Fast Cozy

[No4]

I agree pretty much entirely with that Marc,

The Cozy is a larger aircraft, 18% wider and with 33% more wing area, which at 300 lbs off max weight, is slightly out performed by a smaller aircraft at max weight, at speeds above 180 mph.

(If we agree that RG is worth 20mph, and the csu helps fuel efficiency).

 

 

 

 

So the Cozy's Lift to Drag ratio must be worse at around 200 IAS. Meaning a higher coefficient of drag.

 

However, the best rate of climb speed for the cozy is 20 mph less than the L320; The minimum sink rate is 20 fpm less for the Cozy, and their glide ratios are 1.5 in the favour of the L320, yet they coarsend the prop, whilst setting the Cozy to idle. I'm willing to go out on a limb and say with identical prop, same same numbers.

Furthermore the Cozy achieved almost the same climb performance with a fixed pitch prop as did the Lancair with a CSU.

The Cozy vne is 50 mph below the Lancair.

At 100 mph, the L320 uses as much fuel as the Cozy with fixed gear and a prop out of its speed range.

 

Looking at the chart again, I see the best MPG for the Cozy is 28.6(155 CAS), and the best for the Lancair is 30 MPG (190 CAS).

 

This for me explains the design lift coefficients, which of course do not remain constant with AofA and CAS. I'm not sure how you calculate your lift coefficients, Marc, but I get 0.2 (L320) and 0.18(Cozy) at 200mph and 8000 feet.

Using the design coefficients, I get 130 CAS best speed for the Cozy(Va is 138 CAS) and 180 CAS for the Lancair (Va is 165 CAS).

 

So, one larger aircraft designed for operation between 150 and 200 mph is better( more efficient) at doing that, and the other, smaller, designed for slightly higher speeds is better ( more efficient) at doing that.

 

 

I'm off to NAAFI for a cup of tea

[Wayne Hicks]

Want to try a $$$ for $$$ comparison?

Most Lancair 360s (and now the Legacy) CANNOT be built for under $90K.

 

As for speed, once they turn around and go pick up the other two people left behind, the COZY is MUCHO faster! :-)

 

...Wayne Hicks

[unick3]

I had to chuckle a bit about all the bandwidth given to a few mph.

 

Lets put things in perspective... On a trip to Atlanta (225 nm for me) for example at 190 mph it would take 1:11 hrs. At 220 it would take 1:01 hrs or a difference in 10 min. You could be vectored around by ATC for more time than that just trying to land.

 

Not much savings to justify the cost difference for a Lancair from a Cozy IMHO. Is it really worth spending an extra $5k for retracts to save 10 min on an average trip with the possibility of doing a gear up landing (think $10k rebuild at a minimum) and the loss of flying time in your bird? A friend did a gear up in his Berkut. Cost well over $10k (engine) 2 new wings, new prop, and 8 months.

 

I have had 2 gears ups in my plane for a total repair cost of $0 (just paint, time and left overs from the shop). A week repair time for the first event and lowering the nosegear and taking back off for the second event...

 

Personally I think retracts are way over rated in our planes. A good set of wheel pants and gear fairings will get you a very fast plane at a very reasonable cost.

[shender1]

Wayne,

 

I was thinking the same thing!

[shender1]

I could see having this discussion for the sake of arguing but as far as efficiency goes I think that comparing the cozy to the lance air IS comparing apples and oranges.

 

My goal is to fly faster than I do now. I can throw $50k at the problem or $90k at the problem...seems to me that the cozy is more efficient.

[marbleturtle]

Yes the retracts add significant speed, yes a CS prop adds cruise speed (even a cruise fixed is still somewhat compromised to reduce cavitation on take-off), but I think everyone is missing a big difference between the two aircraft.

 

Take a close detailed look at the Lancair fuselage nose to tail... then look closely at the Cozy fuselage. Then visualize what is happening to the air around them at speed.

 

The Lancairs are made in huge molds that can be designed for perfect streamlining. Now I'm not knocking the Cozy, but the tub is a bit squarish. Creating the perfect aerodynamic shape without molds would be a killer for us to build... so it's something of a compromise (I'll trade 10kts for 2000 extra build hours or $50k in prefab structure prices any day).

 

All things being equal, the Canard design with twin lifting surfaces are more efficient than one lifting surface and one drag generating surface.

 

But things here are not exaclty "all things being equal".

[LargePrime]

BLAH BLAH BLAH!

