Ok I am new to Pylon racers and was wondering about the tail incidence and the best way to get it close to the right way! I have a predator and the kit doesnt seem to come very qwell cut for tail incidence. I did trim in the cutout for the tail to be straight but now is the hard part. How to get it level with the wing. I have not glued it yet so I am curious as to what is a good way to get this on the right way?

SpdRcr

I used a small bubble level and placed it in the V and used a Robarts level on the wing. Get one of those 2-3 dollar bubble levels and use just the little capsule that's got the green stuff in it. Than you can eyeball the wing if you don't have a wing level. Try to get to as close to zero as possable.

The incidence of the saddle may be off. But something you might not have realized is that the stab saddle will look like it has down in it. This is because the fuselage sides are at an angle. If you make the stab saddle look like it is level with the wing saddle, you will have a lot of up in the stab.

If you don't have an incidence meter, they make a valuable addition to your shop. The [link=http://www2.towerhobbies.com/cgi-bin/wti0001p?&I=LXET66&P=7]Robart Wing Incidence Meter[/link] is only $27 and is the prefered meter by many. I also like the [link=http://www2.towerhobbies.com/cgi-bin/wti0001p?&I=LXPW71&P=7]Great Planes AccuPoint Laser Incidence Meter[/link] for $20. It used to come with a small bubble, but they don't say that explicitly on the Tower page. I believe it probably still does as I don't remember it being mentioned back when I got my two.

Mounting the V-Tail is what I hate to do. It seem like there is too much cuss and cry during the cut and try. However, a couple of measurements and a bit of trig with a simple procedure makes this nearly as easy as mounting a conventional tail. OK, nothing is that easy, but then the lower drag and redundant elevator function makes it worthwhile. The drag is lower because there is one less junction between the fuselage and flight surfaces.

First, measure the width of the fuselage where the Leading Edge and Trailing Edge of the V-tail meets the fuselage. Subtract the TE width from the LE width and divide by two. I try to measure this to a 1/32" accuracy, though my eyes are starting to water (CA fumes). Take the Tangent of the angle to horizontal (180 – {V-tail angle})/2, for a 120 degree tail, it’s 30 degrees. So working out the trailing edge position is : [(LE width– TE width)/2] x tan 30. This distance is the amount that the TE of the V-Tail is lower on the side of the fuselage than the LE for zero incidence.

Place the fuselage with the wing mounted so that the leading and trailing edges are blocked up an equal amount (zero-zero) on the obligatory flat surface. Mark the position of the leading and trailing edge of the tail on both sides of the fuselage, making sure that the trailing edge is marked lower than the leading edge on the side of the fuselage by the amount that was calculated. Remove the wing. Make a template of the V-tail’s airfoil cross-section and mark both sides of the fuselage with the bottom of the airfoil. Turn the fuselage at the same angle that the tail is to be mounted and block up so that you can cut into the tail at the correct angle by just making a vertical cut. Turn and repeat. If you are always going to use the same angle, just make a plate that mounts to the firewall that holds the fuselage steady at a 30 degree angle.

Bob

Or, glue in a tail platform that is flat in relation to the wing (zero degrees incidence) and that has a centerline marked accurately on it. Glue the V tail to the platform, lining up the dihedral break of the V with the centerline of the platform. Use a thin bead of 5-minute epoxy for this. Pin the V in place using two straight pins, one at the front and one at the back.

As the 5-minute epoxy cures, eyeball the tail tips from behind to make sure they both stay the same height in relation to the wing. (The wing is flat and level, an easy visual reference.)

When the 5-minute epoxy firms up, fill in the sides and top of the fuselage/tail joint using lightweight epoxy filler or spackling putty. The spackle isn't very strong, so saturate it with CA after it's dry. Then cover with the film or paint of your choice.

Duane Gall
RCPRO

Duane, thats very similar to how Lewis mounts his tails. I believe his kits (Vector and Pacemaker) come with a small v-tail aligning jig that is glued to the bottom of the fuse.

I had intended to stay out of this. There is an easy way. This may or may not apply to the predator. In the side view of my airplanes the elevator hinge line is 90deg to the wing chord line. I designed it that way for a purpose. There are four axes to set.

So with the wing mounted to the fuselage turn it upside down. Block up the wing so the incidence is correct and the tail seat is just resting lightly on the upside down vee tail. Axis one is now set.

Centre the tail in the fuselage. Axis two is now set

Stand a square against the wing T.E. Moving the square along the T.E. as you do it measure from the square all along the hinge line both sides. When it measures the same along both hinge lines axes three and the incidence are set.

Set it up roughly before applying glue.

Ed S

Ed,
Your instructions go the point of setting "axis three"..but at the beginning you say there's four axis' to be dealt with....what's the fourth axis in your instructions?
GS

I have a another solution that I think working very well. (see the pic) this is a tool that I made for gluing the two tail blades together. When mounting the stab on the fuselage
I level the plane so the wing is at o deg. then put the upper part of the tool that fits very well. Then I put a steel ball on it. It will shoe very fast if the stab is down or up wards.

