PA-28-181 Vno below Vc minimum design speed? NOT SOLVED
The PA-28-181 Archer III does not seem to be compliant with Vc min regs, it looks be 7MPH short. Other PA-28s appear OK but not the Archer III:
Vc min for 15lbs/sq.ft wing loading = 147mph EAS PA-28-181 Vno = 140mph CAS What I am missing? From the PA-28-181 Archer III TCDS p. 21,37 Airspeed Limits: Never exceed 171 mph (148 knots) CAS Maximum structural cruising 140 mph (121 knots) CAS Maneuvering @ 2550 lbs. 128 mph (111 knots) CAS Maneuvering @ 1634 lbs. 102 mph ( 89 knots) CAS Flaps Extended 115 mph (100 knots) CAS Certification Basis: PA-28-181: CAR 3 effective May 15, 1956, including Amendments 3-2 and 3-4; paragraphs 3.304 and 3.705 of Amendment 3-7 effective May 3, 1962; FAR 23.207, 23.221, 23.955 and 23.959 as amended by Amendment 23-7 effective September 14, 1969; FAR 23.1557(c)(1) as amended by Amendment 23-18 effective May 2, 1977; and FAR 23.1327 and 23.1547 as amended by Amendment 23-20 effective September 1, 1977. FAR 36, Appendix G, Amendment 36-16 for the PA-28-181 (Archer III), S/N 2890206 through 2890231, 2843001 and up, and 2881001 and up. 3.184 states: § 3.184 Design air speeds. The design air speeds shall be chosen by the designer except that they shall not be less than the following values: Vc (design cruising speed) = 38 √ W/S (NU) = 42 √ W/S (A) except that for values of W/S greater than 20, the above numerical multiplying factors shall be decreased linearly with W/S to a value of 33 at W/S=100: And further provided, That the required minimum value need be no greater than 0.9 Vh actually obtained at sea level. Vno is defined thus: § 3.740 Maximum structural cruising speed (Vno). This operating limitation shall be: (a) Not greater than Vc chosen in accordance with § 3.184. (b) Not greater than 0.89 times Vne established under § 3.739. (c) Not less than the minimum Vc permitted in § 3.184 Additional data for the PA-28-181 Archer III: W/S = 2550lbs/170sq.ft=15lbs/sq.ft From 3.184 above the following applies: Vc (design cruising speed) = 38 √ W/S (NU) 38x √ 15 = 147.17 mph Vc = 147.17 mph Vno = Vc However Vno as per TCDS = 140 mph CAS Not sure what is going on here? Wondering what is actually meant by: And further provided, That the required minimum value need be no greater than 0.9 Vh actually obtained at sea level. V-n diagram from 3.185 for reference if required. https://cimg5.ibsrv.net/gimg/pprune....e82c183929.png V-n CAR 3.185 |
For comparison:
182S under 23.335, pretty close: Max Structural Cruising 140 Knots IAS (138 Knots CAS) Wing loading 17.8lbs/sq.ft 33 √ 17.8 = 139kt Beechcraft F33A under CAR 3.184, well over: Maximum structural cruising 190 mph (165 knots CAS) Wing loading 18.8lbs/sq.ft 38 √ 18.8 = 164mph Note the C182(S&T) (CFR 23.335) are certified in knots rather than mph CFR 23.335 (1) https://rgl.faa.gov/Regulatory_and_G...ElemFormat=gif(in knots) may not be less than - (i) https://rgl.faa.gov/Regulatory_and_G...ElemFormat=gif(for normal and utility category airplanes) |
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From the EASA PA-28-181 TCDS you linked: 6. Requirements elected to comply: None 8. Exemption: None Hence: And further provided, That the required minimum value need be no greater than 0.9 Vh actually obtained at sea level. |
From a very knowledgeable friend. Great to bottom it out!
