Fast Cozy

[LargePrime]

In reviewing the cafe reports for the Lancair and the Cozy Mk IV it seems the lancair is a more efficient aircraft as it has a higher CAFE score. It is faster and more fuel efficent at the same time.

 

This suprised me greatly. One of the great attractions of the cozy is that it is one of the most efficient aircraft a home builder can build.

 

The only advantage I see the lancair has is Retractable Gear (RG) and a Constant Speed Prop (CS). As a tail dragger it should have a dissadvantage to a canard in general.

 

Thank you for your assistance in getting my head around these ideas.

[N65TX]

<<It is faster and more fuel efficent at the same time.>>

That's no surprise, speed is the numerator of efficiency.

 

1. The L320 can use flaps to reduce landing speed, the Cozy designer has to increase wing area

 

2. Two fixed gear legs

 

3. Shorter fuselage, more of a blunt tail

 

4. Fixed pitch prop

 

5. More interference drag from intersections

 

6. Less cooling drag?

 

<<As a tail dragger it should have a dissadvantage to a canard in general.>>

?? Don't know why this would be true, but even if it was, the L320 is a trike.

[LargePrime]

I ment it drags it's tail thru the air, as opposed to putting a flying wing out front, which is about 5% more efficient.

 

Sorry!

I see the Lancair has 76^2' of wing as opposed to the Cozy's 101.4

[No4]

It's an interesting conundrum comparing apples and oranges.

 

If you are comparing airframes, you have to use identical gear, prop, and engine. Comparing one plane with fixed gear, fixed prop, and a carburretor at one weight to another with retracts, constant speed prop, turbo and injection at another weight is misleading.

 

The CAFE Lancair 320 has 170hp, retracts, and a csu, is only a two seater and weighs less than a Cozy.

 

 

 

If you compare the Piper Cherokee series,

Archer 180hp, fixed prop, fixed gear 125 mph

Arrow 200hp, constant speed, retracts, 155mph

Turbo Arrow 200hp, constant speed, retracts, 200mph

All speeds TAS.

All could be called Cherokee 360's.

 

 

So, to compare Airframes, I still believe that with similar engine, undercarriage, prop, and weight, the Cozy airframe comes very close to the others, also being a four seater when most of the others are two.

 

Canards should be more efficient because canard lift is required to maintian straight and level, whilst a plane with a tail may require some downforce on the elevator surface.

 

 

[LargePrime]

If we make everything the same they will be the same. I am asking this question because I see an unexpected result.

 

I see a weight difference of 8#'s Cozy is lighter.

Both fuel injected and normaly asperiated with very simular HP (within 10HP).

 

I see the Cozy with 25 sq.ft. more wing.

 

The only real differance I see is RG and CS prop.

 

Other than that I see no reason for such a large speed and fuel efficency differance.

I see... at 8.5 GPH

cozy vs Lancair

23 vs 27 MPG

195 VS 222 MPH

So thats 12% faster on 20% less fuel at the same fuel flow for nearly equal weight.

 

Assuming Mark Beduhn's cozy and Fred Baron's Lancair are typical of the breeds. (Anyone confirm or deny?) And Assuming the airframs are approximatly equilivant (I would think the canard had an advantage, but I don't know how expensive 25 sq. ft. or wing is. Anyone confirm or deny?)

 

So I ask. Is the CS and RG that large a factor? Or did I miss something?

 

No4. In your example above what was most important to the speed increase? RG or CS. Can we do a percent split of these three?

 

P.S.

"Comparing apples to oranges" and it's abuse is a pet peeve of mine. We compare different things to better understand how they are different and the important factors in the differance and a choice between tham. Apples and oranges are diffucult to because taste is a big part of the valuation. I have no understanding of how to quantify taste.

I do understand how to quantify aircraft. I am just not very good at it yet. So does CAFE. And they are.

[No4]

oranges and tangerines?

 

Are a csu and retracts worth 27 mph?

I would think they could be,

Wouldn't that bring the MPG figures to the same number?

 

As to the split, very tricky.

 

The csu prop is constantly varying it's pitch to account for its rpm, the torque supplied, the TAS, the IAS, and the atmospheric conditions. A fixed prop can be tuned to the same efficiency, but only at one set of the above.

