Canard Forum: Show,Discuss, Learn - Page 384 - RC Groups
 Feb 11, 2012, 10:44 PM who has rabbit ears down Take a look at page 312 for some very important infos about all Rocketman! also, the renolds #'s are an (X +Z) axi only formula! Latest blog entry: Finally getting some airtime!
Feb 11, 2012, 11:39 PM
Registered User

# Long EZ

Rocketman Here are airfoil shapes

http://www.nextcraft.com/berkut01.html
 Feb 12, 2012, 12:22 AM Registered User But Al said something like "twist can generate thrust". Surely that can only be through negative lift at the tip. Positive lift always generates drag, yes? Now that all sounds very simple to me, so what have I missed? Vortices? Hi Nick I think the thrust is to do with the vertical component of the airflow on the outboard LE tilting the thrust vector forward. When aileron moves down increasing lift with lift vector tilted forward it increases "thrust" more so than the drag produced. Regds
Feb 12, 2012, 03:02 AM
Mitch

# Reynolds number.

Quote:
 Originally Posted by Rocketman1092 Hey guys, I'm also considering lengthening the main wing and canard chords to add wing area and help avoid low Reynolds numbers. Thanks!
I'm not an expert in any field, however my understanding of Reynolds numbers suggests that this is an entirely viable way to maximize Reynolds numbers for wings and other flying surfaces (horizontal / vertical stabilizers)

[In the computation of Reynolds number, Re = r V l / m, the characteristic length, l, for a body (fuselage, nacelle) is the overall length, and for the aerodynamic surfaces (wing, tail, pylon) it is usually the exposed mean aerodynamic chord]

Keeping the chord Re# for the wing / canard well above the transition area (~50,000) at stall speeds can help prevent unpredictable stall behavior arising from unstable laminar flow. It is important to note that the Re# for the tip of a tapered wing can be much lower than the Re# for the average chord. For a small, slow flying model, a rectangular wing with a low aspect ratio can make a lot of sense!

Mitch
Feb 12, 2012, 03:10 AM
What could possibly go wrong?
Another Starship, hooray!

Quote:
 My preliminary thoughts for the wing and canard layout are a 1.5 degree root incidence for the main wing with a progressive twist to 0 degrees at the tips, and a 3.5-4.5 degree canard incidence. I'm also considering lengthening the main wing and canard chords to add wing area and help avoid low Reynolds numbers.
Yes.

Of course, what you do with the elevator control quickly overrides the initial canard incidence. The full size Starship has elevons, I believe. None of my models do but I think the next one will.

How big and what materials? Let me know if you'd like any of my files and build photos.

The Starship was also my first canard, though the guys on here persuaded me that a simpler prototype was a worthwhile first step. I did get a lot of help from them. My wife said it looked like an accident waiting to happen, but it worked well, to our surprise!

Hi Dave

I'm scratching my head here! "vertical component of the airflow" - is that the leading edge compressing the air and pushing it up? It still looks to me as if washout is the only way to get a net effect where the drag becomes thrust. If you look again at that photo of the Northrop flying wing I posted, I think you can see that the outboard control panel is split, which suggests no down aileron at all, at least not at the tip.

Modern commercial airliners (and the Starship) all recover some of the energy from the tip vortex using tip fins. The fins have an airfoil shape because high pressure is on the outside. The rudders on the Starship have a differential that favors movement to the outside.

But Al Bowers lecture was suggesting that you don't need tip fins.

We live and learn, if we're lucky. Which golfer was it who said "the harder I practice, the luckier I get?"

