Best Glide

[FastEddieB]

Good thought exercise, re: the effect of wind on best glide speed:

 

Imagine your plane's best glide is 60k. You have an airport right in front of you, maybe an 1/8 of a mile away.

 

Problem is, there's a 60k direct headwind.

 

What might you have to do to make the field?

[josjonkers]

What about wind?

 

However, like Vbr, wind direction and speed have to be taken into account before you can choose the Vbg speed when in a forced glide; for more information on the power-off glide speeds read the 'Know the best glide and minimum descent airspeeds' and 'Know the practical glide ratio and terrain footprint' sections in the 'Coping with emergencies guide'. In lower wind conditions, Vbg is increased in a headwind by around one quarter of the windspeed, but is decreased in a tailwind by a similar amount. In higher wind conditions, say above 25 knots, the speed changes required would be around one half of the windspeed.

 

http://flysafe.raa.a...le2.html#vspeed

 

This is absolutely true and us "old" (meaning ex) soaring pilots are quite familiar with this and it becomes second nature. Kinda rule 15-a-35c from "Soaring 101".

[FlyingMonkey]

Well I'm glad we are all in complete agreement on this subject, just like all others related to flying.

[Ed Cesnalis]

We know best glide is useful if without it we cannot make the field.

 

When is minimum sink useful?

[FlyingMonkey]

We know best glide is useful if without it we cannot make the field.

 

When is minimum sink useful?

 

The only thing I could think of is to buy time to try a restart or fix something.

[Ed Cesnalis]

When is minimum sink useful?

• to buy time to try a restart or fix something.
  
• good for thermaling
  

[paul m]

_{When is minimum sink useful?}

• _{to buy time to try a restart or fix something.}
  
• _{good for thermaling}
  

 

_{Now you've lost me. If i think a field is achievable at best glide would I ever choose instead minimal sink? I will attempt restart while on the best glide, no? On the other hand if I believe no field is achievable or I have already determined to use the chute, I then will use minimum sink to buy time before descending to minimum deploy altitude?}

[Ed Cesnalis]

When the next emergency happens, given some altitude to work with, I will pitch for best glide but it won't matter much because I will select a close field that I clearly have made.

 

Minimum sink will likely come next as orbit down above my field, and give myself time to plan.

 

Minimum energy at time of contact will likely be the most important of the 3 and that means contact at stall speed with minimum vertical speed.

[josjonkers]

When the next emergency happens, given some altitude to work with, I will pitch for best glide but it won't matter much because I will select a close field that I clearly have made.

 

Minimum sink will likely come next as orbit down above my field, and give myself time to plan.

 

Minimum energy at time of contact will likely be the most important of the 3 and that means contact at stall speed with minimum vertical speed.

Spoken by a true (ex or "old" ??) glider pilot!

[Ed Cesnalis]

Josh, I think your right, I did an approach where I had the field made at 0° and then tried to match it or beat it at 15° and I came up way short.

 

Makes me wonder why FD published 63kts at 15°. Also makes me wonder if -6° beats zero?

[WmInce]

. . . " Also makes me wonder if -6° beats zero?" . . .

 

New report forthcoming?

[Ed Cesnalis]

The CTSW flies much differently than the new CTLSi. The discussions on these boards are imprecise. One needs to account for WEIGHT, model, conditions (wind), and density altitude before making any real comparisons or assumptions about glide, landing, climb, flaps, slips, or even trim.

 

Think of it as a non-precision test, it still gets the job done. Repetition can confirm, its pretty obvious when you try it.

 

No-one is arguing that a CTSW flies much differently than a CTLSi but now that you bring it up the similarities are far greater than the differences. Stretching a design has a predictable result, the longer moment arm means more stability in pitch and yaw, and slower response to the rudder and stabilator (if you like that kind of thing.) Of coarse the difference is between a CTSW and a CTLS injected or not. How you deliver the fuel doesn't change how the plane flies unless the CTLSi's decrease in torque has an effect on climb or speed.

 

One needs to account for WEIGHT, model, conditions (wind), and density altitude before making any real comparisons or assumptions about glide, landing, climb, flaps, slips, or even trim.

 

Do you figure that when Josh and I went from 0° to 15° that we failed to account for a change in weight, model, conditions and DA? It still says CTSW I don't think anything changed but my flap setting and the resulting glides available to me at that setting.

[josjonkers]

Josh, I think your right, I did an approach where I had the field made at 0° and then tried to match it or beat it at 15° and I came up way short.