The variable pitch will be heavier. But it guarantees better climb performance and over a range of speeds, altitudes, and temperatures, it will be superior. An engine attached to a csu maintains optimum rpm and manifold pressure. An engine attached to a fixed pitch prop sees it's rpm and manifold pressure all over the place, very often at a non ideal setting.

My guess for a Cozy IO-360, plus 15 mph at 8000 feet.

 

The gear in the Arrow is a heavy contraption, but you can just "feel" the reduction in drag. As the gear comes up, you get noticeable acceleration. If you set the prop to full coarse (least drag) it glides fantasticaly. I understand that at higher IAS the parasite drag outways the induced drag, so top end drag should be greatly reduced.

My guess for a Cozy IO-360, plus 15 mph at 8000 feet.

 

Just my rough guesses, ready to don flack jacket and goggles

but I'm willing to back plus 30 mph, if not more.

[LargePrime]

I dont think you understand how this works. I ask the questions and you give the answers.

 

restating what you said..

 

Are a csu and retracts worth 27 mph and 5 MPG?

 

Given my above assumptions it would seem so.

 

If so very approximatly...

what would just a CSU give?

and what part would just RG give?

 

OK. STOP EDITING YOUR POST.

If it wasn't tricky it wouldn't be worth talking about.

So 30 MPH and 5+MPG Right? Lets get it straight before we get nuked off this board for this blasphemy,

[No4]

OK, no more editing!

Yes I concur plus 30 mph, with appropriate reduction in mpg.

 

I would add that a simple turbocharger (and oxygen mask) is far superior to all of the above!

[Marc Zeitlin]

There's an awful lot of guessing in the responses to your questions. I'll try to interject some data.

 

Originally posted by LargePrime

I see the Cozy with 25 sq.ft. more wing.

And this is a big difference. Going by your numbers, the COZY MKIV has 33% more wing than the Lancair 320/360 (Don't just call it a Lancair - there are many models of Lancair). That's a HUGE difference - there will be 33% more wing profile drag, and depending upon the drag polars of the respective airfoils, the fact that the Lancair will be flying at a higher Lift Coefficient (at the same speed) means that it might even have less induced drag.

 

The only real differance I see is RG and CS prop.

Hardly the ONLY difference, as shown above.

 

Other than that I see no reason for such a large speed and fuel efficency differance.

Drag reduction is by far the most effective thing one can do to an aircraft to make it fly faster.

 

The retract will add somewhere around 10 - 15 mph to these aircraft - that's approximately what people see when they add them to L.E.'s/COZY's. The drag wing difference (reduction) is discussed above.

 

The CS prop will have very little effect on top speed - most COZY/L.E.'s have cruise props, meaning that their propeller is optimized for the cruise regime, not the climb regime. Since Mark Beduhn's COZY MKIV performance is similar to mine, I'll assume he's got a cruise prop as well. Given this, I wouldn't expect to see any difference in top speed due to the CS prop (and COZY's with CS props don't seem to be any faster than those with fixed props). They have better climb rates, especially at high weights and altitudes, but not better top speeds.

 

So I ask. Is the CS and RG that large a factor? Or did I miss something?

See the explanations above. If the #'s for wing area are correct, then it's certainly a drag thing.

[cncdoc]

I was looking at numbers in percentages claimed by Infinty aerospace's RG setup for canard aircraft: 12+ %. That's about 24 mph at 200 mph (give or take an mph or 2)

CS props do dig pretty good. The Commanche 250 I fly has a preference of about 7500 ft where fuel/prop/AoA are peak and gph is about 14 when it is lean and mean 22 square. I can watch the fuel consumption guage and tell whether I'm starting to climb or descend even slightly. If I touch the prop after I have peaked it, it makes a big difference.

I climb out (with power somewhat reduced to keep it cool) with prop advanced and mixture rich and it indicates about 22 gph. The biggest effect on cruise economy is prop control.

By the book it's 14 gph at about 8000 ft at 180 mph and I have never been able to sqeak it any better at level cruise.

So, with CS prop AND RG I would say you could do just as good if not better with the Cozy vs the Lancair in a "fair" contest..

So maybe the Lancair was going downhill?

working in Ohio so I can build in FL

 

Kevin

 

By the time I got done writing my reply, a new one was already up my Marc. I was focusing more on economy than top speed.

