Today's Message Index:
----------------------
1. 07:34 AM - Re: Re: Thrust line...? (william sullivan)
2. 09:30 AM - Prop thrust (B Young)
3. 10:27 AM - Re: Prop thrust ()
4. 10:44 AM - Re: Kolb-List Digest: 3 Msgs - 04/04/21 (Richard Swiderski)
5. 11:28 AM - Re: Prop thrust (Rick Neilsen)
6. 12:04 PM - Re: Kolb-List Digest: 3 Msgs - 04/04/21 (Larry Cottrell)
7. 12:06 PM - Fw: Kolb-List Digest: 3 Msgs - 04/04/21 (Larry Cottrell)
8. 12:42 PM - Re: Fw: Kolb-List Digest: 3 Msgs - 04/04/21 ()
9. 12:47 PM - Re: Prop thrust ()
10. 01:36 PM - Re: Re: Kolb-List Digest: 3 Msgs - 04/04/21 (John Hauck)
11. 02:18 PM - Re: Re: Kolb-List Digest: 3 Msgs - 04/04/21 (Rick Neilsen)
12. 02:31 PM - angle (Larry Cottrell)
13. 02:33 PM - angle (Larry Cottrell)
14. 02:38 PM - Re: Re: Kolb-List Digest: 3 Msgs - 04/04/21 (Larry Cottrell)
Message 1
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| Subject: | Re: Thrust line...? |
Richard- I believe Jack Hart did a lot of experiments with this, and also
made a simple jig to cut down a prop (if memory is correct).
Here is the link to his stuff: http://www.jackbhart.com/firefly/fireflyind
ex.html
Everybody on the List ought to bookmark it.
Bill Sullivan
On Sunday, April 4, 2021, 10:37:18 PM EDT, Richard Pike <thegreybaron@
charter.net> wrote:
Appreciate your thoughts Rick. After a couple weeks of experimenting with t
his rig, puzzling over it, and reading this, I think tomorrow I will order
a couple more longer bolts so that I can get the engine and thrust line bac
k to what it was originally (like Kolb had it), just a couple inches higher
, because so far, the closer I get it to original stock, the better it flie
s. It just needs a bit more elevation so the prop will clear the tube when
the thrust line is stock.
Wind has=C2- been too contrary & trashy to get any accurate readings yet,
but so far the 3.47:1 box & 72" three blade prop looks like an amazing imp
rovement.
--------
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=501264#501264
S -
WIKI -
-
=C2- =C2- =C2- =C2- =C2- -Matt Dralle, List Admin.
Message 2
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Rick said and it got me thinking....
The CG is forward of the position of the prop but
also fairly close to the CG. Press down on the prop and the plane pitches
up, lift and it pitches down. .
Still trying to get this figured out in my mind. So ive gone to the
extreme. I've seen a photo of a low wing plane with the engine mounted on
top of the rudder... The prop is mounted 7 feet behind and above the cg
and center of drag (cdrag) much like the kolb but much further back, in my
mind the physics remains the same but on a larger scale than the kolb.
Because the thrust is higher than the cg /c drag there will still be some
nose down tendancy with increased power. The following examples may (i
hope) shed some light on how to neturalize it.
Now this is where i am taking a good size leap, and if i am wrong I'll
apologize in advance.
Now in the following examples if the angle changes don't register in your
mind the pressure changes to the aircraft... Draw 2 pictures. One of the
aircraft ive described, and one of an engine and prop. Place the second
pic on top of the first, and if needed over exaggerate the thrust angle
even more,,, say 15 and 30 deg. If you ask why i suggested this, ive done
it.
Let's assume that the aircraft is flying straight and level, and the engine
thrust line is parallel to the direction of travel. The thrust is above
the cg/cdrag so there will be an amount of nose down tendancy that can
be compensated for with a small amount of up elevator. When the power is
cut, the nose down tendancy (forces) go away and the nose of the plane goes
up.
I will exaggerate to make a point....
If we raise the front of the engine 2 deg. The thrust above the cg/cdrag
will have a tendancy to push the nose down adding the up pressure from
the prop thrust angle on the tail will require even more up elevator.
When the power from cruise is cut the higher than cg/cdrag is removed also
the 2 deg. uplift on the tail is removed. This should cause a much
greater nose up situation.
