TO - DTIC · 4.1 Air Drag and Lift 7 4.2 Air Flow through the ducts 7 ... From theoretical...
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BRITISH RESTRICTED fiquals LINKED STATES RESTRICTED
RESTRICTED REPORT No: AERO. 2143.
LOG Mq^/4
ROYAL AIRCRAFT ESTABLISHMENT Farnborouejh. Hants.
A PRELIMINARY EXAMINATION OF
HULL AFTERBODY VENTILATION
by
K. M. TOMASZEWSKI, lnz.Lotn.(Warsaw),
A. G. SMITH, B.Sc, D.I.C.
and
G. F. CHALME
wcrcFt. JK
•-
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Class No: 532.582.4.001.57
R.A.E. Report No. Aero. 2143.
July, 1946.
ROYAL AIRCRAFT ESTABLISHMENT. FARNBOROUGH
A Preliminary Examination of Hull Afterbody Ventilation
by
K.M. Tomassewski, Inz. lotn. (Warsaw) A.G. Smith, B.Sc., D. I.C.
and G.F. Chalmers
3U:^:JJ«
Reason for Enquiry
Information was required on the effect on the water forces of ventilating the afterbody of a 3tepped hull, and also on what improve- ment could bo obtained by utilising the dynamic head of the air stream.
Range of Investigation
Examination of the available information shaved that a reduction of ten per cent in resistance might be expected by the efficient supply of enough air in the region of maximum air suction on a hull afterbody. Ducts were designed for a Shetland hull to feed air from the dynamic head pressure in the region of the bows. Measurements of the air and water forces and of the air flow j assing through the ducts were made for a range of attitudes and drafts in the planing region, with the model:
(1) screened from any air flow, (2) in normal air flow conditions, no dynamic head ventilation, (3) in normsJL air flow conditions with dynamic head
ventilation.
Conclusions
Over the planing region there is a general decrease due to the dynamic head ventilation of about ten per cent in resistance/load on water ratio and draft. There is some reduction of pitching moment compared v/ith the unventilated hull in the normal air flow. The volume air flow through the ducts is about 500 cu.ft./oec. full scale at 62 knots, which corresponds to an energy content of about 8 H.P.
The unducted hull in th.. correct air flow is in turn better than the screened hull by about the same amount, although when corrected for air forces these differences can bucome very large. These air forces are however measured with the hull ju3t clear of the water and are of doubtful value.
The tests in air flow and with dynamio head ventilation demonstrate the beneficial effects of ventilation and further tests are required with increased ventilation.
R.A.E. Report No. Aero. 2143.
To examine the interference between air and water flow it is recommended that teats be made
(1) to measure the pressure distribution on the hull in stability and force tests with different degrees of ventilation,
(2) to measure the air forces acting on a hull at different drafts.
•
LIST OP CONTENTS Page
1 Introduction 5
2 Range of Investigation 6
3 Description of model 7
4 Results 7 4.1 Air Drag and Lift 7 4.2 Air Flow through the ducts 7 4.3 Total Resistance Characteristics 8 4.4 Total Lift Characteristics 9 4.5 Total Moment Characteristics 9
5 Attitude, Draft and Total Resistance for zero applied Moment 10
5.1 Spray conditions for zero applied moment 10
6 Separation of air and water forces 11
7 Discussion 11
8 Recommendations for Further rfork 12
9 Conclusions 13
List of Symbols 14
References 15
Circulation 16
- 2
R.A.E. Report No. Aero. 2143-
LIST OP APPENDICES
Calculation of the possible reduction of drag of the "Empire" boat at 57 knot3 full scale by removing air auctions on after- body bottom I
LIST üF T..BLES Table
I Particulars of ventilated Shetland hull
Air lift and air drag for 1:19 scale Shetland hull measured just clear of the water on No. 1 R.^i.E. carriage II
Velocity measurement of air flow through duct with different drafts and attitudes III
Variation of air flow through ducts for take-off conditions at 62 knots full scale IV
Total resistance, draft and moment characteristics of Shetland hull with and without cdr flow and' ventilation V
Water resistance characteristics of Shetland hull with and without ventilation, corrected for air drag and air lift forces VI
algebraical representation of variation of draft with load on water and 3peed over a range of attitudes VII
Air pressure distribution on afterbody bottom of 1 : 16 scale "Empire" boat rat;o3ured at 2A f.p. s. VIII
Variation of mean air pressure along the afterbody of 1 : 16 scale "Empire" boat at 2A f.p. s. IX
Drag and lift on afterbody bottom on 1 : 16 scale "Empire" boat at 24 f.p.s. due to air pressure distribution X
Possible reduction of drag for "Empire boat at 57 knot3 by removing suction on afterbody bottom XI
LIST OP ILLUSTRATIONS Fi£.
1 :•
Model hull lines showing position of ventilation ducts General View- and Exploded view of hull with ventilation ducts Air drag of model Shetland hull on R..\.E. No. 1 towing carriage
(model just clear of water) 3 Air lift of model Shetland hull on R.A.E. No. 1 towing carriage
(model just clear of water) _ 4 Measurement of air flow through ducts 5 Variation of air flow through duct with draft at constant attitude 6 Variation of air flow through duct with attitude at constant lift
coefficient 7 Variation of air flow for take-off conditions at 62 knots full
scale _ 8 Total resistance characteristics of Shetland hull at 4° 38' attitude 9a Water resistance characteristics of Shetland hull at 4° 38' attitude
with correction due to air drag and air lift forces 9b Total resistance characteristics of Shetland hull at 6°38' attitude 10a Water resistance characteristics of Shetland hull at 6°38' attitude with correction due to air drag and air lift forces 10b
K.-i.E. Report No. -ifiro. 2143.
List of Illustrations .(cont'd) fie.
Total resistance characteristics of Shetland hull at 8° 38' attitude
Water resistance characteristics of Shetland hull at 8° 381
attitude with correction due to air drag and air lift forces Total resistance characteristics of Shetland hull at 10° 38'
attitude Water resisto.nce characteristics of Shetland hull at 10° 38'
attitude with correction due to air drag and air lift forces Lift characteristics of Shetland hull at 4° 38' attitude Lift characteristics of Shetland hull at 6° 38' attitude Lift characteristics of Shetland hull at 8° 38' attitude Lift character!sties of Shetland hull at 10° 38' attitude Moment characteristics of Shetland hull at 4° 33' and 6° 38'
attitude Moment characteristics of Shetland hull at 8° 38' and 10° 38'
attitude Attitudes for zero applied moment Total resistance and lift characteristics cf Shetland hull for
take-off with zero applied mor.ent Total resistance and lift characteristics of Shetland hull for
take-off with zero applied moment Spray characteristics on calm water with and v/ithout ventilation
for zero applied moment (No.2 carriage) Location of pressure plotting points on afterbody bottom of
"Empire7' boat Transverse pressure distribution on afterbody bottom at station
corresponding to points 12, 3 and 21 at 24 f.p. s. on 1 : 16 scale "Empire" boat
Longitudinal pressure distribution on afterbody bottom on 1 : 16 scale model of "Empire" boat at speed of 24 f.p.s.
11a
11b
12a
12b 13 14 15 16
17
18 19
20
21
22
23
24
25
4 -
R......E. Report No. Aero. 21^3.