[No4]

Fair point about the props Marc,

On the other hand, if top speed is a function of blade angle/length/and rpm; then by putting retracts on a cozy, but not changing the prop, you might not actualy increase top speed at all. However as I previously stated, it is possible to tune a fixed prop just right.

 

Perhaps it would be more correct to compare a Cozy with CSU and fixed gear and a Cozy CSU and retracts. Either way 30 mph sounds fair. As the question also refers to fuel economy, and engine performance, the csu must play an important part.

 

Either way I still stand by my prediction of equal performance to the Lancair (which one is it again?).

[Marc Zeitlin]

Originally posted by No4

Fair point about the props Marc,

On the other hand, if top speed is a function of blade angle/length/and rpm; then by putting retracts on a cozy, but not changing the prop, you might not actualy increase top speed at all.

It will increase some, but not completely optimally. Merely adding wheel pants to my plane increased my top speed by almost 12 mph, with no prop change. If you tell the prop maker that you're installing retracts, he'll design the prop for a slightly higher speed. If not, just be willing to run the engine at 2800 - 2900 RPM. Many do.

 

Originally posted by No4

Perhaps it would be more correct to say Cozy with CSU and fixed gear compared to Cozy CSU and retracts.

Don't know what you mean here.

 

Originally posted by No4

Either way I still stand by my prediction of equal performance to the Lancair.

Not gonna happen - not without smaller wings on the COZY MKIV (or larger ones on the Lancair 320/360).

[No4]

So wheel pants make 12 mph difference, but removing them altogether from the airflow couldn't make 27 mph difference.

Interesting logic.

 

I've sat in a Lyco plane with the pic explaining to me that 75% power at 8000 feet was 2900 rpm. I just sat there fingers crossed waiting for the bang clunk clunk noises.

Much rather have a csu.

[Marc Zeitlin]

Originally posted by No4

So wheel pants make 12 mph difference, but removing them altogether from the airflow couldn't make 27 mph difference.

 

That's correct. You get about the same difference by removing the gear legs and streamlined wheels from the airstream as you do by streamlining the wheels - maybe a bit more.

 

Originally posted by No4

Interesting logic.

 

There's hypotheses and there's facts. You've got one, I've got the other. Adding retracts to Bill Theeringer's L.E. added about 15 mph over what his plane would do with fixed gear and wheel pants. A COZY's difference would be about the same - the gear is substantially similar. If you don't understand aerodynamics, at least pay attention to what the facts show. If I removed my existing fixed gear with wheel pants (per plans, and the only way to get NEAR 220 mph TAS) and added retracts instead, I'd expect another 15 mph or so.

 

Not only that, but judiciously designed and mounted wheel pants and gear leg fairings (such as those on Klaus Savier's V.E.) will get you another 5-7 mph (or more - Klaus isn't talking, but others that have installed gear leg fairings carefully note changes in that range).

 

Once you have completely optimized the gear (smaller wheels, smaller pants, gear leg fairings, all AOA optimized), you'll have a 5 - 10 mph difference between this setup and retracts. Not per plans, exactly, but a lot closer and cheaper than retracts.

 

My original point was that the wing area business was at least as large a factor as the RG, and that the CS prop is not a factor in top speed on most canards, due to the fact that most have cruise props, not climb props.

 

Originally posted by No4

I've sat in a Lyco plane with the pic explaining to me that 75% power at 8000 feet was 2900 rpm. I just sat there fingers crossed waiting for the bang clunk clunk noises.

Much rather have a csu.

 

To each his own. As I said, a different cruise prop would bring it back down to 2700 RPM. The prop should be matched to the airframe, and a major change in drag characteristics would require a change in prop, too.

[Marc Zeitlin]

Rather than edit my previous reply, I'll add to it. I have gone back and reviewed historical postings regarding retracts, both on Bill's L.E. and other people's calculations (There does not seem to be any published info on the few COZY's flying with retractable gear).

 

My previous recollections were incorrect - I'll now state that it's probable that a stock COZY MKIV with wheel pants would gain about 20 mph by switching to retractable main gear.

 

I'll stand by the other statements regarding wing area, gear drag reduction and CS props.