Begin with 38 √ W/S (NU). Then calculate 0.9 Vh actually obtained at sea level (Actually, it appears that " Vh actually obtained at sea level" would be a flight test value, the "calculation" relates to multiplying the (Test) Vh by 0.9. If the 0.9 Vh is less than 38 √ W/S (NU), then (and only then) use 0.9 Vh. While it is not applicable, you may find a clearer wording in early versions of Part 23. You might also review AC23-8, "Flight Test Guide for Part 23 Airplanes". The beauty of an AC is it will often give guidance on how to determine the correct answer. There would also be more stuff in the NPRM associated with that specific rule - easy if you know where to click on the FAA website/Regulatory and Guidance Library; there is often a link at the bottom of each section, where the background to each Amendment is discussed. Hope this helps. If further discussion is needed, let me know...but we're probably heading into territory that involves a lot of references, like weight growth/wing area increase/power increase as the PA-28 evolved. Superficially, it is unlikely that cruise speed would be greater than 0.9 Vh, so why bother meeting a more stringent requirement - the 38 √ W/S (NU) would appear to be an empirical value that corresponds to a typical Cl max for airfoils of the CAR 3 era, along with the assumption of a "typical" sharp edged gust. Later codes include a gust alleviation factor, as the science developed. |
Haaaaang on.. I know it doesn't strictly apply to 3.184 but from AC 23-19A - Airframe Guide for Certification of Part 23 Airplanes p.26-27
46. Why would I want to define VC as equal to 0.9 VH? Use this definition if you are designing an airplane that is capable of a sustained speed (VC) higher than that obtained by using the wing loading (W/S) formula. Vc min for 15lbs/sq.ft wing loading = 147mph CAS PA-28-181 Vno = 140mph CAS § 3.740 Maximum structural cruising speed (Vno). This operating limitation shall be: (a) Not greater than Vc chosen in accordance with § 3.184. (b) Not greater than 0.89 times Vne established under § 3.739. (c) Not less than the minimum Vc permitted in § 3.184 |
This is still bugging me.
The Dakota also has a Vno less than Vc min design limitations. MAUW=3000 Wing Area=170sqft Wing Loading=17.65lbs/sqft Vc design minimum = 38 √17.65 = 159.63 MPH EAS ≈ 138.72 KEAS Published Vno = 135 KCAS It seems a number of the heavier Cherokees appear to have lower than legal Vnos. The Warrior III for eg. Piper PA-28-161 Warrior III (2440lbs With installation of Piper Kit 88050 STC#: SA00397NY/170sqft) Vc min = 125 KEAS Vno = 122 KCAS With out the paper MAUW increase of the post 1983 Warrior III models Vc min = 122 KEAS ie. spot on. Has Piper done some sort of deal with the FAA here to allow increases in gross weight for the Cherokees without complying with the Vno requirements? For reference here are some other CAR 3 / FAR Part 23 aircraft: All with Vno ≥ Vc min design speed. Piper Comanche PA-24-180 (2550lbs/178sqft) Vc min = 125 KEAS Vno = 139 KCAS Piper Comanche PA-24-250 (2900lbs/178sqft) Vc min = 133 KEAS Vno = 156 KCAS Piper Comanche PA-24-400 (3600lbs/178sqft) Vc min = 149 KEAS Vno = 182 KCAS Cessna 172R (2450lbs/174sqft) Vc min = 124 KEAS Vno = 126 KCAS Cessna P210R(4100lbs/174sqft) Vc min = 162 KEAS Vno = 167 KCAS Beechcraft C23 Sundowner (2450lbs/146sqft) Vc min = 135.3 KEAS Vno = 135.5 KCAS Beachcraft S35 Bonanza (3300lbs/181sqft) Vc min = 141 KEAS Vno = 165 KTIAS ≈ KCAS Mooney M20J (2740 lbs. - S/ N 24-0001 thru 24-3200, 24-3202 thru 24-3217) 2900 lbs. - S/N 24-3201, 24-3218 and ON and S/N 24-1686 thru 24-3200, 24-3202 thru 24-3217 when c/w MAC dwg. No. 940071 and insertion of applicable AFM Supplement into the appropriate AFM/174.8sqft) Vc min = 131 KEAS (2740lbs) or 135 KEAS (2900lbs) Vno = 152 KIAS or 174 KIAS for Serial No’s. 24-0171 and on, (and 24-0002 through 24-00170 if S.B. M20-198 is complied with). Mooney M20M (3368lbs/174.8sqft) Vc min = 145 KEAS Vno = 174 KIAS |
The Vc takes the compressibility correction. Where Vno is only corrected for position error based on what is shown you can't make a direct comparison...that I believe is the reason.