If we lower the front of the engine 2 deg the majority of thrust is still
above the cg/cdrag and the nose down tendancy is countered by down pressure
on the tail from the prop pushing down 2 deg. No elevator is needed and
when we cut power there should be no tendancy for the nose to drop or raise.
Try again with 4 deg of down angle ln the engine.(lower the front of the
engine).. The thrust line is still above the cg/cdrag so a small nose
down moment is still present, but now there is much more down force from
the prop thrust angle. This additional down force to the rear of cg(tail)
should require down elevator to compensate. If we remove power. The
nose drops.
Now I have used a high tail mounted engine in the example. But would
imagine that the same principals apply to the kolbs. The moment arms are
much smaller on a kolb, and because of the shorter moment arms, some of
the angles would be greater.
Burt Rutan is reported to have said that on a bird, every feather makes a
difference in how it flies.. not accounted for in my explanation is
relationship between cg and c lift, Moving cg with fuel burn, changes in
attitude at different flight speeds, climbing or descending, the exact
relationship (arm)between cg/cdrag and the thrust line of the engine prop.
I did however assume the thrust line stayed above the cg/cdrag.
Please remember that the large angle changes in the narration were used to
induce thought, not to be used in real life trials.
Again if i have it wrong, please , someone HELP me understand.
Boyd Young mkiii Utah
Sorry this got overly long
Do not archive
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Just to add a few comments about this whole discussion... (and yeah, all
of this could be wrong too)
You might need a super computer to do the full blown flight simulation..
but the big factors (I believe) are the following:
You have the engine thrust vector.. how much it is pitched up or down.
Considering it's location, I doubt that is the primary contributor, if
changes are slight.
You have the drag of the wing, as profile AND the dynamic drag (due to
producing lift, which changes with speed and angle of attack).. AND there
is a pitching moment caused by how different airfoils react at different
angles of attack.
You have the total aircraft profile drag, which is WELL BELOW the wing,
engine, and thrust vectors.. ie, all of the drag from the fuse, pilot,
landing gear. And all of that changes with the square of the airspeed.
But I would suspect it doesn't change much with the attitude of the
aircraft, (if right side up).
You have the center of mass, which may be only slightly higher than the
center of drag.. considering again, undercarriage, pilot weight, fuel (in
most, behind the pilot but low), and the mass of the fuse
And you have the mass distribution over the whole of the air-frame. If
all the heavy stuff is close in to the center of mass, it's different than
if it is further out. (See ice skaters spinning.. arms in = faster, etc).
We'll HOPE that's not changing while we fly.. but it does have an effect on
how easily the plane pitches, with power changes applied.
Aircraft designs can use a lifting stab.. such that with increased
airspeed, (producing more lift).. the flying stab tends towards keeping it
level, but still climbing. (HP above what is required for level flight,
produces ROC). A positive angle of attack on the flat stab of the Kolb has
a similar, but reduced effect. And the size of the tail area * tail arm
the amount of control authority. Kolb tail feathers are really small in my
opinion, esp compared to those of my Drifter for example.
But the one thing which comes to my mind, is that by having the engine
mounted above and behind both the cg and center of drag and mass, is that
if near stalling, the quick application of power, will A) pull more air
across the wing, reducing the stall point, and forcing the nose down,
reducing the angle of attack. Both good things. But none of the Kolbs are
designed by aero-space engineers (or that I am aware of).. so it may well
have some characteristics which require trim, or human reaction to huge
power change inputs. Flying with my dad (old hat pilot).. and knowing a
little bit about engines in general.. huge/fast power changes are not
ideal, if they can be avoided.. either to accelerate or decelerate! And
with our non-certified engines, if they are running, may be more important
than anything else.
Making changes to a EXP? No problem there, if done carefully and with
some research. And yeah, engine placement is rather easy to edit. If you
are going to re-engineer it, there are a lot of factors, and just as many
things which could benefit from being revised. But it's not a simple
puzzle.
On Mon, 5 Apr 2021 10:30:07 -0600, B Young <byoungplumbing@gmail.com>
wrote:
> Rick said and it got me thinking....The CG is forward of the position of
> the prop but
> also fairly close to the CG. Press down on the prop and the plane
pitches
> up, lift and it pitches down. .
