Where are the Mythbusters when you need them?

[Spin]

Just spent an amusing half hour reading a thread on another forum about aviation myths that get perpetuated from generation to generation.

 

Plenty of leg pulling around the subject, but one that generated some heated discussion was: increasing your rate of climb by "pedaling" the rudder too and fro.

 

Anyone else got any favourites?

 

 

[Spin]

Very true and oh so tempting when the field gradually slides up the windscreen. Quite interesting to experiment with different glide speeds on a calm day, noting what the VSI settles on for each speed range.

 

 

[Guest Qwerty]

Myth;

 

Park timber props horizontally to prevent moisture content draining to the bottom blade. :hittinghead:

 

 

[Guest Cloudsuck]

Gotta say ....go cautiously with the VSI....it.s only telling you what happened 10 seconds ago.

And don't rely on the VSI to give you best glide. It WILL give you minimum sink. Best glide and minimum sink are two totally different thing. If you are flying for minimum sink, you may not make your chosen field.

 

 

[Vev]

And don't rely on the VSI to give you best glide. It WILL give you minimum sink. Best glide and minimum sink are two totally different thing. If you are flying for minimum sink, you may not make your chosen field.

Hi Cloudsuck,

 

 

I think I understand what you have said ..... but can you explain this to me in a little more detail and what this means in a practical sense with situations/examples?

 

 

Cheers

 

Jack

 

 

[Mazda]

Jack the "best" glide speed is the one at the best Lift to Drag ratio, which produces the flattest glide angle and therefore the greatest range. For many light training aircraft the best glide is at around 4 degrees angle of attack. In the glide there is one speed for the best lift to drag ratio, at any other speed the nose will be higher or lower and the angle of attack won't be at the best for lift/drag. So faster or slower than the best glide speed, the angle of descent will be steeper and the range shallower.

 

But the "best" glide speed is for range. If you want minimum sink it is at a much higher angle of attack, maybe right up around 13 degrees, but the aircraft won't glide nearly as far.

 

 

[djpacro]

Veverjg, Noel Kruse tackles your question on page 196 of his free book #1 at FLY BETTER...... It expands on what Cloudsuck stated about the VSI etc.

 

More on the angle of attack on page 79.

 

The whole book is good bedtime reading.

 

 

[Guest Cloudsuck]

Nice one Mazda! For practical purposes, if you are over you landing field and want to buy time (hang in the air) to sort our your landing (into wind etc) use minimum sink. If you are gliding to your paddock, use best L/D.

 

To fly at minimum sink, you need to generate more lift so you are flying at a higher AofA. Unfortunately you are now also flying with more drag as a result. Therefore your glide will be steeper but you will spend more time gliding down that glide slope because you have extra lift. Never think that yu can find best glid speed (best L/D) using a VSI as all you will do is find min sink.

 

 

[Vev]

Thanks for the feedback and info on my question guys.... always something new to learn everyday!

 

Cheers

 

Jack

 

 

[Tomo]

If you're in a Jab with electric flaps that you can control variably, use just a dribble of flap.. just a flick of the switch, and you'll extent your glide performance... Quite noticeable when I was experimenting with it too! I was doing it in a 230 so not sure about the others, but it was quite effective.

 

A lot better than first stage of flap or non at all, the idea is you increase lift, but don't get any extra drag that lots of flap would come with.

 

 

[Guest sirius]

Myth?;

 

Water can enter a sealed 200 litre drum.

 

 

[Tomo]

If they vacuumed every drum it wouldn't... ;)

 

 

[Vev]

Tomo,

 

 

Interesting comment about a using a little flap on the Jab.

 

 

Myth or not???

 

 

A couple of years ago I went to the Cowra fly-in and spoke with the guys from Jabiru and was told that when the 160 is fully loaded just add 1 or 2 deg of flap and it will pick up the tail and increase air speed. I experimented with this and found I picked up 2-3 knots in S&L flight. The Jabiru guys said when the flaps a fully retracted the flaps are in a negative position.

 

 

Cheers

 

Jack

 

 

[Tomo]

Myth or not???

It might be a myth, but it works! :big_grin:

 

 

[Guest sirius]

Myth?;

Water can enter a sealed 200 litre drum.

Its not a Myth;

 

WATER CONTAMINATION IN FUEL DRUMS

 

Fuel drums stored outside should never be stored vertically on end because rainwater can collect inside the rim of drums and can be sucked past the bung, (even though the bungs are tightly drawn), into the drum when cooler temperatures cause contraction of the internal air and fuel. This water now contaminates the fluid and also may, in time, form rust under the drum lid which can flake off and add a particle contamination problem.

