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-   -   Vertical tails (http://www.rcuniverse.com/forum/aerodynamics-76/11207313-vertical-tails.html)

Nitrovein 08-27-2012 02:50 AM

Vertical tails
 
I´m building a plane that´s 90% like the SIG Wonder, meaning it will look like it and be about the same size but I have not used the plans etc from that.
(If this question has been asked 100 times before I apologize, I haven´t looked that hard in all honesty)

Just like the Wonder I´m using two vertical tails without any rudder, but I started to think that maybe a different angle (like a V-tail) would be worth trying.
Or is this asking for trouble when not using any rudder?

Any insight is most welcomed! :)

da Rock 08-27-2012 03:19 AM

RE: Vertical tails
 
The two vertical stabilizers on the Wonder are effective at yaw control. So long as you keep the same side area with your fins, you should have the same results. Of course, your fins will need to be larger, and larger is heavier. Also, the Wonder's fins did not add horizontal area, and yours will. It's not needed of course.

If you're looking for anything other than looks, about the only thing you'll be getting is a minute increase in drag from the interference drag created by surfaces that meet at less than 90 degrees and the very minor increase in drag from any increase in wetted area that would come from larger fins.

There shouldn't be anything of significance that comes from your changes. Give it a try.

Nitrovein 08-27-2012 06:50 AM

RE: Vertical tails
 
Thank you "da Rock" for your reply.

As I don´t have the plans for that plane I´m not sure if my tail is larger or smaller, I will need to look in to that (before I make it).
I don´t have any goals with this plane other than flying it, so my main concern was flight characteristics more than speed. But speed is nice too! :D

BMatthews 08-27-2012 10:25 AM

RE: Vertical tails
 
The fins on the Wonder do more than simply act as fins. They are also the end plates which support the extension piece between the wing and the elevator. Frankly the "wonder" behind the Wonder design is the simplicity and elegance of how the minimalist designed structure works so well.

If you're simply wondering if you can slightly angle the fins which remain in their original spots for a different look then yeah, nothing bad will come from it. You could angle the fins by up to around 15 to 20 degrees from vertical before you'll begin to add any significant amount of effective horizontal damping that would fight the elevator. Beyond simply altering the angle of the original fins I'd want to see a sketch of what you're considering before I could give any ideas on what the effect would be.

Nitrovein 08-27-2012 01:50 PM

RE: Vertical tails
 
I couldn't agree more with you "BMatthews", I think it was the wonder of simplicity that got me interested. Although I have added some futures that I wanted (but maybe not needed) such as dual servos for the ailerons.

I have nothing planed for the tail and no drawing of anything as this has been a freehand build with nothing more then some measurements on a piece of paper.
But the idea is to keep it close to the original, I´m not trying to reinvent the wheel here, just build and fly. :)
The two main things that will set it apart from the original is that I intend to use a longer chord on the horizontal tail plate for good pitch stability. I have also used a semi-symmetrical airfoil.

If I return the question, is there any shape or form to avoid? Maybe I should concentrate to get the drag as low as possible... Speed was after all one of the futures that got me in to this project. :)

(Just too clarify, I don´t own a Wonder and have never seen one in person either, so I might be of on several measurements compared to the original)

BMatthews 09-01-2012 10:38 AM

RE: Vertical tails
 
A model of this sort isn't the type of model that you will "just fly around level" so you don't gain anything by using a camberd "semi symetrical" airfoil. And you risk a lot by having to deal with the pitching moment of the cambered airfoil overpowering the extension and elevator to some extent. So my advice would be to stick with a symetrical airfoil and make the whole model "flat". The amount of up trim you need to fly will easily be set with a little turn or two of the clevis or a click or to at the Tx.

To make the wing easier to build you can also use a flat rear section. Something like this.....

OK, so I got carried away and almost drew the plan needed for the whole model.... :D

Looks like the sketch will need to wait since the RCU server doesn't seem to be accepting images at the moment.

Nitrovein 09-01-2012 04:32 PM

RE: Vertical tails
 
I thank you for taking the time, but no need for any drawings as I´m near complete. :)
The thing that I haven't made yet is the vertical fins and the horizontal tail is just near finished.
Otherwise it´s starting to get it´s clothes on. :)

This will be my fourth plane and my second scratch build of "own" design, so I have no unrealistic hopes of having invented a "new wheel". :)
I wanted to use some leftovers from my first build and try some ideas for the next(?) plane.

