Prevent tip stall with tappered wings  
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Prevent tip stall with tappered wings - 3/10/2008 8:22:05 PM   
borna


 

Posts: 175
Joined: 2/22/2003
From: Boynton Beach, FL, USA
Status: offline 		Hello all,
What is the best way to tame a tapered wings airplain during landing?
I know most answers are land a little hotter, but beside that, is there any simple modification that you can make to the wing to tame the landing?

Thanks
Borna
       Post #: 1

RE: Prevent tip stall with tappered wings - 3/10/2008 8:32:31 PM   
pmw



Posts: 111
Joined: 5/13/2003
From: Quinlan, TX, USA
Status: offline 		Borna,

A few things that will help. Tip plates work well but are unsightly. Putting airflow "fences" on the wing about 2/3rd the span will help greatly. They are difficult to install because you have to determinie the airfoil shape at the point of installation. They look cool and are very effetive. But , the quickest method is to trim both ailerons up a little. Maybe 1/8 to 1/4 inch. I have a plane with this feature mixed into the flap mode of the transmitter. I leave the ailerons in the normal mode until starting the final turn. Then I move the "flaps" to "up" and the ailerons are slightly in the trailing edge up position for landing. It works very well on my plane, but remember, your stall speed will increase a little. Practice at altitude first.

Paul

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PMW

(in reply to borna)
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RE: Prevent tip stall with tappered wings - 3/10/2008 9:00:20 PM   
borna


 

Posts: 175
Joined: 2/22/2003
From: Boynton Beach, FL, USA
Status: offline 		Hi Paul,
So is that prevent the plane from tip stall?

Thanks
Borna

(in reply to pmw)
       Post #: 3

RE: Prevent tip stall with tappered wings - 3/10/2008 9:14:31 PM   
da Rock



Posts: 6376
Joined: 10/11/2005
From: western, NC, USA
Status: offline 		Tapered wings stall from the tips naturally. It's how it is.

There are two ways to twist them however, that have been used by aerodynamic engineers for a very long time.

Aero twist is something you probably can't apply unless you plan to build a new set of wings. But physical twist has worked since it was first used back around the time stalls were discovered. Simply twist both wingtips up a couple of degrees and get them to remain there. If the wing is openbay and covered in plastic film, it's easy. If the wings are sheeted foam, sorry about that.

Now, most tapered wing airplanes were designed to be aerobatic. If yours is something like a CAP or Edge or such, then they were designed to have effective elevators and tip stalling wings. Twist will only help a little if at all with them. Learning to keep the nose down on landing is very effective in preventing stalling on landing. And that's worth knowing, because no matter how much twist you impose on that kind of airplane, even if you can somhow manage to get the entire wing to stall before the tip does, one side will stall before the other no matter what angle it now stalls at. And the airplane falls off on the side that stalls first, no matter if that side stalled at the tip or at the root or over the entire half span.

So, what is your model?

(in reply to borna)
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RE: Prevent tip stall with tappered wings - 3/10/2008 9:30:53 PM   
Rodney



Posts: 4737
Joined: 12/8/2001
From: FL
Status: offline 		The wing twist (more commonly called washout) mentioned above works fine for landing but has an adverse effect for airobatitics. If all you want to do is tool around level and land easily, then go for the washout.

(in reply to da Rock)
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RE: Prevent tip stall with tappered wings - 3/11/2008 2:30:38 AM   
borna


 

Posts: 175
Joined: 2/22/2003
From: Boynton Beach, FL, USA
Status: offline 		Thanks guys for the info. The model I just made ready which I'm about to fly it this weekend is CMP Chipmunk
http://www.nitroplanes.com/such40.html

Also does anyone have experience with this Model?
Also can you tell me from the way the looks of the wing, how would be the stall characteristic of model?

Thanks
Borna

(in reply to Rodney)
       Post #: 6

RE: Prevent tip stall with tappered wings - 3/11/2008 6:58:24 AM   
saramos



Posts: 2211
Joined: 12/6/2003
From: Northridge, CA, USA
Status: offline 		If the plane consistantly tips to one side, you can add a spoiler strip to the opposite wing. A short piece of trianlge on the leading edge. Temporarily install a piece with tape and play with length and position until both wings stall together. Here's a photo of one on a full size F4U Corsair. You can just make it out, ouboard of the gun ports.

Scott


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RE: Prevent tip stall with tappered wings - 3/11/2008 1:32:38 PM   
da Rock



Posts: 6376
Joined: 10/11/2005
From: western, NC, USA
Status: offline 		Yes, Chipmunks are known to be excellent aerobatic airplanes.

If you plan to do aerobatics with it, forget about the washout and learn to land it. A buddy of mine has one that's over 2 years old now. He learned to keep the nose down on landing years before and has never had a problem with any of his models. Matter of fact, he doesn't even consider his Chupmunk as anything other than comfortable on landings. He does consider a CAP of his to be a terror. And yet, he's never lost it on landing even once. It has dipped a wing more than once, but since he understands airspeed, keeping the nose down, and not flaring until about to touch down, those dipping wings were just that, dipping wings.

Tip stalls are not something that's the result of evil magic. They're the fault of the pilot. They are NOT unavoidable. All you have to do is keep the nose down on landing. And that actually is just the sound byte description for simply keeping the nose from pointing up too much. The airplane just keeps it's nose from pointing up too much. Stalls of any type are from one cause and only one cause. The wing is at TOO GREAT an angle of attack every time it stalls. Period.

