Thread: CTSW Best Glide speeds

Other day I was doing some training and my CFI pulled an engine failure. I was in -6 flaps and went to achieve the POH list best glide of 56K and before it got to 56 I felt a stall coming on. I first attributed it to the unstable air and since I already had a good landing spot and needed to loose about 1000ft I decided to just let it stall, get some speed and raise the nose back up. I then realized my flap setting and set it to 0 which allowed me to glide at 56k without stalling but I find the posted best glide speeds are not accurate. I found I glide much better at 65-70 at 0 flaps. I'm not sure where FD got 56 from but I'm finding its not the right number. Even at flaps 15, I glide better at 60-65 than 56. I haven't compared the glides speeds with and without a passenger and now I'm curious. We were close to MTOW. I wonder if the weight changes the glide and if so, how much. Also, isn't posted stall speed at 44 with -6? Why did it stall on me at 56? Possibly a gust from behind? I wasn't yanking back on the stick causing a high aoa....

could it be attributed to density altitude?

Originally Posted by Teamplayer

could it be attributed to density altitude?

I doubt it. We rarely have high DA in Minnesota. I was at about 3000'msl.

Originally Posted by Teamplayer

could it be attributed to density altitude?

no, with high density altitude the indicated airspeeds (including stall speeds) do not change, your ground speeds however do.

i don't think weight is a big factor either, you are looking for your best lift / drag ratio.

Originally Posted by CharlieTango

no, with high density altitude the indicated airspeeds (including stall speeds) do not change, your ground speeds however do.

i don't think weight is a big factor either, you are looking for your best lift / drag ratio.

So CT, your saying that I just need to find what works best for the plane? I would think -6 would give better glide because of reduced drag but then the wings probably produce more lift at 0. Need to find that balance I guess. I got the plane booked for 4hrs on Friday (1 week from my checkride - yikes) and am doing everything I can to cover all bases. I would hate be on my checkride and stall the plane. That would be bad. I must be a slow learner because after 30hrs, I'm still struggling with stuff I should already know. They say the older you get the more hours it takes. I'm 44. At this point hours aren't a concern, I just want to master the beast. My plan for the 4 hours is to have the PTS in my lap and basically do a self test checkride. I am also going to spend some more time doing slow flight which I hope will help.

Hi James,
At zero flaps 60 works well and gives good solid control on the flight surfaces. It also gives you some degree of safety above stall and if you aren't watching the air speed then you have a little time before you stall and it's too late. 55-60 is good for 15 flaps too. With a real engine off scenirio staying too close too stall good be catastrophic if you really do stall close too the ground.

James,

I'm not sure that best glide for the ctsw is published. I think I get best glide at 10 degrees flaps (probably close to 15) and about 62kts.

reducing drag improves the l/d only to a point because you are reducing lift as well. minimum sink is not the same as best glide but it is also a useful speed configuration to know and an easy one to test. i think that minimum sink and best glide are found at the same flap setting.

i question your perception of immenent stall at 56kt

Originally Posted by CharlieTango

James,

i question your perception of immenent stall at 56kt

So do I! The only thing I can think of it was gusty and little rough. I am always careful and watch my aoa. It was a full stall, the nose just dropped while trying to maintain 56k at -6 with power off. I'm going to try to recreate it on Friday and then play with different settings. I usually cross the threshold at about 55K with 0 flaps and power off and have never felt it want to stall before. That's why this has me so curious. I'm going to climb up to about 6000 and do some experimenting with a tail wind. Also, I forgot to mention one of the wheel pants screws was out and it was loose but I can't see that having anything to do with it because it was the rear screw and the wind would hold it in place.

fwiw... 'went up for my BFR last week, did a bunch of stalls including some power off, but never saw anything anywhere near that fast. In fact, it's a chore to get it to stall... Can't trust the pitot speed when AOA is way big, but gps showed around 39kt. Power-on sometimes showed 29kt, because it was just hanging on the prop.
Tim

Hi James,

The Apr 08 edition of the CTSW AOI lists best glide in section 7 as 63kts. I use this number for my students with -6, 0, and 15 flaps and it seems to work well. It is a little conservative based on the power off stall speed but it provides a safe margin from stall and plenty of energy at the flare to stop the descent rate.

Eric Swisher
Copper City Aviation Services