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Originally Posted by AC103
(Post 10323156)
Not sure what is going on here? Wondering what is actually meant by:
Surely 38 √ W/S is the minimum compliance standard while faster aircraft need not prove 30ft/s gust protection at any more that 0.9Vh but must still adhere to 38 √ W/S as the minimum standard. I have used it myself for one or two projects. |
Do you have the guidance reference for that one djpil?
All I can find is FAR23's which suggests the opposite: I assume it doesn't strictly apply to 3.184 but from AC 23-19A - Airframe Guide for Certification of Part 23 Airplanes p.26-27 46. Why would I want to define VC as equal to 0.9 VH? Use this definition if you are designing an airplane that is capable of a sustained speed (VC) higher than that obtained by using the wing loading (W/S) formula. |
Originally Posted by AC103
(Post 10788596)
Do you have the guidance reference for that one djpil?
It goes on to state “with the following understanding” that Vc is less than or equal to 0.9Vh. Again, I don't see that the words in FAR are consistent with that. But who am I to argue with the FAA and their current AC. I am unable to find the first issue of that AC online. The predecessor to that AC is AC 23-3 of 1985 and there is nought in there about Vc. Interesting that the text of CAR 3 is different: “And further provided, That the required minimum value need be no greater than 0.9 Vh actually obtained at sea level.” Quite clear to me. |
I should add that FAR 23 uses similar wordings elsewhere.
"Va may not be less than" ... but goes on to state that "Va need not exceed the value of Vc used in design." Check out the notes on Va in that same AC. "The positive limit maneuvering load factor n may not be less than" ... calculate a number ... "except that n need not be more than 3.8." |
I agree, "And further provided" has an "AND" operator. It looks like the FAA changed their mind or realized that they hadn't been clear and didn't want to invite a whole load of paper MAUW increases.
Please do share any designs you know of that have Vcmin below 38 √ W/S. That would be a very interesting list. I have not managed to find any yet besides the later Cherokees. Don't get me started on design vs operational Va... now that is a proper mess. |
Originally Posted by AC103
(Post 10789443)
I agree, "And further provided" has an "AND" operator. It looks like the FAA changed their mind or realized that they hadn't been clear and didn't want to invite a whole load of paper MAUW increases.
Please do share any designs you know of that have Vcmin below 38 √ W/S. That would be a very interesting list. I have not managed to find any yet besides the later Cherokees. Don't get me started on design vs operational Va... now that is a proper mess. |
How funny, it looks like MAUW could be a Kiwism. https://www.aviation.govt.nz/assets/...ht_Balance.pdf
I can give plenty of examples of types with Vc outside the range given as gospel by that AC |
Originally Posted by AC103
(Post 10789582)
How funny, it looks like MAUW could be a Kiwism. https://www.aviation.govt.nz/assets/...ht_Balance.pdf
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Rarely can a question on here have been researched in such detail before being asked. It took me quite a while to get my head around the detail but was not unwelcome as a distraction from the DIY and 'exercise' groundhog day that is lockdown. The bottom line is I think djpil is correct. If the Vno is not less than 90% of VH then it complies.
