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Tom

Real World Cruise Speeds

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I am interested in building a Cozy Mark IV but see a wide range of cruise speeds in the actual planes. they range from about 180mph to 220 mph.

I would appreciate any info about real world curise speed on 180HP and why the speeds differ so much.

Thanks, Tom

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I'm no expert but from the one ride i had with the plans built plane, lycoming 360 75% power, cruise ias 210@6000 feet and 1100 fpm climb from 3000 to 6000, tanks almost full, front seat weight about 216+160

 

Mike


maker wood dust and shavings - foam and fiberglass dust and one day a cozy will pop out, enjoying the build

 

i can be reached at

 

http://www.canardcommunity.com/

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I've seen references to a Vne of 190 kt, or about 220 mph. Anyone care to back me up on that?


Evan Kisbey

Cozy Mk IV plans # 1114

"There may not be any stupid questions, but I've seen LOTS of curious idiots..."

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With respect to cruise speeds, you'll see a lot of variation because sometimes people are referring to COZY III's and sometimes to MKIV's. Some people have wheel pants and some don't. Some have spinners and some don't. Some have the GU canard and some the Roncz canard. Some have climb props and some have cruise props.

 

I have a 180 HP MKIV with the roncz canard, Catto 3-blade prop and no wheel pants. I've seen TAS of 204 mph so far, and I'm told that wheel pants will add 10 - 12 mph to that.

 

With respect to Vne, the published Vne (as shown in all the literature and owner's manual, as well as the web pages) is 220 mph IAS.

 

Part of the confusion stems from Vne being measured in IAS, while cruise speeds are measured in TAS, so you see people cruising at 220 mph while the Vne is 220 mph, but they're in different measurement systems.

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what i've read is that retracts add 6mph @ 200 mph over well fared fixed gear. Also the speed increase from a properly powered airplane is the square root of the hp increase so:

 

220-180=40=6mph

retracts = 6 mph

 

Nat put a franklin (220 hp i believe) in his cozy and i don't think he saw an increase. He did say it was smoother being a 6

 

Mike


maker wood dust and shavings - foam and fiberglass dust and one day a cozy will pop out, enjoying the build

 

i can be reached at

 

http://www.canardcommunity.com/

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>speed increase from a properly powered airplane is the square root of the hp increase so:

Mike.

This doesnt make sense to me. Why would increasing the power in two jumps be more than in one?

 

Increase the power from 180 - 220 = 6mph.

Increase it from 220 to 260 = 6mph

Increase it from 180 - 260 = 9mph

 

Am I misunderstanding the "rule of thumb"?


I can be reached on the "other" forum http://canardaviationforum.dmt.net

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well, I would say the proper power is 180 not 220 so

the key is the right starting point, as the change from a 100hp cozy to a 200 hp cozy would be more than 10mph

 

260-180=80=9 mph


maker wood dust and shavings - foam and fiberglass dust and one day a cozy will pop out, enjoying the build

 

i can be reached at

 

http://www.canardcommunity.com/

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MT asks about retracts, spinners and 220 HP engines. I don't believe that there is anyone flying a COZY MKIV with THAT configuration, so any projections of speed will be just that - projections.

 

While there may be some questions as to whether wheel pants add 6 or 10 mph, the contention that speed is related to the square root of power is incorrect - actually it's related to the CUBE root. The drag force is related to the square of velocity, and power is force x velocity, so the power required is related to the cube of the speed.

 

This is modified by the fact that we're not only considering profile drag, but induced drag as well. Although in theory induced drag decreases as AOA decreases (speed increase), every airfoil has what's known as a drag bucket (you glider flyers will be familiar with this term) meaning that there's a small range of AOA's within which the drag coefficient of the wing is minimized. As the AOA changes in either direction, the drag can go up considerably.

 

What do these facts imply? Let's assume that a standard COZY MKIV with wheel pants, spinner, and 180 HP engine can top out at 220 mph TAS. If we just increase the power to 220 HP, and make the assumption (incorrectly, but it's all we've got) that the induced drag doesn't change much, that's a 22% power increase (1.22 times as much). Since speed is related to the cube of power, we should see a speed increase of 1.22^1/3 x 220 = 1.07 x 220 = 235 mph, or about 15 mph (7%, at these power and speed settings).

 

Nat didn't see this on his plane, but it's not at all clear that his installation was ever developing full power, or that he had the appropriate propeller for the Franklin. I wouldn't use his installation as an indication.

 

The gear retraction will reduce drag considerably, but since power is LINEARLY related to the profile drag coefficient, reducing drag and increasing power are both related to the cube of speed - a 22% reduction in drag will also give a 7% increase in speed.

