The day a C6-5 almost got me killed

[Donaldsrockets]

Don't the two phrases, "angling [the launch rod] against the wind" and "angling...into the wind" mean the same thing?

I think it sounds like he angled the launch rod in the direction that the wind was blowing rather than angling the rod in the direction opposite the direction of the wind.

For example, if the wind is blowing to the west, you would want to angle the rod to the east. If you angle the rod to the west, going into the wind, you're asking for problems.

 

[MarkII]

I think it sounds like he angled the launch rod in the direction that the wind was blowing rather than angling the rod in the direction opposite the direction of the wind.

Right; angling the rod so that it points in the same direction that the wind is blowing means that you are angling it with the wind.

For example, if the wind is blowing to the west, you would want to angle the rod to the east. If you angle the rod to the west, going into the wind, you're asking for problems.

If the wind is blowing to the west, and you angle the rod to so that it is leaning eastward, you are angling it into the wind. If you angle the rod to lean westward, you are angling it with the wind.

It's totally counterintuitive, but none of us should be angling into the wind, and we should be training others not to as well. I'd also like to see the NAR start to include more information on this in the handbook and occasional safety warnings.

OK, so now I'm TOTALLY consufed....

If you have a brisk wind that is blowing across your launch field from east to west, and you set up your SR-71 on the pad and angle the launch rod into the wind (so that it leans eastward), when the SR-71 launches it will weathercock severely into the wind (nose cone pointing east) and will expend a lot of its energy fighting to go upwind, before dropping to the ground prior to recovery system deployment. I'm with Chan that far.

If you set the SR-71 on the pad and angle the launch rod with the wind (so that it leans westward), when the SR-71 launches it will still weathercock severely (nose cone pointing west this time) and travel with the wind, expending it's thrust to go far downwind and probably well outside of your launch field. The recovery system will deploy while the rocket is in the air, but you'll be lucky if you see it, because the SR-71 will be far, far away at that point. So, other than the fact that the recovery system deploys while the rocket is still aloft, I don't see how this alternative makes the situation any better. The SR-71 goes into cruise missile mode either way.

You might as well point the launch rod straight up in that case. Or else wait for a calmer day.

MarkII

 

[Peartree]

If you set the SR-71 on the pad and angle the launch rod with the wind (so that it leans westward), when the SR-71 launches it will still weathercock severely (nose cone pointing west this time) and travel with the wind...

MarkII

As I understand it... No.

Rockets that weathercock fight to pull *against* the direction of the wind. Weathercocking also (generally) only happens until the rocket gains sufficient speed to overcome the tendency to weathercock, at higher speeds, they tend not to do it so much.

Therefore, angling the launch rod WITH the wind causes the rocket to weathercock INTO the wind and therefore instead of going cruise missile it changes to a direction that is more or less straight up.

Chan is better at this than me, but that is how I understood it when he explained it before. Does that make sense?

 

[Gillard]

i'm with Chan and Peartree on this one, except, if you know that the rocket is prone to weathercocking, don't fly it in windy conditions. two wrongs (weathercock and with wind rod angle) do not make a right.

 

[1974_Trident]

Hmmmm. I must keep this in mind. The SR-71 is among my favorite planes but I would never have gotten a model rocket of one. To me vertical flight of a Blackbird just seen too unnatural. Now that I know the models are prone to horizontal flight I just may give it a shot. On a large vacant field of course.

 

[Verna]

I understand what Chan is saying but it also helps to know the rocket you're flying, and if it's very windy, say 10 mph or more, it's not a good day for a rocket with a lot of drag, better to fly 3 FNC and wait for another time. If you want to see a rocket get to 25' and then turn 175' -200' down range launch a stock built Fat Boy straight up on a day with 12-15 mph wind and see what happens. Once on a day when the winds were a steady 15 mph with gusts to 20 mph, I saw 4 flyers launching Fat Boys at the same launch all follow the same flight path. They barely got off the rod and made a 90* turn, head down range and impact within feet of each other. The only problem was that the winds were just too stiff for that rocket, that day. I didn't understand why it took 4 flights before they were banned for that day.

However, we have routinely flown many rockets at a SLIGHT angle INTO the wind in order to keep them on a small field but we know from experience how each one will fly in a given situation. Randy is amazing at doing that, I won't even describe it because he's unbelieveable at times. Perhaps the angle, regardless of the directions was too great. I have seen flyers launch at huge angles, with not much wind at all.

Most of what we fly are clusters, heavy for what they are and with lots of drag. Our personal, no go, for those rockets is 10 MPH even though many will do well in winds up to 14 or 15 mph but why take the risk to property or limb? It's better to fly something else and live to fly another day.

