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Performance Limits of the Cozy/EZ

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Has there been any analytical performance, stress, or any other kind of modeling done on the Cozy? Most of the figures and performance specs are based upon stock builds and not cover upgrading the power plant, or materials, etc..


What is limit of the amount of speed the airframe can handle, stress on wings, etc... I have seen that Rutan and others have been experimenting with all kinds power plants including jet engines and even a rocket engine. Was this with upgraded construction materials to handle the increase in stress and speed for the airframe? What limits the Cozy from acrobatics? Are there any facts, figures and specs from the bleeding edge of performance on the Cozy?


In another forum I saw someone posted asking about using other materials than fiberglass such as carbon or kevlar to increase stiffness. What say you? I have seen claims of 200mph in the cozy, what about 300mph or does this exceed the performance envelope for the construction and design of the Cozy?



Tis far easier to ask for forgiveness than for permission.

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  • 2 weeks later...

Hallo mlefebvre,

No one has probably replied to your post because it crops up often, and the theoretical arguments often end with people falling out, and the sensible people who build as per plans just want to talk about building.

The highest IAS the Cozy will accept is around 230 mph. If you go faster than that things may drop off. The Berkut canard is made of carbon fibre and will accept 300 mph indicated.


However you could modify a cozy to go to a higher IAS, but it would not be a cozy, it would be up to you to get it right. And if you are asking the question then my answer would be don't do it.


Retractable gear is another option to reduce drag, but it increases weight perhaps, and adds complexity.


A constant speed propeller doesn't add power, but adds efficiency, so it improves all performance, but they cost alot, weigh some, and are heavy on maintenance.


Using an increased horsepower normaly aspirated motor (IO-360 to IO-540) will give better climb, and some increase in cruise.


At altitude, True airspeed increases with a constant Indicated airspeed, so by supplying more power at altitude, which would require supercharging, you could maybe reach 350 mph, but then you have propeller problems, flutter problems, and of course you'll need oxygen.


One builder has a jet engine in his previously rotary powered cozy mk3; The rutan's have a long-eze with a rocket engine, and another with a prototype pulse detonation engine, so anything is possible.


As for aerobatics, the Boeing 707 performed two barrel rolls over a yacht regatta in Seattle before it entered service, and as Tex the test pilot explained to the boss when called in for an interview without coffee "It's a 1-G maneouvre Sir." I've seen Dick Rutan barrel roll his long EZ. Further aerobatics however may either exceed the G loadings and result in break up, or if you entered a deep stall, you might develop such massive sink as to never recover. Again I'd say if you are asking the question, don't do it.


The best flight test report I have read is at



The Coconut King

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