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Kawa rough landing?



 
 
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  #131  
Old September 23rd 19, 08:24 PM posted to rec.aviation.soaring
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Default Kawa rough landing?

On Monday, September 23, 2019 at 1:57:40 PM UTC-4, Eric Greenwell wrote:
2G wrote on 9/22/2019 9:21 PM:
On Sunday, September 22, 2019 at 8:15:41 PM UTC-7, Eric Greenwell wrote:
2G wrote on 9/22/2019 1:43 PM:

The bottom line is that the total drag of the 26e prop+mast+radiator+engine bay doors drops the glide from 50:1 to 17:1. At best, what you are arguing about is the relative contribution of these elements - my bet is on the prop being the largest. But the only thing that matters is the total drag..

Don't forget the massive landing gear that puts the wheel and tire almost entirely
outside the fuselage (and it has doors with a frontal section nearly as big as the
engine doors)!


I'll have to redo my measurements of years ago. I recall getting about 20:1 in
landing configuration, but I can't find my notes. Who did the 17:1 measurement?

Another data point: In 2008, Dr Jack had the belt break on his 26E, stopped the
engine, but was unable to stop the freely spinning propeller. He wrote "From my
GPS trace the glide ratio during the straight portion of my descent, at around 55
kts in flap 3 with prop spinning, as 18.5"

So, gear up, but prop spinning, he was able to glide about 7 NM to an airport,
then encountered some lift and thermalled up, and briefly considered thermalling
the 11 NM to his home airfield, but decided it was smarter to land. Hardly sounds
like a glider in "plummet mode"?


--
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


I had a non start(pilot induced) the other day in my ASG-29E. I was positioned on down wind for my selected field. Rather than mess with the engine(and associated distraction)I put the gear down and landed normally. Since I usually fly a fairly steep approach, I did not sense any meaningful affect on my landing.
FWIW
UH
  #133  
Old September 23rd 19, 09:48 PM posted to rec.aviation.soaring
john firth
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Default Kawa rough landing?

On Saturday, August 31, 2019 at 3:31:32 PM UTC-4, Jonathan St. Cloud wrote:
Not sure how accurate FB translate is, but it appear as if Mr. Kawa had some sort of incident with an electric motor not working and a rough uphill landing. Gas, electric or jet be careful guys!


Re prop drag;
At the end of towing in the Citabria, I would cut the engine and then stall
it to stop the wind-milling. This reduced the for a reasonable L/D.
However, a wind-milling prop running free probably has much less drag than
stationary prop.
Who will perform a test?

John F
  #134  
Old September 23rd 19, 11:08 PM posted to rec.aviation.soaring
Eric Greenwell[_4_]
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Default Kawa rough landing?

john firth wrote on 9/23/2019 1:48 PM:
On Saturday, August 31, 2019 at 3:31:32 PM UTC-4, Jonathan St. Cloud wrote:
Not sure how accurate FB translate is, but it appear as if Mr. Kawa had some sort of incident with an electric motor not working and a rough uphill landing. Gas, electric or jet be careful guys!


Re prop drag;
At the end of towing in the Citabria, I would cut the engine and then stall
it to stop the wind-milling. This reduced the for a reasonable L/D.
However, a wind-milling prop running free probably has much less drag than
stationary prop.
Who will perform a test?


http://www.peter2000.co.uk/aviation/misc/prop.pdf

The article concludes "it depends"; briefly, high pitch - let it rotate, low
pitch, stop it. Other sources pointed out helicopters autorotate to slow their
descent with the engine disconnected, and clearly that's slower than stopping the
blades!

I'm guessing a 26E with a broken belt has more drag from the spinning prop than a
stopped prop, but do not plan any testing; however, I will be happy to do a
comparison glide with another 26E that has the belt removed. That could be done on
the ground, and then glider towed to height required for the test glide.

--
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
  #135  
Old September 23rd 19, 11:52 PM posted to rec.aviation.soaring
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Default Kawa rough landing?

Interesting rotating verses stationary, I always was taught in power that a rotating prop was more drag than a stopped one as the rotating one acted more like a "disc" than just 2 blades stopped. But know real evidence of that.

