by Prof. Dr.-Ing. Elmar Wilczek

organized by DGLR, HAW, RAeS, VDI, ZAL

Hamburg, May 20th, 2021 https://doi.org/10.5281/zenodo.4781082

1 Verein Deutscher Ingenieure Hamburger Bezirksverein e.V. Arbeitskreis Luft- und Raumfahrt

Hamburg Aerospace Lecture Series Hamburger Luft- und Raumfahrtvorträge

DGLR in cooperation with the RAeS, HAW Hamburg, VDI, & ZAL invites you to a lecture

Seaplane Design - A Forgotten Art

Prof. Dr.-Ing. Elmar Wilczek, Expert in Marine Aviation

Lecture followed by discussion Date: Thursday, 20 May 2021, 18:00 CEST No registration required ! Online Zoom lecture Online: http://purl.org/ProfScholz/zoom/2021-05-20

Beriev Be-200 Altair – Courtesy of United Aircraft Corporation (UAC)

A seaplane gives the ultimate freedom of flight with theoretically endless take-off and alighting possibilities along the coast, on lakes and rivers – and not to forget on the open seas. The design of seaplanes is based on the knowledge of aircraft design and speedboat design. The craft must meet buoyancy and lift requirements. Hydrostatic and -dynamic stability has to be matched with the longitudinal and lateral static and dynamic stability in the air. The structure has to withstand water and air loads. Crucial are hydrodynamic resistance at take-off as well as the lift-to-drag ratio in flight and particularly the water loads in defined sea states. Sea plane design has a glorious past, but much of the knowledge is buried in dusty archives. It is even worse if knowledge is lost forever and needs to be reinvented. Elmar Wilczek has taught seaplane design for decades. In his presentation he will focus on particular research results among others: the importance of water spray for hydrodynamic resistance, scale effects, hydrodynamic elasticity for seaworthiness, length-to-beam ratio for hydrodynamics and aerodynamics. He advocates the conservation of seaplane design knowledge and is very open to share the information he has diligently collected.

HAW/DGLR Prof. Dr.-Ing. Dieter Scholz Tel.: (040) 42875-8825 [email protected] RAeS Richard Sanderson Tel.: (04167) 92012 [email protected] VDI Dr.-Ing. Uwe Blöcker Tel.: 015112338411 [email protected]

DGLR Bezirksgruppe Hamburg https://hamburg.dglr.de RAeS Hamburg Branch https://www.raes-hamburg.de ZAL TechCenter https://www.zal.aero VDI Hamburg, Arbeitskreis L&R https://www.vdi.de

Hamburg Aerospace Lecture Series (AeroLectures): Jointly organized by DGLR, RAeS, ZAL, VDI and HAW Hamburg (aviation seminar). Information about current events is provided by means of an e-mail distribution list. Current lecture program, archived lecture documents from past events, entry in e-mail distribution list. All services via http://AeroLectures.de. Modern Seaworthy Seaplanes

Photo AVIC AVIC AG 600 Kunlong, maiden flight December 24th, 2017

Photo Beta Air Photo JMSDF/ShinMaywa Beriev Be 200 Altair, maiden flight 1999 ShinMaywa US-2, delivered to JMSDF in February 2009 Prof. Dr.-Ing. E. Wilczek 2 Seaplane Design – A Forgotten Art Hull Bottom Definitions of Seaplanes (Flying Boat) dead rise rise dead stern bow trim afterbody angle angle chine keel (transversal) step height step forebody afterbody total length of planing bottom

sponson dead rise angle auxiliary float chine flare keel angle beam Prof. Dr.-Ing. E. Wilczek 3 Seaplane Design – A Forgotten Art Design of a High-Seaworthy Seaplane by Konrad Detert 1916

Hydrodynamics Spray Protection Seaworthiness

Sea Strength Buoyancy

Prof. Dr.-Ing. E. Wilczek 4 Seaplane Design – A Forgotten Art Main Requirements of a Seaplane

 Low water resistance

 Low spray water production

 Low impact loads during take-off and alighting at defined seaworthiness

 No tends of oscillations around the pitch axis – no porpoising

 Weather-cock stability and stability around all horizontal axis at drifting by cross wind according to required seaworthiness

 Quick reaction of the seaplane’s air and water rudders during manoeuvring

 Low aerodynamic drag

Essential Towing Tank Testing: Dornier AAA model, Stevens Institute of Technology

