My F3J project - takes flight - Page 2 - RC Groups
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Nov 20, 2009, 10:26 AM
UAS Test Pilot
SpeedMaster's Avatar

It looks very cool indeed.
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Nov 20, 2009, 11:34 AM
Daryl Perkins's Avatar
Roydor - can I ask what your stabs weigh? Are they stiff enough?
Nov 20, 2009, 04:42 PM
In F3J size does matter!
roydor's Avatar

The stabs weigh 33 grams uncovered with both joiner and pin. I expect them to weigh 37-40 grams depending on the covering I chose.
Torsionaly they are the strongest stabs I've ever seen. In terms of bending they're more then adequate (I'd be very surprised if they aren't "Daryl proof").
The first stab I built, I loaded until it broke and then I abused it to see how strong it really was so I have a good feeling about their strength and durability,
The most surprising thing is how resistant they are to LE damage, this is because I took the time to mold a joggle in the leading edge so no Micro balloons to break off and shatter.
I’ve made a set using 25 gram glass and 0.6 mm balsa instead of carbon 90 and Herex but due to overlaps in the spar web, root and tips the weight was not reduced (the fabric for the entire elevator weighs about 8 grams wetted out). Additional weight can be saved in the skin but it’s just not worth the work (probably not more than 5 grams if I’m lucky)
The only way I see to really reduce weight is to get rid of the joiner system and go to a one piece elevator (it will save around 8-10 grams) but I think it’s ugly.
BTW the stab is 7 dm in size.
Nov 20, 2009, 08:50 PM
Detail Freak
target's Avatar
Awesome looking plane; I hope that it flies as great as it looks for you!

Nov 20, 2009, 10:06 PM
Daryl Perkins's Avatar
Thanks Roydor,

I wasn't sure the term "Daryl proof" had made it all the way to Israel.... That stab weight is awesome... very nice

Nov 21, 2009, 02:00 AM
In F3J size does matter!
roydor's Avatar
Attached are pictures of the balsa elevator Vs. the carbon one and a cross section of the first test elevator.
I used the balsa elevator on my modified Perfect:
see post 21

Nov 30, 2009, 09:29 AM
Registered User
jojoen's Avatar
Nice. Looking forward to see it in the air

Dec 11, 2009, 01:14 AM
In F3J size does matter!
roydor's Avatar
I'm afraid that I've made very little progress these past couple of weeks. I did however manage to get the pod ready for radio installation. All the parts fit rather nicely and I think I'll be able to finish the fuse around 600 grams with a front CG. made a ballast system and I can fit in 550 grams of brass, going to make an aluminum ballast of about 250 grams as well. Should be enough, I don't see much reason in a grater resolution of ballasting anyways. Might make a 400 gram ballast bar though, just in case.
I've made the servo tray as far forward as I could and in the nose a 5 cell battery. For receiver I'm going to try the AR7600, it really neat, super compact, super light for a 7 channel Rx.
Dec 11, 2009, 03:18 AM
Registered User
Tuomo's Avatar
May I ask why you have servos in front? That makes longer unsupported length in pushrods. And now you have to make servo mount removable, to take rx battery out.
Dec 11, 2009, 03:40 AM
Registered User
jojoen's Avatar
The receiver is so light (4g) that he can save a lot by pushing servos forward and he could slide the battery inder the servos and in front. He would probably have to go for lipo since his tail is so light so battery will be very small.
Dec 11, 2009, 03:47 AM
Registered User
jojoen's Avatar
Vladimir sells a nice little gadget. 1 lipo and regulator + charger + buzzer in one unit. You can get it with different sizes. The Ukraine team used it for the EC this summer. You can just plug in 12v directly and it will charge. And buzzer tells you voltage and will beep a lot with low voltage.
Dec 11, 2009, 04:38 AM
Registered User
Tuomo's Avatar
Nice new electric stuff. Unfortunately my planes still need some nose weight, so no use investing in lighter rx battery Maybe, some day, Roydor will start commercially producing his "lighter than" air elevators
Dec 11, 2009, 09:50 AM
In F3J size does matter!
roydor's Avatar
Moving the servos forward reduces some nose weight as they are heavier then the RX just as Jojo said. At 600 grams for the entire fuse I need additional 60 grams in the nose in addition to a 5 cell battery. The servo tray holds the battery in place to keep everything from rocking around are disassembles using four screws. The pushrods will be supported all the way so no problem here.
Dec 17, 2009, 05:49 PM
Registered User
Impressive stuff , you really made your self a plastic fantastic !!
Dec 19, 2009, 05:01 AM
In F3J size does matter!
roydor's Avatar
I was asked to give some more information about my elevator so here goes.

