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Old 05-15-2016, 10:21 PM
johnpursley johnpursley is offline
Somewhat Skilled Rocketeer
 
Join Date: Mar 2011
Location: Houston, TX
Posts: 54
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Ol JR pretty much has his head wrapped around things with respect to finless. Just since posting here I've gotten a couple of direct emails about using "guidance" to make "hammerhead" models stable. One was specifically talking about the SpaceX Falcon. As JR stated, that big payload shroud at the front is pretty much the finless equivalent of putting fins at the front. The Falcon 9 might not be so severe as it is a very, very long and slim vehicle...but I would only attempt flying something like the Falcon finless if it were a fairly large model...say, 5-6 feet long.

Why? Because it's easier to make the critter stable (without an active system) because the proportion of the engine weight is a much lower fraction of the total model weight than with a smaller model. The CG will "naturally be fairly far forward and just a little nose weight (to bring the CG ahead of the CP) will go a long way toward offsetting the mass of the motor in the rear. PLUS, a long big model has a much lower natural frequency of oscillation. Still, I would "boilerplate" a smaller model of any finless vehicle away from crowds before "going for it" with a crowd pleaser.

BTW...I boilerplated a BT-70 Gemini Titan years ago with A10 motors (the one presented in this thread is a BT-80 based model). AND...though he didn't spcifically say, Jediboss is the owner of the model and the photos presented here are those that I sent him as the model was nearing completion, they are not of the completed model that he has in his hands now! I added the 7 systems tunnels and (what I call) "clutter" around the scale engines to make it look a bit more realistic since those photos.

---John Pursley
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