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Thread: Verner radial vs. Rotec radial

  1. #1

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    Default Verner radial vs. Rotec radial

    Anybody know anything about the Verner Scarlett radials? I know they're made in the Czech Republic, and a Canadian dealer told me that they carry their oil supply in the crankcase. I have no idea how they prevent the oil from leaking out the bottom cylinders.

    The familiar Rotec R2800 from Australia is a more traditional design with an external oil sump.

    Rotec:

    7 cylinders.
    Bore and Stroke: 80 x 80 mm
    Total displacement: 2800 cc.
    Power: 110 hp @ 3600 engine rpm
    Gear reduction: 3:2 (Rated power at 2400 prop RPM.)
    Dry weight: 102kg, 224 lbs including all bolt-on accessories, but NOT including the external oil tank!
    Diameter: 810mm, 31.9 inches.
    Fuel consumption: 5.81 gph at cruise (From Rotec website.)

    Verner Scarlett 5:

    5 cylinders
    Bore 97mm, Stroke 90mm
    Total displacement: 3325 cc.
    Power: 125 hp @ 3000 engine rpm
    Gear reduction: NONE.
    Dry weight: 85kg, 187 lbs. NO external tank.
    Diameter: I have no idea. Can't find any info. But from the look of it, it's MUCH smaller than the R2800. Will proably fit in a modified Kitfox "bumpy cowl."
    Fuel consumption: 5.5 gph at FULL POWER (3000 rpm)


    My uneducated opinions:

    1. The Rotec looks better. It's obviously intended to be a "traditional" radial. It's gorgeous. If it could cook I'd marry it.

    2. The Verner is actually the wimpiest version of their 5-cylinder series. The same, exact engine is available in a 170 hp version that simply has a higher rated RPM: 3500. And it has a reduction drive. They also have a wicked 190 hp, 4600 rpm SUPERCHARGED version with a reduction drive. That tells me that the standard "Scarlett 5" is very de-rated and is just basically loping along. It is introduced with a 1000 hour TBO. So it appears that the 125 hp version should last a good, long time assuming the engineering is sound.

    3. The Rotec is a more proven design. The Verner Scarlett series was recently introduced, and I don' know of anybody who is using one yet. It's made in the part of the Czech Republica that Hitler wanted real bad when he invaded Czechoslovakia. They're renowned for their aviation and weapons manufacturing. I'd like to think they know what they're doing.

    4. Judging from the photos, the Verner motor uses much shorter connecting rods. The over-square design is clearly a high-rpm one, which allows them to spin the same engine at enormous velocities to achieve up to 4600 rpm. The whole engine is much lighter and more compact than the Rotec. You save 37 pounds over the Rotec without even factoring in the weight of the Rotec's oil tank. That's no small item!

    5. The Kitfox is a pretty tiny airplane, and therefore wants a tiny prop. The Rotec, with it's big gear reduction, wants to sling a relatively long club. The Verner, on the other hand, sounds like it would be happy with exactly the sort of prop that people want to use on a Kitfox.

    Prices are similar. Both use premium mogas or 100LL. The Verner, lacking gear reduction, would be happy using a broader variety of lubricating oils. (No need for gear lube specs.)

    Opinions? If anybody knows, or has heard anything about the Verner Scarlett engines I'd love to hear it. I can't find ANYTHING on the internet, and even the dealers seem to know very little about them. I don't think they've actually sold any yet. If they are what they're cracked up to be they sound ideal for a Kitfox, if somebody wants a genuine radial engine and wants to keep it enclosed in a full cowl. And the weight savings is a VERY big deal for somebody as high on the Bubba Scale as I am.

    www.rotecradialengines.com

  2. #2

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    Default

    Incidentally: Unless I am misinterpreting something, the Verner Scarlett 5 can make its full 125 hp @ 3000 rpm ALL DAY LONG. That's not just a "takeoff power." I am making that assumption since the same engine is also rated to make 170 hp @ 3500 rpm and 190 hp @ 4600 rpm with gear reduction.

    I am further assuming that fuel consumption in cruise would be VERY low, since you wouldn't want to actually be making 125 hp all the time. Combine this thing with an electric constant-speed prop like a Woodcomp or a Warp Drive and I would expect it to cruise along with almost absurd fuel economy.

