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Jimmy Young
Joined: 24 Nov 2007
Posts: 182
Location: Missouri City, TX
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 Posted: Wed Dec 10, 2008 6:46 pm Post subject: trying a new prop |
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Kolbers,
I got a new prop delivered today from Valley Engineering. I hope to
put it on Saturday and if the weather is cooperative I plan to fly.
In my last post I mentioned my plane handled "superb". I need to re-
qualify that remark...it still has marginal climb out performance with
my new Generac engine. It's about half what my old 503 had, at best
about 400 fpm, but probably the average is more like 300. I'd call
that marginal at best. I currently have an IVO 72" 3 blade, set so I
get about 3700 rpm on take-off WOT. Once I'm up to cruise altitude, it
does handle and perform the same as it always did, with the exception
of the climb rate.
The new prop is a 78" 2 blade Culver Prop, pitched at 41. I'll still
have a good 2 1/4" from the tip to the boom tube. I'm going to also
change the spacer from a 3" to a 1 3/4" spacer, since the new prop is
2 1/4" thick at the hub and the IVO is only 1" thick. That should be a
better set up for maintaining prop balance since the prop will be
closer to the engine, and will still keep the prop tips 3 3/4" from my
aileron tubes. The larger spacer was used to allow for the clearance
required between the prop and the aileron tubes for the IVO, which has
a lot of flex. I have a prop thrust tester I can use, and I plan to
check the IVO on a static run up, record the thrust, then change out
to the new prop and see what it produces on a static run up.
I have a question to throw out there for review. If one prop produces
more static run up thrust than another, regardless of whether it is a
2 or 3 blade prop, would it not therefore be a better all around
performing prop in both climb and cruise? If the new prop, which is
not ground-adjustable like the IVO is, allows the engine to reach 3700
RPM on a static run up test, which is where the max HP and torque
values meet on the Generac engine, and if it produces more thrust at
that RPM level, it seems to me it would out-perform the IVO in both
climb out and cruise.
I know no one here know much about the engine I'm using, but wouldn't
these facts hold true for any engine/prop combination?
Thanks for any input,
Jimmy Young
FS II, Houston TX
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Jimmy Young
Missouri City, TX
Kolb FS II/HKS 700 |
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Dana
Joined: 13 Dec 2007
Posts: 1047
Location: Connecticut, USA
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| Posted: Wed Dec 10, 2008 7:17 pm Post subject: trying a new prop |
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At 09:45 PM 12/10/2008, Jimmy Young wrote:
| Quote: | I have a question to throw out there for review. If one prop produces
more static run up thrust than another, regardless of whether it is a
2 or 3 blade prop, would it not therefore be a better all around
performing prop in both climb and cruise?
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No, it might, but it's just as likely to be worse. A prop has to be
optimized for a particular airspeed, which is why we have "climb" props
which are less efficient at cruise speed, and "cruise" props which don't
climb as well but are more efficient during cruise. Or it could be a
compromise. A prop that's optimized for static thrust would have lousy
cruise (and even climb) performance. Taken to the extreme, consider a
helicopter rotor... it's optimized for static thrust but would make poor
(if any) thrust if used as a prop at 60 mph.
-Dana
--
I support drug testing. I believe every public official should be given a
shot of sodium pentathol and asked "Which laws have you broken this week?".
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The BaronVonEvil
Joined: 23 Jun 2006
Posts: 76
Location: Walla Walla, WA.
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| Posted: Wed Dec 10, 2008 8:40 pm Post subject: trying a new prop |
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Hi Jimmy,
Oh I think you are going to open up a can of worms here.
Static thrust is only a partial measure of how a prop may perform. Another
part is velocity of the same air. Basically you could have a huge amount of
thrust by swinging a twelve foot diameter prop that the engine is properly
geared for but, you would have such low velocity that a plane would never
gain enough speed to get off the ground.
