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Vertical Stab Design

Old 01-29-2006, 02:03 PM
  #1  
TCBLightning
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Default Vertical Stab Design

I'm looking for some feedback on my project. I'm building a Duellist and want to modify the tail section after the Mooney. I've made some sketches and wondering what you think.

When I first saw them next to each other (first pic) it looked like I was giving up quite a bit of surface with the mod. But in the second picture with the mod laying over the top of the original it doesn't look that bad.

Thanks in advance for your comments.
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Old 01-29-2006, 02:33 PM
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Tall Paul
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Default RE: Vertical Stab Design

The center of the area of the forward sweep is a couple inches ahead of that on the original.
For a twin, it would be better to move the vertical a bit aft, while maintaining the sweep, for the single-engine problem.
Old 01-29-2006, 03:33 PM
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Default RE: Vertical Stab Design

There's likely enough reserve stability that the shift in the center of area won't be noticed but Paul is technically right. A further advantage to shifting the area back slightly would be that you can alter the hingeline to a more vertical alignment to make the rudder larger for better one engine out compensation. Move the fin to the rear by about 3/4 inch and keep the hingeline the same at the top but make it intersect with the elevator hing line at the bottom . That'll widen the rudder by about 3/4 inch as well.

.... at least that's what I'd do.....
Old 01-29-2006, 09:01 PM
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TCBLightning
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Default RE: Vertical Stab Design

Cool! Thanks for the suggestions.

Here's a pic with the modifications. It looks better.

The first picture is of the old and new drawings. The second picture is the new drawing over the original plans.
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Old 01-30-2006, 12:27 AM
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Default RE: Vertical Stab Design

Well, looks like I should have looked at the first pic a bit more closely. That Duelist is a BIG model I gather. I didn't bother to check the cutting board grid.

My 3/4 inch seems lost in the outcome. Go for another inch and I'd say that would put the fin area back where the original was centered and produce a slightly more vertical hinge line. Although the hingeline doesn't look bad as shown in the new pics.
Old 01-30-2006, 08:09 PM
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TCBLightning
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Default RE: Vertical Stab Design

The fuse is 57" from tip to tail. Wing span is 67".

Just curious if the recommendation to move the stab further back is for the pupose of preserving the length of the tail moment or to increase the size of the rudder? Maybe both?

I'm also going to flip the horizontal stab around so that the leading edge is straight and the rear tapered forward. It will be the same size as the original just backwards to look like the Mooney.

I attached a picture of my first Duellist FYI.

Thanks again for the feedback! This is interesting.
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Old 01-30-2006, 09:50 PM
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Default RE: Vertical Stab Design


ORIGINAL: TCBLightning
...Just curious if the recommendation to move the stab further back is for the pupose of preserving the length of the tail moment or to increase the size of the rudder? Maybe both?...
Definetly a bit of both. Of course how much rudder you want depends on how you fly the model. You obviously have experience with the Duelist so you know more about how it responds to rudder and it's one engine out manners than I do. I just like big controls because I'm a control freak...

Your mods will add a nice bit of character to the design.
Old 11-05-2006, 10:07 AM
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TCBLightning
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Default RE: Vertical Stab Design

I have finally made some progress on this build. Thought I would update the thread.

Thanks for the advise/discussion, it is looking good.
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Old 11-05-2006, 11:27 PM
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batchelc
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Default RE: Vertical Stab Design

TCB,

Some simple math may help. Tail area is only half the picture. Tail Volume is what you should be looking at!

Tail Volume = ((Area Vert Stab + Area Rudder) x Tail Lenth)

Do this for the old and new, make sure they match or the new one is a bigger number. Tail length is the length from the CG to the centroid of the vertical or horizontal stab + rudder/elevator.

So if you move the Vert Stab and rudder close to the CG the area needs to go up as well.

That will help with stability issues.

A less effective rudder will raise your Vmc, the lowest controllable speed at which one engine at full power and one engine dead can be maintained (like when you just took off, one engine dies and you have to clib over a tree, etc).

Your not in the plane so you really dont care about control forces. If you were, your leg would be mad at you with a small rudder - dead leg dead engine....

I would at least match the rudder area and keep the percent of stab and percent of rudder the same.
Old 11-06-2006, 07:46 PM
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TCBLightning
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Default RE: Vertical Stab Design

Thanks for the info batchelc.

The horizontal stab is epoxied in place so I'm comitted to where it is at. It is the same size and in the same place as the original design just flipiped around so the LE is straight and the TE is tapered.

I added to the vertical stab so it actually reaches forward to the F10 former and was considering adding more to the rudder. After I do the math I'll see how it comes out (I knew those algebra classes would come in handy sooner or later!)

My guess right now would be that the center will turn out somewhere under .5" forward of the original design. I'm sure that can be significant in a plane this size.

For what its worth I had done touch and goes on one engine with the yellow and purple model and used less than half of the rudder throw on climb out.

Either way doing the math and adding some meat to the rudder would be some cheap insurance.

Thanks again for the feedback. Good stuff!
Old 11-09-2006, 08:34 PM
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TCBLightning
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Default RE: Vertical Stab Design

After posting the last reply I took a closer look at my design.

When I was building this the area that was availble for the horizontal stab mount was much thinner than I was comfortable with so I butted the stab up against the F10 former as in the original design. I also mounted the vertical stab up against the F10 former as well.

Without doing the math and just judging by the attached picture the centroid of the vertical stab is about 4 inches forward and I decreased the length by about 3 inches.

As I mentioned earlier the horizontal stab is glued and in the original position per the plans so the pitch stability should not be affected. The yaw stability however is a whole other question, specifically with an engine out.

The vertical stab is not glued yet so my plan is to make it extend a little further back and stretch the rudder some to make up for the shortened overall length. That should give me enough to work with...

I'll keep ya posted.
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Old 11-12-2006, 09:37 PM
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batchelc
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Default RE: Vertical Stab Design

The rudder area in the top looks to be a lot more than your mooney style stab. Remember the mooney is a single engine airplane!
Old 03-27-2007, 08:05 PM
  #13  
TCBLightning
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Default RE: Vertical Stab Design

I finally finished and flew the Duellist. There is no real noticable difference in normal flight with the modified stab.

With the added surface there is plenty of rudder. Ultimately it all depends on when you need it and how you use it, and if ya run out of altitude or air speed too soon.....

I hope to get some ariel shots soon.
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Old 03-27-2007, 10:26 PM
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batchelc
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Default RE: Vertical Stab Design

Looks great. Very "classic" old-school mooney from the side.

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