90 degree left turns, going horizontal off the pad

[spacecowboy]

I know how to fix this symptom (it's called NC weight). Several of my rox go off the pad, 20-50 ft up, do a left hand 90 degree turn and finish the flight going horizontal.

FatBoy did it on it's first flight, crashed into a tree 6 ft off the ground. Heatseeker was notorious for this, my second flight of that one, after a maiden flight of horiz, it headed straight for a family in the park, thankfully, it went over them about 50 ft. I had this happen again Sunday with a bird I made out of leftover parts from PLASMA.

If any one can explain this phenomenon, I'm all ears. I think it really has something to do with the launch lug getting snagged up off the pad, because I fly the same bird again, and have way more fun.

 

[Chilly]

It's possible that the rocket's hanging up on the rod, but it's also likely a combination of a) not enough rod, b) not enough thrust, and c) the rocket's out of CG (unstable).

I lost one last week this way, and it was going to be my L1 rocket. I put it up on an Ellis Mtn. G35. It went horizontal about 50-100 feet off the deck and continued under power for maybe a half-mile.

 

[Mike]

Another rocket phoenomenon was somthing I saw at K-Lob last year. A LPR model came off the pad did a complete loop then continued upwards in a straight line! Any explanations how it could of happened?

 

[graylensman]

Dumb luck. It flipped upward as just enough propellant had burned off to slip the CG forward enough to make it stable again.

 

[shockwaveriderz]

are you having launch rod whip? perhaps you need a longer,thicker launch rod? or more nose weight.....or both

 

[GlennW]

The only rocket I have had this problem with is the Estes Space shuttle. (The Masters Series one with the tank and boosters, not that junky cheap one) As I understand, the space shuttle is notorious for this, most flyers including myself think a C engine is not enough power for the thing. I was gonna try an Aerotech single use 18mm D until I found out that no one has 'em and they're not currently making them. Well, I may give it one more try on the C, the one flight I've made so far was on a windy day which may have also contributed to my disastrous flight. Which by the way, I am still repairing the damage from. Oh well, that's the downside to these more complex rockets.

Glenn

 

[swimmer]

SpaceCowboy,

Crashed my favorite Estes Black BrantII in this same manor. Bottom launch lug was a little worn, hung up on rod and when it did come off it made a direct turn left at about 15' in altitude. Needless to say I did salvage the fincan. The remains now sit in a prominent place on my work bench to remind me to pay attention to the small stuff.

 

[Steward]

Ya'll quit tryin' to scare me...!!!

 

[Fore Check]

On the rod whip thing:

I had a couple of rockets whip sharply in the horizontal direction on one launch day. I was using a 60" long 1/8" stainless launch rod. The rod would "bend" or "sag" under its own weight! I switched to the cheap ol' Estes 36" aluminum thingy and the rod whip went away.

I guess what I'm saying is this: Rod whip can be exacerbated by making the rod longer. A shorter rod will have less whip.

If your rod is still whipping at a length of 36-48", you need a heavier rod or a rail.

 

[n3tjm]

I lost a Lil' Nuke on a G104-10T due to rod whip. After that... I bought a rail.

 

[spacecowboy]

Rod whip, if I wasn't flying rox by myself most of the time, I could film and see what's going wrong.

I am using an out of the box Estes pad, and changing out that rod for something a bit more beefy makes good sense.

The bird on the right was the one that gave me problems, I ripped off the fins, and made 'em bigger. That might help. The bird on the left, ooooh, sweet paint job.

 

[ntrance]

This has happened to both PWALPOCO & WOODY's RTF Missile command ARMY. We have a video of then bizzarely launching off the pad, on slow frame advance you can see it whip off the rod and continute to snake every so slightly all the way up until the C6 had stopped boosting, then it goes straight as a die 45 degrees up left.

Another ARMY launch it did a loop the loop around 10 metres in the air, changing horizontal directions while doing so, and landing about 10 ft from the launch pad, then POP ejection charge !