### Images

 Feb 12, 2012, 11:08 AM Purdue Engineering Wow, thanks for all the help guys! nickchud: My model will be around 50" span, CNC milled from pink foam and then either covered or glassed. I do have a couple questions about your build, if you don't mind. Firstly, would you change the incidence angles or thrustline if you had the chance, or did they all work out? Secondly, I see that you used seperate ailerons and elevator control surfaces. Would you forsee any problems using elevons coupled with the canard, as the full-scale Starship did? Finally, how useful is the rudder control? I'm thinking about leaving it out to save weight and complexity. Thanks!
Feb 12, 2012, 11:10 AM
Registered User
Mitch
Quote:
 Keeping the chord Re# for the wing / canard well above the transition area (~50,000) at stall speeds can help prevent unpredictable stall behavior arising from unstable laminar flow. It is important to note that the Re# for the tip of a tapered wing can be much lower than the Re# for the average chord. For a small, slow flying model, a rectangular wing with a low aspect ratio can make a lot of sense!
That sounds reasonable, Mitch. A 5" tip chord is considered minimum. I believe that wing loading should become increasingly lower as model size decreases.

Nickchud
Quote:
 If you look again at that photo of the Northrop flying wing I posted, I think you can see that the outboard control panel is split, which suggests no down aileron at all, at least not at the tip.
Nick, As I see it, the UP reflex at the wing tips will reduce lift on the tips which will prolong the stall at high AOA and behave as washout.

Rocketman, There are excellent build threads on Scale Electric Planes. One is by Nickchud which we are fortunate to have here. IMHO, the wing twist could be avoided on a model. The fuselage center line should coincide with the thrust line and the chord line. Four degrees of canard incidence seems correct. The large center section of the wing should not allowed to lift the model before the canard does.With 1.5 degrees of center chord angle, the motors at zero thrust angle would provide down thrust which seems counter productive.

Charles
Last edited by canard addict; Feb 12, 2012 at 09:15 PM.
 Feb 12, 2012, 11:41 AM Registered User Well, um, NO. Incidence is something that will vary from one plane to another. The numbers batted around here in this latest discussion fall within the range of what's typical, but trying to specify incidences without first studying the details of the plane is like asking what size shoes to buy without first measuring your feet. Wing/fuselage incidence depends on what incidence will make the fuselage level when the wing in flight is at the angle of attack it needs to have to support the plane. Wing/canard incidence ("decalage") and the resulting canard/fuselage incidence depends on what angle of attack the canard needs in flight to make the lift required from it to keep the forces from the rest of the plane in balance. The angle of the thrust line depends on what will make the thrust line pass through the C/G location (in both the horizontal and vertical sense), to minimize the effects of thrust on pitch trim. 5" is by no means a "lower limit" on tip chord. Keeping the taper ratio moderate (0.6 or more) does make the whole tip stalling issue less critical, but much steeper taper ratios (0.3 or worse) are quite reasonable, especially with a suitable dose of washout. I've had models with tip chords less than 1.5" that had perfectly decent performance and handling, including stall characteristics. If you use airfoils and twist that properly take into account the size and shape of the plane and the way it is to be flown, all sorts of things are possible. Don't let these "rules of thumb" paint you into an unnecessary corner. Figure out what you're trying to do, and what you need to do it. If you're unsure, try building some small balsa free flight gliders of your concept before committing to the more expensive R/C design. And, as I said before, the full-scale Starship did not use elevons on the canard nor the wings. It had elevators on the canard, and ailerons on the wings. Trying to get the canard to stall before the wing in all flight conditions, but not too much before, is a demanding enough requirement that trying to make it also do the aileron function (something it would not be good at anyway, because of its shorter span) is not a wise move. Likewise, using elevons on the wing just takes that whole issue of keeping the wing flying until after the canard has stalled and turns that into a "moving target". Again, not a wise move. Charles gets away with it on his planes because his canards are too small to do the full job of providing pitch stability and control by themselves. His planes are actually more of a tailless model, with a little help in pitch from what amounts to a large trim tab on the nose. As I recall from the last time we discussed it in this thread, he's running horizontal tail volume coefficients ("Vht") down around 0.2 or 0.3, where a properly sized tail has a Vht around 0.45 to 0.55, so his canards are about half the size they should be according to the typical range of volume coefficients. Last edited by Don Stackhouse; Feb 12, 2012 at 11:54 AM.
Feb 12, 2012, 12:20 PM
Purdue Engineering
Quote:
 Originally Posted by Don Stackhouse And, as I said before, the full-scale Starship did not use elevons on the canard nor the wings. It had elevators on the canard, and ailerons on the wings. Trying to get the canard to stall before the wing in all flight conditions, but not too much before, is a demanding enough requirement that trying to make it also do the aileron function (something it would not be good at anyway, because of its shorter span) is not a wise move. Likewise, using elevons on the wing just takes that whole issue of keeping the wing flying until after the canard has stalled and turns that into a "moving target". Again, not a wise move.
Don,

