Today's Message Index:
----------------------
1. 04:20 AM - thrustline (Peter Cowan)
2. 07:36 AM - Re: Reducing power on take off versus thrust line. (Richard Pike)
3. 07:48 AM - Re: thrustline (Richard Pike)
4. 08:15 AM - Re: Kolb-List Digest: 2 Msgs - 10/04/21 (Richard Swiderski)
5. 08:20 AM - Re: Re: Reducing power on take off versus thrust line. (william sullivan)
6. 08:56 AM - Re: thrustline (Rick Neilsen)
7. 09:08 AM - Mark III weight and balance (ridefst)
8. 10:53 AM - Re: Mark III weight and balance (Rick Neilsen)
9. 01:22 PM - Thrust line (james.vanlaak@gmail.com)
10. 01:37 PM - Re: Thrust line (Jay Dub)
11. 02:54 PM - Re: thrustline changes (1957grnchev@bluemarble.net)
12. 04:26 PM - Re: Thrust line (1957grnchev@bluemarble.net)
13. 07:14 PM - Re: Mark III weight and balance (Richard Pike)
14. 09:37 PM - Re: Re: Reducing power on take off versus thrust line. (lane jones)
Message 1
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Re:
: 10:48:03 PM PST US
Subject: Kolb-List: Re: Reducing power on take off versus thrust line.
From: "chic" <gcechini@msn.com>
Okay, so I am a little confused here..... If I raise (just) the rear of the
engine
on my Firestar 2 for more prop clearance off the boom tube, am I adding
positively
or negatively to the thrust
Raising just the back motor mount so that the thrustline points lower at
the front is down thrust which results in an in flight nose up force..
Message 2
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| Subject: | Re: Reducing power on take off versus thrust line. |
Reading this thread jarred loose a memory from back in the 70's when guys were
first starting to put gokart engines on Quicksilvers - Don't remember who it was
that said it, but I do remember it was an article in Glider Rider. (Anyone
else used to get that one?)
Basically it was that you wanted the engine thrust line to have the prop perpendicular
to the horizon when the wing was at it's normal angle of attack in level
flight.
--------
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=503423#503423
Message 3
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Correct.
Don't know what you call it, but picture progressively lowering the rear motor
mount (pretend that prop length is not a problem) and you can see that eventually
your thrust line is going to want to make the airplane just do outside loops.
Obvious exaggeration, but you get the idea.
When I went from a 68" prop to a 72" prop, I had to raise the engine to get prop
clearance, and also ended up adding two extra washers under the rear motor mounts,
working on trim. So the rear of the engine is now about 1/8" higher than
the front. But subject to change.
--------
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=503424#503424
Message 4
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| Subject: | Re: Kolb-List Digest: 2 Msgs - 10/04/21 |
chic,
Since your engine is behind the CG, if you raise the rear of your engine
(direct some of your thrust downward) you will take away some of your
forward thrust and add to your downward thrust, which in turn will cause
the nose to be pushed up. Picture a teetter-todder: the CG is the fulcrum;
the engine is on the tail side; and the nose is on the other side. If the
engine is pointed down it will be pushing the whole
teetter-todder downward, but since it is on the tail side, it is also
causing the nose to go up.
On Tue, Oct 5, 2021 at 2:39 AM Kolb-List Digest Server <
kolb-list@matronics.com> wrote:
> *
>
> =================================================
> Online Versions of Today's List Digest Archive
> =================================================
>
> Today's complete Kolb-List Digest can also be found in either of the
> two Web Links listed below. The .html file includes the Digest formatted
> in HTML for viewing with a web browser and features Hyperlinked Indexes
> and Message Navigation. The .txt file includes the plain ASCII version
> of the Kolb-List Digest and can be viewed with a generic text editor
> such as Notepad or with a web browser.