Gary,

That would be the Axis of Ed-vil.

Well a wealth of information you guys are and most of it made sence! LOL I am gonna forget someone mentioned trigonometry! HEHE Well thank you very much and I will let you all know how it comes out. I am still waiting for my engine mount from Jett so it wont be this weekend but maybe next that we will fly it for the first time!

Thank you guys very much!
SpdRcr

Gary,

Ignore Gall's remark, since he got the prop in the eye all of his airplanes are crooked!

In simple terms for Gary, and all those others too timid to ask.

1) A line across the tips of the tail parallel with the top of the wing.

2) Tail centered left to right on the fuselage

3) Tail centered on the fuselage and square with the wing. (Get this wrong and you have a great big Vee rudder offset)

4) Incidence.

Items 3 and 4 happen with the measuring part.

Ed S

I have just assembled a great planes viper which I have been told is a 'predator' and simply screwed the vee tail on and flew it- absolutely no problem so can only assume the 'seat' as glued in is ok. granted it dosen't look right but as some wise man has
previously said the taper in the fuselage will mislead you. have checked my transmitter trim and absolutely ok,
regards trevor h, new zealand.

Ed,

Did you hear that? He called me a "wise man"! Neener, neener, neener!

Although I suppose "wise guy" is close enough to suit you ...

Duane,

Do not get too excited. Trevor is a decent human being. He tries to be nice to everybody. He needs to live in North America for while, we would soon cure him of that!

Ed S

Hey Ed, thanks for your kind words..............no I haven't forgotten the rewound G.bees. they will be sent to you around mid/ end of january. My plug man has been rebuiding his spotwelder complete with holding jigs for the globeed plus a wire container.
The viper is a well built model and I believe anyone who mess's around with the tailplane dihedral seat will only make it worse. Its easily drawn to check the seat angle- I did it yesterday with a bottle of wine as my companion- yes xmas day was yesterday here, and my wife was doing some amazing cooking........ham , turkey, lamb- no wonder I have put on some weight!

The biggest problem with anyone setting up the vee tail for the first time is that the elevators need to be thoroughly checked for correct alignment when connecting the pushrods- its easily done with a 'constant reference'- even a bit of 1/4 square balsa top and bottom of each tailplane panel will give a very good reference point to control the accuracy. The other way is to make up a guide using say 1/4 inch balsa with an accurate slot cut into it the same thickness as the tailplane. Mark a centre line for and aft of the slot and there you have a very suitable jig. It dosen't matter whether you don't sit the template parallel to the centreline of the tailplane- as long as the slot is a tight fit then the centreline will always be correct.
Have a good xmas and new year- regards to you all from new zealand, trevor hendersn.

I've just built my second VIPER and no the tailplane on this model had been assembled wrong in the factory.....the central block sitting above the vee joint was not glued central to the joint and no matter how I screwed the thing together it wouldn't sit correct. I reshaped the actual seat in the fuselage with the Dremel and actually over cut. I had already concluded that the vee block above the joint determined the incidence so with microballoons and expoxy reformed the seat. I bolted the wing to the fuselage, slopped in the microb/ epoxy mix, inverted the whole thing on my bench then sat the tailplane into the tailplane seat and waited for it all to cure.......I now have some rather nice fillets at the fuselage/ veetail junction.....all easy and all realigned. How about the screw holes.....because now the holes don't lineup I simply cut the screws to about quarter length and epoxyied them into the holes. Nobody here knows that they are short and only I will ever need to undo the screws. I suspect this will give a far stronger rear end as I had glued the tailplane alsao to both the front and rear faces of the tailplane cut.
trevor h.

Good solution trevor, I do know of one chap who lost his tail section completely on his test flight. We were at the new Bairnsdale field with B.Murphy and crew for some test flying and socialising just before Christmas 2004 when the incident occurred. Seemed to be a structural problem with the V-tail mount material? Incidentally the aircraft went into a flat spin, once promptly shut down, and only sustained minor crash damage, however this is the only incident that I know of in relation to tailplane compromise in comparison to after factory modification which I feel would be well worth the effort for peace of mind.

you know barry murphy..........oh. he and I are mates so I understand now how your model got broken. He dosen't survive too well on rum, but ask him about the bottle of booze that will still be in his top cupboard that Liz and I took to aussie duty free for him. He turned the colour of the drink in the space of a few minutes...........big t.

I will see him at AMPRA and mention it to him, we got stuck in an irish pub at the last meet at Warnambool because of poor flying whether, worked out quite well for a change.
Schimty

should have been at AMPRA this year but intend going into France for the w/c.....can't go everywhere! Baz has emailed me last night with his FAI pylon results- looks like when he was going well everything was fast -however he also did indicate a few broken needles and I believe a damaged model.....you had better take him to that bottle of booze.
regads Big T.[:-]