I started out with a broken Pike Perfect elevator a friend gave me, It was severely damaged but I could salvage the root interface which suited me fine because I wanted an elevator interface identical to the Perfect since I wanted to be able to use the Perfect Elevator with my rudder on my modified Perfect.
I rebuilt the LE and the Dbox and shortened it so its size was reduced to 7 dm instead the 7.5 dm of the Perfect elevator. The tip shape was changed and shaped to provide lines I was more comfortable with.

After completing the master, shaping, sanding, painting it to perfection I molded it and made joggle molds detachable to the elevator molds. The idea behind the joggle is to have overlapping material in the leading edge and spar to provide a solid load bearing joint. If you compare it to a conventional joint it isn't necessarily heavier as the amount of glue used to join the parts is minimal and the strength is maximized due to the fact that the loads are transferred through the laminate itself and not through glue with microbaloons which is brittle.

In the pictures provided you will see the production stages, the molds, the joggle, the overlapping etc.

The elevator itself has very little material in it, I've found that the outside layer which is 90 grams/m^2 carbon weighs only 7 grams with glue since there is so little material. If I was to change it to 25 grams/m^2 glass I would save just 5 grams which would be mostly added back by overlapping carbon over the glass at the root, tip and web areas (as I discovered when I built a balsa and glass elevator). The reduction in weight was simply not worth the effort and the increase in strength was more than worth it. On a fully molded tail however, changing the glass to carbon would be equal to at least 15 grams more weight which is considerable. In a fully molded elevator the entire structure works to strengthen the elevator in torsion so itís also stiff enough and does not require full carbon construction to achieve the required strength. A d-box elevator however, can suffer from lack of strength if not built correctly and benefits greatly from the carbon construction.

The core is 1.2 mm Herex, same as I used in the wing. It weighed 3.5 grams for the entire elevator, Balsa .6 weighed 3 grams, lighter balsa was out of the question for it would have greatly suffered from hanger rash and at such a thin core would have affected the strength as well. The inner fabric is 25 grams/M^2 glass. The root is reinforced up to the aft location pin and is very flimsy aft of it, where strength is not really required, same at the tip, itís just as strong as is needed.

The spar is made of UD tapered down from 6 mm in width at the root to 2 at the tip, thickness is also tapered from .4 mm to .2 mm. The web is made from the 90 gram carbon of the outside skin (at 45 deg) and an additional 90 gram fabric with 0-90 orientation, adding both to the spar strength and preventing buckling of the web. The trailing edge is a spur of the moment idea, I already started mixing the gel coat for the mold when I decided to leave space for a spar at the TE should I want to glue it with the same glue used to close the two halves, I took a piece of spruce, tape it over and glued it to the parting line just before pouring the gel coat on. this gave me a compartment I could place a carbon strip when closing the two halves, after completing the elevator by gluing in place the ribs and adding carbon cap strips to them I can sand the TE to size, 4 mm at the root going down to 1.5 at the tip, the TE is just .5 mm in thickness. The joiner system weight to those wondering is 3 grams for the joiners, another 1 for the tube and about 1 gram extra of glue, which adds to 5 grams in total. The root is about 1.5 grams so if I had wanted to make a one piece elevator I could have built one at around 30 to 35 grams.

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