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Tail moment arm (tail lever arm ratios)

How long should the tail moment arm be on an aircraft? · Standard part · basis: Design rules and figures from the cited sources; example geometry by Xem Studio

Also called: tail moment arm, tail lever arm, how long should fuselage be rc plane, tail arm length rule of thumb, tail arm to MAC ratio, fuselage length vs wingspan, stabilizer distance from wing, tail arm percentage fuselage length, rc plane fuselage length formula

Exact dimensions. True size, with no printing tolerance added.

sizes
11 in table

Notes

  • The tail moment arm is the distance from the wing's aerodynamic centre (or c.g.) to the tail's aerodynamic centre; it multiplies every newton of tail lift into pitching or yawing moment (Kitplanes, Wainfan).
  • Statistics of 30 transport aircraft put the horizontal-tail arm at about 46% of fuselage length and the fin arm at about 42%, with the horizontal arm about 5% longer than the vertical on conventional tails and about 23% longer on T-tails (Scholz 2021).
  • For light aircraft, Pazmany's data give tail arms of 11.8-15.5 ft on wings with 4.17-5.33 ft MAC, i.e. roughly 2.5-3 MAC (EAA Chapter 62). A short arm needs a bigger tail; Sadraey notes fighters use short arms and transports long arms (quoted in HAW Hamburg thesis).
  • Used on: Piper J-3 Cub, Luscombe Silvaire, Ryan Navion.
  • The file is a reference example built by Xem Studio from the numbers above. Sizes the sources do not fix are illustrative; scale the example to your own vehicle.

Tail moment arm size chart

parametervalue or rangesource
Horizontal tail arm / fuselage length (30 aircraft)46.2% (SD 2.8)Scholz 2021 / HAW Hamburg
Vertical tail arm / fuselage length (30 aircraft)41.8% (SD 4.8)Scholz 2021
Engines on wing: Lh / Lv47.0% / 44.7% of fuselage lengthScholz 2021
Engines on aft fuselage: Lh / Lv44.6% / 36.1% of fuselage lengthScholz 2021
T-tail: horizontal arm vs vertical armabout 23% longerScholz 2021
Conventional: horizontal arm vs vertical armabout 5% longerScholz 2021
Piper J-3: Lh, MAC13.2 ft, 5.33 ft (Lh/MAC = 2.48, derived)EAA62 (Pazmany)
Luscombe Silvaire: Lh, MAC11.8 ft, 4.17 ft (Lh/MAC = 2.83, derived)EAA62
Ryan Navion: Lh, MAC15.5 ft, 5.22 ft (Lh/MAC = 2.97, derived)EAA62
Sh/Sw (J-3, Silvaire, Navion)13.7%, 15.5%, 23.3%EAA62
Sv/Sw (J-3, Silvaire, Navion)5.7%, 7.6%, 7.9%EAA62

Where the files are

Other publishers' files are linked, not hosted. "verify" = check the license at the link before commercial use.

INCAS Bulletin / HAW Hamburg (D. Scholz)Empennage sizing with the tail volume complemented with a method for dorsal fin layout (2021)webPublisher's page; dimensions are facts
HAW Hamburg (Aircraft Design and Systems Group)Empennage sizing: tail lever arm as % of fuselage length (thesis; Table 2.1 typical tail volume coefficients)webPublisher's page; dimensions are facts
EAA Chapter 62 (Stan Hall, from Pazmany 'Light Airplane Design')How Big The TailwebPublisher's page; dimensions are facts
Kitplanes (B. Wainfan)Design Process: Horizontal Tail (2022)webPublisher's page; dimensions are facts

Free files

★ Free files 1 parts. Xem Studio design: free to use, print and sell things from; not to be republished as files. Xem Studio Design License. index.json

tail-moment-arm-tailconventional layout: horizontal span 400 × chord 100, vertical 140 × 114 mm on a 500 mm boom, NACA 0009 surfacesSTEP · STL
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Plain text: sheet.txt · JSON: /api/geometry?object=tail-moment-arm

Tail moment arm (tail lever arm ratios), isometric render of a generated part
Render of tail-moment-arm-tail from the free STEP; not to scale.

Fits with

Tail volume coefficient (horizontal and vertical tail sizing), isometric render of a generated part
Tail volume coefficient (horizontal and vertical tail sizing)19 sizes★ 1 file
Conventional tail (low-mounted stabiliser and single fin), isometric render of a generated part
Conventional tail (low-mounted stabiliser and single fin)5 sizes★ 1 file
T-tail (stabiliser on top of the fin), isometric render of a generated part
T-tail (stabiliser on top of the fin)4 sizes★ 1 file
Cruciform tail (stabiliser part-way up the fin), isometric render of a generated part
Cruciform tail (stabiliser part-way up the fin)2 sizes★ 1 file
V-tail (butterfly tail with ruddervators), isometric render of a generated part
V-tail (butterfly tail with ruddervators)8 sizes★ 1 file
Inverted V-tail (anhedral V), isometric render of a generated part
Inverted V-tail (anhedral V)2 sizes★ 1 file

Questions

What is a good tail arm for an RC plane?

Light aircraft in Pazmany's data run 2.5-3 MAC from wing to tail (EAA62); use that with a tail volume coefficient to set tail area.