My Dart rolls into the ground on launch. Why?  
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All Forums >> RC Airplanes >> Aerodynamics >> My Dart rolls into the ground on launch. Why?
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My Dart rolls into the ground on launch. Why? - 3/27/2006 3:43:07 AM   
CafeenMan



Posts: 3892
Joined: 1/19/2003
From: Spring Hill, FL, USA
Status: offline 		I have no idea what's happening here. I'm throwing the model hard enough that it should have enough speed to fly. It looks a lot like a tip stall followed by a lightening fast roll - always to the left.

There is a very slight warp in the right wing, but even with full right aileron the plane still rolls left. As far as I can tell the model is balanced around the center line. I think it's an aerodynamic thing, not a weight distribution or CG issue.

The model doesn't have a fin, but I don't see how that would effect it like this.

Anybody have any ideas?

* Dart Number One

Thanks,

- Paul

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RE: My Dart rolls into the ground on launch. Why? - 3/27/2006 4:17:34 AM   
BMatthews



Posts: 8668
Joined: 10/4/2002
From: Burnaby, BC, CANADA
Status: offline 		I think you'll find that adding a fin will do the trick. If it was just a pure delta wing then perhaps it could get away with no fin but with that stuff on the nose you effectively added some forward fin area and now you need a proper rear fin to balance it.

Frankly I think it would need a fin regardless. Delta wings are not one of the rare examples of unaided finless flight. Even paper darts have the delta shaped keel that acts like a fin.


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RE: My Dart rolls into the ground on launch. Why? - 3/27/2006 6:11:42 AM   
CafeenMan



Posts: 3892
Joined: 1/19/2003
From: Spring Hill, FL, USA
Status: offline 		Thanks Bruce. I thought deltas were one of the types that can go finless. Shows what I know. Anyway, I'll use precision TLAR for a fin and glue it on with model airplane glue. I can use acetone to take it back off if it needs to be revised (assuming that Earth doesn't remove the fin for me).

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RE: My Dart rolls into the ground on launch. Why? - 3/27/2006 11:19:54 AM   
Strat2003


 

Posts: 602
Joined: 3/9/2003
From: Mt. Pleasant, OH, AFGHANISTAN
Status: offline 		We've had a lot of fun with planes of that type and always had a fin on the bottom, just like the paper versions. We carry them to altitude under the wing of a .60 size tug and release them.......they'll fly inverted, roll, and can even be coaxed into a loop after a long dive!

They also demonstrate the reason competetion sailplanes don't look like that, lol!

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RE: My Dart rolls into the ground on launch. Why? - 3/27/2006 11:26:08 AM   
CafeenMan



Posts: 3892
Joined: 1/19/2003
From: Spring Hill, FL, USA
Status: offline
quote:

ORIGINAL: Strat2003

They also demonstrate the reason competetion sailplanes don't look like that, lol!


Crap... I was hoping to thermal.

Any particular reason for the fin on the bottom? I've already glued one to the top. It should be dry now.

Hopefully I can get this working and learn enough to make something hot for electric or maybe my Webra .32.

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RE: My Dart rolls into the ground on launch. Why? - 3/27/2006 12:20:48 PM   
B.L.E.


 

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Joined: 8/27/2005
From: Austin, TX, USA
Status: offline
quote:

ORIGINAL: CafeenMan


quote:

ORIGINAL: Strat2003

They also demonstrate the reason competetion sailplanes don't look like that, lol!


Crap... I was hoping to thermal.

Any particular reason for the fin on the bottom? I've already glued one to the top. It should be dry now.

Hopefully I can get this working and learn enough to make something hot for electric or maybe my Webra .32.


Nearly anything will thermal in a west Texas dust devil, plastic bags, paper cups, hats, lawn chairs......... Speaking of competition sailplanes, you don't see too many canards or flying wings either. Kind of makes you think of how terrible the conventional airplane is not.

The only reason I can think of for the bottom fin is so that it looks closer to scale.

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RE: My Dart rolls into the ground on launch. Why? - 3/27/2006 3:26:53 PM   
Flypaper 2



Posts: 4192
Joined: 3/29/2002
From: Kingston, ON, CANADA
Status: offline 		Resurrected an old Hustler Delta I built back in the 60s. Couple of Min's. into the flight, one fin came fluttering down. Still flew fine till the other fin decided it had enough and departed. Went into the fastest turning flatspin I've ever seen Although the sink rate was slower than a parachute, In fact it wasn't even hurt in the landing. Glues them back on and still flies like a trooper. So I guess it does need rudder. Also, if not enough fin area, it can get into a mean Dutch Roll.

