Glide Ratio

[NC Bill]

Assuming a frozen prop at MaxGW on a standard day, what distance do you figure to glide for each 1000' AGL?

[chanik]

Stopped is much better than freewheeling so my guess would be 16:1, up from 14:1 glide ratio. I don't know that anyone has tried it empirically though.

[NC Bill]

The POH on page 5-11 says 8.5:1.

 

I calculate that to be less than 1.5nm per 1k'.

 

Figuring all the "perfect situation ingredients" that go into the calculation and for now my planning will be 1nm per 1k'.

[chanik]

http://www.flight-design-southeast.com/CTsw.htm

I've always seen 14:1 quoted. Even a sluggish 172 is 7.5:1 so 8.5 seems pretty low. I guess I'll have to measure it myself some day

[CT4ME]

CTSW sales literature has always referred to 14:1.... engine off...

http://www.flight-de...st.com/CTsw.htm

CTLS, too...

http://flightdesignusa.com/aircraft/ctls/specification/

 

Tim

[NC Bill]

Salesmen...ya gotta love 'em.

[CT2kflyer]

I have a CT2k with the longer wing, and it's advertised with a glide ration of 17/1. In that the SW has the shorter wing, 14/1 sounds about right.

[Jim Meade]

I have a CT2k with the longer wing, and it's advertised with a glide ration of 17/1. In that the SW has the shorter wing, 14/1 sounds about right.

 

What does the POH say? The LS says 8.5:1, kinda. The SW doesn't seem to say. Unless I'm looking in the wrong place. Those two are advertised with 14:1. I wonder about the difference between the ad content and the POH?

[CT2kflyer]

What does the POH say? The LS says 8.5:1, kinda. The SW doesn't seem to say. Unless I'm looking in the wrong place. Those two are advertised with 14:1. I wonder about the difference between the ad content and the POH?

 

The CT2k is document lacking........ in fact some of what I have is in German, not English. Glide ratio is not covered in the POH. Other sources indicate 17/1 for the CT2k, with one pilot commenting that it may be as high as 21/1 - which is doubtful in my book. I'll stick with 17/1.

[NC Bill]

OK - who volunteer to be the test pilot

 

Bill

[Runtoeat]

Roger Lee, do I recall you saying that you've dead sticked your CTSW?

[coppercity]

I'll test it out with our LS and let you know the results ! It will be at some higher density altitudes then most of you fly but it should prove the CT is a pretty good glider for having such short wings.

[coppercity]

Ok, here is the first data point I captured today.

 

First the setup:

 

2009 CTLS, with myself and 1/2 tank of fuel, and a few pounds of stuff in the foot storage. That puts me about 1100lbs.

 

Starting pressure altitude 9000ft, temp 11c, density altitude 10571ft. Ending pressure altitude 7000ft, temp 16c, density altitude 8688ft.

 

Winds aloft light and variable, turbulence none.

 

Test 1:

Flaps 0 and maintaining the book glide speed from the CTSW of 63kias. Engine OFF, prop stopped.

 

At this setting I managed to glide 1.9nm every 1000ft of altitude lost so that calculates out to a glide ratio of 11.5 to 1. Average rate of descent was 645fpm.

 

Test 2:

Flaps -6 and maintaining the book glide speed from the CTLS of 78kias. Engine OFF, prop stopped.

 

At this setting I managed to glide 1.8nm every 1000ft lost giving a 10.9 to 1 ratio. The average rate of descent was 835fpm.

 

 

This is just one quick test, as I get time I will try to do some more longer glides at some lower altitudes and post those results.

On a side note, my engine on idle rpm at 63kias was about 2200 and that reduced the descent rate to about 600fpm so even at idle the engine is making a little thrust. With the engine off and at 78kias the prop/engine will flip over a blade occasionally. Not near enough to start but it does rotate once in awhile. Oh yeah, it gets pretty quiet ithe cockpit with the engine off!

[coppercity]

Hi Roger,

 

It was fun! Always had a airport under me to land on though...just in case. It is a little concerning seeing the prop stopped in front of you!

[Tom Baker]

Hi Eric,

 

Isn't that fun!!!

I love to do that. If I reach over and turn the engine off I can make most CFI's freak out. Most people don't like quite stopped engines. If you take the air speed back up to 100 the prop will turn over fairly easy.

 

I've done this with an old T-Craft before. The T-Craft takes 1000 feet and 120 MPH to restart. No electrical system, and I was not getting out to prop it.

[Runtoeat]

Eric, this is good info. and thanks for publishing this. It gives me knots in my stomach thinking about stopping the engine. For the time being, doing SIMULATED engine out landings will be enough excitement for me. TRUE engine out testing will be with someone sitting next to me with a lot of hours.

 

Recently, I have been working with my check list and wanted to make sure of the "Best Glide" speed for my CTSW. Section 7 of the CTSW POI deals with Engine Failure. Page 7-1 says to establish a "best glide speed of 63 kts" but doesn't say at what flap setting. The next paragraph says to "maintain a minimum speed of 63 kts @ 15 flaps until final approach". I assume from this that the "best glide" then is 15 flaps @ 63 kts. for the CTSW. However, one can also read the CTLS POI and section 3.7 here says that the "best glide speed is 78 kts @ 0 degrees flaps.

