Best Glide Speed

[Admin]

Do I need to put that in my checklist now?

 

 

[Guest Andys@coffs]

The best glide [Vbg] quoted in the POH is with the engine shut down and with the prop stopped which is the minimum drag situation. If the engine is shut down but the prop is windmilling then the prop is generating "reverse thrust" and thus considerable drag in which case the rate of descent at Vbg is greater than you would expect with the quoted L/D.

You know everyone gets caught by this and as such I wonder if there is an RPM (which will be different for each aircraft/engine/prop combo) that is closest to approximating the aircraft with an engine out. If plain old idle induces more drag than a stopped prop then an increase in RPM must at some point approximate a stopped prop. It would be useful for instructors to know that RPM figure and the associated IAS for the most often used training aircraft.

 

That all said, perhaps our tachos arent accurate enough for that RPM figure to be set. MAybe it could be set by reproducing the engine tone. That would make a new skill instructors need, pitch perfection.

 

Andy

 

 

[Guest pelorus32]

You know everyone gets caught by this and as such I wonder if there is an RPM (which will be different for each aircraft/engine/prop combo) that is closest to approximating the aircraft with an engine out. If plain old idle induces more drag than a stopped prop then an increase in RPM must at some point approximate a stopped prop. It would be useful for instructors to know that RPM figure and the associated IAS for the most often used training aircraft.That all said, perhaps our tachos arent accurate enough for that RPM figure to be set. MAybe it could be set by reproducing the engine tone. That would make a new skill instructors need, pitch perfection.

 

Andy

Hi Andy,

 

as I understand it this is a bit of a debated area with multi-engine training. When they do assys these days they don't shut down and feather the engine - think they killed too many doing that. So they try to set the engine revs on the "failed" engine to some revs that approximate "zero thrust". There is apparently some debate on what constitutes zero thrust on any particular a/c. But talking about this the other day with a CFI and multi candidate I think they were using 1700 revs on a Seneca 3.

 

Regards

 

Mike

 

 

[Guest Andys@coffs]

Thanks Mike.

 

I had just finished watching the recently posted video of someone doing their BFR and they did what I, and perhaps most others do, on 1st practise of an engine out, they were too high. They had the engine at idle and as such a real engine failure would have exasibated that overshoot even further.

 

Andy

 

 

[Guest Decca]

Contents of post #30 deleted due possible incorrect/misleading information. Humble apologies.

 

Regards, Decca.

 

 

[John Brandon]

Decca wrote:

 

"Time to get back to basics Guys. A stopped, fixed pitch prop will create the MOST drag. (Flat plate principle).

 

A wind-milling prop will create less drag than the above."

 

Not so. Read www.raa.asn.au/groundschool/propeller.html#windmilling

 

John Brandon

 

 

[Guest pelorus32]

Thanks Mike.I had just finished watching the recently posted video of someone doing their BFR and they did what I, and perhaps most others do, on 1st practise of an engine out, they were too high. They had the engine at idle and as such a real engine failure would have exasibated that overshoot even further.

 

Andy

Interesting thing this. I always use side slip to fine tune my height when I am doing PFLs. I use first stage of flap and then adjust ROD by using side slip if I need it. I keep a bit up my sleeve and then dump it with a side slip. Good fun and much more adjustable than simply adding more flaps.

 

However I find that there is quite a bit of anti feeling about side slipping in both RA and GA. Certainly when I learned to fly gliders it was a part of your daily bread and butter.

 

What do other people think about side slipping?

 

Regards

 

Mike

 

 

[Guest JRMobile]

From http://www.raa.asn.au/groundschool/propeller.html/windmilling

 

"The angle of attack of a fixed pitch propeller, and thus its thrust, depends on the forward speed of the aircraft and the rotational velocity. Following a non catastrophic engine failure the pilot tends to lower the nose so that forward airspeed is maintained while at the same time the rotational velocity of the engine/propeller is winding down. As the forward velocity remains more or less unchanged while the rotational velocity is decreasing the angle of attack must be continually decreasing and at some particular rpm the angle of attack will become negative to the point where the lift component becomes negative ([reverses) and the propeller autorotates, driving the engine. This acts as greatly increased aerodynamic drag which seriously affects the aircraft's L/D ratio and thus glide angles. The drag (including the negative lift) is much greater than that of a stationary propeller, also the engine rotation may cause additional mechanical problems if oil supply is affeted."

 

 

[Guest terry]

Hi Mike, I'm Glad you raised the issue of side slipping here because I too am interested in other pilots opinion. I have noticed on this forum a bias against it which surprises me because both my flying instructors [both very experienced CFIs] made side slipping par for the course. It was not optional. I'm sure it's also in the training syllabus. A few weeks ago before this wind started I did a couple of side slips just so I don't forget how too. The environment that I fly in does not often put you in a situation requiring side slipping, by this I mean there are so many markers like hills, very tall trees etc that give you automatic feel as too your approach on final. not the same I suppose

 

as a big flat paddock with nothing in the back ground or unfamiliar strip. I know that with one of my two instructors side slipping will be part of my bfr when it becomes due and he will expect it carried out correctly and competently. Is this the norm and if not why not. I sometimes detect a resistance from pilots to not stretch the boundarys of their limited experiences, by this I mean taxi, take off, trip, curcuit and land. No practice or excerises to extend their skills, in fact these pilots are often critical of others who do.