 

Makes me wonder why FD published 63kts at 15°. Also makes me wonder if -6° beats zero?

Good thing you didn't bet...

I have not tried -12 (Canada thing) however.

[Roger Lee]

-12 will cost you glide distance. I loose altitude faster in the minus flaps faster than zero.

I believe zero is the best, but as Ed said all conditions brought to bare on each plane will affect that glide.

[C ICEY]

back up in ICEY this morning, set up high, engine off, slowed to 50 to stop the prop and coarsened the pitch to max. Used the garmin glideslope indicator to judge: my best glide was again at 65 with some (maybe 10) flap, 70 with zero wasn't it. Roger is likely correct, all factors all conditions brought to bare....... . Could be the longer wing of the CT2k. Poor buggers who bought those heavy lemon CTSi's.... The difference in glide was negligible, though, in the terms of functional glide, and considering that one has to identify a target that lies within a range that allows for a landing setup which probably will entail a change of flap setting to lower airspeed to the minimum, it makes sense to me to glide it at the closest landing configuration. There is guaranteed to be a lot going on when the decision is made to get to a spot. Changing the flaps is one of those things. The question of whether to pull the chute or to waffle it in would have to have been made quite a bit earlier. another discussion.

[Farmer]

Some time we do and sometimes we don't focus on the glide distance. When we are ten miles South of Honolulu and 900 feet we watch the wind on the ocean and how that reacts with the swells. The gives us the heading needed to reduce the ground (water) speed when we stop flying and transition to swimming. When we are at 8000 feet and thirthy miles from land we constantly calculate a shortest distance to land given the wind speed and direction. This gives us a decision location, turn back or continue. We used to use a radial for locationing that spot before we got DME equipment. Part of the old drill is not necessary in the (all models of) CT because as soon as we gave up on restart we then pull up and get the prop to stop windmilling, that really helps the glide in our older aircraft.

 

We would declare success if we could just make shallow water. Actual land would be a very successful event, airport, dream on. No small aircraft has went in the water here since the one on Maui earlier this year. It does not happen each year. We did a little glide testing a couple of years back and time is air is most import when brisk wind can help, otherwise 0 flaps seemed more likely for our operatrions. Our cruuent plan is BRS at 500 feet and much 7700, 406, check the life vest we always have on.

 

FARMER

[josjonkers]

back up in ICEY this morning, set up high, engine off, slowed to 50 to stop the prop and coarsened the pitch to max. Used the garmin glideslope indicator to judge: my best glide was again at 65 with some (maybe 10) flap, 70 with zero wasn't it. Roger is likely correct, all factors all conditions brought to bare....... . Could be the longer wing of the CT2k. Poor buggers who bought those heavy lemon CTSi's.... The difference in glide was negligible, though, in the terms of functional glide, and considering that one has to identify a target that lies within a range that allows for a landing setup which probably will entail a change of flap setting to lower airspeed to the minimum, it makes sense to me to glide it at the closest landing configuration. There is guaranteed to be a lot going on when the decision is made to get to a spot. Changing the flaps is one of those things. The question of whether to pull the chute or to waffle it in would have to have been made quite a bit earlier. another discussion.

So Mike now do real most convincing test by flying a high approach to an unobstructed rwy and check your aiming point at 0 flaps and then see how you make out once you change to 15 flaps. I will be coming over to collect my beer! (eh eh Earl grey tea I guess ).

[FlyingMonkey]

So for those who did the tests on a CT, if zero flaps looks best, at what speed? Closer to 63 or 78? I'm guessing 63-68.

[FastEddieB]

As a reminder...

 

...counterintuitively, weight does not affect glide ratio nor no-wind glide distance.

 

As long as you adjust Vbg for weight, of course.

[josjonkers]

So for those who did the tests on a CT, if zero flaps looks best, at what speed? Closer to 63 or 78? I'm guessing 63-68.

My experience is around 70 kts.

[josjonkers]

As a reminder...

 

...counterintuitively, weight does not affect glide ratio nor no-wind glide distance.

 

As long as you adjust Vbg for weight, of course.

CORRECT! I Weight does not influence glide ratio/distance. However the heavier you are the faster you need to fly to obtain best l/d. And slower if you are lighter.

[FastEddieB]

Which is why I specified no wind glide distance.

 

It's easy to come up with a scenario where, gliding into a wind, a heavier plane would be able to glide to a runway a lighter plane would come up short of, even with both at their optimal Vbg.

 

Anyone care to try?