 

Read the thread before you post!

 

I dont care about the speed! I want to know how a less efficient aircraft is more EFFICIENT!

It's not that the Lancair is 32 mph faster, it is that it is 32mph faster AND 5MPG MORE EFFICIENT AT THE SAME TIME!

 

If a cozy did 150 and had 5 MPG better I would say fair trade. The cozy is SLOWER and TAKES MORE FUEL.

 

I dont want to know if the Cozy is still good!

I dont want to know about the value of the aircraft!

I dont want to "FEEL BETTER" about the cozy design!

 

I WANT to UNDERSTAND how a cozy is less EFFICIENT than a LANCAIR 320.

 

If you can help, great! If you can't, why are you posting here?

[No4]

Right on Largeprime,

Not an argument as to the $$$$ of modifications, we were comparing airframe aerodynamics.

Why bother to rubbish the thread if you don't care? Some of us have been working pretty hard on this one.

 

From my workings

0 - 150CAS Cozy is more efficient

150 - 180CAS becoming neck and neck

180CAS - Lancair pulls ahead

[shender1]

Why the sarcasm?

 

No one is trying to "rubbish the thread" and every one here is entitled to an opinion.

 

I DID read the post.

 

I happened to think that Marc's description of the comparison of apples to oranges is correct.

 

Have a good day!

[Marc Zeitlin]

Originally posted by LargePrime

I WANT to UNDERSTAND how a cozy is less EFFICIENT than a LANCAIR 320.

 

It seems as though this question has been answered, and the answer is drag. There seems to be general agreement that the RG makes a difference (although the relative magnitude is not agreed upon), and _I_ believe that the wing area makes a difference as well, while the CS prop does not (in cruise). Others believe some or none of the above. You can choose to believe what you like, but there have been no _other_ major factors proposed (well, maybe double the vertical fin area).

 

What is it about the question that's still up in the air (so to speak) for you? It's not like there's some other magical parameter that we've all forgotten about..... is there?

 

Originally posted by LargePrime

If you can help, great! If you can't, why are you posting here?

 

I can understand your desire to have your questions answered, but really, no one controls the content of a discussion as it develops. People post what they believe will either help or be interesting.

[marbleturtle]

Speed at a given weight and HP _IS_ a form of efficiency. Fuel economy is another. The theory involved in comparing two different designs is complex and cannot be simplified below "BLAH BLAH BLAH" levels. Maybe this is just beyond your grasp...

[No4]

Easy Gents!

Cheers Shender, no offense meant.

 

No Marble I think we have about got it.

You are right that the Lanc is more slippery, and smaller.

I agree the naked eye is a very good judge of aerodynamics.

 

I've looked at lift coefficients for ages, and never really understood what they realy meant until last night, using an actual example. I went through an aero book I have that explains it very well.

In the back of it is a long section of aerofoil data.

 

At every angle of attack an aerofoil has a coefficient of lift, and one of drag, and thus a lift to drag ratio.

 

At the optimum AofA (usualy 4') the lift/drag ratio is furthest apart.(Best rate of Climb speed)

At a higher AofA there is more lift, and more drag (think of a Cessna 172 full power, nose up 40 mph)

At a lower or even negative AofA the lift reduces until it becomes less than the drag.(approaching VNE)

 

Think of the difference between a Spitfire wing and a Piper Cup's wing, different aerofoils, different airspeeds. Of an equal span the Cub would lift more weight, but would stop working before the Spitfires has even got started.

 

The Lancair has lower lift and drag coefficients, which means it needs a higher CAS to achieve the same angle of attack. The cozy is designed for slower operation, has more lift, more drag and reaches its optimum AofA at around 120 CAS, at this speed the Lancair will have a higher angle of attack, and a poor lift/drag ratio.

As we reach 200 mph the Cozy's AofA is reducing to 0', and it's lift to drag ratio is decreasing, whilst the Lancair is still at maybe 2' and it's lift to drag ratio is at it's optimum.

 

Thus an aerofoil designed for higher speeds will have poor slow speed performance, and an aerofoil designed for low speeds will require an enormous amount of power to increase speeds at 0' AofA.

 

The Lancair has a faster wing, and thus is more efficient at high CAS.

 

The design coefficients are 0.2 for the Lanc, and 0.5 for the Cozy, which agrees with my theory.

 

Marc, I worked out the Cl for both types and got 0.2 and 0.18, whereas you got 0.05. Could you run me through how you calculated that?

