ELIPPSE propeller, Contact! magaine article

[John]

Corky
Any web address for more info, for the curious!
John


Corky Scott wrote:

> Paul Lipps, an aerospace engineer, has developed a new prop for
> experimentals. He's taken a new look at a lot of issues with props
> and has come up with something that looks really strange, but works
> extremely well.
>
> Among the many things he attempted to incorporate in his prop design
> was to utilize elliptical lift distribution, which many experts
> claimed could not be done, but he's managed to do it.
>
> He also wondered why folks were using flat bottomed turbulent airfoils
> for high speeds. The flat bottomed airfoil coupled with a sharp
> leading edge makes for a prop that has a narrow range of peak
> efficiency, and also creates a lot of drag and noise. After all, the
> tip approaches the speed of sound, what airfoil do you know for near
> supersonic flight has a flat bottom?
>
> Paul decided to use laminar flow symetrical airfoils.
>
> Lift force on a wing is proportional to the square of the velocity.
> That means if you double the speed, the lift force is quadrupled.
> That being the case, you don't need a wide cord at the tip of the
> propeller because it's moving at near subsonic speed. Going that
> fast, it does not have to have a wide cord to produce lift.
>
> Also, because the tip is moving at such high speeds, you need to
> minimize it's size to reduce drag and noise.
>
> So this prop looks like nothing you've ever seen before. It's
> relatively wide at the spinner and expands gradually from there till
> it reached max cord at about the end of the cowling (Lancair 235),
> then suddenly and dramatically narrows from both the leading and
> trailing edges. The narrowing gradually straightens out until both
> edges reach the tip, which is squared off. By the time the you get to
> the tip, the planform has narrowed so much, you'd think that very
> little lift could be developed out there. That's sort of true, the
> majority of the lift is developed at about half the radius of the prop
> although it's distributed all along the radius. The point in
> narrowing down the tip so dramatically is to reduce drag at the tip so
> as to increase efficiency and reduce noise.
>
> Lipp said in the article that those props that have wide tips or those
> techy looking turned up tips are actually pretty inefficient because
> no matter what the shape of the turned up tip (Q Tip comes to mind),
> it's still more area for the shockwaves to form on than just narrowing
> the tip and shearing it off.
>
> Another interesting point he makes is that the prop definately IS
> capable of creating lift even right next to the hub as long as it has
> been given the proper angle of attack. Because the airspeed right
> next to the hub is so low and he's using a symetrical laminar flow
> airfoil which demands a high angle of attack to produce lift, the
> pitch at the hub looks so steep as to be almost flat to the rotation
> of the prop.
>
> But the prop is designed for a fast airplane and when it's moving
> forward, that rate of advancement guarantees that that portion of the
> prop does produce lift.
>
> If I were to attempt to describe the planform so that folks could
> imagine what this look like, think of the glass that fits over the
> wick of an old kerosine lantern. Holding that glass up and looking
> directly at it from the side is a fair approximation of the planform.
> Starting at the base, it widens out, reaches it's maximum diameter,
> then narrows appreciably and somewhat abruptly as it extends to the
> top. The ELIPPSE has that planform, but where it reaches it's widest
> cord (at a little less than half the radius) the shape is more pointed
> there where the prop begins to narrow as you move out towards the tip.
>
> What's intriguing is how narrow the prop eventually gets out at the
> tip. It actually looks ridiculous, at first glance.
>
> But it works. Or at least it works for his lancair 235.
>
> Corky Scott

[Corky Scott]

Paul Lipps, an aerospace engineer, has developed a new prop for
experimentals. He's taken a new look at a lot of issues with props
and has come up with something that looks really strange, but works
extremely well.

Among the many things he attempted to incorporate in his prop design
was to utilize elliptical lift distribution, which many experts
claimed could not be done, but he's managed to do it.

He also wondered why folks were using flat bottomed turbulent airfoils
for high speeds. The flat bottomed airfoil coupled with a sharp
leading edge makes for a prop that has a narrow range of peak
efficiency, and also creates a lot of drag and noise. After all, the
tip approaches the speed of sound, what airfoil do you know for near
supersonic flight has a flat bottom?

Paul decided to use laminar flow symetrical airfoils.