I used a NACA four digit modified airfoil, maybe not the best choice, but the choice I made... :D
It´s 14.2% @ 32% and camber is 1.2 @ 41%. Roughly I might ad, as I cut the trailing edge where it had the right width and then the ailerons will be made separately.

Don´t worry, I have no intention of flying it straight for long, just some low fast passes after a dive!.. Adrenaline sure is nice sometimes! :D

BMatthews 09-02-2012 04:46 PM

RE: Vertical tails
 
1 Attachment(s)
Well, I drew it so I may as well post it. Perhaps you can use the idea for some other model. Here ya go....


Nitrovein 09-03-2012 02:20 PM

RE: Vertical tails
 
1 Attachment(s)
Thank you for taking the time to draw that and I have saved it for future plans. ;)

(My measurements is metric, but I have done a crude converting to inches)
This wing has a chord of 195mm(=7,68" ) + ailerons that I have cut up to 20mm (=0,79" ), I´m not quite sure 9.3% ailerons will do the trick..? But, I will be the first to know! :D
Wing span is 950mm (=37,4" ) but with reinforced wingtips so that I can screw on different types of plates/winglets to try out.
The wing is made up almost like in your drawing, but I have used 5x2mm pine spars (upper and under) and 1,5mm vertical webbing out to the aileron servos.

The horizontal tail is made up of two layers of 3mm balsa wood glued with crossing grain for a total thickness of 6mm (=1/4" ).
It´s 300mm (=11,81" ) in span and 270mm (=10,63" ) in chord with the elevator (being 35mm (=1,38" ). BUT, I might cut down the size slightly and also drill some holes in it. :)

Any good pointers for me so far? :)

[img][/img]

BMatthews 09-03-2012 08:16 PM

RE: Vertical tails
 
My only concern is that it seems rather stoutly built for such a small model. For good slower speed manners I would not want to see a model of this sort weigh more than about 25 oz (700gms) in the ready to fly state. And in fact I'd rather see it even lighter. You can stick a bigger engine on and it'll certainly go up but you may find that if it's heavier than this that it may tend to snap roll out of higher G maneuvers even at high speed and it may not have a nice friendly landing approach. On the other hand if you're on track to come in at under 700 gms all done and ready to fly then never mind my worries, you'll be fine.

Nitrovein 09-03-2012 10:00 PM

RE: Vertical tails
 
It is rather stoutly built, I admit that. :) I´m aiming at 1000g and is well bellow that at this point, but I think I can shave some more of it.
I downloaded the manual for the Wonder and did some reverse engineering to get the measurements in the ballpark.
I have added weight by using dual servos for the ailerons and by adding vertical webbing to the wing (to support the added weight of the servos).
I also made the decision to lay a layer of fiberglass to reinforce the fuselage for the upcoming belly landings, but by doing so I have also made the wood fiber more tolerant for some holes to lighten it.
By using a integrated engine mount I have shaved some weight there to.

The bottom line, I have tried to keep it as close to the original spec as possible, but with a slight twist of my own. :)
I will start to cover the wings today and take it from there as I will then be able to better see if the balance is in the ball park to.

The engine is a project of it´s own... :eek: It kind of started with that and a pile of balsa scrap.
I will be using an old OS CZ-2 that I used in a car when I was young(er). It´s been lightened quite a lot and been given a few tweaks, so it´s more up to date compared to newer (airplane) engines. :)

My main concern is the tail, as in the fins and how long the chord should be of the horizontal tail. I do want to keep it on the sluggish side when it comes to pitch stability, but without taking all of the fun out of it.
So yes, I do want to eat my cookie and keep it at the same time! :D

BMatthews 09-04-2012 10:12 PM

RE: Vertical tails
 
Quote:

.....I do want to keep it on the sluggish side when it comes to pitch stability.....
I'd say you likely picked the wrong design then.

I'm sure when trimmed it won't be bad but the initial flights are going to be... how shall we say it..... "interesting" comes to mind? :D Seriously, find a field of tall grass if at all possible for the first flights. I've found these short coupled models are fine once trimmed. But if things are off by much at all for the first flights it all gets "interesting" REALLY quickly.. As in "BLINK.... Bring the glow plug battery over here, would you?" sort of "interesting".