Introduction
A major design problem in the design of stepped hulls for seaplanes is the efficient ventilation of the afterbody. The supply of sufficient air to the afterbody bottom in the planing region, when the afterbody is clear of the wake from the forebody, has customarily been obtained by suitable design of the step and afterbody geometry.1 However the demand for greater efficiency and the movement towards high water speeds and drafts, has made the problem more severe. • The presence of air suctions under the afterbody is thought to be the primary factor in interaction between the water and air flow assuming that the v/ater flow has just been efficiently separated from the hull bottom by the main step. These air suctions lead to upper limit porpoising instability on disturbance and low drag/lift efficiency at both small and large drafts.
In the last few years several experiments have been made model and full scale to find whether any improvement in ventilation efficiency can be obtained by supplying air direct to the afterbody. These experiments have however been made empirically without examining the nature of the air and water flow over the hull bottom, and had very little success. 3»^f5 '•'-'
It was therefore decided to explore more efficient methods of ventilating the afterbody, >and in the first place to obtain the air supply from the dynamic head of the free air strecm. The design of an effective ducting system v/os considered to depend on:
(a) the position of the duct exits on the afterbody bottom,
(b) the direction in which the air supplied should be ejected relative to the boat,
(c) the dimensions of the ducts,
(d) the volume and pressure of air flow at the duct exits,
(e) the position of the air intake to the ducts when using the dynamic head of the free stream for the air supply.
From theoretical considerations of air lubrication" it was considered that the separation of water flow from the afterbody bottom and reduction of drag is greatest when the air leaves tho duct exits in an .aft direction parallel to the hull bottom. The testa on the Sea-0ttcr5 showed that .the improvement of porpoising stability with ventilation occurs when the duct exits are '•.bout 30 per cent of the beam aft of the step and the attitude exceeds 8° on the forebody keel datum. For positions nearer the step there was very little improvement in the • stability limits.
The pressure distribution on the afterbody of a model "Empire" flying boat has been measured in the R.A.E. tank. It * An analysis of these results given in Appendix I, shows that if the suctions on the afterbody bottom were removed by efficient ventilation then at 57 knots full scale the resistance would be reduced as follows:
:
Attitude degrees
5 7
• 9
Percentage deduction
6 10 • 11
The maximum suctions were shown to be present at from 30 to 60 per cent of the beam aft of the main step and about 25 per cent of the bean
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R.A.X, Report No. Aero. 21^3.
out transversely from the keel. -.
The hull of the Shetland was considered to be a useful form for the experiments to determine whether improvements of the above order could be obtained by ventilation. It was representative of contemporary design, having a straight V step moderately faired in elevation. Such steps, when sufficiently faired, have a very low air drag. Pull scale water pressure measurements had shown that with such a step suctions could occur on the afterbody bottom.9 Duct exits were chosen on the bases of the Enpire boat and Sea-Otter results.
The air was to be ejected aft at 5° downwards with respect to the afterbody keel. The position of the duct intakes would ideally be put in the upper part of the bow, at the stagnation position, so that the air ventilation ducts could also produce some reduction of air drag and increase of air lift as well as reduction of water drag. Since however insufficient data was available on the pressure distribution on the bows the intakes were put at the highest part of the. forebody planing bottom. The ducts were designed for minimum losses of head in the passage from intakes to exits. . ,
The general purpose of this dynamic head ventilation was to show that afterbody ventilation could be considerably improved by the simple introduction of air in a reasonably efficient manner without undue expenditure of energy. The details of practical applications of the results and the effects on stability are left to further investigations.
2 Range of Investigation
•It was customary at the time of writing, to measure water forces on a partial block model behind a screen, so -is to eliminate air interference difficulties.• Tests have therefore been made in three conditions: -
a) screened b) unscreened, without ventilation c) unscreened, with ventilation.
The screened results form part of the general investigation of the effect of air flow on the ventilation of the afterbody, all tests were made on a standard partial model, Fig.1.
The investigation consisted in finding the effect of ventilation, by air flow and duct ventilation, on the resistance, lift, pitching moment and spray characteristics over ?. range of drafts and attitudes. Tests were made by the generalised method10 for the planing range only, i.e. Proude's law was neglected.
The air flow under the carriages was modified by means of flaps to give reasonably 'correct1 air flow conditions. 11 iVeasurements were made on both carriages, Nos. 1 and 2, but only the results on No.1 carriage are given in this report. Results on No.2 carriage confirmed the effect of ventilation but were othervn.se unreliable in absolute value because of drag balance difficulties.
Measurements of air lift and drag were made in air flow with the model just clear of the w:;ter.
Measurements of the air" flow through the ducts were made with pitot static tubf;s, Pig. 5, for different drafts and attitudes over a range of speeds.
Spray conditions were photographed for the condition of zero applied moment for the take-off planing range.
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R.A.E. Report No. Aero. 2143.
3 Description of model
Tests .werts made on a 1 : 19 scaje flat topped resistance model of the Shetland hull. The hull lines and position and dimensions of the ducts are given in Fig.1. Photographs showing a general view and an exploded view of the- model are given in Fig. 2. .
4 Results
The results are presented on a generalised banis in terms of: -
R/A = Resistance/Load on water VAb = Moment aboyt G.G./Load on water x beam V&A /Or [*/ 2v,2 1* wVb = Lift coefficient
draft/beam attitude of keel at main stop.
It is assumed that
R/A, VAb, dA *(*V. *K> i.e. independent of Froude and Reynold's Numbers. The lift efficiency is defined in terns of the relationship between &/b and ^/Cy, which is usually linear at constant attitude. On a simple wedge one would expect the lift to be zero when the draft is aero, Generally ^AV is toton to define draft at any given attitude.
The results for the noael in the unscreened condition will include both air and water forces. In the first instance the results have been presented as total forces i.e. air + water. Later, in paragraph 6, an attempt is made to separate out the ajur f crces.
4.1 Air Prä« and Lift
The results of measurements of the air drag and lift forces on the 1:19 scale model held just clear of the water surface arc given in Table II. Fig3.3 and 4 represent the change in air drag and lift over a range of attitudes and speed for the model hull respectively with and without ventilation. They show that for the model without ventilation there is a change cf air flow conditions in the attitude range ahull = ^° to 60, Tni3 »Uggests that bet-ween these two angles there exists an attitude' at which the air flow separated frda the forebody bottom at the step rejoins the :.fterbody bottom.
Ventilation improves the air flow conditions, smoothing out the lift/attitude curves and reducing the model drag.
4.2 Air flow through the duct3
The results of measurements of air flow through the ducts ore tabulated in Table III for a range of attitudes speed and load on water. Fig3.6 jid 7 represent the variation of air flow with draft and attituc'v-.
The volume of air passing through the duct3 nuiy be conveniently expressed a3 follows: -
If Dj = diimeter of duct b = beam at main step Va = mean speed of air flow over the cross section of the duct V0 = carriage speed or speed of aircraft,
the volume of air passing through two ducts per second is:-
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R.A.E. Report No. Aero. 2143.
2 x % x 2jL x Va
In practice it is convenient to express this volume in non-dimensional units,
volume of air passing through 2 ducts per sec.
°V01 = b2*Vc
cvol = 2 " <• b ' • V
•
which for the hull as tested is:-
^vol = 0.0364 . aA0.
