Best Glide Speed

[Yenn]

Ross. Why would the ASI be near max. "I assume that is the white peg" surely in a spin airspeed is low, especially on one side.

 

 

[facthunter]

Best glide speed..Effect of headwind.

 

Getting back to the original topic of this thread, the effect of wind has not been mentioned. The best glide speed relates to the aerodynamic performance of the aircraft at a particular weight. The intention of knowing and applying this data is to get the best performance out of the aircraft in the engine-out situation.This is only the correct speed in a still-air case, If the best place to land is into wind, from your present position you will have to INCREASE your speed to obtain optimum results.

 

To illustrate the point, imagine that the headwind is equal to your best glide speed. You will not advance towards the point of intended landing at all unless you increase your speed to give yourself a positive GROUND speed. The extra airspeed will cause an increased rate of descent, so you will have less time in the air to range to your landing field. The calculation of the precise speed is difficult, but do some examples on paper to get the principle.At the speeds we operate, the effect is quite significant. The example is only used for simplicity. Nev...

 

 

[Guest browng]

Ross. Why would the ASI be near max. "I assume that is the white peg" surely in a spin airspeed is low, especially on one side.

I assumed he meant the VSI. While airspeed in a spin is stable, you can get quite awesome rates of descent. An Extra 300 can spin at 8,000fpm, and Chuck Jaeger spun an F-104 51,000 feet in 51 seconds!

 

 

[facthunter]

Funny Type.

 

Why are you SHOUTING Ross? & What has happened to your type browng?

 

 

[Guest browng]

& What has happened to your type browng?

It looks ok from here? what are you seeing?

 

 

[facthunter]

Type.

 

It went small half way through. N..No I don't mean what you think. The type...

 

 

[Guest browng]

It went small half way through. N..No I don't mean what you think. The type...

No idea what happened there. I went back and re-typed it, is it ok now?

 

 

[facthunter]

TYPE

 

Yes browng. It's fine thank you. Sorry to have bothered you ,Regards Nev........

 

 

[Ross]

Hi Yenn and others

 

Apologies for NOT having answered your responses before.

 

 

 

Firstly I am doing bold & size 3 lettering because I find it far easier on my eyes. I had a cataract removed from the right eye earlier in the year and it is now great but the left eye also has a developing cataract which will need action soon. The eye surgeon in Wagga booked me in this coming December for an examination when he did the right eye.

 

 

 

From what I understand most modern say after about 1970 or a bit later aircraft will not stay in a spin if the pilot does not intervene. If the spin is initiated and not held in it becomes a spiral dive with a rapidly increasing airspeed which in a glider will be catastrophic in a very short time.

 

 

 

In regards to the excessive ASI only in the IS28 (in my limited experience). The problem is that it rapidly recovers from an accidental spin into a spiral dive but the only view and very sudden change out of the windscreen is solid earth. It almost goes inverted - very scary - with a very rapid increase in airspeed - do not blink.

 

 

 

Need to recover to a normal attitude immediately as you will probably exceed max manoevering speed before you can get the nose on the horizon!

 

 

 

The Blanik on the other hand does a fairly flat spin by comparison and only needs opposite rudder plus an easing of the stick to recover from a spin and usually can recover without the speed becoming excessive. You are starting the recovery from a not very steep nose down attitude although it is falling in the spin (not flying) at 80 knots.

 

 

 

They all need their noses pointing at the ground until the spin is stopped and it starts to fly again with both wings flying instead of one only. Then can you lift the nose and live again!

 

Regards

 

 

[Guest TOSGcentral]

A few more snippets regarding engine-on glides, and a few on engine off glides.

 

As John B has emphasised – a windmilling prop does have a huge bearing on glide performance. What is of more significance (especially for instructors) is that the effect is proportionally greater the less glide performance you have to start with.

 

Back in the early 70’s I did quite a bit of practical research on SF26b and T61a Falke motor gliders when we were developing training techniques in them for ab-inito glider pilots.

 

This was less about the forced landing situation but as much or more on the general glide. The Falke glide is poor and we estimated it at about 14:1 prop stopped (we had no feather setting either) despite what the manufacturers claimed. This was very significant when we had to validly bridge the gap to the pure glider trainers that were doing about 26:1 and we only kept the students in the motor glider for about three hours.

 

During this time we covered basic handling but were primarily after the main judgemental exercises of circuit planning, approach control and landings – all items that are most time expensive in a pure glider.

 

The challenge was further added to because the “gliding purists†(who thought motor gliders were a work of the Devil) insisted on full engine off circuits. Purism only goes so far and the Stamo 1500 motors could not stand the repeated heating and cooling shocks so crankcases and cylinders began dramatically cracking with more time spent changing engines than flying the things.

 

What we did was a lot of test flying in dead calm early morning conditions. Using the VSI and some rather rough and ready calculations we came up with an RPM setting that would give us the L/D we wanted and keep the engine warm at the same time.

 

An important point to note is that RPM is valid for only one airspeed. Increase or decrease airspeed and the prop load changes and consequently the L/D.

 

Later we did more calculations and used the same techniques at higher RPM settings so that we could use a most humble trainer to validly check fly pilots of much higher performance gliders who would have to demonstrate that they could safely get them into paddocks.

