Anyone know much about aerodynamics

[Craig Spence]

Hi all,

 

Im haveing some trouble decideing where to put my Horrizontal Stabilizer on my fuselage (own design).

Its a mid wing model and after doing lots of research as to where to put it, im confused lol!.

 

I have seen pictures of mid wings with the stab higher than the wing and other pics in line with the wing and even some just below the wing.

 

So would I get a difference in performance where I put the stab?, Im thinking of going above the main wing.

 

Also I take it that incidence is the line drawn through the centre of the main wing to the stab and that the stab should be flat and level with this?, is there any consideration I should be putting into this ie.. should I have any degree off of that line or should it always be kept straight.

 

If anyone is confusesd reading this (cos i know i am lol!) please get back to me for a better explanation lol!.

 

Feedback appreciated, cheers all.

[Jonathan Lewzey]

first of all, what type of plane is it?

 

if its aerobatic, most designs (zivko edge, F3A ships, F3Ps, AMs etc) have the wing and tailplane on the thrustline. Don't know exactly why this is, but I think it helps hold the line through aerobatics and helps keep knife edge tracking well.

 

if its a sport design it shouldn't matter too much although there is an argument for keeping the tailplane out of the wash of the wing especially with a short moment arm.

[Klippy]

Hi Craig, my 2p, the centre line of the main wing is a line drawn between the centre of the leading edge and the centre of the trailing edge. On anything but an aerobat this line should 'attack' the air at about 2degrees. Usually we cheat a little bit and place the tailplane at the same angle as the centre line of the fuselage, then pack the main wing to get the 2 degrees incidence. Hope this helps, I'm no expert, hopefully Peter Miller will drop in and put us right!

[Craig Spence]

Hi Jonathan,

 

the plane is based around the Frantic Fun Fly model but im redesigning it to be a mid wing 3D model. The old fuz is going to be modified making it wider, slightly longer, with a higher tail width (to aid knife edge) and with a turtle deck.

Also the tail will be completly different as well, split elevator and complete rudder with tail wheel.

 

Ive been looking at some of the Edge 540's and Extra's and other 3D models and the stab is higher than the main wing. Im thinking that this is because, like you say, to keep the stab out of the wash of the wing. So in effect clean air is allowed to flow over it, I think, but thats what ive come on here for.

 

My other query is should I have the tailplane with camber?, I know most planes with camber on the tail are accounting for weight therefor giveing it camber gives extra lift, I dont think I should have to for this model but its a consideration non the less.

 

What do you think Jonathan.

[Craig Spence]

Hi Tony,

 

I see what your saying about the two degrees or so for the angle of attack, is this something to do with high alpha flight?.

 

Also I would like this plane to fly very slow as well, but also have the poke to pull out of manouvers or trouble.

 

Cheers Tony.

[Jonathan Lewzey]

yeh as its designed for 3D, the tailplane should be in line with the wing set at neutral (+/- 0 deg). The edge and MX series are low wing so the tailplane is higher, but on the edge the wing and tailplane are defintely on the thrustline. The tailplane should be symmetrical section like the wing for equal performance the right way up and inverted.

 

the fuselage doesn't have to be wider, mainly increase its height to aid knife edge. extra width will just add weight and wing area is the best contributor to harriers etc

[Jonathan Lewzey]

btw incidence of the tailplane doesn't help with alpha as you're effectively kiteing the wing through the air with lots of power. if you introduce an incidence angle this makes inverted much worse so its not a pure aerobat

[Josip Vrandecic -Mes]

Hi Craig,may help-Fig1-the airplane before adjustment:in thi example ,the stabis on the thrustline,and the wing is well below.All the incidences are at zero.Fig2-incidence adjustments are made:In this example,if we want to "lower" the stab,compared to the wing,rather than cutting the tail apart,we can adjust both the wing and stab so that their angles are negative t the thrust line.Putting positive incidence into both will raise the stab,compared to the wing.Fig3Acual flight attitude.In this example,this is how the plane in figure 2 will actually fly.Note that droopy tail.A side effect of these changes is that the engine thrust is pointed up,unless the downthrust is adjusted by the same amount as the wing and stab.

by Dean Pappas Via Joe

[Craig Spence]

Hi Jonathan,

 

thanks for the help again, so I think the best idea would be to keep the main wing in line with the thrust line and no incidence and the stab in line with the main wing as well with no incidence.