The energy in the air-stream passing through the ducts may he expressed in H.P. by the formula:-
H.P. = (Volume of air per sec.) P . —•- . rrr
where P = 0.002378 slugs/ft. 3 Va = mean speed of air flow in ft./sec.
For the Shetland at 62 knots full scale Va 2
0.01678 . (v~) H.P. (volume of air per sec.)
In Table IV values of VuAci A» Cvol and the volume flow of air and energy at N.T.P. arc tabulated for a range of attitudes at 62 }-nots (full scale). The variation of the volume coefficient with draft and attitude for the.same 3peed is represented in fig.8. It is shown that there is a rapid decrease in .the rate of volume flow between «hull - 4° and 6°. This result is in accordance with the earlier suggested change of air flow conditions in the attitude range.
The volume of air flowing through the two duct3 at 62 knots full scale is of the order 500 cu.ft. per second and the corresponding energy in the air stream 6 H.P.
4.3 Total Resistance Characteristics
The results of measurements of resistance of the Shetland hull model, with and without ventilation, in "correct" air flav conditions on No,1 carriage, and for a screene-d model without ventilation over a range of attitudes, speed, and load on water, are tabulated in Table V as a ratio R/& together with corresponding lift coefficients ^A/Cy. Pig3.9a. 1Oa. 11a and 12a represent the variation of the resistance coefficient (R/A ; with attitude and lift coefficient CWCy).
Comparison of these resistance characteristics for the model with and without ventilation shows that:-
(a) the resistance coefficient /A of a model with ventilation, i3 smaller than for a model without ventilation over the complete range of attitudes and ,"^/Cv from the hump speed, to the take-off speed,
(b) the reduction of-resistance coefficient and draft is less at large values of *CA/CV,
(o) the reduction of resistance coefficients is higher in the range of attitudes <*K • 4°38' to 80381 than at the extreme attitude «K = 10°38«.
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R.A.E. Report No. Aero. 2143.
Comparison of resistance characteristics for a model without ventilation in "correct" air flow conditions and in screened conditions shows that:-
(a) for «K = 4°38' the difference between resistance coefficients is very small,
(b) for attitudes at and above && • 8°38', the resistance coefficients of a screened model arc smaller than unscreened, but at ti£ = 6°3.8' the reverse is the case.
4.4 Total Lift Characteristic:;
The results of measurements of drafts of the Shetland hull model with and without ventilation in "correct" air flow conditions, and for screened conditions over a range of attitudes, speed, and load on water are tabulated in Table V. Figs.13, 14, 15 and Iß represent the change of draft coefficient tyb with lift coefficient cWi ani- attitude.
In Table VII the variation of draft with lift coefficient is represented algebraically by:-
> (Vcy^) + n
where m and n are constants at constant attitude. The range of •^A/Cy for which this relationship holds is also given.
Comparison of the draft characteristics <Vb for the model with and without ventilation in "correct" air flow conditions, shows that:-
(a) the smallest drafts are for a ventilated model, and the biggest for a screened model over the- complete range of attitudes and /CA/CV in Table VII,
(b) over these ranges of VCy *^e draft characteristics may be represented by parallel straight lines for «K constant,
for the ventilated model these lines pc^js through ^Cy = 0 for <"K = 4°/3$', 6°38" and 10°38\ but at «K = 8°38' */b = 0 occurs at ^A/Cy ^0.024,
(d) over the range of GA/CV given in Table VII the slopes of the lints decrease with increase of attitude, except when
w
4.5
«K = 8°38'.
Total Moment Characteristics
The results of measurements of pitching moment -bout the centre of gravity are tabulated in Table V and represented in Pigs. 17 and 18 in terms of the pitching moment'coefficient */A.b, attitude, speed, and load on water.
Comparison of the results shows that: -
(a) the model with ventilation will run .-,t smaller attitudes than the model without ventilation in the high speed planing range, but at higher attitudes on the low speed range when the rear step is immersed,
(b) the model without ventilation in unscreened conditions will run at smaller attitudes than the model in screened conditions for the whole planing runge.
R.A.E. Report No. Aero. 214-3.
(o) the change of pitching moment characteristics which occurs when the aft step just becomes immersed (o^ = 10°38') is altered by ventilation.
Attitude. Draft and Total Resistance for zero applied moment
From the results for pitching moment, draft, and resistance of the Shetland hull model the attitudes, drafts, and resistance char'-cteristics over the range of speed from just before hump speed to take-off speed were estimated for the zero applied moment case. The attitudes for zero applied moment are plotted in Pig.19, and corresponding draft and resistance coefficients in Fig. 20 us a function of speed or speed coefficient
(G, )
Fig.21 represents ibe change of draft and resistance coefficients with lift coefficient *cü/Cy in the planing region.
Comparison of the results shows that:-
(a) from Cy = 3.5 (hump speed) to Cy = 7 the attitudes for a model .vith ventilation are smaller than without ventilation,
(b) above Cv = 7 there exist two values of the attitude at which M = 0 for a model with and without ventilation,
(c) from Cy = 3.5 (hump speed) to Cy =6.1, the screened model runs at higher attitudes than when unscreened,
(<*)
(e)
(f)
00
(h)
above Cv = 6.1 the screened model has two values of the attitude at which M = 0 and in -the region of Cy = 7 the smaller is lower than that for the model with ventilation,
in the range of Ch/C " 0.08 to GA/Cy »0.24, the resistance coefficient ( /ä) is smallest for a modelwith ventilation,
in this range of- ^/Cy, below 0.155, the resistance coefficient for an unscreened model without ven+ilation is smaller than for a screened model, but above '^ü/Cy = 0.155 the reverse is the case,
over the range of C'A/Cy * 0.09 to C'Vcv -0.24 the draft characteristics mry be represented by parallel straight lines
d/b = m . (/CVCV) + n where m and n are constants (tabulated in Table VII).
over this- range of A/Cv the smallest drafts are for a ventilated model, and the highest for a screened model.
5.1 Spray conditions for zero applied r.iunient
Comparative spray photogr-.phs, for the model of the Shetland hull with and without ventilation for zero applied moment, are given in Fig. 22.
Examination of these photographs shows that in the planing region the 3prny is cleaner for a model with ventilation - probably because of the smaller drafts.
If,
R.A.E. Report No. Aero. 2143.
6 Separation of air and water forces
Gott showed that it is pot possible to consider the water flow as independent of the air flow,0 but made a suggestion that, if a dynamic model is very stable, the resistance tests on a screened model are not likely to be much in error.
In order to check this conclusion in the case of the model of the Shetland hull, the force characteristics a3 measured behind the screen, have been compared with those measured in air flow, corrected for air lift and air drag as measured for the model ju3t above the surface of the water.
If Ra = resistance of a screened model A = load on the water for a screened model D = air drag of the model just above the water surface L = air lift of the- model just above the water surface R = total resistance of an unscreened model by, = load 'on the water for an unscreened model Rw = water resistance of an unscreened model for the normal routine
of water resistance measurements Rff = Ä - D Aw = L _ L.
In Table VI values are tabulated of *"/Aw for a model of the Shetland hull with and without ventilation over a Cange of attitudes, together with the corresponding lift coefficients 4/Cy. Pigs. 9b, 10b, 11b and 12b represent water resistance coefficients over a range of attitudes and lift coefficients '^CA/CV for an unscreened model with and without ventilation, and for a model in screened conditions.