Lift force on a wing is proportional to the square of the velocity.
That means if you double the speed, the lift force is quadrupled.
That being the case, you don't need a wide cord at the tip of the
propeller because it's moving at near subsonic speed. Going that
fast, it does not have to have a wide cord to produce lift.

Also, because the tip is moving at such high speeds, you need to
minimize it's size to reduce drag and noise.

So this prop looks like nothing you've ever seen before. It's
relatively wide at the spinner and expands gradually from there till
it reached max cord at about the end of the cowling (Lancair 235),
then suddenly and dramatically narrows from both the leading and
trailing edges. The narrowing gradually straightens out until both
edges reach the tip, which is squared off. By the time the you get to
the tip, the planform has narrowed so much, you'd think that very
little lift could be developed out there. That's sort of true, the
majority of the lift is developed at about half the radius of the prop
although it's distributed all along the radius. The point in
narrowing down the tip so dramatically is to reduce drag at the tip so
as to increase efficiency and reduce noise.

Lipp said in the article that those props that have wide tips or those
techy looking turned up tips are actually pretty inefficient because
no matter what the shape of the turned up tip (Q Tip comes to mind),
it's still more area for the shockwaves to form on than just narrowing
the tip and shearing it off.

Another interesting point he makes is that the prop definately IS
capable of creating lift even right next to the hub as long as it has
been given the proper angle of attack. Because the airspeed right
next to the hub is so low and he's using a symetrical laminar flow
airfoil which demands a high angle of attack to produce lift, the
pitch at the hub looks so steep as to be almost flat to the rotation
of the prop.

But the prop is designed for a fast airplane and when it's moving
forward, that rate of advancement guarantees that that portion of the
prop does produce lift.

If I were to attempt to describe the planform so that folks could
imagine what this look like, think of the glass that fits over the
wick of an old kerosine lantern. Holding that glass up and looking
directly at it from the side is a fair approximation of the planform.
Starting at the base, it widens out, reaches it's maximum diameter,
then narrows appreciably and somewhat abruptly as it extends to the
top. The ELIPPSE has that planform, but where it reaches it's widest
cord (at a little less than half the radius) the shape is more pointed
there where the prop begins to narrow as you move out towards the tip.

What's intriguing is how narrow the prop eventually gets out at the
tip. It actually looks ridiculous, at first glance.

But it works. Or at least it works for his lancair 235.

Corky Scott

[Corky Scott]

On Mon, 16 Aug 2004 13:12:02 +0000, John > wrote:

>Corky
>Any web address for more info, for the curious!
>John

The man's name is Paul Lipps, of Arroyo Grande, CA.

He left his e-mail address in the Contact! magazine article as:


I'm assuming he put his e-mail in the article because he doesn't mind
folks asking him about the prop.

He also states in the article: "I would like to design propellers for
various and sundry aircraft, but in order for me to design a prop for
a plane, I have to be able to form a drag model of the plane for my
equations. The best way to do this is to have one of my props
installed on a plane and then measure the planes performance with it.
So far I have only two props, and the 2-blade is on loan for a race
plane for Reno."

I too am interested in the prop, but I actually have a prop now and
can't afford to be buying new props. In addition, my airplane
(Christavia Mk4) will be using a Ford V-6 using a 2 to 1 reduction
unit and that spins the prop a lot more slowly than direct drive
aircraft engines. Makes the prop design a lot different. In
addition, it won't be going any 200 mph either. ;-)

Corky Scott

[Greg Reid]

A picture is worth 1000 words -- pretty much literally in Corky's case
:-)

http://www.contactmagazine.com/Issue77/PaulsProp.JPG

I'm quite interested in it myself. All of the stuff that Paul says
about it makes good sense to me. (So why has this idea taken so
long?)

Greg Reid

[Corky Scott]

On 16 Aug 2004 12:42:34 -0700,
(Greg Reid) wrote:

>I'm quite interested in it myself. All of the stuff that Paul says
>about it makes good sense to me. (So why has this idea taken so
>long?)
>
>Greg Reid

I really wonder if the planform for that prop was dictated by the
relatively high cruise speed of the Lancair 235 it's pulling through
the air. It's only 63" in diameter, which is fine for the Lancair 235
and it's 230+ mph cruise speed, but my prop wuffs along at 2000 or so
rpm at what I'm optimistically predicting will be 130 mph.

