Help: Rocket always arcs into the wind

[AcroRay]

I've got a very basic question to ask. Apologies if this is something I should know already, but I spend more time on the skills and technique of building a pretty rocket and prepping it for flight than I do with the mechanics of the flight itself...

For very nearly every flight, my Quest Striker AGM will weather**** into the wind, no matter how minimal the breeze. If I'm fortunate enough to get a relative windless moment at launch, the bird will fly straight up very high. But add a little wind, and it will lose expend potential flight path altitude on a shallow arc into the wind.

I fly it on Estes C6's. It has no nose weight, as per the instructions. It seems to balance out OK. For the recovery system I've got the kit's 'chute on a snap-swivel with Quest's kevlar plus two extra body lengths of cotton/elastic cord and a 3x3 Nomex panel (haven't had to use any wadding with it).

What should I do and how should I trouble-shoot to get this bird to fly higher and straighter?

http://www.rocketreviews.com/ray-acroray-millers-striker-agm.html

[FastCargo]

Well, there are several things that will determine how quickly your rocket reacts to the wind.

1) CG to CP relationship. In general, the closer the CP is to the CG, the more resistant the rocket is to a sideways force (ie crosswind). But, the problem is that it also means it takes a long time for it to correct back to course when it encounters a deviation.

This seems counter to what you would think. If CP is close to CG, shouldn't that mean that the rocket is less stable? It does...but that's because the corrective force is small when it encounters a deviation. But it also means the deviation force has a smaller effect because the moment arm is small (assuming the wind hits all the rocket at the same velocity).

BUT, and this is important, this means the rocket is VERY sensitive at slow speeds to weather****ing. However, at faster speeds, you'll find it's more gust resistant than a bird with a large CG to CP relationship.

2) Speed off the rod. The faster the rocket is at the end of the launch rod, the more resistant it will be to changing direction once it leaves the rod (technically, the faster the rocket, the closer the relative wind is to the initial flight path direction).

3) Mass distribution. If the rocket is like a barbell, with most of the weight even across the airframe to concentrated at the tips, you'll find it's more resistant to deviation. Imagine trying to spin a barbell at the CG verses spinning a bar of the same size, weight and CG location...you'll find the barbell is harder to get started, and harder to stop.

If I had to take a guess, based on what i'm seeing (I don't know the details on the Stryker), the fins appear to be very large relative to the airframe...meaning the CP is pretty far from the CG...ie it corrects quickly into the relative wind.

This is what I think anyway. Hopefully folks smarter than me will be able to shed some more light on the subject.

FC

[AcroRay]

Thanks for all that! This is the only bird I've got that has this severe weatherc0cking problem. (Apart from the Quest X30). I really want to see if there's some way I can get it to straighten up and fly right. :chuckle: It's one of my favorites.

Attached are a couple of pictures. It uses the old MPC Nike Smoke PNC and plastic boat-tail. You can see it going into the wind not far off of the launch rod.

it did come out a bit heavier than what was listed on the package specs.

[Davidtmp]

How many launch lugs does this thing have?? I looked at the picture, and I see one long one. It looks to be half way up the rocket. Is this where yours is?
This could be a potential problem. If you need a 36" rod to get the required speed to hold it's course, but you have only 20" with the lug being where it is and the rocket is loaded up on a pin to keep it away from the fire in aft end, then you may not be getting enough speed to counter the wind at the end of the rod.
The fins don't look to be that big, say like a Big Bertha's. Possibly if the launch lugs were even split, one at the lower end of the rocket, and the other around where the one is in the picture, it may help.
This is the only thing that stuck out to me looking at the picture, other than what FC had said. It may not be a problem either, just something to consider.

[AcroRay]

It's got one rather lengthy lug mounted around center length of the BT, on a standoff. The fins are a bit larger than Big Bertha's, I believe. Although I'd have to compare to my unbuilt Bertha to be certain...

