HobbyKing.com New Products Flash Sale
Reply
Thread Tools
Old Nov 15, 2007, 11:18 AM
Rhinebeck CD-99,00,01,02
Tom Smith's Avatar
New Bern, NC
Joined Mar 2001
3,023 Posts
Way to go Charles. Cliff and I were out flying our canards yesterday. I put 4 flights on my Long EZ. It is so much more fun with the steerable nose wheel installed. Cliff did two on his Georgia Goose. Other guys at the field marvel at our creations. Heck, we do too. Tom
Tom Smith is offline Find More Posts by Tom Smith
Reply With Quote
Sign up now
to remove ads between posts
Old Nov 19, 2007, 08:04 AM
Dr John
pmpjohn's Avatar
Lake Placid, Florida
Joined Dec 2001
2,712 Posts
My local R/C club puts on a static display every year at the local full size fly-in. I managed to get this shot of a Velocity doing a hi speed fly-by just after departure.

John
pmpjohn is offline Find More Posts by pmpjohn
Reply With Quote
Old Nov 19, 2007, 09:10 AM
Registered User
Joined Jun 2005
2,462 Posts
That is a good shot,John, with the prop stopped. Thank you. I had fun at the field Sunday with two canards, a foam Dixie Delta and my Four Star Forty hopped up to 550 watts. A 46 glow out ran me but I was only running a 10-6 prop. Maybe I can get him with the 10-8. He is maxed out. Charles
canard addict is offline Find More Posts by canard addict
Reply With Quote
Old Nov 22, 2007, 12:57 PM
EDF Addicted
MustangAce17's Avatar
Ocala,Florida
Joined Sep 2005
5,339 Posts
here is my latest creation that will take to the skies in the next few days.
MustangAce17 is offline Find More Posts by MustangAce17
Reply With Quote
Old Nov 22, 2007, 05:46 PM
Registered User
Joined Jun 2005
2,462 Posts
Thanks for sharing that, Kyle. It is a neat looking design. What EDF are you using? I hope you will get a video of it. I have been busy trying to keep up with a club member flying his OS 46 powered Ultra Stick or the Stick type look alike, with my E Four Star Forty. I am now building my own light weight Ultra Stick with a Medusa 36-50- 810 for competition with him. It is lots of fun and I might start a thread to show some details. The model may weigh about 3.5 pounds with 700 watts of power. My next canard may be a biplane or a glider with something different from the flat bottom airfoil although the flat bottom is a super performer and I believe it is under rated. Charles
canard addict is offline Find More Posts by canard addict
Reply With Quote
Old Nov 23, 2007, 12:46 AM
Registered User
John235's Avatar
Sydney, Australia
Joined Mar 2006
1,315 Posts
Hi Charles, it is good to hear you may be trying a canard glider design.

I have been toying with many different ideas of a canard glider or an electric glider for some time now. I have finally made a decision about what I will build. I am building it to satisfy my curiosity, and to confirm or disprove some of myths I have heard about canard gliders. I don't have any big expectations about the performance, and I won't be posting a build log this time, rather I will just let you know how it goes when I get it flying.

To make it simple and quick to build it is going to be a small HLG style model with rudder and elevator controls. The main wingspan will be 112cm (44"), and the canard span will be 46cm(18"). I don't expect it to catch thermals, rather I will use with mild slope lift on the cliff at the egde of my club flying field.