Every tip stall you ever saw on landing happened when the pilot let the nose get too high. You not only saw the tip stall happen, but you also got a great lesson in what "nose too high" looks like. Unfortunately, most observers don't notice the AOA at all.

Keep in mind that almost all the IMAC models are very snappable airplanes. Almost every one of them has significantly tapered wings, and there is little inclination of those guys to washout those wings. And they seldom have problems landing those airplanes. Because they know to keep the nose down on landing, until it's time for the wheels to touch.

If all you plan to do is fly around level, put a touch of washout in the wings if you feel more comfortable with it. But even if you don't plan to snap or stunt the sucker, and only bore holes in the sky, keep the nose down on landings and that sucker won't bother you at all.

It's fairly easy to land without problems if you learn to do a couple of things.

1. Don't cut to landing speed until you're about to touch down. It's amazing how many people want the airplane almost stopped in the air before it's even to the end of the runway on the way in.
2. Keep the nose close to level until you're almost to touchdown.

(in reply to saramos)
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RE: Prevent tip stall with tappered wings - 3/11/2008 1:36:55 PM   
da Rock



Posts: 6376
Joined: 10/11/2005
From: western, NC, USA
Status: offline 		Now, what about if that Chipmunk tip stalls in a loop?

Simple, you're holding too much elevator where it flips out of that loop. There are a couple of ways to deal with that.

Adjust the rigging in the airplane to make the elevator less sensitive. Simple to do. Move the elevator pushrod IN on the servo arm, or OUT on the elevator horn.
Quit flying loops on the high rate of your dual rates.
Or learn to lighten up on the TX's elevator stick in loops.

(in reply to da Rock)
       Post #: 9

RE: Prevent tip stall with tappered wings - 3/11/2008 5:26:34 PM   
borna


 

Posts: 175
Joined: 2/22/2003
From: Boynton Beach, FL, USA
Status: offline 		So as many of you said, the wash-out will help the tip stall. Is this means I can mix a little spoileron to help the tip stall during landing?
However my understanding is spoileron will always create more drags so therefore it stall sooner, isn’t true?

If it does stall sonner, is that means it will stall but won’t do a tip stall?

Thanks
Borna

(in reply to da Rock)
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RE: Prevent tip stall with tappered wings - 3/12/2008 1:23:03 AM   
BMatthews



Posts: 8895
Joined: 10/4/2002
From: Burnaby, BC, CANADA
Status: offline 		A stall is a stall. It doesn't matter what causes it.

When the guys are saying to use some spoileron they don't mean stick them up at 70 to 90 degrees. Just reflexing them upwards around 5 degrees will be enough to effectively add a couple of degrees of washout twist to the wing. Note that this is only good if you have conventional ailerons. If you have full span ailerons or strip ailerons then there's no point in reflexing the ailerons since the entire wing will just end up the same. However if you have normal ailerons that are only out on the outer half of the wing then lifting them up slightly adds some " washout twist on demand".

And with only 5 to 7 degrees of deflection you won't be adding an noticable drag at all. It'll be only changing the airfoil shape slightly and altering the overall tip section's angle of attack.


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Bruce-
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(in reply to borna)
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RE: Prevent tip stall with tappered wings - 3/12/2008 2:04:02 AM   
allanflowers



Posts: 872
Joined: 9/26/2004
From: San Diego, CA, USA
Status: offline 		DaRock said: Aero twist is something you probably can't apply unless you plan to build a new set of wings. But physical twist has worked since it was first used back around the time stalls were discovered. Simply twist both wingtips up a couple of degrees and get them to remain there.
-----------
That comment is a little confusing. I assume you really mean twist the REAR of the tip upward - to get washout.

(in reply to BMatthews)
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RE: Prevent tip stall with tappered wings - 3/12/2008 2:18:08 AM   
borna


 

Posts: 175
Joined: 2/22/2003
From: Boynton Beach, FL, USA
Status: offline 		good to know. Since Chipmunk has a full span ailerons, therefore spoileron won't work in my case.


Borna

(in reply to allanflowers)
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RE: Prevent tip stall with tappered wings - 3/12/2008 10:00:07 PM   
da Rock



Posts: 6376
Joined: 10/11/2005
From: western, NC, USA
Status: offline
quote:

ORIGINAL: allanflowers

DaRock said:
quote:

Aero twist is something you probably can't apply unless you plan to build a new set of wings. But physical twist has worked since it was first used back around the time stalls were discovered. Simply twist both wingtips up a couple of degrees and get them to remain there.

-----------
That comment is a little confusing. I assume you really mean twist the REAR of the tip upward - to get washout.


Sorry, I got sloppy on the topic and left out a word. I should have said, "Aero twist is something you probably can't apply unless you plan to build a new set of wings. But physical twist has worked since it was first used back around the time stalls were discovered. Simply twist both wingtips' TEs up a couple of degrees and get them to remain there."

And it can be confusing if you don't know what physical washout is versus aerodynamic washout.

But there is a HUGE bottom line on either. They actually do not fix anything. Best case, they change the AOA of the stall a degree or two. That's it. If you're extremely lucky, that might be enough that you really do get a positive result from the effort, but truth be known, what most flyers get the most benefit from is the effort. Making the effort is enough to get into their heads that the airplane needs to be flown with some special attention given to certain parts of the flight envelope.

BTW, even the term "tip stall" isn't exactly correct.

(in reply to allanflowers)