Launch angle and Weathercocking

[4regt4]

Assuming there is a low to moderate wind, is it better to launch into or with the wind - or just straight up? My biggest concern is to try to minimize the distance it's likely to drift after chute deployment. I often launch on a small field.

I see three scenarios, and I don't have a clue which is best:

1. Launch just a bit off vertical into the wind. Rocket goes "that-a-way", but when parachute opens, it comes back. The problem that I see here is that if the rocket is way overstable, it could weathercock into a near horizontal flight.

2. To prevent the rocket going horizontal, launch just a bit off vertical *with* the wind. It then weathercocks, but not as badly as #1. above. However, it might float quite a ways away after the chute opens.

3. Just go vertical, hope for the best. Maybe it will head a bit into the wind, and then come back.

Many of my rockets are somewhat tall, making them overstable. I've been tilting the rod a bit into the wind, with mixed results. Sometimes I think I over do it.

Or I could just fly shorter rockets.....

Thanks,
Hans.

 

[Steve Shannon]

Never tilt into the wind. That’s a mistake that people usually only make once. I’ve seen too many cruise missiles result from it.
Vertical is usually best, or slightly with the wind. Also, never tilted towards the flight line. A rocket should never fly over the heads of participants during the ascent. Rearrange the range if necessary to fly with a crosswind.

 

[shockie]

In small fields with medium to high winds, it's probably better to use a streamer. Or a smaller chute of a chute with a spill hole or reefed shroud lines.

Lower impulse engines will skip help. Use a 1/2a or A instead if a b or c.

I've used #1 in strong winds but you need to use -2 or -3 delays instead of 4,5,6,7.
This works with small or medium l/d rockets.
Location of your launch site on your field I'd also important.
These will all result in less drift.

Everything above is vases upon my experience with ABC model rockets.

 

[4regt4]

In small fields with medium to high winds, it's probably better to use a streamer. Or a smaller chute of a chute with a spill hole or reefed shroud lines.

Lower impulse engines will skip help. Use a 1/2a or A instead if a b or c.

Well, I *am* using smaller motors, mostly A or B. But the point is I'd like to step it up a notch, providing I can predict or influence the landing area to some extent.

Hans.

 

[bobbyg23]

Mostly straight up. If you are over stable, it will weathercock into the wind for you. I've seen lots of flights into the wind and they usually find the ground before the ejection charge has a chance to go off.

 

[shockie]

Well, I *am* using smaller motors, mostly A or B. But the point is I'd like to step it up a notch, providing I can predict or influence the landing area to some extent.

Hans.

Hans, , you can influence greatly where your model will land. Weather you launch straight up, with the wind or into the wind, they will all land downwind of the launch site ad that's the way the wind us blowing.

Now the difference is, in the above 3 cases, the vertical trajectories will all be different.

With the wind it will go more straight up and therefore will drift longer depending on the recovery device.

Straight up will result in some weathercocking into the wind and recovery ejection will occur slightly up wind and at a lower altitude so it won't drift as far,depending on the recovery device.

Finally if you tilt into the wind, the model will take a more vertical trajectory into the wind up steam of the launch pad.

This will result in the model recovery system being ejected at a much lower altitude upwind and it will drift right over the launch sidedownwind. But not as much as the first two scenarios.

The rockets cg-cp relationship will all effect rhe above: 1 caliber wrathercocking will be less than say 5 calibers stability.

Motor selection and delay times also will effect recovery landing points.

In windy conditions use higher thrust short delay motors abd use streamers rather than parachutes or parachutes with spillholes.

 

[lakeroadster]

Assuming there is a low to moderate wind, is it better to launch into or with the wind - or just straight up? My biggest concern is to try to minimize the distance it's likely to drift after chute deployment. I often launch on a small field.

I see three scenarios, and I don't have a clue which is best:

1. Launch just a bit off vertical into the wind. Rocket goes "that-a-way", but when parachute opens, it comes back. The problem that I see here is that if the rocket is way overstable, it could weathercock into a near horizontal flight.

2. To prevent the rocket going horizontal, launch just a bit off vertical *with* the wind. It then weathercocks, but not as badly as #1. above. However, it might float quite a ways away after the chute opens.

3. Just go vertical, hope for the best. Maybe it will head a bit into the wind, and then come back.

Many of my rockets are somewhat tall, making them overstable. I've been tilting the rod a bit into the wind, with mixed results. Sometimes I think I over do it.

