In going from the 170 to the 170A, Cessna changed the rudder from one that looks like a 140 to one that looks like a 195. Was this just for marketing, or was more area needed?
Karl
rudder area
Moderators: GAHorn, Karl Towle, Bruce Fenstermacher
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GAHorn
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Re: rudder area
Karl, I'm not certain what you mean exactly by "from one that looks like..." etc. They are not the same part number and certainly have different area.
Do you mean the actual rudder itself? Or are you referring to the entire rudder, vertical stabilizer and dorsal-fin area?
The dorsal fin "sweep" immediately ahead of the vertical stabilizer was added to the 170A (and B) but was not original to the 170 (fabric wing) aircraft. It was added for a couple of reasons, one was to improve longitudinal stability and the other was to improve looks.
The rudder itself was different between the 140 and 170, 170A, 170B as a group, in that the 140 rudder did not have a counter-balance area and was smaller in total area. The 170-series used a larger rudder for greater control. (Remember that the 170 is almost 49" longer than the 140 and has a wider CG envelope, therefore it requires greater rudder authority not only for directional control but also for spin-control.
Do you mean the actual rudder itself? Or are you referring to the entire rudder, vertical stabilizer and dorsal-fin area?
The dorsal fin "sweep" immediately ahead of the vertical stabilizer was added to the 170A (and B) but was not original to the 170 (fabric wing) aircraft. It was added for a couple of reasons, one was to improve longitudinal stability and the other was to improve looks.
The rudder itself was different between the 140 and 170, 170A, 170B as a group, in that the 140 rudder did not have a counter-balance area and was smaller in total area. The 170-series used a larger rudder for greater control. (Remember that the 170 is almost 49" longer than the 140 and has a wider CG envelope, therefore it requires greater rudder authority not only for directional control but also for spin-control.
'53 B-model N146YS SN:25713
50th Anniversary of Flight Model. Winner-Best Original 170B, 100th Anniversary of Flight Convention.
An originality nut (mostly) for the right reasons.
50th Anniversary of Flight Model. Winner-Best Original 170B, 100th Anniversary of Flight Convention.
An originality nut (mostly) for the right reasons.
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KarlWK
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Re: rudder area
Yes, I worded that poorly. It was the general shape and area of the vertical stabilizer I was asking about.
Generally, the addition of a strake to the fin implies the designers got the tail wrong the first time around, as on the P-51. Your reply suggests corrections were indeed desired. What were the other problems addressed by this change?
As for aesthetics, I think the 170's tail is far more attractive than the tail of the A and B, but I realize I'm the odd man out there.
Karl
Generally, the addition of a strake to the fin implies the designers got the tail wrong the first time around, as on the P-51. Your reply suggests corrections were indeed desired. What were the other problems addressed by this change?
As for aesthetics, I think the 170's tail is far more attractive than the tail of the A and B, but I realize I'm the odd man out there.
Karl
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DWood
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Re: rudder area
I couldn't agree more. Both of my 48's had the dorsal fin at one time or another. It was remove before I bought my first one and I am removing it from my project. I really don't notice a lack of stability where I would want to add a dorsal, but (by design) I am sure it would help. The biggest issues with the rag wings are lack of flaps and everyone want to call you a 140. They cruise around 130 MPH IAS.As for aesthetics, I think the 170's tail is far more attractive than the tail of the A and B, but I realize I'm the odd man out there.
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GAHorn
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Re: rudder area
It's not a "strake". A strake is usually a seperate fin added to the fuselage to some aircraft to re-direct errant airflow.KarlWK wrote:Yes, I worded that poorly. It was the general shape and area of the vertical stabilizer I was asking about.
Generally, the addition of a strake to the fin implies the designers got the tail wrong the first time around, as on the P-51. Your reply suggests corrections were indeed desired. What were the other problems addressed by this change?
As for aesthetics, I think the 170's tail is far more attractive than the tail of the A and B, but I realize I'm the odd man out there.
