Low & Slow Issue 18 1972

LOW & SLOW 18

' PSEUDO-ORNITHOPTER PROPULSION' (unabridged) written by Grant Smith, If you want to technically pursue this topic with the autlnr, yau may contact him at 2597 Klngstowne Dr., Walled Lake, Michig,m.

Abstract It is pos5:ible to simulate ornithopter operation in a ri~id light weight airfrarre by: vertically shifting the operator's center of gravity while the aircraft follows a cyclic flight path.

This creates a relative motion between the aircraft center of gravity and wing surface which allows a propulsive work input to the system witliout the weight and complexity of jointed wings or pedal-propeller drives. A simplified mathematical model is presentedwhich allows performance estimates based upon assumed pilot input. Indications are that pseudoornithoper proP,ulsion may be a suitable method for propelling man-powered aircraft as 1t allows reductions in the ~ight and complexity of the aircraft while providing a large effective propulsive area coupled with low drag whi e coasting and an effective means of providing arm power assist in a single place aircraft.

Notes to Members: Your new Self-Soar Association address: P.O. Box 1860, Santa Monica, CA 90406 Please direct all correspondence to the above address. However, you are now invited to visit your new headquarters, your Self-Soar Development, Evaluation, Research, and Testing center, known as "S-SA DERT" center--- with the tone that we aim to fly well with the least..... with the least of our brothers and with the least amount of dust and dir_t manufactured into · self-soaring systems. (( that's right: high technology carbon filament as well as ;-e-cycled t;-ash technology.))

S-SA DERT at :1534. Fifth St., Santa Monica, California.

Please use the box number-for corresf!ondence. Phone number willbe given as soon as we get it. Advances processed through S-SA DERT will be published in L(!W &;.SLOW regularly. ANNOUNCEMENT: It is firm now that oar L&S will change its size to 8" x 10" pages and give at least twice as much information as in issu~s 1 through 24. Issue 25 will be titled JANUARY,1973.

S-SA DERT has reviewed all available Rogallo plans in the two most popular categories in orde;- to offe;- plan ::;eekers the best plan in these catego;-ies, The top choices will be retailed by S.SA at 15 each. If YOU come up with a plan better than these two, then we will offer yours instead; the beginne;- desiring a Rogallo plan bas desired tbis·service /;-om Self.Snar, so we will maintain this service. If and when other types become popular, then S-SA will . ehoose a.best among all plans offered in ·the new category. We .will not give this kind of attenticini until there is more than 5 different commercial centers offering plans to new people for a particular type of self-soaring flight system. Choice will be made according to ,the plan •s maximum satisfaction potential.

See L&S 19 for the article "PLAN REWARD" for a list of how our movement's plans can be improved.

S-SA's top choice selection for the present in two popular categories: S5 for the sharp-nosed triangular weigblshift-only control type of Rogallo hang-gli,Jer. Plan and catalog included.

S5 for plan and catalog for the selected plan best presenting a way to go on the high aspect ratio spoiler-weight-shift control Rogallo. This is slower type .... a perfected plan finalizing the type presented in L&S 12.

a

These two plans were selected from over 30 plans offered fo;- sale by vario1115' new self-soaring commercial people.

S-SA does not get any kick-back on sales of parts sold through the catalogues that come with the above plans. The catalogue simply represents to us that the plan offer has a higher satisfaction potential. The plans can be executed without buying anything else from the catalogue, but some people want the option. Plans. will continue to be published in L&S when people ;-elease their copyright to L&S, which we encourage. S-SA DERT will also produce plans for L&S.

PREFACE TO THIS ISSUE Although we all won't be able to follow all of the presentation here given by GRANT SMITH, be assured that you should not forget to return to this concept termed "P-0". Joint-less pumping of mechanical systems is not new, but successful approaches for man-flight is new. We applaud Grant Smith for his persistence in trying to fly man-powered without propellers and without wing-flapping.

Pseudo means false, "It's not nice to fool mother Nature ..... trying to flap without flapping". Self-soaring cannot but gain from In L&S we once referred a serious consideration of P-0 propulsion to a project called 56301 for vertical man-powered flight only, a modified p.Q system. Grant shows us how we might extend oar glides in possibly any self-soar system. Please s~nd your ideas to Editor: Low & Slow, at P.O. Box 1860, Santa Monica, CA 90406 We will expand on t.his p.Q business as experiments show us direction. Try it, tell it. So help.

