[NSRCA-discussion] Wing Sweep Angle?

Mon Dec 9 06:12:38 AKST 2013

If you look at my Dad's Phoenix designs, you will see that as the series went on, he went to less and less sweep.  The Phoenix 3, of which only one was built, had the most, even more than the Phoenix 1, and he quickly abandoned that sweep. The last in the series, the 9 and 10, had only leading edge sweep with a straight trailing edge.  The theory at the time was that sweep added dihedral effect in looping maneuvers and made it more stable.  RVP can answer whether there is anything to this argument or not.

I've never heard him talk about the coupling phenomena during loops that Dave mentions, and I haven't noticed it when flying my Phoenix 6 or 7.  Of course those older designs with the short tail moments by today's standards are harder (IMHO) to fly well in general, and I only dig them out for one BPA event a year, so I really haven't looked for it.  I do know that my Dad specifically designed in pro-roll coupling in the Phoenix 1 in case the aileron servo went out so he had a chance of landing it on rudder!  He mentioned that fact in the article for RCM.  Of course, the Phoenix 1 was designed when reeds were king, before digital proportional, and equipment was less than robust.  It was a radical design for its day, but it wasn't the first with swept wings. The series was arguably one of the most successful in pattern during the 60's and 70's, so something was right with the design.

Jon

-----Original Message-----
From: Dave Lockhart <DaveL322 at comcast.net>
To: 'General pattern discussion' <nsrca-discussion at lists.nsrca.org>
Sent: Mon, Dec 9, 2013 8:04 am
Subject: Re: [NSRCA-discussion] Wing Sweep Angle?

Jon Lowe might jump in at some point……but I recall a discussion years ago related to Don Lowe’s Phoenix series.  I don’t recall the exact numbers, but at a certain amount of sweep, there was minimal (if any) benefit for pattern flying, and even if the correct rudder response (no coupling) was maintained, there was an increased propensity for pro-roll when the wing was loaded (ie, looping) with increased wing sweep.  I know my Dad’s Phoenix 6 definitely exhibited that tendency – no roll coupling in Knife Edge, but minor pro-roll coupling during loops.

Regards,

Dave

From: nsrca-discussion-bounces at lists.nsrca.org [mailto:nsrca-discussion-bounces at lists.nsrca.org] On Behalf Of rcmaster199 at aol.com
Sent: Sunday, December 08, 2013 11:52 PM
To: nsrca-discussion at lists.nsrca.org
Subject: Re: [NSRCA-discussion] Wing Sweep Angle?

Jim,

The root and tip chords do not have ACs per se, but you know that already. The AC of a wing panel is located at 25% MAC and everything I've read on the subject seems in agreement, at least for full scale, so I use that value for my models. I think that's what Smith is alluding to

The actual angle I think is relative to the fuse CL...So if the wing is rectangular, sweep is considered zero by convention (I think) (Ron correct me if there is no convention on this). If sweep is aft, the angle should be straight forward to measure or calculate. If sweep is fore, same thing except the sign is reversed.

For the model wings I use (much higher root to tip ratios than every one else uses), sweep at 25% chord is about 20 degrees to the rear. I haven't found it excessive or insufficient. It doesn't affect the parameters I use for wing vertical location on the fuse (given a specific dihedral angle). This has been tested on 6 original designs so far over the years with somewhat variable sweep angle (a few degrees, maybe as much as 5 degrees delta). The dihedral effect delta has been nil. 

regads

Matt

-----Original Message-----
From: J N Hiller <jnhiller at earthlink.net>
To: General pattern discussion <nsrca-discussion at lists.nsrca.org>
Sent: Sun, Dec 8, 2013 8:04 pm
Subject: Re: [NSRCA-discussion] Wing Sweep Angle?

Thank you that's exactly what I wanted to know. I've changed it on different
airplanes and wanted to use a 'correct' standard reference when listing
design parameters. I'm finding some sweep is good more isn't, in my opinion.
Jim

-----Original Message-----
From: nsrca-discussion-bounces at lists.nsrca.org
[mailto:nsrca-discussion-bounces at lists.nsrca.org]On Behalf Of Ryan Smith
Sent: Sunday, December 08, 2013 2:21 PM
To: 'General pattern discussion'
Subject: Re: [NSRCA-discussion] Wing Sweep Angle?

Hi Jim,

I was always taught to use the aerodynamic center of the root and tip, and
project a line down the span of the wing across these two points. It's
pretty close to 25% generally; it may be a few percent off, but for the
purposes of calculation, it's really close. There are enough variables in
the scheme of things to render that exact enough for our purposes.

I hope this helps.

Best regards,

Ryan

-----Original Message-----
From: nsrca-discussion-bounces at lists.nsrca.org
[mailto:nsrca-discussion-bounces at lists.nsrca.org] On Behalf Of J N Hiller
Sent: Sunday, December 08, 2013 4:17 PM
To: NSRCA Mailing List
Subject: [NSRCA-discussion] Wing Sweep Angle?

Question!
How dose one measure wing sweep angle on tapered wing panels? Is it located
as a percentage of cord?
Jim Hiller

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