>
> Still trying to get this figured out in my mind. So ive gone to the
> extreme. Ive seen a photo of a low wing plane with the engine mounted
> on top of the rudder... The prop is mounted 7 feet behind and above
> the cg and center of drag (cdrag) much like the kolb but much further
> back, in my mind the physics remains the same but on a larger scale than
> the kolb. Because the thrust is higher than the cg /c drag there will
> still be some nose down tendancy with increased power. The
> following examples may (i hope) shed some light on how to neturalize it.
> Now this is where i am taking a good size leap, and if i am wrong Ill
> apologize in advance.
>
> Now in the following examples if the angle changes dont register in your
> mind the pressure changes to the aircraft... Draw 2 pictures. One of
> the aircraft ive described, and one of an engine and prop. Place the
> second pic on top of the first, and if needed over exaggerate the thrust
> angle even more,,, say 15 and 30 deg. If you ask why i suggested
> this, ive done it.
>
> Lets assume that the aircraft is flying straight and level, and the
> engine thrust line is parallel to the direction of travel. The thrust
> is above the cg/cdrag so there will be an amount of nose down
> tendancy that can be compensated for with a small amount of up
> elevator. When the power is cut, the nose down tendancy (forces) go
> away and the nose of the plane goes up.
>
> I will exaggerate to make a point....If we raise the front of the engine
> 2 deg. The thrust above the cg/cdrag will have a tendancy to push
> the nose down adding the up pressure from the prop thrust angle on the
> tail will require even more up elevator. When the power from cruise
> is cut the higher than cg/cdrag is removed also the 2 deg. uplift on
> the tail is removed. This should cause a much greater nose up
> situation.
> If we lower the front of the engine 2 deg the majority of thrust is
still
> above the cg/cdrag and the nose down tendancy is countered by down
> pressure on the tail from the prop pushing down 2 deg. No elevator
> is needed and when we cut power there should be no tendancy for the nose
> to drop or raise.
> Try again with 4 deg of down angle ln the engine.(lower the front of the
> engine).. The thrust line is still above the cg/cdrag so a small nose
> down moment is still present, but now there is much more down force
> from the prop thrust angle. This additional down force to the rear of
> cg(tail) should require down elevator to compensate. If we remove
> power. The nose drops.
> Now I have used a high tail mounted engine in the example. But would
> imagine that the same principals apply to the kolbs. The moment arms
> are much smaller on a kolb, and because of the shorter moment arms,
> some of the angles would be greater.
> Burt Rutan is reported to have said that on a bird, every feather makes
a
> difference in how it flies.. not accounted for in my explanation
> is relationship between cg and c lift, Moving cg with fuel burn,
> changes in attitude at different flight speeds, climbing or descending,
> the exact relationship (arm)between cg/cdrag and the thrust line of the
> engine prop. I did however assume the thrust line stayed above the
> cg/cdrag.
> Please remember that the large angle changes in the narration were used
> to induce thought, not to be used in real life trials.
> Again if i have it wrong, please , someone HELP me understand.
> Boyd Young mkiii UtahSorry this got overly longDo not archive
Message 4
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| Subject: | Re: Kolb-List Digest: 3 Msgs - 04/04/21 |
It seems like there is a lot of confusion regarding the effect of the
thrustline on our Kolbs. I like to take things to their extreme to better
visualize how things work, so bear with me here. Let's assume the
engine/redrive have no weight & we can place them wherever we choose in
relation to the cg. If we place it at the nose of our plane, a downward
thrustline will clearly produce a similar downward force. Similarly, an
upward thrustline will produce and upward force. Now if we place the
engine at the tail, all of the above thrustline adjustments will have an
opposite effect, eg, downward will produce an up force & upward a down
force. Therefore, since the engine is in reality, behind the cg, changing
the thrustline downward will add to the upward force on our Kolbs. The
only thing questionable is "how much change?". For the sake of this
exercise, we can ignore the effect of the moment arm of our raised engine
above the center of drag, because it is a constant, it is built into our
design -we are only considering changes due to thrustline change. If our
engine is 1.5 feet (guessing) behind cg; & if we have 250lbs of thrust
(guessing); & we point the thrustline 90 degrees down then we will have
350 lbs of force trying to rotate our plane *upwards*. But if we
only change the thrustline 3 degrees downward (3.33% of 90) then there is
only 11.7 lbs of upward rotational force being added to whatever other
forces are in reality present. What I think we can safely take away from
this thought experiment is that the effect of a small downward change in
thrustline should produce a small upward change. How significant this
change is, I don't know, but intuition tells me it at most would be felt at
the level of a trimming force & probably not noticeable at all.
