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Old Nov 21, 2008, 07:57 PM
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I am still around and enjoying the discussion. My thanks to all of you for answering questions, presenting new material and for keeping the thread alive. The changing weather has me down a little with less energy for now. Charles
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Old Nov 21, 2008, 10:39 PM
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Charles,
P 81 shows the winglets or wingtip vertical stabilizers held on with screws. As near as I can tell the screws are only in balsa. Is that true or have I missed something?
Thanks, glade
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Old Nov 21, 2008, 10:50 PM
Jets are for kids-of all ages
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John 235,
Thanks for the info, I am glad there are still a few Long-ez models to be had. I hope to be able to build a 44" to 48" span, and make it under 3 lbs. I have a 35-36-1000 motor that would be plenty of power. I just love the look of a graceful canard flying.
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Old Nov 21, 2008, 10:54 PM
Jets are for kids-of all ages
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Just for Information, seems alot of people are not real familier with the way a long-ez or any of the Rutan type canards work. Like trailing edge down on the canard is up elevator, and visa versa. The Vertical Winglets, have a rudder on each that only move outward, NOT inward, so that the major yaw contributor is drag on the inside wing. If you make both rudders move both directions, you will end up with about 1/2 of the yaw control. They are a little weird, but that is what makes them cool.
Roger
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Old Nov 22, 2008, 01:53 AM
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Undercamber probably isn't the right word for the NACA1408. I think it is typical of what is often referred to as a semi-symmetrical airfoil. I had a look at SD8020 on Profili - I don't think its dramatically different from NACA 4 series apart from S8020 being fully symmetrical.

Full size delta jets often have leading edge sweep angle around 55 degrees or more. Obviously supersonic flight is the main reason for this. From my point of view I'd like to experiment with a low-aspect ratio canard model without trying to create a massive leading edge vortex. 30 degrees LE sweep is probably enough for my purposes.

Here is a photo of Burt Rutans very early Vari-Viggen canard. I haven't found too much information about it, so I am not sure of the reasons behind the delta platform. I think it must have taken a lot of bravery from the pilot to do the flight tests, especially considing the high alpha landing approach that is typical delta wing aircraft. Does anyone have comments about this?
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Old Nov 22, 2008, 07:20 AM
Jets are for kids-of all ages
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Delta planform provides the largest lift area with a lower drag profile. The Douglas A-4 Skyhawk, i.e. It was the mighty midget, as it could carry an impressive load. I think Rutan early thinking was maximum lift from the main wing, with the least drag.
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Old Nov 22, 2008, 09:37 AM
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Well, um, No.

As I understand, Rutan was just intrigued with a new Swedish fighter, the Saab Viggen, and designed and built a general aviation recip scaled-down approximation of it.

Deltas make sense for transonic and supersonic flight, and for extremely high-alpha flight. They don't make nearly as much sense for most subsonic applications. They have lousy Reynolds numbers at the tips (a particularly significant issue for our models), poor spanwise lift distribution, extremely poor span for their area, and therefore they tend to have a poor max lift coefficient for the wing (I.e.: much lower than for the basic 2-D airfoil) unless you can get some vortex lift effects working, which is tricky to achieve, particularly at our Reynolds numbers. In any case, the induced drag tends to be very high, and L/D at high lift coefficients tends to be very poor. If you have enough wing area and therefore low enough wing loading to avoid the need for high lift coefficients, then you have too much whetted area and your high speed performance suffers.

If you need something that can be controlled at ridiculous angles of attack (I used to do all sorts of interesting things with my Pibros at alphas above 80 degrees or so), a delta planform can possibly be useful. However, don't expect it to retain energy well, if at all (one of the most difficult maneuvers with the Pibros was a simple loop; if my energy management was anything less than perfect, it couldn't make it over the top), and don't expect it to thermal very well.
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Old Nov 22, 2008, 09:45 AM
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Quote:
Originally Posted by mullinspsm
...The Douglas A-4 Skyhawk, i.e. It was the mighty midget, as it could carry an impressive load.
That had a lot more to do with its power-to-weight ratio. Anything will fly if you put a big enough motor in it.