It is finding the proper balance between engine speed, thrust and velocity
that has to overcome the weight and drag of the airframe to make a good
flying plane.
Basically, I think that your performance issue is a lack of horsepower. It
takes power to lift anything into the air rapidly. Once the plane has
reached a steady cruise, power is typically reduce for economy and
conservation of engine life.
You might have to re-pitch the prop so that on the ground you might be below
peak rpm/torque but, once the engine unloads in the air, the peak torque is
reached. Usually though most people pitch their props for maximum horsepower
and that is usually at a higher rpm than peak torque.
Oh there are so many trade-offs! Basically you are going to have to find
whats best for your application by good ol' trial and error. Two blades are
more efficient than three. One blade is best but, has its own practical
problems of balance issues to say the least. Good luck with the plane and
please be careful.
Carlos G.
Just My $0.02
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mdnanwelch7(at)hotmail.co
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| Posted: Wed Dec 10, 2008 9:48 pm Post subject: trying a new prop |
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| Quote: | I have a question to throw out there for review. If one prop produces
more static run up thrust than another, regardless of whether it is a
2 or 3 blade prop, would it not therefore be a better all around
performing prop in both climb and cruise?
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| Quote: | Jimmy Young
FS II, Houston TX
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Jimmy,
For the problems you've discussed, these are the reasons why I opted for the
in-flight adjustable, electric motor option, for my Ivo Prop.
I expect it should give the best of both worlds. At static thrust I can decrease pitch
substantially, allowing the engine to acheive a higher RPM (into the power band).
Once I'm cruising along, I can crank in quite a bit of pitch, for better dynamic thrust.
Although I haven't flown with this combination, yet. I have had it operational a few
years ago. It was quite impressive to me. The pitch change is quite subtantial, and takes
maybe 7-10 seconds to go from a flat pitch to really steep.
Although this combination may not be for everyone, it seems like a good way to go for me.
Mike Welch
MkIII
_________________________________________________________________
You live life online. So we put Windows on the web.
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lcottrell
Joined: 29 May 2006
Posts: 1490
Location: Jordan Valley, Or
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| Posted: Wed Dec 10, 2008 11:24 pm Post subject: trying a new prop |
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It depends on how he has the plane registered. If EAB he can use it, other wise no.
Larry C
[quote] ---
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NeilsenRM(at)comcast.net
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| Posted: Thu Dec 11, 2008 6:19 am Post subject: trying a new prop |
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Jimmy
This sounds like a good test. Of the composite props on the market the IVO
has the least thrust. That two bladed wood prop should give you alot more
thrust.
Horse power is always important but it is thrust that moves you. A long two
bladed prop turns more HP into thrust. The problem is that there are
compromises. As you get closer to the limit of how big a prop your engine
can handle the smaller speed range your prop work in.
If you configure your prop for best static thrust at max RPM you might over
RPM your engine or limit your cruise speed. The 41 pitch on your prop might
be just right but only testing will tell. I recently cut my prop from a 72
inch to 71 inches to get a wider speed range which it did but it also
increased the HP necessary to maintain the same cruise.
Let us know how it works.
Rick Neilsen
Redrive VW powered MKIIIC
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aslsa.rng(at)gmail.com
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| Posted: Sat Dec 13, 2008 8:49 am Post subject: trying a new prop |
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Jimmy, My experience with the new owners of Culver prop is that they are very good at what they do. I expect you will get some improvement but not that much. It's a heavy engine with low HP. We have a fellow in our EAA chapter who runs the Generac on a Legal Eagle. No need to worry about busting that FAR 103 55 knot limit on top speed. The 503 powered Airbike drivers have to throttle way back to fly with Chris' Legal Eagle. What you should see in static run up RPM is somewhat less than you want to see in flight. With Rotax engines that means 300 to 500 RPM less than full HP RPM.
If your new prop is giving you full HP RPM in flight, you're getting all you can from that prop. If it isn't, your prop search goes on.
