Jump to content

Anhedral tailplane


Martin  McIntosh
 Share

Recommended Posts

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?

Link to comment
Share on other sites

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.

Link to comment
Share on other sites

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.

Link to comment
Share on other sites

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

Link to comment
Share on other sites

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.

Link to comment
Share on other sites

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


Link to comment
Share on other sites

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

Link to comment
Share on other sites

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!

Link to comment
Share on other sites

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

Link to comment
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

 Share

×
×
  • Create New...