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#61
January 11th 04, 12:45 AM
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"Tony Cox" wrote in message link.net...
"Dan Thomas" wrote in message om... The only times I have heard of engine mounts failing on light airplanes is when a prop throws part of a blade, or maybe the whole blade on a constant-speed prop. The imbalance is more than enough to rip the engine off the airplane. Blades will fail when propeller nicks are left untreated and cracks develop. The prop is the most highly stressed bit of metal on the whole airplane, and THAT'S what pilots should be concerned about, not engine mounts. Nah. Properly designed engine mounts would never let that happen. Cessna 185 operated by JAARS Inc, South America, about ten years ago. Threw a blade and the engine tore off the mount before the pilot could shut it down. It turned sideways in the cowl, and the cowl was the only thing keeping it from departing entirely. The O-520 mount is a bed mount; if it had been the usual rear mounting the engine would have fallen off. Dan 
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#62
January 11th 04, 12:50 AM
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*****The O-520 mount is a
bed mount; if it had been the usual rear mounting the engine would have fallen off.**** No, it isn't a bed mount in a Cessna 185. The mount attaches to fourpoints on the firewall. A cessna 206, however, has a bed mount. Karl "curator" N185KG
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#63
January 11th 04, 01:51 AM
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"Gary Drescher" wrote in message
news:j8YLb.15333$na.12586@attbi_s04... "Tony Cox" wrote in message ink.net... Hi Gary. As Julian pointed out, there may be terminology problems here. It may well be that the 172 POH defines Va as you say, but in that case Cessna are telling you something more -- they are telling you specifically that their Va is defined to meet the equality condition in 23.335. So it is really just their own private definition, applicable to that plane and model year only. Yeah, except that the POH (or rather aircraft manual) acquires regulatory force from the FARs, so it's not just a private definition; rather, as usual with the FAA, it's one of several mutually inconsistent definitions that's in official use. (For what it's worth, the Piper Arrow POH gives essentially the same definition as the C172P POH.) I suppose its that old terminology problem again. What can I say? The FAR's are quite explicit on how Va is defined, and that is most definitely _not_ what is in the POH. Thank heavens for the 50% safety factor, or we'd have planes falling out of the sky all over. But thinking again, I don't see the problem even if the POH inherits regulatory authority. It is, after all, only true in the context of that particular make and model (which is consistent with the FAR definition when 23.335 takes the equality). It's only when you extend that definition to cover other planes that it doesn't ring true. Well, the control surfaces don't care how much weight is in the plane (at least to first order). If you yank them lightly loaded, you'll stress the cables and hinges just the same as if you were over gross. So that Va'(w) is flat if you plot it against w. Right, but aren't the wings and control surfaces protected by Vno (a weight-invariant force limit) rather than by Va (a weight-dependent acceleration limit)? That's how I think about it anyway, even if it doesn't match (some of) the official definitions. Vno doesn't say anything about control input. I've always wondered how it is established. Seems like a test pilot would earn his or her money finding out. I've always assumed that the windshield would be the first thing to go... Hope you've found this rant more informative than pedantic! Sure, and I don't mind pedantry anyway. :-) Hey thanks! A strangely interesting subject, don't you think? -- Dr. Tony Cox Citrus Controls Inc. e-mail: http://CitrusControls.com/
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#64
January 11th 04, 01:58 AM
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"Dan Thomas" wrote in message
om... "Tony Cox" wrote in message link.net... "Dan Thomas" wrote in message om... The only times I have heard of engine mounts failing on light airplanes is when a prop throws part of a blade, or maybe the whole blade on a constant-speed prop. The imbalance is more than enough to rip the engine off the airplane. Blades will fail when propeller nicks are left untreated and cracks develop. The prop is the most highly stressed bit of metal on the whole airplane, and THAT'S what pilots should be concerned about, not engine mounts. Nah. Properly designed engine mounts would never let that happen. Cessna 185 operated by JAARS Inc, South America, about ten years ago. Threw a blade and the engine tore off the mount before the pilot could shut it down. It turned sideways in the cowl, and the cowl was the only thing keeping it from departing entirely. The O-520 mount is a bed mount; if it had been the usual rear mounting the engine would have fallen off. What's a bed mount, Dan? I've always thought (hoped) that my 182 cowling would contain the engine. And there is always the fuel line, throttle cable, and battery cable as a last line of defense 
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#65
January 11th 04, 01:59 AM
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"Tony Cox" wrote in message
ink.net... But thinking again, I don't see the problem even if the POH inherits regulatory authority. It is, after all, only true in the context of that particular make and model (which is consistent with the FAR definition when 23.335 takes the equality). It's only when you extend that definition to cover other planes that it doesn't ring true. Agreed. In my short few years as a pilot so far, the planes I've flown (152s, 172s, Warriors, and Arrows) have all had essentially the same definition of Va in their POHs, so I didn't realize it wasn't universal. Hey thanks! A strangely interesting subject, don't you think? Yup. Thanks for the discussion! --Gary -- Dr. Tony Cox Citrus Controls Inc. e-mail: http://CitrusControls.com/
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#67
January 11th 04, 09:21 AM
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On Fri, 09 Jan 2004 02:17:48 GMT, Dave S
wrote: Art.. With all due respect.. you really need to go and review the section on angle of attack and accelerated stalls.. I've been able to intentionally stall a light (ASEL) aircraft in smooth air at Va.. its called a steep turn with extra back pressure. It has nothing to do with "tailwind gusts".. it has EVERYTHING to do with angle of attack. It ends up being a bit slower than Va, but I practice steep turns at 60 degree bank with the stall warning horn blowing. Then add a bit of extra pull to get the beak. Roger Halstead (K8RI & ARRL life member) (N833R, S# CD-2 Worlds oldest Debonair) www.rogerhalstead.com Dave ArtP wrote: On Fri, 09 Jan 2004 01:29:05 GMT, Robert Moore wrote: And I thought that every private pilot was taught that an airplane can be stalled at any airspeed and any attitude. I assure you that I, or a gust of sufficient value can stall your SR20 at 120 kts. By my calculations, if I am flying in cruise it would take a tail wind gust of 56 knots to stall me. I suspect that would fall in the category of sever turbulence and I don't think there is any airspeed that would be safe under those conditions in a single engine normal category aircraft. In any case a stall at cruise altitude should not be a problem but parts (like the engine or the wings) falling off the aircraft would be.