Rick
PS Just for perspective, the B-29 had props 16' in diameter that were geared to run at about 950 RPM at the prop. Of course it had a tad bit more HP than the Generac
do not archive
On Thu, Dec 11, 2008 at 8:18 AM, Richard & Martha Neilsen <NeilsenRM(at)comcast.net (NeilsenRM(at)comcast.net)> wrote:
[quote]--> Kolb-List message posted by: "Richard & Martha Neilsen" <NeilsenRM(at)comcast.net (NeilsenRM(at)comcast.net)>
Jimmy
This sounds like a good test. Of the composite props on the market the IVO has the least thrust. That two bladed wood prop should give you alot more thrust.
Horse power is always important but it is thrust that moves you. A long two bladed prop turns more HP into thrust. The problem is that there are compromises. As you get closer to the limit of how big a prop your engine can handle the smaller speed range your prop work in.
If you configure your prop for best static thrust at max RPM you might over RPM your engine or limit your cruise speed. The 41 pitch on your prop might be just right but only testing will tell. I recently cut my prop from a 72 inch to 71 inches to get a wider speed range which it did but it also increased the HP necessary to maintain the same cruise.
Let us know how it works.
Rick Neilsen
Redrive VW powered MKIIIC
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Jimmy Young
Joined: 24 Nov 2007
Posts: 182
Location: Missouri City, TX
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| Posted: Sat Dec 13, 2008 3:19 pm Post subject: Trying a new prop |
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Richard Gerard wrote:
>>>With Rotax engines that means 300 to 500 RPM less than full HP RPM.<<<
Richard,
I got the new prop on today, but it was just too windy to fly. I did a static run up test with a thrust gauge, and was getting 255 lbs. with the new Culver prop. With the IVO, it was making 195 lbs. The with the new prop, the engine RPM would top out at 3300 rpm. But, with the IVO, the engine would hit 3600 rpm on a static thrust test. Since I didn't get to fly, I have nothing to compare yet regarding performance.
I am at a new airport now, and it's a good airport to test stuff at because it has 2800 ft. of grass runway. The first good calm evening this week I hope to take the plane up and see what the improvements are, if any. At least the new prop is producing more thrust and I hope that translates into better climb performance. I'm leary of any speculation on my part just because of the improved thrust #'s. I guess it is better than finding out it has less thrust than the IVO though. I'll post the results after I go fly it.
Jimmy Young
Houston TX
[quote][b]
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Jimmy Young
Missouri City, TX
Kolb FS II/HKS 700 |
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ez(at)embarqmail.com
Guest
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| Posted: Sat Dec 13, 2008 4:52 pm Post subject: Trying a new prop |
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Jimmy,With those numbers it sounds like you should experience a significant performance improvement.
Please keep us posted.
Gene
On Dec 13, 2008, at 6:26 PM, Jimmy Young wrote:
| Quote: | Richard Gerard wrote:
| Quote: | >>With Rotax engines that means 300 to 500 RPM less than full HP RPM.<<<
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Richard,
I got the new prop on today, but it was just too windy to fly. I did a static run up test with a thrust gauge, and was getting 255 lbs. with the new Culver prop. With the IVO, it was making 195 lbs. The with the new prop, the engine RPM would top out at 3300 rpm. But, with the IVO, the engine would hit 3600 rpm on a static thrust test. Since I didn't get to fly, I have nothing to compare yet regarding performance.
I am at a new airport now, and it's a good airport to test stuff at because it has 2800 ft. of grass runway. The first good calm evening this week I hope to take the plane up and see what the improvements are, if any. At least the new prop is producing more thrust and I hope that translates into better climb performance. I'm leary of any speculation on my part just because of the improved thrust #'s. I guess it is better than finding out it has less thrust than the IVO though. I'll post the results after I go fly it.
Jimmy Young
Houston TX
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