Verner radial vs. Rotec radial

[jonbakerok]

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.

[paulc]

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?

[jonbakerok]

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.

[paulc]

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.

Not sure about that. Here are the actual accounts of one Radial powered Kitfox owner. I’d be surprised if any Rotax (even at 6,000rpm) could match these numbers. No cowl fitted NACA or otherwise!

Due to landing gear length, I know some Rotec/Kitfox owners have compromised performance by running smaller props on there Rotec which is designed to run larger props via its superior torque. 76" diameter is the optimum.

Kitfox Classic IV: Brian Henneman
Engine R2800 MkI
Prop: 76"D x 50"P then to 76”D x 55”P.
Burn: 6 gal/hr
Max RPM: 3600 (via 3:2 gear box)
Cruise RPM: 3000 = 2000 at prop.

Comment (26th June 2002): I did a static thrust test this past weekend and it will pull 480 lbs. Very impressive. More later.
Comment (11th June 2002): Just wanted to let you know I received my new prop a 76"dia. X 55" pitch and the performance really increased. The climb is still about 1500'/min. and the top speed is 130 mph. I can still exceed the red line up to about 3700 rpm. I have been cruising it at 3400 rpm and I am indication 110 -115 mph. I could use about another 5" of pitch to have a really good cruise prop but I will keep this one for demos.
Comment (28th April 2002 “I got in a couple of hour flying this weekend so far and I took Steve up in it with me. With the prop I have on it, it is really a climbing machine. I can peg the VSI at 2000' / min. and that is really going up for a little airplane”

[Joe Meyeres]

This is in response to John Baker on his comment of the Rotec 2800 vs Rotax 912. I have a Classic IV with the Rotec on the nose swinging a wooden 70" Climb Pitched Sterba Prop. At full power straight and level I am seeing 127 MPH, 75% power is 105 to 110 MPH and 65% yeilds around 90 to 95 MPH. I don't know what the Rotax will give you, but if you are looking for speed out of an airplane, the Kitfox is not the greatest choice. It's got alot of drag and the tube and fabric construction some would consider not as durable. However, I would not give up the aesthetic value achieved by putting the Rotec on the nose. It is "robust" and you can not match the sound it delivers. As for the speed... it's a Kitfox, but it sure not the slowest one to the party! I get alot of comments that it looks somewhat like a Beaver or Monocoupe. In my way of thinking, that's not bad company to be in!!! Pictures and videos are available on the Rotec Website at www.rotecradialengines.com

[paulc]

Those sound like pretty darn good numbers to me. Add some wheel spats and I reckon you could add another 5mph, what would that make it, 132mph?

BTW Here's a short movie of Joe's plane in action! http://www.youtube.com/watch?v=wYHdIZuv-K4

[Joe Meyeres]

Paul,

I elected to go with the bigger tires to provide more prop tip clearance, but yes, if you did add wheel pants and clip the wings it would make this airplane into a true Speedster model. (All the other Speedster mods have been done on this airplane.) Those two items could concievable add another 5, 10 maybe even to 15 MPH. And remember this airplane has a climb pitched prop!
The reason I chose the Kitfox is because it had "good" top end, "great" shortfield performance and "great" slow flight characteristics. The Rotec Radial adds so much more to the aesthetics of the airplane. No such thing as a quick turn at the pump though. It always gets crowded before I leave!

[Av8r3400]

Joe, that is an absolutely beautiful bird, no doubt.

Is there a heat muff on the exhaust somewhere for cabin heat? I'd love a Rotec, but I need cabin heat in Wisconsin.

[jonbakerok]

This is in response to John Baker on his comment of the Rotec 2800 vs Rotax 912. I have a Classic IV with the Rotec on the nose swinging a wooden 70" Climb Pitched Sterba Prop. At full power straight and level I am seeing 127 MPH, 75% power is 105 to 110 MPH and 65% yeilds around 90 to 95 MPH. I don't know what the Rotax will give you, but if you are looking for speed out of an airplane, the Kitfox is not the greatest choice. It's got alot of drag and the tube and fabric construction some would consider not as durable. However, I would not give up the aesthetic value achieved by putting the Rotec on the nose. It is "robust" and you can not match the sound it delivers. As for the speed... it's a Kitfox, but it sure not the slowest one to the party! I get alot of comments that it looks somewhat like a Beaver or Monocoupe. In my way of thinking, that's not bad company to be in!!! Pictures and videos are available on the Rotec Website at www.rotecradialengines.com

Hey, didn't say I PREFERRED a Rotax. Heck, I'm using Jabiru in my project. I just have a hard time understanding how a much heavier engine, with larger frontal area, and about the same horsepower can be faster. My theory can't stand up to your facts, though. Must be the prop.

I'm with you, anyway. If I could afford one, I'd take the aethetics over a few knots any day, even if it was slower.

Make me wonder what it could do with a good cowl. If you could just figure out how to make one out of plexiglass!

[Slyfox]

Hay, lets not be cutting down the Rotax. I just put on a 912s and that thing is unbelievable. I myself do not care about looks. It's the performance. I also know that when you have a heavy plane you will loose in handling. My plane handles like no other in my opinion. The empty weight is 650. I can't even emagine an extra 100 pounds. That would mean I would have a one seater airplane. What I mean there is me the wife and 30 pounds of cargo and full fuel, I'm at gross 1200lbs. You guys talk about a 2000vis well I get that with my airplane with the 912s. Plus I can throw my airplane around at low altitudes and have a bunch of fun.

Yes your airplane looks cool. It is a show plane. I rather fly. Sorry, just my opinion. please don't take offense.