I suspect that the larger, heavier Christavia Mk4, with it's STOL wing
and not so fast cruise speed, along with the slower turning but larger
diameter prop would make for a very different looking planform.

Corky Scott

[Daniel]

Greg Reid wrote ...
> ...So why has this idea taken so long?



It hasn't.

Hartman & Biermann investigated & tested such props back in the
1930's. While they do indeed gain a bit in peak thrust, they lose
quite a bit of thrust at take-off. Minor thrust improvements at
cruise have relatively negligible benefits and major losses in thrust
at take-off have significant negative effects, hence such planforms
were shelved for almost all applications. Reference NACA Technical
Report 643.

Daniel

[OSKI 3]

Also read about ELLIPPSE propellor.
In fact I just subscribed to the mag
this morning (Contact!). They told me
that he plans to maket the prop at
competative prices compared to normal
props. I guess further info is on the way.
It looks and sounds practicle, in answer
to why so long in development, Nobody
ever took the design seriously and overlooked the concept. More to him!

Bill OParowski

[Corky Scott]

On 20 Aug 2004 07:04:30 -0700, (Daniel)
wrote:

>Hartman & Biermann investigated & tested such props back in the
>1930's. While they do indeed gain a bit in peak thrust, they lose
>quite a bit of thrust at take-off. Minor thrust improvements at
>cruise have relatively negligible benefits and major losses in thrust
>at take-off have significant negative effects, hence such planforms
>were shelved for almost all applications. Reference NACA Technical
>Report 643.

I'm not positive, because I don't have the article in front of me as I
write this, I'll check tonight, but I don't think this prop lost any
takeoff or climb performance.

As to the planform being like those tested by Hartman and Biermann, I
have not seen their planforms so I can't comment. If you look at the
prop in the picture cited here:

http://www.contactmagazine.com/Issue77/PaulsProp.JPG

Perhaps you can tell me if they are in fact similar.

Corky Scott

[Corky Scott]

On 20 Aug 2004 07:04:30 -0700, (Daniel)
wrote:

>
>It hasn't.
>
>Hartman & Biermann investigated & tested such props back in the
>1930's. While they do indeed gain a bit in peak thrust, they lose
>quite a bit of thrust at take-off. Minor thrust improvements at
>cruise have relatively negligible benefits and major losses in thrust
>at take-off have significant negative effects, hence such planforms
>were shelved for almost all applications. Reference NACA Technical
>Report 643.
>
>Daniel

Ok, I found the NACA Technical Article no. 643 and took a look at the
prop blade planforms they tested. The short answer is they do
resemble the ELLIPSE prop planform... sort of. But there are crucial
differences. All of the props tested start out round at their base
and did not begin to form the blade until what appears to be six to
eight inches away from the hub. That part of the prop, of course,
would contribute nothing towards thrust. The ELIPPSE prop is designed
to produce thrust even right next to the spinner.

Another difference is the extreme width the ELLIPSE prop gains before
it starts narrowing, as well as the sharpness of the planform at this
point where it begins narrowing.

Finally, the tips of the ELLIPSE prop are significantly more narrow
than the planform shown in the NACA report.

The differences appear to me to be significant enough that it would
not surprise me that the ELLIPSE prop actually can improve takeoff,
climb AND cruise, if, and this is a big if, the prop is properly sized
for the power, cruise speed and weight of the airplane.

Corky Scott

PS, it's probably significant that the props were intended for use on
radial engined airplanes. Due to the diameter of the engine, most
propellers were not expected to produce any thrust while the blade
planform was inside the arc of the cowling. Cooling was of sometimes
a problem though and some props for radial engined airplanes had cuffs
installed on the prop blades right next to the hub in an attempt to
direct some air at the engine's cylinders. Check some wartime photos
of the Grumman F3F Wildcat.

[Ryan Young]

Corky Scott > wrote in message >...
>
> He also wondered why folks were using flat bottomed turbulent airfoils
> for high speeds. The flat bottomed airfoil coupled with a sharp
> leading edge makes for a prop that has a narrow range of peak
> efficiency, and also creates a lot of drag and noise. After all, the
> tip approaches the speed of sound, what airfoil do you know for near
> supersonic flight has a flat bottom?

