Dr. Zooch Saturn IB Flights

[illini]

I've flown my Dr. Zooch Saturn IB twice and both flights were less than stellar. Similar problem on both flights resembling tip off:

Flight #1: 10+ mph winds, launched on B6-4, a little squirrely off the pad then laid over on its side and flew horizontal at about 100 - 150'. Safe ejection and recovery before pranging. Figured it was tip-off due to wind.

Flight #2: calm day, launched again on B6-4, no squirreliness on liftoff, but once again took a trajectory toward the horizontal at about 100 - 150'. Again, safe ejection and recovery about 50' shy of the ground.

Just as a point of comparison, my Dr. Zooch Saturn I Block 2 which is about the same size and weight flies beautifully.

Anyone else have the Saturn IB and seen the same problem? Any ideas?

 

[Stymye]

too much nose weight? as the motor burns that would compound the effect.

 

[adrian]

I'd have said too little nose weight! The rocket is marginally unstable and tips over right after launch. Now it's lost some tail weight because some of its propellant isn't there any more, so the CG moves forward. The rocket becomes stable and goes in a straight line.

My A-9 did something similar on its first flight - went horizontal, but crashed before it ejected. The ground was soft enough that the rocket took no damage. I stuffed some more clay into the nose, and the rocket has been flying perfectly on B6-4's in various wind conditions ever since.

 

[illini]

Yeah, I was thinking along adrian's lines. Marginal stability. I PM'd Dr. Zooch to ask him about the correct CG location so I could compare it with mine. No answer yet.

 

[shreadvector]

Nose weight off center?

"Poopy clay" nozzle eroding and vectoring thrust?

Thrust to weight ratio too small for stable speed off the rod?

Originally posted by illini
I've flown my Dr. Zooch Saturn IB twice and both flights were less than stellar. Similar problem on both flights resembling tip off:

Flight #1: 10+ mph winds, launched on B6-4, a little squirrely off the pad then laid over on its side and flew horizontal at about 100 - 150'. Safe ejection and recovery before pranging. Figured it was tip-off due to wind.

Flight #2: calm day, launched again on B6-4, no squirreliness on liftoff, but once again took a trajectory toward the horizontal at about 100 - 150'. Again, safe ejection and recovery about 50' shy of the ground.

Just as a point of comparison, my Dr. Zooch Saturn I Block 2 which is about the same size and weight flies beautifully.

Anyone else have the Saturn IB and seen the same problem? Any ideas?

 

[illini]

Good ideas...

Originally posted by shreadvector
Nose weight off center?

Possibly. The kit comes with the nose weight pre-built into the top of the transition (not the nose/capsule like you might expect). So no idea whether it was centered.

"Poopy clay" nozzle eroding and vectoring thrust?

Seems unlikely since it happened on both flights, but guess its possible. Didn't notice any poopyness on the burnt engines.

Thrust to weight ratio too small for stable speed off the rod?

Don't think so...its about the same size and weight as my Saturn I Block 2 which absolutely loves the B6/C6 engines.

 

[scottrc]

I'm thinking along the same lines. Is it balanced on the vertical centerline as well as the horizontal?

 

[dr wogz]

hey Scott, maybe we shoud lend him a prop balancer!!

https://www.shopatron.com/product/product_id=DUB499/101.0

 

[Stymye]

you may be right .I checked mine and the cg is less than a caliber.

thats without motor.!.. thats also considering that the cp is near the "N" in united states.

 

[illini]

Originally posted by Dr Wogz
hey Scott, maybe we shoud lend him a prop balancer!!

https://www.shopatron.com/product/product_id=DUB499/101.0

Ya know, I actually have a prop balancer around here somewhere. Maybe I should dig it out!

 

[adrian]

Originally posted by shreadvector
Nose weight off center?

I've built a very crude model Natter whose nose weight is well off centre. So is the front cone. Its first flight, on a C6-3, was interesting. In a fairly strong wind, it executed a roll and part loop, straightened out, flew horizontally cross-wind, then landed and ejected. I wasn't sure whether this was instability or a weird weathercock, so I covered both possibilities by adding more nose weight and only flying it on calm days. Subsequent flights on C6-3's have been fine.

"Poopy clay" nozzle eroding and vectoring thrust?

Unlikely if two motors did the same thing, unless it's a whole bad pack. Maybe try another motor from another pack.

Thrust to weight ratio too small for stable speed off the rod?

Possible; it starts off slowly, tips over, picks up speed and becomes more stable. However, my own experience with the above models favours the theory of more nose weight being needed. Especially since another model did something similar, only I never got the chance to see what it would do with more nose weight. That one had a D12-5 in the back and was last seen heading over a row of trees.

 

[illini]

Originally posted by stymye
you may be right .I checked mine and the cg is less than a caliber.

thats without motor.!.. thats also considering that the cp is near the "N" in united states.

Stymye,

You have this model? Have you flown it? Any problems?

 

[shrox]

Off center nose weight is probably not the problem, not enough nose weight is more likely.

Off center? I should know...

 

[shreadvector]

It seems from some replies that some people are not familiar with "Poopy Clay". It is the white, powdery clay used in Estes motor nozzles in years A, B, C, D and just after they switched back to real dates from the letter codes.

It is "Poop". When the motor fires several things can happen and there is no predicting which will occur or in what combination:
* Nozzle may erode larger resulting in low thrust - some models will seem to 'fall' out of the air.
* Nozzle may erode asymetrically resulting in offset thrust - some normally stable models will go unstable or they might make a sudden turn and fly horizontally. Serious fire hazard!

Estes was informed of the problems from the readers of news:rec.models.rockets and they switched clay to the current clay which is "Strong Like Ox" and mottled in appearance.