Prof. Dr.-Ing. E. Wilczek 5 Seaplane Design – A Forgotten Art Courtesy of Dornier Luftfahrt GmbH Low Water Resistance Hull Advanced Slender Hulls

 High length-to-beam ratio lL/bSt = 10 to 15  High beam loading = = » 2 to 3

Blohm & Voss BV 238 V1 (1944)

lL/bSt = 9.3; ca‘ = 2.1 (2.2)

Martin P6M SeaMaster (1959)

lL/bSt = 15; ca‘ = 3.1

Shin Meiwa SS-2A (1968) „Planing Tail“ ~ lL/bSt = 11.6; ca‘ = 3.1

Beriev Be-200 (1999) ~ lL/bSt = 13; ca‘ = 3.8

Prof. Dr.-Ing. E. Wilczek 6 Seaplane Design – A Forgotten Art Low Water Resistance Hull Comparison of Resistance Between Conventional and Planing Tail Hull Bottom

0.3

„The Hump“

0.2 Conventional hull

0.1 -lift ratio ratio [-] -lift

to ‘Planing tail’

Planing mode

Resistance- 0 0.2 0.4 0.6 0.8 1.0

Standardized speed v/vlift off [-]

Prof. Dr.-Ing. E. Wilczek 7 Seaplane Design – A Forgotten Art Low Water Resistance Hull Towing Tank Results with Scale Effect (Sottorf)

Higher model resistance by neglecting friction scale effect (Reynolds number)

Models should never have a beam below 20 cm!

Prof. Dr.-Ing. E. Wilczek 8 Seaplane Design – A Forgotten Art Low Water Resistance Hull Step/Afterbody Ventilation Tests on Dornier Do 18 (Full, 1939)

Pressure gauge  Ventilated step on FF floatplanes

Ventilation ducts  Glassy water: Take-off problems with sponsons if no ventilation  Even Do 26 equipped with ventilation

Step ventilation of a Dornier Do 18 flying boat with sponsons Suction curve in the ventilation duct of the step during take-off run of the Do 18 D-ATEY flying boat at no wind (circular take-off) 1400 Suction in mm Ventilation ducts closed! 1200 water column

1000

800

600 Crossing own wave system after a full circle 400

200 40 80 120 Time in s

Prof. Dr.-Ing. E. Wilczek 9 Seaplane Design – A Forgotten Art Low Water Resistance Hull Step & Afterbody Ventilation Tests on Sunderland (1952)

Step fairing

Step line

Prof. Dr.-Ing. E. Wilczek Ventilation holes 10 Seaplane Design – A Forgotten Art Low Water Resistance Hull Step/Afterbody Ventilation Tests on Sunderland (1952) Water speed 54 knots Keel attitude 8 deg.

4.0 3.5 3.0 2.5 2.0 Atmospheric Keel

Afterbody pressure distribution during a take-off (above) and an alighting skip (below). Step sharp. All vents sealed All pressures in pounds/sq. in. negative below atmospheric.

Water speed 60 knots Keel attitude 8 deg.

3.5 3.0 2.5 2.0 Atmospheric Keel

Test Results:  No suction and skipping if step is fully faired and ventilated  Step must be a sharp break between fore- and afterbody  Reduction of drag and resistance and  Improved directional stability Prof. Dr.-Ing. E. Wilczek 11 Seaplane Design – A Forgotten Art Low Water Resistance Hull Reduced Resistance by Afterbody Steplets or Wedges (Full/Sottorf)

Blohm & Voss BV 222 towing tank model with steplets or wedges on afterbody

 Up to 45% of resis- tance reduction before lift-off  Almost no upper stability limit

Full scale trials on Arado Ar 196 floats

Blohm & Voss BV 238 afterbody equipped with wedges or steplets and “sword fin” (Schwerthacke) Prof. Dr.-Ing. E. Wilczek Seaplane Design – A Forgotten Art 12 Low Water Resistance Hull Reduced Resistance by Afterbody Steplets

Unknown source

Wedge on afterbody of Beriev A-40

Prof. Dr.-Ing. E. Wilczek 13 Seaplane Design – A Forgotten Art Low Spray Generation Principal Sketch of Spray on a Seaplane Hull/Float (Sottorf)

