ILS power settings for C172SP
 

I'm interested to see what power settings (i.e. revs) members use for flying an ILS approach in a C172SP (180 HP) for the following - (a) 100 kts, descending 500 fpm with 10 deg flap and (b) 80 kts, descending 400 fpm with 20 deg flap.

Tolka

In what wind?

Assume 5kt headwind

It's been a long time since I did my IR in a C-172; so, I don't recall the RPM.

However I never used flaps on an ILS in the SEPs I flew.

Any runway with an ILS is quite long enough and ATC would be happier if you flew the ILS at 120kt;)

At that speed I could still make the first turnoff landing at YYZ.

I always use 100 kts.....I reckon 17/1900 RPM in a 172SP ? Just a guess but sounds about right ;)

Not with burst tyres you couldn't.

'However I never used flaps on an ILS in the SEPs I flew.'

'Any runway with an ILS is quite long enough and ATC would be happier if you flew the ILS at 120kt.'

Really? I think there are going to be some interesting replies to those statements. The original question was asking for power settings for 100kts and 80 kts. It sounds as if you are advocating blasting down the ILS for a flapless landing. I did a lot of my ILS pactise at Calais and I can just imagine floating over half of Belgium..........

I'd agree that you certainly don't need flaps for an ILS in a 172. They are plenty draggy enough to lose lots of speed even going downhill from 250' agl. Not having the flaps down also means less configuration change for a go-around.

I did my IR in a 172, and the SOP (from fading memory) was to use about 100 kts flapless on the GS. I can't remember what power settings gave that, though.

I've tried it three ways:

(1) fly the ILS at normal visual approach speed, with flap

(2) fly the ILS at cruising speed, no flap

(3) fly the ILS at circuit speed, no flap

as recommended by various different instructors, until I made my own mind up that I prefer (3).

The problem with (1) is that the approach takes forever, and you've got to remember to raise the flaps on go-around.

The problem with (2) is that as you become visual (real, or taking the foggles off or whatever) the process of slowing down to flap limiting speed is a bit hectic and messy - chop power, pull back on the yoke, lose sight of the runway for a while, full flap, dive back down at the runway, float for miles, ect ect.

For me (3) works best. The approach doesn't take forever, there's no flap to remember to raise on go-around, you're that bit slower than cruise so it's easier to stay on the localiser, and when you become visual you've only a handful of knots to lose before you can put the flaps down, so just chop the power and fly level for a few seconds.

Erm, isn't the original question a little flawed - granted the ones I play with are a bit older, but VFE on a 172 is about 75kts last time I looked - i.e. you'll be flapless at those speeds, and remain so until you slow down, like it or no. (Apologies if the SP's are different and I'm spouting cr*p...)

On the 172's I fly, the flap limiting speed for the first stage is 110kts and all other stages is 85kts. I'm pretty sure it is the same in the SP although I haven't flown one for a while.

Whatever power it takes to fly the designated approach speed. Preferably without flap, and I would use 100K unless I've been asked to keep the speed up for traffic in which case you could go up to 120kts. You can configure for landing from 200 ft no problem once you are visual.

Most light aircraft will give 500 fpm at cruise speed, flapless, with 2000 rpm set. Go try it and see.

I would suggest that, as well as doing it at the book figures, one is trained to fly the approach so the glideslope intercept is reached at the flap/gear limiting speed.

That is the "keep your speed up due to a 737 behind you" scenario.

To avoid rapid engine cooling, one needs to bring the power back gradually while on the glideslope.

My "normal" profile would to be to slow down to 1st stage of flap limiting speed somewhere after the IAF and go 1st stage of flap. Then (assuming ILS here) half a dot before glideslope intercept gear down and power back to approach power setting (say 40% from 65% in a DA42) and pitch for GS (~5° nose down).

I think that the SP 1st stage of flap is about 110 kts, I certainly used to use 1 stage on an IAP @ 100kts.

NOTE: The "White Arc" doesn't indicate when the 1st stage of flap can be put in, but when ALL flap can be put in. Often the 1st stage can go in at a higher speed (i.e. above the white arc).