< Message edited by Flypaper 2 -- 3/27/2006 3:35:36 PM >

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RE: My Dart rolls into the ground on launch. Why? - 3/27/2006 5:53:11 PM   
Tall Paul



Posts: 4561
Joined: 6/23/2002
From: Palmdale, CA, USA
Status: offline 		If the plane has sufficient span and sweep, verticals aren't needed... but watch out for loss of directional control when the speed gets low!
These fly perfectly well as long as they're going fast. but slowed down, they'll fly any old way until they hit the ground.

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RE: My Dart rolls into the ground on launch. Why? - 3/27/2006 6:19:00 PM   
BMatthews



Posts: 8668
Joined: 10/4/2002
From: Burnaby, BC, CANADA
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quote:

ORIGINAL: B.L.E.

......The only reason I can think of for the bottom fin is so that it looks closer to scale.


SCALE ? ? ? ? ? Now THAT'S streching a concept....


Way back when Model Airplane News did a "scale" version with rudder and elevator. The aspect ratio of the dart is so low that the low slung rudder not only yawed the model but also rolled it as well. Hardly pattern precision stuff but it apparently makes the model turn decently enough to move around in fine style.


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RE: My Dart rolls into the ground on launch. Why? - 3/27/2006 11:07:53 PM   
Strat2003


 

Posts: 602
Joined: 3/9/2003
From: Mt. Pleasant, OH, AFGHANISTAN
Status: offline 		Scale? Absolutely! Mine is 29" X 24", which makes it a 2.64 times enlargement of the standard paper dart we all know and love. Check out the Top Gun quality simulated fold lines in the top view pic, lol!

The pics are of one of about three we've tried. Stu Richmond ran a pic of it and another in flight in his column a couple of years ago. It's built up of 1/4" square and covered with whatever was handy at the time. Elevons control it just fine. I rigged a rudder (the mickey mouse linkage visible in one of the views is to de-mix the rudder from the electronically mixed elevons) because it didn't seem to steer well when you pulled the nose up. It helped a little, but not much. The best solution is to keep your speed up since the airplane just seems to settle if you try to slow it down too much.
They all seem to fly a little nose-high, and that's the reason for the fin on the bottom. I think a top mounted one would be blanked out pretty easily.

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RE: My Dart rolls into the ground on launch. Why? - 3/28/2006 1:34:08 AM   
BMatthews



Posts: 8668
Joined: 10/4/2002
From: Burnaby, BC, CANADA
Status: offline 		That's the one that was in MAN. They even had the "fold" lines in the article as well.


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RE: My Dart rolls into the ground on launch. Why? - 3/28/2006 10:34:18 AM   
Strat2003


 

Posts: 602
Joined: 3/9/2003
From: Mt. Pleasant, OH, AFGHANISTAN
Status: offline 		Well, actually it's not the one from MAN, that one had an airfoil shaped wing and an .049 on the back. We were tring for quick and dirty.......and succeeded, lol.

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RE: My Dart rolls into the ground on launch. Why? - 3/28/2006 2:09:26 PM   
CafeenMan



Posts: 3892
Joined: 1/19/2003
From: Spring Hill, FL, USA
Status: offline 		Strat - When I was building plastic models religiously I was hanging out at HyperScale. I asked the question, "If I build a model of a model, is it scale?" I don't remember the answers but it seems to me that if I build a model aircraft and you build a smaller model of it, then yours is a scale model.

Of course, you went in the other direction and scaled up so the paper gliders are the models are yours is the real deal. You've built a full scale airplane.

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RE: My Dart rolls into the ground on launch. Why? - 3/28/2006 11:03:47 PM   
Strat2003


 

Posts: 602
Joined: 3/9/2003
From: Mt. Pleasant, OH, AFGHANISTAN
Status: offline 		So, you're saying I need to notify the FAA?


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RE: My Dart rolls into the ground on launch. Why? - 4/1/2006 11:01:18 PM   
CafeenMan



Posts: 3892
Joined: 1/19/2003
From: Spring Hill, FL, USA
Status: offline 		Thanks to everyone here for their suggestions and feedback. I added a fin to the model and gave it a strong javelin launch today with a friend at the controls. The model flew straight and responded to control input. It flew nearly 300 feet. Flight was less than 10 seconds though so we won't be able to check how it turns by launching this way. I can't throw any harder than I did today.

I'm pretty much set on building another identical model having a Cox Black Widow on the nose. Using a throttled 1/2A engine is more hassle than it's worth and I don't think a throttle will be that useful unless th