 

 

 

[Marc Zeitlin]

Originally posted by No4

At the optimum AofA (usualy 4') the lift/drag ratio is furthest apart. (Best rate of Climb speed)...

 

Actually, there is no "optimum AOA" - it all depends on what you're trying to do. The max L/D for the plane (not just the airfoil) will give you the best GLIDE distance - NOT the best rate of climb speed. They're close, but the best glide is not dependent on the engine, whereas best ROC will occur at the point of maximum excess POWER, and is NOT necessarily at the best aircraft L/D. Best angle of climb (Vx)will occur at the point of maximum excess THRUST, and is slower than (Vy).

 

Originally posted by No4

At a higher AofA there is more lift, and more drag (think of a Cessna 172 full power, nose up 40 mph)

At a lower or even negative AofA the lift reduces until it becomes less than the drag.(approaching VNE)

 

You mean lift COEFFICIENT and drag COEFFICIENT, not LIFT and DRAG here. In level, constant flight, the lift is always equal to the weight, and the drag is equal to the thrust (approximately).

 

Originally posted by No4

Marc, I worked out the Cl for both types and got 0.2 and 0.18, whereas you got 0.05. Could you run me through how you calculated that?

 

I assumed SL conditions. With:

 

Cl = Lift/(Area* Dynamic_Pressure)

DP = 0.5 Rho*V^2

 

So, if:

 

Rho = 1 Kg/m^3 (SL density of air)

Lift = 1685 lb or 764 Kg

Area = 3 m^2 Lancair

Area = 4 m^2 COZY (approximately)

V = 222 mph (100 m/sec) Lancair

V= 195 mph (84 m/sec) COZY

 

Plug in the metric units, and get 0.051 for the Lancair, and 0.052 for the COZY lift coefficients. At 8000 ft, where Rho is lower, Cl will be higher for both. If the COZY flew at the same speed as the Lancair, it's Cl would be 0.036 - about 1/3 lower (not surprisingly, since it's the ratio of wing areas that will set the difference in Cl's).

[No4]

Marc,

You are correct regarding glide speed and rate of climb.

Incorrect of me to say more lift, yes higher lift coefficient, but definitely more drag at high and low AofA.

 

regarding Cl

My book converts the kilos to Newtons, which would pretty much put you one decimal point out by my reckoning.

 

I make the wing areas to be 7 and 9 m2.

 

Which brings us to around 0.2 .

[Jim Sower]

BLAH BLAH BLAH!

Read the thread before you post!

 

That might be a good idea, Large. Let's take it from the top:

 

On the very first response to your original post, SIX reasons for L320 being more efficient than Cozy were suggested:

 

1. The L320 has flaps, the Cozy has to increase wing area

2. Two fixed gear legs v. retractable main gear

3. Shorter fuselage, more of a blunt tail

4. Fixed pitch v. CS prop

5. More interference drag from intersections

6. Less cooling drag?

 

You agreed that #2 and #4 (actually, #4 is easily the least significant of the lot) were factors. You sort of acknowleged #1 (but denied it was particularly important) and ignored the rest.

 

Much of the subsequent pontifications around Cl, Cd, Cdi, etc - particularly inferences that L320 was operating at a Cl of 0.2, the Cozy at 0.5 and that somehow the incredibly higher Cozy Cl might result in less drag - produced rather more heat than light, but you seemed to love it.

 

You ignored repeated admonitions from several people that the difference in wing area was VERY significant.

 

When it was pointed out that the weight (focusing on empty weight, ignoring the 400# difference in GW) comparisons you were using were bogus, Marc was ignored.

 

Arguments around the fundamental aerodynamic efficiencies of the canard configuration as compared to the "conventional" L320 seemed a lot more theological than scientific.

 

Fuselage drag was brought up a number of times and articulated from several different angles. You ignored or trivialized those arguments. When someone sugested that you might want to examine and compare the lines and shape of the Cozy fuselage along side the L320 you dismissed his argument by inferring that the L320 "arrow" was not all that much better than the Cozy "brick" because the brick was shorter.

 

Gobs of detached, turbulent air sucking on the fat end of the Cozy was ignored. Substantially greater prop "masking" of the Cozy and the effect of turbulent air on prop efficiency was trivialized.

 

Differences in interference and cooling drag were ignored altogether. The notion that several hundred lbs greater weight might be important was ignored.

 

You kept coming back to CS prop and retractable gear (the one a trivial factor, the other quite important) and systematically ignored all the other factors.

