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06-02-2012, 12:13 PM
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Join Date: Dec 2008
Location: Los Angeles, CA
Posts: 301
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altitudE loss
I think these experiments are showing a falacy that every young pilot has. That is there is a lot of altitudE loss in the turn. Gliders have long wings ( low span loading) so do not lose nearly as much altitude. But an RV with short wings is going to be losing a lot of altitude just turning around. If one is nervous About laanding straight ahead I would think a box departure would be best.
(Sorry for any errors sent via crappy blackberry)
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06-02-2012, 01:14 PM
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Join Date: Jan 2005
Location: Ottawa, Canada
Posts: 2,357
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Quote:
Originally Posted by Ron Lee
I am not pleased with the airspeed control.
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Ron - Good on you for doing the testing.
You aren't happy with the airspeed control when you were all prepared to do the test, you were at a nice safe altitude, you knew the engine would restart as soon as you pushed the mixture forward and you knew there was no personal risk. Think about what the airspeed control would probably be like if the engine failure caught you by surprise, you were close to the ground and knew you had only one shot to pull this off, and if you screwed up you might die.
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06-02-2012, 01:36 PM
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Join Date: Jun 2005
Posts: 3,275
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Kevin, my poor airspeed control was not letting it get a bit lower. That should have reduced the altitude loss.
I was well away from a stall/spin situation (whether due to "fear" or safe pilotage is subject to debate).
Another factor is that on a typical departure I have turned crosswind before this point. So really I would be looking at a 180 to the crosswind runway.....possibly a 90 degree to a north-south road. There are plenty of open fields.
I just do not see now how I could get the height down to circa 600' or less as others suggest.
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06-02-2012, 03:02 PM
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Join Date: Jan 2005
Location: Ottawa, Canada
Posts: 2,357
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Quote:
Originally Posted by Ron Lee
Kevin, my poor airspeed control was not letting it get a bit lower. That should have reduced the altitude loss.
I was well away from a stall/spin situation (whether due to "fear" or safe pilotage is subject to debate).
Another factor is that on a typical departure I have turned crosswind before this point. So really I would be looking at a 180 to the crosswind runway.....possibly a 90 degree to a north-south road. There are plenty of open fields.
I just do not see now how I could get the height down to circa 600' or less as others suggest.
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The data I have seen from many others seems to be with the engine running at idle, which covers the dreaded "throttle cable breaks and engine suddenly goes to idle" failure case.
The drag with the engine off and a windmilling prop is quite different from what you have if the engine is still running, and the descent rate will be higher. Your testing is much more realisitic from a performance point of view, but it is hard to simulate the "startle factor" you'd have in a real engine failure. Your piloting performance would likely be quite a bit worse in a real engine failure, and that would have an effect on the altitude loss in the turn (assuming you successfully avoided the stall/spin scenario, which is actually quite a big assumption based on actual accidents).
Last edited by Kevin Horton : 06-06-2012 at 04:37 AM.
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06-02-2012, 03:08 PM
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Join Date: Jan 2006
Location: Dallas, TX (ADS)
Posts: 2,180
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One thing to remember is that "RV" means a lot of different things. The -8 is going to be challenged to do this maneuver in the same amount of altitude than the -12 can.
Wing loading is very different amongst the different models. The -12 is the low wing loading champ at 10.4 lb/sf at MGTW. This is a lot lower than my CT, which is 13lb/sf at MGTW. -8 is probably highest around 16lb/sf. So wing loading isn't so much the issue.
It's probably more about aspect ratio. RVs (except the -12) have fairly short wings that produce more drag than a long, high aspect wing that you'd find in a Diamond or sailplane. The -12 is a little shorter span than many other LSAs, but not hugely so.
As far as airspeed, do you have a "floor" approach speed that you use as a hard floor, i.e., no going below it?
I maintain that the most important thing is to know the limits of you and your airplane and obey them.