As a side note and not particularly directed at this thread, I think sometimes adult flyers have so little opportunity to fly that when they get to a field they just have to fly regardless of the conditions even though they know better. While it's no fun to drive several hours and then not launch anything, sometimes it's the correct thing to do. That's happened to us a couple of times but we resigned ourselves to enjoy the flights of other flyers and tried to get some good photos of their flights and make some new friends. We didn't regret not flying and we didn't regret going. It's the risk you take when you travel to a launch, close to home or far away.

Verna
www.vernarockets.com

 

[Verna]

Hmmmm. I must keep this in mind. The SR-71 is among my favorite planes but I would never have gotten a model rocket of one. To me vertical flight of a Blackbird just seen too unnatural. Now that I know the models are prone to horizontal flight I just may give it a shot. On a large vacant field of course.

If you do build one and build it stock, wait for a fairly CALM day and fly it on an A8-3. It should do a perfect Hammer Head Stall. On a windless day ours will spit the chute just as the rocket begins to fall straight backwards. On a B6-4 or C6-5 it will of course go higher and arc over before it pops.

NEVER use a C6-7! :gavel:

Verna
www.vernarockets.com

 

[WOOSHPREZ]

I've had a couple of bad field experiances in the past as well. In one I had launched a rocket which didn't deploy it's recovery device on cue and crashed into a parking lot. It missed everyone and everything but still upset a bunch of "muggles" who thought that we rocket people were doing dangerous things. They were only correct in one important point, the park was simply too well used for us to be there at the same time. We had paid a fee to be able to launch on the specific dates we had arranged. Unfortunately the town never reserved the area for us. They just took our money and let things happen. We learned a lesson. Never fly in an area where there are disinterested parties in the same general area who are not paying attention to what the rockets are doing.
Anything can and does happen when flying rockets. If you have people in the area who aren't aware of the risks and safety code implications then it is best to save it for another day or another field.

 

[NjCo]

If you set the SR-71 on the pad and angle the launch rod with the wind (so that it leans westward), when the SR-71 launches it will still weathercock severely (nose cone pointing west this time) and travel with the wind, expending it's thrust to go far downwind and probably well outside of your launch field.

Just keep in mind that the reason weathercocking occurs is that the control surfaces have a much larger surface area and are affected by the wind disproportionally compared to the rest of the rocket. So the wind will grab the fins and push them along with the wind BUT the rest of the rocket is not so affected.

A straight up boost with large fins and wind will end up with the rocket heading into the wind. Angling the rod the other way (away from the direction the wind is blowing) will result in the wind blowing the control surfaces roughly the same amount which will result in a more or less vertical flight. The wind kind of slides the portion of the rocket with the control surfaces but doesn't move the rest of the rocket as much.

Of course this all applies to rockets with fairly large control surfaces. Rockets with relatively small fins will not be affected as much by the wind. The other factor that also comes into play with these rockets is that they tend to not be as heavy and so have a higher velocity leaving the launch rod which in turn decreases the effect of wind.

It all comes down to knowing your rockets and choosing the appropriate ones to launch given the current field conditions.

Another point that I haven't seen mentioned in this thread is the use of a test flight. I always bring along one of my older rockets and use an engine in that one that is similar to the ones I will be flying for the day. This is usually a minimum diameter rocket of some sort. I launch the test rocket first to check the winds aloft at an approximate altitude equal to what I will be flying for most of the day. Based on this test I might not fly certain rockets, might change the engines in some rockets, might alter the recovery device in some rockets, etc. I usually prep everything I want to fly for the day given the weather forecast but then bring what I need with me to alter my plans given the current conditions at the field.

 

[chanstevens]

As I understand it... No.

Rockets that weathercock fight to pull *against* the direction of the wind. Weathercocking also (generally) only happens until the rocket gains sufficient speed to overcome the tendency to weathercock, at higher speeds, they tend not to do it so much.

Therefore, angling the launch rod WITH the wind causes the rocket to weathercock INTO the wind and therefore instead of going cruise missile it changes to a direction that is more or less straight up.

Chan is better at this than me, but that is how I understood it when he explained it before. Does that make sense?

That's basically got it. Point the rod downwind slightly (which if you want to be precise might be a 5 degree angle). When the model clears the rod, it's at the lowest boost velocity and will therefore be most susceptible to getting knocked around by the wind. The wind will have a greater impact on that big fat wing area than that skinny nose area. That will push the wing downwind, pivoting the nose upwind. The will tend to "correct" the path that started off pointing downwind. If angled properly, the net effect will be a fairly vertical flight, because when it gains more speed over the next 100 feet or so, it will be less likely to weathercock.

