Fin offset 1/8 or 1/4 or 3/8

LAST EDITED ON Jul-28-04 AT 09:53 PM (CDT)
 
I notice each set of plans has a different offset on the fin. Whats up with that??? The engine has an offset, the lead outs have an offset, and now the fin needs to be offset too, WHY? I have seen some plans with an adjustable fin. Is it good to have an adjustable fin? With all the other offsets what if the fin is straight?

>I notice each set of plans has a different offset on the
>fin. Whats up with that??? The engine has an offset, the
>lead outs have an offset, and now the fin needs to be offset
>too, WHY? I have seen some plans with an adjustable fin.
>Is it good to have an adjustable fin?

Yes.

> With all the other
>offsets what if the fin is straight?

It generally flies better.

Not to dust you off, but there are numerous previous threads on this topic, might want to review those. Search the archives for the words

leadout rudder offset

with the .AND. button set, and I think you will find quite a few.

> Not to dust you off, but there are numerous previous
>threads on this topic, might want to review those. Search
>the archives for the words
>leadout rudder offset
>with the .AND. button set, and I think you will find quite a
>few.
>
> Brett

Where is archives? I don't spend much time here I don't know how things work. I clicked the word, archives, there is no option to do a search. What is AND button?

Click on "search" icon. Do as Brett suggested. There isn't even a need to go into the archives, there being several threads this year which will be of interest. At least one of which shows your participation.

My Impact fin suffered some trauma a few years ago (and therein lies a tale), and has warped to different positions since. It's not particularly sensitive to rudder position, but it probably works best straight. The optimal rudder position for other airplanes may be different.

Right when this topic came up, I was gluing the vertical fin/rudder assembly on my Musciano Meet Scientific Bullet. Walt Musciano's plans show a 3/8ths inch offset, but I thought this a bit much on a 24" span model. So I went with less. But who knows until it is in the air.

Windy once opined that, the smaller the airplane, the more offset (both rudder and engine) required. 1/2a's like lots of both.

Phil Cartier builds/kits/offers plans for 1/2a combat models with lots and lots of offset, while his larger stuff uses significantly less. Me thinks that, even without a "V" device, that airplane weight contributes to this stuff.

See Ya

Ive found no fin offset works best, provided you have sufficent lift to steady the airframe.

I tend to agree with the nobler style fin, half airfoil.

Does the same aerodynamic job as having a "straight" airfoil offset.

>Windy once opined that, the smaller the airplane, the more
>offset (both rudder and engine) required. 1/2a's like lots
>of both.

Well, maybe, but I have set up a lot of my Scientific models with very minimal (if any) offset, and they do fine. Currell

LAST EDITED ON Jul-29-04 AT 11:36 AM (CDT)
 
>My Impact fin suffered some trauma a few years ago (and
>therein lies a tale...

...and just how much will it cost to insure your silence in regard to certain portions of said tale?

Windy can do what works for him, but I don't think 1/2A's need either engine or rudder offset if leadouts are adjustible. One of my best flying airplanes had a little sloppy build and actually had engine inthrust. The Cheap Thrill, with its eliptical tips with fixed leadouts, has adjustable rudder. The leadout positon is about right and the rudder has ended up straight.

Some of those West Texans were offsetting 1/2-A engines on Combat planes by about 10 degrees or so. This was back when everyone was using Tee Dees or the early AMEs. Quite a few people still use some, but usually not that much now people are using Cyclons and such. The winds in West Texas can get pretty bad.

LAST EDITED ON Jul-29-04 AT 06:55 PM (CDT)
 
I did a search for Fin Offset and the only thing related to Fin Offset is this post. I did a search for Fin and it found 1000's of unrelated stuff. I did a search for Offset and it found 1000's of unrelated stuff.

I talked to a friend that flies compitation, he says leave the fin OFF. Real airplanes need a fin, control line airplanes have fins just for looks.

Makes sence to me combat airplanes have NO fin.