Vno is defined thus: § 3.740 Maximum structural cruising speed (Vno). This operating limitation shall be: (a) Not greater than Vc chosen in accordance with § 3.184. (b) Not greater than 0.89 times Vne established under § 3.739. (c) Not less than the minimum Vc permitted in § 3.184 Surely 38 √ W/S is the minimum compliance standard while faster aircraft need not prove 30ft/s gust protection at any more that 0.9Vh but must still adhere to 38 √ W/S as the minimum standard. |
I think you talking about an ‘aeroplane’.. Not a car.. Why on earth did you start this discussion with MPH?
The wind is knots, the airspeed indicators are in knots.. The industry uses and knows about knots.. .. Can we start again? |
Originally Posted by advent
(Post 10789912)
I think you talking about an ‘aeroplane’.. Not a car.. Why on earth did you start this discussion with MPH?
The wind is knots, the airspeed indicators are in knots.. The industry uses and knows about knots.. .. Can we start again? |
Originally Posted by 733driver
(Post 10790130)
MPH was quite common in general aviation some decades ago.
Yes indeed alleviated gust values do decrease with increasing speed... |
Arghem... advent, please read post #2! (All of the words and numbers..) Thanks 733driver.
Oggers, kind of you to say and thank you for your input, now what is your response to the later clarification by the FAA in AC 23-19A - Airframe Guide for Certification of Part 23 Airplanes p.26-27 46. Why would I want to define VC as equal to 0.9 VH? Use this definition if you are designing an airplane that is capable of a sustained speed (VC) higher than that obtained by using the wing loading (W/S) formula. I am still interested in a list of any other Vno < Vcmin designs besides the later/heavier Cherokees. I am sure there will be and it will be an interesting list for sure. With regards to the problem taking care of its self, this issue is that if an aircraft design increases its MTOW on paper and then artificially reduce their Vno as their structures are not able to comply with the gust penetration requirements this is an indication of a weaker than required air frame which becomes relevant in descent and this is where it gets more interesting. The Archer III POH specifies a Fuel, Time, Distance to Descend chart based on an engine RPM (2500) and KIAS (122) which puts it an additional 3 knots under Vno, limiting the descent rate to only ~450fpm whilst keeping the engine warm. This configuration is mentioned again in the Descent subsection of Normal Procedures in reference to carb ice. (The Archer III has a cooler air pick up than previous 4cyl PA-28s) so its descent profiles now start to look limited by the low Vno. These Fuel, Time, Distance to Descend charts are published for the later Pipers (Seminole, Malibu, Warrior 161s, Archer 181s etc) and not published by the other manufactures singles mentioned above including popular IFR trainers like the DA-40 and DA-42 where these tables would be more expected. The exception to the above is the later Mooneys. However they configure on a 750fpm descent rate rather than an airspeed likely due to their published Vno being some 20% above Vcmin. Are there any ex Piper engineers here that might know or do we have any friendlies in their current design team? |
Originally Posted by AC103
(Post 10789443)
I agree, "And further provided" has an "AND" operator. It looks like the FAA changed their mind or realized that they hadn't been clear and didn't want to invite a whole load of paper MAUW increases.
Originally Posted by AC103
(Post 10789443)
Please do share any designs you know of that have Vcmin below 38 √ W/S. That would be a very interesting list. I have not managed to find any yet besides the later Cherokees.
Originally Posted by AC103
(Post 10789443)
Don't get me started on design vs operational Va... now that is a proper mess.
