Flaps on a Wot 4 ?

[IanR]

I've just been watching the Extreme Wot 4 video and have noticed that it has conventional looking flaps. However, the flaps did not appear to be used when landing but, immediately the model touched down, the flaps were extended but upwards. I thought flaps were extended downwards to slow down the model on a landing approach. Can anyone tell me what's going on with the Extreme Wot 4 in the video.

And since the Extreme appears to be a scaled up copy of a standard Wot 4, does it follow that a standard Wot 4 could use these standard flaps instead of the (in my opinion) clumsy looking airbrakes that Chris Foss includes in his instructions as an option?

Ian

[Ian Jones]

Well it depends what you want to achieve Ian.

Flaps are to enable an aircraft to fly at a lower speed. To do this they change the shape of the wing to produce more lift. Deploying flaps causes some drag so a lesser secondary effect is speed loss. Flaps are not air brakes. This applies to flaperons too.

Airbrakes are to slow the aircraft down, to do this they typically open a "barn door" to obstruct the airflow. They may also affect lift but this would be a lesser secondary effect.

One or both may be required on an aircraft because of it's design. They may also be needed because of the way it used (including the power/prop setup) and I think it is likely that the latter applies to WOT4s.

So it follows that the decision as to which is best to fit, if any, depends on the model and/or it's intended use.

 

Ian

(apologies if I'm preaching the converted)

Edited By Ian Jones on 04/11/2013 10:57:16

Edited By Ian Jones on 04/11/2013 10:59:21

[Martin Harris - Moderator]

As a non-Ian I feel a bit out of place posting here but I hope you'll forgive me for any intrusion!

I haven't seen the video referred to but it sounds as though the flaps going upwards are to kill lift on touchdown - something that is featured, in effect, by spoilers on many large commercial aircraft.

Edited By Martin Harris on 04/11/2013 11:36:50

[Biggles' Elder Brother - Moderator]

Yeap certainly sounds like that. By lifting the "flaps" upwards, a significant degree the lift provided by the wing is destroyed. Its a technique you can apply on a model that has a strong tendancy to "float"; that is it doesn't want to land! So you come along the strip,, and if you are even a little on the quick side the model won't come down; it just flies down the strip 4 feet off the deck! Only to land 50 yards beyond the strip - a tad embarrasing!

By the sound of it, you said they were deployed after landing I think, this is very light model with a big wing, so you can get an unintentioned take off when taxying fast into wind. One way of getting it down, and keeping it down, would be these sploilers.

I have this arrangement on the flaps on my Phoenix 2000 2m glider. The the lefthand slider on my Tx is set so that zero-flap is in the centre, the bottom half of the slider movement gives me "down flap" so I can add some camber when flying, whilst the upper half of the movement gives me "up flap" to act as a spoiler on landing. You do have to be gentle with the spoiler bit though - if you are too heavy handed it will make the model drop like a stone! But it does mean I can put it down right in the middle of the strip. Actually thinking about it its would make an excellent model for a spot landing competition; that would certainly raise a few eyebrows at club comps!

BEB

[Phil 9]

I think this is the video in question

[malcolm woodcock 1]

I used flaperons on my WOT 4 but had to tame them down, they were a bit fierce, you've got to try out this sort of thing.

[Ian Jones]

If you have been in an aircraft when landing and seen flaps open midway across the chord revealing the ground passing by below... well those are these lift dumping devices.

I use fleperons with no more than 20 degrees of deflection. It doesn't look dramatic but does does facilitate a slower landing.

Edited By Ian Jones on 04/11/2013 13:57:17

[Martin Harris - Moderator]

This is a nice example:

 

...although you might want to skip to about 4 1/2 minutes in...

Edited By Martin Harris on 04/11/2013 13:54:07

[David Ashby - Moderator]

 

Hi Ian,

I photographed and filmed the WOT4 Xtreme. Steve's (reviewer) a great pilot and one of his own personal little set-up traits is to set flaps or ailerons so they can both be flicked up when a model lands, for the reasons BEB describes really.

 

 

Edited By David Ashby - RCME on 04/11/2013 14:11:56

[IanR]

Understood - I think. "Up" flaps are really spoilers.

Any comments, please, on using a conventional flap arrangement on a standard size Wot 4 kit. I'm thinking about my, as yet, un-built Mk3. I like the idea of having flaps to play with so would it be OK to utilise some of the strip ailerons for flaps and increase the throws on the remainder of the ailerons to compensate?

Ian

[Biggles' Elder Brother - Moderator]

In principle there is no reason why not Ian. There are two things to think about.

1. You might not be able to recover all of the aileron power by increasing the throws though without inducing a lot of adverse yaw. But I'm sure it would work OK. The roll rate maybe a little slower - but the WOTTY has roll rate to spare!
2. The strip ailerons won't be massively effective as spoilers - they are a bit narrow. But you'll certainly get enough effect to feel it and for it to be worthwhile - may be just not a massive effect.

