Strake question

[Hans S]

I've been wondering something. It seems a lot of people are going to the extended strake. Has anyone thought of going the other way? What I'm thinking is taking the leading edge of the wing straight to the fuse. I realize that fuel storage would be drastically reduced. I keep hearing that the strake isn't a lifting surface, so, shortening (along the fuse) it shouldn't cause too much issue and it would lighten the total weight of the aircraft. Does the strake/fuse area of attachment really need to be that much to absorb the twisting in the wing, or is all the stress being absorbed in the spar?

 

What I'm thinking is this:

 

1. enough fuel for 3-4 hour flight.

2. fuel pods for those REALLY long trips.

3. Huge advantage in view as it can be taken back almost to the rear seat.

4. less air friction area.

[gontek]

That would be a pretty major change. The strake on the cozy is pretty big, and I don't believe it doesn't contribute to lift. Wing area probably and wing loading include the strake. If the strake is not considered part of the wing in the plan measurements, it would still contribute to wing lift and drag in the physical world. You might make a pretty big difference in interference drag, but you are changing the wing aerodynamics and wing root farings pretty substantially. If engineered carefully I think you might be able to reduce some interference and skin friction drag and add a couple of mph. On the negative, consider stall characeristics as well. Some of that wing area and drag there may contribute to the docile low speed stall characteristics, and you don't want to lose those qualities of a canard aircraft.

[Hans S]

By the time I'm done with building and mods, I won't be registering it as one anyway. It's an experimental. The Cozy plans are just a base. Just as the Long was a base for the Cozy.

 

I'll have to go back and look at the strake extension posts, but I could swear people say that extending the strake is fine as it isn't part of the lifting surface.

[Marc Zeitlin]

I've been wondering something. It seems a lot of people are going to the extended strake. Has anyone thought of going the other way?

The SQ2000's strakes seem a bit smaller than the standard COZY MKIV strakes. Not a huge difference.

What I'm thinking is taking the leading edge of the wing straight to the fuse. I realize that fuel storage would be drastically reduced.

That's a LOT smaller - you'd probably lose 1/2 of your fuel capacity. Remembering that you need VFR/IFR reserves, you'd probably lose 2/3 of your usable trip fuel.

I keep hearing that the strake isn't a lifting surface, so, shortening (along the fuse) it shouldn't cause too much issue...

You're making the assumption that you can make aerodynamic modifications to an airplane based on what you "keep hearing". The strakes most definitely contribute to the lift generation of the aircraft, especially at high AOA's (low speed) - at cruise, they might not be generating much lift, but when slow, they most certainly do. Reducing the lifting surface area substantially is not a path I would contemplate traveling.

and it would lighten the total weight of the aircraft.

Yeah, by about 5-10 lb. Reducing fiberglass usage in lightly loaded sections of the airplane is not an optimum weight reduction scheme.

Does the strake/fuse area of attachment really need to be that much to absorb the twisting in the wing, or is all the stress being absorbed in the spar?

The strake provides most of the twist resistance to moments from the wing - the spar is very small in comparison. While your proposed strake would have more than enough structural stiffness, I don't like it for all the other previously mentioned reasons.

What I'm thinking is this:

 

1. enough fuel for 3-4 hour flight.

2. fuel pods for those REALLY long trips.

3. Huge advantage in view as it can be taken back almost to the rear seat.

4. less air friction area.

1) Won't get that with 2/3 usable fuel reduction

2) PITA

3) No advantage from the front seat - larger advantage from the rear, but the rear seats are rarely occupied, and the view can be enhanced by lowering the rear windows a couple of inches and adding baggage compartment windows in the bottoms of the strakes.

4) Maybe a knot or two, max.

 

Bad idea, IMO.

[Hans S]

O.k. a quick look talks about the CG strake mod and the second to the last line says that Marc thinks the aerodynamics would be negligable:

 

http://www.canardzone.com/forum/showthread.php?t=1297

 

By no means am I saying what they did and what I'm thinking are the same. I'm just wondering how far back you can go with the strake before it becomes a aerodynamic SNAFU.

 

EDIT:

 

Marc sent his post before I posted this. Sorry.

[Marc Zeitlin]

O.k. a quick look talks about the CG strake mod and the second to the last line says that Marc thinks the aerodynamics would be negligable...

Yeah, that's because the surface area of the strake extension is very small, it's right next to the fuselage, and it looks just like the Long-EZ strakes, which is where the idea came from, and the LE obviously works, on a very similar aircraft.

 

What you're proposing is a substantial aerodynamic change, not a minimal one.

[gontek]

Alsio consider you will be changing the aerodynamic center of your wing, aft. CG is also moving aft. That's a lot to consider, you may have to move the wing forward along the fuselage slightly. I agree with Marc in that low speed stall behavior would be of concern, that would be my primary concern.

 

However, I say go for it. Make a bunch of changes, and make it better that it was before. Just be careful and study the changes thoroughly. I bet your proposed change could add 5 to 15 knots max if done right, at the cost of 10-25 knots on the bottom end of the speed envelope. Add Flaps too! Fowler flaps would be cool. or Flaperons and leading edge control surfaces. IBIS has flaps, and the wing planform is more rectangular, without the large strake.

[Hans S]

Well, as I said, I was just wondering if anybody had.

 

Flaps and other mechanical means to make up for the removal of some strake wasn't what I had in mind. More to the question of how far the envelope could go either way.

[Hans S]

The IBIS is the look I was talking about. Thanks, I couldn't remember where to find a pic of what I meant.

[Spodman]

Well, this thing flew with negligible strakes, probably for the same reasons you suggest:

 

 

For the Cozy, I understand the fuel sits at F.S. 103, which is already behind the aft c.g. limit. I expect the strakes only exist as they do as a means of placing this variable near the c of g. Cropping the tanks as you suggest would move the arm of the fuel several more inches behind the aft c.g. limit. I reckon it is a bad idea.

 

I tried to figure out how much volume you would lose but lost interest I'm afraid...