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Author Topic: Origin of the Rear Fin  (Read 1038 times)
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Soc
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« on: January 30, 2016, 08:32:09 PM »

The response to the origin of VTO thread inspired me to ask regular contributors
what they know about the origin of rear fins.
The earliest example I can find (in an old Plans Handbook) is on "Binkie"
a shoulder wing design which appeared in June '51 Aeromodeller.
Beyond that there is a 1/2 A design by Stuart Savage in Zaic '53 plan 44,
P Cameron uses one to get in the '53 Brit team and flies in the '53 world champs,
and Chris Marsh has an impressively modern looking model on the cover of Nov '53 Aeromodeller.
By 55 we have (at least) Dave Posner, Y-Bar and Creep.

I could add scans if there is any interest.

Sean
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« Reply #1 on: February 02, 2016, 07:48:04 AM »

Sean:

Good topic.

I have two thoughts, neither backed up by hard evidence:

* In the olden days of fuselage cross-section, the minimum size was based on fuselage length (length squared divided by 100).  I do remember Frank Zaic discussing that restraint in an early Year Book article about the design of the Thermic 72. Once the cross section rule went away, moment arms got longer and the rudder could be placed behind the stab without problem.

* Mounting the rudder on the stab can cause problems with shifting rudder position affecting flight pattern.  That leaves only four options: Keep the rudder on top and move the stab below (Fubar), put the rudder in front of the stab, put the rudder below the stab, or move rudder behind the stab. (The other problem with rudder on the stab is storage in model box, which can be handled by making rudder removable. Yes, stabs can be keyed, but there is still that chance...)

My father used to stress the importance of reliability. That's why his Battle Axe design from 1956 has the rudder on the bottom, rather then following the rudder-on-stab pattern of one of the Battle Axe's inspirations, the Ramrod. Another hot model of that time, the Royono, had a bottom-mounted rudder.  I really don't recall any American Gas models of the early to mid 1950s with rear-mounted rudders---there certainly were some British ones, though.

The one problem with the Battle Axe was the bottom rudder could be more easily damaged, I'm sure that the more aerodynamically knowledgeable will offer reasons for the rear-mounted rudder being above the thrust line.

Louis

PS The Battle Axe is Nostalgia-leagle; I believe plans for the 1/2A (the only size my father or I ever built) are available through NFFS plans service.  I do know that the design has been scaled both up and down with success.
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glidermaster
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« Reply #2 on: February 05, 2016, 12:27:09 PM »

I have to say that I am surprised this thread hasn't generated more discussion.
My library of old mags and books is not extensive by any means, but the earliest example of a rear fin model I could find is Space Wamp, a 1/2A by Stuart Savage. It's in the '53 Zaic book.

On a personal note, my Dad's power models were forward fin or fin-on-tail until close to 1960. I would have said that FAI was dominated by rear fin designs from about 1960 until the late 70's, but all the 1970s world champs were other variations.
Hagel ('71) - triple fin.
Horcika ('73) - under fin
Oloffson ('75) - triple fin
Koster ('77) - triple fin
Rocca ('79) - forward fin.

John
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« Reply #3 on: February 05, 2016, 03:11:33 PM »

Judging by the names of the winners, it looks like the triple fin was a Nordic thing (the geographic region, not the towline event).  The Italians seemed to prefer the forward fin; some of the Wakefields in the Zaic Year Books are wayyyy forward of the stab leading edge.

No bottom-fin FAI Power winners that I can recall, other then Horcika.  But that was a high-thrust line model. Only high-thrust model I recall with top fin was the Goldberg Viking. (With that name, it should have had triple fins.)

Louis
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gossie
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« Reply #4 on: February 05, 2016, 04:25:35 PM »

Does it really matter where a fin is?   Guess not with so many people using fins in various positions.

My old reliable from way way back has triple fins......one in front of stab. and on end of stab.  Stab. of course is well tied down to stop any movement.
Triple fins were thought I believe to steady the model under climb and keep it going where is was pointed.   Seems to work with this one of mine as it's never crashed and has won and place......If I'm smart enough to toss it into lift.
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« Reply #5 on: February 05, 2016, 04:38:59 PM »

I think every permutation has had success at some time, including tail end plate type (i.e. a triple fin with the centre one missing!).
Here's a summary of World Champs winners. Forward fin has dominated for the last 30 plus years.

John
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« Reply #6 on: February 09, 2016, 07:17:58 AM »

John:

Thanks for chart.  It looks like reliability (rudder firmly on fuselage) trumps fashion (triple fins).

Louis
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« Reply #7 on: February 09, 2016, 04:05:18 PM »

I don't think this counts but in the 1937 or 38 Zaic there is a ROW indoor model with a rear rudder.I also remember a gas model from the late 30's or early 40's that had a rear rudder.I have given away all of my old mags. so I can't verify but I remember thinking to my self that there is nothing new, look a rear rudder way back then.
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« Reply #8 on: February 09, 2016, 08:13:47 PM »

Bruce:

It is amazing how many "new" ideas you can find in the old Zaic Year Books.

Louis

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Soc
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« Reply #9 on: February 10, 2016, 12:13:57 AM »

Here are some pics of early rear fins.

The plan for "Binkie' is on Outerzone. Rear fin but no DT ! So only halfway there. (June '51 AM)

Chris Marsh's rear fin model is on the cover of November '53 Aeromodeller
Martin Dilly is supervising the floatation test.
It would be nice if there was a drawing of this  way ahead  design.

Pete Cameron was on the Brit WC team in '53 flying a rear fin model (Oct '53 AM report)

Dave Posner had a rear fin and VTO in '55 (Aug '55 AM editorial)
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gossie
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« Reply #10 on: February 10, 2016, 03:30:48 AM »

I think that might be George Fuller in the first pic?HuhHuhHuh?
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« Reply #11 on: February 10, 2016, 06:08:43 PM »

Gossie, you are right.
It is some time since I read the caption and somehow my aging brain transmuted Fuller to Dilly.
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« Reply #12 on: February 10, 2016, 06:39:06 PM »

Gossie, you are right.
It is some time since I read the caption and somehow my aging brain transmuted Fuller to Dilly.

Your forgiven Sean.    I also have that magazine.
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« Reply #13 on: February 11, 2016, 12:41:36 AM »

I don't know about the history, but there's an aerodynamic advantage to a rear fin. A conventionally configured aircraft has a much higher moment of inertia in yaw* than in pitch, since the wingtips move a lot more with yaw. The static stability effect from a tail surface is proportional to the distance between it and the AC of the wing, while the damping provided by that surface is proportional to the square of the distance. Since the moment of inertia in pitch is low, it's easy for the elevator to damp out pitch oscillations. However, with the fin, you want a lot of damping to settle down the swings in yaw. This is especially important in RC discus launch gliders, which are rotating when released and need to stop, and to settle down, as fast as possible. So you'll see a rear fin on them. I'm not sure why ff dlg's use a different sort of tail, but then that's not an event I fly. You can also see the rear fin with some RC gliders such as the Supra. Same reason. There have been full sized sailplanes and human powered airplanes set up that way.

Another advantage is less intersection drag.




*You could look at it as the resistance to change in rotation speed. You can feel it if you hold something long and skinny in your hand and try to move it by swiveling your wrist.
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