Should we learn to glide "powered" aircraft?

[old man emu]

In another thread, someone mentioned that the thing they most feared during flying training was stalls. I found them good fun, but I was also trained to recover rapidly. I never did just let the plane go to see what would happen, say 20 to 30 seconds after the stall.

 

Another area of powered aircraft performance is gliding. Who has explored what their aircraft does when you pull the power back to idle to see what the plane will do? I'm happy to accept that the aircraft will descend at its glide ratio if the pilot sets thing up correctly, but can you catch a thermal in it? What about turns and effect of flap? 

 

We go on and on about forced landing practice, simulating engine out, but with about 1500 revs, but does anyone know what their aircraft will do at idle revs? Is it possible to keep an powered aircraft flying about for a long time with virtually no help from the prop?

[Old Koreelah]

Interesting topic, OME. There have been threads about whether an idling prop is a reliable indication of glide performance if the noise stops. My own experimental results didn’t agree with conventional wisdom; I just know that my glide rate is about 1:9 and I can get to anywhere under the wingtip- in still winter air.

 

I’ve met pilots who claim to have cut the engine and thermalled in powered aircraft. They must’ve been good, ‘cos my attempts were abysmal. I won’t be relying on any help from updraughts.

[kgwilson]

If you really want to know how your aircraft glides, turn the engine off. Forced landing practice with engine at idle is not the same as gliding with the engine off. Even at idle some thrust is being produced. It is usually not recommended by instructors or flying schools but turning the engine off on down wind at 1000 feet and landing dead stick is a good way to determine your understanding of your aircrafts glide ratio. You will always need some height buffer in case of sink, unexpected headwind etc but you will learn a lot about your ability and the aircrafts capability at the same time.

 

I flew hang gliders for 20years and every landing is a forced landing without power. I know many pilots will not feel comfortable about this but it will definitely improve your gliding skills and confidence if the fan that stops you from sweating gives up.

 

On a good unstable day with plenty of fair weather cumulus I have pulled the power to idle under a CU with good lift and watched the VSI increase. I've never purposely tried to thermal but I have managed to gain considerable altitude on occasions.

[old man emu]

The reason I said to pull back to idle revs was simply to get as close as possible to an engine stoppage, but with the security of knowledge that the engine is still working. We know that standing on a sealed surface with the engine idling an aircraft is not likely to move forward. So in the air, an engine at idle is not likely to add much to the forward speed due to the aircraft falling under the effect of Gravity.  What I am suggesting is that one goes to a similar altitude that you would practice stalls and operate for a while at near zero power. 

 

As for attempts at gliding being "abysmal", that could be due to two factors - the plane isn't a good glider, or the pilot is not experienced enough at gliding. Practicing in your usual plane will soon tell you what sort of gliding performance it has - a useful bit of knowledge if ever the engine stops for real. If your plane has half decent gliding performance, then you can become more skillful at using that performance. Also it's an economical way to build piloting hours while cheating the Hobbs Meter out of a few dollars.

 

There are three areas of gliding to examine - gliding into wind; with a tailwind, and with a cross wind. Then there's descending gliding turns, and level turns if you can catch an thermal. What are the effects of various stages of flap? Hours of run for everyone!

[facthunter]

I think you are tempting fate by intentionally stopping the motor and I think it's illegal without an instructor. We used to do it way back for in flight engine starts  (without a starter motor) which often finds you at Vne in a dive and running out of sky. . A wind milling prop has the POTENTIAL to have a higher retarding force than a stopped prop. (especially with a turbo prop installation which has a high reduction  ratio. . Most deadstick planes will get a RoD of around 1,000 fpm average during manouvering and that with your actual height above ground gives you an indication of what time you have in the air or what rate of rising air current you need to cancel it out.  A slope soaring situation might suffice but that's ever changing conditions. One night I gained 3.000 feet with power to idle on four engines going Launceston to Hobart due to strong winds near the Central Tiers and associated extensive Lenticular clouds at higher levels. Normal cruse level around 7,000ft. You have to go up or you exceed your safe turbulence speeds when you have already closed the taps.  Those Latitudes are where the strongest winds are (Barring Jetstreams which are high altitude phenomenons.) .Nev

[Old Koreelah]

3 hours ago, old man emu said:

 

...As for attempts at gliding being "abysmal", that could be due to two factors - the plane isn't a good glider, or the pilot is not experienced enough at gliding.

Both these apply in my case.

 

3 hours ago, old man emu said:

...Practicing in your usual plane will soon tell you what sort of gliding performance it has - a useful bit of knowledge if ever the engine stops for real...

 

Good advice for all pilots.