 

When delivered the sealed drum has an airspace to allow for expansion and contraction due to heating and cooling. Heating causes expansion and escape of this air and then when cooled water is sucked past the bungs.

 

For this reason drums should not be stored where rain can collect or cover the bungs. They should be stored horizontally or tilted.

 

Vacuum sealed drums will allow water if the temperature and humidity maintain a fall to below that of when they were filled, or increases above the vacuum, (previously airspace), allowed for expansion.

 

Drums, fuel tanks, and any material subject to porosity can also be contaminated by the Saturated Adiabatic Lapse Rate which is the lapse rate of air which has been cooled to its dew point and is therefore saturated. Further cooling as a result of an ascent will result in condensation and the cooling rate will, (in the lower levels), be a minimum of approximately 1.6 - 2 degrees Celsius per 1000 ft, increasing with height as water content and condensation decrease to a figure approaching the Dry Adiabatic Lapse rate, (which is the lapse rate of unsaturated air which is a constant and dictated by Gas laws).

 

We all know from basic principles of flight theory that the air in which we fly is a fluid in a gaseous state. Therefore any expansion or contraction, humidity increase or decrease, will involves a fluid.

 

 

[Guest rocketdriver]

Jack, just to add to what Mazda said, for the best glide over the ground, which can be vital in, say, an engine out situation, you want to be flying a LITTLE above best glide to allow for the headwind in final. More headwind, more speed .... If you are stuck with a tailwind (heaven forbid), VERY SLIGHTLY slower speeds will give you best glide over the ground. How much depends upon wind strenght and is different for every aircraft and every wind strength.

 

Reason? Think of your path through the air in comparison to the ground in two stages and then add them together. So you are at best glide in still air, you are at best glide over the ground too. Now add a headwind. Every second you are airborne, the wind is "blowing" you backwards in relation to your still air track, so you want to minimise the time in the air to minimise this effect. But do it too much and you loose too much glide performance, so its a balance between the two effects. Same in reverse for a tailwind, but the degradation of your aircraft's glide ratio is much more severe for slower speeds than for higher, so proceed with caution!

 

Bit lengthy, but I hope that helps ....

 

 

[Vev]

Rocketdriver,

 

Many thanks this ... it makes sense and it does help.

 

Cheers

 

Jack

 

 

[Guest Bert Foster]

I suggest all you guys just read FLY BETTER. All that you are discussing is covered in detail in that book.

 

 

[djpacro]

Not quite true, Bert, as he doesn't cover the care of fuel drums but I guess that will be in his next book. I agree that FLY BETTER does deal with many of the myths but we've still got a long way to go with this forum to discuss them, haven't we?

 

 

[Spin]

I suggest all you guys just read FLY BETTER. All that you are discussing is covered in detail in that book.

Nah that wouldn't be half as much fun, got to have a knock down, drag him out fight first! If I remember right the argument about a touch of flap giving you extra speed went all the way to the NTSB in the US after a (727?) did some spectacular aeros due to one leading edge slat deploying in the cruise. Story goes that the old three holer went supersonic during the ensuing dive.

 

 

[Guest Bert Foster]

Not quite true, Bert, as he doesn't cover the care of fuel drums but I guess that will be in his next book. I agree that FLY BETTER does deal with many of the myths but we've still got a long way to go with this forum to discuss them, haven't we?

Yep you are right he doesn't discuss care of fuel drums, but he covers everything else. Maybe you should leave a note on his feedback link and suggest more info on fuel drums.i_dunno

 

 

[facthunter]

727 Leading edge flap extension.

 

Spin I believe that one was with an aircraft holding at height and the crew experimented with the idea of extending a bit of leading edge flap. Clever and sensible pilots who wsh to live long lives, do NOT do this type of thing. There is a prohibition of extending LED's above FL 210 in the OPs manual. Boeing design and build the aircraft , but some pilots think that they know better. Nev..

 

 

[Spin]

Nev, my recollection of that one is the other way around, the SOP amongst crew was to pull the circuitbreaker for the leading edge slats, which deployed in conjunction with the trailing edge flap normally, to allow them to extend a few degrees on the trailing edge. One slat on the leading edge deploying when not wanted was what brought them undone.

 

Anyhow whatever the sequence of events, it was done in the belief that it increased performance.

 

 

[dvschem]

True.....No one has ever failed a flight test/check for "going around"

Very True - and great advice.

 

I called off an approach during my PPL test after I decided it was safer to approach from the other direction. I got a huge well done for it.

 

Never push a bad approach, they never get better with age.

 

 

[pudestcon]

Very Never push a bad approach, they never get better with age.

:thumb_up:

 

Pud