Guys,
How does an EDF unit thrust react to upwind vs. downwind flight? Do going into the wind increase thrust and going with the wind reduce thrust?

Best, DennisT

Just as with any airplane, it's quite important for air (wind) over the wings to create lift. Going into the wind aids lift quicker; i.e., shorter takeoff distances; going downwind does not aid; i.e., much longer takeoff distances. The same holds true for landing; plus, more power will have to be held for landing downwind to keep air over the wings. And, because it's an EDF, we have to depend more on the natural wind. In even more words; the EDF has to generate more ground speed going down wind to get liftoff airspeed than it would going into the wind. And, because more time is spent on the ground going downwind for takeoff, less time is spent in the air. It's as simple as I can put it for me to understand.

Beaner,
I understand and agree as far as the lift goes, what I'm interested in is how wind impacts the fan units performance. As you go upwind and you have the wind blasting into the inlet duct at a constant throttle set poin does the fan naturally put out higher thrust and going downwind does it lreduce thrust?

Best, DennisT

Think of it as dynamic thrust; when the airplane is going into the wind, more (dynamic) air is being passed through the EDF and dynamic thrust increases. Conversely, going downwind less dynamic air is available; consequently, less dynamic thrust is generated.

[:@] .....OooooKay....another new twist on the "downwind turn"  arguement.

The answer, if the plane is in flight, is NO. It can't tell the difference what direction it is flying as there is no "wind" just airspeed, otherwise called relative wind. (exception given to abrupt wind shear or dynamic soaring situations). The model is moving within an airmass.

Besides all that, EDF's do not "unload" in flight to any appreciable degree no matter what.

What he said. All aircraft have two relavent speeds: Ground Speed and True Airspeed. Ground speed is the speed of the aircraft relative to the ground. This speed has zero effect on the airplane except for the time it takes to get from point A to point B. True airspeed is the speed the airplane is traveling through the air relative to the air it is passing through. The engine gets no ram assistance because it will still need to rev up to the speed needed to match the wind speed.

It's a hard concept to visualize, but it's true. I've hovered a real Cessna 152 into the runway when I landed with a 50 knot headwind. I had to gun the gas to full power to make it to the runway on final approach, and then eased the throttle down as I hovered down to land. Going towards the runway with a 50 knot headwind required 100 knots at full throttle (airspeed indicator read 100 knots), while my ground speed was 50. When I got to the runway, I throttled back until the indicated airspeed red 50 knots (zero groundspeed). It requires quite a lot of power to go zero knots ground speed.

Another way to look at it...

Due to its rotation, the earth's surface (and the air surrounding it) are moving eastward at 1000 mph or so.If you take into account the speed of the earth in its orbit around the sun, the atmosphere is moving at many thousands of miles per hour... Do you notice a difference in how a plane flies going east or going west on a calm day? (I'm talking about a model aircraft flying within a few hundred feet of the ground here... let's not get into upper atmosphere phenomena here...)

What the last couple of posts say is correct. Imagine swimming in a river that is flowing. If you closed your eyes you wouldn't know the water was moving. This is what the model experiences in moving air.
There is no difference in thrust upwind or downwind.
A fan unit does not unload in flight it actually loads up slightly because the airflow increases and the fan has more work to do.
Cover one intake up and the revs increase. This is because the fan has less work to do.
I know this from IC Ducted fan days when I had on board tachos.
Also ask Stumax if you don't believe me.
It did suprise me because they do sound like they unload as they come towards you but it's the doppler effect.
Think about a motorbike coming towards you and then going away. The sound changes but the speed of the bike doesn't
Jim

Guys,
The last couple of posts are close to what I was getting at. If the ship is traveling down wind in a 10 mph wind and makes a sharp turn to up wind (i.e. split S) does the Fan unit get any short term boost from the ram air to stabilize the air speed? While the ship was traveling down wind assuming it was at its normal flight speed for the selected throttle setting, its ground speed will be this normal speed plus the wind speed to maintain airspeed. Now when it does the split S and quickly turns into the wind the aircraft could increase speed slightly from the diving turn but as it come full into the wind the ground speed will be the normal airspeed minus the 10 mph wind speed. Since there is a ram blast of air into the inlet ducts does this give a boost to the thrust to help maintain the airspeed? Does the volume of air going through the fan increase with the ram blast? As the last post indicated, the increase air flow should increase the work the fan does but since it is electric the motor will not slow but will try to maintain rpm and draw more amps as needed. Problem is the drag on the aircraft also increases and the net result is the ship slows slightly but with electric it might slow less the IC power.

What happens when the nose is pulled up sharply? Does the fan produce more thrust as the ship starts to slow?

Best, DennisT