An hydraulic windmill is described. It pumps pressurized oil from rotor shaft level to the ground where a motor generator produces electricity. Alternatively, the useful output may be heat. Rotor speed is governed by a flow valve. Over pressure, the result of high wind velocity, rotates the tail to move the rotor blades out-of-the-wind. Loss of oil pressure causes a brake to close as well as to swing the tail to its maximum distance from the rotor plane

Browing, J. A.

Breton 

NASA Technical Reports Server

THE H Y D R A U L I C  W I N D M I L L *  
James  A .  Browning 
Browning E n g i n e e r i n g  C o r p o r a t i o n  
P.O. Box 8 6 3  
Hanover ,  N e w  Hampshire  03755 
ABSTRACT 
The hydraulic windmill pumps pressurized o i l  from 
ro to r  sha f t  l eve l  t o  the  ground where a motor- 
generator produces e l e c t r i c i t y .  Alternat ively,  
the  useful  output may be heat. Rotor speed is  
governed by a flow valve. Over pressure, the  
r e s u l t  of high wind ve loc i ty ,  ro t a t e s  the  t a i l  t o  
move the  ro to r  blades out-of-the-wind. Loss of 
o i l  pressure causes a brake t o  close a s  w e l l  as 
t o  swing the  t a i l  t o  its maximum dis tance from 
the  ro to r  plane. 
DISCUSSION 
Advan tages  of  t h e  h y d r a u l i c  t r a n s m i s s i o n  
p r i n c i p l e  l i e  i n  t h e  s i m p l i c i t y  o f  r o t o r  
s p e e d  c o n t r o l  and t h e  g o v e r n i n g  o f  power 
o u t p u t  i n  h i g h e r - t h a n - d e s i g n  wind r e g i m e s .  
These  f u n c t i o n s  c a n  now be o b t a i n e d  a t  low 
c o s t  and  h i g h  r e l i a b i l i t y .  
We h a v e  made and t e s t e d  two p r o t o t y p e  
mode l s  o f  16-Ft .and 3 1 - F t . r o t o r  b l a d e  
d i a m e t e r .  Power o u t p u t s  were d e t e r m i n e d  
by m e a s u r i n g  o i l  f l o w  and p r e s s u r e .  Spe-  
c i f i c  power l e v e l s  were s u f f i c i e n t l y  h i g h  
t o  warrent t h e  c o n s t r u c t i o n  of t h e  7 1 - F t . ,  
t w o - b l a d e d ,  h o r i z o n t a l  r o t o r  a x i s  mach ine  
p r e s e n t l y  u n d e r g o i n g  t e s t s  on a h i g h  r i d g e  
i n  Lebanon,  N . H .  ( s e e  F i g u r e  1 ) .  
We h a d ,  i n i t i a l l y ,  s e l e c t e d  a downwind 
ro to r  p o s i t i o n .  L a t e r ,  d u e  t o  i n f o r m a t i o n  
re leased  by the  N.A.S.A. c o n c e r n i n g  u n d u l y  
h i g h  c y c l i c a l  r o t o r  s h a f t  t o r q u e  s t r e s s e s ,  
we s w i t c h e d  t o  t h e  upwind r o t o r  p o s i t i o n  
w i t h  c o n v e n t i o n a l  t a i J .  
The d e s i g n  shown i n  F i g u r e  2 p r o v i d e s  a 
c rank-a rm a t  t h e  e n d  o f  t h e  r o t o r  s h a f t  t o  
power a d o u b l e - a c t i n g  h y d r a u l i c  c y l i n d e r .  