And every gram you can manage to make it under the 1000 mark will make it that much better a model. I know that Sig shows it up around a Kg but really with that much wing area it's simply going to be a nicer model the closer you can get to 700.

Nitrovein 09-05-2012 02:51 AM

RE: Vertical tails
 
I hear you! :)
I´m not the best to express what I mean and sometimes I get words "lost" in the translation.
I´m well aware of that this plane is not any stable trainer and for that I´m thankful as those types of planes are the ones that I struggle the most with.
Let me put it like this, if this design is a 2 out of 10 in stability, then I´m aiming at 2,2 rather then 1,8. ;)

I´m what they call an aggressive pilot, but I will take it easy anyway until it´s trimmed in okay. :)
I have trained so much in the sim that the first time ever I took a plane to the sky I tried everything from inverted, loops, rolls etc. Second time, I was hovering.
I have never been to an airfield, but have fields of tall grass where I live so that part is covered. :)

I tossed everything on a scale and was as objective as possible and I´m in the 8-900g span, not to exact yet but a receipt that I´m on the right track.
For an engine that´s still in the upper range of the weight scale compared to others of the same size and for adding dual aileron servos and fiberglass etc, I have done all right so far.

Time to start finishing the tail section! :)

HighPlains 09-05-2012 06:08 AM

RE: Vertical tails
 
It should be a fairly mild flying airplane if the CG is well forward. I built something about like it almost 40 years ago from a control line combat kit called the "Guillotine" that was an old 60's design before the high aspect designs took over. It had a wingspan of around 38 inches, twin booms that I added fixed vertical stabilizers to, and no fixed horizontal surface, only a moveable elevator about 4 inches back. Very stable easy to fly airplane on a .19 engine that only had aileron and elevator control. Good luck with your design.

Nitrovein 09-06-2012 03:54 AM

RE: Vertical tails
 
Thank you "HighPlains"!

A airplane of this size is not the end of the world if it´s not everything I hoped for. It´s just to get more builds "under my wings" and to try. :)
But I do know that there is a lot of combined experience on this forum and that is something I´m open for.

Nitrovein 10-03-2012 03:29 PM

RE: Vertical tails
 
1 Attachment(s)
I thought I should update this thread, for those that´s interested. :)
As always, other things has interfered in the build process, but it´s near the first flight now.

The plane ended up right at 880 grams + fuel (75cc).

But for the million-$ question, should I add some sort of winglets?
I didn't cover the wingtips to carefully as this was the idea from the start, but as the weight is already a bit high I wonder if it´s worth it...

The planes CG is at 28-30% right now and it needs about 1-2 grams on one wingtip if I want to balance it 100% lateral.


I took some pics of it the other day, not the best pics but I wanted to see it outside in daylight.
It looks like a quilt, but that´s what you get when your to cheap to buy more covering! :D
[img][/img]

BMatthews 10-04-2012 06:35 PM

RE: Vertical tails
 
You certainly don't need tip plates unless you want them. I'd just fly it as it is and see what it does. Later you can add tip plates if you like to see what effect they have.

Nitrovein 10-04-2012 10:16 PM

RE: Vertical tails
 
That make sens! :)
My thoughts are that they might help to support/act like a ski when landing, so that the wing doesn't grab hold of the ground.

But, right now I´m quite eager to get this thing in the air! :D

BMatthews 10-06-2012 04:44 PM

RE: Vertical tails
 
Small models of this sort stop dead on grass landings with less than a couple of feet worth of skidding as a typical landing. So the tip plates as landing skids are really not needed. If you'll be landing on pavement then that's a whole other deal. In that case you'll want some abrasive resistant belly skid as well as something like wire wiskers or some other skid on the tips.

Nitrovein 10-07-2012 07:11 AM

RE: Vertical tails
 
I will be landing mostly on tall grass.

But the first flight I got a "dead-stick" and ran out of room to sort things out for a good landing, struck a branch on a tree and hit the ground. [:@]
Not too much to fix, so it should be airborne in a couple of days. :)
I will most likely be adding some sort of winglets to try out and then their there, if I should need them as skis.

The plane was a handful at first, but I got it in trim and then it felt very nice. :)


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