drag race question

[spacecowboy]

At the last "club" launch, yeah, us and our wives, we witnessed some pretty weird stuff during the 4 drag races we had (single controller, with a whip, so time delay is not an issue really).

The wind was 10-20+ (I'm also a sailor, so this is accurate).
The 2 pads were 2-5ft apart for all launches.

EVERY drag, the rox crossed over each other and went in opposite directions (right roc went left, vice-versa). This is also weird, burning motors out of the same box on identical rox, but one leaves a whole lot quicker than the other.

The question is :
Would engine blast induce this criss-cross behavior, or is this just a fluke ????
Check out one pad shot below, and thanks in advance....

 

[astrowolf67]

What type of controller are you using?

Something you might try, use an ohm meter and measure the resistance of each igniter. Take note of which one has the lower resistance, and which rocket it's installed in. I'd bet that's the one getting the jump off the pad. Also factor in the resistance of the leads of your clip whip.

As far as the rockets crossing each other, I dunno bout that one

 

[Micromeister]

Humm! my troop, rocket club and on my own I've launched a bunch of DRAG RACE models. Even dragged Satrun-V's awhile back
can't say for sure, but I'd think your crossing models had more to do with the wind than the motors. if one model blocked the breeze for a time that might be enough to throw the other model a curve. most of our Drags end up with the models staying on the side they started on. Like these two berthas, this Drag rack dual pad is only 24" long so I don't think the distance between models makes a lot of difference.

 

[Fore Check]

Is it possible that your launch rods were aimed - if ever *so slightly* - on divergent paths?

 

[Mike]

When in the flight did the rocket cross? Just off the rod there could be something (but I doubt it) higher up probably a fluke.

 

[xxxREKxxx]

Originally posted by Micromister
Like these two berthas, this Drag rack dual pad is only 24" long so I don't think the distance between models makes a lot of difference.

That's a great shot of the Bertha DR. We've got a scout launch coming up in May and I think we'll have to introduce the boys to the fine art of draggin'.
Bob

 

[wwattles]

I'm probably gettin' way down in the weeds here, but wasn't there something about the Bernoulli principle that stated that fluid in motion has a lower pressure than a fluid with less motion? If that is the case, then the disturbed air in the wake of the first rocket could be causing a slight localized decrease in air pressure. This would result in an apparent "pull" of the second rocket towards the wake. That rocket would also experience a decrease in drag due to the decreased pressure, accelerate, and cross through the wake, and out the other side.

Or maybe my aerodynamics are a little too rusty (haven't studied that since 1996!).

WW

 

[spacecowboy]

I'm going to take another look at the films we shot, but I really think this is more than just a fluke. . . . Right off the pads, and I think Bernoulli was a tad active. It would whip one rocket left, and the other right. Yeah, the rods weren't exactly straight up, which probably contributed to the effect. Whatever, a lot of good drags, standing there on the ground wondering why the birds have their turn signals on . . . .

 

[sandman]

the disturbed air in the wake of the first rocket could be causing a slight localized decrease in air pressure. This would result in an apparent "pull" of the second rocket towards the wake. That rocket would also experience a decrease in drag due to the decreased pressure, accelerate, and cross through the wake, and out the other side.

You might be on to something there.

NASCAR drivers do it all the time...it's called drafting.

sandman

 

[prowlerguy]

When you are conning a ship alongside during underway replenishment or flying in very close formation, you have to account for the tendancy of object moving through a fluid in close proximity to be pushed together. However, your timing would have to be very good and the pads very close together for two small models to have that effect in air, I would think.