US2351645A - Adjustable fan blade construction - Google Patents

Description

June 20, 1944.

T. H. TROLLER ADJUSTABLE FAN BLADE CONSTRUCTION Filed Oct. 17, 1942 3 Sheets-Sheet l meaaarb. 71 01191 June 20', 1944. 1:. H. TROLLER ADJUSTABLE FAN BLADE CONSTRUCTION Filed Oct. 17, 1942 3 Sheets-Sheet 2 mew/-15. Yin/75 June 20, 1944. T. H. TROLLER 2,351,645

ADJUSTABLE FAN BLADE CONSTRUCTION Filed 001;. 17, 1942 3 Sheets-Sheet 3 7200/10/45. Waller 9 327% Patented June 20, 1-944 2,351,645 ADJUSTABLE FAN BLADE CONSTRUCTION Theodor H. Troller, Akron,

Ohio, assignor to La- Del Conveyor & Manufacturing Company, New Philadelphia, Ohio, a corporation 01' Ohio Application October 17, 1942, Serial No.

5 Claims. (Cl. 230-114) The invention relates generally to propellers for pitch of the blades is adjustable to vary the volume and pressure or the fluid ilow. 5 More specifically, the invention relates to an adjustable blade construction in which the noise normal to the longitudinal axis 01' the However, when Justed to have a increases.

I have discovered that in a fan blade having generally a streamlined section with a leading edge portion of a substantial thickness, it is more It is therefore invention to provide an adjustable blade con-.-

with a leading edge portion of a substantial thickness. which will maintain throughout the pitch adjustment range a substantially constant small clearance between the outer duct and the blade tip at its trailing edge.

A more specific object is to maintain this substantially constant small clearance at the trailins edge without too greatly increasing the clearance at the leadin edge.

However, the center of gravity of the blade should be kept as nearly as possible in the turning axis of the blade preferably with the turning axis extending through the blade hub and radially of the propellerhub;

eluding torque.

. Accordingly, another object is to provide an adjustable propeller blade construction creating a minimum noise level in operation without substantially shifting the center of gravity of the blade from its turning axis.

Another factor which must be considered is maintaining the pitch adjusting mechanism as simple as possible for obvious reasons, and it is therefore a further object of the present invention to provide a novel adjustable propeller blade construction with minimum noise level in operation and with a relatively simple pitch adjusting mechanism.

These and ancillary objects are attained by the improvements, parts, designs, relationships and combinations comprisin the present invention,

a preferred Referring to the accompanying drawings in which a preferred embodiment of the invention is shown by way of example,

Figure 1 is a fragmentatry elevation looking in 2 at the end of a propeller fan having conventional adjustable blades;

Fig. 2 is an enlarged fragmentary view similar to Fig. 1 shovn'ng the clearance between a blade tip and the outer duct;

Fig. 3 is a longitudinal fragmenitary sectional view of a propeller fan having a preferred embodiment of the novel adjustable blade construction, part of the fan hub being broken away to show the blade adjusting mechanism;

Fig. 4 is an enlarged fragmentary view as on line 4-4, Fig. 3;

Fig. 5 is a detached plan or radial view of the blade shown in Fig. 4;

' Fig. 6 is a view similar to Fig. 4 of another embodiment of the invention in which the design of the fan blade is slightly changed; and

Fig. '7 is a detached plan or radial view of the blade shown in Fig. 6.

Similar numerals refer throughout the drawings.

While I have shown a preferred form of my novel adjustable blade construction in the drawings, it will be understood that the invention contemplates variations in the design and mounting of the adjustable blades, as long as such variations are within the scope of the appended claims.

Referring to Figs. 1 and 2 of the drawings the conventional propeller fan indicated generally at 5 has adjustable radially projecting blades 6 journaled in the fan hub on turning axes X and Y coinciding with radii of the fan. These blades 6 are of a conventional type for propeller type fans for moving pressure fluids, and as shown the axes X and Y intersect the tips of the blades at points substantially centrally located with respect to the leading edge I and the trailing edge 8 of each blade.

In the position of pitch adjustment of the blades shown in Fig. 1 the tip of each blade 9 forms an arc which provides a small and uniform clearance between the inner surface H! of the outer duct H and the tip 01 the blade throughout its length. In this position of the blades, which is indicated in full lines in Fig. 2, the blades are at their lowest angle of pitch with respect to a transverse plane, and as the pitch is increased to a greater angle, the blades will assume a position substantially like that shown in dot-dash lines in Fig. 2, in which the clearance between the blade Y axis is the same as in the full line position, but the clearance at the leading and trailing edges is considerably increased. This condition is due to the fact that as the angle of the blade is increased the tip approaches a position in line with a longitudinal element of the duct, which element is a straight line, so that the more the angle is increased the greater the clearance will be at the leading and trailing edges of the blade tip.