 

[Stymye]

Illini, yes I have one , I am in the primer and paint stage, I have not had a chance to fly it yet.

 

[illini]

Originally posted by stymye
Illini, yes I have one , I am in the primer and paint stage, I have not had a chance to fly it yet.

In that case, I'd advise not gluing on that capsule until after the first flight in case it needs more nose weight.

 

[Stymye]

agreed, ,Luckily I was very close to attaching it but have not done that yet.I may hold off on painting till I do some flights.
and post results.

 

[illini]

Please do post the results of those flights. I'd really like to know if others are having this problem, and if nose weight fixes it.

 

[Dr.Zooch]

FYI- my test flight bird, which flew well on both a B6-4 and a C6-7 had only a .4 oz nose weight located where your kit's .5 nose weight is located. So my no-motor CG is where the camera targets are located on the wrap. I'm wondering if your CM, which I was turning by hand at the time that you got your kit, may be off somehow? It is highly unlikely that an advanced builder, such as yourself, has made any sort of simple construction error, so this problem concerns me. Did you change any components- parachute, shock cord, screw eye- so on? Still, this kit is way over-powered even on a B6-4. You'll see from the RockSim file that the CG and CP would take a lot to squeeze together. It sounds almost as if the coast phase is being corrupted aerodynamically. If it weren't for the fact that you are an advanced builder, I'd say the LES may be off center. Did you try and fly it on a C6-7? Do it and if the thing crashes, I'll send you another kit to build and try again.

Also- what were the WX conditions at the time of flight?

 

[illini]

Originally posted by Dr.Zooch
It is highly unlikely that an advanced builder, such as yourself, has made any sort of simple construction error, so this problem concerns me.
...

Also- what were the WX conditions at the time of flight?

Flattery will get you nowhere...

Weather conditions were as in the opening post above. 10+ mph on first flight. Calm...dead calm...on the second.

I looked my model over again last night, looking for any asymmetries or other nastiness. Tubes out of alignment. Funky CM's (not to be confused with funky glue putty). Anything that would put this thing on an arcing trajectory. Nothing obvious. My advanced builder credentials remain intact.

As far as mods go. Pretty much stock except for adding an engine block with kevlar shock cord (included elastic cord tied to that). Also replaced the chute with same size orange mylar.

Already told Wes, but for the others here: My model weighs 2.68 ounces with the empty CG just above the thin black line on the wrap (about where the ullage motors are located). This would have more margin than Wes's prototype.

Will put it up again at the next launch and see how it goes.

EDIT: The poopy B6-4 theory may be gaining credibility here.

 

[rstaff3]

I suggest you carefully package that model and send it to me for further evaluation

 

[Dr.Zooch]

I'll do everything up to and including sending you new parts so that you can change them out, to help you resolve this problem. We may end up sending you one of the Apollo CMs from the Saturn I kits, which is weighted differently, to see if that does the trick. Also, the newer Saturn IB kits are stocked with 67# paper for the tanks- slightly reducing the mass.

 

[illini]

I'll give it another go as is and see if I can get it to find the vertical. Let you know what happens then. Really not seeing any deficiencies with the model. Looks like it *wants* to fly...but gravity is winning the day so far.

 

[Dr.Zooch]

I had an S-I stage that I was building for display which is made from current kit components- including the new lightweight tanks, and was going to represent the SA-5 kit. I'm diverting that hardware to become a Saturn IB to check on this issue. (My prototype has much heavier components in the S-I stage and is 1/2 inch longer in the thrust structure.) As soon as the glue is dry on the new model I'll attempt to fly it on B6-4s and duplicate your problem.

My prototypes are constructed to give the worst case flight configuration (i.e. .1 less ballast, heavy gluing, flat leading edge fins and so on) for flight. I added a bit to the fin size, then each of the Saturn kits was launched in heavy winds- all of this to help insure that the buying public would get a stable kit, as theirs would have a bit more ballast, larger fins and likely be launched in better WX. The Saturn I fins, for example, are 15% larger than scale on the flight version.

ANYONE out there with one of my IB kits- please report flight results to [email protected]

 

[Stymye]

will do .Mine is ready to fly, But I will have to wait for the weekend as I get home from work untill after dark.

 

[Dr.Zooch]

I'm rushing to get this production model finished by the weekend. WX permitting I may do a schoolyard launch on a B6-4 rather than wait for the Feb. 5th MDRA launch.

I took the prototype and broke it off at the interstage (because the S-IB stage is larger and heavier than a production kit) then took a kit out of stock at random and robbed it of its adapter and spacecraft, wrap sheet and balsa stock. That way I can quickly reproduce a production kit for testing.

 

[illini]

I PM'd this to Dr. Zooch to help calm poor Wes's nerves. Posting it here for everyone else's benefit. I'm leaning toward drag separation being the cause of my flight problems. Bottom line, my transition is somewhat loose fitting into the BT. I didn't *think* it was loose enough for drag separation to occur. But the more I think about it, the more I think this is the cause due to the combination of looseness and weight in the transition. The weighted transition, CM, capsule, and tower are one piece, and they are relatively clean, aerodynamically speaking, compared with the lower section with those 8 funky tubes and fins. Once the model reaches coast phase, the momentum of the relatively clean, weighted transition/nose carries it free of, or at least partially separates from, the draggy base. If it doesn't completely separate, then it at least comes loose far enough for it to tilt slightly, forming an aerodynamically cambered lifting surface. I'm betting a little tape on the shoulder of that transition is going to fix this.

 

[Dr.Zooch]

I just got back from the MDAR launch and the Saturn IB flew just fin in ALL configurations.