 

Thanks for the help there, what do you think about camber on the tail?, I dont think its gonna be of any benifit but would like opinions.

 

Cheers Jonathan.

[Craig Spence]

Hi Josip Vrandecic -Mess,

 

Thanks for the time youve put into helping there. There is only one problem though, I cant see what it is that you have put up for me, maybee its my cheap computer.

 

Thanks for the help though and the time.

[Craig Spence]

Oh Jonathan,

 

I forgot to say about widening the fuz. The main reason behind it is for room for radio installation, in the old type fuz its very tight and doesent give you much room to move the CofG about.

Also I will have to fit an extra servo in this time for the rudder and maybee a bar for this further down. On the old fuz I mounted the rudder servo to the tail.

 

When I say extra width as well its only around 2cm so its very minimul.

 

Just a thought though, would haveing a wider fuz with alot of surface area on the bottom increase slow flight ability as you have a bit more surface area, not lift though?.

 

Cheers again Jonathan. 

[Josip Vrandecic -Mes]

Sorry Craig it is my mistake look again please ......Thank so much regards Joe.

[Craig Spence]

Hi Joe,

 

that look's very good and clears things up a little, so am I right in saying that the stab should be higher than the main wing?.

 

It looks like that on most models ive been looking at, its ever so slight but the stab is always higher. I suppose the thing I never took into account was the incidence line with the stab but you have cleared that up for me now, Ill go with figure 1 Joe.

 

Thats very helpfull indeed Joe, thanks.

 

What do you think with that decision?.

 

Cheers Joe.

[Jonathan Lewzey]

none of those diagrams joe has included (while helpful) have the wing and tailplane on the thrustline. the closest is fig 1, but this isn't a true mid wing like the zivko edge.

 

changing the fuselage by 2cm width shouldn't change it that much so go for that, just watch the length of the ailerons as most ailerons go right up to the side of the fuz.

[Craig Spence]

Hi Jonathan,

 

my one will closely resemble figure one although both the main wing and the stab will be on the thrust line, even if I wanted to change it, looking at my drawings I dont really have much of a choice in the matter.

 

As for the ailerons, I havent looked that far ahead yet but I would like to have them, as you say full ailerons.

 

I think I will start them from the fuz all the way to the tips, but well see.

 

Cheers Jonathan.

[Jonathan Lewzey]

Posted by Craig Spence on 31/03/2010 14:46:48:

 

my one will closely resemble figure one although both the main wing and the stab will be on the thrust line, even if I wanted to change it, looking at my drawings I dont really have much of a choice in the matter.

 

As for the ailerons, I havent looked that far ahead yet but I would like to have them, as you say full ailerons.

 

 

 thats what i had in mind .

 

the thing with the ailerons: just watch that as you're modifying an existing design you don't build the ailerons too long and they foul the fuselage sides but as you say you don't have to worry about that for now.

 

best of luck with the project

[Craig Spence]

Hi all, Ive just been doing some research again and ive found some other interesting pictures of planes.

 

Jonathan, this is a Zivko Edge and you can see that the stab is higher than the main wing, also it looks like the thrust line goes through the leading edge of the wing to the trailing but the stab is above that. I wonder if this is like this for washed air over the main wing, giveing clean air to the tail.

 

Again another Zivko Edge with the same stab arrangement.

 

This Edge 540 also has the same stab arrangement, there must be a reason for this and I muct know before I decide what im going to do.