CH
  #136  
Old September 24th 19, 01:24 AM posted to rec.aviation.soaring
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Default Kawa rough landing?

We should get an aero engineer to comment but in simple terms the AOA of the prop can become negative with a windmilling prop(depending on pitch design and rotational speed). If that happens you get negative thrust.

  #137  
Old September 24th 19, 04:26 AM posted to rec.aviation.soaring
2G
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Default Kawa rough landing?

On Monday, September 23, 2019 at 5:24:13 PM UTC-7, wrote:
We should get an aero engineer to comment but in simple terms the AOA of the prop can become negative with a windmilling prop(depending on pitch design and rotational speed). If that happens you get negative thrust.


Here is a study of the subject:
http://www.peter2000.co.uk/aviation/misc/prop.pdf
Conclusion: it depends.

In this paper the same conclusion is reached (note the date):
http://naca.central.cranfield.ac.uk/...report-464.pdf

Tom
  #138  
Old September 26th 19, 08:21 PM posted to rec.aviation.soaring
5Z
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Default Kawa rough landing?

On Monday, September 23, 2019 at 10:57:40 AM UTC-7, Eric Greenwell wrote:
I'll have to redo my measurements of years ago. I recall getting about 20:1 in
landing configuration, but I can't find my notes. Who did the 17:1 measurement?


When I had my '26E, I once flew several self launches to pattern altitude, shut down the engine and landed with the prop extended. It was a complete non-event and felt the same as a pattern and landing in an ASK-21. I like to fly a high and steep final so maybe that's why. I probably used less spoiler in the '26E to maintain the same approach angle. I also applied landing flaps sometime between base and final.

When making a "straight in" type final glide with just a couple hundred feet arrival when some distance out, I'd pick a (or already have one in mind) a few miles out if it still looked marginal. I'd then start the engine, make a few orbits over the safety field to gain altitude, then motor home. Once home, I'd retract the engine part way to cool it and make a landing.

I once joined a ASW-20B in an extremely weak thermal, shut down the motor and again lowered it to the slightly extended cooling position. We were pretty much even in climb and even while gliding to another thermal a mile or two away. So my takeaway there is that at speeds around 60 knots, the open engine doors and partly extended engine produce negligible drag.

IMHO, the dire warnings about poor LD on the POH are there to avoid any liability if someone decides to sue after an engine extended mishap. Or to be a bit kinder, like what we tell new glider pilots about thermalling low - stop trying to stay up and just land once at XXXX above ground.

5Z
Now flying ASW-27b
  #139  
Old September 26th 19, 09:13 PM posted to rec.aviation.soaring
Eric Greenwell[_4_]
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Default Kawa rough landing?

5Z wrote on 9/26/2019 12:21 PM:
lowered it to the slightly extended cooling position.


The "slightly extended cooling position" is about 30 degrees from the fuselage.
There is still all the stuff hanging in the breeze: the propeller, the radiator,
almost the entire mast, and the doors are fully open. It looks dreadfully draggy
to a pilot circling in the same thermal with you, but it's just like Tom says: the
drag is so small, you don't know it's there.

--
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
  #140  
Old September 26th 19, 09:30 PM posted to rec.aviation.soaring
JS[_5_]
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Posts: 624
Default Kawa rough landing?

On Thursday, September 26, 2019 at 1:13:07 PM UTC-7, Eric Greenwell wrote:
5Z wrote on 9/26/2019 12:21 PM:
lowered it to the slightly extended cooling position.


The "slightly extended cooling position" is about 30 degrees from the fuselage.
There is still all the stuff hanging in the breeze: the propeller, the radiator,
almost the entire mast, and the doors are fully open. It looks dreadfully draggy
to a pilot circling in the same thermal with you, but it's just like Tom says: the
drag is so small, you don't know it's there.

--
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



Got so concerned with staying under the LAS Class B once, didn't completely put away the ASH26E mast until after a cruise to the second thermal. A bit noisy but no big deal.
Once climbed in the 26 together with a Discus 2. I still had the mast in cooling position, the D2 was "P7". Impressed!

Enjoying Fred Drift this time, Seems like Kawa was being condemned for nothing.
Jim
 




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