I have personally been thinking about this a lot as I am installing a Hirth
3202 which has a .75 to 1 inch higher thrustline than the Rotax. I plan to
test the effect of changing the thrustline myself. But then a harder
question still remains (assuming the change is noticeable): since any
change of thrustline off of the actual line-of-flight is wasted energy, we
have to ask if this "waste" of energy to accomplish better trim would be
more efficiently delt with by the induced drag of changing trim at the
tail? Which is the most effective way of extracting the most energy from
our thrust, as both methods of trim take away from our forward speed and
upward lift? This is a more formidable question to answer for me. I am
sure there is an answer, but I haven't put in the effort yet to find it.
Maybe someone here already has this knowledge to share? -Richard Swiderski
On Mon, Apr 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:
>
>
> http://www.matronics.com/digest/digestview.php?Style=82701&View=html&Chapter 21-04-04&Archive=Kolb
>
> Text Version:
>
>
> http://www.matronics.com/digest/digestview.php?Style=82701&View=txt&Chapter 21-04-04&Archive=Kolb
>
>
> ===============================================
> EMail Version of Today's List Digest Archive
> ===============================================
>
>
> ----------------------------------------------------------
> Kolb-List Digest Archive
> ---
> Total Messages Posted Sun 04/04/21: 3
> ----------------------------------------------------------
>
>
> Today's Message Index:
> ----------------------
>
> 1. 09:27 AM - Re: Thrust line...? (Rick Neilsen)
> 2. 07:37 PM - Re: Thrust line...? (Richard Pike)
> 3. 09:32 PM - Re: Kolb-List Digest: 2 Msgs - 03/30/21 (chic)
>
>
> ________________________________ Message 1
> _____________________________________
>
>
> Time: 09:27:35 AM PST US
> From: Rick Neilsen <neilsenrm@gmail.com>
> Subject: Re: Kolb-List: Thrust line...?
>
> Nick/All
>
> It seems like John Hawk did some testing to see the effects of thrust line
> changes and found no differences. From that I decided that the best thrust
> line would be directly in line with the direction of flight.
>
>
> There are two factors that are part of the equation, center of drag and
> center of balance. The prop on most Kolbs is above the center of drag so we
> get pitch changes with power changes. Hang your plane from the center of
> balance (CG) position. The CG is forward of the position of the prop but
> also fairly close to the CG. Press down on the prop and the plane pitches
> up, lift and it pitches down. So if you set the thrust line a bit down from
> the direction of flight the plane will pitch down more than it already does
> with power increases, not good. Set the thrust line a bit up and the plane
> will pitch down less with power increases which is good but it pushes the
> plane down and that is really not a good thing.
>
>
> The moment arm between the CG and the prop is very short in comparison to
> the moment arm of the horizontal stabilizer and elevators so any pitch
> considerations are most efficiently handled by the tail. So I suggest that
> the prop thrust line be set directly in line with the direction of flight
> which is something around 3-5 degrees up from the bottom of the wing.
>
>
> As usual this is worth what you paid for it.
> Rick Neilsen
> Redrive VW Powered MKIIIC
>
>
> On Sat, Apr 3, 2021 at 8:52 PM Nick Cassara <nickc@mtaonline.net> wrote:
>
> >
> > Kolbers,
> >
> > I have been interest in the talk about desired thrust line. I took a piec
> e
> > line and attached to the front of my engine mount plate, I then walked it
> > back to the tail, and lowered the string until it was making contact with
> > the whole upper surface of the mount plate. The string ends up 4 inches
> > above the end of the boom tube. The center of the prop is 8 inches above
> > the string linei.e.12=99=99 above the top of the boo
> m tube end.
> >
> > My Kolbra is the prototype, of the Kolbra=99s.
> >
> > Nick Cassara
> > Palmer, Alaska
> >
> ==========
> ==========
> ==========
> ==========
> ==========
> >
> >
>
> ________________________________ Message 2
> _____________________________________
>
>
> Time: 07:37:12 PM PST US
> Subject: Kolb-List: Re: Thrust line...?