TODR
__________________
Doug "The Other Doug Reeves" Reeves
CTSW N621CT - SOLD but not forgotten
Home Bases LBX, BZN
Last edited by the_other_dougreeves : 06-02-2012 at 03:11 PM.
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06-02-2012, 03:24 PM
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Join Date: Oct 2006
Location: Glendale, AZ
Posts: 256
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Similar test in a different AC
I did the same "impossible turn" excercise in a Cirrus SR22 and came up with performance numbers for that airframe. Same set up (road for runway, at altitude, etc), airspeed numbers a little lower (90 KIAS - which is very near best glide and typical for that state of a TO) and a 45 degree bank (had to work up to that). Half flaps because that is the POH take off configuration. One key finding was the return to the airport turn needs to be into the wind to lessen the distance you got away from the centerline of the runway (this turns out to have a big effect actually). You really have to nail airspeed control and keep the turn tight, not a lot of margin from an accelerated stall. Lower speed was also important, since speed increases the radius of the turn - letting the plane speed up hurt a lot. Did lots of them to get to this level.
I was able on only one occasion to make 600 feet work (since I never was able to repeat it I consider that an anomoly). I got with practice to be pretty regularly able to make 700 feet work. In real life I would want some margin beyond my demonstrated 700 feet to even remotely consider trying it.
Thanks for doing this test, perhaps my findings can help. My RV is not flying yet, but when it is I will repeat the test in it.
Quote:
Originally Posted by Ron Lee
I did my first tests today. I decided on a road that would be used to start the procedure. My energy state was 120 MPH indicated, 700' AGL and 800 FPM climb.
Up to altitude and do several tests pulling the mixture to cutoff...engine stops running then idle mixture in again. It works as it should. Prop never stops.
Climb up to 5000-6000' AGL and set up the target airspeed and climb rate. At the road, mixture to cutoff. I started pushing the nose down too quickly since I wanted to wait a few seconds. Thirty degree bank. IAS always above 100 MPH indicated and when over the runway I had lost 1200'.
Second try I bank 45 degrees. Airspeed still too high and again around 1200' lost.
I am not pleased with the airspeed control. Plus if I am higher, I am also further from the airport so will have to make adjustments the next time I try it.
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__________________
Roger Whittier
RV7A Quick Build, Tip Up
N1MY Reserved - Canopy finished - Wings mated, Engine hung, electrical 95%
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06-02-2012, 05:38 PM
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Join Date: May 2008
Location: Brisbane Qld. Aust.
Posts: 2,271
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Interesting post Roger.
Kevin is quite correct, you must know the numbers and how you will react if it goes quiet.
The difference is Kevin, from making good pilotage straight ahead, or slightly left or right, or all the way around to a road or taxiway or another runway.......you still have to fly there. If you are scared witless because you have not trained for this, you are going to underperform anyway.
I have said this several times before, know your aeroplane, my -10 will do what a -6 will never do. Know your aeroplane. Know your available options.
Practise carefully .....plenty written already.
A good pilot is never surprised when an engine fails after take off, he is surprised when it does not.
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06-03-2012, 10:54 AM
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Join Date: Jan 2006
Location: Dallas, TX (ADS)
Posts: 2,180
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Quote:
Originally Posted by rwhittier
One key finding was the return to the airport turn needs to be into the wind to lessen the distance you got away from the centerline of the runway (this turns out to have a big effect actually).
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It's a huge advantage to turn into the wind. Obvious, but you're unlikely to do it unless you practice.
The one thing that amazed me - and made me change my flying habits - is that I used to climb to about 500ft at Vx. When I tried the 180 return doing this, I was so high that I barely had enough runway to land on, even slipping like crazy. Climbing out at Vy, I'm able to return to the runway much easier. So now, I climb at Vx only to about 100ft and accelerate to Vy. Now, this is for a very slick airframe like the CT, probably different for RVs.
TODR
__________________
Doug "The Other Doug Reeves" Reeves
CTSW N621CT - SOLD but not forgotten
Home Bases LBX, BZN
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