Logo
Builders' Plan Gallery  |  Hip Pocket Web Site  |  Contact Forum Admin  |  Contact Global Moderator
October 14, 2019, 04:04:36 AM *
Welcome, Guest. Please login or register.
Did you miss your activation email?

Login with email, password and session length
 
Home Help Search Login Register
Pages: [1]   Go Down
Print
Author Topic: How does a sub-fin effect the pattern?  (Read 557 times)
0 Members and 1 Guest are viewing this topic.
wmazz
Bronze Member
***

Kudos: 0
Offline Offline

United States United States

Posts: 41

Topic starter


Ignore
« on: April 12, 2018, 06:11:00 PM »

I noticed older models like the Astro-Star and other similar older models use a sub fin, and many
newer designs do not?

Why, and what are the advantages or disadvantages?

Thanks


Bill M.
Logged

Horse Power == Speed, RPM != Speed
flydean1
Gold Member
*****

Kudos: 18
Offline Offline

United States United States

Posts: 966



Ignore
« Reply #1 on: April 12, 2018, 10:45:14 PM »

Again, you are posing good questions.

Many of the older designs had sub rudders.  One reason is to avoid the difficulty that comes with pacing the fin on the stab and becoming hyper sensitive to the stab keying.  T-Bird, Starduster, Space Rod, many others.

The fin position has a slight effect on the power phase imparting a roll effect.  I could have this backwards, but I think a top fin rolls to left and bottom to right.  That also helped the hi-thrust designs which must roll to right while turning left and the pylon designs which must roll left while turning right.  To do otherwise is to convert all your hard work into toothpicks.  Don't ask me how I found this out. Sad

The very latest designs solve all this with the rear fin behind the stab.  The Pearls and Mavericks are good examples.  Some even have a slight sub-fin as well.  These are all pylon designs.  Don't recall a rear fin hi-thrust but there may be some out there.

Again, I may have the roll effect in reverse.  Me, I just find out what the successful folks are doing, and do likewise.

Hopefully, Hepcat and others will chime in with a more complete (compleat?) explanation.
Logged
wmazz
Bronze Member
***

Kudos: 0
Offline Offline

United States United States

Posts: 41

Topic starter


Ignore
« Reply #2 on: April 13, 2018, 03:30:57 PM »

I posted 3 pictures of models with a large sub fin, a medium sub fin, and
no sub fin.

I am curious if the sub fin on the AstroStar has an effect on the pattern,
or is it there to act as a bumper, on a DT landing?

Based on your description the sub fin is used to counteract the effect of
rudder (fin) during the power pattern.

It seems like my best option is to not include a sub fin, unless flight testing
suggests that it may be helpful.


Bill M.
Attached files Thumbnail(s):
Re: How does a sub-fin effect the pattern?
Re: How does a sub-fin effect the pattern?
Re: How does a sub-fin effect the pattern?
Logged

Horse Power == Speed, RPM != Speed
Pages: [1]   Go Up
Print
Jump to:  

Powered by MySQL Powered by PHP Powered by SMF 1.1.21 | SMF © 2015, Simple Machines Valid XHTML 1.0! Valid CSS!