I have found by actual experiment that with this type of adjustable blade the more the angle of pitch of the blades is increased, the greater is the increase of noise as against that produced by a similar fan of such higher pitch which would have its smallest itip clearance at such a pitch, and also the pressure built up by the fan is lower than that built up by a similar fan having minimum tip clearance at such higher pitch.

In the novel adjustable blade construction shown in Figs. 3, 4 and 5, the fan includes an outer duct or fairing [3 which is preferably cylindrical throughout the portion of the duct surrounding the nose l4, propeller blades and to similar parts tip and the duct at the which passes through vanes 16. The outer duct is preferably made up of adjoining sheet metal sections as indicated at l1 and 18, which are secured together by suitable means such as flange rings I9 clamped together by bolts (not shown).

If desired, the outer duct may be provided opposite the nose It with a door or hatch indicated at 20 which is adapted to be easily removed in a suitable manner for gaining access to the fan hub to adjust the pitch of the blades. The inner fairing preferably includes the nose l4 and a cylindrical housing section 2| which may enclose the motor, and the housing section 2| is preferably supported within the outer dudt by means of the straightener vanes [6 which serve to straighten the flow of air from the propeller blades IS. The hub section 22 of the inner fairing in which the propeller blades 15 are mounted is preferably located between the nose H of the housing section 2|, and its outer surface is cylindrical and conforms to the housing section 2| and the rear part of the nose so as to provide a smooth streamlined air flow along the inner fairing.

The hub section 22 preferably includes an annular rim 23 provided with a plurality of circumferentially spaced sockets 24 in which the shanks 25 of the propeller blades iii are journaled, and the turning axis of each blade passes through the center line of the shank 25.

Preferably the central portion 26 of the fan hub is keyed on the motor shaft 28 by means of keys 29 in a usual fashion, and the blades l5 are held in their sockets 24 by means of clamping collars 3U engirdling lthe shanks 25. As shown, the means for adjusting the pitch of all of the blades may include studs projecting from straightener the collars 30 and having rounded heads 33 which are received in sockets 34 provided in an adjusting spider 35 journaled'on the fan hub and held in adjusted position by means of screws 36 accessible from the exterior of the hub housing 22 and through the door 20 in the outer duct.

This pitch adjusting mechanism per se forms no part of the present invention, but is described in detail and claimed in the copending application of Charles N. Bebinger Serial No. 449,609, and entitled Pitch adjusting mechanism for propellers; said copending application and present application having the same assignee.

As viewed in Fig. 4 the radius Z of the fan, the shank 25 and is the turning axis of the blade [5, intersects the tip 31 of the blade at a point relatively close to or adjacent the trailing edge 38. In my invention, the adjustable blades preferably have generally a streamlined section with a leading edge portion of a substantial thickness. As viewed in Fig. 5 the tip of the blade is slightly offset from the axis Z in order to bring the center of gravity of the blade as nearly as possible in the axis Z and still have the Z axis substantially intersecting the blade tip. In other words a compromise is effected between having the Z axis actually intersect the tip and having the center of gravity in the Z axis.

In Figs. 6 and '7, the blade I50. is designed so that the Z axis actually passes through the tip 31a near its trailing edge 38a, in which case the center of gravity of the blade is thrown farther away from the Z axis. Obviously, the blade may be designed so that the tipoccupies any location between or approximating the locations shown in Figs. 5 and '7, and in all such variations the Z axis is to be considered as substantially intersecting the tip-of a substantially dynamically balanced blade near its trailing edge, for accomplishing the purposes of the present invention.

In Figs. 3, 4, 5, 6 and 7 the blades l and Mia are shown at their lowest angle of pitch adjustment, andpreferably in this position the tip 31 or 31a of each blade, when viewed axially of the fan as in Figs. 4 an are which provides a uniform small clearance between the blade tip and the inner surface ,39 of the cylindrical outer duct section ll.

As the blades l5 or l5a are adjusted about their turning axes Z from the lowest angle (angle a) of pitch adjustment, which position is shown in full lines in Figs. 4,, 5, 6 and 7, to a greater angle as shown in dot-dash lines, the clearance between the blade tip and the duct at the Z axis remains constant while the clearance at the leading edge 4! or Ha increases materially and the clearance at the trailing edge 38 or 38a increases by a very slight amount due to its proximity to the turning axis. The tip clearance in the region of the leading edge portion during ad- J'ustment of the blade pitch varies more than the tip clearance in the region of the trailing edge portion whereby the maximum tip clearance occurs substantially where the blade is the thickest.

At the base of each blade l5, the rim 23 of the hub section 22 is slotted as shown at 42 to allow for adjusting movement of the blade base.