 

Just to broaden this issue a little into actually switching off the engines of ultralights in flight - a few points are worthy of note.

 

When motor gliders began being registered in AUF there was some political tension generated with GFA who understandably became alarmed. So did I! I pointed out (quite emphatically to the powers that be) that we had no training syllabus for them, especially for engine off circuit planning, running out of height in the circuit procedures, nor approach control via spoilers or airbrakes. Furthermore we had no trainers in schools for basic training or valid BFRs and very few instructors anyway capable of doing this work in a responsible manner. While most suppliers were offering valid training as a condition of sale – this would not help the situation when the aircraft was later sold on in the second hand market.

 

To my understanding a background arrangement’ was made with GFA that AUF would only register motor gliders that were ‘conventional aircraft’ in that they could taxi normally, and would not register anything with the retracting engine on a pylon type thing that generally do not taxi conventionally (although some can be so operated if you know what you are doing!).

 

In addition, Middo put a ban on any ultralights being flown engine dead unless in an emergency – so that sort of got around the training aspect on the face of it – but not to all of us who had been there. Have you ever tried a powered approach in an even modestly performing motor glider? A powered assisted approach is a very alien business because the thing is going to go for bloody miles in ground effect anyway so it becomes axiomatic that you have to be able to use the approach aids – and be trained to avoid misusing them!

 

The whole thing did not get much publicity and did not I think reach the Ops Manual, but it caused a lot of angst amongst the aircraft suppliers who found that their expensive imports had been registered but now were not allowed to be. The (then) Tech Manager wore the brunt of that when it was actually a Board responsibility.

 

I do know that AUF came very close to being sued and I am sure would have lost heavily as there were no grounds to stand on. The person mainly involved (not Michael Coats) had his money wrapped up in unsaleable aircraft and could not afford to mount the case – so it all went quiet.

 

A more mainstream view of this deliberate engine out situation can be recounted as follows. I am not in favour of the practice myself (especially in anyway poorly performing aircraft) but some people certainly are!

 

I had a situation at Watts Bridge where a CFI began repeatedly flying in and using the place for dead stick training. He was an experienced glider pilot as well so there was not a skill problem. The problem is that you can rapidly turn a simulated emergency into a very real one if somebody abruptly gets in your way when you are near the ground and has not seen you!

 

I stepped in and ordered him to desist – or go do it somewhere else as I was sick of writing accident reports for other people, plus I was keeping Watts training accident free and had done so for years. I sort of out-ranked him as both a Pilot Examiner and CFI – but he carried on doing it elsewhere – and one of his students wore the consequences as did a lot of others that particular day.

 

Instructors have to remember that they are minor gods in the eyes of students and their example will be copied – particularly if they make something inherently hairy appear just a normal part of flying.

 

So an ex student of this CFI (who is now dead incidently) had a Gazelle out over the Glasshouse mountains (which is extreme tiger country) and decided to get his eye back in on pure gliding. So he switched the engine off because he had done so often before! It did not re-start! A Mayday and a deal of local excitement later he did get the thing going again and the day was “saved†and we all avoided a bit of stupidity being justifiably reported by an ever eager media!

 

I would recommend that all flying schools do take a look at simulated engine outs in terms of leaving some residual power to effect a reasonable glide angle, then use this as part of their standard training.

 

I certainly adopted my motor glider experience to my Thrusters and gave much more valid glide judgemental training as a result, in terms of both on and off airfield forced landings.

 

As a final word – on side slips. When you are flying traditional low inertia, high drag ultralights there is a far more effective technique than a side slip – this is the Drag Dive.

 

Here you are using the idling propeller as a very effective airbrake and so can combat the tendency to get too close in too high and (as another post on this thread points out) actually train students to get into overshoot situations. The spin off benefit of the Drag Dive is that the aircraft stays aligned on the approach path without any unusual activity.

 

You simply force the nose down against the prop drag, can take off up to 300’ very rapidly with little airspeed gain and once the approach “picture†looks normal then recover to the normal approach attitude and get on with it as normal – the airspeed rapidly settles to approach speed as well.

 

That is just too easy on the draggy types – but how often is it taught?

 

Aye

 

Tony.

 

 

[Guest Andys@coffs]

Tony

 

Thanks for the post, some interesting things to consider in there.

 

Andy

 

 

[vk3auu]

I suspect that if you are gliding into a headwind at your best glide and the wind is such that you are making no headway, then that is the best that you will do, because if you try to increase your ground speed by going steeper, although your airspeed will increase, the vector in the horizontal plane will get shorter as the vector in the vertical plane increases. It is all to do with drag and the business of not being able to stretch your glide you know.

 

David

 

 

[Yenn]

vk3auu.

 

If you are gliding with no headway just land. You will not break anything, just take care when you open the canopy or step out.

 

 

[facthunter]

Increase glide speed.

 

Yenn & vk3auu, You have to INCREASE your glide speed in these circumstances to have ANY groundspeed. To descend vertically may not be the optimum if it is into shark infested waters, you are at a fair height and the coast is within reach. When you try to stretch the glide you RAISE the nose and slow below the best glide speed, and you have a steeper STILL AIR glide angle as a result. When, with a strong headwind, you lower the nose and increase your sink rate, you balance that disadvantage by obtaining some (or an increase in) groundspeed. Thanks for responding to my point. Nev.