Another ARMY launch nice arc and buried itself into the sand/grass then delay charge poped th BT backwards.
Very comical !!

So even the RTFs are designed unstable.

WOODY used the clay from the Fireflash and it has sorted the ARMY, and it really flies nice on C6-7s

Download SPACECAD from www.spacecad.com and enter your build your rocket with your details. And see if shes stable.

ARMY is <1 BAD ESTES !!!!!


Al.

 

[Fore Check]

Originally posted by ntrance
This has happened to both PWALPOCO & WOODY's RTF Missile command ARMY. We have a video of then bizzarely launching off the pad, on slow frame advance you can see it whip off the rod and continute to snake every so slightly all the way up until the C6 had stopped boosting, then it goes straight as a die 45 degrees up left.

Another ARMY launch it did a loop the loop around 10 metres in the air, changing horizontal directions while doing so, and landing about 10 ft from the launch pad, then POP ejection charge !

Another ARMY launch nice arc and buried itself into the sand/grass then delay charge poped th BT backwards.
Very comical !!

So even the RTFs are designed unstable.

WOODY used the clay from the Fireflash and it has sorted the ARMY, and it really flies nice on C6-7s

Download SPACECAD from www.spacecad.com and enter your build your rocket with your details. And see if shes stable.

ARMY is <1 BAD ESTES !!!!!


Al.

If you check out EMRR under Estes - OOP kits you can find a review of the army and navy rockets, including RockSim files that are reviewable with the demo version. I think our very own Bruce Levinson (teflonrocketry) submitted all the info.

His files show both rockets to be unstable on C engines without nose weight. I have never had a problem with the Navy rocket on a C without the weight (a matter of Russion roullette, I imagine) but the Army was a real problem. The kids sure thought it was thrilling, tho!

**as the Army rocket crazily loops off the pad**

"OOH! DADDY!! LAUNCH IT AGAIN!!!"



Goofballs......

 

[GoBang]

Rod whip--use a welding rod from your friendly neighborhood home supply store (Menards--mentioned first because they support Indy Car racing!--or Home Depot or Lowes will have them. They come in four foot lengths so you'll have to cut it down a bit, and you'll have to give it a rub with WD-40 and steel wool every so often, but it's worth it. You can get 1/8, 3/16, and beyond if you're really ambitious.

On the other hand, depending on the age and source of your motors, it's still possible you suffered from "poopy clay" syndrome and thrust vectoring...

 

[bobkrech]

The Fat Boy and Heatseeker are normally stable rockets and should fly just fine from a standard Estes 1/8" launch rod. If you built your rockets according to the stock plans, they should have the proper cg/cp ratio and be aerodynamically stable if they are leaving the launch rod at the proper velocity.

This unstable behavior typically happens when the rocket leaves the rod with a velocity that is too low for the fins to be effective. This can happen 1.) if the rocket hangs up on the launch rod, 2.) if the launch rod is too short, or 3.) when you are launching on a very windy day, or 4.) the motor is simply too small for the rocket.

In 1.) the rod may be dirty, the launch lug may have some glue or dirrt in it, or the rod could be bent. Any of these conditions can cause the rocket to hang the rod and leave with a lower than normal velocity.

For 2.) most Estes rockets want a 3 ft long launch rod. If you rod is considerably shorter, the velocity leaving the rod may be too low for the fins to be effective.

In 3.), if you use a standard length rod in a strong wind, the fins will stall even if the rocket has its normal velocity due to a high angle of attack caused by the crosswind.

In all of the above cases, the fins have stalled and do not supply a restoring force keep the rocket going straight up.

In 1.) and 2.) the rocket will start to tip over around its cg, but as long as the motor is still firing, the velocity increases and at some point the fins and body provide enough lift. I've seen an Estes V2 take a right hand turn 20 ft above the ground and go into a cruise missile mode for about 200 yards before crashing.