 

Again and again, some are very slight yet others are very noticeable, I need to know as im very obsesive lol!, the wife wont get a straight conversation out of me, the other day I fell asleep on the sofa and was speaking about the main wing of a plane in my sleep lol!.

 

Help please.

 

Cheers lads.

[Josip Vrandecic -Mes]

Dear Craig ! In my competition time 1980. (FAI -F-1-C) Mostly of us were seting up stabilizer as high as possible(over influence of  propeller  torbulation). "T-TAIL" shape is ideal,but hard to make in the past.Today everything is possible.Yours choice is compromise....like all in aerodynamics...and life- time  Best wishes and magical flights  Joe.

[Erfolg]

I thought the reason for mounting the tailplane above the main wing chord line, was to keep it out of the main wing downwash.

 

Yet there are plenty of examples where they are in line.

 

It seems to be older models where the tailplane is much lower than than wing, this is probably a practical means of removing it for transport.

 

The main issue is , does it matter, if so why?

 

Erfolg

[Craig Spence]

Hi Joe,

 

so basically your saying that the stab above the main wing could be better but suck it and see sort of sketch lol!, ive heared this before lol!, but as I say im very obsseive, I need to know why lol!.

 

Cheers Joe and point taken.

[Craig Spence]

Erfolg,

 

Im in the same state of thinking as yourself ie.. downwash from the main wing but again asking the same question and hopeing someone know's why.

 

Does it matter?, I think it does because if it didnt why would they design it like that lol.

[Simon Chaddock]

Craig

If you are designing for full 3D aerobatics the plane should fly as easily inverted as the right way up so everything should be in line with the thrust line, symmetrical wing and tail sections and no incidence.

Don't kid yourself, the experts make it look easy but such a design requires "hands on" flying all the time and it will fly equally well in any attitude -  including straight down!

[Craig Spence]

Thanks Simon,

 

good feedback, of course there will always be some trial and error but we will see how it turns out, hopefully quite well. Im by no means saying im going to create a 3D machine but im hopeing that it will fly quite well and do some basics, I have only be flying for just over a year now but I am hopeing to learn 3D flying I just need a decent tutor which hard to come by.

 

Ive had a few 3D planes now and love them, Im buying a cheapy tomorrow to learn without fear if you know what I mean.

 

Its the ST Models MX2 and I hope to throw it around to no end until I have the confidence to do the same on my balsa models (of course every model is different).

 

Anyway, back on track, I have done quite a bit of research and some of that is on here.

Well see how it turns out.

 

Cheers Simon.

[Simon Chaddock]

Looking at down wash.

In conventional configurations in normal flight the tail plane will above the wing down wash. The issue is mainly what happens when flying slowly.

To maintain lift at slow speed the wing is at a higher angle of attack and thus creates a more pronounced down wash.

To achieve this angle of attack the tail will be lower and it can enter the wing down wash which will upset the aerodynamics of the tailplane. This can be useful as a stall warning to the pilot.

Note however the prop wash from a powerful single engine may completely mask the down wash effect of the tailplane.

A high mounted tailplane (T tail) will delay the point where the tail enters the wing down wash and this improves pitch control at slow speed but as they found out with the Trident airliner at extreme angles of attack the airflow over the tailplane can be so disturbed it looses effect and the plane can enter a stable unrecoverable "super" stall.

Model aerodynamics are a bit different to full size anyway so in most cases its simply "suck it and see"!     

[David Gilder]

Time I put a bit in here me thinks!!!

 

I was of the understanding that an "all in line" was best for full aerobatic and would also need symetrical wing!  

 

High tailplane has the tendancy to get caught in tubulent air off main wing when in high alpha or stall due to airflow line over wing when high angle of attack produced.

 

Low tailplane will have same effect when high alpha and stall but inverted!

 

All depends on what type of manouvres you want to fly but i would suggest that "all in line" may be easiest and most suitable for normal aerobatics.

 

Hope all goes well.