 

It's my intention to practice side slipping every time I go flying until I become comfortable with it. [which I not at present]I would be very interested in the technical operational effect of side slipping on the plane in various weather conditions, carried out at different altitudes and distances to cover in a side slip, could you for instance side slip continuously and what air speed would you develop. I wait in eager anticipation for your responses.

 

Regards Terry

 

 

[Guest Flyer40]

Terry/Mike, I like your point. We've all heard about the Canadian who successfully dead-sticked a 767 and controlled it all with a side slip. I believe the side slip is an important and useful control technique that all pilots should be competent in. Like Mike says, a side slip gives you far more control over your approach than simply dragging it in with flaps.

 

But it depends on the aircraft type and the flying technique associated with it. For example in the Citabria I rarely use flaps, usually fly a glide approach and use side slip to wash off any excess speed or altitude (I was taught to fly this way and it keeps me in tune for a forced landing). It's very different in the Cessna where it's always a powered approach, always with flaps, and side slips are not permitted in the Cessna with flaps.

 

Another thing to consider is that I've found some passengers, usually the inexperienced ones, don't like the sensation of a side slip.

 

Despite all that I'm a big fan of the side slip.

 

 

[Yenn]

If you use flaps alone to control rate of descent you will get to a point where you may be too low and slow and cannot retract flaps without losing a lot of lift.

 

Using flaps if you are gettimg low just release some of the control pressure and you are flying properly.

 

The only reason to not side slip is if the design of the plane prevents it.

 

 

[Guest terry]

Thanks guys for your comments, It's seems we are all in agreement. Can anyone help with the stresses and strains on the aircraft

 

Regards Terry

 

 

[Guest browng]

What do other people think about side slipping?

I agree with you entirely, some types positively demand a side-slip, my J3 for instance. I was discussing this with a fairly young instructor not long ago, and it became apparent that there was considerable confusion between the side-slip and the forward-slip, and that he really didn't know the difference. A side-slip is ideal for crosswind conditions, but if you want to lose height while staying tracked down the centerline, a forward-slip is the correct maneuver. The forward-slip moves the heading away from the low wing, but does not change the track. The slide-slip keeps the aircraft's longitudinal axis parallel to the centerline, but the aircraft moves sideways toward the low wing, into the crosswind. The technique is essentially the same, but with a different ratio between roll and yaw inputs.

 

 

[Mazda]

Has anyone here actually performed glides with the prop stopped? I had to do it as part of my aerobatic training. The engine was shut down in flight and the nose raised until the prop stopped. It's quite eerie being airborne and looking at a stopped prop. In my limited experience in doing this, the aircraft DID glide well. I'm advised that with engine shut down, the air flow to cause the prop to drive the engine against its compression results in more aerodynamic drag than if the prop had been stopped.

 

I think the side slip is essential to learn. (I'm including all slipping in this term for simplicity). In things like Citabrias I'd prefer to slip than use flap, and remember some types don't have flap at all. In a Pitts I'd use slideslip for both rate of descent and visibility. Another factor is in gusty wind conditions. Using a lot of flap makes landing in gusty crosswinds more difficult.

 

Some aircraft cannot be slipped (check the manual) due to the fuel pick up being uncovered, however if the engine has already failed I'd be using slip if necessary!

 

 

[Guest terry]

Hi Mazda, yes I have flown a tecnan p92 with the engine turned off and the prop stopped and glided back to the runway. It is a funny feeling to have no noise at all. I was surprised to see how easy and uneventful the trip was. and also how the plane just continued to fly with ease. One off the best excerises my instructor did with me. It help me to understand the principles of flight better.

 

Regards Terry

 

 

[Ross]

I have seen GA aircraft with full tanks taxying at Griffith with fuel pouring out the end of the wing as they turn sharply on the ground and that is only for a few seconds.

 

 

 

Can an extended version of this occur in an extended side slip?

 

 

 

I don't know how many aircraft have overflows in the outboard end of the wings.

 

 

 

 

 

Regards

 

 

[Guest Flyer40]

I've noticed the 182 will often vent some fuel when turning onto the runway with the tanks full to the brim.

 

I guess a more relevant problem might be using a side slip on approach at the end of a flight with a very low fuel level which could cause a fuel porting problem. A fuel imbalance is more likely to be a problem if flying uncoordinated for an extended period.

 

A side slip would be likely to cause an erroneous IAS indication in some aircraft, but given the circumstances for using a side slip I wouldn't think it would be a problem.

