Microlighters

Flying over the dam the other day, in a solid cross wind, I was wondering.............

Picture the scenario. In the middle, over a dam. Quite a moderate wind from the one side - for the sake of the argument - 90 deg from the side. Engine quits. Do I turn into the wind, slower ground speed, but better height retainment, or do I turn with the wind. Fall from the sky, but better ground speed.

Which gives me the better glide ratio?

Logic tells me that you glide slope (ft. per minute descend) will remain the same once you reach the optimal airspeed, lets say 65 mph, does not matter if it is into the wind or downwind. Turning into the wind you will reach the 65mph airspeed faster and thus lose less alt. Turning downwind you will lose more alt as it will take you longer to reach the desired airspeed (65mph) thus losing more alt than turning into the wind. I guess the determining factor will be how far you will have to glide in terms od distance on the ground. Downwind-higher groundspeed (at 65mph airspeed) = longer distance on the ground but you would have wasted more alt to get to the desired airspeed. Headwind = slower groundspeed and maybe a shorter distance on the ground but less wasting of alt to reach the desired airspeed that could allow you to extend the distance on the ground. I guess the main issues will be at what airspeed you were flying before the motor went bust and how strong the wind is blowing.

There is always the airspeed vs. alt question.

Ok let me have it if I`m wrong.

I am not a Guru. Unless there is no option, NEVER, NEVER EVER turn downwind! Turning upwind you will still lose altitude but not as fast as turning downwind and you wont need to sacrifice altitude to regain speed. Upwind will give you the slowest impact speed if decent was properly managed. Same rule applies when having power loss on take off, NEVER turn back to runway.

If you fly over water,you must be gliding distance from the dry side...so ,low level over water is not a good thing .

If you fly over water,you must be gliding distance from dry land...so ,low level over water is not a good thing .

nicow wrote:If you fly over water,you must be gliding distance from dry land...so ,low level over water is not a good thing .

Ja, ja Nico, maar ek wil weet, watter kant gaan ek kies as die enjin my los, wind op, of wind af.

M I Claase wrote:Upwind will give you the slowest impact speed if decent was properly managed.

I am buying into that. I am wondering which one gives you the better gliding distance.

Splinter wrote: I guess the determining factor will be how far you will have to glide in terms od distance on the ground.

That is the question. Everything being done by the book, AS, etc, will I glide further upwind or downwind. Wind up will obviously give you more time to sort your sh!t, but I'm thinking distance I am over water

Wind up you'll have a longer gliding distance ,downwind you'll have a greater and faster sink rate ,(and less time to sh&t yourself )

Downwind at best endurance speed (generally slower than best glide speed) will get you the most distance. But you are going to hit the deck much faster...

I agree. upwind longer in air but not gaining more distance

crazydoc wrote:I agree. upwind longer in air but not gaining more distance

How can you stay in the air longer flying upwind, or downwind. The aircraft knows nothing about the 'wind', as it is flying along with the air mass.

Just as an example, use a Jabiru J120. Best glide speed is 65kts. At this speed, it sinks at around 500fpm. If you are at 1000' when the engine fails, and you immediately go to best glide speed (65kts) you will lose 500 feet per minute, so you will land in 2 minutes (1000' / 500fpm).

If the wind is 10kts, and you are flying into the wind, your speed over the ground is 65kts-10kts = 55kts, and the distance over ground that you will cover is 55nm/60*2 = 1.8nm .

If you fly downwind, speed over ground is 65kts+10kts = 75kts. Distance over ground will be 75nm/60*2 = 2.5nm .

So given these speeds, you will travel 30% further downwind than upwind. BUT you will also be hitting the ground 30% faster, which is 80% more energy - which you would really want to avoid, unless you are guaranteed of a nice smooth and clear spot to land!

justin.schoeman wrote:The aircraft knows nothing about the 'wind'

I have had instructors say, turn into wind so we can get a better rate of climb. Duh? ROC stays the same for a given airspeed, its only ground distance over time that changes. (I am only talking about light aircraft and not considering inertia etc)

If you kept a constant speed and took out a stopwatch, it will take exactly the same amount of time to get to the ground whether you are 'into' or 'down' wind. The machine doesn't know or care about the ground until it hits it.

Good topic and reminds us that we should always fly with a safe LZ in sight.

justin.schoeman wrote:How can you stay in the air longer flying upwind, or downwind. The aircraft knows nothing about the 'wind', as it is flying along with the air mass.

False sense of time, cause everything happens much slower.

justin.schoeman wrote:If the wind is 10kts, and you are flying into the wind, your speed over the ground is 65kts-10kts = 55kts, and the distance over ground that you will cover is 55nm/60*2 = 1.8nm .

If you fly downwind, speed over ground is 65kts+10kts = 75kts. Distance over ground will be 75nm/60*2 = 2.5nm .

This is what makes it interesting. If one is marginal over water, not meaning low level, but 1 000' or something, and distance to shore is If the donkey quits, your training will kick in, and one will tend to turn into the wind. The safer option will then be to turn with the wind. Rather hit the shore at 90 mph, than the water at 40. In your calculations, even a 10 kts wind will give you 700m extra gliding distance.

For the sake of the discussion, obviously ignoring all other factors like better landing spots etc. I just don't want to swim.

I would like to throw power setting into the mix here. All the arguments so far were around the same airspeed, but what about the same power setting. According to me I would require less power to fly 65Mph (IAS) into the wind than 65Mph (IAS) with the wind?

So in an engine out scenario, obviously no power so the power setting for upwind or downwind will be the same. This is where I don't agree with Justin's comment that you can not stay in the air longer upwind. This statement is true for the same speed, but according to me not the same for the same power setting. During an engine out your power setting for upwind or downwind will obviously be the same, but the aircraft will have a significantly different attitude trying to maintain 65Mph in a (15kt wind) upwind than trying to maintain it downwind. I do believe this lower nose attitude going downwind might nullify any gain in ground speed that you would get going downwind.

mak wrote:I would like to throw power setting into the mix here. All the arguments so far were around the same airspeed, but what about the same power setting. According to me I would require less power to fly 65Mph (IAS) into the wind than 65Mph (IAS) with the wind?

So in an engine out scenario, obviously no power so the power setting for upwind or downwind will be the same. This is where I don't agree with Justin's comment that you can not stay in the air longer upwind. This statement is true for the same speed, but according to me not the same for the same power setting. During an engine out your power setting for upwind or downwind will obviously be the same, but the aircraft will have a significantly different attitude trying to maintain 65Mph in a (15kt wind) upwind than trying to maintain it downwind. I do believe this lower nose attitude going downwind might nullify any gain in ground speed that you would get going downwind.

IAS is a pressure instrument - it measures the force exerted by the air that the craft is moving through. This will be directly proportional to the drag, and therefore the power required. There is no way you will need more power to get the same IAS into the wind.

Justin

I am not saying more into the wind, I am saying more power downwind, but I get the principle of what you are saying. What about your aircrafts attitude in an engine out scenario flying into a 15kt wind or downwind of it?