Apr 24, 2012, 10:00 AM less is more United States, CA, Marina Joined Sep 2006 2,749 Posts From what I'm reading the "adjustable thrust line" concept would most likely need to be adjustable in flight and be tied to the throttle setting. Atleast it would if you wanted power to be pitch neutral at any setting. Does that sound right? Kent Latest blog entry: My kind of Zagi
Apr 24, 2012, 10:15 AM
less is more
United States, CA, Marina
Joined Sep 2006
2,749 Posts
Quote:
 Originally Posted by HerkS The best way to visualize it is to ask "where is the drag produced, and where is the thrust aimed."
This makes sense to me. That is, the thrust should push directly through the Center of Drag. Otherwise, the thrust will create a pitch moment.

The CG could be wildly different than the Center of Drag depending on fuselage design. An example of low CG (which produces a pendulum effect) is C5A. This low CG would not affect the thrust line. The thrust line remains tied to the Center of Drag.

Kent

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Latest blog entry: My kind of Zagi
 Apr 24, 2012, 12:34 PM I don't like your altitude Joined Sep 2011 3,143 Posts Let's see if Ive got this right.On a linear twist wing with a constant chord,ignoring any drag from the prop and housing,and say 10o of twist.If the prop shaft is at 5o it is on the centre of drag? Stuart
Apr 24, 2012, 03:03 PM
Herk
Virginia USA
Joined Jun 2007
1,630 Posts
Quote:
 Originally Posted by Stupot46 Let's see if Ive got this right.On a linear twist wing with a constant chord,ignoring any drag from the prop and housing,and say 10o of twist.If the prop shaft is at 5o it is on the centre of drag? Stuart
Depends on dihedral - and twist really. On a clean flying wing you could assume that the center of drag is somewhere about the AC on the MAC. If the wing has a lot of dihedral then down thrust would help because the drag production is probably centered above the center of the motor. Also the natural twist will produce a nose up moment when speed increases - (ie at higher power setting) so down thrust can help with that as well.
 May 14, 2012, 04:49 PM I don't like your altitude Joined Sep 2011 3,143 Posts Since Richard posted the drawing of the HoXVIII I've bee wondering how I could build this wing,one of my favourite Hortens,without paying for cad work.I've done measuring on the plan of the VII,and think I could adapt it. My question is,would these airfoils work if blown up 50 or even 100%.At the larger size,which I would prefer,the centre would be 840mm long and 120mm at it's thickest point. I'm thinking foam,a two piece centre section split down the centre and each wing done in 3 sections.This would make the cutting easier and should give me a reasonable facsimile of the twist.The finished plane would be in 3 sections with the outer wings attaching at the u/c legs. Stuart
 May 14, 2012, 06:02 PM Herk Virginia USA Joined Jun 2007 1,630 Posts Where will you put the cockpit? And who will get in and fly it??
 May 15, 2012, 01:33 AM I don't like your altitude Joined Sep 2011 3,143 Posts I've got one of those little kids who race camels stashed in a box under my bed.It will only be just over 2.4 m span,so not that big. What prompted my question was Jens problem shrinking the Manatee,which I know is an extreme case. Stuart
May 15, 2012, 01:11 PM
Joined Sep 2011
3,143 Posts
This is the revised drawing.Not the best pic,but I think it shows where I'm going with this.I intend starting cutting this as soon as the VII is a compete airframe, as a time filler.The bigger sections will be good practice before I have a go at a Colibri.
So- does the panel think this will work aerodynamically? I would appreciate comments,as I don't want to spend time makings drawings to be blown up if this is not a practical project.
Regards Stuart

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 May 18, 2012, 09:13 AM I don't like your altitude Joined Sep 2011 3,143 Posts One for our boffins.Is there a way to work out the volume of a wing.I'm trying to come up with a guesstimate of the weight of foam so I can see what sort of power would be needed to get this thing off the ground. Regards Stuart.
 May 18, 2012, 09:21 AM Deniable plausibility Derbyshire, UK Joined Aug 2008 2,311 Posts Wing area in m^2 * 0.66 * density of foam (in kg/m^3) should give a decent 'ballpark' figure for the mass of foam in kg. Richard
 May 18, 2012, 10:27 AM I don't like your altitude Joined Sep 2011 3,143 Posts Thanks Richard,that should get me started. Regards Stuart.
 May 19, 2012, 03:38 AM I don't like your altitude Joined Sep 2011 3,143 Posts Does anybody in the uk know of a source for 100 mm thick foam.The stuff I usually use is Polyfoam xps 500/1200/50 from Wickes.This has a density of 30.I can't seem to find anything online that doesn't have some facing material attached. Regards Stuart
May 20, 2012, 06:48 AM
Joined Sep 2011
3,143 Posts
At a loose end today,can't get any gear till Tuesday(the lhs guys go flying sun/mon-what's the world coming to!)
So I did a drawing to get a sense of the size of this beast.All the measurements taken off the iPad screen;I just stretched the half span to 12cm and went from there.
I slimmed the wheels a touch,and I need to check the u/c angle off a bigger printed copy,otherwise it looks ok.
I should be able to get a max.60 mm edf in the nacelles so power should be adequate.Good wheel bearings and a firm tyre methinks.
Not quite as scary as I thought it might be;just the pylon design to work out.
Regards Stuart