Question for our math professor: Turning point over water?

[fantom]

Not looking good for the single crew of an SR22 earlier today

 

Stay safe out there

 

Going down in the Channel, either under the chute, or ditching with fixed gear, isn't very encouraging.

[eaglebkh]

Here it is in 4 easy steps.  My approach calculates an average wind vector throughout the duration of the descent, and uses that to calculate a new wind-corrected glide range.

 

1) You'll have to calculate an AVERAGE wind velocity (speed + direction) through all of the winds aloft altitudes (3k, 6k, 9k, etc).  You can do this mathematically or approximate.  To do this mathematically, calculate the 'x' and 'y' direction component of each wind vector.  X = windspeed*cos(winddirection); Y = windspeed*sin(winddirection).  Average the X's and Y's to get Xavg and Yavg.  The new total average wind speed = squareroot((Xavg*Xavg) + (Yavg*Yavg)).  Average wind direction = tangent(Yavg/Xavg).

 

2) With the average wind speed and direction, you can calculate a new average descent ground speed for the glide (use E6B or whatever).  Use the reverse-course bearing.

 

3) Calculate glide range at altitude (I'd suggest memorizing the glide ratio in NM per thousand feet - always a useful quantity), and then multiply by (avg descent GS)/(Vbg) to calculate the wind-corrected glide range.  If ground speed is higher than Vbg, then you'll glide farther - likewise for the opposite.

 

4) As you cross the shore outbound, the time to reach the decision point is simply the wind-corrected glide range divided by CRUISE ground speed; decision time = (wind-corrected glide range)/(cruise GS).  Subtract off any time that it would take to recognize the engine failure, abort the flight and make the 180, as these quantities would penalize that overall time that you could stray from land.

 

At the point when you leave land, start the timer.  These equations could be loaded into excel or some other spreadsheet tablet app.  Most all inputs would be known prior to take-off, except for the actual ground speed.  The key assumption in this method is that you will spend equal time in all of the winds aloft altitudes.  Hope this helps!

[yvesg]

Thanks Brandon for all the detail. I have the vests in hands now (They are not bulk nor heavy) so I feel that I have all needed to cross if I need to.

Yves (Almost on his way to Oshkosh, via Madison)

[orionflt]

I have made the flight (in my C model) going to Osh numerous times, I try to make the trip over the lake at 8000 ft or higher. Where I cross I'm over water for about 80 miles, during that time there is approximately a 20 mile stretch that you cannot make land. As previously stated I am always looking for boats and calculating distance to splash if I lose an engine so that I know where I want to aim to provide the best chance for a quick rescue. I also carry co2 life vests that I can keep in my seat pocket and have it readily avilible.

Brian

[aviatoreb]

Hey Yves, Did you launch yet?  Still in Ottawa or on your way to Oshkosh?

 

Here is a lecture style notes just for sake of discussion.  I hope its not overkill.  Disclaimer - this is just for fun discussion....and use at your own risk...this is not a recommendation in anyway.  Just some fun musing by a math prof discussing something for arguments sake and nothing more.  Note my example 3 where for my own personal use I tend to fly very very high assuming all my assumed numerical values are grossly wrong.  I want to be able to fly to one side at all times - rather than the usual requirement to be able to fly to one or the other sides at all times.

[yvesg]

Wow.. that is kind of a bit on the complex side. Thanks Erik and all the others. We are preparing today to fly westbound getting closer to Oshkosh. Lake crossing will probably happen tomorrow morning if everything falls in place... so many things to get ready.

We might be lucky and get a wind from the north, which will simplify things a lot and decrease the uncertainties. If the wind is perpendicular to our flight path, the turning point shall be near the middle... or shortly before that I assume.

Thanks again.

Yves

[aviatoreb]

Wow.. that is kind of a bit on the complex side. Thanks Erik and all the others. We are preparing today to fly westbound getting closer to Oshkosh. Lake crossing will probably happen tomorrow morning if everything falls in place... so many things to get ready.

We might be lucky and get a wind from the north, which will simplify things a lot and decrease the uncertainties. If the wind is perpendicular to our flight path, the turning point shall be near the middle... or shortly before that I assume.

Thanks again.

Yves

 

Well - as I said - I didn't do all that when I crossed myself - I just figured that with a 3 miles to each 1000ft glide ratio in the full feathering prop rocket, then at 20,000ft I could glide 60mi with no wind. So even over the far shore of the crossing I could glide back to the shore where I started, and a little bit of tail wind only helps.

 

What time you leaving?  My son and I may go to the bicycle time trial race tomorrow evening that starts right outside the air museum at rockliffe.

[DaV8or]

Is it really that bad to just stay within glide of the shore the whole time? How much time do you really save and isn't the view of the shoreline more interesting than the open water? It is just a trip for fun, right?

[carusoam]

Dave, you are right....but,

When in a Rocket, with math skills, fly high and really fast. 'cause you can.

Keep appropriate life jackets in the event of total miscalculation!

I like the full feathering prop glide ratio...

Best regards,

-a-

[Piloto]

Yves, if after all this talk and calculations if you still don't feel confortable on doing it, fill up your bath tub with cold water and get in with your pilot attire. After two hours in it make your decision. Hope it helps.

 

José

[aviatoreb]

When in a Rocket, with math skills, fly high and really fast. 'cause you can.

 

 

Hmmm...I think I should make that into a tshirt.

 

 

Is it really that bad to just stay within glide of the shore the whole time? How much time do you really save and isn't the view of the shoreline more interesting than the open water? It is just a trip for fun, right?

 

 

It can save a good bit of time/distance not going around to the south and navigating all the cities on the southern side of the lakes, Buffalo, Cleveland, Chicago....

 

 

Yves, if after all this talk and calculations if you still don't feel confortable on doing it, fill up your bath tub with cold water and get in with your pilot attire. After two hours in it make your decision. Hope it helps.

 

José

 

 

Yeah.....here is the story of a local pilot from our area who had a mysterious engine failure over Lake Huron in his C150.  Departing from Watertown, NY KART to Michigan direct into the wind....some of us suspect fuel exhaustion.  I think he was cruising at 2500ft over lake Huron to the middle....  Amazingly and thankfully he survived 17 hours before being saved - he had no survival gear.  One tough dude.

 

http://abcnews.go.com/US/crash-pilot-survives-17-hours-floating-lake-huron/story?id=14173080

 

 

Fly very high and make sure there is still fuel in your tanks!

[yvesg]

Erik, I am already half-way near Detroit more precisely Sarnia, ON. Piloto, you are right about the cold water. We'll make the decision tomorrow after the weather briefing. Still unsure. I crossed lake Ontario a few years back but it is narrower... we'll see.

Dav8for, I might choose your option. You are right that all this flying is for pleasure. Lets not excite the devil!

Yves

[yvesg]

OK folks, went accross this morning. No weird sounds when in the middle. Here is a picture...crossed at 8.5 thousands

Safely landed in Madison.

Yves

[yvesg]

Looks like the iPAD turned that upside down... not much difference with the horizon though!

Yves

[aviatoreb]

Looks like the iPAD turned that upside down... not much difference with the horizon though!

Yves

 

Are you doing acrobatic again?....

[yvesg]

This clip shall be a bit better...

Yves

[Piloto]

Well done Yvesg!!!. Now you are ready for the one on your backyard.

 

José

[carusoam]

I like the copilot flying while Yves does the important video-ing!

Best regards,

-a-