Comparison of those resistance characteristics shows that:-
(:0
(t)
(c)
the water resistance characteristics ifor an unscreened model in the range of attitudes <*K = 6°38' and <*£ • 8°38' are much smaller than for a screened model, , . , •
in this range of attitudes for small values of &/Qv differences may bo over l+Ojb and for high values of *Gä/Cv over 6fa,
for attitudes "K = .4°38' and a„ = 10°3K* it is difficult to reach any definite conclusion because of the scattered nature of the points for the unscreened model.
In fact, D and L probably do not represent air drag and air lift for a model running on the surface of the water. rhe3t corrected results were therefore not used for discussing the duct ventilation character- istics.
7 L"i3Cun3ion
The test results recorded in this report may be considered from two points of view, (1) of practical importance, i.e. of how the character- istics of the hull may be improved by dynamic head ventilation, and (2) the general effect of air flow on the water forces.
IJynnmic head ventilation has been shown effoctivo in the following respects. •
(a) It improves the air flow around the model in the regior. oi the change of air flow conditions especially at high speedr- (e.g. for the Shetland hull in the range of attitudes aK = 6°38' to «ft = 8°38').
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. R.A.L. Report No. Aero. 2143-
(b) It reduces the attitude for zero applied moment in the planing condition between the hump and take-off speed. ' For the Shetland hull the average value of reduction being about ^°.
(c) It reduces the resistance and draft of the model, i.e. lifting force at constant draft. •
increases
(d) The reduction of the resistance is particularly marked at high speed and in the range of attitudes where changes of air flow conditions occur.
(e) In the range of attitudes where changes of air flow conditions occur there is a rapid reduction in the volume of the air passing through the ventilating ducts, (for the model of Shetland hull over 20£). This is accompanied by a reduction in the energy of the duct stream of the air from the order of 6 to 3 H.P. at 62 knots full scale.
The general effect of air flow on water forces, based on the tests on screened and unscreened model of the Shetland hull shows that:-
(a) It is especially important in the range of attitudes where changes of air flow condition occur.
(b) The total resistance and draft for a screened model of the Shetland hull are greater than when unscreened.
(c) tfhen corrections are made for air lift and drag forces the water resistance of en unscreened model becomes much smaller than that of the screened one and at high speeds the differences may amount to over lfO?j in the critical range of attitudes.
(d) The air flow reduces the attitudes for zero applied moment by about ^°.
Both the effect of the ventilation ducts and the effect of air flow would appear to correspond to different degrees of afterbody ventilation. Unfortunately there is as yet no data on whet standard of ventilvtion is achieved under full scale conditions.
It is known however that porpoising stability is generally better full scale, although it is as yet not certain whether this is becruse of less severe disturbance conditions or better ventilation. The fact that both trim attitudes and stability limits tend to be lower full scale th.ji model scale appears to point to better ventilation as at least part of the reason.
Model scale, the achieved efficiency of ventilation could be estimated by comparison of the draft characteristics with those of a forebody only. Proposed wedge measurements will provide systematic data on this aspect, but full scale generalised data on stability and force characteristics are essential for scale effects.2
8 Recommendations for further work
Results of the experiments described in this report show that even for the comparatively stable hull form of the Shetland there is considerable interaction between the air and water flow under the afterbody. It has been shown earlier that resistance measurements made on an unstable model behind a screen are of doubtful significance because of air-water interference^, ::in& xt now appears that screened measurements on fairly stable hull3 may also be doubtful. There is how- ever little quantitative data on the nature of the air flow and its inter- action with the water flow. This will be obviously dependent on both
- 12 -
.,
R..A.E. Report No. Aero. 2143.
the air flow conditions and the hull form and in particular the degree of ventilation of the afterbody.
The following series of tests are recommended to measure and understand better the characteristics of* ventilation \nd interference.
(1) Stability and trim tests with trie dynamic model of the Shetland using (a) the same dynamic head ducting used on the resistance model (b) an external air supply in order to obtain comparison with model and full scale measurements.
(2) Repeat force measurements on -the resistance model with a faired superstructure to reproduce more representative air flow conditions over the afterbody, and xn addition tests with an external air supply. The effect of wings end slipstream might also be looked into and examined if* found important.
(3) Measurements of the air prt-ssure distribution on the hull for both selected dynamic and resistance model te3t conditions of (1) and (2).
(4) Wind tunnel measurements of the nir forces acting on a hull in the presence of ground over c range of attitudes ind dr?J"t3, and in the presence of v/ings and slipstream. This is to provide evidence on the validity of the air iift end drag corrections based upon measurements made just clear of the writer.
9 Conclusions
It is concluded from tht.se tests that at a given speed and lo.d on water ventilation of the afterbody "bottom of the Shetland hull by dynunic head pressure, reduces the resistance and draft of the hull approximately ten per cent (model tests) over the whole planing range. For zero applied moment there is a corresponding increase in the lifting force of the hull and a reduction in attitude of h .If a degree. This reduction of resistance and increase of lifting force is of the same order as calculated for the "Empire" bo:.t, issuming th-.t the measured air suctions on the afterbody bottom were removed. It was also found that natural ventilation due to the presence of normal air flow has a big but unknown influence on the water forces.
To understand better the nature of the air flow and its interaction with the water flow it is recomraended that further experiments be made to measure ,
(1) the pressure distribution, the total forces, porpoising stability and trim for different degrees of ventilation.
(2) air forces acting on a hull for different attitudes, drafts and speeds.
- 13 -
R.A.E. Report No. Aero. 2143.
Angles;
«a°
ß°
A °
LIST ÜF SYXBJIS
attitude relative to the forebody keel afterkeel angle relative to the forebody keel
overall deadrise angle deadrise angle at keel doadrise angle at chine mean doadrise angle
Lengths:
Forces:
b b' a la.
R
R« D L A. A A.
Pressures P Pin
Aloment: K
Velocity:
va
Acceleration: g
Density: w P
SUUSBLi H.P
Coefficients:
R/A d/b M/Ab
bean local beam draft diameter of front part of ventilated duct distance aft from main step along datum line of hull distance beamwise from central line of hull
total dri.g of hull afterbody drag due to pressure distribution on bottom air drag air lift load on the water at rest load on the water afterbody lifting force due to pressure distribution on afterbody Force on afterbody bottom due to pressure distribution
local pre33ure mean pressure
= pitching moment about CG.
speed of aircraft or towing carriage 3peed of local uir flow
= acceleration due to gravity
= density of sea .water • 64.4 lb./ft. 3 = density of air '= 0.002378 slugs/ft. 3
• energy in the air-strean passing through ducts in H.P.
„A =
CA =
• = velocity coefficient (Froude Number) rg.b
w.b3
A
w.b3
= static beam loading coefficient
= beam loading coefficient
resistance coefficient draft coefficient pitching moment coefficient
- 14 -
'VCv
°vol
R.-i.E. Report No. Aero. 2143.