Fu l l -wave  r e c t i f i c a t i o n  o f  t h i s  f l o w  i s  
made by f o u r  check  v a l v e s  a t t a c h e d  t o  c y l -  
i n d e r  p o r t s .  The o i l  p a s s e s  t h r o u g h  t h e  
v e r t i c a l  mas t  a b o u t  which  t h e  w i n d m i l l  
r o t a t e s  t o  f a c e  t h e  wind .  The s o l e  r o t a t -  
i n g  s e a l  i s  t h e  c y l i n d e r  p i s t o n .  ( I n  o t h -  
e r  cases  o t h e r  t y p e s  o f  pumps c o u l d  b e  
u s e d .  ) 
The p r e s s u r i z e d  o i l  p a s s e s  t o  t h e  g round  
where  p r e s s u r e  v a r i a t i o n s  a r e  damped by 
a h i g h - p r e s s u r e  a c c u m u l a t o r .  The p r e s -  
su re -compensa ted  f l o w  c o n t r o l  v a l v e  l i m i t s  
t h e  maximum o i l  f l o w  r a t e  t o  p r o v i d e  a 
cons ta 'n t  r o t o r  s p e e d .  A p r o p e r l y  s i z e d  
h y d r a u l i c  motor  d r i v e s  t h e  g e n e r a t o r  a t  
t h e  c o r r e c t  s p e e d .  S e v e r a l  h y d r a u l i c  
w i n d m i l l s  may be  o p e r a t e d  i n - p a r a l l e l  t o  
power a s i n g l e  g e n e r a t o r .  
q h e  work of t h i s  program has been sponsored i n  
par t  by the  Department of Energy under Contract 
NO. DE-FG01-80IR10320. 
6 
R 
1 
I l l  
From t h e  motor  t h e  o i l  p a s s e s  t o  a low- 
p r e s s u r e  a c c u m u l a t o r  p r e - c h a r g e d  w i t h  
n i t r o g e n  t o  a p r e s s u r e  s u f f i c i e n t  t o  l i f t  
t h e  o i l  t o  t h e  c y l i n d e r  and t o  power t h e  
t a i l - g o v e r n o r  and  s a f e t y  d e v i c e s .  
O t h e r  components  of  t h e  h y d r a u l i c  c i r c u i t  
of F i g u r e  2 i n c l u d e  a manual  s h u t - o f f  
v a l v e  w h i c h ,  when c l o s e d ,  a s s u r e s  a n  e f -  
f e c t i v e  b r a k i n g  a c t i o n  t o  t h e  a l l o w a b l e  
p r e s s u r e  r a t i n g  o f  t h e  h y d r a u l i c  e l e m e n t s .  
I n c r e a s e  of  p r e s s u r e  above  t h i s  i s  l i m i t e d  
by a p r e s s u r e  r e l i e f  v a l v e .  A water pump 
151 
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o r  o t h e r  m e c h a n i c a l l y  powered d e v i c e  may 
be s u b s t i t u t e d  f o r  t h e  g e n e r a t o r ,  
F i g u r e  3 i l l u s t r a t e s  a n  a l t e r n a t i v e  de -  
s i g n  which p roduces  h e a t  i n  p l a c e  o f  me- 
c h a n i c a l  e n e r g y .  R o t o r  s p e e d  i s  l i m i t e d  
by c o n t r o l l i n g  t h e  d i f f e r e n t i a l  f l o w  f rom 
t h e  c y l i n d e r .  The i n c r e a s e d  amount o f  
f l o w  on t h e  p i s t o n  down-s t roke  ( e q u a l  t o  
t h e  r o d  d i s p l a c e m e n t  vo lume)  must p a s s  
t h r o u g h  t h e  f l o w  c o n t r o l .  A d e s u r g e r  
i s  r e q u i r e d  t o  p r o v i d e  smooth v a l v e  a c -  
t i o n .  A s  a c c u r a t e  s p e e d  c o n t r o l  i s  n o t  
n e c e s s a r y ,  t h e  c o s t  o f  a w i n d m i l l  p ro -  
d u c i n g  h e a t  i s  much l e s s  t h a n  t h a t  gen-  
e r a t i n g  e l e c t r i c i t y .  E f f i c i e n c i e s  a r e  
much g r e a t e r  a s  l o s s e s  i n  t h e  c i r c u i t  a p -  
p e a r  as u s e f u l  o u t p u t - - h e a t .  We e s t i m a t e  
t h a t  a g i v e n  s i z e  w i n d m i l l  w i l l  p roduce  
a b o u t  60% more e n e r g y  when t h e  o u t p u t  i s  
h e a t  r a t h e r  t h a n  e l e c t r i c i t y .  