> From: "Richard Pike" <thegreybaron@charter.net>
>
>
> Appreciate your thoughts Rick. After a couple weeks of experimenting with
> this
> rig, puzzling over it, and reading this, I think tomorrow I will order a
> couple
> more longer bolts so that I can get the engine and thrust line back to what
> it was originally (like Kolb had it), just a couple inches higher, because
> so
> far, the closer I get it to original stock, the better it flies. It just
> needs
> a bit more elevation so the prop will clear the tube when the thrust line
> is
> stock.
>
> Wind has been too contrary & trashy to get any accurate readings yet, but
> so far
> the 3.47:1 box & 72" three blade prop looks like an amazing improvement.
>
> --------
> 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=501264#501264
>
>
> ________________________________ Message 3
> _____________________________________
>
>
> Time: 09:32:36 PM PST US
> Subject: Kolb-List: Re: Kolb-List Digest: 2 Msgs - 03/30/21
> From: "chic" <gcechini@msn.com>
>
>
> You have a 750 LB gross weight and that is what you should watch along
> with the
> weight and balance which is critical......How much does your plane weigh?
> Mine
> is about 400lbs empty so that will leave about 350lbs for people, fuel, &
> any
> luggage/coolers ect. 10 gal gas is 60lbs so that leaves 290lbs in mine for
> pilot/pass.
> I am 6'4" and I fit in mine so your height should work and if you are
> 290lbs or less you would work in mine! Hope that helps
>
>
> Read this topic online here:
>
> http://forums.matronics.com/viewtopic.php?p=501265#501265
>
>
--
*Click on to Richard's Blog: <http://GodStuffRichard.blogspot.com>
<http://GodStuffRichard.blogspot.com> *
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Message 5
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1957
Very informative but even reading between the lines I missed the conclusion.
Rick Neilsen
Redrive VW Powered MKIIIC
On Mon, Apr 5, 2021 at 1:30 PM <1957grnchev@bluemarble.net> wrote:
>
> Just to add a few comments about this whole discussion... (and yeah, all
> of this could be wrong too)
> You might need a super computer to do the full blown flight simulation..
> but the big factors (I believe) are the following:
>
> You have the engine thrust vector.. how much it is pitched up or down.
> Considering it's location, I doubt that is the primary contributor, if
> changes are slight.
> You have the drag of the wing, as profile AND the dynamic drag (due to
> producing lift, which changes with speed and angle of attack).. AND there
> is a pitching moment caused by how different airfoils react at different
> angles of attack.
> You have the total aircraft profile drag, which is WELL BELOW the wing,
> engine, and thrust vectors.. ie, all of the drag from the fuse, pilot,
> landing gear. And all of that changes with the square of the airspeed.
> But I would suspect it doesn't change much with the attitude of the
> aircraft, (if right side up).
> You have the center of mass, which may be only slightly higher than the
> center of drag.. considering again, undercarriage, pilot weight, fuel (in
> most, behind the pilot but low), and the mass of the fuse
> And you have the mass distribution over the whole of the air-frame. If
> all the heavy stuff is close in to the center of mass, it's different than
> if it is further out. (See ice skaters spinning.. arms in = faster, etc).
> We'll HOPE that's not changing while we fly.. but it does have an effect on
> how easily the plane pitches, with power changes applied.
>
> Aircraft designs can use a lifting stab.. such that with increased
> airspeed, (producing more lift).. the flying stab tends towards keeping it
> level, but still climbing. (HP above what is required for level flight,
> produces ROC). A positive angle of attack on the flat stab of the Kolb has
> a similar, but reduced effect. And the size of the tail area * tail arm
> the amount of control authority. Kolb tail feathers are really small in my
> opinion, esp compared to those of my Drifter for example.
>
> But the one thing which comes to my mind, is that by having the engine
> mounted above and behind both the cg and center of drag and mass, is that
> if near stalling, the quick application of power, will A) pull more air
> across the wing, reducing the stall point, and forcing the nose down,
> reducing the angle of attack. Both good things. But none of the Kolbs are
> designed by aero-space engineers (or that I am aware of).. so it may well
> have some characteristics which require trim, or human reaction to huge
> power change inputs. Flying with my dad (old hat pilot).. and knowing a
> little bit about engines in general.. huge/fast power changes are not
> ideal, if they can be avoided.. either to accelerate or decelerate! And
> with our non-certified engines, if they are running, may be more important
> than anything else.
