Powered vs. Power at idle landings.

This forum has been developed to discuss flight instruction/University and College programs.

Moderators: sky's the limit, sepia, Sulako, Right Seat Captain, lilfssister, North Shore

User avatar
Colonel Sanders
Top Poster
Top Poster
Posts: 7512
Joined: Sun Jun 14, 2009 5:17 pm
Location: Over Macho Grande

Re: Powered vs. Power at idle landings.

Post by Colonel Sanders »

power off landings from 200 feet
For the newbies: There is a tremendous amount of
folklore surrounding radial engines and power-off
descents with respect to the danger descending with
the power off, and the prop driving the engine.

With a boxer Lyc or TCM (NOT geared), it is perfectly
acceptable for the prop to drive the engine, which
happens with the power off, and is more noticeable
with constant speed props. I do this in the Lyc-powered
Pitts and TCM-powered Maule all the time. Fantastic
source of drag. In the Maule, I never need to use full
flap or even sideslip. In the Pitts, I can approach at
ridiculous speeds on short final, pull the throttle back
and let the 3-blade prop stop me.

With a geared TCM (eg GTSIO-520) if you pull the
throttles all the way back 'way up high and do a power
off descent with the props driving the engines, you
will damage the gear drives. Don't do that.

Now onto radial engines. If you pull the power all
the way back on a radial engine - carefully, it is
supercharged after all - and let the prop drive the
engine, there is a danger that there will be a lack
of lubrication in the main bearing.

Back to .. From 200 feet, you probably won't
do any damage because if the props do drive the
engines, it will be of extremely brief duration.
---------- ADS -----------
 
Chuck Ellsworth
Rank 11
Rank 11
Posts: 3074
Joined: Sat Sep 22, 2007 6:49 am
Location: Always moving

Re: Powered vs. Power at idle landings.

Post by Chuck Ellsworth »

Radial engines need smooth throttle and RPM changes when increasing or decreasing power.

Radial engines have counter weights which will change the rotational forces in the engine, therefore smooth, slow changes of power will help give the longest engine time before needing overhaul.

The counter weights are very noticeable when shutting down a radial engine, that is what that clacking noise is as the RPM drops to zero..
Now onto radial engines. If you pull the power all
the way back on a radial engine - carefully, it is
supercharged after all - and let the prop drive the
engine, there is a danger that there will be a lack
of lubrication in the main bearing.
I have around fifteen thousand hours on radial engines and about forty years working on them as a mechanic.

All the radial engines I flew had direct drive oil pumps and as such the oil pressure is a result of RPM, not manifold pressure.


I never ever saw any reduction in oil pressure caused by reducing manifold pressure when approaching with throttles closed.
---------- ADS -----------
 
User avatar
Colonel Sanders
Top Poster
Top Poster
Posts: 7512
Joined: Sun Jun 14, 2009 5:17 pm
Location: Over Macho Grande

Re: Powered vs. Power at idle landings.

Post by Colonel Sanders »

http://www.precisionengines.com/pdf/oilBulletin.pdf
for war birds and some other non-fleet aircraft, the power may be changed abruptly or reverse loading can occur. This greatly increases the loading on the master rod bearing momentarily. When a multi-grade oil is used and these changes occur, the load on the master rod can force all of the oil film out of the clearance between the bearing and the journal. When this happens, the bearing material can makemetal to metal contact with the crankshaft surface. This will start to hammer the soft bearing material

That article is actually about radial engines and multi-grade
oil (which is good in the winter, but not good in the summer)
but it gets the point across.

It also explains why I only run W120 in radial engines.
---------- ADS -----------
 
Chuck Ellsworth
Rank 11
Rank 11
Posts: 3074
Joined: Sat Sep 22, 2007 6:49 am
Location: Always moving

Re: Powered vs. Power at idle landings.

Post by Chuck Ellsworth »

Yes C.S. that is correct.

The reverse loading is partially cased by the counter weight chance of force......
.....

....HOWEVER ..slow smooth throttle and pitch changes avoid that problem.

just like slow smooth throttle and pitch changes are absolutely necessary in your geared C421....reverse loading of the gear box.

How many licensed pilots do you run across that ram the throttle from idle to full power on then take off so fast it is a blur?
---------- ADS -----------
 
User avatar
Colonel Sanders
Top Poster
Top Poster
Posts: 7512
Joined: Sun Jun 14, 2009 5:17 pm
Location: Over Macho Grande

Re: Powered vs. Power at idle landings.

