Landing a light twin
 

Hi everyone,

I’m transitioning from landing a Cessna 172 to a Cessna 310 light twin, and I have a question about the landing technique.

When I aim to touch down at the same spot, I notice I need to reduce power much earlier in the Cessna 310 than in the Cessna 172. Is this due to the variable pitch propellers, or is it related to the increased momentum from the additional engine, which might cause a longer floating distance?

Thanks in advance for helping!

At least primarily, its going to be down to higher inertia - largely equivalent to the much greater momentum from the heavier airframe. Same reason why if you pull power in an ultralight you lose speed immediately.

I reckon your best bet is to take advice from random strangers on the internet.

And also please record your progress and post online so we can all lau… sorry learn from it.

FML :ugh:

Momentum?
Higher approach speed?
2 engines at idle produce more thrust than 1 engine at idle.
Different view over the nose may lead you to perceive that you are further from the touch down zone in the 310 than at the same distance in the 172. Hence you may be cutting power in the 310 closer to the spot than you think.
Be aware that the 310 wings are closer to the ground so ground effect / cushion could lead to a longer float.
Different winds will lead to different ground speeds.
All these are little things but they add up.
You will soon learn where the “right spot” is. You won’t need or have time to think about each various factor. “Practice makes perfect.”
Remember learning to ride a bike? Terribly difficult but a week later you could not recall what all the fuss was about..after all it is so easy.
Enjoy the 310.

Maybe take an instructor with you?

Having flown a few different types over the years, I'm of the opinion that you should take each one as it comes and not think too hard on the whys. Having said that, you're probably seeing some variation in the strength of ground effect due to the low vs high wing, but I don't know, just fly the plane.

And one more: Ground effect happens earlier in a low wing aircraft.

Huh?? No mate. Piston props produce more drag than thrust at idle, so net drag. That's why they descend like a brick when you close the throttles. Jet's still produce forward thrust at idle (about 4-5% ish of maximum) so they need a shallower descent and need a lot of runway if you are not on Vref. It was a long time ago but i remember powering light twin all the way down to just above the ground; But bizjets (Challenger) you need to start creeping the thrust back at 30-50ft.

Too obvious. Expensive, too.

The engine isn’t what gives you momentum, it’s weight.
The 310 is about twice the weight of a 172 and your approach speed is 20-30kts higher.
As always, you need an experienced instructor for in type.

I learned to fly in a Cessna 152 Aerobat, traded up to a 172 Skyhawk, and wound up as a partner in a 320F Skyknight (which had belonged to A.J. Foyt.) Ground effect was definitely more noticeable in the low-winged aircraft.

- Ed

Joke …Tell that to a float plane approaching a dock…..Joke Over

My mistake, I was just trying to cover all the bases as to what could be a factor. Idle thust would be a very minor factor.

EPR (engine pressure ratio) is the main thrust indication in some jet engines. It is the ratio of pressure in front of the engine to behind the engine (simplified). All the ones I have flown had a number below 1 at idle descent, so no forward thrust. The Citation Bravo would do 5000fpm VMO at idle without speed brakes)*. The 320NEO when you go to idle in the flare as a pronounced nose down from the drag, very much doubt it has forward thrust even at approach idle, never mind flight idle. Sure, it's not like a turbo prop with the props at full fine, but it's not forward thrust. A320 I would reduce to idle around 30' +/-20' depending on gust/weight/approach angle/runway slope. New to the 737, but they teach start reducing below 30', idle just before touchdown (I think that is too low, but new to the airplane....)

)* best I have done was a 32 minute flight, with 6 minutes at FL370 for engine trend monitoring after MX.

Speed and weight will do it.

ATC: "(Call sign) contact Hong Kong Director 119.5 MHZ with call sign only

XYZ “ Hong Kong Director, this is ahhhh, Cessna 310 XYZ, Heavy”

Close the power at the same moment you start your flare. Never been any different from spamcan to Airliner. The height and timing of the flare is the big one.

Hey skc,
Don't overthink it. Do what comes naturally, reduce power to idle at your flare point and stop the sink with elevator, As has been previously said, it works the same for most aircraft up to B747 and that I can guarantee..
Obviously if you're uncomfortable, go out with a competent instructor for a few circuits and let it fall into place.

You really don't need to tell me what EPR is....... Yes, below 1.00 then the intake drag > gross thrust out the back but that is a factor of TAS/MN & i was talking about on final approach at relatively low speeds, that is after all the title of the thread "Landing". Yes, i'm sure there will be net drag with very high bypass ratio's, such as the LEAP engine on the NEO 10-11:1 BPR but i was flying the CF34 a more conservative 6.4:1. (and it was an N1 only engine, I'd much prefer EPR too.) I don't think the earlier fan engines (RB211 etc at 4-5:1) went below 1.00, not regularly anyway. Yes, I generalised too much with the jets. However a pure prop will always produce net drag at idle, i have vague recollections of the instructor setting "zero thrust" on the "failed" engine during training. I was glad to get away from MEP's after qualifying tbh, awful things!
And sure a bizjet will descend fast if you push it down and go at Mmo, but it's not a very efficient, elegant or comfortable way of doing things is it?