>
> Making changes to a EXP? No problem there, if done carefully and with
> some research. And yeah, engine placement is rather easy to edit. If you
> are going to re-engineer it, there are a lot of factors, and just as many
> things which could benefit from being revised. But it's not a simple
> puzzle.
>
> On Mon, 5 Apr 2021 10:30:07 -0600, B Young <byoungplumbing@gmail.com>
> wrote:
> > Rick said and it got me thinking....The CG is forward of the position of
> > the prop but
> > also fairly close to the CG. Press down on the prop and the plane
> pitches
> > up, lift and it pitches down. .
> >
> > Still trying to get this figured out in my mind. So ive gone to the
> > extreme. Ive seen a photo of a low wing plane with the engine mounted
> > on top of the rudder... The prop is mounted 7 feet behind and above
> > the cg and center of drag (cdrag) much like the kolb but much further
> > back, in my mind the physics remains the same but on a larger scale than
> > the kolb. Because the thrust is higher than the cg /c drag there will
> > still be some nose down tendancy with increased power. The
> > following examples may (i hope) shed some light on how to neturalize it.
> > Now this is where i am taking a good size leap, and if i am wrong Ill
> > apologize in advance.
> >
> > Now in the following examples if the angle changes dont register in your
> > mind the pressure changes to the aircraft... Draw 2 pictures. One of
> > the aircraft ive described, and one of an engine and prop. Place the
> > second pic on top of the first, and if needed over exaggerate the thrust
> > angle even more,,, say 15 and 30 deg. If you ask why i suggested
> > this, ive done it.
> >
> > Lets assume that the aircraft is flying straight and level, and the
> > engine thrust line is parallel to the direction of travel. The thrust
> > is above the cg/cdrag so there will be an amount of nose down
> > tendancy that can be compensated for with a small amount of up
> > elevator. When the power is cut, the nose down tendancy (forces) go
> > away and the nose of the plane goes up.
> >
> > I will exaggerate to make a point....If we raise the front of the engine
> > 2 deg. The thrust above the cg/cdrag will have a tendancy to push
> > the nose down adding the up pressure from the prop thrust angle on the
> > tail will require even more up elevator. When the power from cruise
> > is cut the higher than cg/cdrag is removed also the 2 deg. uplift on
> > the tail is removed. This should cause a much greater nose up
> > situation.
> > If we lower the front of the engine 2 deg the majority of thrust is
> still
> > above the cg/cdrag and the nose down tendancy is countered by down
> > pressure on the tail from the prop pushing down 2 deg. No elevator
> > is needed and when we cut power there should be no tendancy for the nose
> > to drop or raise.
> > Try again with 4 deg of down angle ln the engine.(lower the front of the
> > engine).. The thrust line is still above the cg/cdrag so a small nose
> > down moment is still present, but now there is much more down force
> > from the prop thrust angle. This additional down force to the rear of
> > cg(tail) should require down elevator to compensate. If we remove
> > power. The nose drops.
> > Now I have used a high tail mounted engine in the example. But would
> > imagine that the same principals apply to the kolbs. The moment arms
> > are much smaller on a kolb, and because of the shorter moment arms,
> > some of the angles would be greater.
> > Burt Rutan is reported to have said that on a bird, every feather makes
> a
> > difference in how it flies.. not accounted for in my explanation
> > is relationship between cg and c lift, Moving cg with fuel burn,
> > changes in attitude at different flight speeds, climbing or descending,
> > the exact relationship (arm)between cg/cdrag and the thrust line of the
> > engine prop. I did however assume the thrust line stayed above the
> > cg/cdrag.
> > Please remember that the large angle changes in the narration were used
> > to induce thought, not to be used in real life trials.
> > Again if i have it wrong, please , someone HELP me understand.
> > Boyd Young mkiii UtahSorry this got overly longDo not archive
>
>
Message 6
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| Subject: | Re: Kolb-List Digest: 3 Msgs - 04/04/21 |
I've followed this thread through all the different replies, and I once
rode in a Mark three that dived for the ground when full power was pushed.