In 3) with a stiff cross-wind, the rocket tips but you get a tumbling aroung the cg as the fins alternately make lift and then stall. This is more probable when the rocket has a 5:1 or less thrust to weight ratio. I have seen a marginally stable rocket spin 4 complete revolutions around its cg at 50 feet above the pad until motor burnout in a 15 mph wind when launched with a standard length rod.

The solutions are simple.

Make sure the rod is clean and straight.

Check to see that the rocket slides freely on the launch rod.

Use a rod at least 3 ft long for the basic Estes rockets. If the wind is above 10 mph, use a 4ft or longer launch rod so the rocket leaves the rod with a higher velocity. Also use motors that provide a 10:1 thrust to weight ratio when the wind is above 10 mph.

Lastly, if you modify your rockets and make them significantly heavier than stock, you may change the cg/cp relationship which reduces stability and you may have to fly it with higher thrust engines to get a stable flight. A 5:1 thrust to weight ratio is the minimum for a standard length rod in winds below 10 mph.

Bob Krech

 

[spacecowboy]

My FatBoy, after going horiz into a tree, I turned around with a loss of ego, and flew it perfectly (it has since flown off the same pad - that I've used with the same rod since - with maximum coolness). Heatseeker never flew correctly. Cruise missile mode is uncool in a crowd, and it never really did anything but cruise or spin uncontrollably. Both rox, stock builds.

Apparently, Mr. Krech went to the same "flight school" I did.
My Executioner did nothing but cartwheels in a very heavy wind. Then I put an E30 in it, beaut flight except for reco failure.

My personal belief is that a temporary "puff" of wind, at an inopportune time, like engine ignition, starts rod whip right about the time the roc starts moving, and the moving roc exacerbates the whip condition.

I'm really wondering (and I'm sure this subject has been broached before), has anyone built a custom pad that DOES NOT whip ????

 

[bobkrech]

Spacecowboy

Rod whip does not cause a rocket to do acrobatics. It will cause a rocket to ascend straight but non-vertically, and only to the extent that tilting the launch rod would. Usually the only bad result from rod whip is that you have a longer walk to recover your rocket. (It's easy to avoid rod whip by using a larger diameter rod or use a rail.)

When a properly balanced (cg ahead of cp) rocket goes wild, the cause is due to aerodynamic forces usually having nothing to do with rod whip.

To restate what I have said previously, rockets gone wild have insufficient velocity for the fins to maintain aerodynamic control after leaving the launch rod. This permits some outside force, either wind, gravity or both, to cause the rocket to tip and deviate from a vertical flight path.

(This can happen if the launch rod is dirty or the launch lug is too tight and the rocket hangs up, but this is easy to avoid by simply sliding the rocket up and down the rod to check that the rocket slides freely on the rod.)

If the rocket motor has marginal thrust, it will continue to accelerate as it tips and will eventually gain enough velocity for the fins to become effective and then the rocket goes on a straight but near horizontal flight path. That's the cruise missle mode. It this happens, you usually hit the ground before your parachute has a chance to deploy properly and damage your rocket.

If the rocket motor has insufficient thrust to gain enough velocity for the fins to gain aerodynamic control, it can sit and spin about its cg or loop above the pad until the motor burns out. The fins have stalled due to a high angle of attack created by the crosswind and become effective during only a fraction of a revolution but that's enough to kept the rocket in the air. This happens only when the winds are high (remember the wind on the ground is less than the winds aloft due to drag of the ground). If this happens, your rocket simply drops from about 50 ft after burnout and it may not be damaged too badly if you're lucky. If you're not so lucky, a rocket gone wild can cause personal injury or property damage.

Don't use a low-thrust, long-burn engine on a windy day. Use at least a 10:1 thrust to weight ratio motor if the wind is 10 mph or higher and you won't have a rocket gone wild.

Bob Krech