Copyright

© by Joe Faust, 1972

7

TABLE OF NOTATION

w X

Aircraft gross weight - pounds Maximum vertical center of gravity shift - ft

Effective center of gravity shift - ft The acceleration factor gross weight rrrust be multiplied by to determine the actual load aero dynamically supported u,d,r, Subscripts used to denote the up, down, or rest stroke, or (x) any stroke in general or x Acceleration of the system center of gravity-ft/sec2 a Time duration of the subscripted stroke - sec t Coefficient of lift S, Coefficient of drag with subscripts p for profile and i CD for irrluced drag Aspect ratio IR V Velocity - ft/sec Air density - pounds/ft3 '°r, Ll.ft force - pounds Drag - pounds D Wing area - rt2 A A correction factor to account for cyclic pitch changes The ratio of average vertical speed to average horizontal speed /3 Specific drag Ds R Rotation of' the lift veetor relative to vertical - radians Overall propulsive ef'f'iciency ~ G.S.T. Gross specific thrust Subscripts used to denote horizontal & vertical components h,v X

G

,.,.

I.

INI'RODUCTION

Recent construction of' ultralight aircraft and interest in man powered flight has created a desire for propulsion systems suited to the specific requirements of' this type of' craf't. The Pseudo-Ornithopter (P-0) propulsion principle presented herein is proposed as a suitable method f'or propelling man powered aircraft as well as providing auxiliary man power assist for ultralight gliders. As suchJ it will be competing against pedal-propeller drives used in virtually all successful man powered aircraft to date and should rightfully be compared against them.

II.

OBJECTIVE

P--0 propulsion was developed in an attempt to minimize or eliminate the following problems associated with pedal-propeller drives.

1 -

The pedal to propeller gear ratio and propeller pitch is generally a fixed value, therefore, ~osing an off' design penality for many flight conditions.

2 -

Effective pedal force is but a fraction of actual pedal f'orce due to crank geometry.

3

3 -

Work stroke duration and rest stroke duration are.not independent variables.

4 - Cyclic torque variation causes off design propeller operation and high drive line peak stress.

5 - Rest periods and glides :impose a large propeller drag penality.

6

The large propeller diameter requires placanent compranises and complicates the drive train with associated weight penalties.

7 - Supplemental arm power is not available with a single crew member.

8 -

Pedal lever length may not be optlrnurn for a given pilot and flight condition.

In searching for a solution to tnese problems we naturally consider ornithopters as this is a known alternative. Ornithopters do in fact control or eliminate many of the above problems. The joints, geometry and linkages associated with a typical flapping wing, however, provide many problems of their own.

Investigation into the operating principles of flapping wings indicates that the pr:lmary requirement is that there be relative movement between the wing area (up force) and the center of gravity (down force).

A bird provides this movement quite naturally by flapping his wings.

An ultralight pilot would naturally provide this movement by flexing his arms and legs. By using this method he can eliminate many of the previously cited problems without suffering the structural disadvantages of flapping wings.

III.

DESCRIPTION

A 150 pound pilot croutches low in a 50 pound ultralight, his feet resting on a foot pad and hands gripping a support. Both may be rigidly attached to the ultralight airframe. Then, the operator extends his arms arrl legs to a semi-standing position. In doing so he raises his center of gravity (CG) 1-1/3 FT. and imparts 200 ~-lb.work to the system.

The system (ultralight plus operator) CG is raised one foot in relation to the wing. No moving structural components are required. The operators' natural joints provide all the required movements. In addition, the hand brace may pivot in any of several modes to provide a means of airer~ control while doubling as a support to aid in balancing the operator.

THE USE OF lHf ROGALl.O F1GURE OH 'THE COVER Jr.NO HERE IS ONLY

TO BE TAll;EN AS AN ARTISTIC DEVICE. HOW.EVER, DO NOT LET THIS STOP US FROM INVENTING PRACTICAL SOLUTIONS TO THIS P.O QUESTION. P.O. CAN 'ft'ORI( WELL WITH ATTEMPTS AT GUST SOARING., PERHAPS. WHO WILL BE THE FIRST TO SEND IN EVIDENCE THAT THEY HAVE BECOME THE FIRST TO HA.VE SIGNIFICANTLY USED P.O. FOR EXTENDING;.. NO-WIND GLIDE IN A SELF SOAR SYSTEM?

