He said, "distance over the ground" while you are discussing movement through the airmass. He has it right. Though I would swap some of his words for clarification: best glide angle -> furthest distance achieved & best L/D -> L/D max.

Again, angle relative to the ground, he is right. Relative to the air, I would swap terms as mentioned above just for clarification.

Again, in terms of ground location as his post suggested before, he is right.


Unless you have a variometer equipped, speed to fly is irrelevant. A glider pilots speed to fly accounts for lift, sink, headwind, and tailwind. Interestingly enough, lift/tailwind result in flying closer to, or at, min sink, a slower speed. Conversely, a sink/headwind results in increasing your speed to fly above Vbg. The reason was already given by ryan; reducing or increasing the effects of the moving airmass, both up/down and forward/backward.


Ryan: I wouldn't have any issues with the engine one as engines build, to my very limited knowledge, is fairly linear. Increase piston size x% increases fuel flow y% and power z%. Drag curves are not linear, leading me to believe, as UAC seemed to confirm, there is a limit to the rule of thumbs usefulness.

I do introduce it, though I only gloss over it. I much rather focus on judgement required to pick a landing site and skills to safely fly at or near best glide until the flare. If pilots did that, I suspect 90 percent of the engine failures encountered would result in a safe landing.

In response to your real world experience, you had a particularly unusual situation. For the most part, we are talking about what speed to fly when total power is lost. Your situation would have been best if flown at min sink with the engine as lean as possible, I assume you did this.

 

I don't mean to beat the dead horse, but I am really against this sort of thinking for the airplane pilot. Here's why:

1. You don't know the magnitude or direction of the headwinds or tailwinds in most cases unless you have a wind vector on board. You are guessing about all this at a time when there are far better things to be doing given your engine just quit. And if you do happen to have a wind vector on the cockpit panel, now you have to watch the thing as you turn the airplane in the wind which is a heads-down activity you could really do without.

2. As discussed, not flying the Vg speed robs you of precious time that you could be using to address the dead-stick situation.

3. Why do you need more distance over the ground anyway? The chances of not being near a suitable landing site concurrent with being in headwind or tailwind conditions where you happen to know what those winds are and where they are coming from is unlikely. Furthermore, these winds may change as you descend, and in fact are likely to do so. Why not just use Vg, the speed at which you have the most time and as far as you know, distance to land?

4. This speed we are talking about is not technically a best glide speed. It is a ground-based best distance speed under known wind conditions, a "speed to fly" as the glider crowd puts it. I do not ding them for using something that works for their purposes, but I point out they are not very commonly our purposes as airplane pilots. The whole discussion is perhaps an interesting engineering topic, but it is confusing a more valuable issue- that of using the best glide speed as defined universally by aircraft engineering texts and pilot training manuals for use in emergencies.

I rest my case, Your Honor.

 

*bangs gavel*

 

I'll give you my thought process during that situation (after thinking about what was wrong):

1) The Atlantic is a pretty big place
2) Ditching is going to suck:
a) it's starting to get dark (my current course is making it worse) -it's going to double suck being in the ocean at night
b) high-wing airplane
c) how am I'm going to get this 40lb life raft out of the airplane and then inflate it - it'll probably sink

3) Wow the Atlantic is big... I can see how people get lost out here and never found (note: avoid ditching)
4) Thank God for true airspeed (vs. indicated)
5) No one is ever going to believe me that the fuel valve stuck to one side!

 

Did you declare? If not, did you at least use pan, pan, pan? If you don't know what that is/does/provides (anyone else reading this, not directed at ryan) you should research it!

Sounds like your thought process was:

oh ****...
no one will believe...
oh ****...

My only question is, why didn't you think of the sharks man!

 

Actually every center was a little out of range (on the longest leg over water - about 400nm) - A Jet Blue flight out of PR relayed my request to contact San Juan Center. After a few freq changes and finally being able to receive them (and visa versa)... I told them I had a fuel valve problem, only feeding one tank now - Turks are too far to turn back, there looked like a significant weather build-up over PR, so diverting to Punta Cana (my alternate) was really an easy decision...

I didn't want to blow things out of proportion, and I'd been flying since about 2am that day (it was about 5pm then), but I thought about it some more... I was diverting from my eAPIS (so I asked him to inform US Customs - which never happened), the Atlantic is a big place... giving them my present lat/long and fuel left/persons on board/course would not be a bad idea if worse came to worse.

How accurate are the 172 fuel gauges?

The controller wished me luck, chatted a little bit, and then switched over to Punta Cana ...So I actually declared with them. That airport is pretty busy, when I passed over the coast my fuel gauge was sitting on about 1 gal - turned base for 9 and it started coughing, shut off on the apron.

Didn't speak much Spanish, so trying to get AVGAS was a bit of a challenge... finally did - had to go to the tower to file an official IFR paper flight plan (which was in Spanish), because it was night time (night time in the Islands means IFR). The plane needed to be in PR that night, so I figured with one good tank the jump from shouldn't be too hard. In hind sight I should have probably waited until someone checked out the airplane, but that's the kind of decisions no sleep will get you...plus the logistics of getting an A&P at that airport, well I wasn't too sure about anyways. Of course they didn't have any low-enroute charts for Dom Rep... so I had to use a high-alt to mark my way points. It's only a little over an hour.... so no big deal. Landed at Aguadilla (Borinquen), US Customs AIAs surrounded my plane... told them about what happened, they were pretty cool about it all (after a brief search).

The A&P in PR said that the "ball" in the fuel valve disconnected and got stuch in the right tank, so only the left would feed.