>
> HTML Version:
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> ===============================================
> EMail Version of Today's List Digest Archive
> ===============================================
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> ----------------------------------------------------------
> Kolb-List Digest Archive
> ---
> Total Messages Posted Mon 10/04/21: 2
> ----------------------------------------------------------
>
>
> Today's Message Index:
> ----------------------
>
> 1. 06:33 AM - Re: Fitting request (Rick Neilsen)
> 2. 10:48 PM - Re: Reducing power on take off versus thrust line.
> (chic)
>
>
> ________________________________ Message 1
> _____________________________________
>
>
> Time: 06:33:53 AM PST US
> From: Rick Neilsen <neilsenrm@gmail.com>
> Subject: Re: Kolb-List: Fitting request
>
> Paul
>
> I have a Kolb MKIIIC. It is located at the Hart/Shelby County airport in
> Michigan. Take the Badger (car ferry) across lake Michigan to ludington and
> it is app 20 miles south. You are welcome to test fit in it. I'm heading to
> Florida for the winter Oct 21 so if you are going to check it out please do
> so quickly.
>
> Rick Neilsen
> Redrive VW Powered MKIIIC
>
>
> On Sat, Oct 2, 2021 at 7:49 PM prhutson <prhutsonwi@gmail.com> wrote:
>
> >
> > Is there anyone with a Mark III anywhere near south-central Wisconsin
> that
> > would let me sit in their Classic or Xtra for a fitting? I am 6'3" but
> > longish torso. Failed a fit in a Sonex today. There was no one around
> at
> > Airventure this year when I stopped by for a fitting in a Mark III there.
> > Thanks!
> > Paul
> >
> > --------
> > Paul Hutson
> > Middleton, WI
> >
> >
> > Read this topic online here:
> >
> > http://forums.matronics.com/viewtopic.php?p=503382#503382
> >
> >
>
> ________________________________ Message 2
> _____________________________________
>
>
> Time: 10:48:03 PM PST US
> Subject: Kolb-List: Re: Reducing power on take off versus thrust line.
> From: "chic" <gcechini@msn.com>
>
>
> Okay, so I am a little confused here..... If I raise (just) the rear of
> the engine
> on my Firestar 2 for more prop clearance off the boom tube, am I adding
> positively
> or negatively to the thrust line?
>
>
> Read this topic online here:
>
> http://forums.matronics.com/viewtopic.php?p=503414#503414
>
>
--
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Message 5
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| Subject: | Re: Reducing power on take off versus thrust line. |
If you pick up the rear, it will push the nose down. Imagine picking up th
e rear about 2 feet.
On Tuesday, October 5, 2021, 01:48:07 AM EDT, chic <gcechini@msn.com>
wrote:
Okay, so I am a little confused here..... If I raise (just) the rear of the
engine on my Firestar 2 for more prop clearance off the boom tube, am I ad
ding positively or negatively to the thrust line?
Read this topic online here:
http://forums.matronics.com/viewtopic.php?p=503414#503414
S -
WIKI -
-
=C2- =C2- =C2- =C2- =C2- -Matt Dralle, List Admin.
Message 6
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I am concerned people might not understand the negative impact of using
thrust to counter power induced pitch changes.
First, your effective thrust will be reduced. The impact is related to
total thrust and the amount of change of thrust line.
Second, the down thrust needs to be countered by increasing the angle of
attack of the wings which adds drag and increased stall speed.
What is the total impact? Really hard to say but just grabbing an
unrealistic number out of the air does a disservice to our readers. There
have been a lot of smart people designing and building Kolb airplanes for a
lot of years. If it was beneficial and that easy everyone would be flying
our planes that way from the very start.
Rick Neilsen
Redrive VW Powered MKIIIC
On Tue, Oct 5, 2021 at 7:22 AM Peter Cowan <cowan.phc@gmail.com> wrote:
> Re:
> : 10:48:03 PM PST US
> Subject: Kolb-List: Re: Reducing power on take off versus thrust line.