 

I note for your first test that you did 0 degree flaps at 63 kts. Should the "best glide" have been 15 degree and 63 kts. as the CTSW POI section 7.0 (seems) to show? Also, I see that your 2nd test was at -6 flaps @ 78 kts. Should your "best glide" have been what the CTLS AOI section 3.7 says: "Best glide speed is 78 kts. @ 0 flaps?

 

I'm not trying to argue here, just trying to figure out what best to shoot for, should the "oh sh*t" event ever occurs.

[FastEddieB]

ESection 7 of the CTSW POI deals with Engine Failure. Page 7-1 says to establish a "best glide speed of 63 kts" but doesn't say at what flap setting.

 

I don't think flaps can ever help glide ratio, given that they increase drag.

 

I could be wrong on this, and will pull out Aerodynamics for Naval Aviators to look it up if requested.

 

The CT, with negative flaps possible, might make this even more complicated.

[coppercity]

Hi Dick,

 

I did that setup mainly for my own curiosity. as I get time to collect more data points I will hit the other configurations and speeds.

 

In order to keep things simple for my students I have selected 63kias for best glide at -6 to 15 deg flap settings. It may not provide the best glide ratio for all scenarios but it is one number that provides plenty of margin from stall, provides a good amount of time aloft and plenty of energy for stopping the descent for landing. Once you go beyond 15 deg flaps you are committed to landing and should use 54 KTS then to around 48 KTS just prior to touchdown. it is good practice to do power to idle approaches to a spot landing. When you can consistently touchdown within a 100 ft of your intended landing zone, smoothly, and without power assist, you are really learning to handle your aircraft well. It's tough to do when there are wind gusts and thermals so knowing how to handle power on approaches is just as important. Also be careful with the CT power off and high flap settings because it does bleed speed off quick if you flare to high your going to land hard, and that isn't good for any plane. I know you old Navy pilots fly like that but it's not for LSA!

[Runtoeat]

Hi Eric. Thanks. Your results will be interesting.

[Jim Meade]

My friend Don Gurnett is a very good glider pilot and quite knowledgeable about aerodynamics. He offered the opinion that negative flaps would increase speed but not improve the zero degree flap best glide.

[DocRon]

This subject area is a perfect example of why I wanted (and needed) to join this Forum. Terrific information presented by highly competant people. I really appreciate it.

[FastEddieB]

BTW,

 

How does an increase in weight affect the distance you can glide?

 

Discuss...

[NC Bill]

Always wanted to be a "test pilot" - not just a "testy old pilot".

 

So I took the challenge. But not before I convince my friend and glider instructor to go with me.

 

Eric at Coppercity was patient and answered a bunch of questions first.

 

Long story short, after counting 1001-1002-1003 before any reaction and prop stopped at DA 4600', Glide speed 75 kts, Temp 17C, 1250 lbs GW, the CTLS got between 8.5 and 9.0 on 3 attempts.

 

FWIW from now on I'm choosing 1.5nm for each 1k' AGL. Just hope my reactio time is within those 3 seconds

 

The gooder news is I also tried the dreaded 180 degree turn, again after a 3 count, and was pleasantly surprided to be able to bring the CTLS around with an altitude loss of between 300' and and 325'. But my friend the glider instructor (commercial pilot and A&P) cautioned me to use the following as a guide to returning to the runway of departure. Only once you have completed the 90 degree turn to X-wind should you attempt and engine out return to the runway in a powered plane. So from now on my plan is unless I can LAND straight ahead I pull the BRS over 200' AGL and until I'm X-wind when I will attempt a return to the runway.

 

That's just me...your mileage may vary, no guarantees expressed or implied.

 

Bill

[josjonkers]

BTW,

 

How does an increase in weight affect the distance you can glide?

 

Discuss...

 

The gross weight does not affect the distance you can glide. This remains the same given any weight.

What does change is the speed at which you achieve best l/d. The heavier the plane (glider) the faster the best l/d speed is.

 

This is the reason why sailplanes put water balast in their wings to go faster around a particular course and dump that at the end of the day when thermal conditions become weaker and they need to lighten up to still use the (now) weaker thermals so they can still climb in these , whereas they might not be able to if they are too heavy.

 

Hope this helps.

 

Regards,

 

Jos

[FastEddieB]

The gross weight does not affect the distance you can glide. This remains the same given any weight.

 

Jos,

 

Bingo!

 

It's hard to conceptualize, but given a calm day, from 5,000', a CT made of balsa wood weighing 200 lbs and one made of lead weighing 20 tons would glide the same distance.

 

I imagine the balsa wood plane gently wafting down at just a few knots, and the lead plane screaming down at hundreds of knots, but in theory they would hit the ground at the same point.

 

Just one of those counterintuitive things that keeps flying interesting!