In actual operation, I have found that with this novel adjustable blade construction when the blade pitch is increased to its maximum limit, the noise level and the output of the fan are not substantially adversely affected as compared to these conditions in a fan having blades at the same pitch with a uniform close clearance between the blade tips and the outer duct.

It is apparent that if the blade were so constructed that the turning axis Z would substantially intersect the tip exactly at its trailing edge 38 or 38a the clearance between the tip at its trailing edge and the outer duct would be maintained constant for all angles of pitch adjustment of the blade, but in this case the clearance at the leading edge ll of the tip would be more greatly increased so as to endanger producing too much turbulence in the air stream at those points with a possibility of increasing the noise level because of that condition.

Also, if the Z axis substantially intersects the trailing edge of the blade tip itis more difficult to design a blade having its center of gravity located substantially on or near the turning axis, and if the center of gravity is materially shifted, centrifugal force in operation will set up bending moments, and additional stresses including torque, in the fan.

Accordingly, the turning axis of the blade is preferably located relative to the trailing edge as indicated at Z, in order to accomplish the purposes of keeping the clearance at the trailing edge of the tip as small as possible without introducing too much clearance at the leading edge and without setting up additional stresses in operation to any substantial extent. I have found that in a fan of about 29 inches diameter, that good re sults are obtained when the turning axis Z substantially intersects the blade tip at a distance of one-half inch to one and one-half inches from its trailing edge.

By constructing the improved adjustable blade so that its shank extends radially of the fan and turning the blade about its shank, the pitch adjusting mechanism may be of maximum simand 6 is curved to describe portion whereby the maximum plicity while maintaining the fan substantially I in static'and dynamic balance.

I claim:' 1. Propeller fan construction including an outer substantially cylindrical duct, a fan axially of substantial thickness, each of said blades hay ing close clearance between the tips thereof and the outer duct during adjustment of the blade pitch between said predetermined limits, the tip clearance in the region of the leading edge portion during adjustment of the blade pitch varying more than the tip clearance in the region of the trailing edge portion whereby the maximum tip clearance occurs -substantially where the blade is the thickest.

2. Propeller fan construction including an outer substantially cylindrical duct, a fan axially rotatable within said duct and including a hub, blades journaled in the hub, means for turning the blades on their axes for adjusting the blade pitch within predetermined limits, each of said blades having a trailing edge portion and a leading edge portion, said leading edge portion being of substantial thickness, each of said blades at one position of the pitch adjustment having close minimum clearance between the tips thereof and the outer duct in both the regions of the leading edge-portion and of the trailing edge portion, each of said blades at other positions of pitch adjustment having maximum clearance in the region of the leading edge portion and minimum clearance in the trailing edge portion, whereby the maximum tip clearance occurs substantially where the blade is the thickest.

3. Propeller fan construction including an outer duct, a fan axially rotatable within said duct and including a hub, blades journaled in the hub, means for turning the blades on their axes for adjusting the blade pitch within predetermined limits, each of said blades having a trailing edge portion and a leading edge portion, said leading edge portion being of substantial thickness, the turning axis of each blade passing through the region of the trailing edge portion thereof, each of said blades having close clearance between tips thereof and the outer duct during adjustment of the blade pitch between said predetermined limits, the tip clearance in the region of the leading edge portion during adjustment of the blade pitch varying tip clearance in the region of the trailingedge tip clearance occurs substantially where the blade is the thickest.

4. Propeller fan construction including an outer duct, a fan axially rotatable within said duct and including a hub, blades journaled in the hub, means for turning the blades on their axes for adjusting the blade pitch within predetermined limits, each of said blades having a trailing edge portion and a leading edge portion, said leading edge portion being of a substantial thickness, the turning axis of each blade passing through the region of the trailing edge portion thereof, each of said blades at one position of the pitch adjustment having close minimum clearance between the tips thereof and the outer duct in both the regions of the leading edge portion and of the trailing edge portion, each of more than the I said blades at other positions of pitch adjustsaid leading edge portion being of substantial ment having maximum clearance in the region thickness, each of said blades having close clear- 01 the leading edge portion and minimum clearance between tips thereof and the outer duct ance in the trailing edge portion, whereby the during adjustment of the blade pitch between maximum tip clearance occurs substantially said predetermined limits, the tip clearance in where the blade is the thickest. the region of 'the leading edge portion during 5. Propeller fan construction including an adjustment of the blade pitch varying more than outer duct, a fan axially rotatable within said the tip clearance in the region of the trailing duct and including a hub, blades ioumaled in edge portion whereby the maximum tip clearance the hub, means for turning the blades on their 10 occurs substantially where the blade is the thickaxes for adjusting the blade pitch within preest, the center of gravity of each blade lying near determined limits, each of said blades having 9. its turning axis. trailing edge portion and a leading edge portion, THEODOR H. TROLLER.

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