Aerodynamics Discuss the physics of flight revolving around the aerodynamics and design of aircraft.

My Dart rolls into the ground on launch. Why?

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Old 03-26-2006, 10:43 PM
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CafeenMan
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Default My Dart rolls into the ground on launch. Why?

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?

[link=http://www.airfieldmodels.com/gallery_of_models/rc/dart_number_one/index.htm]* Dart Number One[/link]

Thanks,

- Paul
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Old 03-26-2006, 11:17 PM
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Default RE: My Dart rolls into the ground on launch. Why?

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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Old 03-27-2006, 01:11 AM
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Default RE: My Dart rolls into the ground on launch. Why?

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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Old 03-27-2006, 06:19 AM
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Default RE: My Dart rolls into the ground on launch. Why?

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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Old 03-27-2006, 06:26 AM
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Default RE: My Dart rolls into the ground on launch. Why?


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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Old 03-27-2006, 07:20 AM
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Default RE: My Dart rolls into the ground on launch. Why?


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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Old 03-27-2006, 10:26 AM
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Default RE: My Dart rolls into the ground on launch. Why?

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.
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Old 03-27-2006, 12:53 PM
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Default RE: My Dart rolls into the ground on launch. Why?

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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Old 03-27-2006, 01:18 PM
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Default RE: My Dart rolls into the ground on launch. Why?


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 ? ? ? ? ? [sm=spinnyeyes.gif] 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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Old 03-27-2006, 06:07 PM
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Default RE: My Dart rolls into the ground on launch. Why?

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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Old 03-27-2006, 08:34 PM
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Default RE: My Dart rolls into the ground on launch. Why?

That's the one that was in MAN. They even had the "fold" lines in the article as well.
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Old 03-28-2006, 05:34 AM
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Default RE: My Dart rolls into the ground on launch. Why?

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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Old 03-28-2006, 09:09 AM
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Default RE: My Dart rolls into the ground on launch. Why?

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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Old 03-28-2006, 06:03 PM
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Default RE: My Dart rolls into the ground on launch. Why?

So, you're saying I need to notify the FAA?

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Old 04-01-2006, 06:01 PM
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Default RE: My Dart rolls into the ground on launch. Why?

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 the model is a real handful. I'm crossing my fingers on that one.

I've done a more thorough update on the steps that got me to this point on my website. There's more to come. I'm enjoying this project!
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Old 04-01-2006, 07:15 PM
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Default RE: My Dart rolls into the ground on launch. Why?

You'll probably be disappointed with the model's flight characteristics.
These very low aspect ratio planes tend to depart when trying to turn.
Find a slope nearby, the wind will substitute for your arm to get the thing in the air, and you -might- get some flight time on it.
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Old 04-01-2006, 09:30 PM
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Default RE: My Dart rolls into the ground on launch. Why?

Quote:
ORIGINAL: Tall Paul

Find a slope nearby, the wind will substitute for your arm to get the thing in the air, and you -might- get some flight time on it.
Tall Paul,
CaffeenMan is in FL I have yet to see much of a slope on that sandbar. LOL

How about an Estes motor.

There use to that type of launch down there.
Best of luck with the dart however you power it Caffeen Man.
Regards
Paul
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Old 04-01-2006, 10:06 PM
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Default RE: My Dart rolls into the ground on launch. Why?

There are some pretty tall ant mounds right in my yard.
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Old 04-01-2006, 11:40 PM
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Default RE: My Dart rolls into the ground on launch. Why?

Quote:
ORIGINAL: CafeenMan

There are some pretty tall ant mounds right in my yard.
LOL
Yea, I someone I know that lives down there down there has mentioned that sort of thing.
At least you can go fly in Feb. without the -5 wind chills....


With the Cox Black Widow in it, a min. or so of fuel; you can do the typical sail plane type of flight, right up to the dead stick landing.
Sounds like a plan to me...

Regards,
Paul
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Old 04-01-2006, 11:50 PM
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Default RE: My Dart rolls into the ground on launch. Why?

Iron Eagle - I rent and the yard is *supposed* to be the landlord's responsibility per the lease. My yard is nothing but ants and weeds. The yard guy mows it with a weed-eater - seriously.

I've probably spent $200 on various ant killers in the past 3 years. Every time I use the stuff I get up the next morning and it's all piled up by the front door and the ants are there en masse pointing at me and laughing.

As far as the dart goes, I don't know how I did it exactly but the plan on my site and the plane I built are not the same size. I'm going to redo the plan to match what I built and add the fin. Maybe some other guys will build it and modify it and hopefully we can all learn something.

Tall Paul - I'm sure you're right about the turn ability of this model. I'm not expecting much. As long as I can turn it around I'll be happy. What I'm actually trying to achieve is a fast model without all the work of figuring it out on a more conventional plane (or the $$$ for a racing engine).

If it doesn't work, then lessons learned. I don't mind when my ideas fail unless I don't learn anything in the process. I'm sure you remember Ken Willard. I don't think anyone in this hobby affected me more than he did. He was always trying unconventional stuff that he knew should work and he was right most of the time. I remember his struggles with that 1/4 scale Stits biplane that had something like an 18" wingspan. But then I think he also had a background in aerospace which is something I don't have.
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Old 04-02-2006, 12:37 AM
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Default RE: My Dart rolls into the ground on launch. Why?

You might try a bungee or a hi-start to get some altitude to glide from.
They can always be used later for gliders.
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Old 04-02-2006, 12:42 AM
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Default RE: My Dart rolls into the ground on launch. Why?

Actually, we're going to tie a bunch of rubber bands together, launch off a PVC pipe and see what happens (really).
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