[No4]

"If you don't understand aerodynamics, at least pay attention to what the facts show"

Not sure who you think you are and where you get off Marc.

 

It's not in a canard but my experience of retracts and csu is 25 knots true which is 29 mph improvement.

Infinity who make the gear claim 25 mph.

 

We were comparing the airframes, and trying to ascertain the improvements in performance from retracts and csu, to then compare the airframes.

Even you agree on 20 mph, which takes us, with reference to the CAFE report to 215 mph and 25 mpg.

Not a million miles from 222 mph and 27 mpg is it?

If per chance you might be wrong, and I, perish the thought, am correct, then we have 225 mph and 27 mpg. Bingo Largeprime.

 

Pretty similar performance in my book.

 

The cozy is 4.5 feet wider, or 18%

the l320 chord is 48" tapering to 29", the cozy 93 tapering to 21

wing area is 76sqft for the l320 and 101.4 sqft on the cozy, or +33%

the thickness ratios are similar

the loading is between 1 and 3 lbs more per sqft on the l320

The power to weight ratios are almost identical.

 

 

Quoting Marc "And this is a big difference. Going by your numbers, the COZY MKIV has 33% more wing than the Lancair 320/360 (Don't just call it a Lancair - there are many models of Lancair). That's a HUGE difference - there will be 33% more wing profile drag, and depending upon the drag polars of the respective airfoils, the fact that the Lancair will be flying at a higher Lift Coefficient (at the same speed) means that it might even have less induced drag."

 

l320 lift coefficient is 0.2, the cozy's is 0.5.

 

 

A 33% increase in wing area does not mean a 33% increase in profile drag. Profile drag is the wetted area presented to the airflow, nothing to do with surface area. 1 *10 and 10 *1 have the same area 1/10th frontal area. The Cozy is wider by 18%, yet it's wings end narrower and thinner, so you cannot guess the increase in Form drag, or the induced drag.

 

CSU vs Fixed Pitch for economy, performance, engine longevity; no contest.

 

Back to the 24 hr ration pack and ready for the artillery....

 

 

 

 

[Marc Zeitlin]

Originally posted by No4

Not sure who you think you are and where you get off Marc.

OK, look. I'm not looking for a fight here. You questioned me ("Interesting logic"), I questioned you back. Let's get off each other's backs and get back to the aerodynamics.

 

Originally posted by No4

A 33% increase in wing area does not mean a 33% increase in profile drag.

You're correct - it's late, and I was referring to the parasitic drag, which does in fact scale with exposed surface area, which is 33% larger on the COZY wings.

 

Originally posted by No4

l320 lift coefficient is 0.2, the cozy's is 0.5.

How do you figure that? Assuming the 320/360 is 10% faster, and the COZY 10% heavier, with 33% larger wings, the lancair will be cruising at a Cl that's 98% that of the COZY. You can play with those #'s a bit if you like, but you won't get a factor of 2.5 in the Cl difference.

 

Depending upon the location of each airfoil's drag bucket (or drag minimum, if there's no bucket), the 320/360 MAY actually have a slightly higher drag coefficient than the COZY. A possibility - that's all I said.

 

Originally posted by No4

Back to the 24 hr ration pack and ready for the artillery....

No artillery.

 

My original statement was that without making the wing(s) smaller, the COZY couldn't have the SPEED of the Lancair 360. The retract will certainly get you closer, the CS prop will do almost nothing, but the aerodynamics indicate that less surface area will be necessary to get the same speed. If that were not the case, every plane would have really big wings in order to get slow landing speeds, without giving up anything on the top end. (And if your claim regarding "frontal area" being the only thing that was important was correct, all planes would also have very low aspect ratios and very deep chords).

[Jim Sower]

I just got here. Been out and about all day. I think Marc couldn't be more right on this one. 33% more wing area is HUGE. How fast would a Vari-EZ be with CozyIV wings? Along with everything else, it's 33% more wetted area. BTW, did we only count _horizontal_ _main_ wing area, or do we throw the *two* winglets (which are *each* somewhat bigger than Lancair vertical stab)? Do we compare canard area with horizontal stab? Anyway, however we calculate and score all that area, one could argue that it's something of a triumph that we get as close as we do to the Lancairs on speed.