4

If the operator squats under the same one gravity acceleration he was experiencing when he stood up, his body will absorb all the energy he expended in the power stroke reducing the cycle efficiency to zero.

If, however, the operator could return to the squatting position under a reduced G load, the loss would be r~uced proportionally and a network would be imp2."?ted to the system.

This may be summarized by the following equations : 3 Gross Work/Cycle Net Work/Cycle Cycle Efficiency

Wx Wx

1.0

Gd (Ga - Gu)

Net Work Gros~·work

2.0 l -

Gu

3.0

Oct

Where: Wx is the product of weight times distance

(relative to the wing) of CG movement for the operator or operator plus ultralight system.

Gd is the average G load on the standup (operator pushes down) stroke.

Gu is the average G load on the squat down (operator pulls anus and legs up) stroke.

Notice that optimum cycle efficiency is obtained by squatting down under zero or negative G conditions.

FIGURE

1

',,/IWG

PATH---._

2

This is what happens when a child pumps a swing. He raises his CG at the high G bottom of the arc and lowers his CG at the low G top of the arc.

3

The "UP" stroke is hereby established as the squatting motion to pull arms and legs up while the "OOWN" stroke is the standing movement which involves pushing down on the surrounding structure.

-5-

When this cycle is enployed on an ultralight, the a:!rcraf't reacts to the operators actions by rollowing a cyclic night path (Figure I).

We will assume ror now that the operator is positioned on the aircraft center or gravity so that pitch tr1m changes caused by the operators motion may be ignored. Thus, when the operator pushes down, the aircraf't; responds by accelerating downward in a constant pitch attitude.

The resulting downward wing velocity causes the angle or attack to increase, iricreasing the lift and providing an upward acceleration to the system CG. The increased lift soon balances the operators downward push and.the wing continues at constant velocity while the operator is accelerated upward.

As the wing lift vector increases in magnitude it also rotates rorward (to remain perpen:Mcular to the airnow) providing a horizontal thrust component. The opposite occurs on the up stroke. The lift vector shrinks in size and rotates rearward creating a drag component while the operator accelerates downward. As a result the two strokes combine to either reduce drag or to :impart a net thrust to the system (Figure 2).

-I GROSS ~THRV ST GR05S DRAG

Ne"T THRU.Sr

1o ri1~s

I-

~~

LEVEL

DOWN'

FIGURE'

-6-

"---2

VP

IV.

CYCLE ANALYSIS

Cambin:l..ng this up and down motion into the saw tooth path of figure

3A allows the perfonna.nce to be determined by averaging forces on the up and down strokes respectively. In practice this stroke can never be achieved as ~t requires infinate wing accelerations at the sl:arp saw, tooth peaks.

A more realistic stroke is shown in figure 3B where the peaks have been rounded to correspond with the finite accelerations.

The saw tooth of figure 3A may be modified to more closely apprmdnate the actual stroke by including a rest period at each peak as shown in figure 3C. This rest period will cause a performance deterioration due to the work time lost and the reduced effective stroke length.

X

= X - 1/2 au tu tr

Where :

~ tu

= aa. td

4.0 and a = 32.2(G - LO)

As iroicated the up and down strt>ke need not be of equal time duration. For a given effective stroke length (x) and up stroke G load, the up stroke time duration (tu) is directly proportional to forward speed (V) and inversely proportional to wing loading (L/A).

5.0 5.1 Down stroke time duration is limited by the stalling lift coeffident and is inversely proportional to both speed and wing loading.

6.0 6.1 Therefore, the higher the wing loading the higher the maximum permissable frequency. The smaller the stall margin the higher the ratio of taftu.

These factors can be noticed in bird flight and we can expect there will be some optimum speed and cycle for each flight requirement.

Matching of ht.man factors to aircraft dimensions will also be required.

For these reasons, further analysis will be more meaningful if typical values are in:l.icated. Reference to the tables will be helpful in this regard or the reader may use the following discussion and equations to find his own typical values.

4

An investigation into the force, mass, velocity relationships

indicate large vertical accelerations and low vertical terminal velocities. Therefore, a large portion of the stroke is at nearly constant vertical wing velocity and path 2A is a reasonable starting approximation.