I'm fairly certain that the Starship had elevons working in conjunction with the canard - they appear in the cutaway drawing here: http://rps3.com/Files/Starship_Cutaway.jpg and also several times in the Starship's maintence manual. In fact, the word "aileron" doesn't appear even once in the 1000+ pages of the manual, just "elevon".

Regardless, would you suggest that using the main wing's control surfaces as ailerons only would be the way to go?
Feb 12, 2012, 12:23 PM
Registered User

# Signflyer's GNOT-EZ

Built and flew that design.
Differential thrust works well.
Flies very stable even underpowered but only one flight due to poor landing.
The problems I had all relate to my building and flying, not the design. See:
https://www.rcgroups.com/forums/show...0&postcount=25
No idea whether the KF profile does anything. It certainly makes it easier to rum the wires through the wing.

### Images

Feb 12, 2012, 12:35 PM
What could possibly go wrong?

# Phew!

Brilliant! Many thanks for all the work you have put into that Don.

At the first reading, I have to say "My brain hurts". But I did understand enough to make me believe that reading it again will pay dividends.

I don't like using elevons, or any fancy linked control surfaces on my canards, being a believer in the KISS principal. I didn't think they had them on the Starship till I found this diagram on Bob Scherer's website. I hungrily accept that the diagram is wrong. Having said that about the KISS principal I did use elevons on the delta duck I built. I think it helped shorten the take-off run, perhaps by reducing the pressure under the TE resulting from ground effect. Another trick I tried with one of my twin water planes was differential thrust, linked to the rudders. That was useful on the water and very interesting in the air.

Rocketman, have you seen this little Starship, which is just getting near to its maiden flight?

Presently, I'm home alone and making progress on my monster Starship, I'll post some pictures in a moment. I have a cunning plan for the rudders, borrowed from something I saw on this thread before. By the way, I didn't put rudders on my 46" Starship. On the larger model, I find that when I use them I have to add some up elevator. Makes nice flat turns though.

The plan for the rudders I refer to is to use servos attached only by strings to pull a lever in front of the hinge line. (I have to have 2 as the wings are detachable). So the rudders only function on the inside of the turns. They will be kept from flapping by a piece of flat acetate cut from some packaging or other and placed on the opposite side of the hinge so that they gently oppose the lever. If you see what I mean.

I'm delighted to see all this extra activity here!

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Feb 12, 2012, 03:10 PM
What could possibly go wrong?

# Starship wings

If your wife asks you what we do while she's away, show her these pictures. To build this plane has taken a lot of space, only available when you're home alone

I've used 6mm x 0.8mm cf strips. One piece in each wing is upright all the way to the tip. In other places as cap strips top and bottom of the depron spars. For the inboard section, there is more wood and there will be more when I can get some 6mm balsa to use in the spars in place of the depron in the outer parts of the wings. To fix the outer wings there are 8mm cf tube with 6mm tube sliding in and out as they are removed. This tube also helps to stiffen the structure.

I'm learning to use white Gorilla Glue and I like it a lot in this context. Lightweight, very strong, not brittle, gives me time to slide things into place. It's very important to use plenty of weights or tape to stop the foam running amok.