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Originally Posted by djpil
(Post 10790416)
Perhaps Francis Donaldson could fill in the history and perhaps explain why the AC mangles the text of the rule instead of changing the rule…
…The Aviat Husky series is one that I am very familiar with. The current model A-1C has W/S of 12 so 33 √ W/S = 114 kts but Vc used in design and Vno is 103 kts… …I like the bit in AC 21-19A about "For airplanes where VA>VS√n, the pilot would have to check the maneuver; otherwise the airplane would exceed the limit load factor."... Perhaps the subject of another thread. You are not constrained to use these minimum values. Indeed, if your aircraft has high performance in terms of a high cruising speed, the value of Vc would be much greater than the minimum. Additionally: It is recommended that Vc should not be less the 0.9 Vh 43 Appendix A: On the list of 32 preventive maintenance items. (c) Preventive maintenance. Preventive maintenance is limited to the following work, provided it does not involve complex assembly operations: If a task or maintenance function does not appear in the list, it is not preventive maintenance. https://www.faa.gov/about/office_org/headquarters_offices/agc/practice_areas/regulations/interpretations/data/interps/2009/Coleal%20-%20(2009)%20Legal%20Interpretation.pd Yes, crews can check the tire pressure under Part 91 AND Even though the introductory text of subparagraph (c) states that "preventive maintenance is limited to the following work....", in view of the broader definition of preventive maintenance in section1.1, we believe that such limitation is not controlling. we also believe that the… sentence in Advisory Circular 43-12A, Preventive Maintenance … is overly restrictive the lists are better viewed as examples of the tasks in each category-they cannot be considered all-inclusive There are, no doubt, many "simple or minor preservation operations [tasks]" and many" replacement of small standard parts not involving complex assembly operations" performed daily, especially on small general aviation aircraft, that the agency would consider to be preventive maintenance, though they are not included in the 32 listed items. It is our understanding that Flight Standards' Aircraft Maintenance Division is planning to clarify this issue in a future revision to the AC. Yet the regs and the AC still say they cannot to this day. Thanks for the Husky You are totally on the right track with Va. Yes probably for another thread. It may well have already been flogged here due to the AA587 accident. I sure would love to talk to a Piper engineer to understand which structure they believe would not be able to withstand loads at proper Vc min for its wing loading. |
Originally Posted by AC103
(Post 10790189)
Oggers, kind of you to say and thank you for your input, now what is your response to the later clarification by the FAA in AC 23-19A - Airframe Guide for Certification of Part 23 Airplanes p.26-27
FYI per the Archer III POH Speed Power chart 5-21 Vh is 133 KTAS = 153 MPH 0.9 = 135.75 MPH so a Vno of 140 MPH CAS is conceivable if we ignore the above AC but personally I would prefer not to ignore a later clarification. Understood from Piper's perspective this is hindsight. With regards to the problem taking care of its self, this issue is that if an aircraft design increases its MTOW on paper and then artificially reduce their Vno as their structures are not able to comply with the gust penetration requirements this is an indication of a weaker than required air frame which becomes relevant in descent and this is where it gets more interesting. |
Originally Posted by oggers
(Post 10794949)
"At the end of the day the FARs of the time said Vc need not be higher than 0.9VH, and it seems that is what Piper did.
The Vno of the Archer 3 didn't change from the Archer 1. To my mind if they needed to reduce Vno in order to achieve a higher weight this is not a weaker airframe, it is the same airframe optimised for a different task. Also note that the in Rev 44 of the PA-28 TCDS the Archer III was given a Va of 108KCAS, later changed to the 111KCAS at 2550lbs – 89KCAS at 1634lbs we have now (rev. 59). Unclear as to why. It looks like original Hershey bar winged PA-28s use 112KCAS for Va. When the longer winged Archers came out it went down to 110KCAS then 108 with the taper wing, then revised to the range we have now. Also noteworthy is the reduced aileron control surface movement limitations in the taper wing PA-28s even when compared with the long Hershey bar winged Archer. (25/12.5 vs 30/15) The first taper wing aircraft, the 1973/4 PA-28-161 Warriors, had the spar failure issues and early serial numbers that also ended up with reduced aileron control surface movement limits. I appreciate your thoughts oggers but I think the later heavier Cherokees are an example of an outlier here. |
I would say that all the Cherokees share an equivalent task. The heavier ones are now more boxed in on descents. |
Originally Posted by oggers
(Post 10795604)
Hello again. The objective fact remains that the aircraft structure meets or exceeds the regulatory strength requirements if, and only if, operated within the certified flight envelope, the same as any other aircraft. You have specifically mentioned descent being an issue twice now but I don't undertsand what you are getting at there?