>I did a search for Fin Offset and the only thing related to
>Fin Offset is this post. I did a search for Fin and it
>found 1000's of unrelated stuff. I did a search for Offset
>and it found 1000's of unrelated stuff.
>
>I talked to a friend that flies compitation, he says leave
>the fin OFF. Real airplanes need a fin, control line
>airplanes have fins just for looks.
>
>Makes sence to me combat airplanes have NO fin.
>
>Gary Weaver [email protected]

Gary, puhlease. These were the instructions:

"Not to dust you off, but there are numerous previous threads on this topic, might want to review those. Search the archives for the words

*****leadout rudder offset*****

with the .AND. button set, and I think you will find quite a few."

Brett

Not one of us told you to search for fin offset.

>I did a search for Fin Offset and the only thing related to
>Fin Offset is this post. I did a search for Fin and it
>found 1000's of unrelated stuff. I did a search for Offset
>and it found 1000's of unrelated stuff.

Uh, yeah, try "leadout rudder offset" on the SSW "Search" function. Not Google.

>I talked to a friend that flies compitation, he says leave
>the fin OFF.

Wow, a competition flier! Those are pretty rare around here...

>Real airplanes need a fin, control line
>airplanes have fins just for looks.

Maybe sometimes, but not on any of my airplanes. It needs to be there.

There is an excellent article by "The Iceman" Bob Whitely on "What works". He describes that some fin offset is required to eliminate adverse yaw due to prop wash swirl curling over the top of the fuselage. The amount varies with plane, prop, etc. Adjustability would be a good thing.

Does anyone remember the Berkley Aerotol rudder(spelled sumpin like that) ?
It consisted of a spring loaded rudder.
When the plane went fast, the rudder was pushed more to neutral; when tne plane slowed, the rudder,s spring overcame the wind speed and aded more offset,
Did it work?
I really can,t say .
Maybe Gary can try this and let us know.

Bob Hunt gets away without a fin. He may start using one to avoid all the teasing he was getting at the Nats.

When I was a tad, I was amazed that my Ringmaster flew better and had more line tension with no fin than with its offset fin.

On the other hand, I've had to add a fin to some combat planes.

Flight Streak has BIG FIN ,LITTLE OFFSET.

LAST EDITED ON Jul-30-04 AT 06:21 AM (CDT)
 
I have never needed a fin on a combat airplane. If the lead outs are in the correct place no fin is required. My 1st Voodoo had a problem but once I got the lead outs in the correct place it flew great. My Combat Cat flies better than the Voodoo. The combat cat flies better in a strong wind than the voodoo, I think its because the voodoo tail boom is made like a fin. The combat cat wing tips are stream lines and affected less by the wind. I built another voodoo with no fin shape tail boom and it flies even better than my 1st voodoo, then I added the combat cat style wing tips and it flies even better in a strong wind. My Russian F2D combats all flies better than the voodoo or combat cat. If its too windy to fly stunt I can always fly combat. Well...not always but 20 mph wind is not a problem for combat.

>I have never needed a fin on a combat airplane. If the lead
>outs are in the correct place no fin is required. I can fly
>in a much higher wind with no fin.

There you go, Howard, case closed.

What a week for SSW.

>I talked to a friend that flies compitation, he says leave
>the fin OFF. Real airplanes need a fin, control line
>airplanes have fins just for looks.
>
>Makes sence to me combat airplanes have NO fin.
>
>Gary Weaver [email protected]

That's an interesting comment and giving it some consideration it
may be well worth investigating. In unteathered flight, too
small a fin produces "Duch roll" instability. The fuselage tends
to turn side on to the airfolw and does so until the fin can overcome
this dendency and yaw enertia. As the yaw corrects, inertia builds
and the yaw overshoots the other way and so on.

Too large a fin results in spiral instability. Any side slip causes the plane to wheather cock producing higher speed and lift on the outside wing tip. The outside wing lifts further increasing the side
slip and so on into a spiral dive.

Fin size is a ballance between these two instabilities.
Piloted planes err on the side of spiral instability because it's
more comfortable and easier to control while free flight err toward
Duch roll for safety. In CL, yaw is mostly controled by the lines
so the fin is less important. What happens if the lines go slack?
If the fin is large, the plane will sid slip into the circle, the
bank will increase and the plane spiral in. If the fin is small the
fuselage will yaw it back out again, lifting the inner wing (in
theory). Of course other factors come into play but this should be
the effect of altering fin size.