3 
71-Ft.  w i n d m i l l  i n a r e g i o n  of a d e q u a t e  
wind s p e e d s  amounts t o  n e a r l y  80 ,000  KW- 
H R .  I t  i s  t h o u g h t  t h a t  o v e r  80% of  t h i s  
becomes a v a i l a b l e  f o r  l a t e r  u se .  T h i s  i s  
t h e  e q u i v a l e n t  of  2 ,000  g a l l o n s  o f  o i l  
burned  i n  a b o i l e r .  To t h i s  s h o u l d  be 
added  t h e  h e a t  g e n e r a t e d ' d u r i n g  t h e  5 
w i n t e r  months ,  
A l though  t h i s  h e a t  a n a l y s i s  i s  o n l y  s p e c -  
u l a t i v e  a t  t h i s  p o i n t ,  t h i s  u s e  of  wind 
e n e r g y  must  n o t  b e  o v e r l o o k e d .  I n  p l a c e  
o f  t h e  h e a t  e q u i v a l e n t  o f  2 ,000  g a l l o n s  
of o i l  t h e  w i n d m i l l  would have  p roduced  
a b o u t  50 ,000  KW-HR fff e l e c t r i c i t y  d u r i n g  
t h e  same 7'-month p e r i o d .  A t  $1 .20/Gal  
of o i l  t h e  h e a t  s a v i n g s  are  $2 ,400 .  A t  
$O.OS/KW-HR t h e  e l e c t r i c  s a v i n g s  amount 
t o  $2 ,500 .  The h e a t - p r o d u c i n g  u n i t  i s  
less e x p e n s i v e  t h a n  f o r  e l e c t r i c i t y .  
Thus ,  h e a t  g e n e r a t i o n  c o u l d  be t h e  b e s t  
u se  o f  t h e  h y d r a u l i c  w i n d m i l l .  
c t 
To make a w i n d m i l l  h e a t  g e n e r a t o r  p r a c -  
t i c a l ,  means s h o u l d  be  a v a i l a b l e  f o r  h e a t  
s t o r a g e  d u r i n g  t h e  summer f o r  c a s e s  where  
t h e  h e a t  i s  o n l y  u t i l i - z e d  d u r i n g  c o l d  
months.  S t o r a g e  i n  t h e  ground a p p e a r s  
f e a s i b l e .  S e v e r a l  g r o u p s  a r e  s t u d y i n g  
t h e  u s e  of r e l a t i v e l y  non-permeable  a q u i -  
f e r s  f o r  h e a t  s t o r a g e .  
I n  s o l i d  r o c k  s u c h  as g r a n i t e  e a c h  100 
f e e t  of 8 - i n c h  d i a m e t e r  w e l l  b o r e  w i l l  
a o c e p t  o v e r  5 KW of h e a t .  Thus,  50 KW 
of h e a t  can  be "pumped" i n t o  r o c k  u s i n g  
5 w e l l s  e a c h  somewhat o v e r  200 f e e t  deep  
and s p a c e d  c o r r e c t l y  a p a r t ,  The t o t a l  
h e a t  s t o r e d  o v e r  a 7'-month s e a s o n  by a 
Where s p e e d  c o n t r o l  is gove rned  by a n  i m -  
pedance  i n  t h e  h y d r a u l i c  c i r c u i t ,  max- 
imum power o u t p u t  may be l i m i t e d  by match- 
i n g  t h e  a v e r a g e  peak  o i l  p r e s s u r e  t o  a 
f i x e d  p r e s s u r e  of l o w e r  v a l u e .  T h i s  t y p e  
of g o v e r n o r  i s  s k e t c h e d  i n  F i g u r e  4 where  
low and  h i g h - p r e s s u r e  c y l i n d e r s  a r e  shown 
a t t a c h e d  t o  t h e  c a r r i a g e .  The t a i l  sup-  
p o r t  arm can  move h o r i z o n t a l l y  a b o u t  a 
b e a r i n g  mounted on t h e  c a r r i a g e .  O i l  
p r e s s u r e  i n  t h e  l o w e r  c y l i n d e r  c a v i t y  i s  
t r a n s m i t t e d  t h r o u g h  a r i f l e  d r i l l  h o l e .  