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Originally Posted by AC103
(Post 10796062)
To be fair I think I very clearly spelt out the operational considerations around descent with comparisons in post #21
With regards to the problem taking care of its self, this issue is that if an aircraft design increases its MTOW on paper and then artificially reduce their Vno as their structures are not able to comply with the gust penetration requirements this is an indication of a weaker than required air frame which becomes relevant in descent and this is where it gets more interesting. The Archer III POH specifies a Fuel, Time, Distance to Descend chart based on an engine RPM (2500) and KIAS (122) which puts it an additional 3 knots under Vno, limiting the descent rate to only ~450fpm whilst keeping the engine warm. This configuration is mentioned again in the Descent subsection of Normal Procedures in reference to carb ice. (The Archer III has a cooler air pick up than previous 4cyl PA-28s) so its descent profiles now start to look limited by the low Vno. These Fuel, Time, Distance to Descend charts are published for the later Pipers (Seminole, Malibu, Warrior 161s, Archer 181s etc) and not published by the other manufactures singles mentioned above including popular IFR trainers like the DA-40 and DA-42 where these tables would be more expected. The majority of other manufactures including Piper for its other aircraft chose to design around the more onerous interpretation that is not in direct conflict with later advice from the FAA and provides a more useful and safer operational envelope.. So this is absolutely not an objective fact The AC is: "not mandatory.....not a regulation.....not the only means of compliance". Other manufacturers have complied with certification by using the other of two alternative and equally valid criteria in the regulations. The reg has since been reduced to something vague by the new FAA part 23, but the original certification basis is still extant in EASA land where: "(3) VC need not be more than 0·9 VH at sea level." This aircraft is fully compliant. There is no "deal with the FAA here to allow increases in gross weight for the Cherokees without complying with the Vno requirements?". because it complies with the pre-existing foreign regs too. You are barking up the wrong tree. |
Originally Posted by oggers
(Post 10796825)
Ok, so the quote below is what we are talking about from post 21:
The key point in there is where you say "descent profiles now start to look limited by Vno". Would you prefer the recommended descent speed was higher than Vno or where exactly? The structure does comply with the gust penetration requirements. You are reading too much into this. The recommended descent profile is 'nice to have'. It is not a limitation. It is not even an unduly limiting recommendation because it turns out to be one knot faster than a 75% cruise at 4000' DA (according to Fig 5-21 of the POH). The aircraft is certified. That is the fact. Its flight envelope provides the same safety factor of 1.5 between limit loads and ultimate loads as every other certified aircraft. The AC is: "not mandatory.....not a regulation.....not the only means of compliance". Other manufacturers have complied with certification by using the other of two alternative and equally valid criteria in the regulations. The reg has since been reduced to something vague by the new FAA part 23, but the original certification basis is still extant in EASA land where: "(3) VC need not be more than 0·9 VH at sea level." This aircraft is fully compliant. There is no "deal with the FAA here to allow increases in gross weight for the Cherokees without complying with the Vno requirements?". because it complies with the pre-existing foreign regs too. You are barking up the wrong tree.My objective when discussing Aviation via an HID is to stimulate deeper understanding and help protect the communities I care about from potentially risky dark corners. There are many of those in this world worth shining a light on, this is one of them. And your objective here? There is no doubt the later heavier Cherokees are an outlier by a meaningful margin on declared Vno relative to wing loading that does impact operations and safety margins when compared to its peers, and there is also reasonable ground that the designers may have misinterpreted the regs. If the regs were written as follows there would be no question on the interpretation, § 3.184 Design air speeds. The design air speeds shall be chosen by the