|Oct 09, 2010, 03:17 PM|
flap design help required for swept wing
I'd like some assistance with the size and placement of pitch neutral flaps on my latest swept wing.
Norm posted some guidance on another thread, but I'm afraid I couldn't quite get my head around it (I can be a bit slow on the uptake sometimes ).
I'm really happy with the way this slope wing flys, but it would be good if I could place it a bit better for landings as the glide usually sees me going round a few times before 'arriving'.
Hopefully the plan will give you the info you need, the cg is 5mm behind the root trailing edge.
Thanks in advance
|Oct 09, 2010, 03:35 PM|
I dont think you can have pitch neutral flaps on flying wings, due to them just acting as elevons. However, you could use split flaps like on the B2 spirits, also known as decellerons, but that depends on how much you like engineering
Or, you could integrate air brakes into your design, along the centre of gravity. Along with a bit of elevator mixing on your transmitter that should keep it going straight and true
|Oct 09, 2010, 03:50 PM|
WHY NOT THIS STYLE ?
It was used in a tailed glider but it does offer uniform drag on top and bottom
with a simple torque rod actuation.
|Oct 09, 2010, 09:09 PM|
|Oct 09, 2010, 09:11 PM|
|Oct 09, 2010, 09:35 PM|
I'm busy this weekend but I'll see what I can make of this next week. Just a guess but there may not be much room on the TE for flaps at such a high sweep angle. I don't recall ever seeing Curtis describe how he sized the flaps on "Tinamou". Maybe you could ask him.
|Oct 10, 2010, 03:21 AM|
Many thanks Norm, I'll give Curtis a shout and post here if we get a result
|Oct 10, 2010, 01:36 PM|
With a Flying Wing ANY Trailing edge changes are going to effect PITCH.
Camber flap actuation is necessarily going to induce DOWN pitch.
All speed changes are going to be from either Elevator motion, which is merely
changing the overall airfoil shape, more or less reflexed
OR due to some airbrake action.
So when someone wants a "flap" on a flying wing, I think AIRBRAKE.
Because IF you change any portion of the TE then some other part of the TE
is going to have to compensate for induced pitch. AKA CROW
So you are back to Air brake again.
Surfaces that are split and go both up & down simultaneously
and are pitch neutral, are, again, Air brakes.
From an above post - decelerons
Spoilers, on the other hand, can be placed so as to NOT effect pitch.
But again what are they doing - slowing the craft down - AKA Air brakes.
The decision is WHAT is going to be the easiest to build and actuate.
If you have separate Ailerons and Elevators already
THEN using radio programming you can CROW it and need do nothing more.
If you have integrated the controls into a single moveable surface on each side
aka ELEVONS then your choices are either Spoilers or
and addition TE surface like the Decelerons or some other speed brake notion.
|Oct 10, 2010, 02:06 PM|
There are numerous examples of flaps on flying wings that have little or no effect on pitch.
If you look at the Multibumm wing, it doesn't have flaps but......
...it has inboard surfaces that act as an elevator but with an upward deflection giving down pitch (like a cannard).
As this model can also be flown with conventional outboard elevons (downward throw for pitch down) it must therefore follow that somewhere along that trailing edge there is a location for a correctly sized control surface that would have no effect on pitch if deflected up or down.
The key is working out what that optimum size and location is....I must track down a copy of 'Tailess Aircraft in Theory and Practice'
|Oct 10, 2010, 02:41 PM|
Please post that theory when you find it. thank you.
To my way of simplistically observing FW dynamics they are a merely a combination of forward CG which is offset by reflex for stability and control.
IF , due to some combination of sweep back and Washout,
some portion of an FW is NOT contributing to the overall Lift
then I have to wonder what is it there for ?
So my simplistic view is,
IF any portion of the wing is contributing to lift
then a TE change is going to effect pitch.
Elaborate designs with changing Foils blends and sweeps and washouts
tend to have optimum speeds as opposed to wide speed ranges.
They are aimed at the NO TIP PLATEs or NO Vertical surface goal.
I'm talking about designs based on piles of charts and graphs and calculations.
From all the plethora combat and similar designs with tip plates
it appears that you can get away with a wide range of aerodynamics
and not be to tricky about it.
I've build a wing with Marske's P3 foil with taper & sweep & washout similar to HIII planform
and been able to thermal it as well as Slope it and it would stay On Track
if the elevator was slowly moved back to FULL UP. Just a Mushing forward.
BUT I did have tip plates for insurance.
If you like calculations and math - Go for it.
If you like quicker builds and simpler flying fun - Go for it
If you want a purist's no vertical surface wing - Go for it.
Better yet, do them all - as long as it's FUN !
|Oct 10, 2010, 09:52 PM|
If you have a swept flying wing, an inboard flap does more than just act as an elevator and cause the wing to pitch down when it's deflected.
Even though it does deflect down as an elevator surface does, it also changes the effective twist of the wing rather dramatically. Such a twist change has the same effect as adding up elevator control at the same time as the flap deflects downward - even though the outboard surfaces don't move to compensate.
If the initial wing twist, the wing sweep angle and the flap size and location are balanced just right you can indeed create a design that has very little pitch change when the flaps are deflected.
I'm not sure that it's possible to put all those variables into a computation that will work at model scales, but I can assure you that I have owned and flown swept flying wings that have little or no pitch effect from the deflection of normal inboard flaps. Perhaps Norm has done it and if he is able to figure out how he did it, he may be able to offer you some starting points.
It should be obvious that it will not work this way on a flying wing with little or no sweep.
|Oct 11, 2010, 03:39 AM|
Thanks for your input, and everyone else's so far. Intuition tells me with the right balance, you can acheive non pitchy flaps. Part of the inspiration for trying this was your electric wing with that is armed with effective flaps Herk.
A not so local library has told me they can order in a copy of 'Tailless Aircraft in Theory and Practice'. So hopefully I can get my hands on it by the end of the week.
|Oct 11, 2010, 08:02 AM|
Thanks for sharing your models plans. I sure would like to see some flight photos or videos!
Tinamou was a scaled up version of a flying wing that Herk Stokely designed. I don't believe his had flaps. As far as flap placement went it was not thought out well (but they work great!) and the dimensions were based on where I needed to have removable tips for transportation since it was a 100" model. Well actually it was designed on paper as 100" but I decided to add more sweep so it's now a 95" span model. As said back in Post #8 when I deploy the flaps the outer elevons are then moved upwards to counteract the pitching moment change. It was quite easy to trim out in flight at altitude and she is very stable and controllable with flap deployment during landing. My flaps are way too big and are quite effective. If I were to build another Tinamou I'd reduce the span of the flaps and increase the span of the elevons. It looks like the area you have left your flaps will be about right.
I realize this doesn't answer your question but I hope the spreadsheet "Flying Wing Calc" available at www.TailwindGliders.com will help you out with the twist calculations.
Here's two screenshots from the spreadsheet (Calc).
|Oct 11, 2010, 08:41 AM|
As I thought, there's scope for me to move the cg back some then, I've got nose weight I can remove in gradual increments and this will allow me to dial out the slight reflex my elevons have.
So your flaps were a 'suck it and see' approach? I did see in your youtube footage that there was some up elevon with flaps down.
Here's a brief part the third flight.
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