It is likely its not getting enough distance on the rod prior to leaving it, though. That sounds very likely.

[scsager]

Ray - does your rocket really weigh 11 oz as Quest advertises? If you are only seeing 400 ft in dead calm air, I suspect you need more than C6 power.

Try an Aerotech D10 or D21. It may be the "fix" you need.

[FastCargo]

Ray - does your rocket really weigh 11 oz as Quest advertises? If you are only seeing 400 ft in dead calm air, I suspect you need more than C6 power.

Try an Aerotech D10 or D21. It may be the "fix" you need.

Yeeesh...11 ounces on a C6? If it weighs at least that much, I'll bet it's slooow coming off the rod. I suspect that's your issue right there...

FC

[LW Bercini]

I know it's CHAD, but a spin tab solves all kinds of arcing and weatherc0cking issues

[Jerry Irvine]

It's got one rather lengthy lug mounted around center length of the BT, on a standoff. That is likely the main cause of the problem. Firstly I suggest lugs be mounted at the rear of the rocket and one at the CG (2 lugs) which optimizes rod usage. The fact you have an effective fin on the side, near the middle and perhaps even forward of the CG is if nothing else a contributing factor.

People mis-interpret wind. Wind may be low near the ground but wind speeds vary with altitude, sometime a lot. It is a boundry layer approximating zero speed on the ground and "high" speed about 100 feet. Whatever high is.

I see the rocket design has a relative high L/D, relatively large and four fins, the secondary fins are relatively small and relatively rearward located for such things.

I wonder if your parachute is dislocating during boost. I also wonder if you are getting rod whip which can look like weather***. Also a single central lug, standoff or not, can result in rod binding and thus promote rod whip more than almost anything.

I would also make the standoff just as short as possible and with the dual lug comment as short as possible because they are fins.

http://www.rocketreviews.com/image-on-the-launch-pad-for-maiden-flight-april-30-2011-tripoli-pittsbughr-600-64620.jpg

http://www.grc.nasa.gov/WWW/k-12/airplane/Images/boundlay.gif

http://www.venturausd.org/projectlearning/solidfuelrockets/files/img_2475_l.jpg

http://www.rocketryforum.com/attachment.php?attachmentid=28083&d=1283205123

Just Jerry

[AcroRay]

Thanks, Jerry, and the rest of you guys for input!

The Tripoli Pittsburgh launch site does tend to have crosswinds at higher altitudes. Usually a bit higher than this bird manages to make, though.

I still have to double-check the weight, but it is rather heavy.

The launch lug has been an issue. I got a rod hang-up that resulted in a bad crash & broken fins on the thing's second flight. Part of it was due to corrosion on the rod. But at other club members' advice, I cut down the launch lug's length. It is still pretty big, though, so I do like Jerry's & David's suggestions of two smaller lugs and smaller standoffs. The challenge with making the standoffs shorter, though, is that the nose cone really sticks out far from the body.

But I do believe I'll put it on the bench this summer and try those suggested modifications!

Next, though, I'll get more accurate weights, CP and CG measurements. C6's are the biggest engines in my inventory. (Budget usually keeps my household at Blast Off Packs for our seasonal engine compliment.) The Aerotech D10 /D21 might be part of the solution, but I think that'll significantly increase my cost-per-launch a bit higher than I like. Humn...

[Jerry Irvine]

Part of it was due to corrosion on the rod.320 grit sandpaper, a tissue and maybe WD-40 and a tissue too.

[Davidtmp]

I would say with a weight of 11 ounces, you'd really need an 18mm reload. Either the D13 or D24 would get it off the rod. If I do my calculations correctly, you don't want much more than 4 ounces to safely get it up straight on a C6. My Patriot flys nice on C6, but it's just under 3oz. My Delta Wedge is just under 2oz, but has a large fin surface area, and I don't usually fly it in the wind because it just rocks the rod. So lots of things to consider.