A deep fuselage with a long nose will produce more yaw instability.

If we use only a fixed fin, a larger fin of high aspect ratio ought
to more effectively counter but not eliminate precession (yaw due to gyroscopic forces in a turn).

These are some of the interrelated and opposing relationships that need ballancing in a design.

In the old days, we used to use fin offset as an extra counter
measure against line drag (to be sure to be sure) but that was
not a good idea IMHO.

If you get a power failure in a wingover, the last thing you want
is spiral instability and an offset fin may help to keep the plane in yaw but a small fin and a deep long nose fuselage may well be a
better solution to yaw the plane so a quick run may save the day.

Just thinking through some theory.

>That's an interesting comment and giving it some
>consideration it
>may be well worth investigating. In unteathered flight, too
>small a fin produces "Duch roll" instability. The fuselage
>tends
>to turn side on to the airfolw and does so until the fin can
>overcome
>this dendency and yaw enertia. As the yaw corrects, inertia
>builds
>and the yaw overshoots the other way and so on.
>
>Too large a fin results in spiral instability. Any side
>slip causes the plane to wheather cock producing higher
>speed and lift on the outside wing tip. The outside wing
>lifts further increasing the side
>slip and so on into a spiral dive.
>
>Fin size is a ballance between these two instabilities.
>Piloted planes err on the side of spiral instability because
>it's
>more comfortable and easier to control while free flight err
>toward
>Duch roll for safety. In CL, yaw is mostly controled by the
>lines
>so the fin is less important. What happens if the lines go
>slack?
>If the fin is large, the plane will sid slip into the
>circle, the
>bank will increase and the plane spiral in. If the fin is
>small the
>fuselage will yaw it back out again, lifting the inner wing
>(in
>theory). Of course other factors come into play but this
>should be
>the effect of altering fin size.
>
>A deep fuselage with a long nose will produce more yaw
>instability.
>
>If we use only a fixed fin, a larger fin of high aspect
>ratio ought
>to more effectively counter but not eliminate precession
>(yaw due to gyroscopic forces in a turn).
>
>These are some of the interrelated and opposing
>relationships that need ballancing in a design.
>
>In the old days, we used to use fin offset as an extra
>counter
>measure against line drag (to be sure to be sure) but that
>was
>not a good idea IMHO.
>
>If you get a power failure in a wingover, the last thing you
>want
>is spiral instability and an offset fin may help to keep the
>plane in yaw but a small fin and a deep long nose fuselage
>may well be a
>better solution to yaw the plane so a quick run may save the
>day.
>
>Just thinking through some theory.
>
>
>Regards,
>Ken

I saw a picture of a airplane in a magazine that had 2 fins. The fins were both very short, 1 fin was on the top side of the fuselage like we normally do, the other fin was on the bottom where the tail wheel is. What the deal with that?

>Makes sence to me combat airplanes have NO fin.

Depends.

Back when we were flying Slow Combat, most people used the smallest fin they could get away with (one was required in the rules). Then along came Pat and Mike Willcox with these HUGE plywood rectangles glued to the end of the boom. With it, they could fly upwind in a gale, where everyone else couldn't follow. The idea was that with the huge fin area in the back, when you were upwind, the wind would yaw your plane outwards, and downwind, it would have the opposite effect.

>>Makes sence to me combat airplanes have NO fin.
>
>Depends.
>
>Back when we were flying Slow Combat, most people used the
>smallest fin they could get away with (one was required in
>the rules). Then along came Pat and Mike Willcox with these
>HUGE plywood rectangles glued to the end of the boom. With
>it, they could fly upwind in a gale, where everyone else
>couldn't follow. The idea was that with the huge fin area in
>the back, when you were upwind, the wind would yaw your
>plane outwards, and downwind, it would have the opposite
>effect.

I can see where this will work. Very interesting idea. I have always tried to reduce wind resistance. I figure when the airplane is up wind the wind is blowing against the side of the fuselage and tail fin pushing the airplane towards the center of the circle. Reduce the size of the fuselage and fin then the wind is not a problem.