Deltas can provide high lift if you can get the vortex lift thing working for you. However, they do it at the expense of very high required angle of attack (which is why the Concorde had to have the drooping nose and tall, spindly landing gear) and extremely poor drag (i.e.: about 3 or 4 to one L/D). On a jet, especially a first or second generation fighter class aircraft, on landing approach that's an advantage.

The throttle response of the earlier jet engines in particular was very poor, so the strategy was to get the plane as draggy as possible in final approach configuration, so that almost full throttle was needed to stay on the glide slope. If a go-around was needed, it was a lot quicker to drop the nose and retract the gear and flaps than it was to open the throttle and wait for the turbine to spool up. Modern jets still tend to use this method.

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I think Rutan early thinking was maximum lift from the main wing, with the least drag.
Max lift, maybe. Least drag, NO WAY. If that was true, the majority of sailplanes would be deltas.
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Old Nov 22, 2008, 10:17 AM
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Glade, I just used 3/8 screws into the thick hard balsa tip ribs of mine. Holes of 1/16" dia. were drilled first. You may want to apply some thin ca to the holes before attaching. One rudder got bumped loose and I just glued on a 1/32" hardwood plate and re-drilled. Regarding the Viggen it seems that with the large wing area up close to the fuselage, a stalling wing tip would have very little effect. The Long EZ uses a really large wing base with high aspect ratio outer wing sections. If a symmetrical airfoil is used for the main wing, I suggest that the leading edge should be raised 1.5 degrees relative to the thrust line to let it lift the rear load prior to the rotation. My flat bottom airfoils had about 1.5 degrees of effective alpha when the flat bottom was parallel to the thrust line. The Millennium Slow Stick was my first and only trial with the symmetrical airfoil. Charles
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Old Nov 22, 2008, 02:59 PM
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John. Sorry it seem that the dxf I have has a few misplased points wich created a lttle tip on the bottom at the te of the profile, I double checked and it is semisemetrical.

Deltas have a lot counting agains them but I love the for the looks and a lot of my co pilots think they are difficult to fly - wonder why boeing and a few others are looking into wings and deltas for their next generation aircraft?

Personally I'll use a 45 deg sweep for the fun and looks with a 30 - 33 % scaled down for the canard. But I've gor a 60 size stick wing to build for 2 25cc engines - a 25cc twin stick.

Thinking of it may I should buid 2 wing and use one for my canard
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Old Nov 22, 2008, 08:24 PM
Jets are for kids-of all ages
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Don I know what you mean about deltas having more drag, but there are some advantages as in the A-4 again. ( The choice of a delta wing, for example, combined speed and maneuverability with a large fuel capacity and small overall size, thus not requiring folding wings, albeit at the expense of cruising efficiency.) quote from Wiki. However the A-4 was never over powered. I have a friend with an Enforcer. (Laddie Mikalasko) Delta wing, 50 heli engine, he also added a canard to help with elevator. It is very graceful in flight, and lands at a snails pace. Very height lift wing, and it is not transonic, but fast for a model. We generally deal in oz. or maybe couple of pounds per square foot, where as real planes (man carrying) go hundreds of pounds per square foot. Considering the speed of a Vari-Viggen, The wing planform probably didn't matter.
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Old Nov 23, 2008, 09:48 AM
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Mullin, Any chance of getting a picture of Laddie's canard delta? Your description of the controlled landing kicked up my interest.
Charles
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Old Nov 23, 2008, 10:58 AM
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Quote:
Originally Posted by mullinspsm
Don I know what you mean about deltas having more drag, but there are some advantages as in the A-4 again.
I'm not implying that the delta planform was a bad choice on Ed Heinemann's part for the A4. What I'm pointing out is that a great deal of the reasons that made it appropriate in that case do not apply in general, and particularly to a typical R/C model application.

Quote:
( The choice of a delta wing, for example, combined speed
When the drag in question is wave drag and the need for extremely low thickness to chord ratio on the airfoil, due to transonic or supersonic operation. Not appropriate to our situation.