 

Hope that clears things up somewhat.

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Okay. Now I have a headache. I need an ice pack.


Evan Kisbey

Cozy Mk IV plans # 1114

"There may not be any stupid questions, but I've seen LOTS of curious idiots..."

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You need to be crystal clear on the notion that all the pontificating around speed increase gained from retract is based on ... are you ready for this ... BULLSHIT!! Everyone is speculating and is heavily influenced by his own personal attitude and prejudices. The only part of the whole discussion that can be taken seriously at all is Marc's math. I am not aware of ANY Cozy (III or IV) **FLYING** with retractable gear. Nat and the true believers will get pretty shrill telling you that it costs you fuel and weight and gains you maybe 5 kts or less. There is a credible body of thught that it *gains* you fuel and (if the Velocity folks are to be believed - they have FG and retract models of otherwise identical airplanes) retractable gear buys you more than 5 kts increase. Typically more than 10. The best thought out, most rational discussion on the subject that I have heard is at:

 

http://www.geocities.com/plmjohnson/

 

The guy has his sh*t together. Much more than anyone else I have heard on the subject.

 

Nothing really dramatic is going to happen. Marc has the math right. Cube roots are NOT giant strides. But progress is progress.

 

Settle this issue and you'll be a hero and a pioneer :) ... Jim S.


...Destiny's Plaything...

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i was not being cozy specific, i was being general, over all airplanes. One thing is for sure, very few speed mods live up to thier advertised increase or computed increase value. I want speed big time and I know how i will get it, turbo or supercharging and intercooling and constant speed prop - HP at altitude is my personal solution wether it is in a diesel or 360

 

Mike


maker wood dust and shavings - foam and fiberglass dust and one day a cozy will pop out, enjoying the build

 

i can be reached at

 

http://www.canardcommunity.com/

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>I want speed

Me too. I'm not sure a constant speed prop will get you more top speed. I went with a wood prop optimized for top speed. I'll handle the take-off and climb issues with more power (Turbo 13B). The other thing you can do to maximize speed is, of course, to minimize drag.

I did the following:

 

Clean cowl lines (no cheeks - possible with 13B engine)

Cowl flap to release unneeded cooling air at speed

LSE spinner

minimal air scoops - I'm hoping to get away with the plans NACA and a fan for ground ops. I even made my NACA air scoops closable and sealed the nose when the gear is up. The only other thing I can think of to reduce drag would retractable gear or gear fairings.


I can be reached on the "other" forum http://canardaviationforum.dmt.net

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i've been told to get the use of the power at altitude, the prop will help allot. It's only and extra 7,000 or so


maker wood dust and shavings - foam and fiberglass dust and one day a cozy will pop out, enjoying the build

 

i can be reached at

 

http://www.canardcommunity.com/

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If the Vne is correct, then retracts, variable p prop, etc won't help if you have the power to push up to 220 indicated anyway. I do like the idea of a constant speed prop for extra slow down help but at only (?) $7000 I may just get by with an air-brake.


This ain't rocket surgery!

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>minimize drag

 

That was my planend solution as well. I don't plan on any major plans deviations at this time, I suspect I'll mostly limit myself cosmetic afterthoughts such as wheel pants and fairings.

 

A couple questions:

 

1.> Mr. Slade mentions cowl flaps. Can you elaborate? I have an idea what they are, but I haven't dealt with an aircraft that uses them as of yet.

 

2.> How much will the quality of the finish affect drag? Do diffrent finishes have an impact on drag? I was reading an article about something called "ambient" drag too. I'm intensely curious about this aspect.


Evan Kisbey

Cozy Mk IV plans # 1114

"There may not be any stupid questions, but I've seen LOTS of curious idiots..."

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<... I want speed big time ...>

Don't we all ...

<... I know how i will get it, turbo or supercharging ...>

Let's do the math as Marc recommends. Absent specifics to the contrary, I will assume that your turbocharging is intended to normalize power at altitude - that is, maintain 30" MAP up past 10,000' altitude.

 

There are Cozys that credibly make 180 kts at 8000' which is regarded as 75% power. Let's suppose that 100% power is 200 hp. 75% would be 150 hp. if we "normalize", we get back to 100%, which is 33% more than what we had (100% is a 33% increase over 75%). Normalization has therefore increased our power to 133% of what we needed to make 180 kts. 1.33^(1/3) = 1.1 airspeed ratio.