We don't all drag our airplanes down a 3 degree glide path to thousands of feet of paved surface. One size does not fit all. Find out what techniques work best in the airplane you are operating and for the environment.

I find that, for an idle power full flap steep approach, adding a little power in the flare can be the best technique.

Apologies, was assuming lack of experience....
320CEO: 1.05 EPR: 250 clean, 210 F1, 180 F2, Vfas on the GS. 320 NEO GTF: it depends... EPR definitely better for hand flying.
Definitely remember zero thrust settings, have about 5k on MEP, great times when you are young and invincible!
And you are correct, I am pretty sure I never did a flight idle descent in a bizjet with pax, as they would for sure have had something to say.

That’s interesting. I fly IAE for over 10 years and I have no clue about EPR value. Lol. I will have a look on my next flight. I’m 90% of the time landing A/tHR off on NEO and CEO ( with EPR) I only use the N1 and speed trend for reference. It’s always around 45/50% on all A320/321. And in the cruise above FL300 pitch 2 degrees N1 80 % you will always be above GD and below VMAX. The only time I used EPR is in cruise with ATHR off to match the thrust on both engines since it’s supposed to give a more accurate thrust value than N1.
I did not fly twin pistons for a while but I remember cutting the power too early was much less forgiving than A320.. But like pizza express says, as long as you flare at the right time, cutting the power during flare like any plane should work just fine. Only practise on type you will find what is more appropriate. On Airbus I do exactly as per fcom and it works like a charm. 30 feet RA I flare and cut the power. But in reality they behave slightly differently: on A320 with IAE, you could cut the power at 100 feet and still not worry about the energy; the idle thrust is quite high and I believe since the engines are much smaller they create less parasite drag. Do that on a CFM or NEO especially with flaps full … It might be another story… :}

EXDAC
please tell what Aircraft you fly that you need to add power in the flare? If you mean flying a stabilised approach (dragging it in) not sure what difference that makes. In fact on a steep glide approach flying light aircraft, with idle power I seem to have no need to add power in the flare, as well as regularly landing an Airbus on glide paths exceeding 4 degrees. Genuinely interested in the operating technique you are following?

Best part about EPR on the CEO is that the scale is much bigger in the range you use. To set cruise power in the CEO it is around 1.LVL for .78 (so if you are level off at FL370 set the donut at 1.370, and wait what happens, less for light and cold, more for heavy and hot). If you level off after descent at low altitude just set the donut at 1.05 when you see alt cap and wait. Much easier than trying to guess if cruise power will be 78% or 81%, and so much easier to set, same for the 40-55% flying around low just because of the linear scale for N1. Yeah, NEO flaps full will drop at idle!

Over 40 years ago when I started flying tailwheel SEL I was shown that, at the end of an idle power approach, adding 100 rpm just before touchdown would make 3 point landings much easier. It gives a second or two more time to get the sink rate close to zero and to establish the perfect 3 point attitude.

Unlike an Airbus, a light taildragger flown at minimum safe approach speed has no excess energy and stops flying when flared to 3 point attitude. Of course, if you flare perfectly every time from an idle power approach that 100 rpm over idle is not needed.

One element missing so far in this discussion. In most** light twin-prop aircraft, the propellers are "blowing the wing" and adding some lift directly via propwash flow (in addition to overall airspeed).

One can be adding (or losing) lift directly by throttle setting, not just by prop pitch and IAS changes.

That cuts both ways - in such a twin-prop, leaving a little power in during the flare can cause more "float" — but chopping the throttle too fast can cause the twin to flop onto the runway as that "propwash lift" around the wings vanishes instantaneously, even before the IAS changes much.

In the C172, that will not happen much (if at all). Its propwash mostly impacts the fuselage, and the remainder is passing under the high wing-roots.

**There are exceptions - Cessna Skymaster, Dornier Do28 Skyservant, all-pusher-prop configurations that at most "suck" the wing - (no remarks from the peanut gallery! := :E ), etc.)

See the Dash 7. Four engine, huge props, Flaps 45 for extra drag, so high power producing lots of lift at very low speeds.

Flying the 737 what I found annoying because it was so unnecessary, were pilots who had the habit of giving a "burst" of power at the flare. Their excuse was it made for a smoother touch-down. I called it a 'nervous Nellie' technique.

IIRC, we rarely needed flaps 45, even for 7,5 degrees approach/800m rwy. No need to add power for flare in the Dash7 - but also no chopping levers to flight idle.