Post by Colonel Sanders »

What I teach in the 421 is to find a clear patch of
pavement - no stones - then brakes on, and bring
the MP up to 25 inches. This spools the turbo-
chargers up.

Release the brakes, then smoothly bring the throttles
up to 39.5 inches. Hands a blur in the cockpit is almost
always bad news. A good pilot is always miles ahead
of the airplane, and rarely moves fast in the cockpit :wink:

Back to radial engines ... the master rod bearing is
under tremendous stress, and as such must be babied.
There's a whole lot of torque constantly being transmitted
through it!
---------- ADS -----------
 
Chuck Ellsworth
Rank 11
Rank 11
Posts: 3074
Joined: Sat Sep 22, 2007 6:49 am
Location: Always moving

Re: Powered vs. Power at idle landings.

Post by Chuck Ellsworth »

Just killing a bit of time I read this whole thread again and am puzzled by this post.

Dh8Classic wrote this.

Looks like you found your golden arm.
I have no idea what that means???
---------- ADS -----------
 
User avatar
YYZSaabGuy
Rank 8
Rank 8
Posts: 851
Joined: Wed Aug 04, 2010 7:32 am
Location: On glideslope.

Re: Powered vs. Power at idle landings.

Post by YYZSaabGuy »

. . wrote:Just killing a bit of time I read this whole thread again and am puzzled by this post.

Dh8Classic wrote this.

Looks like you found your golden arm.
I have no idea what that means???
., on page 1 of this thread, CS posted that he'd be interested in hearing from any of the "golden arms" on AvCanada who routinely approach with turbines spooled all the way down. Your responding post noted the shuttle as an example of a power-off approach, and Dh8Classic was humorously pointing out to CS that he had just found his "golden arm", i.e. the shuttle pilots. It got a smile out of me.
---------- ADS -----------
 
Chuck Ellsworth
Rank 11
Rank 11
Posts: 3074
Joined: Sat Sep 22, 2007 6:49 am
Location: Always moving

Re: Powered vs. Power at idle landings.

Post by Chuck Ellsworth »

Ahhh.... Thanks.

Sometimes I don't connect the dots because they are to obvious. :mrgreen:

This one though I think I do understand.
You're not. However, the argument that power-off provides more controllability is simply not true.


To increase controllability with no power all one needs is higher airspeed...

....for instance suppose you are approaching power off just above the stall speed and you quickly move the elevator to full nose up your biggest worry is stalling the airplane.

Conversely if you are approaching power off just below VNE and you quickly move the elevator to full nose up you will not have anymore worries because your control effectiveness will be so high you will break the airplane.
---------- ADS -----------
 
User avatar
Colonel Sanders
Top Poster
Top Poster
Posts: 7512
Joined: Sun Jun 14, 2009 5:17 pm
Location: Over Macho Grande

Re: Powered vs. Power at idle landings.

Post by Colonel Sanders »

Yes, with high speed - and the ability to turn on
and off large amounts of drag - one has plenty
of controllability, with no power!

For example, if you had speed brakes, spoilers,
a drag chute, and a tailhook with wires on a
12,000 foot long runway, you could approach
power off at tremendous speed.
---------- ADS -----------
 
Chuck Ellsworth
Rank 11
Rank 11
Posts: 3074
Joined: Sat Sep 22, 2007 6:49 am
Location: Always moving

Re: Powered vs. Power at idle landings.

Post by Chuck Ellsworth »

Yes C.S. that is why I could not let this comment stand without challenging it.
You're not. However, the argument that power-off provides more controllability is simply not true.
---------- ADS -----------
 
photofly
Top Poster
Top Poster
Posts: 11306
Joined: Tue Jan 18, 2011 4:47 pm
Location: Hangry and crankypated

Re: Powered vs. Power at idle landings.

Post by photofly »

Why do we train like marching soldiers to fly forced approaches only at best glide speed? From which, any deviation of airspeed - up or down - results in a steeper glide.
. wrote:To increase controllability with no power all one needs is higher airspeed...
.'s right, of course. If you have a field in close enough range, wouldn't it make more sense to fly a forced approach at, say, best glide+10? Then you've got some controllability by pitching up, or down.

Heresy, I know - but why not?
---------- ADS -----------
 
User avatar
Beefitarian
Top Poster
Top Poster
Posts: 6605
Joined: Wed Dec 01, 2010 10:53 am
Location: A couple of meters away from others.