 

Our cruise airspeed at 30" MAP at 8000' (where our unboosted MAP was 22.5")has increased by 10% to 198 kts. A nice increase. Of course, you're at SL power, so you are experiencing SL fuel flow. If you have a CS prop, that's maybe $10,000 plus associated maintenance expenses - not a pretty sight if Velocity folks are to be believed. There's enough riding on this to warrant very careful study of what you're giving for what you're getting.

 

Just doin' the math .... Jim S.


...Destiny's Plaything...

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MT asks about Vne and top speeds:

 

You are forgetting that Vne is in IAS, and Cruise speeds are in TAS. There is no COZY around that has enough power to operate at IAS's of 220 mph (~192 kts) at altitude. See the performance graphs for the COZY at:

 

http://www.cozybuilders.org/performance/cruise.html

 

You can see that at 7000 ft., max IAS is 180 kts., and at 14,000 ft., max IAS is 162 IAS. This says nothing about TAS, which must be calculated, but you won't bust Vne except in a dive with a 180 HP (or even 200 HP) COZY.

 

Evan Kisbey asks about cowl flaps and surface finish:

 

Cowl flaps are doors which control how much air goes through the engine cowling. A large portion of the total aircraft profile drag is cooling drag caused by airflow through the engine compartment, and the airflow is sized so that at low airspeeds, there's still enough air to cool the engine in a climb. At high speeds, less cross sectional inflow is needed, since the mass flow of air is much higher. Cowl flaps are usually placed at the inlet to the cowl to limit the air intake at high speeds, and thereby reduce cooling drag.

 

Other than the canard, the surface finish is completely meaningless. That's the only laminar flow region of the whole plane. It'll look like crap, but you can have weave showing everywhere and you will have a hard time measuring the speed difference.

 

I've never heard of "ambient drag" - sounds like something from the Beach Boys "Pet Sounds" album.

 

Dust asks about TAS at 15K ft., using Jim Sower's calcs as a starting point:

 

As Jim points out, turbo-normalizing will get you back to 100% power (up to some altitude, depending upon your turbo and waste gate). If we check the web page indicated above, we can see that at 14K ft., the IAS is about 162 kts at 2800 RPM, but this will be about 60% power, due to the decreased air density.

 

If we want to get back up to 100% power, we'll either need a different prop (or a CS prop) to keep the RPM below 2700/2800, and we'll get about 18% more airspeed out of the 66% more power. This will get us an IAS of 191 kts at 14K ft., which is about 240 kts TAS or so.

 

Remember, this is at 100% power - you won't be doing this for long. This is also right about at the Vne (220 mph = 192 kts), and at altitude Vne will slightly decrease, so this would be a really bad idea unless you'd like to do extended Vne testing.

 

Hope this helps.

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Another issue that will have to be dealt with when you turbo [normalize] at altitude is cooling. As Marc pointed out, an NA engine produces maybe 62% power at 14000'. Your Cozy will reject about that much heat - 62% of SL capacity. Although you can boost to 100%, there is not enough mass air flow to properly cool the boosted engine. You will have to increase cooling capacity (read DRAG) in order to operate at boosted levels. This added drag penalty will eat significantly into the relatively modest gains in airspeed bought with those BIG power gains.

 

Klaus Savier OTOH has a Vari-EZ that makes 250 mph with an O-200 engine (which, of course, nobody knows how much power it is actually producing :). Check the heavy hitters and water walkers at RACE events and pay very close attention to what they do. They regard the reduction of airframe and cooling drag as the key to increased speed. They expend much more effort and time reducing drag than increasing power. There are some big, powerful engines at RACE events, but they are not as dominant as you might imagine. I was certainly surprised at the relatively modest increase in speed that is associated with upgrading from O-235 to O-320 (which, in relative terms, is what you propose to do with your turbo.

 

Modest return on investments in power are also caused by weight. The Cube Root relationship between power gains and increased speed assumes, IIRC, that the more powerful engine is exactly the same weight and fits exactly the same package as the less powerful engine. Since weight is drag, it might be a little wiser to use the FOURTH root of the power increase to get you into a more accurate rough estimate. Now, it's looking like drag, which increases speed as the square root of drag ratio might be more fertile ground to plow in your search for blinding speed :)

 

We haven't even begun to discuss props, which is a black art even on a GOOD day.

 

Do all the math carefully before you spend a lot of money. Talk to the folks who have been there. These airplanes have been around for a long LONG time. You're not the first guy or the smartest guy who decided he would go very very fast by the simple expedient of bolting on a bigger motor.

 

Just a theory .... Jim S.


...Destiny's Plaything...

