Glide Speed - Flaps Up v. Down

[minitour]

Reviewing for a stage-oral in the 152, I was just checking myself on the "emergency" checklist items that (I feel) I should have completely memorized in case there isn't time to verify using the paper checklist.

One thing that hung me up was the "Emergency Landing (no Engine)" checklist.

My initial thoughts were:
Trim to 60
Troubleshoot checklist (re-start)
Then basically undo all the stuff you did in the re-start checklist for the emergency landing. Things like the mixture all the way out, shutoff valve, ignition off, throttle closed, etc...

What I missed was the airspeed and I can't figure out why it's different.

For every other checklist it's "Airspeed -- 60 KIAS" the first thing on the checklist. Well for this one it's "Airspeed -- 65 KIAS (flaps UP) 60 KIAS (flaps DOWN)"

I understand flying slower with flaps down to increase the glide ratio, but I don't understand why all of the other checklists use 60 and this one uses 65.

It's probably something really simple that I'm overlooking, isn't it?

-mini

 

[MarineGrunt]

Are we talking a checklist out of the POH or your school's checklist? Either way, go with the POH.

My only thoughts about the different airspeeds is that as your gross weight increases, so does your best glide speed.

 

[minitour]

Are we talking a checklist out of the POH or your school's checklist? Either way, go with the POH.

My only thoughts about the different airspeeds is that as your gross weight increases, so does your best glide speed.

The POH.

It's under "Forced landings" and "Emergency landing without engine power"

I just was going through the checklist kind of "dry flying" the plane and called out "60 knots" and then the rest. When I checked it, it was 65 with flaps up...totally blew my mind. It's the only checklist in here with a different glide speed ( I don't count the engine fire one b/c I'm setting a speed to put out the fire, not to glide).

Don't get it

-mini

 

[MarineGrunt]

Not sure. Maybe it means pitch for 60 until you get the plane cleaned up, then 65. Ask one of your CFIs who might be a little more familiar with the checklist.

Good luck on your check.

 

[Goose Egg]

I'd say do what the POH says, and definitely consult your CFI. It also wouldn't hurt to look up the old terms minimum sink speed and speed to fly (consult your nearest soaring manual.) But understand that there will always be a change in performance with a change in configuration.

-Goose

 

[midlifeflyer]

Different model year? Modifications? Looking at the best glide for failure after takeoff instead of emergency landing checklist?

The other piece is that best glide speed varies by weight. So the checklist "best glide" tends to be a ballpark number to begin with.

 

[minitour]

Thanks for the help! I'll see if I can find out what's up widit...if I find anything interesting, I'll let y'all know.

-mini

 

[Goose Egg]

The other piece is that best glide speed varies by weight. So the checklist "best glide" tends to be a ballpark number to begin with.

Too bad they don't publish a speed polar curve(s) for the 172. It'd be easy enough to make one yourself anyway.

-Goose

 

[uwochris]

The best glide speed is based the AOA where total drag is minized. With flaps down, you should reduce your IAS in order to maintain the max glide ratio. This is obviously contradictory to what the 152 POH says (Vg= 60knots, however, it mentions that the speed to use in the event of a forced landing for the approach and landing is 65 knots).

The only thing I can think of is the effect on the sink rate. Perhaps using 60 knots is more efficient, however, 65 knots gives a better result for the approach itself. With my experience in the 152, I know that if you were doing an engine out approach at 60 knots or less, you'd probably be coming down pretty fast. This is just a guess though.

 

[qmaster3]

One thing that hung me up was the "Emergency Landing (no Engine)" checklist.

My initial thoughts were:
Trim to 60
Troubleshoot checklist (re-start)
Then basically undo all the stuff you did in the re-start checklist for the emergency landing. Things like the mixture all the way out, shutoff valve, ignition off, throttle closed, etc...


-mini

MINI,

Another great memory aid that was taught to me.

A-B-C-D-E


Altitude

Best glide (I know this was your ??)

Choose landing spot

Diagnose-left to right on panel

Emergency-radio 121.5, mayday, kiss your ass goodbye, etc

 

[Lead Sled]

Going back to what Goose Eggs said about polar curves...

Normally the penalty for flying faster (with in reason) than the appropriate glide speed is less than flying slower. You should always follow the POH in matters like this; but when there's a discrepancy, it's probably better to err on the high side.

When it comes to an actual off-airport landing, the critical factor is to fly the airplane to a stop. You'll probably want to make the initial touchdown as slow as you can - consistant with aircraft controllability. Remember, if you double the touchdown speed, you multiply the kinetic energy four times. The survivability of a crash is a function of how quickly the kinetic energy is dissipated. If you’re lucky you’ll have a flat smooth surface, but throw in some rocks, trees, etc. and you quickly see why survivability, off-field, can be a big question.

Back to polar curves...

All glider pilots are familiar with them. I've said this before, if I were King of the Universe I would make glider time mandatory for all pilots. The "feel" that you develop when learning to fly sailplanes will help you in all of the fixed-wing flying that you do. The confidence that you develop in the ability to handle an engine failure will be in valuable.

'Sled

 

[Xavier]

I fly the 152 and my instructor says pitch for 60. He has never said anything about pitching for 65, but I don't use the checklist but every once and a while because he put a bit hint on memorizing the checklist rather than having to bust out the checklist every time even on practice, and he always told me 60, and that is also what it says on the book I study for it.

 

[MTpilot]

what they mean is...

They want you to pitch for best glide at first (65) of course you don't put in flaps until you've got your field made, then once you have full flaps they want you to pitch for 60 because the airplane will handle fine at that speed with flaps, also you will hit the barn, ditch, fence, irrigators, trees, rocks, water or whatever going slower. The idea is to get minimum safe airspeed before you touchdown, so that you can survive your poorly planned approach. Make Sense?