    And it's about half the price of a shiny new 912S.

    This engine sounds too good to be true. Somebody please give me a dose of reality.
    Last edited by mickey; 09-26-2008 at 03:31 PM.

  3. #3

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    Default radials

    mickey
    i cant imagine anyone that doesnt salivate at the sound and looks of a radial. i think you probably give up alot of cruise speed/horsepower as they have alot of drag and frontal area. no matter how attractive the verner might sound i wouldnt even consider one till a more than a few were over here and flying. as far as prop diameter i would put 800 tires on and then a big dia prop if i had a geared radial. the prop wash over the wings from the larger prop i think would give better stol performance and maybe a slower stall if you were carrying a little power. i am only guessing though. if on the other hand i found a rotec under the christmas tree or something i wouldnt be unhappy. keith

  4. #4

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    Reliability with the Verner is certainly a concern, since it'll be my narrow behind up there.

    Another slightly less "out there" idea:

    http://www.experimentalfuelinjection.com/

    How about a Rotax 914 turbo with electronic fuel injection and ignition? Fully redundant computers are an option. He uses an oil-to-water cooler, so you only need to worry about a radiator in the airstream.

    As you can see, I'm not somebody who is content with the status quo. But I've got good life insurance.

    Edit: If the Verner engine fits inside the standard "bubble cowl" then drag and frontal area won't be an issue. That's a big "if", though, since I can't find any info on the diameter of the engine.
    Last edited by mickey; 09-26-2008 at 09:42 PM.

  5. #5
    Administrator RandyL's Avatar
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    Default

    Mickey,

    "Radial engine" and "fast" don't normally go in the same sentence. Of course that huge frontal area and all those fins are enormously draggy. Since good high DA operation is your goal I'd look really hard at a 914, possibly with tweaks and improvements as you've mentioned.

    I don't know if you've built any airplanes before but I can tell you that as soon as you deviate from any of the well-engineered kits you are taking construction time up by a factor of at least ten. Kitfox offers a standard FWF installation kit for the Rotax and everything is completely thought out for you and proven to work. All needed parts are provided. With any of these other installations you're on your own for everything. First there's designing the systems, then there's finding and fabricating all the parts, then there's testing to see if each system works, then there's the inevitable revision iterations. Not trying to discourage you, just point this out. Still, this is experimental aviation and we're all free to try different things, and that's good so long as you're up for the challenge, and that's how we advance the state-of-the-art.

    Personally, given your objectives of speed and good high-DA performance, the 914 seems ideal, and there should be plenty of room for experimentation to keep you happy. I know I like to tweak things myself and am seldom happy just following the plans without some attempt at *improvement*. Heck, I'm barely into my Kitfox project and I've already got a "Mods" page on my project web site. Who knows what will end up there by the time I finish.

    FWIW,
    Randy Lervold
    TeamKitfox.com Admin Emeritus
    Day job: www.dynonavionics.com

  6. #6

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    Default

    Killjoy.

    Well, I DO still own plans for a Hatz Bantam. And I intend to build it someday. That one will have a radial for sure. I think you're right about the value of a turbo engine for my intended purpose.

    I'd REALLY like an excuse to use a turbodiesel........

  7. #7

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    Default Re: Verner radial vs. Rotec radial

    Quote Originally Posted by RandyL View Post
    Mickey,

    "Radial engine" and "fast" don't normally go in the same sentence. Of course that huge frontal area and all those fins are enormously draggy. "
    FWIW,
    Nonsense.

    Radial powered Focke-wolf 190 was faster than the Inline powered Spitfire and P51.

    Race planes such as the Gee Bee's were unbeatable, Even now days Rare Bear at the Reno races is the fastest of the lot. All radial powered.

    Air cooled engines need to be cooled, if they be round, flat or inline, makes no difference. Cooling equals drag period.

  8. #8

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    Default Re: Verner radial vs. Rotec radial

    Quote Originally Posted by paulc View Post
    Nonsense.

    Radial powered Focke-wolf 190 was faster than the Inline powered Spitfire and P51.

    Race planes such as the Gee Bee's were unbeatable, Even now days Rare Bear at the Reno races is the fastest of the lot. All radial powered.