Planing mode

rearward spray water

trough DR Increase of resistance by spray water wetting of afterbody bottom

b nat pressure area bSt

lateral spray water 14 Prof. Dr.-Ing. E. Wilczek Seaplane Design – A Forgotten Art Low Spray Generation Spray Intensity Depending on Step Loading and Length-to-Beam Ratio Sottorf Davidson/Stout 20 W Optimum Design c'  K  bl )( 2 a   b3 2 L St 15 W St (light spray) ' K2 = 0.018 W ca K2  2    bl lL 2 LW St )( [-] bSt

St 10 /b L 3   cWb ' 8 St aW

6 Maximum Design (heavy spray)

-beam ratio l ratio -beam K2 = 0.022 to 4

Max. Overload Length- (excessive spray)

K2 = 0.025 2

E. G. Stout: Development of High-Speed Water-Based Aircraft, 1950

0.08 0.1 0.15 0.2 0.4 0.6 0.8 1.0 1.5 2 3 4 5 6 Step loading c ‘ [-] a 15 Prof. Dr.-Ing. E. Wilczek Seaplane Design – A Forgotten Art Low Spray Generation Groove Type Spray Suppressor

Tilt fairing Conventional hull bottom frame shape Bottom with Groove Type Spray (with chine flare) Suppressor and fairing

Additional resistance and drag, impact load?

Forebody of ShinMaywa US-2 with GTSS

Unknown source Prof. Dr.-Ing. E. Wilczek 16 Seaplane Design – A Forgotten Art Low Spray Generation Influence of Planform and Camber on Spray Drag (Tulin/Wagner)

Spray Production is a Measure of Hydrodynamic Quality of a Hull!

Combination of rounded planform and concave camber on BV 238

Courtesy of Beriev Round keel at bow of Be-200

Prof. Dr.-Ing. E. Wilczek 17 Seaplane Design – A Forgotten Art Low Water Impact Loads Structural Elasticity (Viking Boats) and High Seaworthiness

Vikings used boats with structural elasticity to cross the Atlantic!

Courtesy of Dornier Luftfahrt GmbH Dornier Do 24 at sea trials, North Sea 1937 (sea state 4)

No model tests allowed due to Cauchy‘s Law! Courtesy of Marintek, Norway

Prof. Dr.-Ing. E. Wilczek 18 Seaplane Design – A Forgotten Art Low Water Impact Loads Sea State Statistics & Limitations 100 BVF 36, Bgr.II Bgr.III 90

80

70 Amphibian US-1 60 Amphibian AAA Flying boat BV 238 (3 m wave height) 50 Flying boats BV 138, Do 24, Do 26 40

Indic Ocean 30 Sea State State LimitsSea of Seaplanes [%] Flying boat P5M Pacific Ocean 20 Cumulated Frequencies Frequencies Cumulated of Sea States and Flying boat PBY Atlantic Ocean Catalina 10 Mediterranean Sea

0 © Dr. Wilczek 1993 0 1 2 3 4 5 6 7 8 19 Prof. Dr.-Ing. E. Wilczek Sea state [-] Seaplane Design – A Forgotten Art Low Water Impact Loads Influence of Elasticity and Deadrise on Alighting Impact (Ebner/Sydow)

Ebner‘s water load formula rigid wedge bottom being introduced into the (FAR 23/25, JAR 23, German BVF 36 5.1 CS 23) zx red  210  vcccmP  N N elastic flat bottom mred = mass reduced to point of impact (BVF 36) c0 = weight coefficient acting on on acting c1 = “sea state” limitation coefficient

elastic wedge bottom c2 = keel shape coefficient (BVF 36) v interpolation = alighting speed the hull/float bottom bottom hull/float the Normal force force Normal

A steep wedge increases considerably the  = keel angle k = spring coefficient hydrodynamic resistance! v0 = impact speed l = impact length w = water density Standardized keel   k  angle coefficient v0 w l

Prof. Dr.-Ing. E. Wilczek 20 Seaplane Design – A Forgotten Art Low Water Impact Loads Water Loads Depending Exponentially from Impact Speed (Sydow/Schmieden)

Beam coefficient:  3 Gb 

with b = beam (of float or hull) G = gross weight  = specific weight (water)

Checked for twin floatplane with keel angle  = 150°,

Normalized Normalized max. impact force spring stiffness k = 500,000 kg/m

Exponent 1.5, used by BVF 36 (Ebner)

Exponent 2, used by FAR 25 etc.

