Go Back  RCU Forums > RC Airplanes > Tips & Techniques
How to Avoid the dreaded Snap Spin??? >

How to Avoid the dreaded Snap Spin???

Notices
Tips & Techniques Want to share a tip or special technique you have either in the workshop or at the flying field or race track? Post it right here!

How to Avoid the dreaded Snap Spin???

Old 09-24-2002, 10:34 PM
  #1  
Junior Member
Thread Starter
 
Join Date: Sep 2002
Location: GA
Posts: 9
Likes: 0
Received 0 Likes on 0 Posts
Default How to Avoid the dreaded Snap Spin???

I have reduced my H9 Cap 232 40's elevator to below the low rate and it still snaps when you pull back hard on the elevator. I can't do a loop without my heart skipping a beat!! I don't have a computer radio so I have just moved the servo and control horns to the lowest throw they can possibly give. Would moving the CG do anything for that?
Old 09-24-2002, 11:13 PM
  #2  
Senior Member
My Feedback: (1)
 
Join Date: Dec 2001
Location: Oxford, MS
Posts: 3,241
Likes: 0
Received 0 Likes on 0 Posts
Default How to Avoid the dreaded Snap Spin???

Yes... If you move the CG forward it will reduce the tendancy for the airplane to snap. You should be able to fly ANY airplane through a loop progressively pulling harder without it snaping out on you.


DR
Old 09-24-2002, 11:37 PM
  #3  
Senior Member
My Feedback: (10)
 
C_Watkins's Avatar
 
Join Date: Jun 2002
Location: Douglasville, GA
Posts: 1,071
Likes: 0
Received 0 Likes on 0 Posts
Default How to Avoid the dreaded Snap Spin???

Well, believe this or not...

The CG should be set correctly. Too far forward can actually increase snap tendencies
in some instances, because you have to use more elevator. Sometimes you can help
alleviate the problem by moving the weight toward the rear of the MFG recommended range.
(Thereby being able to use less elevator, and being less snap prone)
In any case, until you get very comfortable with the airplane, enough to adjust the
CG to suit your wants and needs, you should stay within design specs with it.

The Cap is a snappy airplane. The heavier it gets, the snappier it will be. (As wing load goes up)

Some count this as a "good thing", as snaps are desirable maneuvers to some of us.

Sorry, but I have to disagree with the "ANY" airplane statement.
Perhaps, if you have washout built into the wings, and if the tail surface is large enough,
and if the elevator control isn't too much... but that's a far cry from "any"

As for loops in general... unless we're talking about a funfly type plane... you should feed
in the elevator more slowly, as opposed to "pulling back hard" on the stick. It isn't required.

HARD elevator is what you do, in combo with rudder (& maybe aileron) when you WANT to snap
Old 09-25-2002, 12:16 AM
  #4  
Moderator
My Feedback: (58)
 
rajul's Avatar
 
Join Date: Jun 2002
Location: Missouri City, TX
Posts: 8,250
Likes: 0
Received 3 Likes on 3 Posts
Default How to Avoid the dreaded Snap Spin???

Hi folks, sorry for my basic question but what is snap spin and why is it related to high elevator throw ? Thanks for the info..............
Old 09-25-2002, 12:36 AM
  #5  
My Feedback: (158)
 
scale only 4 me's Avatar
 
Join Date: Jan 2002
Location: Avon Lake, OH
Posts: 10,396
Received 52 Likes on 50 Posts
Default How to Avoid the dreaded Snap Spin???

I have to agree with C_Watkins
Sounds like it might be nose heavy
What your experianing is called a "High speed stall"
yanking on the elevator with those narrow wing tips can make the Cap stall/snap even if your CG is set perfectly

A nose heavy plane will tend to high speed stall where as a tail heavy plane will slow speed stall.

I typically like to set up my Aerobatic planes with an "Aft CG". This makes them more aerobatic and less prone to high speed stalling.
you just have to watch it when coming in for langing or flying very slow

Try setting the CG to the back off the range shown on the plans. once you get comfotable you can move the CG back more if you like

And ease into those loops don't yank the sticks so much, unless you trying to do a snap roll

Good luck
Old 09-25-2002, 01:20 AM
  #6  
Moderator
My Feedback: (58)
 
rajul's Avatar
 
Join Date: Jun 2002
Location: Missouri City, TX
Posts: 8,250
Likes: 0
Received 3 Likes on 3 Posts
Default How to Avoid the dreaded Snap Spin???

This may not be the best forum to ask this, but can someone explain aerodynamically the phenomenon of high-speed stall or snap spin ? Thanks...........
Old 09-25-2002, 02:23 AM
  #7  
Junior Member
Thread Starter
 
Join Date: Sep 2002
Location: GA
Posts: 9
Likes: 0
Received 0 Likes on 0 Posts
Default Reply Spin Stall

Lots of good input but I noticed a discression on were to put the CG. Is is more weight to the front or back for less snaps. I would rather have a high speed snap than a low speed snap b/c I don't want it to happen when I am landing.
Old 09-25-2002, 02:46 AM
  #8  
Senior Member
My Feedback: (10)
 
C_Watkins's Avatar
 
Join Date: Jun 2002
Location: Douglasville, GA
Posts: 1,071
Likes: 0
Received 0 Likes on 0 Posts
Default How to Avoid the dreaded Snap Spin???

