Estes Screaming Eagle

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Performance nut

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Since this is not a conventional rocket, figured I would ask this question here. Anyone know the CP measurement for the Estes Screaming Eagle?
 
I'd be interested to know what it is as well.

I've just bought the rocket and have a pile of bits waiting to be assembled.

SO.
 
Space Oddity,

I received Estes's response:

"Hello,

There is no "calculated" CP for the rockets - glue, paint, engine use, etc....these all affect the CG of each rocket. However, there is a system we use here at the rocket ranch. First, measure the overall rocket length and place a mark at half the length. Next, load the rocket with a motor, stuff wadding/chute in the tube and mark the current CG. Ideally the CG will be forward (toward the nose cone) of the center of the rocket that you measured. For stable flight, the CP needs to be forward of the CG. You can add some weight (modeling clay works good) to the nose to move the CG forward.


So it seems that Estes assumes CP is somewhere below the center of the rocket so they play it safe and say the CP is the center. So my next step I guess is to perform a swing test and keep adding weight to the rear until it gets unstable. I'll measure Cg and call that my Cp. Will not be precise but might be better than center estimate.
 
That's great, thanks.

It's good to get an insight as to how Estes design these things. Seems a bit hit or miss to me.

There are two large lumps of clay with the Screaming Eagle kit. The instructions say to compress it all into the nose cone. I think I'd rather add less weight to keep the rocket lighter. I'll follow the instructions though.

I'm a bit confused by their response. They say "For stable flight, the CP needs to be forward of the CG". I thought it was the other way round, though I suppose it depends on their definition of fore, aft, forward and behind.

Thanks again,

SO.
 
I agree, I think they have that reversed. CG should always be at least one diameter AHEAD the CP. Example, you have a 2" diameter tube then the CG should be at least 2" ahead of the CP.

...Fudd
 
I have built at least 3 of these rockets and up scaled one to 24mm motors, they are great rockets.
Use the amount of clay they give you and DON"T use an A motor it will not give it enough thrust to get going (even B's motors are iffy)
and in the swing test you tape the string to the center balance point with the biggest motor in it, add weight to the nose not the tail until in flies horizontal.
View attachment 169092
View attachment 169093

I flew the up scale once, she did very well, but couldn't find her in the crops at our field. :sad:
 
I want to shorten the tube and go dual cluster in the back. This obviously requires more nose weight but how much?

And yeah, I wasn't impressed with their response. Seems a lazy way to do business and her Cg/Cp relationship was incorrect. Then again, they don't calculate Cp so...

Sent from my @#$%& phone using Tapatalk
 
I have built at least 3 of these rockets and up scaled one to 24mm motors, they are great rockets.
Use the amount of clay they give you and DON"T use an A motor it will not give it enough thrust to get going (even B's motors are iffy)
and in the swing test you tape the string to the center balance point with the biggest motor in it, add weight to the nose not the tail until in flies horizontal.
View attachment 169092
View attachment 169093

I flew the up scale once, she did very well, but couldn't find her in the crops at our field. :sad:

Nice rockets, damn shame they disappeared. :(

The reason I want to add it to the rear is because I have one built already and don't want to dig out the clay. I want to see when it becomes unstable so I can get a better estimate of Cp. Only way I can think to shift the Cg backwards is to keep adding weight to the rear of the rocket. I considered doing the rocket in a sim program but the profile is unusual and I probably wouldn't trust it even if I portrayed it accurately.
 
I have to thank you Performance nut,
While at Red Glare in MD. this past weekend, I had a chance to buy three 24mm CTI 6 grain G-motors with case for a good price, even thou I didn't have a rocket to fly them in. It was my daughter's idea to buy them, she is always pushing me to build bigger or faster rockets. After reading this post I went off looking online for a rocket that I'd want to build for the motors not thinking twice about it.
then it dawned on me !!

Well, as my favorite cartoons main character says
"I think I know what we're going to do today"

View attachment 169204

so thanks
 
Cardboard cutout method will give you a conservative CP.

Lay the rocket on a piece of cardboard and trace around the outside. Cut this out and balance it on a pencil point. That balance point is a good estimate of the CP. For rockets like this one that are not symmetrical, do a second cutout but with the rocket on it's side. Do the balancing act again, then average location of the two points.

Add nose weight until your model balances ahead of the CP point. If you are going to shorten the Screaming Eagle you will need more nose weight. If you are going to add another motor, you need to add more nose weight.

kj
 
I want to shorten the tube and go dual cluster in the back. This obviously requires more nose weight but how much?

And yeah, I wasn't impressed with their response. Seems a lazy way to do business and her Cg/Cp relationship was incorrect. Then again, they don't calculate Cp so...

Sent from my @#$%& phone using Tapatalk

Second the Cardboard cut-out Laterial CP calculation but add a side view cutout as well then average the two for your LCP location. Mark the model body 1 to 1.5calibers ahead of the LCP mark and add nose weight to the model until loaded- ready for flight, it balances at that point. Your new GC.

When I've converted several Estes Models to 3 motor clusters (SR-71, Deep Space Transport, Geo-Sat HLV, Grey-Hawk, NASA Pegasus) to name just a few.
The process used to rebalance the model with additional nose weight is to add the mass for All additional materials used and the mass of ONE of the Additional motors (largest impulse and delay expected) to as far forward as your clay, B-B's or my preferred Nose weight material #9 Lead shot secured in epoxy will allow.

I have a screaming eagle sitting in the bag waiting for the spirit to move me to Cluster convert it;)
Hope this helps.

013Lp06a_3-C6 SR-71 Blackbird Liftoff(Manassas Va)_07-1990.jpg

021-b1b-sm_Geo-Sat 3 C6 LiftOff_07-21-90.jpg
 
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Those look great! A two engine cluster is what I'm looking for. If you can do three, two has to be possible. Thanks for sharing. =)

Sent from my @#$%& phone using Tapatalk
 
Sure!
Two motor clusters are a bit easier to ignite as well.
I haven't really opened or looked all that closely at the Screaming Eagle kit. If it has side intake ducts that run the length of the main body tube it may be easier to convert to 3 motor rather then having to butcher the aft end of the kit to install (I'm assuming) two 18mm motor mounts. Not that it can't be done but if the model has a BT-50 or BT-55 main body getting two BT-20's to transition will require a good bit of "Alteration" including adding epoxy fillets to reinforce the forward ejection reduced area.

I think I'll take a closer look at this kit, Have a Launch Planned this weekend so maybe next week if I get a chance.
 
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Very awesome! Definitely post pics.

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How is your build coming? I got started with mine the other day.

View attachment 169975 wings and tail fins, w/BT 70

View attachment 169976 3/32 dado to set tails in with epoxy

View attachment 169977 drawing of intakes I still have to cut them out, trying to decide on how much of a taper to make on the ends of intakes, I guess I'll go with 1-1/2" then I can trim them if I want to.

View attachment 169978
 
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