Vertical Stabilizer FILLETS?
 

I'm building a 4* 40 and the vertical stab just does not seem "strong" enough to me and I was thinking about trying to make some sort of fillets to strengthen it.

1) Are they needed?

2) Any suggestions what they should look like?

3) Is it alright to make them from balsa and soak them with CA?

I will leave this one to people actually experienced in the 4*40. I haven't owned one.

You can take triangle stock and glue it to the fuselage and vertical / horizontal fin. Then sand a small radius on the exposed part of the triangle. when fillets do not need to be big, i just use filler and work it into the corner like the tile layers work the cement into the tiles. Either a pre-fab radius tool or the tip of my finger, depending on how big I want the radius.

See answer to question 2. Soaking in glue will just add weight. Make sure the bonding surfaces have enough adhesive. Aditional adhesive will just add weight.

Hope that helps.
Rafael

I had a 4*40 years ago, never added anything to the vertical stabilzer to strengthen it, worked well for me.

I have used triangle stock sanded on at least the forward end between the stab and fuse on many trainers over the years. Usually I cover the piece first leaving bare wood on the gluing area and remove any covering from the area on the stab and fuse where the piece will go. CA works fine. Adds alot of strength and very little weight. If you think the area is weak why wait until the vertical fin breks off in flight? This is an easy upgrade with little downside.

Hi David,

I am not familiar with the 4*40, but if you download the instruction manual for the Ultrasport 40 from great planes, they have a rather neat way of doing it. It involves using a dummy vertical and horizontal stabilizer as a guide to help you shape the fillet. This blends it into the turtle deck. Not sure if the 4* is similar or not.

Calvi

Tom,
Sounds like its a 40 sized sport plane. Would such a model need fillets?....I'd say No if the vertical had reasonable thickness like 1/4" or so, and its base was also solid, at least 1/8" stock

If you wanted to add some fillets, fine. Triangle stock would work great, but make sure it is contest grade and as light as possible. Another way to make it as light as possible ( strictly for looks) is to shape 1/32" sheet around a dowel first to get a curved sheet. Sand the edges to taper and use thin ca to glue them, but no need to soak them

in the event of a nose over in tall grass or bad landing the rudder may break loose right at the fuse line, if you beef it up with fillets the rudder may break in half on a bad flip over landing.
The other day I was positioning my plane on a grass strip leading it around by the rudder and I broke the rudder loose from the fuse, wish I would have put filets in that one!

If I understand you right, you would rather build a model for the crash rather than for flight? Okay with me!!.....

I just built a Mid Star, which is very similar to the Four Star. Like you, I was worried that that the butt joint would break easily, so I used balsa triangle stock to reinforce the vertical stab. I just glued the two triangle pieces in place with Titebond. I didn't soak them with CA. I've nosed over several times and the joint has held up. But of course I don't know how the joint would have held up without the triangle stock.

I am not familiar with the 4* 40, however the best way to make the vertical stab more "rigid" is to add "braces" @ an angle of 45 deg from the top part of the VS to the horiz stab on each side. This could be done with thin pushrod material or using cables (in that case you would ad two more cables for the bottom of the HS to the bottom of the fuse. It's very effective & used on full scale too . Hope this helps, I can provide a pic or 2 if needed.
Cheers V.

No actually the opposite, I rather it left as a break away, the plane I refered to actually crashed that day because the rudder layed down on me during a maneuver ( It had cracked from me grabbing on it to position it on tall grass runway)

I like Vasek's idea of the wire brace's .. I make my own , I use crimp on elect connectors and 2 56 cap screws along with 2 56 threaded rods . It strengthens up the tail of your planes a lot ..You can also use bike spokes but I find the thread is usually a bit different .. Its okay if you use plastic clevises ..

Another avenue would be a filet of Epo-Grip #30 Paste. Just smooth and feather it out with water and a drop of dish soap and once cured monocote over it.

Well Erik,

I used the Epo-Grip to do the fillets on the underside of my Ultrasport horizontal stabilizer. I mixed it with microballoons to keep the wieght down. It looks good ,the soapy water does a nice job. I am not so sure that Monocote will stick all that well, I don't really need to cover it as it is beneath the stabilizer but will try covering it anyway.

Calvi

Thanks for the tips guys. I'm going to try Epo-Grip & micro balloons , I'm disabled now but that sounds like something I can do with only 1 hand.

David

Hi David,

Just make sure to tape down your piece of cardboard or whatever you are going to mix up the Epo-Grip on, it is so thick it is tricky to mix it with two hands let alone one, I am sure glad I picked up a pallet knife to mix mine with.

Calvi.

Thanks for the heads up, I would have made a BIG mistake. I've got to go to the hobby store to get the micro balloons and on the way back I'll swing by the local art supply store and grab a pallet knife. So then all I need is some tape and a little luck, thanks again.

David

Hi David,

I tried some monocote on the fillet this morning and it did stick, not as well as to balsa, but it does stick. So how is your hand coming along, you got bitten by a prop did you not?

Calvi

Hi Calvin,

I plan to try it tomorrow (dinner thing tonight) when it warms up a little more. Glad to hear the monokote stuck for you, as I plan to do the same thing.

No prop, I wasn't that lucky. I had a massive stroke back in 2004 and my right side has never recovered. I can move it but the fine motor skills, the fingers and the ability to control my right hand.

So now I build, s-l-o-w-l-y with one hand and help from my friends, old and new!

I was an advanced builder of warbirds before my stoke and now I have to learn to do things all over. My son flies the planes since I cannot. This is my first plane that required stabilizer fillets, I was used to wing fillets but not tail feathers. Thanks again for the help, I'll continue to let you know how things turn out.

David

So sorry about your stroke David, I am glad you are still building, the more you use your right hand the more new pathways you will build in your brain(at least that is what I have read) who knows maybe you can recover to a state where you can fly again.

Calvi

The 4*40's I've built come with triangle blocks to gusset the vertical fin to the horizontal stab. Easy and all you need to do is round the ends a bit to make them look nice. I always glued them in after covering and mounting the tail. Then cut a piece of covering to do the gusset. I've never broke the fin off a 4* Look back at the instructions or plans it should show triangle stock there.

Peace,
J

The best of luck with your recovery .. It is a slow process ...I too am recovering from a stroke and one of the things I am most thankful for is the understanding and support of my friends

I'm recovering very slowly, 9 years in August and counting and just happy to be here. You really find out who your true friends are, I got a few surprises from my list of friends.