V Speeds (New Owner)

[GAHorn]

Karl, I'm not confused about it. But this (and most other) airplane is not a "glider". It's a powered aircraft that, when the engine stops, the pilot is probably most interested in buying "time" to troubleshoot, restart, look for a field. He's not likely to be trying to "stretch" to some distant point, but more likely to find a suitable place nearby to set it down.... at the last possible moment. I'm actually thinking of the usual "recommended" glide speed. But it's good to used the correct terminology, of course. Thanks again.

Brad... no reason to be angry over the discussion. This is a Cessna 170 site and I naturally thought we'd be thinking about a 170 when discussing a question which poses the "best glide speed" for a 170.... rather than some obscure, unknown, undocumented airplane someone we've never heard from might have once owned. Karl has given a much better method to find the speed if it's undocumented, I think, rather than looking at the undersurface of the wing relative to the horizon.
An example that comes to mind is a low wing airplane, or an airplane without the classic airfoils that have relatively flat lower surfaces. Hawker jets glide much farther at significantly higher speeds than Vy. (The terminology used with that airplane is usually Venr or Verc.) No chance for the pilot to look under the wing... in fact the swept wing is pretty much out of view from the cockpit.

[bradbrady]

George,
I'm not angry....Once again, I think you missed the gist.....If there is no information......where do you find it? all I am saying is there is ways to figure out what is needed with out an engineer's degree (sorry about that Miles)

[lowNslow]

But this (and most other) airplane is not a "glider". It's a powered aircraft that, when the engine stops, the pilot is probably most interested in buying "time" to troubleshoot, restart, look for a field.

Hmmm, if the engine quits - sounds like a glider to me.
I got your point, but depending on the circumstances "best glide" may be the better option than "minimum sink". I guess the important thing to remember is to slow down rather than to continue burning altitude at trimmed cruise speed. I only bring this up because terminology does matter, you wouldn't confuse "best angle" of climb vs. "best rate".

[GAHorn]

Ok, Brad. Sorry if I missed the inflection. (Easy to do with the unspoken word.)

Karl,... except for the relatively insignificant effect of the engine's propulsion, ... wouldn't a quick-and-dirty approximation be:
minimum sink ~ Vx
Best glide ~ Vy

[lowNslow]

I'm not sure, but I would guess they are very close. It would be interesting to run a polar on the 170 to see what the numbers really are.

[Jr.CubBuilder]

I like this thread, it's some interesting stuff I hadn't thought about before. The basic training for a PPL doesn't really cover this very well and probably doesn't need to, I think it falls under the category of continued learning. I've been thinking about getting my glider rating this summer, this is causing me to give that more consideration.

The best glide speed in the owners manual or POH is just a number that works well, and gives the pilot something to shoot for while he/she is trying not to freak out and figure out why the fan's quit blowing. Beyond that it's just a number, while one shouldn't take flying advice from the web without a grain of salt, discussions like this are food for thought. One could probably stretch out the glide path of the 170 by trimming for a bit higher speed 80-85mph indicated(?). Would trimming for 65-70mph indicated reduce your vertical speed? I don't know, but I think I'll look into it when things start thawing out and I start flying again. Given the mediocre glide of planes like these in comparison to a soaring machine I think the effects of wind would be best taken into consideration as they pertain to a landing spot unless you happen to have gobs of altitude. If you know you can make the target (ie it's moving down in visual reference) great, but if it's stationary and you're coming down from 7000'agl you'll be pooched if the headwind picks up closer to the ground.

[cessna170bdriver]

all I am saying is there is ways to figure out what is needed with out an engineer's degree (sorry about that Miles)

No offense taken whatsover, Brad. Aerodynamics is not my flavor of engineering anyway. I don't know any more about best glide/minimum sink vs. best climb/best angle than it took to pass the private written over 30 years ago. I'm sure I know LESS than the average glider pilot. (Living here in Tehachapi, I have only myself to blame for that one.)

George said something earlier that he would automatically go for minimum sink so as to maximize the time aloft to try to sort out a problem. Well, I think that's a good first reaction, but in the event you determine that you aren't going to restore the status quo from the pilot's seat while airborne, it would be handy to know what speed and any other parameter you need to adjust to minimize the glide ANGLE so you can maximize your choices for a spot to safely become ground-borne.

Don't some GPS's or EFIS's calculate a near-realtime sink angle or glide range, or a list of airports within gliding distance? All the required data is there...

Miles

[lowNslow]

I've been thinking about getting my glider rating this summer, this is causing me to give that more consideration.

I would have to say getting my glider rating was the most fun and most educational rating I've gotten. Unfortunately, unless you have access to a good glider club it can be expensive to get the rating. It will quite a bit cheaper if you already have the power rating. If you do get the rating I'd encourage you to get some glider cross country training as well.

[lowNslow]

Don't some GPS's or EFIS's calculate a near-realtime sink angle or glide range, or a list of airports within gliding distance? All the required data is there...

Miles

I don't know what they have for powered aircraft, but some of the GPS computers for the high performance gliders are pretty sophisticated. They use the polar for what ever glider your flying and will adjust for any ballast added.

[HawkerCFI]

In support of my learned colleague, GAHORN, perhaps it might be interesting to look at this TCDS information on the FAA's site. Its kind of nice to go to the source. It supports the 115 mph number for the three models.
http://www.airweb.faa.gov/Regulatory_an ... enDocument

[Robert Eilers]

I am late to this discussion - just back from a week in the Bahamas. I agree with George and Miles regarding going to minimum sink rate first thing - while you are sorting out next steps following an engine failure. The GPS equipment I am familiar with will provide nearest airport information - but, the nearest airport may not be the most "makeable" airport depending on winds aloft. Most GPS units will provide you with ground speed and ETE which should allow you to calculate time to the emergency airport you have selected. However, in the aircraft we fly and at the altitudes we commonly fly we generally have 10 minutes or less in the air and generally don't have much more than 7 to 10 miles in which to operate. Choosing the "nearest" airport as displayed by the GPS may be a bad decision if it requires you turn into a 20 knt headwind. In my opinion, when the engine quits look directly below or within a mile or two of your current location and pick the best field available - farmer or otherwise.