It wil use a polyhedral wing, and may look similar in some ways to the "Nacard" design published by Airborne magazine in Australia. Probably the biggest difference is that I am not planning to use any dihedral on the canard wing. As far as I know I know, for good pitch stability, canards should use a more cambered section on the front wing, and a less cambered section on the main wing. In line with this I will be using a Drela AG36 airfoil section on the main wing, and an Eppler 205 section on the front wing. These are both flat bottomed airfoil sections, but the AG36 is thinner at 8.17% thickness and has more Phillips entry which results in less camber.
John235 is offline Find More Posts by John235
Reply With Quote
Old Nov 23, 2007, 02:47 AM
Registered User
Zurich
Joined Apr 2006
3,590 Posts
John, note this: 35 years ago someone I knew built and flew a very nice looking high aspect ratio lightly loaded Canard sailplane (winch launch). It flew beuatifully and looked very nice up there .... however, because it flew slowly, especially when it was "going" upwind, the pilot had to continually remind himself which end was the front!
xlcrlee is offline Find More Posts by xlcrlee
Reply With Quote
Old Nov 23, 2007, 06:42 PM
Registered User
Joined Jun 2005
2,462 Posts
John, It's great to hear from you and glad you have been watching. My glider will probably look like your nacard design with the motor up front. The tiny and powerful Medusa 28-32-1500 will be used with the battery to the rear. I see no reason to not use the flat bottom airfoils since it will fly upright. I do hope you will treat us to a picture or two as you go along. Xlcrlee, That glider friend of yours needs to fly more canards. I have been flying a few of my conventional planes lately (11 total) and have had to re-learn the three point landing. My club is big on glow and gas and I have been trying to compete with them with my electrics. They may get interested if I can show duration and performance.The battery expense seems to be the stopper on large models. Charles
canard addict is offline Find More Posts by canard addict
Reply With Quote
Old Nov 23, 2007, 08:47 PM
Registered User
St Catharines Canada
Joined May 2002
883 Posts
Hi guys

I've been lurking off and on and decided to come out of my tree regarding John235's post on canard gliders. I love flying wings and I love canards and would be very interested to see what you come up with. The delta shown below is the first such that I've built. Yes its a rocket glider. But I don't care what others think about that, Its the most fun way for me to get it up there.

I currently have a 65" wing partly made up for a canard flying wing of AG46 flavour. My use of the canard is not so much to carry load as its quite obvious with the delta that its not that big but only to take the reflex out of the main wing. What would be your considerations on this?

Richard
The Tellurian is offline Find More Posts by The Tellurian
Reply With Quote
Old Nov 23, 2007, 09:03 PM
Registered User
Joined Jun 2005
2,462 Posts
That's interesting, Richard! I suppose that the little canard really does help to hold up the front end. Did you use the area of it to figure the CoG? Thanks for showing it. Comments anyone? Charles
canard addict is offline Find More Posts by canard addict
Reply With Quote
Old Nov 24, 2007, 01:10 AM
Registered User
John235's Avatar
Sydney, Australia
Joined Mar 2006
1,315 Posts
Quote:
Originally Posted by The Tellurian
I currently have a 65" wing partly made up for a canard flying wing of AG46 flavour. My use of the canard is not so much to carry load as its quite obvious with the delta that its not that big but only to take the reflex out of the main wing. What would be your considerations on this?
Richard, I am not really clear on the layout of your project. I assume that a 65" wing is unrelated to the delta you referred to.

I think that a well designed canard should be a more efficient glider than a flying wing, since I think that efficiency is compromised when reflexed airfoils are used for flying wings. I like the approach of using a canard with hinged elevators, because it is a way of using a variable camber lifting airfoil to control the pitch and speed of the model. My biggest concern is that if the canard wing is flying too close to the stall, the overall efficiency is going to suffer, so I hope to minimise this problem by choosing a forward wing of the correct size and layout, and avoid using COG that is too far forward. To minimise the affect of the canard wake on the performance of the main wing, I prefer the canard wake to flow below the main wing. My reasoning is that the high pressure flow on the airfoils lower surface is less sensive to turbulence caused by the wake.
John235 is offline Find More Posts by John235
Reply With Quote
Old Nov 24, 2007, 09:05 AM
Registered User
Don Stackhouse's Avatar
United States, OH, Bradford
Joined Jun 2005
4,029 Posts
Quote:
Originally Posted by John235
...I think that a well designed canard should be a more efficient glider than a flying wing, since I think that efficiency is compromised when reflexed airfoils are used for flying wings.
Yes and no. Reflexing does hurt the max lift coefficient, which means more area is required to make a certain amount of max lift, which means extra whetted area and more skin friction. However, the extra area required by a canard's wing to make sure it does not stall before the canard, exacts a similar penalty. Also, there are a number of ways to achieve positive static pitch stability in a flying wing besides using reflexed airfoils, and not all of them require compromises of this nature.