The l o w - p r e s s u r e  c y l i n d e r  l ' sees l '  t h e  low- 
p r e s s u r e  a c c u m u l a t o r  p r e s s u r e  less  t h e  
h y d r o s t a t i c  p r e s s u r e  d r o p  i n  t h e  o i l  c o l -  
umn. A 4 - inch  d i a m e t e r  c y l i n d e r  o p e b a t -  
in@; a t  a n e t  p r e s s u r e  of  50 PSIG a p p l i e s  
a force  of 630 pounds a g a i n s t  t h e  m'ovable 
t a i l .  T h i s  f o r c e  w i l l  k eep  t h e  t a i l  i n  
t h e  " r u n n i n g "  mode u n t i l  a g r e a t e r  coun t -  
e r f o r c e  i s  produced  by t h e  h i g h - p r e s s u r e  
c y l i n d e r .  S e l e c t i n g  a c y l i n d e r  h a v i n g  a 
I - i n c h  e f f e c t i v e  a r e a  on i t s  r o d  s i d e ,  a n  
a v e r a g e  o p e r a t i n g  peak  p r e s s u r e  above  
630 PSIG w i l l  commence t o  move t h e  b l a d e s  
1 5 2  
out -of - the-wind .  When t h i s  h i g h  maximum 
p r e s s u r e  d r o p s  d u e  t o  a l o w e r i n g  o f  wind 
v e l o c i t y  t h e  a d j u s t a b l e  v a l v e  a l l o w s  t h e  
t a i l  t o  move toward  its' " r u n n i n g "  p o s i -  
t i o n  
It  i s ,  o f  c o u r s e ,  a l w a y s  p o s s i b l e  t h a t  
t h e  h y d r a u l i c  c i r c u i t  c o u l d  l o s e  a l a r g e  
amount of  o i l  by l i n e  l e a k a g e  or damage 
t o  a n  e l e m e n t .  The o p e r a t i o n  of b o t h  
s p e e d  and power g o v e r n o r s  would c e a s e .  A 
" f a i l - s a fe"  mechanism h a s  been i n c o r p o -  
r a t e d  i n t o  t h e  d e s i g n .  The t a i l  r o t a t e s  
i n t o  i t s  "running1f  p o s i t i o n  o n l y  when a 
s e t  o i l  p r e s s u r e  v a l u e  i s  exceeded .  
Below t h i s ,  a c o u n t e r w e i g h t  ( n o t  shown i n  
t h e  f i g u r e s )  p u l l s  t h e  t a i l  t o  i t s  f u r t h -  
e s t  p o s i t i o n  from t h e  r o t o r  a x i s .  I n  ad- 
d i t i o n ,  t h e  b r a k e  mechanism i s  a c t i v a t e d  
a u t o m a t i c a l l y .  The b r a k e  i s  a l s o  d e s i g n -  
ed t o  o p e r a t e  when undue  v i b r a t i o n s  a r e  
s e n s e d  by a we igh t  h e l d  i n  u n s t a b l e  equ-  
ili br ium . 
CLOSURE 
The d e s i g n  o f  t h e  71-Ft.  h y d r a u l i c  wind- 
m i l l  h a s  a t t e m p t e d  t o  r e d u c e  c o s t s  w h i l e  
max imiz ing  r e l i a b i l i t y .  These  c o n s i d e r a -  
t i o n s  p r e c l u d e  t h e  u s e  o f  f e a t h e r i n g  
b l a d e s ,  l i m i t  t h e  number of b l a d e s  t o  two, 
and r e d u c e  communication between r o t  a t  i n g  
s t r u c t u r e s  and t h e  g round  t o  t h e  o i l  c o l -  
umn i t s e l f .  Judgement o f  t h e  r e l a t i v e  
s u c c e s s  of  t h e s e  d e s i g n  p a r a m e t e r s  must 
a w a i t  r e s u l t s  of t h e  t e s t i n g  p e r i o d  which  
i s  o n l y  now commencing. 
