# General Aviation folk, I need your help again ~ **URL:** \ **Category:** In My Humble Opinion\ **Created:** [February 19, 2016, 12:30pm UTC](https://boards.straightdope.com/t/general-aviation-folk-i-need-your-help-again/746545 "2016-02-19T12:30:57Z")\ **Posts on this page:** 11\ **Page:** 4
**Author:** ![LSLGuy](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/lslguy/32/5813_2.png) [@LSLGuy](https://boards.straightdope.com/u/LSLGuy)\ **Post date:** [March 16, 2016, 11:39pm UTC](https://boards.straightdope.com/t/general-aviation-folk-i-need-your-help-again/746545/61 "2016-03-16T23:39:27Z")
> [@Magiver](#): > > … > You’d be surprised at how many people can’t look at a prop and tell which way it’s supposed to turn. :eek: Those people might be airplane steerers, but they sure as hell aren’t pilots. ---
**Author:** ![Johnny\_L.A](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/johnny_l.a/32/1084_2.png) [@Johnny\_L.A](https://boards.straightdope.com/u/Johnny_L.A)\ **Post date:** [March 17, 2016, 2:13am UTC](https://boards.straightdope.com/t/general-aviation-folk-i-need-your-help-again/746545/62 "2016-03-17T02:13:16Z")
> [@LSLGuy](#): > > :eek: Those people might be airplane steerers, but they sure as hell aren’t pilots. When I was 12 an F-4 pilot from NAS Miramar gave my mom a BuWep flight jacket to give to me. (Mom worked at Gibbs Flight Service.) The nameplate had my name, and underneath it, AIRPLANE DRIVER. ---
**Author:** ![GusNSpot](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/gusnspot/32/436_2.png) [@GusNSpot](https://boards.straightdope.com/u/GusNSpot)\ **Post date:** [March 17, 2016, 5:34am UTC](https://boards.straightdope.com/t/general-aviation-folk-i-need-your-help-again/746545/63 "2016-03-17T05:34:01Z")
> [@Magiver](#): > > That’s not true of all aircraft engines but probably true with the Lycoming. You don’t want to do that to Rotax engines as it can draw air into the oiling system. > > I don’t know if you’ve ever rebuilt a [dry vacuum moto](http://www.sdsefi.com/8061.jpg)r but the graphite vanes are set up to move in one direction only and are fragile. > > You’re right that it’s dangerous to move the prop and that’s why I brought up the warning about mag switches not grounding properly on shutoff. But I move the prop as if I’m starting it. > > You’d be surprised at how many people can’t look at a prop and tell which way it’s supposed to turn. And Continental, Franklin, P&W round engines Kinner, Jacobs, Ranger inline inverted and some which are a bit rare. I don’t know about dry vacuum MOTORS but dry vacuum pumps in my experience are just fine with a few backward hand turns when rotating a prop backwards. I have never lost a pump even when an engine runs backward for a second or so on shut down. They are more delicate than a wet vacuum pump but … I agree, always be very careful around propellers, of any kind. I have no experience with Rotax engines. Do they even have valves of the traditional kind? I am a big guy so Ultralight Airplanes and I don’t mix much. ---
**Author:** ![Johnny\_L.A](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/johnny_l.a/32/1084_2.png) [@Johnny\_L.A](https://boards.straightdope.com/u/Johnny_L.A)\ **Post date:** [March 18, 2016, 1:31am UTC](https://boards.straightdope.com/t/general-aviation-folk-i-need-your-help-again/746545/64 "2016-03-18T01:31:18Z")
Is Dave following this thread? ---
**Author:** ![Gunslinger](https://avatars.discourse-cdn.com/v4/letter/g/4491bb/32.png) [@Gunslinger](https://boards.straightdope.com/u/Gunslinger)\ **Post date:** [March 18, 2016, 9:15am UTC](https://boards.straightdope.com/t/general-aviation-folk-i-need-your-help-again/746545/65 "2016-03-18T09:15:06Z")
Head injuries suck, glad to see he’s recovering well. But yeah, he was probably turning the prop to adjust the timing or something and it popped. I know there are certain procedures for tuning car engines that require you to manually turn the crankshaft, but cars don’t have a different ignition system. Y’know how lawnmower manuals tell you to disconnect the sparkplug wire before mucking about underneath? That’s because lawnmowers have always-on magnetos, and if you turn the blade to scrape off a bit of goop behind it, it MIGHT fire the engine, and on a mower the sharp bit is on the leading edge. Reminds me of the possibly-apocryphal story about a guy walking through the danger arc of a running prop, somehow miraculously going between the blades, and upon realizing his mistake, turned around and went back the way he came and … well, apparently you only get one miracle a day. :eek: ---