 

 

[facthunter]

Side slipping loads on aircraft.

 

If the speed at which the manoever is performed is not too high. the airframe loads should not be of any concern. Specifically the rudder & fin will be subject to hinge and bending loads, some twisting of the fuselage, and some variation to lift loads & centre of lift in the wings. None of these are of a high order and present no significant structural problem.

 

If the slip is performed at high speeds, the manoeuver is less effective, feels very unpleasant and is harder to control, and the airframe is stressed more.

 

Note. A big skid is not a sideslip. A sideslip should achieve a fair amount of wing down. There are sideloads on everything in the aircraft, including the fuel, and if you are low in it , air could be introduced into the fuel system.

 

Airspeed is controlled in the normal way, ie ,with elevators, but the nose may appear to be a bit higher than normal for the same airspeed. The airspeed will under-read,(as the pitot is at an angle to the airflow,) but not by much. If the airspeed is just above normal approach (allowing for weight) the sideslip is most effective, as the purpose is to achieve a STEEPER approach without building up extra airspeed. Gain plenty of proficiency before performing this manoeuver close to the ground, as the controls are crossed-up, and the recovery must be smoothly & positively executed. Have fun! Nev...

 

 

[Guest pelorus32]

G'day Nev,

 

great to see you back again.

 

Whilst you posted after the event, I did take your advice to "Have fun". :;)3:

 

http://www.recreationalflying.com/forum/showthread.php?t=5257

 

I hasten to add that there was no discernible side load on the wheel, despite Ben's digital trickery.

 

The biggest issue was to lose a bundle of height - we were thermalling all the way around the circuit - rather than managing the cross wind which was not much of an issue.

 

Regards

 

Mike

 

 

[facthunter]

Fun..

 

Thanks, So I see. Airliners may be designed to land with a fair amount of drift, but it's always an awful thing to touch down with a lot of side load, and just ask the U/C to cop it. ( Not that I'm suggesting that you would do that). It's always harder on sealed surfaces as the extra grip makes the process more unforgiving. Nev...

 

 

[Guest pelorus32]

Hi Nev,

 

The interesting thing about this is that from the cockpit there was no side load when the RH wheel touched down. I had full left rudder in by that time and it appears that the wheel touched quite gently and the a/c pivoted around it.

 

When I saw the video I was quite surprised as it appears that the a/c was still travelling sideways on touch down. The only time the RH wheel lifts is when the LH wheels touches down. I blame Ben entirely - for the bit of trick editing

 

Certainly it did not feel like one of those xwind landings where you think "oh hell I didn't get her sorted before touchdown", quite the reverse.

 

Just looking at it again I wonder whether the fact that we went from substantial L wing down to substantial R wing down at touch down might have actually caused the a/c to be stopped laterally at touch down. As we already had rudder in at touchdown the a/c just pivoted.

 

Hard to know. What I do know is that I've stuffed up xwind landings often enough to know what it feels like. This one didn't!

 

Regards

 

Mike

 

 

[Old Koreelah]

I love side slipping, but have heard a stall can result if prop wash disturbs airflow over the down wing. Not nice near ground. Maintain airspeed and straighten up with plenty of height.

 

Old Koreelah

 

 

[Guest browng]

I love side slipping, but have heard a stall can result if prop wash disturbs airflow over the down wing. Not nice near ground. Maintain airspeed and straighten up with plenty of height.Old Koreelah

Since the side-slip is used to increase rate of descent without significantly increasing airspeed it is unlikely that you will be carrying much power. Some types, particularly those tandem types soloed from the rear, have no forward visibility in the approach attitude and must be slipped to see the runway. Low wing types are slightly more prone to a stall from the slip than high wing types as the 'down' wing is in the aerodynamic shadow of the fuselage, particularly with flap deployed. Many flap equipped types can only be safely slipped 'clean'. To slip any aircraft at high power settings is asking for trouble, as the result will be not just be a stall, but a stall/spin, and possibly in some types a 'flick/spin'. My personal preference for low momentum types is to slip off a glide approach anyway, as I was taught never to 'drag it in on power', but to approach high, and slip it away in case of an engine failure on finals.

 

 

[Guest landmann]

David's 701 sounds like a sailplane to me at 7 to 1. The most I would hope for in a REAL emergency in my Savannah ADV would be 5 to 1. On the other hand should I be on top with a small hole I can come down full flap at 25 degrees nose down at 55 miles per hour and 1800 ft per min sink.

 

Martin

 

 

[Ross]

When I used to fly sail planes, an instructor and the pilot notes said that for a Blanik L-13 the quickest way down without damaging it, was a spin where the supposed vertical airspeed was 80 knots (If my memory serves me correctly). I did it once from 8,000 feet down to about fully recovered at 2,000 feet AGL.

 

 

 

I would not try it in an IS28 where the ASI needle would probably rapidly approach a little white peg that I like to stay away from.

 

 

 

Regards