Now, of course, a rocket that flies straight up and deploys at apogee on a windy day is going to drift a ways. That means a longer walk and possibly a lost model. If it's too windy to fly it straight up and recover, don't fly it. Period.

When you try to outsmart the wind by pointing into it, you amplify the weathercocking so as to almost guarantee a horizontal flight path, which runs the risk of losing the model in the opposite direction, and often winds up not being nearly as short a walk as you'd hoped. If anything, leave the rod vertical, allowing the weathercock to tilt it a bit upwind but not extremely so.

I know how frustrating it can be to arrive at the field anxious to fly a specific model and find the weather is not cooperating, but trying to [fudge] with the flight path is not a very bright risk. You are MUCH more likely to lose or damage the model, shred the recovery, etc. than if you simply fly the field/conditions and stick with straight up flights. Think about it--we try to select the "right" delay that will result in deployment at or near apogee, which is the lowest velocity of the fight and lowest stress on the chute. Is there EVER a point on a horizontal trajectory when it's OK to deploy, low velocity and low stress on the chute? Would the same folks who think it's a good idea to fly horizontal/upwind also agree that it's a good idea to avoid delays entirely and just go with -0's? After all, a -0 is going to reduce altitude, which would result in less drift and walking, right? Isn't that the objective for the fly-into-the-wind crowd?

Even a 5-minute check online of weather conditions before heading to the field can help ease the disappointment.

Read the comprehensive report Ted Cochran and the NAR safety committee have published on launch safety. IIRC two main causes/findings of serious accidents are related to rockets landing in bad areas (near cars or people) and recovery failures (which often leads to landing in bad areas). Angling into the wind to shorten a recovery walk is a really bad, ineffective idea that we don't adequately teach and train our folks enough about.

 

[MarkII]

I'm not sure if that's always true. Control surfaces that turn the rocket so that the surfaces present the smallest cross-section to the wind (i. e., weathercock) can tun either way to achieve that alignment. Granted, by virtue of its stable design and because of thrust, rockets will tend to orient themselves to point into the wind. But with a bit of help, such as having the launch rod angled downwind, I can see how the fins, taking the path of least resistance, orient themselves to present the smallest cross-section by aligning the rocket to head downwind. After all, it's already pointing that way anyway while it sits on the pad if the launch rod is angled in that direction. The wind, which won't have a velocity anywhere close to that of the rocket during most of the boost and coast, would not be enough to cause the rocket to rotate more than 90°, turning it around while it is under thrust so that it pointed into the wind.

The SR-71 has the motor mounted in the tail; the fin surfaces are all essentially ahead of the nozzle exit. I can see how a boost glider that has a forward-mounted motor, in which the nozzle exit is ahead of most of the wing area during boost, will naturally pitch up and into the wind. But unless the SR-71 has canards or elevators that angle upward, I don't see how it would essentially reverse direction under boost so that it went from taking a downwind trajectory off the downwind-pointing launch rod to heading upwind. The weathercocking tendency will cause it to align its vertical axis to be parallel to the wind direction; with the help of the angled launch rod, it could achieve that parallel alignment by pointing the nose downwind. That seems like a distinct possibility to me, at least.

MarkII

 

[kelltym88]

Well, there really is only one way to be sure.

Take an SR-71 out on a windy day (not too windy mind you), and angle the rod away from the wind and launch. Record results. Then angle rod into the wind. Record results. Post findings here.

 

[MarkII]

I have been discussing hypotheticals in response to the advice to angle the launch rod away from the wind (with the wind, downwind, or whatever). I haven't questioned the warning about angling the rod into (up, against) the wind, but just speculating that angling it downwind might not always produce a desirable result, either. I should mention that I have never had either the SR-71 or the Night Wing. My preference, if I did have one of these rockets, would be to do what I said at the end of post #32 - wait for a calm day to fly it. But it might be an interesting thing to test if I ever get one: on a breezy day (not one that is so windy that I wouldn't launch anyway, but just one that, you know, rustled the leaves pretty good) go over to my local field, angle my launch rod 15° to 20° downwind, and then observe the flight path that my model takes when I launch it. If my rocket does sail with the wind, it won't get very far because the woods at the edge of the field will stop it. I won't get an opportunity to try it until next May, though.

MarkII

 

[Micromeister]

I'm having trouble understanding the logic of this, Chan. I'm with you as far as not angling a weathercock-prone rocket into the wind (it just makes the weathercocking worse, while causing the rocket to waste thrust fighting the headwind), but how does angling it away from the wind help the situation? Won't that also cause a rocket like the SR-71 to readily weathercock, too, but this time fly with the wind? I am just having difficulty visualizing other possible outcomes.

