Nukemzzz Posted August 29, 2020 Report Posted August 29, 2020 2 minutes ago, skykrawler said: . The SR-71 design was 1966. The P-51 had one of the first laminar flow wings. Slide rules are just calculators - the engineering is the same. Yes, but it doesn’t hold a candle to the capabilities of today using our workstations and FEA analysis. They had a finite budget for limit testing as well. Quote
DXB Posted August 29, 2020 Report Posted August 29, 2020 15 hours ago, Jeff Reiter said: I saw an old picture of a Mooney m20c with about 20 people standing on the wing, showing the extraordinary strength of the money wing. So why is 140 miles per hour the limit for speed in rough air? this makes no sense to me. if it has a strong wing, then why isn't the speed more like 175 miles an hour for rough air? Note in 1969 Vno for the M20C was raised to 175mph and Vne went from 189mph to 200mph. There was no associated structural modification in the aircraft in the 1969 model year to justify the change. So I basically treat 175mph as Vno in my '68C. I don't mess with Vne, but I don't think tail flutter issues come into play until well above 200mph. Quote
Nukemzzz Posted August 29, 2020 Report Posted August 29, 2020 One factor not mentioned yet: people weighed less in the 60’s. 1 Quote
aviatoreb Posted August 29, 2020 Report Posted August 29, 2020 1 hour ago, Nukemzzz said: Yes, but it doesn’t hold a candle to the capabilities of today using our workstations and FEA analysis. They had a finite budget for limit testing as well. I have always been amazed what was achieved with the lowly slide rule era by those highly skilled and courageous engineers. In so many fields, but certainly including those specific examples from aeronautical engineering, the p51, and the SR71. 2 Quote
aviatoreb Posted August 29, 2020 Report Posted August 29, 2020 13 hours ago, kortopates said: So lets say it was 20 people per wing X2 and assume 150 lbs average per person - that's only 3000 lbs per wing totaling 6000 lbs The Mooney like most every GA aircraft is certified to handle a positive load factor of 3.8 G's. With a Max gross weight of 2575 lbs. X 3.8 = 9,785 lbs! Clearly the wing has to hold up all that weight. So there is nothing remarkable about putting all those people on the wing, the weight is still well below certification requirements for any light GA plane. Nor does it relate directly to any of the V speeds other than saying you can exceed that 3.8 G limit above maneuvering speed with a sudden full defection of any flight control.. But it sure was effective marketing though since many were very impressed by it! Your analysis is spot on - thank you! The detail that did always make me wonder about for that picture - the people must have been told to stand very carefully in specific locations on the spars of the airplane since I would think that standing on the skins themselves not over the spars would deform the skins and perhaps even break the skins. As much as I am sure the wing could take it - I wouldn't want 40 people standing on my wings, even if they were my friends... Quote
David Lloyd Posted August 29, 2020 Report Posted August 29, 2020 The OP asked why so slow? Va is the speed above which full control displacement may overstress part of the airplane. Usually we think of pulling the wheel back hard enough to pull more than 3.8 gs that our Mooneys are rated for and breaking off a wing or tail. On some of the older designs, sometimes limits were set lower than the actual but unknown limit (we know it is this strong by quite a bit but don't know exactly how strong). There is some safety factor built and regulated into that. I think a 50% factor without failure. A lot of other stuff can break: seats, control mechanisms, motor mounts, crankshaft flange attached to that big gyroscope, etc. Examine Va a little and find it is also weight dependent and should be thought as a maximum number. Flying by yourself with half tanks and no baggage? Va decreases by a factor of actual weight compared to maximum gross weight. Did I say that correctly? Vno is a whole other set of stuff. I think certified planes are tested to Vd, 10% over Vne. Some other airplanes that are rated for 4.4 gs do have a higher Va than our Mooneys, all things considered. RVs are 6 gs at lower than gross weights, either 4 or 4.4 at gross. Did you read that link above about the K/Rocket? Descending turn in cloud from 9600 to 8200 at an average of 3500 