Answer this basic question

[shades]

This applies to all prop driven aircraft, but in our hobby, only applies to 'leccy planes. When the motor is cut on a battery powered plane, which causes the most drag, allowing the prop to windmill or applying the brake so it doesn't spin. It seems to me that allowing the prop to windmill would cause less drag, but I have seen it written that the opposite is true? Lets have some opinions, and may be an explanation.

[Gareth Wallis]

A prop that windmills will give you the most drag.Usefull to slow aircraft for landings but for gliders you need a folding prop to get the least drag when gliding.

[GrumpyGnome]

Hi guys,

a stopped propellor gives less drag. Alasdair (?) Sutherland gave an explanation of why in one of the model mags ..............

Something to do with the swept radius I think !

On a leccy plane, try it and see - the difference can be quite noticeable.

GG

[shades]

Thanks for the comments guys. I've been flying a Pico Jet for quite a while and sometimes a GWS Corsair. The Corsair is terribly under powered, having to run it flat out just to stay in the air. However, I have just converted it to brushless, and suddenly I can do stunts with it. Whey hey!
I find it really hard to land now though, as it is much lighter and seems do run out of momentum just before a safe landing speed, and lands heavy. I need more practice I think. I find it quite a tricky thing to fly.

[John MacDonald]

Windmilling prop,(or an idling prop with I.C.engines) causes drag. Thats the reason for folding props!
The less pitch the prop has, the greater the drag effect.

[Danny Fenton]

I might be wrong but I think on yachts the prop is locked when sailing as it gives less drag through the water, different medium but same principle

[Aslan]

Hi Danny.Prop on plane is pulling,prop on boat is pushing.....same medium,different principle.

[Dave Harbour]

I agree, the windmilling prop is being spun round by the airflow over the blades causing quite a lot of drag.
If you own an electric glider, for instance, with a speed controller with a break facility and a folding prop, try gliding around with the break engaged and the prop folded and then try removing the bridge for the break from the speed controller and let the prop windmill, you will see a big difforence in the glide characteristics and the amount of time you spend in the air.

[Stephen Grigg]

Sometmes my fun Cub glides passed and the prop is happily turning and other times it glides passed and its perfectly still, have never noticed much difference but thats just me I expect

[Romeo Whisky]

One consideration you may not be aware of is that some makes of ESC use the brake setting to also determine how the Low Voltage Cut-Off works.

With these ESCs If you set the brake to OFF, the LVC will also adopt a "Soft" operation, which is to say that when the battery voltage nears the LVC point the motor will slow down which gives a good warning that you need to land asap, but in doing so also reduces the drain on the battery which slightly raises the battery voltage.  It is a useful safety feature as it buys you both a warning and a few extra moments to get the model down safely before it goes deadstick.   This is also more relevant to a powered model than a glider.

(This does not apply to all ESCs and some offer soft cut-off as a separate programming feature).

[Romeo Whisky]

Another reason why gliders usually have the brake ON is to get the folding prop to fold.  If it is still windmilling it won't fold.   I was always taught that for fixed props you have the brake off, and folding props you need it on.