    Air cooled engines need to be cooled, if they be round, flat or inline, makes no difference. Cooling equals drag period.
    I think your logic only applies to golden age aircraft when the cowl is a carefully designed NACA cowl, as in your examples. Until the invention of the NACA cowl, water-cooled designs were generally faster.

    The concept of the NACA cowl is to create enough jet boost from the cowl exits to overcome the radial's frontal area. It squeezes the cooling air to increase its velocity after heating, much like a jet does. The combination of the jet boost plus the radial's lighter weight gives better performance, which is why radials ruled for most of the golden age despite their frontal area.

    The Kitfox bumpy cowl is definately not a NACA cowl, and I doubt that a 125 HP radial would fit inside it anyway. But if it did, it would be an interesting question, since in that case both alternatives would be suffering the same frontal area penalty. Maybe the radial would be faster, since it has more power and can swing a bigger prop. Or that gain could be offset by the weight penalty, which would cause the angle of attack to increase. It would be an interesting experiment.

  9. #9

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    Default Re: Verner radial vs. Rotec radial

    Quote Originally Posted by jonbakerok View Post
    I think your logic only applies to golden age aircraft when the cowl is a carefully designed NACA cowl, as in your examples. Until the invention of the NACA cowl, water-cooled designs were generally faster.
    Hmmm not sure about that. I don’t think Rare Bear or the Fw190 were "golden era" the golden era was 1920-1930's.

    In fact as far as piston powered aircraft are concerned these were the high water mark, before the kero burners came to be in the 1940-50's

    Would the Germans have had NACA technology at their disposal during the peak of WWII? Oh and let's not forget Japan's Zero, Russia's I 16 Polikarpov's all as fast as bullets. Definitely not slow!

    NACA cowl or not, it’s a complete fallacy to associate radials only with slow speed. The OX5 was an inline V8 and powered the Jenny Bi-plane was just about the slowest thing around. So do we say that V8's are slow or that Jenny's are slow?

  10. #10

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    Default Re: Verner radial vs. Rotec radial

    Quote Originally Posted by paulc View Post
    Hmmm not sure about that. I don’t think Rare Bear or the Fw190 were "golden era" the golden era was 1920-1930's.

    In fact as far as piston powered aircraft are concerned these were the high water mark, before the kero burners came to be in the 1940-50's

    Would the Germans have had NACA technology at their disposal during the peak of WWII? Oh and let's not forget Japan's Zero, Russia's I 16 Polikarpov's all as fast as bullets. Definitely not slow!

    NACA cowl or not, it’s a complete fallacy to associate radials only with slow speed. The OX5 was an inline V8 and powered the Jenny Bi-plane was just about the slowest thing around. So do we say that V8's are slow or that Jenny's are slow?
    We're getting a little off-topic here, but since the board traffic has been a little slow lately, I'll bite...

    Sorry about my sloppy use of the term "golden age", but my point is still valid. You need a NACA cowl to make a radial go as fast as an equivalent inline engine. That's how the Focke-Wolf, Zero, and Gee-Bee did it. NACA developed the cowl in 1927 (just checked Wiki). The design was in wide usage throughout the 30's.

    The OX5 in your "Jenny" was a 400 pound V8 that barely made 90 horsepower. Not a reasonable comparison. Consider the Spad 13's Hispano-Suisa or Fokker D7's Mercedes, both of which were must faster than the equivilent poorly cowled rotories of the same period

    Rare Bear is a special case. That's a huge, dual-row radial with twice the horsepower of the Mustangs it races against. It goes fast by sheer brute strength, but it's still as likely to lose any given race as it is to win.

    Frontal area has more to do with how fast a plane flies than horsepower. Without a special cowl to overcome the radial's larger frontal area, the smaller profile of an inline water cooled engine will win every time. The two may have the same theoretical cooling drag, but the cooling efficiency of cast fins hanging perpendicular to the breeze is much less than water transferring the heat to the closely-spaced thin aluminum fins in a radiator behind a duct.

    No need for theory, though. We've got proof. Several Kitfoxes are flying with that beautiful Rotec on the front. None of them are as fast as a 100 hp Rotax. Speed is not why you put a radial on a Kitfox.

    Please don't think that I don't like radials just because I'm aware of the limitations. I'd give up a few knots for that look any day.

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