it had achieved for altitude.

Needless to say I landed, stowed my gear and went for a beer.

The above event is outside (way outside) the normal performance parameters of this glider and it held up. After hundreds of flights I have yet to encounter any “worrying” traits regarding the rigidity of the wing structure, either along its length or torsional. The covering contributes a lot to torsional rigidity as well.

Oct 12, 2012, 02:00 PM
Registered User
Hello Mike and thank you for your answer.
Judging from your little scary event the wing seams to be strong enought.
Hope the Mythos was cold

Oct 13, 2012, 07:57 AM
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mikmerl's Avatar
I see you’ve been around.

All six of them were very cold.

Oct 18, 2012, 09:15 PM
Ask me about VTPR
oldscooler's Avatar
Can someone post all the airframe and wing specs with weights please? What airfoil does it sport too?

Oct 19, 2012, 12:12 AM
Registered User
mikmerl's Avatar
See the manufacturer’s page for this glider, all the info you need is here.

You can download the manual as well.

Oct 20, 2012, 12:04 PM
Originally Posted by oldscooler
Can someone post all the airframe and wing specs with weights please? What airfoil does it sport too?

Here you go:

Zb/Esprit Model

Airfoil : MH 32
Wing area : 1090
Wing loading : 10.5-11.5 oz/sq.ft.
Empty weight : 46 oz. (1300g)

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