FPM and a groundspeed of 240 knots when it came apart. Earlier in level flight I think the groundspeed was about 190 knots. NTSB said the there was some kind of induced flutter that removed the elevators, then horizontal stab, then rudder, then wings and deposited them over a half mile. Mooney said flutter could occur above 241 knots calibrated air speed. Vne is 196 knots. Any doubt about what happened? Can any of you Rocket guys descend at 3500 FPM without exceeding Vne without pulling all power? No, didn't think so. Imitate those numbers and get the same results. I think that plane was about to dig a hole, it just got broke on the way. The picture of 20 people on the wing, I remember seeing a picture like that of a J. Maybe a reenactment? I also remember reading, probably in Flying about Mooney testing the ultimate strength of their wing. Their test rig broke at something like 11 gs. Quote
carusoam Posted August 29, 2020 Report Posted August 29, 2020 6 hours ago, Jeff Reiter said: how do rv's and other comparable aircraft compare with our speed limitations? I understand the concept of breaking up, but a "fast" Mooney M20C with a 132 mph limitation? seems ridiculous. What about later model Mooney's. what is their rough air limitation and why higher than the C? Someone said that the tail may come off, but that only happened with a wooden tail, so why blame the tail? I love my Mooney C, but I want to fully understand why so slow? Jeff are you looking for a cognitive debate, or are you seriously interested in an answer? If your C has a 132mph limit... That is what was published in your POH... POH limitations are set via testing the airframe... under many in-flight conditions. POH writers use Margins of safety to ensure the plane is reusable after a flight... The real world has more conditions than can be planned for... or budget wise tested for... Most often, the plane isn’t at fault, when its limitations get exceeded... The more you know about your plane, the better off you will be... it is very helpful to understand why Va works... and how it is affected by gross weight... Imagine stalling being the better choice while in cruise, over tearing the wings off. (Tough choices, yours to make) Imagine not remembering how Va affects the stall speed as you descend into a turbulent zone above the ground... Imagine what it is like when you remember you left the T/O flaps in while accelerating towards cruise speed... Or, leaving the gear up until that last Gumps check.... Imagine thinking 132mph isn’t very fast... What other vehicle do you have access to... that is this light, this old, this not brand new... to go this fast in, comfortably and efficiently? Keep in mind other limitations that are greater... VFR into IMC.... Running out of fuel... IFR into thunderstorms... Icing... Don’t be too focussed on one limitation, when there are several that can be equally dangerous... Thanks to Krawler for the nifty color graphics... Imagine using distraction as a sales tool... Hey everybody! (non-educated consumer...) look how strong our wing is! (inverted bending load) If our plane can withstand this advertising phenomena... it is surely the right plane for you.... The competitor’s plane that is known for falling apart when control was lost in IMC... wasn’t the main lifting wing... Pay no attention to the man behind the curtain.... These are not the drones you are looking for... PP thoughts only, not a CFI... Best regards, -a- 1 1 Quote
aviatoreb Posted August 29, 2020 Report Posted August 29, 2020 1 hour ago, David Lloyd said: Did you read that link above about the K/Rocket? Descending turn in cloud from 9600 to 8200 at an average of 3500 FPM and a groundspeed of 240 knots when it came apart. Earlier in level flight I think the groundspeed was about 190 knots. NTSB said the there was some kind of induced flutter that removed the elevators, then horizontal stab, then rudder, then wings and deposited them over a half mile. Mooney said flutter could occur above 241 knots calibrated air speed. Vne is 196 knots. Any doubt about what happened? Can any of you Rocket guys descend at 3500 FPM without exceeding Vne without pulling all power? No, didn't think so. Imitate those numbers and get the same results. I think that plane was about to dig a hole, it just got broke on the way. And worse than that even - it was likely in convective weather - so those speeds in extreme turbulent air. So the gust loading must have been huge at the same time the speed was huge. Where as the speed should have been not out of the yellow in anything but smooth air but better Va in turbulent air. So the speeds were more than double Va. 1 Quote
