Do weathercocking rockets tend to weathercock MORE if launched INTO the wind?

[BABAR]

I’ve thought it might be a good idea to launch weathercocking rockets into the wind, so the breeze would bring them back, but the one time I tried it (I think it was a WAC Corporal in the 1970s ) it went cruise missile eventually horizontal into the wind and I never saw it again. Since then I’ve avoided launching rockets with weathercocking into the wind. Is this a myth?

 

[OverTheTop]

If you launch into the wind it will almost certainly weathercock upwind even more. That's what the physics says .

I can see what you are trying to achieve, just don't overcook it. It is all part of learning to fly!

If you launch downwind on a windy day the weathercocking will likely make the rocket fly more vertical if you judge it right. There will be, of course, a longer walk downwind as the rocket will translate further downwind in the breeze during ascent

 

[cls]

I believe Stein's Handbook of Model Rocketry has a diagram showing exactly this.

(Sorry, my copy is packed away right now, or I would double check)

 

[Steve Shannon]

I’ve thought it might be a good idea to launch weathercocking rockets into the wind, so the breeze would bring them back, but the one time I tried it (I think it was a WAC Corporal in the 1970s ) it went cruise missile eventually horizontal into the wind and I never saw it again. Since then I’ve avoided launching rockets with weathercocking into the wind. Is this a myth?

Not a myth. Your observations are exactly correct. And nearly every new flyer tries to launch into the wind, thinking their rocket will be blown back under chute. We’re constantly having to tell new flyers not to tilt into the wind. I’ve seen certification flights fail because the flyer tilted into the wind, their rocket became a cruise missile, and when the chute ejected it stripped or zippered.
Launching into the wind is the most common serious noob mistake I can think of.

 

[mh9162013]

I launch into the wind all the time, but it's not to get a more vertical launch. Instead, it's to make it more likely the rocket lands where it's supposed to.

 

[lakeroadster]

So, thinking this through, wouldn't it make sense to tilt the rocket slightly with the wind?

 

[Steve Shannon]

So, thinking this through, wouldn't it make sense to tilt the rocket slightly with the wind?

View attachment 529911

Yes, and with high power rockets that have large stability factors or that have low thrust to weight ratios we often do that. The result is a more nearly vertical flight.

 

[BigMacDaddy]

We should also moderate this with "nose heavy rockets" which tends to exacerbate the windcocking problem. I have found that nose heavy rockets tend to arc more badly once they start doing so (and angled launches as well as windcocking can be a couple of reasons to start arcing)...

 

[astronwolf]

We should also moderate this with "nose heavy rockets" which tends to exacerbate the windcocking problem. I have found that nose heavy rockets tend to arc more badly once they start doing so (and angled launches as well as windcocking can be a couple of reasons to start arcing)...

And add to that rockets that leave the launcher moving slower than average. Examples are just about any "big" Estes rocket powered by the D12. They weathercock like crazy. Short stubby ones like the Big Daddy are notorious.

At the range I help manage, angling launch rods toward the parking lot and nearby houses is prohibited. I occasionally get flack for being such "an appendage" for enforcing this rule. Many can't imagine that they could ever possibly be "that guy" who causes a club to loose its field.

 

[rocketguy101]

Living in Oklahoma, wind is a constant factor with our launches. Once during a club launch, a newbie launched an egg lofter with an egg on board and angled the rod upwind to reduce the walk without saying anything to anybody. The rocket went horizontal about 50 feet off the ground and hit the ground before the ejection charge fired. It started a grass fire which we were able to put out quickly thankfully. I put his model in Open Rocket and simmed the conditions and they matched the results we saw. We had a safety stand-down and started checking the rod angles for everybody before proceeding with the launch.

The kid (and his dad) was puzzled why his rocket flew horizontal, so I put together this presentation for a club meeting to explain what happened and showed everybody how to use OR or Rocksim to see the affect of launch angle on the flight profile. I didn't use the young man's example, but did have an over-stable model of my own that I actually tried 3 different launch rod angles at a launch to demonstrate how the sim can reflect real life.

I know this isn't really "advanced" but remember I was presenting to a group of Jr High/Sr High club members!

 

[shockie]

I’ve thought it might be a good idea to launch weathercocking rockets into the wind, so the breeze would bring them back, but the one time I tried it (I think it was a WAC Corporal in the 1970s ) it went cruise missile eventually horizontal into the wind and I never saw it again. Since then I’ve avoided launching rockets with weathercocking into the wind. Is this a myth?

This is exactly what it will do. The one thing to remember is to use the shortest delay as. possible, as the rocket will be at a low altitude. 3 seconds max. A longer delay might result in it coming in ballistic.

So engine selection is paramount. A higher thrust motor will not weahercock as much as a lower thrust one. A shorter thrust duration will not weathercock as much as a longer duration thrust.

So you would want a higher thrust/lower thrust duration motor

Also as you probably know the cp cg relationship > 1 caliber will result in even more weathercocking.. see TAMR or Gordon Mandells dynamic stability articles in the old Model Rocketry magazine at Ninfingers website.

 

[mh9162013]

What kind of launch angles are we talking about?

If launching at 5-15 degrees off vertical leads to a cruise missile, wouldn't launching fully vertical result in similar results?

 

[smstachwick]

Stine depicted exactly this in his Handbook and implies that it’s most convenient for recovery. What he neglected to show in the diagram was the hazards presented by failed ejection.

I do believe he exaggerated the angles for clarity, too.



If you don’t want your rocket going “bye-bye!”, down-power it or adjust your recovery system. Adjust your launch angle only as a last resort, or just don’t fly it in high wind. Whatever you do, don’t let go-fever undermine safety.

The Safety Code permits launching with the GSE pointed up to 30 degrees from vertical, but realistically speaking, most LPR fields aren’t large enough to allow this on typical motors with an adequate degree of safety, so RSOs would usually be right to prohibit this. At DART we always fly straight up and only adjust the GSE if the wind starts blowing rockets towards spectators while under chute. Poor conditions may occasionally force us to reduce the ceiling to 500 ft but thankfully I didn’t see that happen last season.

 

[OverTheTop]

If launching at 5-15 degrees off vertical leads to a cruise missile, wouldn't launching fully vertical result in similar results?

It will still weathercock, but not to the same degree.

The weathercocking is really a trigger for a gravity turn. So you get increases based on at least those two factors compounding. Non-linear so not entirely intuitive. Weathercock more and get a faster and more significant gravity turn.

 

[4regt4]

I've made the mistake of tilting into the wind too much, resulting in the dreaded cruise missile. Now if I tilt at all, it's 2deg max. OpenRocket shows a significantly different flight for many/most rockets with just that tiny angle. I use a plumb bob from the rod tip that has a length such that 1/2" deviation from vertical at the end of the line equals 1deg. I seldom tilt, and the plumb bob helps to see if the rod is indeed vertical, or how much it's tilted.

Hans.