LIST oF SYMBOLS (Cont'd)
A (W.v2.b
2)2 = lift coefficient
R-R^ A-Ar ( R "*) . (~~S ) . 100 = percentage reduction of
drag due to removing suction on afterbody bottom
Volume of air through 2 ducts per sec.
b2.Vc
No. Author
1 A.G. Smith H.G. White
2 a.G. Smith
3 I.iV. iicCaig ff.M, Inverarity
4 J.R. Dawson
5 G.L. Fletcher
6 H.G. rfhite
7 C.B. Baker
8 G.P. Gott
E.J. ?.'j • • A.G. Smith R.-i. Shaw •*'. JAorris
10 «V.J. Reinora
11 K. Tomaszewski S. Raymond G.F. Ohalmnra
REFERENCES
Title, etc.
A review of porpoising instability of seaplanes Report No. H/Res/173. A.H.0.77M. February, 1944.
.in examination of some problems of large seaplane design and methods of investigation Tech.Note No. Aero. 1748. -i.R.C.9405. Jan., 1946.
The water stability of the "Coronado" flying boat Report No. H/Res/176. ^.R.C.8063. Aiay, 1944.
Tank tests of two models of flying boat hulls to determine the effect of ventilating the step N.XUC.ü. Tech.Note No. 594.
Tank test on the water stability of the supermarine Sea-ütter. Report No.Aero. 1927. ...R.C.7851. iViarch, 1944.
Note on Air lubrication of seaplane hulls Report No. H/Res/170. February, 1944.
Tank test on a model of the "Empire" flying boat Report No. B.A. 1678, A.R.C.5213. M»y, 1941.
Interference between *.ir Flow -Jid Vater Flow in Seaplane Tank Testing. Aerö. Tech. Note 1460. ii.R.C.7906. July, 1944.
rfater performance of Sunderland R.4774 with step fairing. Report fl/Res/l40. December, 1940.
-i generalised method of examining the hydrodynamic force characteristics of seaplanes planing on the water surface Report No. Aero. (Unpublished).
The _iir Flow under the towing carriages in the R....E. Seaplane T'-nk Tech.Note No.Aero. 1743. June, 1946.
15 -
R..-..E. Report No. Aero. 2143.
Attached:- Bras. 19111 - 19H0T, Neg3. 69371 - 69374 Appendix I Tables I - XI.
Circulation: - C.S.(A) D.G.S.R.(A) D.S.R.(A) A.D.A.H.B.(Res.) (.tction copy) A.D.S.R. (Records) S.D.D.A.R.D. P.D.T.D. R.T.P./T.I.3. (110 + 1) IJ.D.A.R.D. (Serv. ) D.D.A.R.D. (Ci.-.) D.D.R.D. (Perf.) A.D.R.D.S. A.D.R.D.N. A. & A.E.S. M.A.E.S. (2)
(40) A.R.C.
16 -
E.-i.E. Report No. ,-j.ero. 214-3-
.-LPFEHDIX I
Calculation of the possible reduction of drag of the "Empire" boat at 57 knots full scale by removing air suctions from the
afterbody bottom. •HH
In research on afterbody bottom ventilation it is very useful to know the possible reduction of drag by removing the air suctions on the afterbody bottom. Prom work done in the R.^.E. seaplane tank''0 on the "Empire" boat calculations have been made for one speed (57 knots - full scale).
Prom reference 8 and unpublished data the pressure distribution w-os determined for attitudes 5°, 7° and 9° on the afterbody bottom of the "Empire" boat. Pig.23 represents the location of the pressure points and table VIII values of the pressure for the 1 : 16 model at 24 f.p.s. For each lateral section of the afterbody bottom the pressure distribution was plotted as sbxnvn in fig. 24. The mean values of the pressure for each section were found using a planimeter and are tabulated in Table IX. Table IX also gives the mean values of the pressure components, in the plane of symmetry of the hull, pm . sin f). °'/b, where b' is the local beam, and b the beam at the step. In fig. 25 the variation of these components along the afterbody keel line is plotted for attitudes 5°» 7° and 9°. The resultant forces normal to the afterbody vrere then found by means of a planimeter. These forces and their horizontal and normal components to the water line are given in table X.
If R, A are drag and load on water for the "Empire" boat hull with - suction on the afterbody bottom*, and Ra and && drag and lifting force on afterbody bottom due to the suctions, as tabulated above, the drag of the hull without suctions vri.ll be:-
R» « (R-Ra) . (-p)
and the percentage reduction of drag by removing suctions on the afterbody bottom: -
II
n = 100 = (1 f) Sv (1 " X) 100
The results given in table XI show that forihe ''Empire" boat at 57 knots the possible reductions of total drag are:-
5° more than 6£ 7° more than 10/:- "I
17
' R.-1.E. Report No. Aero. 2143«
T.3LE I
Particulars of Ventilated Shetland Hull
Model Scale 1:19 '•-""
All up .Weight 120,000 1b.
Static Beam Loading Coefficient C^ 0.96 •
Beam (at step) b = 12 ft. 6 ins» : ""
Forebody + Beam, Ratio 3.5 (reference to point of step)
Afterbody + Beam, Ratio 3.3 " "
Unfaired Step Depth % of Beam (at keel) -
Centre of Gravity Position;
Above Datum at Main Step 16 ft. Forward of Step Parallel to Datum Line 5 ft. 2 ins.
Keel.Angle to Hull Datum 2°38'
Afterkeel Angle to- Forebody Keel 7 35'
Step Included Angle in Plan 136°
\
Deadrise Ancle on Forebody at Aiain Step:
Deadriae Angle at Keel ©K = 30°
Destäriae Angle at.Ghina...8x, = 15° '"
Mean Deadri3e Angle . 0m = 25°- - ."" -
The shape and position of ducts relative to the 'hull is'given in Fig. 1.
18
R.A.E. Report No. xiero. 2143.
TABLE II
Air Lift and Air Drag for 1:19 Scale Shetland Hull Measured .just clbar of the Water on No. 1 P.. i.E. Carriage.
Model Scale I b =. 7.88" . ^ 0 Speed
vith Ventilation Vithout 1 /entilation vc Keel
(f.p.3.) Lift Drag Lift Drag
U»" Vgxb (lb.) (lb.) (lb.) (lb.)
2°38' 0.02 0.14 40331 0.15 0.02 0.14 0.10 6°38' 16 0.15 0.02 0.17 0.15 3.49 8°38' 0.15 0.02 0.16 0.17
10°38' 0.15 0.02 0.19 0.13
2038' 0.31 0.13 0.36 0.23 4033. 0.35 0.13 0.36 0.28 6°38' 28 0.41 0.13 0.46 0.42 6.10 Q°3S' 0.43 0.13 0.41 0.35 10O381 0.45 0.13 0.50 0.37
2°38' 0.43 0.43 0.53 0.35 4033. 0.50 0.40 0.53 0.40 6°38' 36 O.65 0.38 O.67 0.59 7.85 8°38' 0.70 0.43 0.59 0.45
10°38' 0.75 0.43 0.71 0.54
T.3LE III
Velocity Measurement of ^ir Flow through Duct with Different Drafts and .ittitudes
«K° Keel
Model (b = 7
Scale .88")
va nr Flow Sueed _ _. . . _ ... —-=.- : r"—• for Pitot Position: Vc Carriage Speed
Speed
(f.P. s.)
Load on water A (lb.)