-7-

FIGURE

3

WING PATH PROFILES

CENTER OF GRAVITY

1~ MIN'

MAX.

A -

SAWTOOTH WING PATH

8 - AC Tl/AL

/

--- -- ' ......

vvl 1\/G

PATH

t COAST

,.-.,.f -- .... ' '

~_,_J_..,.,, f

C - APROXJMAT/ON 8

OF

X

ACTVAL

PArH

Given aspect ratio and profile drag coefficient, lift coefficient for max:imum LID and rnin1murn sink may be determined by equations 7 .0 and 8.o respectively.

Where C0p is asstnned constant.

Appropriate velocities may be determined by equation 9. o.

1/2

1/2

v f;~pcJ 3o[kAJ e

=

or

C

L

9.0

ft/sec

= 1/2 L/A 2 V

9.1

Using these values as a guide we may choose an operating CL or velocity for future calculations. Assuming a profile drag coefficient for the aircraft, lift/drag ratio, sinking speed, and power required is determined by equations 10.0: 11.0 and 12.0 respectively.

C2 LID=~ Where CDi = ~ 'I(~ Cnp + CDi

10.0

Sink= ..:{_

ft/sec

11.0

Power= Sink

Gross Weight

LID

:ft·

lb I sec

12.0

The lift/~ag ratio represents the angle of" glide, while sinking speed is useful to deterniine soarability. The power requirement indicates the degr-ee of success to expect ror a man powered flight ( see figure 4) • For pumping flight, the average G load(%) is related to the up For straight line flight (i.e., no and down G load by equation 13.0. turns or zooms) the average G load must be 1. 0 and equation 13 reduces to equation 13.1.

13.0

13.1

Ga= 1.0 T tu (l.O - Gu) td

-9-

Assuming a constant horizontal velocity canponent, equations 14. 0 and 14 .1 may be used to calculate the required up and down stroke lift

coefficient.

Gu Cr.u = Cr.r Gr

14.o

CLd = Cr.r Ga

14 .1

Gr Up and down stroke lift vector rotation may be calculated by equations 15 and 15.1.

A math check is made by use of equation 16.0.

!\i = Rct

=

,y

(Cr...r - CLu) 2 17

'}""

(Cr.r - ~u) 2 rr

Where radian measure is 15.0 used and the factor '( ~ included to allow or any cyclic wing pitch 15.1 variations.

td 16.0

l~I= tu Up and down stroke times are calculated by equations

17 and 17 .1.

A math check is obtained by canparing the time ratio with that used in equation 13. o .

Iterate with equation 4.0 to obtain the appropriate value of x.

17.0 17.1

The operating cycle is now defined for the speed, steady state lift coefficient and stroke variables chosen. We will do well to pause for a moment and consider the wisdom of our choice. Are the lift coefficients and times reasonable or should new values be chosen?

V.

PERFORMANCE DE:rERMINATION

Lift is defined as the force perpendicular to the airflow and generally has a large vertical and small horizontal canponent. Drag is an order of mgnitude smaller than lift and is parallel to the airflow. Perforniance may be determined by suntning forces in the horizontal direction while the airfoil oscilates about a horizontal flight path and time averaging to determine the net thrust or drag force. This force may then be compared with other parameters to detemine vertical speed and climb/descent angles.

Calculations may be simplified by neglecting the vertical drag components as this small force caq::,onent combined with low vertical speed minimizes errors. Calculations will be made in tenns of specific thrust or specific power, i.e. thrust/pound or power/pound gr>oss weight.

-10-

i

For non-flapping flight., performance may be calculated via the li~ drag ratio.

Specific thrust req'd.

Where j3 :

l

L;D

+ R

18.0

r

Vertical Speed/Horizontal speed

Specific power req'd.

V

LID

+ vertical speed

19.0

For powered (flapping) flight, calculations involving the lift/~ag ratio should not be used on the up stl70ke due to the small or negative lift values which may be encountered. Instead, we will calculate the I profile and induced drag separately.

If horizontal velocity is assumed constant, profile drag is constant throughout the cycle.5 Specific profile drag

20.0

Constant throughout cycle The specific induced drag for each stroke of the cycle may be evaluated in a similar manner and t:iJlle averaged. !