 

Haven't heard much about the intangibles (that means really REALLY hard to quantify) yet.

 

The Cozy gets BIG a plus on trim drag since we have both flying surfaces sharing lift responsibility. That's a big deal. Cozy main wing only has to produce lift in the amount of maybe 70% of aircraft weight. Lancair main wing has to lift all of the aircraft weight plus offset the negative lift produced by the horizontal stab to trim it - which might amount to as much as 115% of aircraft weight (Marc - is 15% close or should it be more like 10% or so?). So Lancair will have induced drag for maybe as much as 130% of AC weight (so we get back in trim drag the equivalent of some of that wing area we gave away from not having flaps).

 

I have to give the Lancair the aerodynamic advantage of clean air over the main wing. On the Cozy, the airflow over the main wing is dirtied up by the turbulent flow behind the canard so the strakes (not primary lifting surfaces I know) and part of the main wing lift are compromised by dirty air off the canard.

 

Lancair has an advantage in prop efficiency in that the whole prop disc is in clean air and prop masking by the engine is considerably less than Cozy. I don't believe CS props are optimized for cruise in that the "optimum" "twist rate" from root to tip will vary with pitch. What works best at cruise will be plumb crummy on TO so you give back some of the advantage of variable pitch by compromising between TO and cruise requirements.

 

A plus to Cozy for having the smoothest aerodynamic transition from the tip of the nose to the canopy. Lancair cowling OTOH is about as slick and tight as it can be. The slope from air inlet profile (rather more sleek than the cozy cowl outlet) from its initial profile to the firewall profile is all high pressure *attached* flow. Increased drag, obviously, but not nearly as much of it as Cozy gets when the air flow can't make the radical turns as its cowl tapers from the firewall to the outlet and flow detatches and goes turbulent thus aggrivating the dirty air entering the prop disc (examine the performance gains achieved by EZs in that realm - that Cozy can never replicate on account of the much wider firewall). Lancair also has that "pressure recovery" reverse taper in the aft fuselage that has to help and which Cozy has no prayer of replicating (listen to the claims by the EZ speed merchants attributed to applying that to just the spinner).

 

As fixed gear planes go, I recon EZ/Cozy are (or can be, with some extra work) about as low drag as you can get. As to retracts, I'm not certain, but I believe that Lancair, Velocity and SQ2000 all have "open" main wheel wells in that about 1/3 of the tire is visible with gear retracted. If this is the case (someone help me out here) I believe that the drag penalty is pretty significant - a whole lot more than what it looks like on first blush.

 

Anyway, there's lots of factors that are difficult to quantify. The most important of all, arguably, is each individual's opinion on which of these birds looks more snarky and will draw a bigger crowd on the ramp:)

 

My .02 .... Jim S.

[No4]

Lift co efficients are straight out of the CAFE reports. Which the thread was started to compare,as is the 222mph versus 195mph at 8.5 gph; weights were considered the same, horsepower the same.

 

The cozys drag co efficient must be higher than the L320, but it appears the lift/drag ratios are similar.

 

Parasite drag is not to do with the wings, it refers to pitot tubes, props, aerials, and undercarriage. Form drag or profile drag is that of the frontal area of the aircraft, and skin friction drag refers to the surface area. Induced drag being that created by lift.

 

The Cozy has more wing area, yet is shorter by nearly five feet. Skin friction drag may even be less, it depends on the total surface area.

 

I think Marc, if you re read your last paragraph you have summed up the dilemma for all aircraft designers, you want the wing as wide and narrow and thin as possible, yet at the same time as short, deep and as long as possible.

 

By the way, I didn't say that was all their was to aerofoil design.

 

Still standing by my assertion of very comparable performances at 8.5gph.

 

 

 

[LargePrime]

Marc

According to the CAFE reports noted above...

How do you figure that? Assuming the 320/360 is 10% faster,

14%

and the COZY 10% heavier

 

Cozy is 8# LIGHTER, not 120#s heavy

You can play with those #'s a bit if you like, but you won't get a factor of 2.5 in the Cl difference.

Before we all play, lets get the right numbers.

 

If you check your numbers first you wont have to retract them.

 

Jim, with all due respect...