> From: "chic" <gcechini@msn.com>
>
>
> Okay, so I am a little confused here..... If I raise (just) the rear of
> the engine
> on my Firestar 2 for more prop clearance off the boom tube, am I adding
> positively
> or negatively to the thrust
>
> Raising just the back motor mount so that the thrustline points lower at
> the front is down thrust which results in an in flight nose up force..
>
Message 7
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| Subject: | Mark III weight and balance |
Getting close to my first flight, and I've found that I need 82lb of steel shot
in front of the passenger seat to get my CG around 30% (20.2" back from LE)
Does this seem normal, or is something weird?
Total flying weight would be 748lb (326 left, 371 right, 50 tail)
I'm 195lb / 6', so pretty average size.
Rotax 582, three blade composite prop
BRS in front of engine
Both fuel tanks full (about 10 gal total)
No doors, just windshield
Original mesh seats
Seems to be in good shape like this, just way more weight that I was expecting
to need!
Thanks,
Franklin
Read this topic online here:
http://forums.matronics.com/viewtopic.php?p=503429#503429
Message 8
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| Subject: | Re: Mark III weight and balance |
Franklin
82 lbs does sound excessive. I have a MKIIIC with a redrive VW engine. I
seem to recall that my engine is a bit heavier than normal and was a bit
behind the CG so I moved my battery to the nose cone. When all weighed and
calculated my plane will stay in the safe aft CG range as long as the only
person on board weighs at least 160lbs. The forward range couldn't be too
far forward with passengers loading well over max allowable weight.
Revisit your calculations but stay safe. For your first flights anchor some
weight on the floor of the passenger area just to be safe.
Rick Neilsen
Redrive VW powered MKIIIC
On Tue, Oct 5, 2021 at 12:11 PM ridefst <fmgeiser@gmail.com> wrote:
>
> Getting close to my first flight, and I've found that I need 82lb of steel
> shot in front of the passenger seat to get my CG around 30% (20.2" back
> from LE)
> Does this seem normal, or is something weird?
> Total flying weight would be 748lb (326 left, 371 right, 50 tail)
> I'm 195lb / 6', so pretty average size.
> Rotax 582, three blade composite prop
> BRS in front of engine
> Both fuel tanks full (about 10 gal total)
> No doors, just windshield
> Original mesh seats
>
> Seems to be in good shape like this, just way more weight that I was
> expecting to need!
>
> Thanks,
> Franklin
>
>
> Read this topic online here:
>
> http://forums.matronics.com/viewtopic.php?p=503429#503429
>
>
Message 9
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I have been biting my tongue on this thread for a while but have to say a
few things. And yes, I am an engineer.
Remember that thrust losses from pitching the engine are going to be very
small. The thrust loss varies with the cosine of the angle. So for small
angles the loss is small.
The pitching force of the airplane results from the sum of the forces
acting on it at that moment. The sum yields a resultant force vector and
its relationship to the center of gravity tells whether it is up or down.
On takeoff, there is negligible aerodynamic drag so the thrust line is a
major force to accelerate the airplane. If it is not pushing through the
center of gravity there will be a pitching moment. On Kolbs, it is
obviously down.
During the takeoff roll, there is a force from the rolling friction of the
wheels. It is obviously well below the center of gravity, so it also
pitches down.
Early in the takeoff the drag on the wing is relatively low so its
contribution is fairly low, but as airspeed increases it grows. At maximum
level speed the drag of the wing is a major part of the total drag that
obviously equals the thrust from the engine (hence maximum level speed).
Other sources of drag, like the fuselage and landing gear legs will tend to
pitch nose down. But remember that the thrust of the engine on a Kolb is
pushing pretty close to the centerline of the wing, so those two forces are
largely offsetting.
Finally, the downforce on the tail is what we use to balance the rest. If
we had the horizontal tail in the wake of the prop we would see a downforce
proportional to the power setting. High power with high tail downforce.
Look at certified pusher prop planes, mostly amphibians. Lake Amphibian,
Seabee, and others all have big tails in the middle of the propwash. There
is a reason for that.