Normalized impact speed Prof. Dr.-Ing. E. Wilczek Seaplane Design – A Forgotten Art 0.57 21 NO TENDS OF OSCILLATIONS AROUND THE PITCH AXIS – NO PORPOISING

https://images.app.goo.gl/dJVEwQ76EAvVfbbd6 22 No Tends of Oscillations Around the Pitch Axis – No Porpoising Porpoising Limits of a Seaplane (Full/Lechner/Sottorf) Turn around lateral axis

 Oscillation in pitch and heave – way of aircraft C.G.

unstable

Natural or free trim angle Upper por- poising limit Influence of weight, wind  and flap deflections Lift-off stable Trim angle angle Trim Planing mode

unstable 1st Maximum of Lower por- resistance (hump) poising limit

Prof. Dr.-Ing. E. Wilczek Seaplane speed v 23 Seaplane Design – A Forgotten Art No Tends of Oscillations Around the Pitch Axis – No Porpoising Influence of Modifications of Fore- and Afterbody (Sottorf)

Steplets on afterbody Concavity of the bottom before the step

7 Unstable area with steplets 6

Lift-off * [°] 5 

4 Stable area Upper porpoising 3 limit Trim angle angle Trim w/o steplets 2 Concavity of forebody bottom 1 lower porpoising Unstable area limit 0

Prof. Dr.-Ing. E. Wilczek Planing speed v 24 Seaplane Design – A Forgotten Art Weather-Cock Stability and Stability Around All Horizontal Axis Characteristics at Different On-Water Operations

 Static stability with regard to capsizing  Weather-Cocking at mooring

Correlation between Wing Span – Mass Density – Stability (Wenk) • seaworthiness requirements • flight mechanics requirements 0.1 • buoyancy requirements and • design parameters of the a/c

0.05 Upper limit for hull w/o lateral buoyancy devices

0.05 0.10 0.15 0.20 coefficient of the hull of hull the coefficient Shape related stability related Shape Ratio of height a between CG and F to half wingspan s [-]

Prof. Dr.-Ing. E. Wilczek Seaplane Design – A Forgotten Art 25 Weather-Cock Stability and Stability Around All Horizontal Axis Maximum Wind Speeds for 1-t-Aircraft When Taxiing in a Circle without Crabbing Wind direction (Laute)

Moving speed Wind velocity vw = for G = 1.0 to v = 4.43 m/s for G = 1.0 to

Line of max wind speed (without capsizing) Heeling of the a/c into direction of hatched area, direction of arrows indicates direction of capsizing.

Prof. Dr.-Ing. E. Wilczek 26 Seaplane Design – A Forgotten Art Weather-Cock Stability and Stability Around All Horizontal Axis Lateral Stability of a Taxiing Twin Floatplane (Ebner/Full)

(w/o and with crab angle (10°); Ve = floatplane velocity)

26 Ve = 15 m/s 24

22

20

18 0 16

14

12

10

8 4.5 m/s 6

4

Righting or capsizing moment M [mkN] M moment capsizing or Righting w/o crab angle 2 with crab angle 0 2 4 6 8 10 12 14 Prof. Dr.-Ing. E. Wilczek Inclination or heel angle j [] Seaplane Design – A Forgotten Art 27 Weather-Cock Stability and Stability Around All Horizontal Axis Oblique Towing Test Apparatus Measuring Transversal Force, Yawing and Rolling Moment (IfS)

Heading Longitudinal model axis

Yaw angle 

Prof. Dr.-Ing. E. Wilczek Seaplane Design – A Forgotten Art 28 Parameters:  360° measurement in heading  several trim and heel angles according to requirements

Courtesy Dornier Luftfahrt GmbH

Prof. Dr.-Ing. E. Wilczek Seaplane Design – A Forgotten Art 29 Low Aerodynamic Drag Aerodynamic Drag of Conventional Hulls/Floats

Drag ratio • Features creating drag Development phase to seaplane Aerodynamic body 69% circular cross sections

stern upwards 78% circular cross sections

83% V-shaped planing bottom

85% Flying-boat w/o steps

Flying-boat 100% with steps

Prof. Dr.-Ing. E. Wilczek 30 Seaplane Design – A Forgotten Art Low Aerodynamic Drag Advanced Slender Hull Bottoms

Blohm & Voss BV 238 V1 (1944) Courtesy of MBB, Hamburg l/bSt = 9.3

Martin YP6M-1 SeaMaster (1959) Courtesy of Martin Corporation l/bSt = 15

Prof. Dr.-Ing. E. Wilczek Seaplane Design – A Forgotten Art 31 Courtesy of Dornier Luftfahrt GmbH 3232