What I've found is that it's reasonably straightforward to design a flying wing with equal or better efficiency (compared to both canard and conventional layouts) at one particular operating point (airspeed, altitude, power setting, etc.), but typically very difficult to achieve that over a range of operating points. However, certainly not impossible, and in many cases an industrious, alert and meticulous designer can in fact achieve a fairly significant benefit from a flying wing layout over a surprisingly wide range, IF he/she works hard enough and smart enough.

Quote:
I like the approach of using a canard with hinged elevators, because it is a way of using a variable camber lifting airfoil to control the pitch and speed of the model. My biggest concern is that if the canard wing is flying too close to the stall, the overall efficiency is going to suffer,
That's largely a matter of airfoil selection/design. It's not whether or not it's close to stall, it's more a matter of whether that airfoil is operating within its most efficient range (which for many airfoils is fairly close to stall).

Quote:
so I hope to minimise this problem by choosing a forward wing of the correct size and layout, and avoid using COG that is too far forward.
However, it has to be forward enough to provide positive pitch stability, and to guarantee that the canard stalls first (those two criteria are related to each other, but not the same). At the same time, you must have enough pitch authority available from the canard to be able to lift the nose over the desired range of airspeeds and lift coefficients. There is a narrow "window" of canard lift you have to hit, too much lift or too little lift from the canard both cause problems. If it was easy, somebody else would have done it already!

Quote:
To minimise the affect of the canard wake on the performance of the main wing, I prefer the canard wake to flow below the main wing.
Not really a practical proposition. We're not talking about the relatively thin sheet of disturbed airflow from the canard's boundary layer (which at our Reynolds numbers is going to be largely dissipated by the time it reaches the wing), we're talking about the canard's downwash field, which has a total height roughly equal to the span of the canard, angling aft and downward a few degrees for a very long distance (much longer than the plane's length, as it gradually merges with the wing's downwash field) behind the canard. The downwash angle varies with the canard's lift coefficient, becoming more downward at higher lift coefficients, and parallel to the relative wind at a canard lift coefficient of zero.

A flying surface makes lift by deflecting air downwards, and the more lift, the more the deflection. As you raise the nose to increase lift coefficient, the canard moves higher relative to the wing, but it's downwash increases, so the net effect is to tend to keep the wing blanketed by the canard's downwash over the entire operating range. Mother Nature doesn't like to give us any breaks, at least most of the time.

Quote:
My reasoning is that the high pressure flow on the airfoils lower surface is less sensive to turbulence caused by the wake.
Yes, in general, the upper surface airflow on a flying surface is more sensitive to disturbances than the lower surface flow, at least at fairly high positive lift coefficients. It has to do with adverse pressure gradients on the rear portion of the upper surface that make life difficult for the upper surface airflow and make it prone to separation. There is more on this in the "Ask Joe and Don" section of our website:
www.djaerotech.com

In general, it's tough to keep the airflow attached on top at high lift coefficients, but it can also be very tough to keep it attached on the bottom at low lift coefficients, especially for more highly-cambered airfoil sections.

However, turbulation can be a good thing at our Reynolds numbers. Our airflow tends to be laminar, which means there is no mixing between the layers. Because of this, the kinetic energy the boundary layer has available to fight its way through an adverse pressure gradient (the area of the airfoil's upper surface approaching the trailing edge, where the flow is slowing down and the pressure is rising) is only what it had to begin with, minus what it lost through skin friction while flowing over the forward portions of the airfoil. Some turbulence can cause mixing between the boundary layer and the layers above it. This increases skin friction drag, but it also infuses some fresh energy into the boundary layer, maybe just enough to help it get through the adverse pressure gradient region without separating.

OTOH, the turbulence from the canard wake is not likely to help much in this regard. Turbulators on the airfoil surface itself are much more effective. Martin Hepperle's website has a good discussion on turbulators, including how to size them.
Don Stackhouse is offline Find More Posts by Don Stackhouse
Reply With Quote
Old Nov 24, 2007, 09:56 AM
Registered User
Don Stackhouse's Avatar
United States, OH, Bradford
Joined Jun 2005
4,029 Posts
Quote:
Originally Posted by The Tellurian
Hi guys

... I love flying wings
Me, too. Hard to design well, but can have significant benefits in the right application when done just right.

