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  #1  
Old 01-06-2021, 06:46 PM
Mdragon Mdragon is offline
 
Join Date: Nov 2020
Location: Jacksonville Florida
Posts: 19
Default Technique for descending from altitude

I知 a new pilot and new RV9 owner. I知 still trying to figure out a good technique for a nice controlled descent into my destination airport. I値l be cruising along at 170 mph, say at 4500 feet, and then have trouble losing the altitude and speed by the time I get to the pattern. I have a fixed pitch prop.

What do most of you do to gradually bleed off speed and altitude? Any particular rpm, TAS?

My plane just want to glide and glide and keep its speed.
Not a bad thing, but haven稚 quite figured it out yet.
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  #2  
Old 01-06-2021, 07:01 PM
crabandy crabandy is offline
 
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Location: Ottawa, Ks
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Use your Vnav to configure your descent. If I’m getting a good tailwind and temp up high I’ll stay up longer and use 800-1000 fpm. If I wanna leave the power in and and pick up speed in smooth air I’ll use 200-400 fpm. Both cases I aim to be at pattern Alt 3-5 miles out with an incremental pull to idle as I level over a couple miles sets me up nicely for flap speed as I approach the pattern.

Using C172/Pa28 power settings for the pattern in an RV won’t work, if your at 160 knots/level just off idle a mile or so from downwind should set you up close.
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  #3  
Old 01-06-2021, 07:18 PM
Robin8er Robin8er is offline
 
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Location: Socal
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Here is a simple technique:

Take your current altitude and subtract the altitude to loose and divide by 500 fpm. That is how many minutes out you should start decending.

Example: cruising at 9500 feet, pattern altitude is 2500 feet. Altitude to loose is 7000 feet. Divide that by 500 = 14 minutes.

Add about 2 minutes for the slow down. So 16 minutes away from the airport at cruise speed/altitude start your decent at 500 feet per minute and you'll arrive at pattern altitude about 3 miles before your airport, which will allow you to slow down and enter the pattern.

Whats awesome is all you need to do is throttle back a little, no need to touch the trim. This keeps the engine from cooling too fast and also allows for a nice comfortable decent.

Sometimes it's surprising how early you have to start down. The other day I stated down 40 miles out and thought "that can't be right" but with a good tail wind and alot of altitude to loose it was infact correct.
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  #4  
Old 01-06-2021, 07:25 PM
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bhester bhester is offline
 
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Location: Hopkinsville, KY
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I agree VNAV is your friend. I set mine up for 500 fpm 1000 above waypoint and a couple miles before waypoint. You’ll get an approaching VNAV message, activate it and if you don’t have an autopilot on follow your VNAV indicator. Easy Pasy :-)
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  #5  
Old 01-06-2021, 07:28 PM
David Paule David Paule is offline
 
Join Date: Dec 2009
Location: Boulder, CO
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One subtle thing is that as you descend, the manifold pressure increases as the air gets denser. For a fixed-pitch prop you'll probably see that as increased rpm. With either prop, you need to gradually reduce throttle as you descend.

Don't forget to increase the mixture, too, if you've leaned for the cruise.

Dave
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  #6  
Old 01-06-2021, 07:42 PM
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bruceh bruceh is offline
 
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My easy rule of thumb is to plan for 5 miles per 1000' of descent. I just trim to 500' per minute descent and pull back the RPM's from cruise (around 2470) to 2200 RPM. If I'm cruising at 147-150 Kts, then without pulling the power I'll be easily doing 155+ Kts, which is fine if the air is smooth. Once I hit the Delta airspace (4 miles out), I can throttle way back to 1500-1700 RPM in order to slow down and fine tune the descent to pattern altitude.
I also will put the pattern altitude into the EFIS. On the Skyview, it will show an "arc" on the screen where you will hit that altitude. The EFIS will also give you VS guidance to meet that altitude at your waypoint.
If you really need to slow down in the RV-9A, throttle to idle and keep holding altitude. Several miles later you'll be at Flap speed.
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  #7  
Old 01-06-2021, 07:43 PM
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DanH DanH is offline
 
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Quote:
Originally Posted by Mdragon View Post
I知 a new pilot and new RV9 owner. I知 still trying to figure out a good technique for a nice controlled descent into my destination airport. I値l be cruising along at 170 mph, say at 4500 feet, and then have trouble losing the altitude and speed by the time I get to the pattern.
Easy head math. Multiply altitude above pattern x 2 x miles per minute to know how many miles out to start a standard 500 FPM descent. In your example you want to lose 3.5 thousands while traveling at almost 3 miles per minute. So, 3.5 x 2 x 3 = 21 miles. 150 mph would mean 3.5 x 2 x 2.5 = 17.5.

Normal part of the RV transition for many.
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  #8  
Old 01-06-2021, 08:13 PM
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MacCool MacCool is offline
 
Join Date: Aug 2020
Location: central Minnesota
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My goal is to be at 90 kt and pattern altitude 10 miles from the the airport and entering the VFR approach I've put into Foreflight (which in turn has been sent to my EFIS over wifi). I use an app called Descent Calculator. For me, it simplifies the math but if you're really smart, you can do it in your head. At the appropriate calculated distance out, I pitch at about -2.5 at 20 inches and 2300 RPM, which usually gives me -500 FPM. Airspeed is whatever. If I'm that high, I pull back to 2100 RPM and will pitch for 1000 FPM. When I hit pattern altitude, I come back to 15 inches and 2100 RPM, and at 90 kts will put in 10 degrees of flaps. I fly 90kts into downwind and then will slow to about 80 kts and put in another 10 degrees of flaps. Once I turn final, I'll be at about 70 kts and adjust power appropriate to my landing spot.
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  #9  
Old 01-06-2021, 08:19 PM
ty1295 ty1295 is offline
 
Join Date: Aug 2011
Location: Jeffersonville, IN
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As mentioned plan ahead and come down at a nice pace. For me I have the dynon HDX and it will show me what FPM I need to decend to get to pattern altitude, when it gets close to 500 I set A/P or trim to attain that.

Best way I have found in the 9 to loose altitude close in, and not gain speed is to get it slowed down first, point it down and you will just convert altitude to speed. Slow it down to flap speed, get the flaps out, keep it slower and it will come down much better.
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  #10  
Old 01-06-2021, 08:33 PM
BobTurner BobTurner is offline
 
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Location: Livermore, CA
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Quote:
Originally Posted by MacCool View Post
My goal is to be at 90 kt and pattern altitude 10 miles from the the airport ...
That strikes me as unnecessarily low for that far out.
1. I try to descend at a rate that gives me a chance of making the airfield if the engine should quit.
2. 700 or 1000 over a city or town 10 miles out just creates ill-will from non-pilots, and may even be an far violation.
3. My home field is in a valley. 10 miles out at pattern altitude puts me underground!
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