Or I could just fly shorter rockets.....

Thanks,
Hans.

Tilt the launch rod with the wind for weathercocking, into the wind for parachute hang time.

It's a balancing act.

You can use Open Rocket to help determine what angle the launch rod should be by editing the simulation and inputting the actual wind speed and then tilting the launch rod to get the rocket to land close to the launch pad. You'll need to use the "Export" function and review the data in Excel.

This helps to take the parachute out of the equation, so you are just looking at weathercocking.



Here's a summary of simulations for my AHPLA.

 

[cls]

Tilt the launch rod with the wind for weathercocking, into the wind for parachute hang time.

I know what you mean, but the words are backwards.

With the wind conventionally means in the direction the wind is blowing. In to the wind means the direction it's coming from.

I had a heck of a time trying to explain this to regular folks, learning to sail. It's all in relation of in to the wind, no go for sail boats.

 

[lakeroadster]

I know what you mean, but the words are backwards.

With the wind conventionally means in the direction the wind is blowing. In to the wind means the direction it's coming from.

I had a heck of a time trying to explain this to regular folks, learning to sail. It's all in relation of in to the wind, no go for sail boats.

With all due respect... I am pretty sure you don't know what I mean. ​

Tilt the launch rod with the wind for weathercocking, into the wind for parachute hang time.

It's a balancing act.

When a rocket weathercocks, it tilts and flies into the wind. So, to counteract that, you tilt the rod with the wind.​

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When a rocket descends with a parachute, it floats with the wind. So, to counteract that, you tilt the rod into the wind.

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[cls]

Yes, that's what I said, thanks

 

[Steve Shannon]

With all due respect... I am pretty sure you don't know what I mean. ​

When a rocket weathercocks, it tilts and flies into the wind. So, to counteract that, you tilt the rod with the wind.​

View attachment 531199​

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When a rocket descends with a parachute, it floats with the wind. So, to counteract that, you tilt the rod into the wind.

View attachment 531198​

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Understand that a rocket launched into the wind has a very good chance of becoming a cruise missile or at least opening its parachute at a higher than optimal speed. We try to discourage it at organized launches, especially for high power rockets.

 

[Sandy H.]

Understand that a rocket launched into the wind has a very good chance of becoming a cruise missile or at least opening its parachute at a higher than optimal speed. We try to discourage it at organized launches, especially for high power rockets.

I'll consider this an "I learned something today" moment. I'd say over the past 30 years I turned most 'normal' shaped rockets into the wind and have had mostly normal recoveries. Extremely overstable rockets got the vertical treatment and short/fat rockets also would launch vertical as they sometimes seem testy in general.

At the end of the day, I rarely launch in anything other than mild wind, so it may have been a non-issue in most circumstances, but I had always assumed it was common practice to launch into the wind to minimize the walk. I'll pay more attention in the future.

Sandy.

 

[lakeroadster]

Understand that a rocket launched into the wind has a very good chance of becoming a cruise missile or at least opening its parachute at a higher than optimal speed. We try to discourage it at organized launches, especially for high power rockets.

Thanks Steve.

I fly LP and MP, and when I say tilt, I'm talking like 6 degrees. Not much at all. Open Rocket helps to determine the angles, and it pretty much always less than 10 degrees.

 

[ksaves2]

Understand that a rocket launched into the wind has a very good chance of becoming a cruise missile or at least opening its parachute at a higher than optimal speed. We try to discourage it at organized launches, especially for high power rockets.

Yup,

That's the whole idea of having a large launch site so one can point a rocket a few degrees downwind to get a slight curve in the path to a good apogee. I've hardly pointed a rocket upwind except with modrocs trying to avoid ground obstructions. Play with a simulator and it only takes a few degrees downwind to achieve a nice apogee. Do multiple runs. Eyeballing the angle is fine and most of the time it's ever so slight. It varies from rocket to rocket for a multiplicity of reasons but the more you fly the rocket the better one will get at setting the angle. I don't believe it's hard for beginners to master once the concept is grasped.

The big plus is one gets a good apogee and a low energy deployment. Low energy due to fact the rocket has spent its upward momentum and is just starting to come down when the electronics or motor delay blows the charges. It's not at a high speed sideways parabolic arc at deployment that leads to zippers in cardboard rockets. Kurt