Specific induced drag Where x indicates the appropriate value for the stroke involved, and the relationships t!o;: ct- nJJo cl.(.,_J' c,_ """> are used in the transformation. .frlR. %

Average specific induced drag

22.0 1T~

5

I

In actual practice profile drag is a function of angle of attack\ This may be corrected for by assuming an appropriate average Cctp or by using a lower than actual aspect ratio to include the profile drag variation with induced drag. For s:lmplicity, we will use the Cdp for steady flight at the ~hosen velocity and assume this is accurate enough. and does vary throughout the cycle.

-11-

The quantity in brackets{Li.Di) is the factor induced drag is increased by,due to the unsteady flapping flight. Some investigators may argue that induced drag appears to decrease on some ornithopters.

If so, this is probably due to the starting and stopping wing vortex, factors not considered in this investigation. Until shown otherwise· we will rerna.in conservative and assume that equation 22.0 is valid but admit that induced drag may be lower than calculated.

Combining the profile and in::luced drag equations yields the total specific drag CDs).

Ds = ~ + CLL!..Di CL fr/1c.

23.0

As the pumping G loads approach 1.0 or the pumping time becomes insignificant compared to the rest tiIJle this equation reduces to the steady state flight drag and thus may'be approximated by 1 + L/D. , In addition to the horizontal drag force there is a horizontal lift force component (gross thrust) which must be considered whenever the wing path is not horizontal. This may be calculated by use of the Wing path deviation from horizontal which is equivalent to the lift vec~or rotation.

I

I

Specific horizontal lift component

~ w=GTanR

Where the relationships W=Lv/G and Tan R = LhfLv are used in the transformation.

24.0 Time averaging yields the average gross specific thrust (GST).

GST = Gd td Tan Rct- Gu tu Tan Ru = - x (Gd - Gu ) tt V tt

25.0

Where the negative allows the use of absolute values for angles and the relationship Tan R(x) = _x_ is used in the transformation.

V t(x) Net specific thrust (NST) is obtained by subtracting the total specific drag from the gross specific thrust.

I 26.0 NST = ..E._ (Gd - Gu) - [c!2£ + CLADi] V tt ~ "ff'fR For level unaccelerated flight the net specific thrust must be zero. Otherwise it is equal to the climb or descent angle (P) or an acceleration factor.

-12-

Propulsive efficiency ir:q:)ut.

f/

1/e is obtained by dividing output by

27 .o

_ output _ Specific Thrust Required e - Input - Gross Specific Thrust

Z7 .1

Assuming the net specific thrust equal to ,P equations 10 • 0 an::l 26. 0 we find

I

I

and substitutirig

CL

1f'iiJ. .SDi 28.0i

1-

1/e = 1, O - Induced Drag Increase

I

28.1

Gross Thrust I

Overall efficiency may be obtained by multiplying the propulsive efficiency (Equ 28} by the cycle efficiency (E.qu 3).

i

Solving equation 27 .1 for {J

we find tha.t the climb/descent! angle

{f) is equal to the propulsive efficiency times the gross specific: thrust minus the non-p~ing drag/lift ratio.

1

Where 1? e may be evaluated from equation 28. o

Realize that p~ing.

lip is equivalent to the lift/drag ratio whilf I

13

For level flight we see that the gross specific thPust I!Rlst equal the inverse of the lift/drag ratio times propulsive efficiency.

1.0 "le L/D

30.0

Tables 1 through 3 show typical values of performance which may be expected.

Table 1 assumes values which are typical of todays ultralight technology. While the performance is not spectacular, it is adequate to gain experience and demonstrate the feasibility of pseudoornit~opter propulsion. With ground effect and slight refinements, flighfs comparable to the Wright Broth1rs 1903 attempt could be expected.

Tables 2 and 3 assume aircraft parameters typical of a second or third! generation of ultralights. Even though little opt:imumiza.tion has been done, figures look promising for a true self launching sailplane or even Kremer competition attempts.

Calculations were made by assuming the non-underlined values.

The underlined values were then calculated using standard engineering practice and the equations contained in this report. The values given are meant as an example only and do not represent a completed design study.

PSEUD-ORN!TIIOPTER PO'v/ER

1000

OUTPUT

PNYS/C,4LLY FIT

cj

"Qi ..J

J...:.