153 
QUESTIONS AND ANSWERS 
J.A. Browning 
From: J. Tangler 
Q: For heating, how does your rotor load match compare to a system using a heat churn? 
Also, which approach do you consider more cost effective and why? 
A: Larger amounts o f  h e a t  can be handzed e a s i l y .  In a d d i t i o n ,  p o s i t i v e  speed c o n t r o l  
and overpower c o n d i t i o n  controZ are i n h e r e n t .  Mechanical o u t p u t ,  or e l e c t r i c ,  i s  
p o s s i b t e .  I b e l i e v e  t h e  h y d r a u l i c  u n i t  more c o s t  e f f e c t i v e .  
From: A.D. Garrad 
Q: 
A: About 80% f o r  a cyZinder pump-to-motor combination f o r  s h a f t  power product ion .  
How lossy do you expect your hydraulic transmission to be? 
Nearly 95% f o r  h e a t  us ing  generous amounts o f  thermaZ i n s u l a t i o n .  
From: J.A.C. Kentfield 
Q: What is the blade airfoil section? Do you require a high torque-at-low-speed char- 
acteristic? 
A: We have used a deZta c r o s s - s e c t i o n  blade r e a l i z i n g  higher e f f i c i e n c y  wouZd have 
resuZted  w i t h  o t h e r  des igns .  I t  was s impler  t o  c o n s t r u c t .  High torque-at- low 
speed c h a r a c t e r i s t i c  i s  b e s t .  
From: F.S. Stoddard 
Q: Do you have any idea what the overall transmission efficiency is? 
A: Answered above. 
From: R. Shaltens 
Q: What is blade construction? What diameter? kW output? 
A: SteeZ tube t r u s s  d e s i g n  w i t h  cross-brac ing .  Tubing covered w i t h  pZywood which, i n  
t u r n ,  has f ibergZass-epoxy c o a t i n g .  The r o t o r  diameter  i s  7 2  f t .  We have designed 
for about 20 kW i n  a 1 5  mph wind. 
From: F.W. Perkins 
Q: How much does the machine cost, especially compared to an electric machine? 
A: ConsiderabZy l e s s .  Speed c o n t r o t  accuracy i s  n o t  required .  A l s o ,  t h e  h igh-  
pressure  accumutator ,  hydrauZic motor,  and generator  are a b s e n t .  AbsoZute c o s t  
f i g u r e s  f o r  commercial d e s i g n s  i n  Zarge q u a n t i t i e s  cannot ,  y e t ,  be e s t i m a t e d .  
From: Anonymous 
Q: What airfoil section is used for the rotor blades? 
A: Answered above. 
From: W.C. Walton 
Q: Do you think the failures Waldron showed were due to lack of sophistication or to 
failure to apply basic engineering? 
A: Lack of  s o p h i s t i c a t i o n  probabZy r e s u l t s  i n  Zowering overalZ e f f i c i e n c y  vaZues--not 
t o  t h e  f a i Z u r e s  r e p o r t e d .  B a s i c  engineer ing  i n c l u d e s  good d e s i g n ,  mode2 making 
and t e s t i n g ,  and r e d e s i g n .  The Zarge amount o f  funding ( i n t e r n u 2  o r  ex ternaZl  
has n o t  been avai labZe  t o  s m a t l ,  new o r g a n i z a t i o n s .  CertainZy a m a l 2  windmi21 can 
achieve  optimum d e s i g n  more eas iZy  than  a Zarge one. Sponsors  have skipped t h i s  i m -  
p o r t a n t  s t e p  o f  a we22 thought  o u t  engineer ing  program. Perhaps,  they  shouZd have 
incZuded t h i s  s t e p  r a t h e r  than  pZaeing t h e  blame eZsewhere. L i s t e n i n g  t o  t h e  ma- 
j o r i t y  of t h e  p r e s e n t a t i o n s  i t  becomes e v i d e n t  that .  a major conceptual  advancement 
can only  come from t h e  engineer ing  en trepreneur .  
154 


The hydraulic windmill

Abstract

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