Don't forget to check your spam folder if you don't get an activation email after joining!!

FES Down and side thrust

Here is where you can discuss to your hearts content the merits of sustainers.
Post Reply
Phill Tadman
Posts: 398
Joined: 18 Aug 2015, 20:38
Location: South Cambs

FES Down and side thrust

Post by Phill Tadman »

Hi all,

Does anyone have any recommendations for building in down and side thrust when fitting a FES to a 1/3 scale Antares?

In a recent RCME article, 6 down and 3 right was suggested (I think this was using the wing centre line as a reference).

Calculations predict a thrust to weight ratio of about 0.5 so not a rocket like climb which perhaps could be compensated for by trim.

Thanks

Phill

Jolly Roger
Posts: 387
Joined: 30 May 2015, 20:35
Location: Sutton Bank, North Yorkshire

Re: FES Down and side thrust

Post by Jolly Roger »

Hi Phill,

Some of it depends on whether you’re sawing off the nose ( :o ) and using a spinner or have the drive shaft poking out of the tip of the nose.

With a spinner, your thrust angles are largely determined by the profile of the model’s nose. So typically 3 to 5 degrees down thrust (measured to the wing’s LE to TE chord line) and no side thrust. This is ok but the model may lift its nose when power is applied. No drama if you’re ready for it, and you can, as you say, fix it with an elevator mix.

If you just have the prop shaft extending out of the nose then you could go for 6 to 8 degrees down and a couple of degrees side thrust. I wouldn’t worry too much about the exact values.

In terms of power, I read on RCG of a 1/3 Antares with as little as 55W/lb achieving ROG. I’m guessing that was pretty scale!... i.e. a long take off run over a smooth surface. I just ground tested my 14kg DG505 yesterday and am getting 65W/lb. I think that should be plenty of power to ROG (it’s the same as my 1/3 Cub)... my worries are more about prop to ground clearance. I don’t like dollies but think it may be unavoidable.

Hope this helps.

Cheers,
Rog (hopefully without a dolly ;) )

john greenfield
Posts: 544
Joined: 18 Mar 2015, 07:52
Contact:

Re: FES Down and side thrust

Post by john greenfield »

Hi Phil

I would not bother with any side thrust. With a small prop disk and long wings, it really is not necessary but some downthrust will help stop the nose coming up too much in the climb. Any amount is only a guess but something like 3 to 4 deg seems about right. On the Antares use the flaps to control any excess climb under power. Set up a "motor" flight mode and if the model climbs too much under power Raise the flaps a little. this is more efficient than flying with loads of down elevator to control the climb.

AEB
AEB = Aeronautical Energiser Bunny (with thanks to CW)

Elliot Howells
Posts: 232
Joined: 18 Mar 2015, 08:18
Location: West Wales
Contact:

Re: FES Down and side thrust

Post by Elliot Howells »

Hi Phil,

I think I used 8 degrees down (no side) on my ASH26 at 12Kg and 1:3 scale.

She flies straight as an arrow at that. 2.5Kw on a 14x10 so plenty of go!

Ell.

Phill Tadman
Posts: 398
Joined: 18 Aug 2015, 20:38
Location: South Cambs

Re: FES Down and side thrust

Post by Phill Tadman »

Thank you all!

Really useful information.

Just need to steel myself to start the conversion!

Phill

Jolly Roger
Posts: 387
Joined: 30 May 2015, 20:35
Location: Sutton Bank, North Yorkshire

Re: FES Down and side thrust

Post by Jolly Roger »

For info, I’m sure I’ve seen a photo on t’internet of a full-size Antares with FES, just in case you were having any “but it’s not scale” qualms. I’m on my 4th FES and it’s given every model a massive shot of extra fun, peace of mind and flying time.

User avatar
terry white
Posts: 558
Joined: 18 Mar 2015, 21:08
Location: wareham,dorset.england

Re: FES Down and side thrust

Post by terry white »

Here, here Roger, and to say nothing of the safety aspect a motor can provide to get one out of trouble if necessary.
Its just shear madness and shortsightedness of clubs that ban the FES from their slopes these days.Having said that it is now only a handful of die-hard clubs that do. Especially as you say the models are now completely,100 per cent scale as per the full size. I would erge all 'modern scale' modelers to give it a try, believe me you wont go back.There are enough FES flyers here on this forum now to give the newcomer to FES all the help they could want.

Post Reply