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#68
January 11th 04, 09:29 AM
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On 9 Jan 2004 14:18:14 -0800, (Dan Thomas)
wrote: (Doug) wrote in message . com... Kershner's "The Advanced Pilot's Flight Manual" has the following definition for Va. Va - The maneuvering speed. This is the maxiumum speed at a particular weight at which the controls may be fully deflected without overstressing the airplane. Note that this definition DOES NOT say that the airplane will stall before it breaks due to turbulence. Now, Va is commonly taught as turbulent air penetration speed. But nowhere in the definition does it say that Va will protect the airframe from damage due to turbulence. Doesn't have to. Pulling full up elevator loads the wings the same as a strong vertical gust; both increase AOA and the airplane and occupants both feel increased G loading. At or below Va the airplane will stall and thereby unload the structure somewhat if the AOA reaches stall angle, and the load factor won't exceed the designed structural limits. IF you are cruising at Va and encounter a vertical gust that causes a stall right at the design limit you survive. What happens when you hit a vertical gust of twice the velocity of the first? According to the ABS and Airsafety Foundation, you are going to break your airplane. Va is lower at lower weights because the airplane is going to tend to change direction more easily in a gust or sharp pull-up, and the directional change keeps AOA below stall angle and maintains the high wing loading. Lowering Va will allow it to stall sooner. Everybody fears wing failure, but many airplanes will suffer tail failure first. Bonanzas and 210s are famous for such accidents, with a Roger Halstead (K8RI & ARRL life member) (N833R, S# CD-2 Worlds oldest Debonair) www.rogerhalstead.com VFR pilot entering IMC and losing control. He pops out of the overcast at 400 feet in a screaming spiral dive, and promptly pulls up hard. The stabilizer fails downward, then the airplane pitches forward onto its back and the wings fail downward (negative Gs). Dana
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#69
January 11th 04, 02:38 PM
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Roger Halstead wrote
IF you are cruising at Va and encounter a vertical gust that causes a stall right at the design limit you survive. What happens when you hit a vertical gust of twice the velocity of the first? According to the ABS and Airsafety Foundation, you are going to break your airplane. Again referencing a couple of previous posts: ------------------------------------------------------- Quoted from Aerodynamics for Naval Aviators: "As a general requirement, all airplanes must be capable of withstanding an approximate effective +/- 30 foot per second gust when at maximum level flight speed for normal rated power. Such a gust intensity has relatively low frequency of occurrence in ordinary flying operations. The highest reasonable gust velocity that may be anticipated is an actual veritical velocity, U, of 50 feet per second." ------------------------------------------------------- And from FAR 23 Section 23.333: Flight envelope (c) Gust envelope. (1) The airplane is assumed to be subjected to symmetrical vertical gusts in level flight. The resulting limit load factors must correspond to the conditions determined as follows: (i) Positive (up) and negative (down) gusts of 50 f.p.s. at VC must be considered......... (ii) Positive and negative gusts of 25 f.p.s. at VD must be considered........... -------------------------------------------------------- Now since 50 fps is the highest reasonable gust that may be anticipated, and all aircraft are designed to withstand this gust all the way up to Vc, what causes the wings to come off? As Dana has posted: VFR pilot entering IMC and losing control. He pops out of the overcast at 400 feet in a screaming spiral dive, and promptly pulls up hard. The stabilizer fails downward, then the airplane pitches forward onto its back and the wings fail downward (negative Gs). Yes, I understand that older aircraft may have been certificated to only a 30 fps gust value, but as pointed out in AFNA above, that will be encountered very infrequently and in my opinion, never outside of a thunderstorm. In fact, the aiframe must withstand the 25 fps gust (not far from 30 fps) all the way to the maximum demonstrated dive speed. The aircraft is already designed for the maximum anticipated gust. There is no gust "twice the velocity" for which the aircraft is designed. Is there some reason that you don't copy/paste or at least provide a url for the material that you have referenced? Who is (are) the ABS and what engineering credentials are possesed by members of the AOPA's Airsafety Foundation? Bob Moore
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#70
January 11th 04, 08:30 PM
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"karl" wrote in message ...
*****The O-520 mount is a bed mount; if it had been the usual rear mounting the engine would have fallen off.**** No, it isn't a bed mount in a Cessna 185. The mount attaches to fourpoints on the firewall. A cessna 206, however, has a bed mount. Karl "curator" N185KG The mount attaches to the firewall, but extends underneath the engine and attaches to four mounts on the *bottom* of the case. These are the mounts that failed, not the tubing. The engine in question was resting on that structure when the noise was finished.
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