I built an original Firestar and owned a Mark 3X. Both were nice flying
airplanes with large pitching moments. I also owned a Buccaneer amphibian,
Rans S-12, Sportflight Talon, Drifter, CGS Hawk, and Super Hornet. All had
similar but different pitching responses. I thought the S12 was the worst,
but the Buccaneer was close behind.
In general it is not hard to learn to control this, but it does require
attention. A power loss on takeoff may require a strong nose down push to
keep from stalling. If you forget that you will be in trouble. I never
worried about it for myself because I flew the planes a lot, but I did not
want to loan them to someone who was not familiar with the characteristics.
Frankly, I love pushers but not this pitching moment. Someday I will build
a custom machine with the horizontal tail in the slipstream to minimize the
effect.
Message 10
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"Someday I will build a custom machine with the horizontal tail in the slipstream
to minimize the effect."
I was glad to see you had a CGS Hawk. They still have a high thrust line but the
curved boom tube was to get the tail into the prop wash so you had some response
once you added some power. Also, in my Hawk the engine sat a lot lower
than on the Firestar 2 I'm building. My prop centerline was about even with
bottom of the wing on my 1991 Hawk Arrow. The drag on the landing gear definitely
gave a pitching down moment but I'm surmising the Firestar I'm building will
be a lot worse since the engine will sit so high in comparison.
Jay
Message 11
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| Subject: | Re: thrustline changes |
Re: Thrust line comments
Put a tractor prop on the nose, and it has a fairly long arm. But
mounting 2X the HP above and behind (AND CLOSE to) the CG will be
different. Seeing all of these posts, reminds me of the following:
Prop thrust is greatest as slow speeds
Stab/Elevator effectiveness is least at slow speeds
Take off roll requires ground roll drag, also causing an additional
forward pitching moment.
Wing pitching moment is variable (on most airfoils, depending on AOA and
airspeed(?)
When considering thrust angle variables.. to what? CG, center of mass,
or center of drag?:
There is the CG measured with the AC level. Does anyone know the center
of mass on their Kolbs??
Or the center of drag which changes a lot with airspeed, loading, and
being on the ground, or in the air. I would assume induced drag is near
constant above stall speed, if level flight is maintained with trim.
But parasitic drag goes up with the cube of the speed, and drag on
take-off depends upon grass height, tire pressures, ground firmness and
TOW.
What doesn't change, is the number of questions asked when a perfectly
good airplane flies very differently with 2X the horse power initially
intended. A very small increase in opposing leverage could be
accomplished with only slightly larger Stab and Elevator! My Drifter is
very similar to my Kolb configuration, and yet the tail areas must be
twice as large! I never noticed ANY pitch issues flying the Drifter.
But I didn't bolt on 100 HP either!
If people are going to be arbitrary with a design which had minimal tail
area initially, why not improve THAT!?!? Oh, I forgot, you can't do
that with just a few washers! LOL There isn't hardly anything that can
be changed on an airplane, that doesn't affect a LOT of different
aspects.
Message 12
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Very Weird! I only see and reply to the list via my email. I no longer
log on. I only saw the response from James Vanlaak JUST NOW.. and very
much appreciate what he wrote! What I found odd, was having not seen
his post before I wrote mine! So I was not trying to trump his words.
Thanks James for the much better (technical) description!
Message 13
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| Subject: | Re: Mark III weight and balance |
Something doesn't sound right. I have done a lot of mods to my MKIII but nothing
to move the weight fore or aft much, I have a 582 and need no ballast.
I assume you are using the Kolb forms on page 41, 42 & 43 of "The Yellow Book"?
If not, PM me, I'll email them to you. FWIW, here is my W&B:
--------
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=503443#503443
Attachments:
http://forums.matronics.com//files/mkiii_wandb_166.jpg
Message 14
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| Subject: | Re: Reducing power on take off versus thrust line. |
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