**Author:** ![saje](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/saje/32/3631_2.png) [@saje](https://boards.straightdope.com/u/saje)\ **Post date:** [March 18, 2016, 11:18am UTC](https://boards.straightdope.com/t/general-aviation-folk-i-need-your-help-again/746545/66 "2016-03-18T11:18:02Z")
> [@Johnny\_L.A](#): > > Is Dave following this thread? I mentioned it to him, but he’s not much of a message board kinda person. He appreciates all the kind words and thoughts though! ---
**Author:** ![LSLGuy](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/lslguy/32/5813_2.png) [@LSLGuy](https://boards.straightdope.com/u/LSLGuy)\ **Post date:** [March 18, 2016, 1:19pm UTC](https://boards.straightdope.com/t/general-aviation-folk-i-need-your-help-again/746545/67 "2016-03-18T13:19:14Z")
> [@Gunslinger](#): > > … > Reminds me of the possibly-apocryphal story about a guy walking through the danger arc of a running prop, somehow miraculously going between the blades, and upon realizing his mistake, turned around and went back the way he came and … well, apparently you only get one miracle a day. :eek: Pretty much has to be apocryphal. About the slowest idle I’ve ever seen is 600 RPM = 10 revs per second. On a 2-bladed prop that’s 20 blade passages per second = one chop every 50 milliseconds. A non-obese person is about 12" deep. To pass between 2 chops he/she has to be traveling at least 12" per 50 milliseconds = 20 feet/second = 13+ mph. That’s a dead sprint for an ordinary athlete. When sprinting we’re thicker than 12" due to arm swing & leaning forward. If it ever happened at all (which I doubt) I’d sooner believe somebody walked \*under \*a prop on a big airplane and happened to pass through the arc at a low point in his/her gait, \*juuust \*clearing the bottom of the prop. Most folks’ heads bob up & down an inch-ish during the course of a complete step. On the return trip he/she missed the low spot and got the top of their brain Cuisinarted. ---
**Author:** ![Johnny\_L.A](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/johnny_l.a/32/1084_2.png) [@Johnny\_L.A](https://boards.straightdope.com/u/Johnny_L.A)\ **Post date:** [May 15, 2016, 5:03pm UTC](https://boards.straightdope.com/t/general-aviation-folk-i-need-your-help-again/746545/68 "2016-05-15T17:03:03Z")
How’s Dave doing? ---
**Author:** ![saje](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/saje/32/3631_2.png) [@saje](https://boards.straightdope.com/u/saje)\ **Post date:** [May 15, 2016, 8:20pm UTC](https://boards.straightdope.com/t/general-aviation-folk-i-need-your-help-again/746545/69 "2016-05-15T20:20:11Z")
Happiest guy on earth right now, since he was cleared to fly again yesterday and went up for a 90 min tool-around on his own today 😃 ---
**Author:** ![Johnny\_L.A](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/johnny_l.a/32/1084_2.png) [@Johnny\_L.A](https://boards.straightdope.com/u/Johnny_L.A)\ **Post date:** [May 15, 2016, 8:30pm UTC](https://boards.straightdope.com/t/general-aviation-folk-i-need-your-help-again/746545/70 "2016-05-15T20:30:19Z")
> [@saje](#): > > Happiest guy on earth right now, since he was cleared to fly again yesterday and went up for a 90 min tool-around on his own today 😃 Excellent news! Congratulate him on the reinstatement of his medical, and his flight. 🙂 ---
**Author:** ![GusNSpot](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/gusnspot/32/436_2.png) [@GusNSpot](https://boards.straightdope.com/u/GusNSpot)\ **Post date:** [May 15, 2016, 9:03pm UTC](https://boards.straightdope.com/t/general-aviation-folk-i-need-your-help-again/746545/71 "2016-05-15T21:03:43Z")
Way to go Dave. That saddle still fits see. 😃 [Previous page](https://boards.straightdope.com/t/general-aviation-folk-i-need-your-help-again/746545.md?page=3)