Guest Posted August 29, 2020 Report Posted August 29, 2020 Mooney wings don’t compare to these wings! Clarence Quote
ZuluZulu Posted August 29, 2020 Report Posted August 29, 2020 18 hours ago, aviatoreb said: That one rocket break up - this is from a vague memory of reading about it many years ago - was an airplane in convective leading to loss of control and then dramatically overspending in a dive. I, too, have been known to dramatically overspend in a dive. BT, DT. 1 2 Quote
ZuluZulu Posted August 29, 2020 Report Posted August 29, 2020 21 hours ago, Jeff Reiter said: I saw an old picture of a Mooney m20c with about 20 people standing on the wing, showing the extraordinary strength of the money wing. So why is 140 miles per hour the limit for speed in rough air? this makes no sense to me. if it has a strong wing, then why isn't the speed more like 175 miles an hour for rough air? Was it this photo or a different one? Quote
carusoam Posted August 29, 2020 Report Posted August 29, 2020 Speaking of reenactment... Many an MSer stood on the wings of M20E #1 a couple of years ago, prior to it being parted out... It really demonstrated how many people can stand on a wing that is 50 years old... Still has nothing to do with how well a real plane survives the awesome forces of a pilot losing control of his plane... 1) Airplane manufacturers test things up to a certain limit.... (of their choosing) 2) They publish those limits with a margin of safety in the POH... 3) When flown within the limits of the POH... the plane is nearly guaranteed to be reusable for the next flight... 4) The edges of performance get a bit fuzzy, and can change with age, cleanliness, and the weather... 5) it is highly recommended to stay within the limits of the POH... 6) when exceeding the limitations set in the POH, you become known as a test pilot... 7) Good test pilots know the limitations of their machines, and their own skills, and have a fitting plan B, when plan A falls apart... It wasn’t my fault... the DIVE caused my over spending.... -a- Quote
carusoam Posted August 29, 2020 Report Posted August 29, 2020 Just now, ZuluZulu said: Was it this photo or a different one? Expect that to be the official re-enactment of the original black and white photo taken back in Al Mooney’s days... About the forces in the pic.... Notice where the gear is compared to most of the load... this is why people have mentioned the negative Gs being applied to what looks like an ordinary positive load... The balance of forces keep everything from accelerating.... Best regards, -a- Quote
aviatoreb Posted August 30, 2020 Report Posted August 30, 2020 5 hours ago, ZuluZulu said: I, too, have been known to dramatically overspend in a dive. BT, DT. Yeah. Autospell didn't like over-speed and changed it to what it liked better - overspend. Autospell. gotta love it - not. 1 Quote
PT20J Posted August 30, 2020 Report Posted August 30, 2020 9 hours ago, aviatoreb said: Your analysis is spot on - thank you! The detail that did always make me wonder about for that picture - the people must have been told to stand very carefully in specific locations on the spars of the airplane since I would think that standing on the skins themselves not over the spars would deform the skins and perhaps even break the skins. As much as I am sure the wing could take it - I wouldn't want 40 people standing on my wings, even if they were my friends... Well, actually not! In flight, the wing lifts the fuselage. Remember the lift vector? It points upward. These folks are sitting on top of the wing. Their (combined) weight vector points downwards. Another way to think about it is that the wing supports the fuselage in flight. The weak point is where the wing attaches to the fuselage. That's why some airplanes have a zero fuel weight limitation. Some of the gross weight has to be out in the wing or the wing attach bending moment gets too high. Skip 3 Quote
