That TLAR doesn't look right

On Sunday, July 12, 2015 at 8:08:41 AM UTC-7, wrote:
A 180 turn can definitely be performed within 600 feet, but then it has to be done quickly, with a good bank angle, and there is little room for adjustments in elevation. A safe 180 turn type of approach (naval aviator) requires (I think) bank angles that are less than 45 to have the room and time to adjust the rate of descent. In some way it is like having a curved base leg. But you may not do it safely if you are too close.
Please Dan correct me on this, I am not used to do the naval pattern.


Look at the landing pattern in some IGC files on OLC. I don't think you will find many that use a 45 degree angle.

Just for curiosity, I looked at the recent landings at Hobbs of one of the competitors. When he passed the touchdown spot on downwind on July 1, he was roughly 450' above it and 1900' away. This is a ratio of 1:4, not 1:1. The next day his numbers were roughly 700' and 2200', for a ratio of 1:3.

I doubt if anyone can find many IGC files with numbers of 600' and 600'.

OK, I think we have (at least) two different ideas being discussed here, attached to the 45 degree value.

If you look at the article (which I have) one 45 degree reference is to the angle from the base-turn corner looking back to the touch down point. This is a common reference for almost any rectangular pattern described in a myriad of training manuals. It works pretty well for locating the base turn position, provided that enough altitude remains to complete the pattern.

There is the second reference to 45 degrees, which places the glider above the touch down point at the same distance laterally. This is the point (pun intended) where I think we have a few differences of opinion, mainly due to differences in altitude on the downwind. A lower performance (also slower) glider can easily be at 600' lateral displacement and have time and altitude to make corrections on the base leg due to the slower speed.

A faster, higher L/D glider needs a lot more distance/time to dissipate energy and being 600' laterally abeam the touch down would create a significant challenge, both with the turns required to intercept final and the 45 degree base base turn reference.

The article covers the extended downwind as a function of glider performance and clearly explains the need for adjustment.

Having said all that, at our field both a higher and wider pattern is typically flown and I believe the reference angle abeam the touchdown point is often closer to the 30 degrees noted by others.

MB

On Sunday, July 12, 2015 at 5:31:27 PM UTC-6, SoaringXCellence wrote:

A faster, higher L/D glider needs a lot more distance/time to dissipate energy and being 600' laterally abeam the touch down would create a significant challenge, both with the turns required to intercept final and the 45 degree base base turn reference.


Not really. EASA CS-22 paragraph 22.75 under which most high performance gliders were certificated says:

"It must be shown that the sailplane has a glide
slope not flatter than one in seven at a speed of
1·3 Vso with air brakes extended at maximum weight."

So basically all JAR-22/CS-22 gliders have less than 7:1 L/D with the spoilers open.

I've done several 45 degree angle of depression approaches with an early model DUO and it worked out fine.

An interesting discussion. As a long time user and proponent of the
TLAR method, I had not thought much about what the actual angles were.

Really easy to check with SeeYou and an IGC flight log. When I checked
my last 2 flights I found a pretty consistent 1km offset, with
altitude usually around 600 ft (opposite touchdown point, not pattern
entry). This is a 5:1 slope, about 12 deg. This is in a Ventus C.

Bob

On Sun, 12 Jul 2015 11:18:59 -0700 (PDT), wrote:

text deleted...

Just for curiosity, I looked at the recent landings at Hobbs of one of the competitors.
When he passed the touchdown spot on downwind on July 1, he was roughly 450'
?above it and 1900' away. This is a ratio of 1:4, not 1:1. The next day his numbers
were roughly 700' and 2200', for a ratio of 1:3.

I doubt if anyone can find many IGC files with numbers of 600' and 600'.

Bob Gibbons wrote on 7/12/2015 5:10 PM:
An interesting discussion. As a long time user and proponent of the
TLAR method, I had not thought much about what the actual angles were.

Really easy to check with SeeYou and an IGC flight log. When I checked
my last 2 flights I found a pretty consistent 1km offset, with
altitude usually around 600 ft (opposite touchdown point, not pattern
entry). This is a 5:1 slope, about 12 deg. This is in a Ventus C.

Bob


I found the same thing in the 4 or 5 of my flights that I checked that I
flew in my ASH 26 E, generally turning onto the base leg at 1000' AGL. I
don't think I could get down in time if I were to use 45 deg angle to
the runway while on downwind, even with the 40 degree landing flaps and
good spoiler.

--
Eric Greenwell - Washington State, USA (change ".netto" to ".us" to
email me)
- "A Guide to Self-Launching Sailplane Operation"

https://sites.google.com/site/motorg...ad-the-guide-1
- "Transponders in Sailplanes - Dec 2014a" also ADS-B, PCAS, Flarm

http://soaringsafety.org/prevention/...anes-2014A.pdf