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Air Plane, Ground Beef

Science brain teasers require understanding of the physical or biological world and the laws that govern it.


Puzzle ID:#16848
Fun:*** (2.46)
Difficulty:*** (2.74)
Submitted By:airhead3***
Corrected By:cnmne




Pete the Pilot was trading flying stories with Aaron the Arrogant, when Aaron started in on a particularly juicy tale: "Well, I got that story beat. There I was, rolling down the runway for takeoff in my Piper Twin Comanche. Suddenly, as I was approaching takeoff speed, a cow just ambled onto the runway right in front of me! I pulled back hard on the controls and got into the air, and I swear I don't know how I didn't graze that cow's back! He he, 'graze,' no pun intended", Aaron deadpanned, elbowing Pete jokingly. Sensing he was losing his audience, though, Aaron quickly continued, "But that's not all! To top it off, not 5 seconds after takeoff, my left engine quit on me!" To this, Pete raised an eyebrow in interest. Aaron gestured self-assuredly as he went on, "Thankfully, I was able to use my skill and lightning reflexes to save the situation. I immediately went to full power on my right engine and pulled the nose up to keep the plane in the air and all I had to do was make a quick turn to land on the perpendicular runway to my left", Aaron finished with great gusto. Pete, with an amused look on his face, said, "Well, that's a great story, Aaron, but because you are sitting here telling it, I know it didn't actually happen." How does Pete know?


Pete knows that a cow on the runway isn't out of the question for a small airport, but it's the second half that he has a beef with (sorry, I couldn't resist the pun). Pete knows about an aerodynamic phenomenon called Vmc Roll in multi-engine airplanes, where the airplane can, at the loss of an engine in certain conditions, lose control and roll over. An engine failure on a twin-engine propeller-driven airplane (such as the Twin Comanche) creates a tendency to turn into the dead engine due to both asymmetrical thrust and the drag from the windmilling propeller on the dead engine. (Think rowing a boat only from the right side, and in addition dragging the left oar through the water.) Further, the propellers normally create what is called induced acceleration over the wing, creating additional lift. (The propellers act as fans, creating faster moving air over the wings, and consequently, more lift.) When only one engine is working, that wing is then generating more lift than the wing that is no longer receiving induced acceleration, so the plane will want to roll into the dead engine. Vmc, or "Velocity minimum controllable" is an airspeed below which the rudder no longer has enough effectiveness to counter these turning/rolling tendencies caused by an engine failure, and the plane can then enter a Vmc Roll. Because of his already slow speed caused by cow-evasion maneuver, Aaron's situation was ripe for a Vmc Roll. His reaction of immediately increasing the power on the good engine would have only exacerbated the situation, due to the increased induced acceleration over the right wing creating even greater differential lift (stronger rolling force). Also, Aaron's left turn into the bad engine would have made the circumstances even worse. Had Aaron reacted the way he stated, he would have flown the airplane right into the ground (and most likely inverted). Although it may be counterintuitive, the correct action would have been to *reduce* power in the right engine and point the nose slightly downward to increase the airspeed above Vmc to give the rudder enough effectiveness to counter the aerodynamic tendencies. While Pete the Pilot is glad his boastful friend is sitting there to tell him this story, Pete knows Aaron is full of hot air.

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Mar 10, 2004

I'm not a pilot but I know from experience that when I tell stories to people in my profession, I don't tell stories that they would easily find to be false. I imagine that Aaron knew that his story was false because he is an experienced pilot and that he knew that Pete would figure it out. I think that in this situation, Aaron would knowingly be making a fool of himself.
Mar 10, 2004

While obviously this is an exaggeration, there are some pilots I've come across that are so interested in telling that good story they fabricate certain elements - often into areas beyond their specific expertise. While Vmc Roll should be common knowledge for multi-engine pilots, the vast majority of single-engine pilots may have never even heard of it. Perhaps part of Aaron's fabrication is that he owns a Comanche (single-engine), not a Twin Comanche. BTW, where did you glean that Aaron was an experienced pilot?
Mar 10, 2004