Lancair has an advantage in prop efficiency in that the whole prop disc is in clean air and prop masking by the engine is considerably less than Cozy.

This is incorrect. A pusher is more efficient by about 5% over a tractor. Pusher wins because air entering prop disk is slower (Can add energy to the air easier) and the accelerated air does not add drag to the airframe.

 

I also understand that the canard wake can be used to add lift to the wing. I am way over my head on harnesing wake turbulance energy.

 

What I am trying to understand is how a canard pusher, which should be 10-20% MORE efficient, is 10-15% LESS.

It seems we have identifyed 3 key differences. CS prop vs fixed. RG vs Fixed. And 25 sq. ft. more wing.

[Jim Sower]

<... the fact that the Lancair will be flying at a higher Lift Coefficient (at the same speed) means that it might even have less induced drag." ...>

 

Not clear on how a higher Cl buys you a lower Cdi. Here I always thought higher Cdi was inevitable with increase in Cl.

 

<... l320 lift coefficient is 0.2, the cozy's is 0.5 ...>

 

Just how was that arrived at?

 

Anyway, I'm losing track of what the squabble is actually about. Reread the original post and the first couple of responses. Seems CAFE made a simple declarative statement to the effect that Lancair is faster/more efficient. Don't know how we can argue with that, CAFE's results being so well documented.

 

But nevertheless, we who can't quantify much of anything at all are now trying to parse all of the factors that go into the CAFE result, guessing at some, ignoring others and (predictably enough) getting hopelessly tangled up in our underwear. It would be nice if someone would explain exactly what any of this means in the cosmic scheme of things:)

 

If the Lancair is 14% faster, all we have to do is increase power by about 50% and we'll go just as fast. Of course fuel economy might suffer a tad.

[LargePrime]

What I am trying to understand is how a canard pusher, which should be 10-20% MORE efficient, is 10-15% LESS.

It seems we have identifyed 3 key differences. CS prop vs fixed. RG vs Fixed. And 25 sq. ft. more wing.

 

The "squabble" is how much each of these contribute, or if we missed other key differences.

 

And Jim. The Lancair320 is also 5 mpg more efficient. It's not just faster, it is more efficient. THAT BLOWS MY MIND! I want to understand that.

[Jim Sower]

<... A pusher is more efficient by about 5% over a tractor. Pusher wins because air entering prop disk is slower ...>

 

That would seem to be the case only to the extent that pusher in question is not travelling as fast as the tractor being compared. What, pray tell, causes the air to slow down going over the pusher airframe, and if it does, how do you keep it from bunching up between the nose and the prop? Where does the excess go? What about the efffect of much of the air entering the pusher prop disc is detached and turbulent?

 

<... I also understand that the canard wake can be used to add lift to the wing ...>

 

I doubt it, what with the elevators flopping around altering the downdraft from moment to moment and all. In any event, I've never heard of an occasion where it does. Have you?

 

<... What I am trying to understand is how a canard pusher, which should be 10-20% MORE efficient, is 10-15% LESS ...>

I would be inclined to revisit the premise. Where is that carved in stone? In some particular aspects it may very well be, but overall I suspect it probably is not.

 

<... It seems we have identifyed 3 key differences. CS prop vs fixed. RG vs Fixed. And 25 sq. ft. more wing ...>

Let's not presume that those are the only differences or even the only important ones. They are perhaps the most obvious at this juncture, but I outlined a number of others that have been largely ignored so far.

 

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

[No4]

"<... l320 lift coefficient is 0.2, the cozy's is 0.5 ...>

 

Just how was that arrived at? "

 

Page 11, both CAFE reports

 

 

"Anyway, I'm losing track of what the squabble is actually about"

Trying to compare airframes, discounting gear and csu, refering to CAFE reports.

 

So far we can say RG is worth 15 to 30 mph on the Cozy, bringing the

performance pretty close.

 

"But nevertheless, we who can't quantify much of anything at all are now trying to parse all of the factors that go into the CAFE result, guessing at some, ignoring others and (predictably enough) getting hopelessly tangled up in our underwear. It would be nice if someone would explain exactly what any of this means in the cosmic scheme of things"

 

Speak for yourself Jim, if you are not interested or have anything constructive to say then don't bother to post.Personaly I've found it a very interesting and educational experience to analyse these reports. I think we have done a pretty fair job so far, sorry if you are disappointed.

