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Anhedral tailplane

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The F3A aerobat

The F3A aerobat

Years of testing, development and evolution have moulded today's competition pattern ship, yet to the untrained eye the design cues aren't always obvious. Mike Williams, highlights a few key details

Martin McIntosh16/01/2018 14:54:56
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2391 forum posts
930 photos

I see from Mike Williams` article on here that he says the current trend for anhedral tails is to make roll maneouvres more linear with less need for aileron differential and rudder correction.

When Hanno introduced his Curare he said that it was to lessen the tail end swing coming out of a stall turn. Which is correct I wonder?

Nigel R16/01/2018 15:18:42
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1159 forum posts
259 photos

Both, either, or possibly neither. With a side order of smoke and mirrors.

I don't think Hanno was above playing a little mind games with his competitors.

He was quoted after retirement as saying something along the lines of "I made them a bit different because otherwise we couldn't have sold the new one".

The same holds true of competition kit in a myriad of different sports. Most of the tiny differences are there to make sure the kit can be sold to the competing punters who want the best kit available and, it helps, if 'the latest' is 'the best'.

Usain Bolt wasn't fast because he had shiny gold trainers.

Etc.

onetenor16/01/2018 15:35:37
1599 forum posts

In one or two cases the anhedral T/P is a place to put a pair of wheels.

J D 816/01/2018 16:45:30
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809 forum posts
53 photos

I the fullsize world such things as anhederal tail plane are often an aerodynamic fix for problems at a certain point in the speed range/angle of attack. The F4 Phantom fighter/bomber started out with a plane flat wing and tail plane but ended up with a dog tooth leading edge wing with dihedral tips and a steep anhedral tail which gave it that distinctive Phantom look. Most models do not have that much of a speed range.

Martyn K18/01/2018 09:28:07
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4538 forum posts
3162 photos

I heard that the anhedral tail helps the back end track linearly in a roll. If you think of a dart with 3 feathers- however I am not sure if that was true or not. If it was effective, you would still see it today but the fact is it seems like a fashion statement that died out in the early 80s

The technical differences between Magic and Calypso were enormous but Hanno still won consecutive w/c with those two models

Edited By Martyn K on 18/01/2018 09:28:36

Denis Watkins18/01/2018 10:21:48
2661 forum posts
136 photos

Do you know, it could just be that Hanno could fly

You come across these guys now and again at the shows and at the field

They are brilliant to watch

Pete Collins18/01/2018 10:33:40
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72 forum posts
2 photos

Any aeroplane is always a compromise. We like to make our aerobats fly as straight as possible with no control interactions, but that's not always possible. For example, if the rudder is on the top of the aeroplane, ie not equal about the centreline, then it will always produce an adverse roll. ie Give left rudder and the aeroplane yaws left but also rolls right. Nowadays you compensate for this by using a Tx mix and just dialling in a little left aileron with the rudder, but back in the day we didn't have that option, so the cure was to have a degree or two of dihedral to give some yaw-roll coupling. This then made the aeroplane less well balanced in other areas, ie less laterally stable when inverted, so you added a little anhedral to the tail to compensate and so on. After developing this theme through several models and tweaking the angles etc, you could end up with a model that flew straight without any control interactions or adverse effects! It's much easier nowadays.

Robert Welford18/01/2018 11:16:27
82 forum posts
1 photos

My understanding is Hanno used an anhedral tailplane on the Curare to eliminate rudder-roll coupling when in knife edge. As Pete says: it is much easier nowadays using mixers to compensate for any interaction.

ron evans18/01/2018 12:06:34
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344 forum posts
22 photos

Many moons ago I made a Hawk for PSS, ( the one in my avatar ), it flew well enough but using a bit of top rudder in point rolls would upset the maneuver.

I decided to try the rudder on its own, so pulling out of a dive at speed, right rudder would yaw the model right, then do an odd sort of barrel roll to the left, scrubbing off lots of speed in the process. I was always careful using rudder at speed from then on. Holding the model head on in the hand and yawing it, the all moving anhedral tail would show a lot of top surface on one side, helping the adverse roll, along with the rudder well above the model center line

Some years later at a full size airshow I had a chat with a Hawk pilot and he said that above a certain speed (350 knots I think) the full size had a similar reaction. I wonder why the Hawk was given an anhedral tail.

Ron


Nigel R18/01/2018 12:33:05
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1159 forum posts
259 photos

Might be as simple as bringing the tailplane down into clean air when at high alpha, like landing, similar to Phantom.