Quote:
and I love canards
They sure look cool! They're a bit like pusher props, in general they aren't the best choice from a purely performance standpoint, but in certain specific applications, when designed right, they can have advantages.

Quote:
... The delta shown below is the first such that I've built. Yes its a rocket glider.
Those are fun! Just don't stand directly downwind during launch, or you can go "IFR" as the exhaust cloud envelopes you shortly after liftoff, a very bad time to suddenly be unable to see the plane! (Guess how I know!) Probably not so much of an issue for a free-flight boost glider, but highly undesirable for an R/C model.

Quote:
But I don't care what others think about that, Its the most fun way for me to get it up there. I currently have a 65" wing partly made up for a canard flying wing of AG46 flavour. My use of the canard is not so much to carry load as its quite obvious with the delta that its not that big but only to take the reflex out of the main wing. What would be your considerations on this?
The fact that it's a canard requires that it be making a significant amount of lift (in proportion to its area) compared to the wing, in order to achieve positive pitch stability. You also have the criterion that it must stall before the wing, in order to avoid pitch divergence at stall.

As I mentioned in my other post, there are other ways to achieve pitch trim and pitch stability in a flying wing (including a delta) besides reflex.

Deltas work well for the problems of supersonic flight. However, they have naturally high induced drag, which generally makes them poor for gliding performance and for retaining energy while maneuvering. For example, they generally do not thermal well. You can counter this with more wingspan, but then your high speed performance suffers from too much whetted area and skin friction.

However, 3-d airflow, particularly the vortex formation along the leading edge at very high angles of attack ("high alpha"), can result in some incredible lift coefficients for deltas (albeit with very high drag), as well as stable behavior and handling at very high alpha. This is why the Concorde didn't need wing flaps, but did need the drooping nose and very tall landing gear. For exteme maneuvering that can open up some interesting possibilities.

I've done some pretty bizarre maneuvering with my Pibros delta-winged glider. I don't live near any really good slopes, but I found that a hook on the belly a few inches behind the nose, and a 30' bungee in our back yard (I live on a farm, with large fields all around) could provide some pretty exciting flying with very litle cost and hassle! The plane was not good at thermalling, and care had to be used to avoid too much up elevator during loops (pull too much alpha and lift coefficient and the induced drag kicked in, like throwing out an anchor, and the plane couldn't make it over the top of a loop), but fully controlled flight to alphas around eighty dgrees or so was no problem. Flat spins were spectacular, and a sudden pitch-up would bring it to a sudden and complete halt (momentarily, of course, until gravity took over) in mid-air, just like that Bugs Bunny cartoon where he brings that diving 4-engine military transport to a sudden halt just above the ground by putting on the "air brakes".

The addition of a canard to a delta, with the interaction of its tip vortices with the leading edge vortices along the wings, could make things really interesting, although whether that's good or bad would depend on the details of the specific design and how it's flown. It might also be very interesting to experiment with the size and location of those leading edge notches on your design. Those could have some influence on the formation and stablity of the leading edge vortices in high alpha flight.
Don Stackhouse is offline Find More Posts by Don Stackhouse
Reply With Quote
Old Nov 24, 2007, 10:35 AM
Registered User
Joined May 2003
60 Posts
OK, I figured out the canard that I have is the Astro-blaster.

The last time I flew it (~2yrs ago) I slapped an Axi 2212/34 on it (all I had on the bench).

It flew fine, but wasn't fast enough for me. What kind of motor should I get for it?
Obviously the cheaper ($) the better.
BlitzK is offline Find More Posts by BlitzK
Reply With Quote
Old Nov 24, 2007, 11:14 AM
Registered User
Joined Jun 2005
2,462 Posts
Blitzk, Is this your model? http://www.rcgroups.com/forums/showt...er#post6147220 The Medusa 28-32-1500 with 3 cells and an 8-4 APC will go 185 watts, If you want more, the motor can handle 206 watts and even more with their heat sink. It weighs only 2 ounces like your AXI and is more efficient. Charles
canard addict is offline Find More Posts by canard addict
Reply With Quote
Reply


Thread Tools