Enum StreamerModel 

#[non_exhaustive]
pub enum StreamerModel {
    Filippone,
    OpenRocket,
}

How a streamer’s drag area is estimated. A streamer of length l and width w has a planform (one-side) area S = l w and an aspect ratio AR = l/w.

The two models disagree by a factor of about four in drag area, so docs/physics/recovery.md sets out what each is fitted to and how each compares with the only free-drop data in hand (the decision record on streamer and tumble drag, ADR-013).

Variants (Non-exhaustive)

Non-exhaustive enums could have additional variants added in future. Therefore, when matching against variants of non-exhaustive enums, an extra wildcard arm must be added to account for any future variants.

Filippone

J. Carruthers and A. Filippone, “Aerodynamic Drag of Streamers and Flags”, Journal of Aircraft 42(4), 2005, pp. 976-982, on the planform area, from wind-tunnel tests of cotton streamers at AR 3.3 to 30 and 6 to 18.9 m/s. It fits one power curve per planform area:

• C_D = 0.561 AR^−0.480 at S = 0.025 m² (eq. 2; Figure 2’s trend line reads 0.561 AR^−0.4795),
• C_D = 0.6514 AR^−0.6075 at S = 0.05 m² (the trend line on Figure 3, which the text does not repeat as an equation),
• C_D = 0.405 AR^−0.494 at S = 0.075 m² (eq. 1; Figure 4 reads 0.4046 AR^−0.494).

hpr interpolates between neighbouring curves linearly in ln S and holds the end curve outside the fitted range. That interpolation is hpr’s, not the paper’s. All three are needed because C_D is far from linear in ln S: at AR = 3.3 the middle curve sits 0.3% below the smallest area’s rather than 63% of the way to the largest’s, so blending only the extremes reads 18% low there.

The correlations are for streamers clamped at the luff; the paper measures more drag when the luff is free, which is what a descending streamer has.

This is the default: on the one free-drop measurement in hand that a flat correlation should fit (Kidwell’s unpleated streamer) it is 9% fast where Self::OpenRocket is 88% fast. Both are fast on his pleated streamers, which neither models (docs/physics/recovery.md).

OpenRocket

The OpenRocket technical documentation v13.05, Appendix C (printed pages 113-118): C_Dm = 0.034 ((ρ_m + 25 g/m²)/(105 g/m²)) ((l + 1 m)/l) on the planform area, fitted to wind-tunnel tests of model-rocket streamers (w 0.01 to 0.09 m, l 0.2 to 1.0 m, surface density 10 to 80 g/m², 6 to 12 m/s), with a stated 12 to 27% error on an independent set.

Use it to compare with OpenRocket. Against Kidwell’s free drops it is low in drag area by 4.2 times on his flat crêpe streamer and 7.8 times on his pleated Micafilm one, which is 88% and 154% fast in descent rate (docs/physics/recovery.md).

Implementations

impl StreamerModel

pub const FILIPPONE_ASPECT_RATIO_RANGE: (f64, f64)

The aspect ratios AR = l/w the correlations were fitted over. Outside it they only extrapolate, and as AR → 0 the power law runs away (C_D → ∞), which is why a flight refuses a strip wider than it is long (MIN_STREAMER_ASPECT_RATIO).

pub fn drag_area_m2( self, length_m: f64, width_m: f64, surface_density_kg_m2: f64, ) -> f64

The drag area C_D S of a streamer, m².

surface_density_kg_m2 is the fabric’s, which only Self::OpenRocket uses. Outside the ranges each correlation was fitted over this extrapolates; a flight refuses the shapes that make it meaningless (crate::Simulation::with_recovery).

Trait Implementations

impl Clone for StreamerModel

fn clone(&self) -> StreamerModel

Returns a duplicate of the value.

fn clone_from(&mut self, source: &Self)

Performs copy-assignment from source.

impl Copy for StreamerModel

impl Debug for StreamerModel

fn fmt(&self, f: &mut Formatter<'_>) -> Result

Formats the value using the given formatter.

impl Default for StreamerModel

fn default() -> StreamerModel

Returns the “default value” for a type.

impl<'de> Deserialize<'de> for StreamerModel

fn deserialize<__D>(__deserializer: __D) -> Result<Self, __D::Error>

where __D: Deserializer<'de>,

Deserialize this value from the given Serde deserializer.

impl Eq for StreamerModel

impl Hash for StreamerModel

fn hash<__H: Hasher>(&self, state: &mut __H)

Feeds this value into the given Hasher.

fn hash_slice<H>(data: &[Self], state: &mut H)

where H: Hasher, Self: Sized,

Feeds a slice of this type into the given Hasher.

impl PartialEq for StreamerModel

fn eq(&self, other: &StreamerModel) -> bool

Tests for self and other values to be equal, and is used by ==.

fn ne(&self, other: &Rhs) -> bool

Tests for !=. The default implementation is almost always sufficient, and should not be overridden without very good reason.

impl Serialize for StreamerModel

fn serialize<__S>(&self, __serializer: __S) -> Result<__S::Ok, __S::Error>

where __S: Serializer,

Serialize this value into the given Serde serializer.

impl StructuralPartialEq for StreamerModel