3 hours ago, old man emu said:

 

 

[facthunter]

Planning and executing a good descent will show how much you are aware of your planes virtues and limits. If you have extra height to lose you can descend faster and convert your potential energy into higher Inertia and save time. IF you want keep the engine warm, you descend at a lower ROD with part power and you may also choose to go a bit faster or just descend earlier so less time at cruise power.. If you know and understand the planes L/D characteristics, you can do cruise climbs or increased airspeed for extra cooling without wasting much fuel. Into wind use a higher cruise speed and with a tailwind do the opposite for best range. . ALL these best speeds apply to the weight at the time. Heavier equals faster and lighter slower,  like your stall speed. Nev

[Yenn]

Gliding also depends upon the current thermal activity. I have been in a Victa, going up at 1000' fpm with the throttle right back.That of course didn't last, but you can get a reduction in descent during a glide if you can find a thermal.

Anyone who doesn't know what their plane can do with engine shut down as far as possible is not really trying. I believe it is bad airmanship to use power to come in for landing and that is confirmed by the number of GA pilots who lose an engine on finals and cannot make the strip.

I definitely would not recommend shutting down the engine and conducting a landing without power. Just look at the number of pilots who stuff up a landing with power. Do you think you could shut off the engine and then bounce the landing without an engine to recover and get away with it. By all means shut down the engine and try a landing, but for safety make that landing at at least 1000' above GL. Even then you will not learn what to do if you bounce, because you will not bounce at 1000'.

[old man emu]

15 hours ago, old man emu said:

We go on and on about forced landing practice, simulating engine out,

That was the only reference I made in my original post that mentioned the word "landing". I wasn't talking about that at all, yet the discussion has drifted into that specific area of flight.

 

What I am advocating is that instead of grabbing a plane for a session of circuits and bumps, people should go out to where aerobatics are safe and spen a good bit of time just messing around with the aerodynamic performance of their aircraft at near zero engine power. As Yenn suggests:

5 minutes ago, Yenn said:

Gliding also depends upon the current thermal activity. I have been in a Victa, going up at 1000' fpm with the throttle right back.That of course didn't last, but you can get a reduction in descent during a glide if you can find a thermal.

For a while I was having a go at slope soaring with an RC glider. It had a motor that I could use to get out of trouble, but the object of the game was to launch the plane with motor, then shut it off at the required altitude and try to use the wind, the orographic uplift and any stray thermals to maintain of increase altitude and to fly for as long as possible without the motor. It was fun - despite my genetically inherent disability for flight.

 

If trying a bit of gliding in your powered aircraft is not a part of recreational flying, what parts are?

[facthunter]

it's rarely going to be suitable to do much. I've adjusted my track a few times en route to take advantage of a slope but it's pretty rare and perhaps more of a distraction to what you are doing or should be doing (looking outside and knowing where you are.. I've flown ( as many have) some planes that imitate a brick in the way they glide, so gliding is brief.. Where are all these GA planes which have engine failures  because they are using power on approach? Idling motors are also prone to stopping, because an idling motor is running at it's slowest speed, where it does it reliably. You are meant to check the idle on each commencement of Taxi and they all stop when the fuel is empty.  (One of the most common causes of them going quiet.)..Nev

[Student Pilot]

To the original  question.......................................yes

[facthunter]

Perhaps you might elaborate just what this means to you. ? Nev

[rgmwa]

I practice gliding, stalls and slips on most flights to try and keep reasonably proficient. Another useful exercise is to slow the plane in 5 knot increments down to about 55 kts and practice shallow coordinated turns to get a feel for how it behaves as you get closer to stalling speed. Do this at a safe height of course.

[Student Pilot]

During training we should explore all facets of flight. Once you get into a particular aircraft you should know what it does, how it handles various conditions of flight. I agree with OME on his first post. An aircraft with a stopped prop glides a lot differently to one at idle, it helps to know your aircraft.

[Kenlsa]

The true glide performance at mtow in my SP 500 is 65kts. By true I mean the prop is not providing any thrust or breaking force. At 1200rpm (settles at this rpm at 65-70 kts in the landing circuit) the prop is providing a breaking force and will not give you your actual performance so you can feel the true picture.

 

My ARDU mate did the calculations for zero thrust on my 60x44 prop at various speeds to ascertain best glide.

 

I gave the formulas somewhere but suffice to say after all the testing was done in still air, the maths gave us 2000 rpm for zero thrust and 65kts was best glide. Note that rpm varies at chosen speed for zero thrust.

 

Last couple of times I have done my BFR, I have throttled to 2k for my “engine failure” so as to simulate actual performance.

