Logo
Builders' Plan Gallery  |  Hip Pocket Web Site  |  Contact Forum Admin  |  Contact Global Moderator
December 09, 2019, 07:35:48 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: Staying in Trim & Too Much Weight  (Read 504 times)
0 Members and 1 Guest are viewing this topic.
ScienceGuy
Gold Member
*****

Kudos: 12
Offline Offline

United States United States

Posts: 636

Topic starter


Ignore
« on: August 14, 2018, 03:41:30 PM »

Why do some planes fly pretty consistent day after day while others seem to vary? I thought using a covering that changes a great deal with humidity was the major part of it but it seems there is more to it than that. I have to believe the aerodynamics of some planes results in a plane that has greater stability and the plane is a little more tolerant in slight variations in the trim. I know wood changes with weather conditions and I would assume plastic does to a smaller extent. Many years ago when I first started flying radio control glow planes I remember people warning about the plastic pushrods and how they would change with temperature. The speed of the aircraft multiplies the trim issues.



As I build new planes I go to the extra effort to build in screw adjustments for rudder and stabilizer. I find that I am making small adjustments on different days; it is not just get one trim adjustment and leave it forever. Sometimes it seems the trim changes throughout the day.

My goal with my competition free flight models has been just to get consistent flights so I can get as much experience as possible without breaking it. After three years I am starting to think more about the performance. Recently I have been working with ½ A Streak glow model. Throughout the first several flying sessions I worked getting a consistent climb and transition. Some of the short first flights were rather nerve racking, on a couple of occasions the plane did a loop after launch, one time it pulled out just as it hit the ground.

 

With a washin wedge on inside right panel and tiny amount of right rudder some of the time, the power pattern is good and the plane transitions well. The issue now is it comes down too darn fast, at first I thought I was just launching into bad air but that cannot be the case on every flight. My theory now is the plane is just too heavy; it weighs 6 ounces while other people have built the plane to slightly less than 5 ounces. My Basic Yeller Pee Wee 30 model which has slightly less wing area weighs much less than 4 ounces; a big difference.
Logged
flydean1
Gold Member
*****

Kudos: 20
Offline Offline

United States United States

Posts: 984



Ignore
« Reply #1 on: August 14, 2018, 05:52:35 PM »

Your Smarty may have a flow separation issue on  the upper wing surface.  I haven't seen it on many with little or no spars in the front region of the airfoil will do this on occasion.  That is why many added turbulation spars on Stardusters, and similar.  Perfect climb and transition then it would sink sorta semi-dethermalized to the ground.  Starduster-X grew turbulator spars for that reason.  Don DeLoach first suggested it to me. 

The Nos Gas rules allow adding one spar in the forward third of the wing because so many in that era had slick upper surfaces.  Obviously, if the wing is covered, you're out of luck but there is still a solution.  If you covered it with plastic, you have two options. 

One, cover the upper surface from the leading edge to the high point of the airfoil with tissue and dope it down the 25% dope.  The rough surface will help generate energy in the boundary layer and delay flow separation. 

Another, which I have used with some success such that even if I have turbulator spars, I still do this.  Get some Polyurethane spray.  Mask off the forward surface up to the high point from the rest of the wing.  You want a sharp transition from the sprayed surface to the rear portion of the upper airfoil, sorta like what you would get with the tissue.  Spray a fog on the area from about 6 feet out.  You want a dry spray that sticks to the surface.  Wait about 15 minutes and do it again.  Checking with a strong light shining tangentially to the surface you will notice little "bumbs" sort of like the dimples on golf balls.  Keep at it until the surface looks fairly rough.  I will be like very fine sandpaper.  Maybe like 400 grit.

It worked so well on my ancient T-Bird that I do it on virtually every plastic covered plane I build.  The brand I use is Minwax Fast Dry Clear Satin Finish.  In any case, if you do the tissue over top you will need it to fuel proof the nitrate dope.  I think the spray would be the lightest solution.
Logged
royv
Bronze Member
***

Kudos: 1
Offline Offline

United Kingdom United Kingdom

Posts: 34



Ignore
« Reply #2 on: August 15, 2018, 04:35:41 AM »

If it's gliding steeply on every flight are you sure the CG is far enough back?  As the decalage is reduced during power phase trimming it's easy to end up with an under-elevated glide.  My experience is that flow separation only effects slower-flying models than 1/2A's but mine are turbulated by the structure and tissue covering.  Another thing occurs to me; if you are covering a tradition balsa and tissue structure with film the wing may lack the torsional stiffness to resist the aerofoil's pitching moment at high speed which can lead to under-elevation as the model enters glide mode (as well as all sorts of other effects on the climb).  Cured by covering with tissue.  Interesting to hear the outcome.
Logged
ScienceGuy
Gold Member
*****

Kudos: 12
Offline Offline

United States United States

Posts: 636

Topic starter


Ignore
« Reply #3 on: August 15, 2018, 09:06:47 AM »

The Streak does have one spar in front plus main spar but the Smarty that I have framed up has none, might be good to add. My Sniffer has no spars on the top.

Last evening I did test glides off a small hill with Streak, Basic Yeller, and Sniffer. Not much wind but a little, but I did repeated tests. At times the Streak would out glide the Basic Yeller (light Pee Wee 30) but other times Basic Yeller did much better. It was apparent the lighter model glider slower, it also has a long tail moment and smaller stab.

Bill Kuhl
Attached files Thumbnail(s):
Re: Staying in Trim & Too Much Weight
Logged
flydean1
Gold Member
*****

Kudos: 20
Offline Offline

United States United States

Posts: 984



Ignore
« Reply #4 on: August 15, 2018, 10:34:40 AM »

rovv's remarks are worth considering.  Generally in these days on power models we use adjustments in pitch trim for the power pattern, and trim glide by adjustments in the CG. 

Try adding some tail weight a little at a time.  Hand gliding can get you close, but better yet, power up an get some altitude as you say it transitions well.  Go in small increments, adding tail weight until it very gently stalls, then remove a little and make it permanent.

Your screw adjustments to stab and rudder show great forethought. 

I would also  consider roughening up the forward section of the airfoil with the poly spray.  From the photo I couldn't tell if it were plastic or tissue.  Adds little weight.
Logged
ScienceGuy
Gold Member
*****

Kudos: 12
Offline Offline

United States United States

Posts: 636

Topic starter


Ignore
« Reply #5 on: August 15, 2018, 10:42:27 AM »

The covering is Polyspan lite, a little heavier than tissue but it seems to keep structure rigid and does not sag with moisture. Certainly worth trying to move CG back but I think lesson learned too I need to build lighter in the future.

Bill Kuhl
Logged
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!