Post by Beefitarian »

The one issue being you need to get rid of that +10 preferably before touch down.
---------- ADS -----------
 
photofly
Top Poster
Top Poster
Posts: 11306
Joined: Tue Jan 18, 2011 4:47 pm
Location: Hangry and crankypated

Re: Powered vs. Power at idle landings.

Post by photofly »

Not a problem. You have to transition from best glide into the flare, anyway, and we're already accomplished at increasing the descent rate and losing energy with extra drag by lowering flaps and/or side slipping.
---------- ADS -----------
 
Chuck Ellsworth
Rank 11
Rank 11
Posts: 3074
Joined: Sat Sep 22, 2007 6:49 am
Location: Always moving

Re: Powered vs. Power at idle landings.

Post by Chuck Ellsworth »

Lets not skew this subject to far.

Generally speaking using the airspeed recommended for the airplane is the best method to use during the approach.

Controllability at that airspeed should not be a concern whether or not you are using power on the approach, the power off approach will be steeper than when using power.

With some high drag airplanes you can get rid of excess airspeed very quickly.
---------- ADS -----------
 
User avatar
Beefitarian
Top Poster
Top Poster
Posts: 6605
Joined: Wed Dec 01, 2010 10:53 am
Location: A couple of meters away from others.

Post by Beefitarian »

True but you can slow down even more quickly if you are already going the slowest safe speed.

The next thing is, "Well, 10 knot faster worked pretty good. Next time I'm going to try 25." Some nice test pilot guys already found the best glide speed. Should be ok to go a little faster but I prefer to have a reason for decisions like that.

If it's pretty bumpy and gusty out you probably want to add a few knots.
---------- ADS -----------
 
BTyyj
Rank 7
Rank 7
Posts: 537
Joined: Mon Nov 08, 2010 1:11 pm
Location: CYYJ

Re: Powered vs. Power at idle landings.

Post by BTyyj »

. . wrote:Lets not skew this subject too far.
Hasn't it been already?

Like . has pointed out, controllability is based on airspeed; the aircraft doesn't know if the engine is full or idle, just its velocity.

But, what if you've gone below the angle at which the best glide speed will get you to the field, at power idle and zero flaps?
---------- ADS -----------
 
photofly
Top Poster
Top Poster
Posts: 11306
Joined: Tue Jan 18, 2011 4:47 pm
Location: Hangry and crankypated

Re: Powered vs. Power at idle landings.

Post by photofly »

Some nice test pilot guys already found the best glide speed.
Best glide speed doesn't get its name because it's the best one to use; it gets its name because it takes you the furthest from a given altitude. "Best" is not to be taken as value judgement on its suitability in all circumstances.

Which is what I'm asking about: from the point of view of making it without power to a nearby field, best glide is thoroughly suboptimal from the point of view of controllability; however you deviate from it, you're coming down more steeply.

The only case when best glide is actually "best" is when the field you've picked is at the outer limit of reachability, in which case the choice of field itself is probably suboptimal, and you'd be better off to pick another one that's closer, glide a little faster, and have more control.

Wouldn't you?
---------- ADS -----------
 
User avatar
Colonel Sanders
Top Poster
Top Poster
Posts: 7512
Joined: Sun Jun 14, 2009 5:17 pm
Location: Over Macho Grande

Re: Powered vs. Power at idle landings.

Post by Colonel Sanders »

You have to transition from best glide into the flare
Actually, the United States Navy doesn't bother
flaring to land, even when they aren't landing on
an aircraft carrier!

With the right landing gear, flaring is optional.
---------- ADS -----------
 
photofly
Top Poster
Top Poster
Posts: 11306
Joined: Tue Jan 18, 2011 4:47 pm
Location: Hangry and crankypated

Re: Powered vs. Power at idle landings.

Post by photofly »

I believe their motto, having a dig at the USAF, is "flare to land, squat to pee"
---------- ADS -----------
 
User avatar
Colonel Sanders
Top Poster
Top Poster
Posts: 7512
Joined: Sun Jun 14, 2009 5:17 pm
Location: Over Macho Grande

Re: Powered vs. Power at idle landings.

Post by Colonel Sanders »

Their unusual landing technique involves full
throttle at touchdown. When landing on a
runway with no wires - and two afterburners -
this can lead to interesting results.
---------- ADS -----------
 
Post Reply

Return to “Flight Training”