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#31
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preparing for commercial oral and practical
Mark T. Dame wrote:
For both my private and commercial rides I was required to do a W&B for takeoff and landing fuel loads. Additionally, for my commercial ride, I had to account for the gear position, as Matt said, giving you four different configurations. This was another point of emphasis for my DE. Different examiners have different favorite topics. For the purpose of the original question, my suggestion stands. I'm not questioning your experience, just relaying mine. My private and instrument rides were with a retired USAF type popularly locally known as Colonel Goddammit. I also did some of my single and multi 135 checkrides with him. He had his quirks to be sure and God help you if you attracted his attention. First his fingers would start tapping his legs, faster and faster until finally the blast would come, blistering the side of your face. You'd be deaf in one ear and your hair would look like you'd been riding a motorcycle... sideways. Sometimes I'd **** up intentionally just to get it over with. My commercial checkride was with a more mellow character who was a DE, former chief pilot for a commuter, and current chief pilot for a high priced charter outfit. Multiengine checkride was with a similar type associated with one of those weekend multi schools. Later 135 rides were with an airline captain who owned a courier service on the side and with a longtime freight dog chief pilot. I never had to do W&B in more than one configuration my entire flying career. Frankly, until I read the OP's note a couple of days ago, I'd never heard of this being done. Now it's my turn to say: I'm not doubting your experience; it's just very different from mine. Could it be this is one of those quirks courtesy of somebody at your local FSDO who focuses on this as a way to trip people up? -- Mortimer Schnerd, RN mschnerdatcarolina.rr.com |
#32
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preparing for commercial oral and practical
Mark T. Dame wrote: Additionally, you do have the gear in both positions in flight. You have it down at take off. You need to make sure that putting it up isn't going to put your CG outside of the envelope right after take off when you are still low, slow, and nose high. This could lead to a departure stall. When you are landing, you put your gear down well before you touch down, and you will be low and slow on final. The difference between gear up and down may be a factor. Bull****. Somebody mentioned that the gear will make a 1/2" difference in CG. I personally don't believe that, it's way too much. But assuming it's true no airplane falls out of the sky by going from the CG on the aft limit to 1/2" past the aft limit. |
#33
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preparing for commercial oral and practical
Mortimer Schnerd, RN wrote:
My private and instrument rides were with a retired USAF type popularly locally known as Colonel Goddammit. Talk about unneeded pressure on a checkride... I never had to do W&B in more than one configuration my entire flying career. Frankly, until I read the OP's note a couple of days ago, I'd never heard of this being done. Which just goes to show, even though we all fly by the same regulations, things are not always the same. You can see those differences even from FBO to FBO in the same area. Could it be this is one of those quirks courtesy of somebody at your local FSDO who focuses on this as a way to trip people up? Possibly, but I would put my money on the DE. She has her own ideas about what's important and what's not. She also tends to be pretty thorough, but like most DE's she has her favorite things. My CFI (who had done his commercial checkride with her a couple of years earlier) gave me a list of things that I absolutely had to have ready. I don't recall the entire list, but the W&B with both gear configurations was one of them. -m -- ## Mark T. Dame ## CP-ASEL, AGI ## insert tail number here ## KHAO, KISZ "There is a theory which states that if ever anyone discovers exactly what the Universe is for and why it is here, it will instantly disappear and be replaced by something even more bizarre and inexplicable. There is another which states that this has already happened." -- The Restaurant at the End of the Universe, Douglas Adams |
#34
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preparing for commercial oral and practical
Newps wrote:
Bull****. Somebody mentioned that the gear will make a 1/2" difference in CG. I personally don't believe that, it's way too much. You don't have to believe it. If it's in the book, that's what you use. It's not a matter of opinion. It is what it is. But assuming it's true no airplane falls out of the sky by going from the CG on the aft limit to 1/2" past the aft limit. No it doesn't. It affects the stability, the stall speed, and the ability to recover from a stall. In an Arrow, I don't think it will matter a hill of beans, but in a Cutlass, it might. But the point of the conversation is preparing for the commercial checkride, not whether or not raising the gear on a specific model of airplane will move the CG too far aft for safe operation. -m -- ## Mark T. Dame ## CP-ASEL, AGI ## insert tail number here ## KHAO, KISZ "Help stamp out and abolish redundancy!" |
#35
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preparing for commercial oral and practical
Somebody mentioned that the gear will make a 1/2" difference in CG. I personally don't believe that, it's way too much.