[Roger Lee]

The problem is it will never be ideal for any emergency. You'll have to contend with something. The book says 14:1 and I'll be happy with 9:1 because of all the factors and landing sites that are out of our control, not to mention the poor fine tuning and decisions a pilot will make during the emregency.

 

Plan for the worst and be happy with the best if you really need it.

[Jim Meade]

The problem is it will never be ideal for any emergency. You'll have to contend with something. The book says 14:1 and I'll be happy with 9:1 because of all the factors and landing sites that are out of our control, not to mention the poor fine tuning and decisions a pilot will make during the emregency.

 

Plan for the worst and be happy with the best if you really need it.

 

 

"if you really need it"

 

I don't agree with this philosophy. It's like the idea of always fly with lots of gas. It sounds good but it does not give the pilot objective information upon which to base a decision, and in extremis, the pilot is likely to guess or hope. [Airlines do not fly with "lots of gas" because it costs money to tanker fuel - they plan carefully and know how much gas they have, which is by IFR regulation 45 minutes at cruise speed after their destination. The key is they have a built in alternative which we in LSA land often glibly pass of rather than actually plan for so the 45 minutes is enough in an emergency.]

 

My plane tested 9:1 (engine off prop stopped) and I won't count on it for anything more than that, whether the book says 14:1 or not. If I'm in the position where I need 14:1 to glide to an airport, I am sure that (absent a favorable wind) I will not make it so I won't spend a millisecond planning or dreaming about it and therefore trying for the unattainable.

 

This doesn't mean I won't analyze and consider the wind to see how it would move the ground track of my 9:1.

 

If Roger had said, "be happy with the best if get it." I'd have been happier, but that still implies lack of objective planning.

 

One problem is that if one's engine quits at altitude, one is likely to be concerned. That concern might affect how one thinks. Having 9:1 in my head that I am confident I can do is better than having maybe 14:1 or something close, maybe, I hope, could it be...... One will be worried enough without trying to figure out if one can hold 14:1 as well as a test pilot flew it and an advertising man rounded the numbers off.

 

In reality, I'm sure Roger and all of us would agree that given an engine out at altitude, one would want to establish best glide, pick out a landing spot well within the capability of the airplane and the pilot, try a restart and then, if one has time and thinks it will make anyone feel better, call ATC or dial in 121.5 if nothing else. (You guys like me who monitor Center on longer trips will be comforted to know that most likely an airliner if not Center would hear and relay a call if things got that bad.)

 

So, all of us would want to land needing well short of 9:1, let alone 14:1 if at all possible.

 

 

 

 

 

 

 

[FastEddieB]

(You guys like me who monitor Center on longer trips will be comforted to know that most likely an airliner if not Center would hear and relay a call if things got that bad.)

 

 

Off topic reminder:

 

4/4386 SPECIAL NOTICE... NATIONAL AIRSPACE SYSTEM INTERCEPT PROCEDURES. AVIATORS SHALL REVIEW THE FEDERAL AVIATION ADMINISTRATION AERONAUTICAL INFORMATION MANUAL (AIM) FOR INTERCEPTION PROCEDURES, CHAPTER 5, SECTION 6, PARAGRAPH 5-6-2. ALL AIRCRAFT OPERATING IN UNITED STATES NATIONAL AIRSPACE, IF CAPABLE, SHALL MAINTAIN A LISTENING WATCH ON VHF GUARD 121.5 OR UHF 243.0. IF AN AIRCRAFT IS INTERCEPTED BY U.S. MILITARY AIRCRAFT AND FLARES ARE DISPENSED, THE FOLLOWING PROCEDURES ARE TO BE FOLLOWED: FOLLOW THE INTERCEPT'S VISUAL SIGNALS, CONTACT AIR TRAFFIC CONTROL IMMEDIATELY ON THE LOCAL FREQUENCY OR ON VHF GUARD 121.5 OR UHF GUARD 243.0, AND COMPLY WITH THE INSTRUCTIONS GIVEN BY THE INTERCEPTING AIRCRAFT INCLUDING VISUAL SIGNALS IF UNABLE RADIO CONTACT. BE ADVISED THAT NONCOMPLIANCE MAY RESULT IN THE USE OF FORCE. WIE UNTIL UFN.

 

Bolded mine. And still in effect, I'm pretty sure.

 

In my experience, a huge percentage of pilots are not aware of this requirement. If not on flight following, I switch to 121.5 as soon as I'm clear of the traffic pattern on departure, and it stays there unless I have to switch to another frequency enroute.