 

Ken

[Old Koreelah]

22 hours ago, Kenlsa said:

...Last couple of times I have done my BFR, I have throttled to 2k for my “engine failure” so as to simulate actual performance.

Interesting approach, Ken. Not familiar with the SP 500; does it have a six or a four cylinder engine?

At 2000 rpm my J2.2 is producing as much power as the old Starke-Stamo engine did flat chat; my little Jodel can actually takeoff and gently climb. In normal flight this airframe seems to roughly match the performance of a J-120.

[Kenlsa]

Old K.

mine has a 2.2. I will see if I can find the workings he used for my plane and prop numbers.

Ken

[kgwilson]

2000rpm in my Jab 3300A powered aircraft is a slow cruise of around 80 knots. For a glide approach RPM  sits around 1000 which is 780-800 rpm static on the ground. It will roll on smooth tarmac at idle as well. This is why I commented that the engine even at idle is producing some thrust compared to flying it dead stick.

[Jase T]

Just out of curiosity, how many of you fly glide (throttle at idle) approaches when you land? Do you pull power to idle abeam the touch down point? On base? Or do you fly a powered approach (by that I mean relying on power until the flare) every time? Yes I realise some types with higher wing loading won't do it and will need power. 

[kgwilson]

If I am going to do a glide approach I pull the throttle downwind abeam the threshold at 1000 feet & then turn on to base which I adjust left or right depending on the day (lift/sink/headwind) always keeping high enough to make the runway & then use flap as required to make it happen. I probably do glide approaches about 1 in 5 landings. I more often than not use some power but prefer tight circuits so never drag it in on the engine. If I am high I will do a fairly tight descending turn on to final at about 70 knots & 1000 fpm down, level off, bleed speed & flare a couple of feet off the deck. This is at my home aerodrome of course & I have 1000 or 1200 metres of runway (seal and grass) to play with.

[Kenlsa]

Looks like I'm getting old, the 2000rpm should have read 1500, sorry for the confusion.

Found the original computation and this was further tested (still cant find the file though) in still air at 65kts that gave the best glide. 

 

You should be able to work it out and test for your own prop/plane combo.

 

Happy computing

 

ken

Best Glide RPM - Copy.docx

[turboplanner]

18 minutes ago, Jase T said:

Just out of curiosity, how many of you fly glide (throttle at idle) approaches when you land? Do you pull power to idle abeam the touch down point? On base? Or do you fly a powered approach (by that I mean relying on power until the flare) every time? Yes I realise some types with higher wing loading won't do it and will need power. 

J170

30 degree turn to base at 45 degrees from start of runway

Power to idle

When below 70 kts 1 stage flaps

maintain 65 kts on base and final, with elevator

land 1/4 down runway without using power.

 

I was just joking then; use power to maintain glideslope.

 

Cherokee Warrior

Late downwind stage 1 flaps, slow to 90 kts 

Turn base when start of runway 45 degrees off wing tip, slow to 80 kts

Turn final, full flap, slow to 70 kts

Use power to maintain glideslope, land at the end of the piano keys

Adjust glideslope with throttle if necessary

[Old Koreelah]

2 hours ago, turboplanner said:

J170

30 degree turn to base at 45 degrees from start of runway

Power to idle

When below 70 kts 1 stage flaps

maintain 65 kts on base and final, with elevator

land 1/4 down runway without using power.

Take 10kt off those numbers and that’s what I do in my Jodel.

Every landing is a glide approach; haven’t done what’s called a powered approach in yonks, but I must admit to using a trickle of power on the rare occasion my approach gets a bit low. I always close cowl flaps right down to keep a bit of heat in the engine in case I need it.

[Tex]

Every landing should be on glide slope IMHO, but I do fly gliders 🙂 You should (MUST) know best glide speed of ANY aircraft you are flying and also min sink speed. I will be corrected on this but I think (particularly with more than one blade) a prop at idle (or free spinning) actually creates more drag that a stationary prop. Ergo: you will glide better with a prop that has stopped than one which is still turning.

 

Any aircraft can climb in lifting air without thrust, just depends what the min sink speed/sink rate is vs the lift available and how you could use it - including how much skill/knowledge/experience you have. If it was really dangerous to turn the engine off then no soaring in any type of aircraft would be allowed. You should all do your self a favour and go do some training in a glider. As an aviator it will be the best money (and probably least) you ever spent on relevant training.

Edited November 30, 2020 by Tex

[Bosi72]

8 hours ago, Tex said:

 🙂You should (MUST) know best glide speed of ANY aircraft you are flying..

Just to add, if you fly faster, the distance decreases. If you fly slower, the distance also decreases..