BEB

[Martin Harris - Moderator]

Why not cut out some larger flaps from the foam and face them (and the cutouts) with balsa if you haven't built the wings yet? This would allow you to use less of the aileron's span and I suspect that the inboard aileron portion lost will be fairly ineffective anyway.

[GrumpyGnome]

The Wotty in my avatar has flaperons. Two servos side by side operating an aileron/flap each.

Definitely reduce aileron authority although only noticeable for aeros - and why would I do those with flaps deployed ...... ? Just to see what happens

Reduces take off run nicley - altough it was never exactly prolonged. Slows down the landing a little - but it lands at ridiculously slow speed anyway. Relatively useful in allowing a steeper landing descent, although a nice sideslip does that too.............

Just dd it 'cos I could, not 'cos it needs them at all.

GG

[GrumpyGnome]

P.S. my flaps only go down ..................

[IanR]

Thanks for the replies, gents.

BEB, would aileron differential counteract the adverse yaw?

Martin, yes, I follow you.

GG, "...'cos I could, not 'cos it needs them.." I like your thinking.

Ian

[Biggles' Elder Brother - Moderator]

Yes Ian. But I'd "suck it and see" first. You may very well find that for standard aerobatic and the like the aileron authority is still all that you want it to be without having to increase the throws dramatically - even though the ailerons are smaller.

Martin has a good point - the inboard portion of the ailerons contirbute less anyway - simply because they act over a shorter lever arm.

Of course if you intend prop-hanging it the loss of the inner ailerons is much more of a problem!

BEB

[Martin Harris - Moderator]

Posted by Biggles' Elder Brother - Moderator on 04/11/2013 17:50:11:

Of course if you intend prop-hanging it the loss of the inner ailerons is much more of a problem!

BEB

3D flight mode - couple flaps with ailerons....sorted!

[Mr.B.]

A little off topic but...the full size F4 phantom and early B52s used spoilers and aileron for roll control. ie the aileron has no up movement. Instead a spoiler is deployed to destroy lift and make the wing drop. Later model B52s had no ailerons at all, just spoilers for roll control. I have never understood the advantage of this method. As most aircraft still use conventional ailerons was it a design blind alley? Inverted roll performance would be, err interesting but then if you are inverted in a B52 you have bigger problems. B52s are unlike Vulcans in that respect.

[Braddock, VC]

IanR when you get round to building your wottie you'll find chris foss has added some variations inc. inboard spoilers and also increasing the chord of the abbreviated ailerons.

My own view is that the model doesn't really need the addition as if you practice at flying with an increased angle of attack you'll be really surprised at how slow the model will fly.

Incidentally if it starts an involuntary wing waggle bang the throttle wide open as it will stall pdq.

[IanR]

Braddock, yes, I like the idea of practicing to become proficient at slow landing approaches. Its that sort of thing that stops you from batting about the sky a bit aimlessly.

And then I suppose I could droop the ailerons a bit to provide a flap function - but I've heard that that can be akin to adding downwash (Washin, washout ?) with the danger of tip stalling.

I know - I think I'll not bother with the flaps at all, but thanks for a most illuminating discussion, everyone. I'll buy myself a Multiplex Funcub and play silly buggers with that.

Ian

Edited By IanR on 04/11/2013 21:43:00

[cymaz]

I thought I might resurrect this thread. This winter I should really get my Wot4XL recovered. It’s looking very tatty.

Now I know a bit more about dope and nylon, that’s the way to go. Then get it painted.

 

Once the airframe is stripped, it might be a convenient moment to add flaps and put some landing lights in the wings. 

I am open to ideas, opinions, photos and hints and tips.

 

All the best.?

[Andy48]

10 hours ago, cymaz said:

I thought I might resurrect this thread. This winter I should really get my Wot4XL recovered. It’s looking very tatty.

Now I know a bit more about dope and nylon, that’s the way to go. Then get it painted.

 

Once the airframe is stripped, it might be a convenient moment to add flaps and put some landing lights in the wings. 

I am open to ideas, opinions, photos and hints and tips.

 

All the best.?

You'll need to hurry up, there's only a week of winter left.

[cymaz]

Correct! meteorologically speaking. Though the way things are going, we might yet have to survive a nuclear winter.?

 

However, I’ve mucked about with a spare 8ch Rx and my Futaba 18mz today. I’ve managed to get the flaps to work independently when deployed and the slave to the ailerons when not in use. 

 

[GrumpyGnome]

Mixing is fun! My Ultrastick has independent flaps in flight mode 1, fully coupled in flight mode 2, and ailerons working as butterfly/crow opposing flaps in flight mode 3.

 

Back to original question... Never had an xl but my wot4 had flaperons and landed at walking pace

[Simon Chaddock]

Just to add my two penny'oth they are definitely being used as spoilers.

As a tail dragger with a pretty thick wing it would be prone to lifting a wing or even taking off again right after landing as the tail came down to the ground with even a slight gust of wind.

My only surprise is how small they are!