aviatoreb Posted August 30, 2020 Report Posted August 30, 2020 36 minutes ago, PT20J said: Well, actually not! In flight, the wing lifts the fuselage. Remember the lift vector? It points upward. These folks are sitting on top of the wing. Their (combined) weight vector points downwards. Another way to think about it is that the wing supports the fuselage in flight. The weak point is where the wing attaches to the fuselage. That's why some airplanes have a zero fuel weight limitation. Some of the gross weight has to be out in the wing or the wing attach bending moment gets too high. Skip ...so then what - I need to call back my 40 friends I invited to the hangar for tomorrow to stand on my wing for a mooneyspace picture? 1 Quote
kortopates Posted August 30, 2020 Report Posted August 30, 2020 ...so then what - I need to call back my 40 friends I invited to the hangar for tomorrow to stand on my wing for a mooneyspace picture? Yeah, we need to hang them from the wing to test the positive G loading or use the folks on top to test the -G loading. Skip and Clarence are right - I had the sign backwards and signs are important!But I don’t think we’ve ever seen a Mooney wing separate from cockpit - the steel cage ensures it’s well attached to the spars. Sent from my iPhone using Tapatalk 2 Quote
Blue on Top Posted September 28, 2020 Report Posted September 28, 2020 Back into the fire! (I don't think these internal to the post emojis count against me ... although I have over-emojied on Facebook before, too ) WINDSHIELD - If the windshield were to ever come out, it would be pulled away from the airplane. The exception is a bird/drone strike where it will come inward. WHAT FAILS (wing, tail or fuselage) - It depends on the margin of each of these assemblies. There is a 50% safety factor (or more) on all parts to account for manufacturing tolerances, corrosion, fatigue, etc. There may be "margin" above these values because materials don't come in infinite thicknesses (composite structures are design to the 150% safety factor) FLYING SURFACES - These are the wing, horizontal tail surfaces and vertical tail surfaces. Loads imposed on them are proportional to the square of airspeed (Q or dynamic pressure). PEOPLE ON WING - Totally a marketing thing. I believe that Clyde Cessna was the first to do this to show Walter Beech that an internally-braced monoplane could be as strong as a biplane. BTW, Clyde and Walter were good friends. The load on the wing is not only negative Gs, but it is also trivial. Each wing (left and right) take a little less than half the gross weight PER G. So, divide your gross weight by 2, multiply it by maximum, maneuvering G load (3.8), and then add the 50% safety factor. Now you know what the wing will take. ZERO FUEL - Most small, GA airplanes don't have a zero fuel weight (a couple do). Trying to keep this simple, let's say your Mooney has a 1,000 lbs. useful load. We fill the tanks first (600 lbs.) and put the remaining 400 lbs. in the cabin with a couple people and baggage. Fuel actually relieves wing bending loads. In other words, the forces trying to bend a wing would be half the gross weight, minus half the weight of the wing, minus half the fuel weight (i.e. 2600/2 minus 250 minus 300 (or 750 lbs. ... per G)). Now if we fuel for a short trip (100 lbs.) and fill the cabin with people and baggage, it looks a lot different. It becomes 2600/2 minus 250 minus 50 (or 1000 lbs. ... per G). Wing fuel relieves wing bending loads. Vne - Vne is typically determined by several factors with drag and flutter MARGIN being the major players. The airplane must be shown to be free from flutter 20% beyond Vdive which is typically 50 mph/knots beyond Vne). There are several upset maneuvers that must be flown to prove an airplane flown at Vne will not exceed Vdive during these maneuvers. Va - Now for the big one. Va is the airspeed at which SINGLE, full-travel flight control inputs will not break the airplane OR the flight control systems. Think about that really, really long aileron push-pull tube in the leading edge of the wing (I know more than I can say). Why does Va change with weight? It's not the wing or horizontal tail ... it's everything else. Here's a short example. Say we gross at 3,000 lbs. with a 4G limit (I'm making the numbers easier). The wings must lift 12,000 lbs. Now, with the same airplane, we fly at 1,500 lbs. At 4G the wings are only lifting 6,000 lbs. At the lighter weight, we could go to 8Gs to arrive at the same 12,000 lbs. of wing lift. BUT, and here's the kicker, everything else in the airplane still has the 4G limit (and isn't dependent/driven by aerodynamic (airspeed) loads). Let's take a 200 lbs. pilot for example, at 4Gs that's 800 lbs. The seat, attach