..... ~

4.1 ):

~

Data from:

80o

Shenstone, B. S., "Man-Powered Aircraft" in OSTIV Publication VIII, 1966

?00

IQ

lq

P/LOr

900

Wilkie, D.R., "Man As An Aero Engine," J. Royal Aercnautical Socieity, Vol. 63, Oct., 1959

6,00

1.q.lfP 500

1/00

300 200

/00

0

L-~~~--'-~~~~'---~~~-'-~--~J__-~~~~~~~~ 2-

3

TIME

14

'{

M/NUT£S

FIGURE 'I

(p

Table .l SPECIFICATIONS Span

36

Operator wt Empty Wt

Gross wt

ft

Area 200

ft 2

150 50 200

lb. lb. lb.

Wing Loading 1.0

Aspect Ratio

Actual .Q..:.5_ Effective 12.0

lb/ft lb/ft

Span Loading ~ .02 .02 .04

Airfoil Clark Y 1. 4 CL Max Parasite Drag 4 ft 2@1.0 C -t A T~al

GLIDING PERFDRMANCE @Max LID I

ft/sec V

15:1 LID

1.8

ft/sec Sink

365

14:1 LID

2.39 ft/sec Sink

478

ft!sec ~ower

@Operating Conditions .8 CL

33,5 ft/sec V

CYCLE PARAMfil'ERS

,5 tu/td

1.0 ....

1.0

ft X

Ga

1.0

Gr

0

Gu

1.5

0

CLu

1.2 CLd

.127 Ru

.0637

CL= .0212 'f'T.~

,7l

ft X

tu .1664 sec td ,3328 sec 2 tr .2

sec

tt .6992 sec

Ra ~Di= 1.3562

Specific Induced Drag = . 0287 Specific Profile Drag= ...J22Q___ Total Specific Drag

'T/ e = 83% Glide Ratio = 30

= .07876

Gross Specific Thrust= .04546 : 1

Net Specific Thrust

= -,0333

Input Power 304

ft# I sec

POWERED PERFDRMANCE V, ....e...rt..:::.::ic""'al"'=-!:JSp~e::.::ed:.::,....---=-1.:..:.1~2,___....::ft:...:::!../.::;sec=.

I

15

I

Table 2

SPECIFICATIONS Span 42

Area 150

ft 2

Operator Wt 150 50 Grosf: wt 200

lb. lb. lb.

Wing loading 1. 333 lb/ft Span Loadlng .-!i.:1£ lb/f't

Einpty Wt

Airfoil FX - 05191 1. 4 Parasite Drag 4 ft2@ .1 I

Aspect Ratio

Actual l2._ Effective 18

Cr, Max CDo + A Total

GLIDING PERFORMANCE @ Max L/D

~CL 1±Q__ ft/sec V

37-5 L/D 1.06

ft/sec Sink =?1=2"----=ft=-=-f:.;se::;.:c;;...:;...Po=w=-=e::.r

37 .5 LID l.06

ft/sec Sink 212

@ Operating Conditions ft/sec V

ft/lsec Power

CYCIB P.ARAMEIERS i I

1. 0 (' 1,0 ft X

.5

ituftd

0

Gu

1.5

- - .uU

0

t:,.

1.12 ~

-ll9Ru

.0597 Ra

Ga

1.0

• 75

ft X

Gr

tu .157

sec

ta .314

sec sec

2 tr .2 tt .671

sec

CL_ .013127 '11:.?.- - - -

Specific Induced Drag= .017734 Specific Profile Drag = • 0160 Total Specific Drag

= • 03373

Gross Specific Thrust= .041915

"le=~ Glide Ratio = 122 : l

Net Specific Thrust

= .00818

Input Power 335

ft# I sec

Cl:imu

POWERED PERFORMANCE Vertical Speed

.328

ft/sec

16

VI.

CONCLUSIONS

This brief investigation in:licates that Pseudo-Ornithopter propulsion is worth considering. It appears that a worthwhile perfo:rmmce gain is possible with ultralight aircraft. In exchange we must provide 1) stµ'ficient room for the operator to move about, 2) a reliable structure and 3) considerable muscular output.

A four foot vertical height is considered sufficient for most operators. This is slightly larger than the area required for efficient pedal operation.

4 reliable structure is required regardless of propulsion system.

This is not considered a problem because pumping loads are of the same general magnitude as gust loads.

