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Valenta Salto FES setup - thrustline.

Fans and Thermals.
John Wighton
Posts: 7
Joined: 05 Mar 2021, 13:59
Location: ESSEX

Valenta Salto FES setup - thrustline.

Post by John Wighton »

I am setting up a Valenta Salto with a Hacker FES drive. A50-16L, 100A ESC, folding prop TBC.
The Hacker FES drive has a bearing that is bonded inside the nose, this is set with a plastic guide. I am using 1/4in threaded rod to provide visual guidance for the thrustline.

I will use zero degrees beta (lateral) but there should be some downthrust. I estimate about 4 deg is needed based on similar set ups in large gliders (4.4m Alpina Magic).

Has anyone got a similar setup that they can provide down thrust angles for?

Not scale but equally relevant - same question for a Multiplex Alpina Carbotec. This one is being set up for high speed on/off power aeros.

Regards
John
Jolly Roger
Posts: 573
Joined: 30 May 2015, 20:35
Location: Sutton Bank, North Yorkshire

Re: Valenta Salto FES setup - thrustline.

Post by Jolly Roger »

Hi John,
Yes I think 4 or 5 degrees downthrust is about right relative to the wing datum…I think that’s what I used on my Alpina. I’ve used as little as 2 degrees but needed to mix in some down elevator to prevent the model ballooning.
Rog
Elliot Howells
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Joined: 18 Mar 2015, 08:18
Location: West Wales
Contact:

Re: Valenta Salto FES setup - thrustline.

Post by Elliot Howells »

My 2 cents...

Just to contradict Roger, because he's so tall. :lol: :lol:

I've found 8 degrees of downthrust to be optimal so far - and if you err, then you're mixing in a little up instead of down. My 6m ASH and 4.5m B4 both have 8 degrees, if you look at the little foam MPX gliders, they use much more.

I FES'd an ASW17 years ago and this needed lots of mix to correct insufficient down thrust (down trim) and when I throttled off at the to p of the climb, she'd balloon terribly - so less than ideal.

Cheers, Ell.
John Wighton
Posts: 7
Joined: 05 Mar 2021, 13:59
Location: ESSEX

Re: Valenta Salto FES setup - thrustline.

Post by John Wighton »

Both replies very useful. 8 deg seems a lot but looking at my Alpina Magic which requires around 60% down elevator in the climb. That is set to 0 downthrust.

I will try 8 deg.

That equates to 14mm over 100mm of shaft length (SIN 8 deg).

The next step is deciding the Zero datum of the fuselage. I can measure the wing incidence and guess the rigging angle (2.5deg). Then measure off that.
Elliot Howells
Posts: 333
Joined: 18 Mar 2015, 08:18
Location: West Wales
Contact:

Re: Valenta Salto FES setup - thrustline.

Post by Elliot Howells »

I was surprised, given that my big petrol powered models seem to need around 4 degrees to be optimal.

You'd think also, that with the long moment arm of gliders, you'd have a better lever to counteract the the pitching effect...

EDF's however seem to require zero downthrust and only jets need side thrust to avoid melting the tail!

I do love this hobby, it's the challenges that make it interesting eh?

Best of luck, do report back with your findings, Ell.
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Trevor
Posts: 161
Joined: 19 Jul 2016, 16:29
Location: Hampshire
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Re: Valenta Salto FES setup - thrustline.

Post by Trevor »

If you need excessive downthrust, there's a good chance the glider is nose heavy. The key is to establish whether the model is indeed pitching up because of the thrust or is it just because of the increase in speed? If it is the latter, that's a sign of nose heaviness. The good old fashioned dive test is the way to find out: From a level glide, push the nose down gently (not 45 degrees, as is sometimes advocated!), release the stick and observe what happens. If the model pulls out promptly and maybe even tries to climb, then it clearly is going to pitch up with increased speed. Fighting this with more and more downthrust is not really the way to go. Move the cg back a bit, re-trim, and repeat the test.

Usual apologies apply re: grandma and egg sucking :D

Trevor
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