Karl
The designers did not "get the tail wrong the first time around".... the dorsal fin was added because the wing changed from the earlier fabric-covered wing to a NACA 2400 series all-metal, tapered wing. This required an aileron change to a frieze-type ailerons, also. The planform of the new wing changed the stall characteristics and the yaw characteristics with the new wing and flaps. Meanwhile the CAA (forerunner of the FAA) had changed the certification rules regarding directional stability in the critical balked-landing-climb configuration...so adding the dorsal fin prevented abnormally large yaw with full rudder deflection in-flight, in order to meet the new rules.
According to Cessna Test Pilot W.D. Thompson, the dorsal fin addition is not noticeable to the pilot "except for a slight deterioration in rudder control during taxi operations" (presumeably in strong crosswinds.) He considered the new certification rule on directional stability "an ill-concieved FAA regulation" that imposed an unnecessary adverse penalty on weight and performance. So you see, Dan, removing the dorsal from your ragwing is probably a good idea.DWood wrote:... I really don't notice a lack of stability where I would want to add a dorsal, but (by design) I am sure it would help. ...
'53 B-model N146YS SN:25713
50th Anniversary of Flight Model. Winner-Best Original 170B, 100th Anniversary of Flight Convention.
An originality nut (mostly) for the right reasons.
50th Anniversary of Flight Model. Winner-Best Original 170B, 100th Anniversary of Flight Convention.
An originality nut (mostly) for the right reasons.
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KarlWK
- Posts: 21
- Joined: Sat Dec 26, 2009 1:14 am
Re: rudder area
A most informative reply, gahorn; thank you.
As for strake, I may well be wrong in using that word. I simply couldn't recall the official word for such extensions to the leading edge of a wing. I seem to recall the extensions used on the wings of the SR-71 and the FA-18 are called that. Or was it "chine?" Regardless, I'm happy to stand corrected.
As for strake, I may well be wrong in using that word. I simply couldn't recall the official word for such extensions to the leading edge of a wing. I seem to recall the extensions used on the wings of the SR-71 and the FA-18 are called that. Or was it "chine?" Regardless, I'm happy to stand corrected.
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GAHorn
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Re: rudder area
A strake can be added to the leading edge of a wing.... but to be so-called it would be directly attached to the fuselage.
'53 B-model N146YS SN:25713
50th Anniversary of Flight Model. Winner-Best Original 170B, 100th Anniversary of Flight Convention.
An originality nut (mostly) for the right reasons.
50th Anniversary of Flight Model. Winner-Best Original 170B, 100th Anniversary of Flight Convention.
An originality nut (mostly) for the right reasons.
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KarlWK
- Posts: 21
- Joined: Sat Dec 26, 2009 1:14 am
Re: rudder area
Isn't the forward extension to the 170A tail fin attached to the fuselage?
It seems "dorsal fin" is the common name for such an aerodynamic extension to the tail fin, but "dorsal extension" would be a more descriptive name. Many WW-II designs sprouted these after a year or two in service, so it is often a "fix," one perhaps necessitated by increases in performance?
"Strake" appears to have no fixed definition. The Vari-Eze had one so named, but this appears to have been a fuel tank. The F-16 has one, but on the high performace jets, this is to improve airflow over the main wing at high angles of attack.
On the 170A, I at first thought the dorsal extension might serve as much as a fence as anything, to prevent air from slipping over the rear fuselage too easily, letting that portion of the fuselage better serve as a stabilizer. gahorn's description of the effect on the 170 suggests a more subtle effect, one with which I an not familiar. Again, thanks for the information.
It seems "dorsal fin" is the common name for such an aerodynamic extension to the tail fin, but "dorsal extension" would be a more descriptive name. Many WW-II designs sprouted these after a year or two in service, so it is often a "fix," one perhaps necessitated by increases in performance?
"Strake" appears to have no fixed definition. The Vari-Eze had one so named, but this appears to have been a fuel tank. The F-16 has one, but on the high performace jets, this is to improve airflow over the main wing at high angles of attack.
On the 170A, I at first thought the dorsal extension might serve as much as a fence as anything, to prevent air from slipping over the rear fuselage too easily, letting that portion of the fuselage better serve as a stabilizer. gahorn's description of the effect on the 170 suggests a more subtle effect, one with which I an not familiar. Again, thanks for the information.
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