Today's Message Index:
----------------------
1. 08:24 AM - Re: Jetting puzzler (slingshot003)
2. 08:47 AM - Re: Jetting puzzler (slingshot003)
3. 10:26 AM - Re: Re: Jetting puzzler ()
4. 12:52 PM - Re: Re: Jetting puzzler (Rick Neilsen)
5. 07:45 PM - Re: Jetting puzzler (Richard Pike)
Message 1
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| Subject: | Re: Jetting puzzler |
Richard,
That is a puzzler. Raising gear ration unloads the engine which would require
leaning the carbs, but you pitched the prop accordingly so the load should have
returned to normal. This was the case for full throttle so why was it not the
case for cruise? My guess is that the Warp Drive prop has similar characteristics
at full throttle as your previous prop, but it also has different characteristics
at cruise compared to the previous prop. Since Warp is turning slower
and since it is probably stiffer, it probably had much less induced twist
at cruise compared to the previous prop so it does not bite as much air, thus
less loaded, thus leaner carb at cruise. You loaded (pitched) the Warp to match
the load of the engine at full power so that would guarantee that the jetting
would be the same because the previous setup was also matched for full power.
It would then seem that the Warp behaves differently at midrange & turning
slower than the other setup, thus demanding a leaner midrange jetting. This
would be my theory. -Richard Swiderski
Read this topic online here:
http://forums.matronics.com/viewtopic.php?p=501451#501451
Message 2
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| Subject: | Re: Jetting puzzler |
Richard,
Since you had a significant decrease in demand for fuel at cruise rpm, it would
be interesting for us to know if at that same rpm did your cruise speed remain
the same or even increase? If so, then we would know how to increase the range
of our Kolbs, as less fuel for the same or more speed would mean a more efficient
setup. Maybe you could take note and let us know?
Also, do you have the data regarding the change of thrust at full power compared
to your initial setup? Theoretically we know it should be more, but is it significantly
more? Can you tell "by the seat of your pants" at take-off?
Thanks, -Richard Swiderski
Read this topic online here:
http://forums.matronics.com/viewtopic.php?p=501453#501453
Message 3
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| Subject: | Re: Jetting puzzler |
The reason we have PRUs is not to just add weight and complexity. It's to
turn a larger prop at a speed that keeps the tips from going super-sonic or
even close. And as for props? Well you don't see any wind-mill farms with
6' propellers! The larger prop is more efficient, right at the get go.
And yet that makes for larger gyroscopic loads and heavier bearings, and in
many cases, a longer landing gear for ground clearance.
On Tue, 20 Apr 2021 08:46:58 -0700, "slingshot003" <i2bxtn@gmail.com>
wrote:
>
> Richard,
>
> Since you had a significant decrease in demand for fuel at cruise rpm,
it
> would be interesting for us to know if at that same rpm did your cruise
> speed remain the same or even increase? If so, then we would know how to
> increase the range of our Kolbs, as less fuel for the same or more speed
> would mean a more efficient setup. Maybe you could take note and let us
> know?
>
> Also, do you have the data regarding the change of thrust at full power
> compared to your initial setup? Theoretically we know it should be more,
> but is it significantly more? Can you tell "by the seat of your pants"
at
> take-off?
>
> Thanks, -Richard Swiderski
>
>
>
>
> Read this topic online here:
>
> http://forums.matronics.com/viewtopic.php?p=501453#501453
>
>
>
>
>
>
Message 4
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| Subject: | Re: Jetting puzzler |
There is a whole lot of science that I don't understand but I learned a bit
with my VW. You get a bunch more thrust moving a bunch of air slowly than
less air quickly but it isn't that simple. When you have a small prop
accelerating a small amount of air a lot you have a wide range of effective
speeds that the prop provides thrust. If you have a bigger prop the speed
range is less. I think a prop is most efficient when the prop is close to
the real pitch of the prop, like a screw going into a piece of wood. I
assume when you pull power to cruise you unload the prop because your are
getting close to the real pitch of the prop. You should be happy with your
big slow turning prop but there is a trade off. Do you pitch the prop for
best cruise at cruise RPM or best climb at full power at best power RPM.
The most common is to set the pitch for best power in climb, but you may
find that your cruise is slower than you want. I set my pitch for best
cruise speed at the recommended cruise RPM and live with lower climb
power/RPM. I spend most of my time at cruise. I have a abundance of thrust
with the big slow turning prop so it isn't a big deal. A few years ago I
cut 1/2" off the prop tips to get more climb thrust but I ended up with
less cruise and climb thrust.
There has to be people out there that have some real prop knowledge, what
do you think.
Rick Neilsen
Redrive VW Powered MKIIIC
On Tue, Apr 20, 2021 at 11:26 AM slingshot003 <i2bxtn@gmail.com> wrote:
>
> Richard,
>
> That is a puzzler. Raising gear ration unloads the engine which would
> require leaning the carbs, but you pitched the prop accordingly so the load
> should have returned to normal. This was the case for full throttle so why
> was it not the case for cruise? My guess is that the Warp Drive prop has
> similar characteristics at full throttle as your previous prop, but it also
> has different characteristics at cruise compared to the previous prop.
> Since Warp is turning slower and since it is probably stiffer, it probably
> had much less induced twist at cruise compared to the previous prop so it
> does not bite as much air, thus less loaded, thus leaner carb at cruise.
> You loaded (pitched) the Warp to match the load of the engine at full power
> so that would guarantee that the jetting would be the same because the
> previous setup was also matched for full power. It would then seem that
> the Warp behaves differently at midrange & turning slower than the other
> setup, thus demanding a lean!
> er midrange jetting. This would be my theory. -Richard Swiderski
>
>
> Read this topic online here:
>
> http://forums.matronics.com/viewtopic.php?p=501451#501451
>
>
Message 5
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| Subject: | Re: Jetting puzzler |
You guys are great; thanks!
I still do not have any good numbers because the wind around here for the last
several weeks has been totally uncooperative. Went flying yesterday morning to
try out a different prop pitch setting and managed to peg the vario both ways
twice within 30 seconds. WHEEEE!!! But not much good for gathering data...
Seat of the pants is amazing, and I am having to relearn a few things. I used to
start the takeoff roll stick back while gradually, smoothly feeding in full
throttle, stick forward/raise the tail, accelerate some more, lower the tail,
fly.
Now - If I start the takeoff roll with stick back and gradually, smoothly feed
in full power, it simply lifts off well before it ought to, even as you are getting
the stick forward, and it's typically in a right yaw and left roll. Not
good and most unnerving.
So I quit that. 2/3 throttle and ease the stick forward until it feels right, then
full throttle and lift off, feels perfect. It still gets off the ground in
half the distance it used to.
So far it looks like the climb rate is about 25-30% better, and cruise might be
about the same as before at similar rpm's, but right now it's hard to say. Can't
wait for some decent air to get some real numbers.
--------
Richard Pike
Kolb MKIII N420P (420ldPoops)
Kingsport, TN 3TN0
Forgiving is tough, being forgiven is wonderful, and God's grace really is amazing.
Read this topic online here:
http://forums.matronics.com/viewtopic.php?p=501458#501458
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