designer except that they shall not be less than the following values: Vc (design cruising speed) = 38 √ W/S (NU) = 42 √ W/S (A) except that: (a) For values of W/S greater than 20, the above numerical multiplying factors shall be decreased linearly with W/S to a value of 33 at W/S=100: (b) The required minimum value need be no greater than 0.9 Vh actually obtained at sea level. But they do not say that. They says this: § 3.184 Design air speeds. The design air speeds shall be chosen by the designer except that they shall not be less than the following values: Vc (design cruising speed) = 38 √ W/S (NU) = 42 √ W/S (A) except that for values of W/S greater than 20, the above numerical multiplying factors shall be decreased linearly with W/S to a value of 33 at W/S=100: And further provided, That the required minimum value need be no greater than 0.9 Vh actually obtained at sea level. This begs the question what are they 'providing' for. What they were actually providing for is later clarified in AC 23-19A - Airframe Guide for Certification of Part 23 Airplanes p.26-27 Why would I want to define VC as equal to 0.9 VH? Use this definition if you are designing an airplane that is capable of a sustained speed (VC) higher than that obtained by using the wing loading (W/S) formula. § 3.184 Design air speeds. The design air speeds shall be chosen by the designer except that they shall not be less than the following values: Vc (design cruising speed) = 38 √ W/S (NU) = 42 √ W/S (A) except that for values of W/S greater than 20, the above numerical multiplying factors shall be decreased linearly with W/S to a value of 33 at W/S=100: And further provided, for an airplane that is capable of a sustained speed (VC) higher than that obtained by using the wing loading (W/S) formula, the required minimum value need be no greater than 0.9 Vh actually obtained at sea level. This is the interpretation that majority of design teams complied with including Piper teams for their other models. As an operator this is reassuring as it requires designers to build stronger aircraft with wider envelopes that don't have their descent profiles as tightly boxed in between engine care and Vno as these later Cherokees. This has a significant real world impact on tactical options available during normal operations for dealing with weather, ATC etc. Again please review the post on the Coleal Interpretation to understand why there are still may ambiguous and just plain off the reservation regs still in black and white today that the FAA do not want us to comply with as written. If I was to guess I would say that there was some doubt about the longer tapper wings being able to cope with a normal >38 √ W/S based Vc combined with pressure to increase the MTOW for things like air con maybe, especially considering the number spar issues and changes to Va and control deflection limitations that occurred as this wing was introduced. It would be very nice to hear from a Piper engineer involved though as that is just a guess. |
Originally Posted by AC103
(Post 10797061)
What they were actually providing for is later clarified in AC 23-19A - Airframe Guide for Certification of Part 23 Airplanes p.26-27
Originally Posted by AC103
(Post 10797061)
If the regs were written as follows there would be no question on the interpretation
Originally Posted by AC103
(Post 10797061)
This begs the question what are they 'providing' for.
I distinctly recall my old Uni lecturer, Henry Millicer, telling me about FAR 23 flight envelopes as above. He was fresh from being Chief Designer of the Aircruiser back in the '60s. The CT/4 was developed from the Aircruiser and the current model, the CT/4E (aerobatic, higher weight than earlier variants and 50% more power), has a Vc of 147 kts (same as previous variants) per the NZ TCDS but my calculated Vcmin is 162 kts. |
AC103, you say:
This begs the question what are they 'providing' for. What they were actually providing for is later clarified in AC 23-19A - Airframe Guide for Certification of Part 23 Airplanes p.26-27 "(3) VC need not be more than 0.9 VH at sea level" |
Originally Posted by oggers
(Post 10798745)
.....clearly stated in the source regulation. Read in context with the rest of 23.335.a it means that if the chosen Vc is less than 33.√(W/S) it must be at least 0.9 VH.
https://cimg3.ibsrv.net/gimg/pprune....e5413e883a.png Furthermore, the old CAM400.pdf (faa.gov) is quite clear with "... the required minimum value need be no greater than 0.9Vh". |
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