MarkII

Mark:
I agree with Chan completely. And like Chan as soon as I read the word angled into the wind I knew what was comming... even worse the fact that the model was angled in the Direction of other people. That's porbly the bigger mistake. Guys NEVER fly in the direction of others under any conditions!
I can't believe the number of people who somehow believe flying a model into the wind is a good idea.

When flying in breezy conditions all free flying models tend to fly INTO the wind regardless of their stability. As a matter of fact the more stable the model the more likely it will weathercock into the wind as they almost always over correct oscillating around the CG during flight. By angling the model Slightly "with" the wind your model has a much better chance of having a "more vertical" flight then if pointed straight up at launch, As models WILL tend to over correct themselves into the wind or in this case tend toward Straight up by the end of flight. Flying With the Wind is one of the ways Compeitition flyer increase their chances of having a Better or Higher flight on those windy days at the field. To be honest this is very BASIC aerodynamics covered well in TR-100 and the Alpha book of basic model rocket flight.
Being one of those who has been flying Clustered SR-71's for decades I would NEVER fly a SR-71 in any configuration into the wind. It's just not wise with any overstable or weathercock prone model period.

 

[dragon_rider10]

Ok, I've been out of pocket for the weekend and I see my thread has generated some lively discussion. Most of it constructive. To suggest that I give up rocketry and take up scrapbooking I find a bit insulting, but I know that it's a bad idea to take a forum post too seriously. I am not trying to absolve myself of responsibility here- the action of the rocket is directly related to at least one bad decision I made that day. I suppose when I questioned the SR-71 viability as a kit it sounded like I was blaming Estes. That response was based on hearing on more than one occasion from folks with more experience than me that the SR-71 had a reputation for erratic flight. I may want to change the name of the story to "The day I almost got myself killed".

To clarify, as best as I can remember, I did point the launch rod slightly (5-6 degrees)against the direction of the wind. This was not in the direction of the soccer game. Doing this has served me well in the past flying other Estes kits for years. The logic here is that the rocket will boost up and at recovery float back with the wind back to the launch site.

Again, I see this as a learning experience (and have adjusted my flight operations because of it). I'm hoping that others won't make the same mistakes.

 

[rocketman]

That was of course, until i saw the thread on clustering one the other day.

That was my thread! *proud*.
On a more serious note:
Someone I know used to fly rockets on an exposed field, next to a main road. Everything was fine, until when one day he chose to fly an estes space shuttle (I don't know which model exactly) on it. Part of one of its wings broke off during flight, and it turned and flew at ~150mph Across a main road:y::y:! Luckily, no-one was hurt but he never flew (or indeed found) that rocket again, and only used the field when it was ~0-5mph wind.

:merry-christmas:all,

Tom

 

[jadebox]

I think everyone's right!

If your goal is to reduce the distance you have to walk to recover the rocket, angling the rod into the wind will usually result in a shorter walk by enhancing the rocket's tendancy to fly into the wind resulting in deployment at a lower altitude further downrange.

If your goal is to not have your SR-71 fly into the ground, then angling the rod with the wind is a good idea because it will usually counteract the tendancy of the rocket to fly too sharply into the wind.

Of course, safety should be the primary concern and the rod angle should be positioned to avoid flying the rockets over or into locations where people are.

-- Roger

 

[dragon_rider10]

I think everyone's right!

If your goal is to reduce the distance you have to walk to recover the rocket, angling the rod into the wind will usually result in a shorter walk by enhancing the rocket's tendancy to fly into the wind resulting in deployment at a lower altitude further downrange.

If your goal is to not have your SR-71 fly into the ground, then angling the rod with the wind is a good idea because it will usually counteract the tendancy of the rocket to fly too sharply into the wind.

Of course, safety should be the primary concern and the rod angle should be positioned to avoid flying the rockets over or into locations where people are.

-- Roger

Perhaps I should glue some legs and fur on it next time. Seems to work pretty well!

Hey, Roger, did you see your free plug?

 

[MarkII]

OK, OK, I surrender....

It's impossible for a rocket to arc over while its motor is thrusting and fly with the wind. Nope, no sir, not ever. Rockets, regardless of design, are fundamentally incapable of doing that. It's a physical impossibility. Even if a rocket is launched in a hurricane, it will still fly into (against) the wind. At least until its fins are torn off. Can't possibly do otherwise. Violates every known law of physics. In the entire history of rocketry, no one has ever seen a rocket turn and fly with the wind. And no one ever will. Because it can't happen. Don't try to tell me otherwise.

There. Can I come back inside now? It's cold out here.

MarkII