Then stay with a CG more in the middle to the front of the
manufacturer's recommended settings.

The Cap is meant to be aerobatic though... just remember that it won't
float in like a trainer, and that you can't haul back on the stick
like you can with a lot of other planes, without snapping or tip-stalling.

Don't go too far forward on the CG, or you'll end up running out of
elevator on landings, and possibly tip stalling the thing anyhow.

It's just a different bird. If you've got the incidences set right,
and the CG in the recommended range, you'll just have to learn
its idiosyncrasies from there, and fly it the way it wants to be flown.
Old 09-25-2002, 01:42 PM
  #9  
Member
 
Join Date: Apr 2002
Location: APO
Posts: 68
Likes: 0
Received 0 Likes on 0 Posts
Default snap roll

Okay...
here we go...I'll do my best...dodging the daggers as I go.

There is an airspeed for which every plane (wing or more specifically..airfoil) will stall. An example.... Your plane falls out of the air and drops in on the runway at say...20mph. This is when the angle between the relative wind and airfoil are excessive for a given weight. I will not discuss the difference between airspeed and groundspeed. This is better for another discussion and very hard to measure from the ground.

Anyway, assuming you do not change your wing configuration...ie. add flaps, swing wings, etc... this stall speed is affected greatly by the plane's actual weight. Put two identical planes side by side....add 1 lb to one and it will stall sooner...or another way put...at a higher speed. Thus, we say the heavier plane has a higher stall speed.

Okay, lets look at the effects of weight on the plane (airfoil). At a 60degree bank turn maintaining level flight (no altitude gain or loss) and without slowing down, the aircraft is pulling 2 Gs. This is fact... This 2Gs is also known as 2 times the weight of gravity. Thus, your 5 lb plane now weighs 10 lbs. Pull 10 gs and your 5 lb plane weights 50 lbs. In this configuration, the stall speed of the aircraft increases dramatically with the new temporary higher weight of your plane.

So...weight on the plane...real or G-induced has an adverse effect on the stall speed of your plane. This G-induced environment is not limited to level turns. It is most prevalent while pulling out of a loop. This is usually a high G pull.

During this high G pull it is possible for the stall speed of your plane to increase so much that it exceeds your current speed and you stall a wing. The wing that stalls first...and they usually don't stall together on high perf planes... drops and the flying wing keeps lifting. Thus, a roll/yaw is induced.

When the wing drops and the plane begins to snap roll, you should immediately reduce elevator. This reduction reduces g-loading and reduces stall speed. The stalled wing may start flying again allowing you to gradually increase elevator to round out the bottom of your maneuver without loading up the aircraft.

So...to prevent this... You want to be able tighten your loops and turns without stalling. You must reduce your overall plane weight (as this is multiplied at higher G loading), reduce your elevator throw, or increase the airfoil size (bigger wing or different camber).

As a sidebar note. An already heavy plane (or one with a small wing area) will high-speed snap more easily with a more nose heavy CG. This is because more elevator is needed to bring the nose up. This increased elevator increases G-loading which increases aircraft weight which increases stall speed and SNAP.

Oh and one more cool thing...as a plane slows into a full stall the order in which you lose flight control effectiveness is Ailerons, elevator, then rudder. This is why rudder is always so effective in slow flight. Also, why when you kick in full rudder during a full up elevator you get a great snap roll. As the plane's airspeed increases the flight controls come back in reverse order...first rudder, elevator, then ailerons.

more than .02 but he asked...got more? Please send to me direct. I don't get here to often since we have so many bad guys in the world these days.

hawk
Old 09-25-2002, 01:58 PM
  #10  
Moderator
My Feedback: (58)
 
rajul's Avatar
 
Join Date: Jun 2002
Location: Missouri City, TX
Posts: 8,250
Likes: 0
Received 3 Likes on 3 Posts
Default superb !!

Hi Hawkco, first of all, thank you very much for your short discourse on high/low speed stalling. The fact that I managed to read and understand it in a single pass (no mental "stalling" ) shows that you wrote it very well. I also appreciate better why rudder control is used at landing, and the importance of building light - which is why I won't be doing much mod to my 4*60 after all ! Again thanks for your time...................
Old 09-25-2002, 08:42 PM
  #11  
Member
 
Join Date: Apr 2002
Location: APO
Posts: 68
Likes: 0
Received 0 Likes on 0 Posts
Default stall

Your welcome!

hawk

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are On


Thread Tools
Search this Thread

Contact Us - Manage Preferences Archive - Advertising - Cookie Policy - Privacy Statement - Terms of Service

Copyright © 2024 MH Sub I, LLC dba Internet Brands. All rights reserved. Use of this site indicates your consent to the Terms of Use.