eastlondoner

Hi guys.
Hope you can help.

I'm building a few different 'stick' designs for sport flying. I was told by one guy who is an experienced builder (and haven't seen him for a while otherwise I would've asked him this myself),who had built several own-design r/c planes that I should try and keep the tailplane/ stabiliser in line with the thrust line, to help with flight characteristics.

Can anyone verify or explain if this really makes a difference? I've got the incidence/ empennage sorted, the moment, side-thrust etc all OK, this is kinda the last thing I need to get my head around before drawing up some final plans.

There's obviously T-tail designs and other configurations out there that I've seen that don't follow this... so does it really matter if the tailplane/ stabiliser isn't in line with the thrust line?

Steve Steinbring

It somewhat depends upon what type of aircraft your talking about. If its a pattern type aircraft the tail, wing, and thrust incidences can/will make a great deal of difference in how an airplane performs aerobatically. There can be some differences in incidences depending upon the airfoil used and type of aircraft to be flown, ie. trainer, sport flyer, pattern and so forth.

I usually setup my pattern ships with the horizontal stab set at zero to the thrust line, the wing at a half a degree positive and about a degree of down thrust. The aircraft is then be flown and adjustments made if required.

Hope this helps.

AA5BY

On your sticks, having no cowl ring to align with a spinner gives you freedom to adjust down thrust if flight dictates it.

Down thrust is most often to adjust for asymmetrical foils that produce increasing lift at greater engine power settings or as Steve says if there is positive wing incidence. If your wings have symmetrical foils and are zero incidence, then consider setting down thrust at zero and changing if necessary.

eastlondoner

Thanks for your help, guys. As it's just a 'stick' design for sport flying, I was wondering if the stab being in line with the thrust line was critical or not. Like most sticks it'll have a typical semi-symmetrical airfoil, 1-1.5 degrees of positive incidence on the main wing, I'll start the stab at zero degrees. I'm not too concerned with all the other aspects as I'm confident it'll be fine (i.e. 2 degrees of right thrust etc), but the stab's relation to the thrust line was one aspect I wasn't sure about.

If the stab isn't going to be really affected for not being in line with the thrust line on a simple sports plane, then I guess it should still fly/ handle well enough for basic sports flying, if it's not in line with each other?

pimmnz

The important relationship is that between the stabiliser and wing. That and the weight will determine the 'Straight and Level' cruise speed. Your balance point will determine the degree of pitch stability. Down (and side) thrust may be altered to suit your own personal preference to how the model responds to thrust changes. This is a bit simplistic, but for 90% of what we fly, these will hold true.
Evan, WB #12.

AA5BY

Several ways of looking at things exist. One way is that there is a reference line through the plane and stab, wing and engine thrust are referenced to that line. Because the line is purely arbitrary, others will use the stab as the reference and wing and engine thrust are listed relative to it.

In my minds eye, I choose the more pragmatic choice... the part of the model that is fixed and not adjustable becomes the reference point, and I discard the airframe shell lifting forces as minor for sport flying.

On smaller models with very often glued and fixed stabs... the stab is my reference line. On one larger model I have, the plug in wings fit into pockets so adjusting them is not practical and the stab is on a tube so it is easy to shim the pin points. On that model the wing is the reference line.

eastlondoner

Thanks. [8D] OK so from what I'm reading, it seems that, for just sport flying, the stab being or not being on the thrust line isn't an issue that'll impact directly on the model's performance, but rather the other usual factors mentioned.
Cool. Thanks for everyone's help with this; it's appreciated.

speedracerntrixie

My Feedback: (29)

The original Stick design had a symmetrical airfoil. All the airplanes that I have flown that had little to no rudder to elevator control cross coupling had the stab on the thrust line. However, if you build it with the stab on the bottom I don't think it would be an issue. Set the wing to .5 degrees positive and the engine, stab at zero. Start with 3 degrees right thrust.

eastlondoner

Thanks; really useful information, speedracerntrixie. That's very reassuring as that's kinda close to what I was planning to do. [8D]

Top_Gunn

My Feedback: (6)

On my last Ultrasport 40 I lowered the stab about an inch so that it would be on the thrust line, as was the wing. It seemed to reduce roll coupling somewhat and didn't introduce anything bad.

rmh

The location of the stab is highly overrated
the DRAG when the elevvator is operated should remain somewhat the same related to the thrust but there is quite a bit of latitude here
I went through experiments with this over n over when I was building pattern models
I recently tried it again on small indoor aerobatic stuf - same results .
If you are after some magic hands off in all attitudes configurations you will likely find you can get close but never perfect - gravity seems to affect how planes actually respond
strange, that