I showed the calculation. It's in the Arrow book. But assuming it's true no airplane falls out of the sky by going from the CG on the aft limit to 1/2" past the aft limit. No, but with thinking like that, if you decided to fly an inch out of CG and ended up an inch and a half... Jose -- Quantum Mechanics is like this: God =does= play dice with the universe, except there's no God, and there's no dice. And maybe there's no universe. for Email, make the obvious change in the address. |
#36
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preparing for commercial oral and practical
Most of the DE's that I've encountered have a certain amount of "teacher" in
them that is very often only slightly contained. I feel that the DE's who ask about CG changes with gear movement are trying to teach more than torture a student the fact that you don't necessarily have to move people, baggage, cargo, or fuel to have a CG change. Sometimes, depending on the airplane ( and you are preparing to fly bigger and more complex airplanes) an aircraft's CG will change due to a normal flight operation, such as extending or retracting the gear. I don't think the magnitude of the CG change that is the emphasis of the DE's questions or teachings, rather the fact that it can change. I think this lesson is meant to point out the importance of a complete understanding of W&B as applied to each particular aircraft using the proper W&B and POH information. Jim |
#37
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preparing for commercial oral and practical
Mortimer Schnerd, RN wrote:
Mark T. Dame wrote: For both my private and commercial rides I was required to do a W&B for takeoff and landing fuel loads. Additionally, for my commercial ride, I had to account for the gear position, as Matt said, giving you four different configurations. This was another point of emphasis for my DE. Different examiners have different favorite topics. For the purpose of the original question, my suggestion stands. I'm not questioning your experience, just relaying mine. My private and instrument rides were with a retired USAF type popularly locally known as Colonel Goddammit. I also did some of my single and multi 135 checkrides with him. He had his quirks to be sure and God help you if you attracted his attention. First his fingers would start tapping his legs, faster and faster until finally the blast would come, blistering the side of your face. You'd be deaf in one ear and your hair would look like you'd been riding a motorcycle... sideways. Sometimes I'd **** up intentionally just to get it over with. My commercial checkride was with a more mellow character who was a DE, former chief pilot for a commuter, and current chief pilot for a high priced charter outfit. Multiengine checkride was with a similar type associated with one of those weekend multi schools. Later 135 rides were with an airline captain who owned a courier service on the side and with a longtime freight dog chief pilot. I never had to do W&B in more than one configuration my entire flying career. Frankly, until I read the OP's note a couple of days ago, I'd never heard of this being done. Now it's my turn to say: I'm not doubting your experience; it's just very different from mine. Could it be this is one of those quirks courtesy of somebody at your local FSDO who focuses on this as a way to trip people up? I think it is just different DEs checking different things. To me W&B is one of the things you don't skip as discretionary. Much of the stuff covered on a check ride is stuff that won't kill you if you don't know all of the details. Things like what every stinkin antenna on the airplane is for. I can count on zero fingers the number of times in 30 years of flying that I had to know that to save my life. OTOH, if you take off at the aft CG limit and retracting the gear puts you 1/2" or so past the aft limit, this has the potential to kill you. Same with fuel burn. If you have an airplane that shifts CG aft with fuel burn, this can cook your goose later in the flight. Violating rules of the FAA is one thing, but trying to violate the rules of physics is quite another. Matt |
#38
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preparing for commercial oral and practical
Mark T. Dame wrote:
Jose wrote: Now, as Jose pointed out, on the Arrow it's not very significant Actually I wasn't implying (half an inch) that it wasn't very significant - when the CG range is only a handful of inches, it's significant. And certainly when you're near the edge it bears watching. At the risk of arguing semantics, I wasn't saying "insignificant" only "not very significant". I don't have my Arrow book here, but I believe the CG range is around 10 to 12 inches. If you load well within the envelope, the half inch is not going to have an appreciable affect on aircraft performance. But I'm getting off topic: what should someone expect on their commercial checkride. Make sure to do a W&B for gear up and gear down with takeoff fuel and landing fuel. If the examiner doesn't care, then no big deal, but if the examiner wants to see it and you didn't do it, then you have a strike against you. On checkrides, you'll get plenty of strikes without creating ones that could be easily avoided by a little bit of prep work. Even if the examiner doesn't want or expect it, it can't hurt to have it (unless you do it wrong). Yes, and it is also just good operating practice, check ride or no. I have it in my spreadsheet so that it calculates both CG locations and all I have to do is enter the fuel expected at takeoff and at landing. Balance isn't something to be taken lightly. Being 200 lbs over gross typically isn't a big deal (I'm NOT recommending it), but being an inch aft of the CG limit can be fatal. Matt |
#39
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preparing for commercial oral and practical
Jose wrote:
Somebody mentioned that the gear will make a 1/2" difference in CG. I personally don't believe that, it's way too much. I showed the calculation. It's in the Arrow book. But assuming it's true no airplane falls out of the sky by going from the CG on the aft limit to 1/2" past the aft limit. No, but with thinking like that, if you decided to fly an inch out of CG and ended up an inch and a half... I don't see a half inch of change, but it is still a fair amount (0.34"). Here is my spreadsheet calculation from my last flight. Unfortunately, the formating from Excel gets hosed pretty badly. The point is that nobody knows for sure how far past the aft limit is too far for any given flight condition and operating past the aft limit at all is just dumb. The only thing dumber is not even knowing that you are aft of the limit. Matt Piper Arrow PA28R-3009 N3705T Quantity Weight Arm Moment Airplane empty 1552.65 84.53 131253.15 Oil 15.00 29.50 442.50 Fuel 50 300.00 95.00 28500.00 Pilot and front seat passenger 385.00 85.50 32917.50 Rear passengers 125.00 118.10 14762.50 Baggage 30.00 142.80 4284.00 Gear retraction 819 2407.65 88.11897493 212159.65 Gear down 88.45914066 212978.65 Gear up Gross Weight (2500 max) Center of Gravity Total Moment |
#40
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preparing for commercial oral and practical
"Mark T. Dame" wrote in message ... Newps wrote: Bull****. Somebody mentioned that the gear will make a 1/2" difference in CG. I personally don't believe that, it's way too much. You don't have to believe it. If it's in the book, that's what you use. It's not a matter of opinion. It is what it is. The POH for this PA-28R has "Moment due to retracting landing gear = +819 in-lbs" beneath the CG Range and Weight Chart, so I'm going to plan accordingly for the exam. Thanks for the heads up! -c |
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