I just imagined that the requirements to become a licensed pilot would make a person experienced in multiple areas so that they could handle difficult situations or fly different kinds of planes.
Mar 11, 2004

curtiss -

There are a lot of different types of licenses for pilots, and each is for a specific type of plane (Imagine having a specific drivers license for SUVs or sports cars, or sedans, and being required to take a separate test for each. Now imagine that some cars have two engines, complete with two gas pedals and two tachometers...etc, and you can see how different that would be to drive). While the basics of flying are similar, a pilot licensed to fly a Comanche wouldn't be legal or able to safely fly a Twin Comanche (or vice-versa) until receiving additional training and certification.
Calling a pilot experienced just by virtue of having a license is like calling a 16 year old an experienced driver because they passed the driving test. Granted, it's MUCH more difficult and involved to get the basic pilot's license (the Private Pilot Certificate) than a driver's license, and involves a minimum of 40 hours of flight training (which involves a ton of training on how to handle the difficult situations one may encounter in that type of airplane). But compared to, say, the 1200 hours required to become an airline pilot (or the 30,000+ hours many airline pilots have), that 40 hours is next to nothing experience-wise. I hope this helps, and I truly appreciate the comments! Let me know if I can provide any more clarification or insight.
Jun 27, 2004

whoa! that answer was a little much for me. lamens terms, please.
Jul 09, 2004

hersheykiss8908 - I tried to keep the answer as clear as I could, while still being complete. It is a very tough battle to wrestle down all of the aviation terminology into something more palatable to, well, a layman. To help you understand in simple (though incomplete) terms, just think about the rowboat analogy cited in the answer. If there are specific words or ideas that could use clarifying, or if I can explain something further, please let me know! I appreciate your comments.
Sep 26, 2004

I don't think all that explanation was necessary? I mean... you don't need to have taken physics or know about planes (I just started physics this year and am definitely no pilot) to realize what would happen in that situation, with one dead engine.. clearly there would've been a serious imbalance, and you should be reducing the right engine instead of increasing, and pointing the plane nose down instead of up.

Also, the best thing to do in that sitch (assuming it was possible) would be to hit the eject button
May 31, 2005

airhead3, great job on the answers! I like how you add extra info, it makes it more interesting. I love airplanes and I hope to get my pilots license someday. It's fun to learn the science behind it all! Thanks for teaching me some new things!
Nov 10, 2005

that was very interesting! my dad wants to get his pilots license so he talks about different airplanes and stuff alot. i didnt get the answer, but i knew it once i saw it. maybe i should spend more time thinking. (haha MORE time? try any time! )
Jan 19, 2006

Excellent teaser. Answer came to me pretty easily but I can see it being hard for a nonpilot to answer. Still, you've salvaged my hope in this site hehe. Thanks.
Apr 09, 2008

I'm not a pilot or a physics professor, yet I found that fun and easy!
(user deleted)
Jul 14, 2008

I am a career pilot, military/civilian for 30+ years. I flew a twin comanche back in the early 80's and it was a running joke that if you lost an engine, the remaining engine would carry you to the scene of the crash. It was extremely underpowered. What killed his story for me was that he said he "slammed in full power" anyone that knows anything about small piston engine planes knows, you are using MAX POWER just to get in the air. There is no more, no reserve, zip, nada, nuttin honey.

Next, he never mentioned pulling up the gear, and I can promise you that a Twin Comanche will NOT climbout on 1 engine with the gear down. The fact that he went to the left is not only believeable, but inevitable. If he had said to the right you would KNOW for sure he was lying, because you can't do it.Period. Imagine 2 ox pulling a wagon, and the one on the left drops dead, the wagon is going left right now.... Not only is the right ox still pulling.. but is now dragging the dead one along.. he also never feathered the left prop which you would need to do immediately.

Do you train for these things? Absolutely, they happen! I had 8 engine failures in one year. You get good at them after a while. The last reason you knew it was BS... he's a PILOT... all pilots are full of BS.. I know... I am one.

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