Quote:
and maneuverability
A delta does minimize span for a given area, and reduces the mass in the tips, which can help reduce roll inertia and damping, and improve roll rate. However, on models it's usually not too difficult to get high roll rates (to the point that the limiting factor is the human pilot's ability to mentally stay ahead of the airplane) without resorting to a delta planform, so this advantage isn't really significant for our applications.

Quote:
with a large fuel capacity
True, if you're using a "wet wing" type of fuel tank, and can't put that fuel in the fuselage. Not generally an advantage for a model.

Quote:
and small overall size, thus not requiring folding wings,
Big advantage for a full-scale carrier-based aircraft.

For us, small size does help transportability of a model. OTOH, if the delta model is small, you could just make a smaller scale conventional planform model with that same span. Unlike on manned aircraft, we generally are pretty free to make our models whatever size we want. The delta's potential span issues aren't really an advantage or disadvantage in our case.

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albeit at the expense of cruising efficiency.)
Along with efficiency in a number of other regimes as well. In the case of the full-scale A4, they needed lots of drag on landing approach so they could keep the engine spooled up in case of a go-around, so the high drag was actually a benefit for the A4. With single-seat, single-engine jets the standard procedure for dealing with an engine failure is to eject. They do not try to land "dead stick" because the plane becomes essentially unflyable without the hydraulics. It's reasonable to assume that essentially all landings of that aircraft would be with the engine working, and that it needed to be at a high power setting.

In our case, that high drag combined with our far lower power density could make the plane a handful on final approach. Also, even on electric models we have a pretty high frequency of needing to make dead stick landings (in comparison to their frequency on full scale aircraft), so we need adequate glide and flair capability with no power.

Quote:
quote from Wiki. However the A-4 was never over powered.
"Over powered" is a subjective opinion, and very dependent on the context of where you're applying the term.

It was a very small, lightweight airplane, the epitome (at least in its class) of Tony Fokker's axiom "Simplicate and add lightness." Compared to other jets in its speed and payload class it didn't have an enormous engine. However, for its size it had plenty of power, enough to overcome the drag penalties of the delta layout, which themselves are probably relatively small compared to the drag penalties of all that stuff they had to hang under the wing.

Quote:
I have a friend with an Enforcer. (Laddie Mikalasko) Delta wing, 50 heli engine,
"... if you put a big enough engine in it."

Quote:
he also added a canard to help with elevator. It is very graceful in flight, and lands at a snails pace.
The appropriate question in this discussion is how a plane designed for the same mission profile but using another planform would compare to that. Yes, a delta can be made to fly well. I've designed and built some of them myself that do that. However, some folks here are erroneously implying that it's fundamentally better than other planforms in certain ways, and (again erroneously) that those ways still hold true for our typical models.

Quote:
Very height lift wing, and it is not transonic, but fast for a model.
But is it inherently faster than a conventional planform for a given power and size, in the subsonic operating realm? If that was the case, then the vast majority of modern pylon racers, both models and full-scale, would be deltas.

Deltas are fine if we're more interested in looks, or if we're building a scale model. The Skyray is one of my own personal favorites for really beautiful aircraft, and definitely on my "to do" list.

However, don't claim something is fundamentally better in terms of efficiency in a specific class of applications (such as subsonic aircraft, including models), when that simply isn't the case. If we're trying to maximize the performance of our designs, we have to be objective and honest with ourselves.
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Old Nov 23, 2008, 01:58 PM
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I have no idea how this got loose - sorry for taking up space!

All I can think is that I intended to say something wondrous, but wifey drug me off to 'work' - a snag of being married to a workaholic who runs her own company (along with a copywriter/editor/coffee maker and GP skivvie - me!)
and the 'send' key got hit by mistake

Regards

Dereck
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Old Nov 23, 2008, 08:10 PM
Jets are for kids-of all ages
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This is a picture of my friends enforcer, from about seven years ago. He still has it and still flies it. It really is a fun plane to watch. Like I said (Fast.... and Slow...)
Roger
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