 

"I dont want to "FEEL BETTER" about the cozy design!"

Actually, I got the impression, rightly or wrongly, that you were exactly interested in that. You seemed much less interested in "understanding why the Lancair was faster and more efficient than the Cozy" than in coming up with a way to subvert the CAFE results so that your pride and joy would once again reign supreme in the realm of speed and efficiency.

 

I'm sorry that N65TX and Marc and I and the others were not able to tell you what you wanted to hear. We did however, tell you in some considerable detail, articulated repeatedly in several different ways, what you asked to hear.

 

At the risk of repeating myself ...

A flawless line of reasoning, based on a false premise leads us right through the lookin' glass!!!

[Norm M]

A co-worker who has a PhD in aerodynamics (not that a degree means anything on these forums...) shared the following arguments/ counter arguments about canard vs traditional configuration efficiencies.

 

Conventional aircraft requires that the tail surface has an upwards force on it during flight, thus adding weight that the main wing must carry, and additional drag. However, it is a relatively light force, and a relatively efficient airfoil for the horizontal stabilizer.

 

Canard aircraft have both the canard and the main wing contributing lift, thus you are not creating aerodynamic forces which must also be lifted by the main wing. However, the canard airfoil is relatively inefficient, and relatively highly loaded. Thus, the induced drag is greater.

 

Seems to me that most airplanes tend to have a sweet spot for airspeed where they perform quite well. Save some horsepower, save some fuel, fly a little slower. Spend more horsepower, burn more fuel, fly a little faster. But if you want to go a great amount faster, it begins to take so much more horsepower that you get in trouble with engine weight and stuff like that.

 

Everybody wants a really fast plane so they can brag about it, but most people are just fine with throttling back, letting the plane be a bit more quiet, and improving the fuel efficiency.

 

I didn't build my plane to race or to win beauty contests. I built it to fly back and forth to Northern Minnesota from Central Iowa, and it does a great job at that!

 

Now, I need to go finish those wheel pants, install the prop spinner, and order that super duper cruise prop so I can brag to my flying buddies about how fast this plane is!

 

Regards-

Norm Muzzy

[marbleturtle]

Your right Norm... sorta.

 

Given two aircraft generating the same total lift at the same airspeed, the canard will produce more induced drag than a conventional tail. This is because the canard is responsible for generating some of the total lift of the aircraft and induced drag is a factor of lift. So, I can see how a canard wing will generate more drag than an elevator on a conventional tail.

 

 

But taken together as a whole the main wing of a canard is assisted by the lift of the canard, whereas the wing of a conventional aircraft must lift both the weight of the aircraft and the downforce of the tail.

 

He mentions the "relative inneficiency" of the canard. Isn't efficiency dependent on the design of the canard airfoil? Is there a high AOA for stall or something else inherent in the configuration that good design can't overcome? Just curious. Maybe you could prod the Phd for more details.

[Norm M]

Imagine what the canard would look like if it were scaled up to the same square footage of a main wing. Big, blunt, thick wing. Heck, amongst ourselves, we don't even know what it really looks like, what angle it should be mounted at, or how to get enough clearance for the elevators to move up and down!

 

The wings on really fast planes are quite thin. The canard is certainly not a thin airfoil. Thus, I suspect there is going to be more drag from it than if it were a more pleasing airfoil shape. And, on a canard plane, it is carrying a significant percentage of the airplane weight. (I am way outside my area of expertise, and need to quit posting...)

 

I don't need to justify why I built a Cozy instead of a Lancair. It is real simple. I could afford to build and fly a Cozy. My coworker who is building a bush plane doesn't need to justify his plane to me either. His mission requirements, personal style, and choice of materials is just different from what I wanted for the first plane that I built.

 

We need to make sure that we don't try to become elitist about our choice, or other people's choice of planes. Any plane that is safely built, completed, and flown is a true accomplishment. Doesn't matter if it is a Lancair, a Berkut, a RV Quickbuild, a Pietenpol, or an EZ. Playful ribbing may be part of the game. Especially when we are in public, we need to support homebuilt aircraft, and focus on how it can be the right way for general aviation to continue to move.

 

I would encourage anyone with the proper motivation to build a plane. Understand the mission profile, assess your capabilities, research, choose a design, and move forward.

 

Regards-

Norm Muzzy

[dust]

LOVE THE DESIGN and you may be part of the 20% that completes you project.