I I

Muscular output is a problem. My opinion is that i f man could fly like a bird 90% of the people would be too lazy to fly. We are talking of that remaining 10% and they are f'ree to work as much as they like.

The more ambitious can fly farther and faster and on days when others may not feel it worth the effort. But, like the buzzard, those others will *e out when conditions are right and an occasional pump may be made to ai1 in reaching that next thermal.

I

~eviewing the pedal-propeller problems listed in Part II we have achieved the following.

I

I

1

-

:There is no fixed gear ratio for flight. However, pumping f'rejquency is limited by forward velocity. More detailed investigation ,is required in this area.

I

2 - :100% of the leg force is effective as an input power. ilosses may be greater.

Inertia

3 - IWork stroke and rest stroke time duration are independent but !limited by flight speed.

4 - lcyclic operation requires the wing to operate over a wide range !of CL values.

5 - !There is no drag increase while resting.

6 - :Additional structure and drive train requirements are eliminated.

7 - Supplimental arm power is available.

8 -

1

Stroke length is variable at any time.

Whether this is an improvement remains to be determined. is certain is that additional investigation is in order.

18

All that

Table

3

SPECIFICATIONS Span

42

ft

Area

Operator Wt 150 50 200

f't 2

150

lb. lb. lb.

~ty Wt Gross Wt

Aspect Ratio

Actual ]2_ Effective 18

Wing loading 1. 3~3 lb/f't Span Loading 4. 7 lb/ft

Airfoil FX - 05191 1.4 Parasite Drag 4 f't2@ .1

~ Max Cno + A Total

GLIDING PERFORMANCE @ Max L/D I

. 75 CL

40

f't/sec V

37, 5

LID

1. 06 ft/sec Sink _21_2_---'ft~f.!=.se,::.:ca:...,;..!Po""w1::e=r i

@Operating Conditions .:.12.__CL

40

I

ft/sec V

37.5 LID

1.06 ft/sec Sink 2:::1:=2:...._...,ft,_!!Lfs~er.>ec'--'R"'oa,w=er.

CYCLE PARAME:l'ERS

I

1.

0.,.

tu ,157 sec

,75 ft X

1.0 ft X

.3

Vtd

0

Gu

1.3

Gd

_o_ C1,u

.975

Cw

2 tr .2

.119 Ru

.0358

Rd

tt

CL 'fr~

.01327

1.0

td .523 sec

Gr

A Di= 1.2459

sec

.8703sec

Specific Induced Drag = • 01653 I Specific Prof'ile Drag = Total Specific Drag

I

• 01333 /

= • 029861

17 e = 88%

Gross Specific Thrust =

•0280

Glide Ratio = 539 : 1

Net Specific Thrust

-.00185 I I

!

POWERED PERFDRMANCE Vertical Speed - • 07 f't/sec :....:.::...=..::...:.:::c....;.e.-==--~.:----'-.:.._c_

Input Power 298

17

ft#/seJ

r I

VII.

RECOMMENDATIONS

Numbers can be chosen to show Kremer competition or better performance but, proof of operation will be in a flight demonstration.

Attempts at Pseudo--Ornithopter propulsion whether successful or not' will do much to define problem areas and indicate the validity of the assumed values. Very little is known about cycle limitations. How fast can one pump? What is the optimum cycle considering human factors? How does structural flexing affect performance? What percentage of the total arm power is available? Trial flights are recommended as a means to answer these questions.

The cycle chosen for the example was chosen by the best guess method. A thorough investigation of propulsive efficiency for various cycles and speeds is required. This should be run in conjunction with the flight test program as the questions arise; "can the operator perform this cycle", or, "which cycle can the operator perform best"?

ICARUS 4 P.O.?

Why not? Watch the stress problem as you test 1hese new designs. It could just be that pilot induced oscillation worries could be handled by deft control with a skill developed from daily practice. A pole yaulter does not clear 16 feet at the start.

The dedicated may just find that P.O. will provide a chalbnge akin to camp&titive tree- climbing, up-stair racing, rope climbing, hill-cross-country running ...

For the less energetic, we can hope far simple time-of-flight extensions via P.O. or far a method of keeping worm during those long flights in cold airs. There is no doubt that P.O. can lead to averstressing ships. Many Hang Loose ships were destroyed when pilots moved in the cockpit ever so slightly.

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From ell of us to you: space below for starting o safety section in your notebook: ~