1 2 3 4 5
2°38' 5.5 0.172 0.92 1.03 1.01 _
4°38' 5.5 0.172 0.98 1.05 1.04 - - 6°38' 16 5.5 0.172 0.97 1.03 1.02 - - 8°38' 5.5 0.172 0.95 0.98 1.01 - -
10°38' 5.5 0.172 0.92 0.92 0.96 - - 4° 38' 10.1 0.155 < .7- 1.01 0.98 0.88 0.75 6°38* 24 8.9 0.146 0.95 0.90 0.88 0.86 0.71 8038' 7.5 0.134 0.75 0.77 0.80 O.63 0.42
10°38' 6.2 0.122 0.78 0.74 0.81 0.70 0.46 2038' 5.5 0.098 0.9P 0.98 0.94 - - 4038' 5.5 0.098 0.89 0.91 0.88 - - 6°38' 28 5.5 0.098 0.84 0.88 0.85 - - 8038' 5.5 0.098 0.85 . 0.86 0.80 - -
10°3R' 5.5 0.098 O.83 0.87 0.85 - - 2°38 • 5.5 0.076 0.99 0.98 0.96 - - 4°38' 5.5 0.076 0.88 0.38 0.86 - - 6°38' 36 5.5 0.076 0.85 0.84 0.82 - - 8°38' 5.5 0.076 0.85 0.83 0.81 - -
10°38' 5.5 0.076 0.90 0.91 0.89 ~
19 -
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R.A.E. Report No. Aero. 2143.
TABLE VI
,.ater Resistance Characteristics of Shetland Hull with and without Ventilation (Corrected
for Air Drag and Air Lift Forces)
0 aK Keel
Speed of iodel
(h = 7.88"]
(f.D. 3.)
;.ith Ventilation without Ventilation
ST Ew
4°38' 6°33' 8°38'
10°38'
12
0.218 0,201 0.202 0..222
0.338 0.332
. 0.324 0. 320 .
0.234 0.205 0.197 0.216
0.341 0.332 0.327 0.320
6°38' 8Ö38'
10°38' 16
.0.185 0.189 0.219
0.237 . 0.229
0.220
0.182 0;187 0.221
0.236 0.229 0.220
6038' 8°38'
10°38' 20
.0.161
.0.195 0.232
0.175 . 0.166
0.157.
0.155 0*185 0.242
0.174 C.166 0.156
40331 6°38' 8°38'
10°38'
24
0.190 0.166 0.198 0.236
0.143 0.133 0.122 0.110
0.208 0.151 0.189 0.216
0.143 0.133 0.121 0.109
4°3&' 6°39' 8°38'
10°38'
28
0.207 0.177 0.209 0.349
0.111 0.100 0.086 0.071
0.208 0.157 0.188 0.373
0.111 .0.100
0.082 0.071
4°38' 6°36' 8°38'
32 0.262 0.192 0.214
0.076 . 0.070 0.051
0.291 0.156 0. 305
0.079 0.070 0.052
4°38' 6°38'
36 0.202 O.I67
O.063 • 0.041
0.293 0.196
0.063 0.041
'^äBLE VII
'ilgebraical Representation of Variation of Draft with Load on »Vater and Speed over a Range of Attitudes
«K° Keel
*-*x^*n The Range
of ^
. ipplicable
ffith Ventilation
Without Ventilation
Without Venti- lation Screened
m n m n 91 n
4°38' 6°38' 8°38'
10°38' Zero Applied Moment
0.0113 0.0095 0.0103 0.0083
0.0072
0.000 0.000
-0.022 0.000
0.034
0.0113 G.OO95 0.0103 0.0083
0.0072
0.010 0.018 0.000 0.014
0.047
' . • 113 0.0095 0.0103 0.0093
O.OO72
0.017 0.029 0.009 0.021
0.054
O.O9O-O.145 0.075-0.180 0.055-0.230 0.075-0.220
0.090-0.240
- 23 -
it.A.E. Report No. Aero. 2143.
TABLE VIII
Air Pressure Distribution on Afterbody Bottom of 1 : 16 scale "Empire" boat, measured at 24 f.p.a.
Pressure Point
No. b b
p = pressure (lb •/ft.2)
a=5° Ra 7° R. 9°
1 19 10
0 0.478 0.840
0.275 -0.7224 -0.8004 -0.9044
-0.8056 -0..9303 -0. 8836
-0.7224 -O.8264 -0.7380
2 20 11
0 0.464 0.783
0.869 -0.6185 -.0.7796 -0.6757
-0.8056 -1.0083 -0.7588
-0.4781 -1.0707 -0.5093
3 21 12
0 0.435 0.739
' 1.420 -0.4796 -0.5925 -O.4574
-0.5977 -0.8004 -0.5509
-0.5041 -O.5509 -O.4262
4 22 13
0 0.466 0.681
2.017 -O.2390 -0.3742 -0,0259
-0.2806 -0.5405 -0.2705
-O.4366 -0.3690 -0.5200
5 23 14
0 0.377 O.638
2.580 -0.1351 -0.2599 +0. C200
-0.1559 -O.4366 -0.2599
-0.2806 -O.4678 -0.4262
6 24 15
0 0.333 0.579
3.119 -0.1455 -0.2027 +0.0416
-0.1671 -0.3014 -0.1871
-0. 2806 -0.3846 -0. 3950
7 " 25 • 16
0 0.319 0.522
3.739 -Ö.1351 -0.2287 +0.0520
-0.1871 -O.291O -Ü.1871
-0.3326 -0.3534 -0. 3742
8 26 17
0 0.304 0.493
'4.334 -0.2080 -0.2495 -0.0104
-0. 2599 -0.2495 -0.1871
-0.3638 -0.3534 -0.3118
9 27 18
0 0.275 0.420
4.869 -0.2183 -0.2599 -O.1663
-0.2390 -O.3OI4 -0.3534
-0.3599 -0.3326 -0.0000
24 -
R.A.E. Report No. Aero. 2143.
TABLE IX
Variation of Hean Air Pressure Along the Afterbody of 1 : 16 Scale "Empire" Boat at 24 f.P. s.
Pressure Point
No.
Pn (lb./ft. 2) Pm x aiz] ß x bl (lb./ft.2)
a = 5° a = 70 a = 90 a = 50 a = 70 a x 90
1,19,10 -0.9317 -1.0349 -0.9526 -0.7814 -0.8680 -0.7986 2,20,11 -0.8165 -1.0775 -0.7499 -0.6727 -0.8878 -O.6179 3,21,12 -0.5118 -0.6680 -O.4932 -0.3939 -0.5141 -0.3795 4,22,13 -0.2634 -0.3894 -0.4884 -0.1884 -0.2765 -0.3493 5,23,14 -0.1944 -0.2874 -0.4110 -0.1282 -0.1893 -0.2706 6,24,15 -O.I59O -0.2600 -0.3900 -0.0936 -O.1530 -O.2226 7,25,16 -O.I736 -0.2789 -0.4200 -0.0938 -0.1508 -O.2271 8,26,17 -0.2175 -0.2828 -O.4279 -O.IO32 -O.1342 -0.2030 9,27,1S -O.234O -O.3233 -0.3006 -0.0972
' -0.1344 -0.1249
TABU-: X
Drag and Lift on Afterbody Bottom on 1 : 16 Scale "Kmpire" Boat at 24 f.P. B. Due to Air Pressure Distribution
ix *-° - a„° P
(lb.) 2 P x 0 _ lb.)