Edited By Nigel R on 18/01/2018 12:33:39

ron evans18/01/2018 13:03:24
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344 forum posts
22 photos

Could be Nigel, but whatever the reason it adds to the character of the aeroplane.

Model Hawks with flat tails just don't look right.

Willyuk18/01/2018 13:11:59
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170 forum posts
22 photos

The anhedral tailplane is not dead. The latest F3a designs from B.J.Park have the option of an anhedral all flying stab. They seem to work quite well, used by the UK team in the recent world cup in Argentina.

Martyn K18/01/2018 13:33:41
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4538 forum posts
3162 photos
Posted by Denis Watkins on 18/01/2018 10:21:48:

Do you know, it could just be that Hanno could fly

You come across these guys now and again at the shows and at the field

They are brilliant to watch

Sadly, you wont see Hanno Fly again. He is very poorly indeed.

Nigel R18/01/2018 14:20:32
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1159 forum posts
259 photos

Shame.

I know he was top table F3A in 1973, which must make him nearly 80 now?

Robert Welford18/01/2018 16:18:01
82 forum posts
1 photos
Posted by Nigel R on 18/01/2018 14:20:32:

Shame.

I know he was top table F3A in 1973, which must make him nearly 80 now?

He was in his mid-20s when he won the World Championship in 1977, so I would think he's probably in his mid/late-60s now.

I'm very sorry to hear that Hanno is not well. He's an inspiration to this day!

Edited By Robert Welford on 18/01/2018 16:31:51

Edited By Robert Welford on 18/01/2018 16:32:12

Piers Bowlan18/01/2018 18:06:38
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1228 forum posts
36 photos

BAe Hawk, Swept wing, short coupled tail moment, long nose moment. Probably, laterally strong stability, - less yaw stability= tendency to Dutch roll. Perhaps the tailplane anhedral is to correct for this? (a yaw damper would too) Nigel R, - Yes, you could be right. It wouldn't be a Hawk without anhedral!

Martin McIntosh18/01/2018 19:54:04
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2391 forum posts
930 photos

Interesting replies. I put one on a Dalotel-ish model and it had the effect of increasing the dihedral. This was negated by moving the cg further back and it turned out quite good in the end. Only really did it for nostalgic reasons and to make it look a bit different.

chris Bond - Bondaero18/01/2018 21:24:50
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118 forum posts
50 photos

Could not resist this picture of the Agenda that Willyuk refers to above13012596_839540702817599_6991429007157226154_n.jpg

Piers Bowlan19/01/2018 05:30:00
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1228 forum posts
36 photos
Posted by Pete Collins on 18/01/2018 10:33:40:

Any aeroplane is always a compromise. We like to make our aerobats fly as straight as possible with no control interactions, but that's not always possible. For example, if the rudder is on the top of the aeroplane, ie not equal about the centreline, then it will always produce an adverse roll. ie Give left rudder and the aeroplane yaws left but also rolls right. Nowadays you compensate for this by using a Tx mix and just dialling in a little left aileron with the rudder, but back in the day we didn't have that option, so the cure was to have a degree or two of dihedral to give some yaw-roll coupling. This then made the aeroplane less well balanced in other areas, ie less laterally stable when inverted, so you added a little anhedral to the tail to compensate and so on. After developing this theme through several models and tweaking the angles etc, you could end up with a model that flew straight without any control interactions or adverse effects! It's much easier nowadays.

"Rudder on top of the aeroplane, i.e. not equal about it's centreline, then it will always produce adverse roll" Any adverse roll effect even with a large rudder solely above the longitudinal axis of the aircraft will be minuscule compared with the pro-roll effect of the aircraft wings. For example, take a mid-winged aircraft with zero dihedral. If you apply left rudder, tail moves right, right wing accelerates and generates more lift, also the fuselage will tend to blank a small segment of the left wing. That will cause a rolling moment to the left as a result of the asymmetric lift. Obviously for an aircraft with dihedral the effect is even more pronounced. Further effect of yaw is roll in the same direction, - according to all the textbooks.

What I do agree with is that any aerodynamic fix, be it frise ailerons, wing fences, turbulator strips, anhedral tails or whatever, these fixes generally tend to work best at one speed or one regime of flight. An improvement in one area of flight may have a downside in another.

As for 'Any aeroplane is always a compromise', never was a truer word said! 

 

Edited By Piers Bowlan on 19/01/2018 05:42:49

Nigel R19/01/2018 08:36:44
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1159 forum posts
259 photos

cracking photo Chris

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