 

Enjoy the build

 

Mike

[Wayne Hicks]

There are 1.5 things that aren't really discussed in their proper light. Burt claimed several "advantages" to his pusher design. The one he freely admits to being wrong about is the efficiency of the pusher over the tractor. He was proven wrong and he'll freely admit that a tractor is more efficient than a pusher.

 

Burt also designed the Long EZ wings to include a significant drag bucket as the airspeed is increased. He did this in an attempt to keep you and me from adding horsepower to gain more airspeed.

 

Talk to the berkut guys and they will tell you that they redesigned the airfoils to reduce this drag bucket.

 

As for all this theory being bantored about? The proof is in the pudding. Just look at the speeds for this year's AirVenture Cup race. If you're building a Cozy to be faster than a Lancair, then buddy, you're building the WRONG airplane.

 

As I said before, (and a second to Nick Ugolini), if you want to save $50K and haul all the Lancair's camping gear in addition to yours, then the Cozy IS THE PLANE to build! So what if you arrive 5 minutes after they do? Just have them reserve your parking spot for you and point out where the restrooms are!

 

Wayne Hicks

[marbleturtle]

I for one am in love with the design... not just the sharp looks but the economics as well. I could fly first class the remaining years of my life for what most high speed aircraft cost. I can't justify the expense. When I go to the airport and see what people are spending to cruise at 120-160, or see one of those aircraft sitting back in a corner of a hanger, parts everywhere, waiting for the owner to finish the paperwork on his second mortgage before the mechanic finishes the MOH... I ride off on my motorcycle thinking I can't wait to hear the reaction when I finally get my $50k 220 mph glass arrow built and moved to my small town FOB/General Store/Gun Range.

 

That said, I think many of us are always interested in improvements, no matter how great the designe may be. A little competition is the mother-in-law of invention.

[Jim Sower]

Well put Wayne. I was looking at some of the numbers posted, evidently from the CAFE report. They indicate, as Marc pointed out, that despite virtually identical empty weights, the Cozy has about 870# payload while the L320 only about 500#. Deducting something upwards of 300# for modestly sized pilot and passenger, you have, respectively upwards of 500# and under 200# left for fuel and luggage, nav-bag, etc.

 

If a Cozy owner and his hangar mate flying an L320 decide to fly from Cleveland or somewhere to Sun-Fun, the Cozy will get there first because the Lancair will have to turn around somewhere in GA. The Cozy guy will arrive with his tent, cook stove, cooler full of steaks and luggage for the week. The L320 guy will be lucky if he can load a tooth brush and a change of skivvies.

 

My purpose in owning an airplane is cross country flying, and arriving at my destination is more important to me than getting a close up view of a lot of enroute air patches. Therefore, to me, range and payload are major factors in evaluating efficiency - how many legs to my destination and what do I have when I get there.

[Marc Zeitlin]

Originally posted by No4

regarding Cl

My book converts the kilos to Newtons, which would pretty much put you one decimal point out by my reckoning.

 

I make the wing areas to be 7 and 9 m2.

 

Which brings us to around 0.2.

Correct on all counts. Another late night brain fart in unit conversions while typing quickly.

 

However, the difference in Cl's is still minuscule - a few percent at most.

[CBarber]

Finally a couple of post I actually undestand. <g>. Since effecientcy was one of the topics in chief, the fact that just one additional fuel stop for the Lancair on a long XCountry would put the Cozy "ahead" seems to speak well for the Cozy as to total efficiency (I know, not total "flight" effecientcy)...plus the idea of steaks on board.....

 

I am not kidding, even for this non engineer layperson, this has been a very interesting thread. It still (at least to me, being uninitiated to the finer points) still seems to be an "apples to puppies" comparison. I would not expect a corvette to perform the same as a Jaguar XJ sedan (even though for a while, the Jag was the "fastest" sedan made...a short while). Both sweet cars, but I can put four, plus luggage, in my Jag in comfort, cruise at 80 mph in a very comfortable environment. Now the Corvette will get to 80 faster, but it is very difficult to get 4 folks inside....I tried in my Dad's '77 vett back in my high school days. If two of the passengers where not cute girls, we would not have even tried <g>.

 

Now, if I put a 238 hp Renesis on my Velocity FG, then I could.......oh, never mind.

 

All the best,

 

Chris

www.LoneStarVelocity.com

[LargePrime]

Glad you liked it.

 

Interesting that it seems the single largest performance improvment we can make is retractable gear.