 

 

<... What I am trying to understand is how a canard pusher, which should be 10-20% MORE efficient, is 10-15% LESS ...>

I would be inclined to revisit the premise. Where is that carved in stone? In some particular aspects it may very well be, but overall I suspect it probably is not."

 

Using the CAFE figures at 8.5 gph

 

"If the Lancair is 14% faster, all we have to do is increase power by about 50% and we'll go just as fast. Of course fuel economy might suffer a tad."

 

Don't agree with that I'm afraid, as I think we have established.

 

I agree the prop at the front is more efficient , but on the cozy's side it has undisturbed flow over the canard, fuselage and wing.

 

Anybody found the matches? Sure is dark down here.

[Marc Zeitlin]

Originally posted by LargePrime

Before we all play, lets get the right numbers.

 

OK. 14% faster. Empty weight of that Lancair was 1187.5 lb. - empty weight of THAT COZY MKIV was 1179.3 lb. There's your 8 lb. However, no one flies at empty weight, by definition. Gross weight of the Lancair was 1685 lb, while the gross weight of the COZY is almost 400 lb more, at 2050 lb. What weight would you like to use? Pick anything between 200 lb. over empty up to gross.

 

Originally posted by LargePrime

If you check your numbers first you wont have to retract them.

 

There's nothing to retract that had anything to do with the CAFE reports - the issue was my faulty recollections of discussions held 7 years ago. I've admitted my mistake and corrected it.

 

Also, as indicated below, the small differences in speed and weight discussed above will have very small effects on the flight Cl of each plane - there will be a few percentage points difference.

 

Originally posted by LargePrime

A pusher is more efficient by about 5% over a tractor. Pusher wins because air entering prop disk is slower (Can add energy to the air easier) and the accelerated air does not add drag to the airframe.

 

While it may be true that the accelerated air doesn't add drag in pusher, the air entering the prop disk is actually faster, due to acceleration around the fuselage (as Jim stated). Also, the air entering the prop is more turbulent, due to the interference from the fuselage and fuselage/wing junction, so the efficiency difference here may be extremely difficult to tell. Call it a wash.

 

Originally posted by LargePrime

What I am trying to understand is how a canard pusher, which should be 10-20% MORE efficient, is 10-15% LESS.

I've seen the claim of canard efficiency advantage a lot (not just here). While in theory this may be true, it required that all else be held constant, and by definition, when comparing canard pushers with conventional tractors, all else is not constant, and teasing out the many confounding factors is extremely difficult. In practice, canard and conventional configurations are about the same. Interestingly enough, David Lednicer, a well known aerodynamicist, recently stated on rec.aviation.homebuilt that for RANGE, a conventional aircraft will always beat a canard.

 

Originally posted by LargePrime

It seems we have identifyed 3 key differences. CS prop vs fixed.

2 Key differences, with respect to top speed. CS will help on climb rate, ground roll, and descent rate, but not on the top end, for the reasons stated previously.

 

Originally posted by LargePrime

 

RG vs Fixed. And 25 sq. ft. more wing.

 

And here's the difference - more drag on the COZY MKIV.

 

 

Originally posted by No4

Lift co efficients are straight out of the CAFE reports.

 

Yes, and they refer to the "design" Cl (whatever that means). Which airfoil are they referring to on the COZY, the canard or the main wing? Since no-one I know in the canard community has ever seen a drag polar for the modified Eppler, and no-one has been able to drag one out of John Roncz for the 1145, I don't know where that 0.5 came from.

 

At any rate, the fact that someone claims that the airfoil was designed to operate at a certain Cl says nothing about what Cl it IS operating at at any given airspeed - that's a function of weight and wing area (and air density). For identical airspeeds and weights, the smaller wing on the 320/360 means that it will be operating at a higher Cl.

 

Even at higher speeds (14% if you like) and the same weight (8#, wherever that came from is not worth calculating), the lift coefficients are essentially identical. Let's assume both planes cruise at the speeds indicated in the CAFE report, and that both are at the Lancair's gross weight of 1685 lb (to pick something equivalent). The Lancair's cruise Cl will be 0.052, while the COZY's cruise Cl will be 0.05.