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Evan asks about cowl flaps. As Marc says, they are often on the inlet, but they can also go on the outlet. This was the most convienient to implement, so I installed a flap which allows air straight through the bottom cowl and out of the boat tail. I think some of the drag from a NACA relates to back pressure as the air builds up and can't get out fast enough. Using the flap I "should" be able to adjust the air being forced through the rads to the optimum needed, providing, of course, that there's enough in the first place.

 

See http://kgarden.com/cozy/chap23d.htm search for "cowl flaps" for pictures.


I can be reached on the "other" forum http://canardaviationforum.dmt.net

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well, we all look at things different.

My buddy just bought a 1956 vtail bonanza fo 60,000. engine 700 hrs, airframe 5500hrs, old instruments, medium old radios, old interior, it's a really nice plane, but it aint no COZY.

 

I have a partner in this plane, so everything costs me 50%. I am building this plane for two reasons

 

I love to make things(my other hobby is building furniture 6 days a week).

 

I want a modern airplane that's really fast.

 

My choices for this are the cirrus or columbia, each of these cost ALLOT more than I plan to spend and as far as operating costs, try 17 gph on a 300 horse and costly annuals, etc, etc.

 

Turbo normalizing/intercooling/CS prop give the plane more speed and more options for altitude, if i can get 250 mph or more at altitude I BE A HAPPY CAMPER. If those "extras" cost me 10% or 15% or 20% of the cost of a cirrus or columbia ,cool, I didn't have to pay the whole cost and i'll be faster and I built every part of it (well, almost every part).

 

It's not a big deal, it is what I want. I'm taking 6 or 7 years partying, i mean building and paying for it, cheaper than going to the golf course each week.

 

Life is good and we are really lucky to be able to do this stuff.

 

Mike


maker wood dust and shavings - foam and fiberglass dust and one day a cozy will pop out, enjoying the build

 

i can be reached at

 

http://www.canardcommunity.com/

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Mike,

I share your goals. I would like to cruise at 250 kts (and would happily settle for anything over 200). Cirrus and Bonanza and etc. are not choices at all for me. Do they have a Cirrus RG? If not, I doubt they'll ever see anything over 200 kts without a hideously big motor.

 

Anyway, I'm looking at Phil Johnson's approach except that I'm partial to turbo 13B rather than Subaru. The math tells us that drag reduction is a better approach to increased speed than adding power. There are, of course, distinct limits as to how much drag you can eliminate and less obvious limits on power that can be added, but at this point I am convinced that an RG system that fully covers the wheels is the biggest single step I can take to boost speed. The next biggest thing I believe is a carefully cowled, carefully cooled turbo normalized rotary driving the mother of all wood/composite props.

 

I am inclined to go with John Slade and Greg Richter and ignore takeoff and climb performance, setting up the prop exclusively for high end cruise. I'll have the power to take off by brute force, and climb at very high speeds, so I'm not really giving anything away.

 

As John has intimated, managing cooling drag will become a REALLY big deal, and his very creative cowl flaps might just be the ticket. I have been thinking about NACA inlets on the aft turtleback for the intercooler (ala Velocity) as a possible low drag solution. Phil seems to think he can make 250 mph (maybe 220 kts) with a 230 hp NA Subaru. Assuming that's true, a turbo normalized 13B at around 15k' should make 250 kts cruise if we do everything right. I believe a well faired, fully enclosed RG is a pivotal requirement. I used to be VERY skeptical about the Infinity RG. Phil ran the math with me and I now am much more comfortable around the issues that used to bother me. It seems ideal, what with fully enclosed wheels and no hardware in the fuselage. That means you can buy back the apparent fuel penalty by filling the space now occupied by the Cozy gear with a sump tank (the need for which I beat to DEATH on another thread):).

 

I aim to let John and Greg develop the engine for me. Phil is building his own prop (Al Wick did that with great success with his EJ-25 cozy) so I may go that route. Under $200 a pop props are clearly the way to go when you're squeezing that last couple of kts out of a system and envelope that nobody has explored extensively.

 

My budget being what it is, I don't have a clue how I'm going to do all this sh*t. Maybe I'll have to go back to work (gawd forbid) or maybe GWE will come in for me :)

 

It's doable, but it ain't easy. Well thought out elegant solutions trump brute force :) .... Jim S.


...Destiny's Plaything...

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Well, I'm for both, everything fared as well as i can do it and add some good ole brute force and we will see what comes out.

 

But, I want an airplane engine in mine, i save the auto engines for my cars and trucks.

 

Mike


maker wood dust and shavings - foam and fiberglass dust and one day a cozy will pop out, enjoying the build

 

i can be reached at

 

http://www.canardcommunity.com/

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