A Ra = P x sin («K° " ?a°) ObJ
5» 70
2°30' 0030'
-1°30'
0.252 0.336 0.319
0.252 0.338 0.319
0.011 0.003
-0.008
TABLE XI
Possible Reduction of Drag for Full Sale "Empire" Boat at 57 Knots by Removing Suction on Afterbody Bottom
0 a
R (lb.) (lb.)
Ra. (lb?) (Ibf)
E A R' = • K (lb.)
n« *• z ioo# K " A _ A a
5° 7° 9°
5570 3359 2867
17203 13926 10649
45 12
-34
1033 1384 1305
1.064 1.110 1.141
5194 3014 2543
6.7 10.2 11.3
25
Nf 1*1111. MMRT Af M II«
FIG. I.
® » 1 1: :S |i ®
r- -
8' i 1 r- *
5 • » o m i_ 1 & • S
© in i 1 s • • 3 * S
® Ü ! 1 0 • t N Ml •. . | Z 8
<=> 8« II • > > »j I 3
® » <i
; i e • • t» • •
® 5- •> 0
! « 1 1 1 1 ®
> S 1 TjTi <r)
1 « 1 I i 1 ® 5 • 1 » 1 i I l
® in *
5 • i ä 1 i i i ® W 4
fit • a 1 I i 1
® m 4
i ä > a 1 I i 1
® <• * 3 S > a 1 I i i
© w <
9 S 0 1 l 1 1
• o
I -J 1 I «* d •> or l_ t.
«
8
2
5
FIG. 2
GENERAL VIEW AND EXPLODED VIEW OF HULL WITH VENTILATION DUCTS
'FsT? I 9 5 4«
I9.»9U2.S:
REFT.AE.RO 8J4-3.
FIG. 3.
0-5
WITH VEVT " -
0-4- /
Ifl -J
00-3 <
a tf 0-2
0-1
2° 38
/
Itf V 38' " 6° S8' Y 8-38'
JO» 38',
MEMH CURVE
+^
0-Q •«"""""" V F.PS.
5 2 0 2 5 3 0 3!
AIR DRAG OF MODEL SHETLAND HULL ON R.A.E. Nol TOWING CARRIAGE.
(MODEL JUST CLEAR OF WATER.)
49)tJJ3.Sf
VENT. WITHOUT VENT.
AERO 2143.
FIG-3-CONTD.
AIR DRAG OF MODEL SHETLAND HULL ON R.A.E. No.l TOWING CARRIAGE.
(MODEL JUST CLEAR OF WATER.)
M0.19H4.S.
REPT. AERO 214-5.
FIG.4.
£^^b 8
AIR LIFT OF MODEL SHETLAND HULL ON R.A-E. No.| TOWING CARRIAGE .
(MODEL JUST CLEAR OF WATER)
.Npjtyjs.«; REPT. AERO 214-3.
FlG-4- CONTD.
AIR LIFT OF MODEL SHETLAND HULL ON R.A.E. No.I TOWING CARRIAGE.
(MODEL JUST CLEAR OF WATER)
W.W&A
1 in
u> ö
t in r- 6
<•> s Ö
CVI 8 ö
— o o o
1-
i *k
REPORT AERO 2143.
FIG. 5.
to l—
2
UJ
INOJSIZ.JI
\4 _ AIR SPEED THROUgj DUCT Vfe " SPEED OF AIRCRAFT!
REPORT AERO 2143.
FIG. 6.
VARIATION OF AIR FLOW THROUGH DUCT WITH
DRAFT AT CONSTANT ATTITUDE.
»IMA REPORT AERO 2143.
FIG. 7
VARIATION OF AIR FLOW THROUGH DUCT WITH ATTITUDE AT CONSTANT LIFT COEFFICIENT.
N9.I.9U?**- REPT. AERO 214-3
FIGS. 8,9- 0-16
O- 14
OI2
0-10
O-0810-015
VARIATION OF AIR FLOW FOR TAKE-OFF CONDITIONS AT 62" KNOTS (FULL SCALE)
EEZZI3 FIG.9.
0-3
A) TOTAL RESISTANCE CHARACTERISTICS OF
SHETLAND HULL AT 4° 38'ATTITUDE.
B) WATER RESISTANCE CHARACTERISTICS OF SHETLAND HULL AT
4° 38' ATTITUDE (WITH CORRECTION DUE TO
AIR DRAG AND AIR LIFT FORCES.)
NOJ9J20.S.
6+0
R
0-35
CK50
025
020
015
KK-6'38'1
REPT. /kERO 214-3.
_FIG. IO.
— WITH VENTS. • WITHOUT VENTS
* WITHOUT VENTS (SCREENED)
A) TOTAL RESISTANCE CHARACTERISTICS OF SHETLAND HULL AT 6° 38' ATTITUDE.
0-3
02
0-1
R S
T I*K-6'3»'| X
H— WITH VENTS. •._ WITHOUT VENTS.
— WITHOUT VENTS (SCREEN ED]
B) WATER RESISTANCE CHARACTERISTICS OF SHETLAND HULL AT 6° 38' ATTITUDE (WITH CORRECTION DUE TO AIR DRAG AND AIR
LIFT FORCES.)
M9I2I.S.
0-3
0 2
locwB'aa-l
REPT AEfcO 214.3.
~~ FIG, »I. WITH VENT, WITHOUT VENT. WITHOUT VENT. SCREENED
A) TOTAL RESISTANCE CHARACTERISTICS OF SHETLAND HULL AT #38' ATTITUDE .
0-4-L
0-3
0-2
R
Essm -+ WITH VENT. -^— WITHOUT VENT.
•-X WITHOUT VENT. SCREENED.
B) WATER RESISTANCE CHARACTERISTICS OF SHETLAND HULL AT 8f 38' ATTITUDE.
(WITH CORRECTION DUE TO AIR DRAG AND LIFT FORCES)
NP.I9IJ52.S
0-4
0-3
REPT. AERO 2)4-3.
FIG. 12.
II 0^^-10*381 «WITH VENT.
—® WHOUT ÄNT. —•*•• — WtTHOtfT VENT SCREENED
A) TOTAL RESISTANCE CHARACTERISTICS OF SHETLAND HULL AT itf 38' ATTITUDE .
0-2
B) WATER RESISTANCE CHARACTERISTICS OF SHETLAND HULL AT IO° 38' ATTITUDE (WITH
CORRECTION DUE TO AIR DRAG AND LIFT FORCES).
1*123.5.
0*2
4
01
<te-
l^^4-38'l
0 /7s
i
REPT. AERO 2143.
FIGS. 13,14. FIG. 13.
1- WITH VENT. &• — WITHOUT VENT. X WITHOUT VENT. SCREENED.
TJT I Cv 1 -
LIFT CHARACTERISTICS OF SHETLAND HULL AT 4° 38' ATTITUDE.
oL
lcCt-6' »'
I •WITH VENT.
WITHOUT VENT. •*--— WITHOUT VENT. SCREENED,
FIG.I4-.
0-2
LIFT CHARACTERISTICS OF SHETLAND HULL AT 6° 38' ATTITUDE.
f;N9.l*t24.ft. REFT. AERO 214-3.