Look at the bottom of an A-4 - only slightly supersonic, but still.
Dead-ass flat. <this is a trick answer, having to do with the delta
planform, which is notoriously airfoil insensitive.>

And generally, prop tips DO NOT get supersonic. Mach .8 at most.

Finally, prop airfoils do not seem to make much difference. Look down
mid-page of this link for a discussion of real-world results with prop
airfoils: http://users.lmi.net/~ryoung/Sonerai/Carve_Prop.html
"Sensei" is a practical man of wide experience familiar to readers of
this newsgroup. Warnke props had/have an excellent rep, but this IS
about a 3rd hand rumor.

> Paul decided to use laminar flow symetrical airfoils.

There are people who do it. Having carved a prop meself, I will say
it's a WHOLE lot easier to manage a flat back side than a hollowed-out
one. Plus, you end up with a pretty thin trailing edge, which is
pretty hard to manage in wood.

Dr. Martin Hepperle, a German Aerodynamicist, has created a whole
family of laminar prop airfoils.
http://www.mh-aerotools.de/airfoils/index.htm I looked at using his
airfoils for my prop (which hasn't flown...), but gave up - for the
time being.

I don't know if they have ever been built into a full scale prop, let
alone tested.

> Lift force on a wing is proportional to the square of the velocity.
> That means if you double the speed, the lift force is quadrupled.
> That being the case, you don't need a wide cord at the tip of the
> propeller because it's moving at near subsonic speed. Going that
> fast, it does not have to have a wide cord to produce lift.
>
> Also, because the tip is moving at such high speeds, you need to
> minimize it's size to reduce drag and noise.

All this is true, but real live props need tips both wider and thicker
than ideal for reasons of structure, and flutter. Carbon fiber and
CAM has made possible shapes that could only dream about in the past.

> Another interesting point he makes is that the prop definately IS
> capable of creating lift even right next to the hub as long as it has
> been given the proper angle of attack.

True, but not much lift, again, because the airspeed is so low in
close to the spinner. And what is the efficiency, I.E. Lift to Drag
ratio of that portion of the prop? It may be absorbing more
horsepower than it is worth in thrust, even at high speeds.

Is this the same Paul Lipps that designed Light Speed Engineering's
ignition system?
http://www.lsecorp.com/Company/TheTeam/LSE_Team.htm

I'd love to see Paul's airplane run the CAFE Triaviathon, which
measures both climb and cruise performance, and compare it against a
"stock" Lancair 235, which I suspect the CAFE Foundation has data on.
Paul is near enough to Santa Rosa to make it possible.

I don't mean to spit on the man's props at all. I'm just engaging in
the dialogue, and showing my skepticism. It looks to me as if Paul's
props MAY show some improvment on his airplane, but I'm skeptical of
how much.

I've been meaning for some time to subscribe to CONTACT! Articles
like this one leave me no excuse.....hurray to Pat Panzera for finding
and publishing such interesting information.

[ELIPPSE]

The 3-blade ELIPPSE prop on the Lancair 235 doesn't use a symmetrical
airfoil; it's a highly-cambered NACA 63 series laminar flow airfoil,
with 13% thickness. It would probably be best defined as a 63 3 513.
Thin and symmetrical prop airfoils have very low L/D ratios, making
them unsuitable for high-efficiency props. The 3-blade ELIPPSE prop
designed for the "Phantom" biplane racer at Reno 2004 allowed it to
smoke the field. The plane went 20 mph faster (241 mph vs. 221mph) on
245 less rpm. See the write-up in the Fall 2004 "Sporstman Pilot",
www.sportsmanpilot.com .

[Corky Scott]

I had originally posted some information regarding the ELIPPSE prop
here and confess to remaining extremely interested still. The concept
of the prop planform and airfoil design demonstrates some very astute
thinking to me, although I'll be the first to admit I do not know as
much about props as I'd like. That's why I'm glad Paul has joined the
group.

It turns out that despite his being skilled enough with computers to
work with them to design the prop, he has not until his first post a
few days ago, posted to a newsgroup before. It's a new world for him.

Please let's not drive him away. The world of homebuilding in general
and props in particular can use fresh approaches to old problems.

Thanks, Corky Scott