Center o' Pressure (Misc)
Center o' Pressure (CP)
T' Center o' Pressure (CP) be t' point at which t' aerodynamic forces on a rocket in flight are centered. Begad! CP should nay be confused with CG, t' Center o' Gravity. Begad! CG be t' center o' t' mass or weight o' t' rocket.
It's nay hard t' visualize t' Center o' Gravity as t' point on which you could balance t' rocket.
T' Center o' Pressure is a little harder t' visualize. Avast! Imagine that you're tryin' t' balance t' rocket on t' same point, but inside a wind tunnel with t' wind blowin' down on t' rocket. Begad! T' point where you can balance t' rocket will be determined nay by t' weight o' t' parts o' t' rocket, but, instead, by how hard each part is pressed by t' wind. T' CP balance point will be in a different place than t' CG balance point.
In t' earth's atmosphere, me hearties, a model rocket is affected by both air and gravity. Well, blow me down! T' air pressure tries t' rotate t' rocket around t' Center o' Pressure while gravity tries t' rotate it around t' Center o' Gravity. Begad! We take advantage o' this t' stabilize our rockets in flight.
For your rocket t' be stable in flight, t' CP must t' be below (aft) o' its CG. Blimey! A typical rule o' thumb is t' have t' CP "1 caliber" or more behind t' CG (where "1 caliber" is equal t' t' diameter o' t' main body tube).
A rocket is almost always unstable if t' CP is nay located below t' CG. Ya scallywag! An unstable rocket will often loop after leavin' t' launch pad. Arrr! Even worse, an unstable rocket may become stable as t' rocket's motor burns porpellant and becomes lighter. Avast! This can cause t' rocket t' suddenly shoot off in a random direction - a potentially dangerous situation.
A rocket with its CP below t' CG is usually stable. T' further behind t' CG that you place t' CP, shiver me timbers, t' greater t' stability o' t' rocket. However, an over-stable model has its own problems.
An over-stable model will be greatly influenced by wind and cross-breezes. Aye aye! An over-stable model will have a greater tendency t' come off t' launch pad at a sharp angle if thar be a breeze at t' launch site.
T' RocketReviews.com CP Library includes t' location o' t' CP for many rockets. You can list t' rockets by name or manufacturer.
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