structure, floor, etc. are designed for 800 lbs. plus a 50% margin for 1,200 lbs. at that location. Now, at the lighter weight, although the wing is good to 8Gs, the pilot seat, attach structure and floor are NOT designed for 1,600 lbs! This is also the case for the engine, engine mount, baggage compartment, etc. Interestingly, I just had a customer explaining a camera installation in a Cessna 310. The whole camera mount (and large hole in the belly of the airplane) were all good. Then he casually, matter-of-factly, mentioned putting 250 lbs. of camera electronics in the baggage compartment. When I asked what the baggage limitation was he stated 150 lbs. They are now rearranging equipment to satisfy that limitation. Hope this helps! And thanks, @carusoam, it's good to be alive 5 1 Quote
RobertGary1 Posted September 28, 2020 Report Posted September 28, 2020 On 8/28/2020 at 4:20 PM, Jeff Reiter said: I saw an old picture of a Mooney m20c with about 20 people standing on the wing, showing the extraordinary strength of the money wing. So why is 140 miles per hour the limit for speed in rough air? this makes no sense to me. if it has a strong wing, then why isn't the speed more like 175 miles an hour for rough air? Hmm, mine is 175 mph. -Robert Quote
RobertGary1 Posted September 28, 2020 Report Posted September 28, 2020 On 8/29/2020 at 11:45 AM, carusoam said: it is very helpful to understand why Va works... and how it is affected by gross weight... He's asking about Vno, not Va. He's talking about the speed limited to smooth air... Vno. The maximum structural cruising speed. Do not exceed this speed except in smooth air. The upper limit of the green arc. Va is maneuvering speed. -Robert 1 Quote
ArtVandelay Posted September 28, 2020 Report Posted September 28, 2020 I believe that all of the tails are held on by the same two 1/4” diameter bolts. ClarenceAnd our engines are held on by 4 such bolts. :-) Quote
ArtVandelay Posted September 28, 2020 Report Posted September 28, 2020 I wonder how much of the wing strength is necessary to support the landing gear and the shock loads from hard landings. I believe the plane is dropped from several feet for certification testing. Quote
RobertGary1 Posted September 28, 2020 Report Posted September 28, 2020 1 hour ago, ArtVandelay said: I wonder how much of the wing strength is necessary to support the landing gear and the shock loads from hard landings. I believe the plane is dropped from several feet for certification testing. Isn't that test just for seat G forces? The gear can push up into the wing and dump fuel and still pass I thought. -Robert Quote
carusoam Posted September 29, 2020 Report Posted September 29, 2020 5 hours ago, RobertGary1 said: He's asking about Vno, not Va. He's talking about the speed limited to smooth air... Vno. The maximum structural cruising speed. Do not exceed this speed except in smooth air. The upper limit of the green arc. Va is maneuvering speed. -Robert in discussions of breaking up in flight, I often reference Maneuvering speed... Long story short... I don’t recall what exactly the details were that would bring up planes falling apart... But, it is good to understand how staying under maneuvering speeds will better protect the plane from folding.... ...and, that changes with gross weight... +1 for BoT’s input of the day.... It is good to be alive... Now I have to go re-study all the Vspeed names... in case I got that incorrect... Best regards, -a- Quote
ArtVandelay Posted September 29, 2020 Report Posted September 29, 2020 Isn't that test just for seat G forces? The gear can push up into the wing and dump fuel and still pass I thought. -Robert Don’t think so, I found this verbiage, no mention of seats: Sec. 23.723 — Shock absorption tests. It must be shown that the limit load factors selected for design in accordance with §23.473 for takeoff and landing weights, respectively, will not be exceeded. This must be shown by energy absorption tests except that analysis based on tests conducted on a landing gear system with identical energy absorption characteristics may be used for increases in previously approved takeoff and landing weights.The landing gear may not fail, but may yield, in a test showing its reserve energy absorption capacity, simulating a descent velocity of 1.2 times the limit descent velocity, assuming wing lift equal to the weight of the airplane. Quote
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