FIGS. 15,16. FIG.I5.
LIFT CHARACTERISTICS OF SHETLAND HULL AT 8' 38' ATTITUDE.
* r FIG.16.
LIFT CHARACTERISTICS OF SHETLAND HULL AT IO° 38' ATTITUDE.
>jo 19125. S.
Axb
05-
0 4-
0 3
02
0 1
00-
01
02
0-3
04
05
M TOTAL MOMENT I Axb * LOAD ON THE WATER X BEAM |
REPORT AERO EI43.
FIG. 17
1 WITH VENT
« WITHOUT VENT * WITHOUT VENT SCREENED
t
MOMENT CHARACTERISTICS OF SHETLAND HULL AT 4°38' AND 6'38' ATTITUDE.
N?.J9l2fi.Ä REPORT AERO 2143"
FIG. 18.
-O'S -0-4
MOMENT CHARACTERISTICS OF SHETLAND HULL
AT 8°J8'AND IO° 38' ATTITUDE.
NOJSK7S
REPORT AERO 21*3.
FIGS.I9CZO.
S 10is » 2S35~33 r.PS. "^v
FIGI9 ATTITUDES FOR ZERO APPLIED MOMENT(Ns| CARRIAGE.)
F.RS.
FIG2O.T0TAL RESIST-CLIFT CHARACTER^OF SHETLAND HULL FOR TAKE OFF WITH ZERO APPLIED MOMENT (N2 I CARRIAGE)
N01SI28.S.
REPT. AERO 214-3.
FIG.2I.
TOTAL RESISTANCE AND LIFT CHARACTERISTICS OF SHETLAND HULL FOR
TAKE OFF WITH ZERO APPLIED MOMENT. (No. I CARRIAGE)
WITH VENTILATION FIG. 22.
WITHOUT VENTILATION
«EL 5 SO C=OM C¥« 1-745 oc KEEL s'js' C4- 0-82
•e KEELS'SOC,» OK C,» 1-745 _ <* KEEL 5*3 6' Ca » 0-82
o^jEEL SV C4 - O • 72 C„ • frM g KEEL •' 20' C, . O • 72
oc KEEL 8 14 Cj- 0-72 C, • 2-62 =c KEEL l'jo'c.. 0-72
SPRAY CHARACTERISTICS ON CALM WATER WITH & WITHOUT VENTILATION FOR ZERO APPLIED MOMENT (NO 2 OARUSE)
; mmnw, i.i» -
r
FIG22.CONT
»,
> WITH VENTIWTION WITHOUT VENTOTTON
^^TJ B
«KEEL£|VJC»« 0-72 Cv«2tt « KEEL S'ZO'C.B 0-72
«B. I0*e'ca« 059 C, « 3 49 «c KEEL 10*32 C4 • o- 39
«EL9*29'Ca» 0-30 Cv'436 « KEEL 9*14 CA= 0-49
SPRAY CHARACTERISTICS ON CALM WATER WITH & WITHOUT VENTILATION FOR ZERO APPUED MOMENT (N<> 2 CARRIAGE.)
fSSSESPJSSrl «1*74 IT*H«|
WITH VENTILATION
FIG.22.CONT. WITHOUT VENTILATION.
I
g KEEL S*SO' C4 • 0-41 C« HO « «ML 6*2' C» » 0-41
«e KEEL 3'ZO' C„ = 0-33 Cv • 7-65 «e KEEL 3*3»' C4 « 0-34
SPRAY CHARACTERISTICS ON CALM WATER WITH & WITHOUT
VENTILATION FOR ZERO APPLIED MOMENT (N° 2 CARRIAGE.)
! fWMWWG HPK • '«'» w f. ! 63J7i
N9-JBIÄÄ
•
REPORT AERO 2143.
FIGS.23C24.
FIG 23 LOCATION OF PRESSURE PLOTTING POINTS ON
AFTERBODY BOTTOM OF "EMPIRE" BOAT.
FIG. 24 TRANSVERSE PRESSURE DISTRIBUTION ON AFTERBODY BOTTOM AT STATION CORRESPONDING TO POINTS 12, 3 AND 21 AT 24 F PS. ON 1:16 SCALE
"EMPIRE* BOAT.
NO.I.SßQiS. REPT. AERO 214-3.
FIG.25.
MAIN STEP.
LONGITUDINAL PRESSURE DISTRIBUTION ON AFTERBODY BOTTOM OF 1-16 SCALE MODEL OF
"EMPIRE* BOAT AT SPEED OF 24 F.P.S.
RESTRICTED TITLE: A Preliminary Examination of Hull Afterbody Ventilation
AUTHOR(S): Tomaszewski, K. M.; Smith, A. G.; Chalmers, G. F. ORIGINATING AGENCY: Royal Aircraft Establishment, Farnborough, Hants PUBLISHED BY: (Same)
ATO- 9048
(None) OalO AODtCT NO.
AERO-2143
July ' 46 Restr. Eng. HBfl lUUITOATlOKS
49 I photos, tables, graphs ABSTRACT:
Measurements of air and water forces and air flow through hull ventilating ducts were made for a range of attitudes and drafts in the planing region with model under various air flow conditions. Tests indicated that for given speed and load conditions, ventilation of afterbody bottom of the Shetland hull by dynamic Bead pressure reduces resistance and draft of hull approximately 10% over whole planing range.
DISTRIBUTION: Copies of this report may be obtained only by U.S. Military Organizations SUBJECT HEADINGS: Hulls - Afterbody - Ventilation (49698.12) DIVISION: Water-borne Aircraft (21)
SECTION: Planing (4)
ATI SHEET NO.: R-21-4-1 Air Documonts Olvtilon, Inrolllnonco Department
Air Matortol Command Old TGCHNICAl INDEX
RESTRICTED WrtfjhNPattoreon Air rorco OOH
Dayton, Ohio
TITLE: A Preliminary Examination of Hull Afterbody Ventilation
AUTHOR(S): Tomaszewski, K. M.; Smith, A. G.; Chalmers, G. F. ORIGINATING AGENCY: Royal Aircraft Establishment, Farnborough, Hants PUBLISHED BY: (Same)
ßTO- 9048
(None) OHIO. naBtcf NO.
AERO-2143 fUnilSrtlNO AOENCY NO.
(Same) Don
July ' 46 DOC OAS3. COUNTCT Restr. Gt. Brit.
IAKGUAOI pAoa
49 ItUUtTOAnONS
photos, tables 1 graphs ABSTRACT:
Measurements of air and water forces and air flow through hull ventilating ducts were made for a range of attitudes and drafts in the planing .region with model under various air flow conditions. Tests indicated that for given speed and load conditions, ventilation of afterbody bottom of the Shetland hull by dynamic dead pressure reduces resistance and draft of hull approximately 10% over whole planing range.
ru \&
JMQV li DISTRIBUTION: Copies of this report may be obtained only by U.S. Military Organizations
SUBJECT HEADINGS: Hulls - Afterbody - Ventilation (49698.72) DIVISION: Water-borne Aircraft (21) SECTION: Planing (4)
ATI SHEET NO.: R-21-4-1 Air Documents Division, InTcilinonco Doportmont
I Air Moloriol Command AIB TECHNICAL INDES Wrlghr-Pattoroon Air Porto Qa.o
Dayton, Ohio