Didn't like it at all, and didn't feel that it was airworthy either. Anyway
I was curious about the difference in my HKS on my firestar. So I stuck the
?protractor? on the bottom of the wing as it sat in my hanger and found
that the bottom of the wing measured 38 degrees, I then stuck it on the
engine plate and found that it read 30 degrees. So my 60 horse engine is 8
degrees flatter than the wing.
With this configuration and trimmed for straight and level flight at 5400
rpm's. Max sustained cruise is 5800 for the HKS. If I go to full throttle
of 6100 rpms the plane climbs, rather than nosing down. In other words I
can climb at neutral input from the stick.
Not real sure if any of this answers your question or not, but it seems to
me that a difference of 8 degrees flatter compared to the wing should get
one to where the plane operates best.
for what its worth.
Larry
Message 7
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| Subject: | Fwd: Kolb-List Digest: 3 Msgs - 04/04/21 |
---------- Forwarded message ---------
From: Larry Cottrell <lcottrell1020@gmail.com>
Subject: Re: Kolb-List Digest: 3 Msgs - 04/04/21
I've followed this thread through all the different replies, and I once
rode in a Mark three that dived for the ground when full power was pushed.
Didn't like it at all, and didn't feel that it was airworthy either. Anyway
I was curious about the difference in my HKS on my firestar. So I stuck the
?protractor? on the bottom of the wing as it sat in my hanger and found
that the bottom of the wing measured 38 degrees, I then stuck it on the
engine plate and found that it read 30 degrees. So my 60 horse engine is 8
degrees flatter than the wing.
With this configuration and trimmed for straight and level flight at 5400
rpm's. Max sustained cruise is 5800 for the HKS. If I go to full throttle
of 6100 rpms the plane climbs, rather than nosing down. In other words I
can climb at neutral input from the stick.
Not real sure if any of this answers your question or not, but it seems to
me that a difference of 8 degrees flatter compared to the wing should get
one to where the plane operates best.
for what its worth.
Larry
--
*The older I get, the less tolerant I am of those who are intolerant of
others.*
*If you forward this email, or any part of it, please remove my email
address before sending.*
Message 8
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| Subject: | Re: Fwd: Kolb-List Digest: 3 Msgs - 04/04/21 |
Hi Larry!
When you are at cruise is the wing 6-8 positive? That would put the
engine thrust at 0. What's the stab angle, as compared to your wing/engine
measurements. I'd guess it's less than the engine, to produce some tail
down to balance the engine push over effects.
On Mon, 5 Apr 2021 13:05:43 -0600, Larry Cottrell
<lcottrell1020@gmail.com> wrote:
> ---------- Forwarded message ---------
> From: LARRY COTTRELL
> Date: Mon, Apr 5, 2021 at 1:04 PM
> Subject: Re: Kolb-List Digest: 3 Msgs - 04/04/21
> To: kolb-list@matronics.com [2]
>
> Ive followed this thread through all the different replies, and I once
> rode in a Mark three that dived for the ground when full power was
> pushed. Didnt like it at all, and didnt feel that it was airworthy
> either. Anyway I was curious about the difference in my HKS on my
> firestar. So I stuck the ?protractor? on the bottom of the wing as it
sat
> in my hanger and found that the bottom of the wing measured 38 degrees,
I
> then stuck it on the engine plate and found that it read 30 degrees. So
> my 60 horse engine is 8 degrees flatter than the wing.
> With this configuration and trimmed for straight and level flight at
5400
> rpms. Max sustained cruise is 5800 for the HKS. If I go to full throttle
> of 6100 rpms the plane climbs, rather than nosing down. In other words I
> can climb at neutral input from the stick.
> Not real sure if any of this answers your question or not, but it seems
> to me that a difference of 8 degrees flatter compared to the wing should
> get one to where the plane operates best.
> for what itsworth.
> Larry
Message 9
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Like the first line, it says, "to add a few comments".. So two conclusions
could be drawn. Each plane is different, from configuration, loading, W&B,
HP and prop, etc. And "Your results may vary".
On Mon, 5 Apr 2021 14:28:26 -0400, Rick Neilsen <neilsenrm@gmail.com>
wrote:
> 1957
> Very informative but even reading between the lines I missed the
> conclusion.
> Rick NeilsenRedrive VW Powered MKIIIC
> On Mon, Apr 5, 2021 at 1:30 PM wrote:
>
> Just to add a few comments about this whole discussion... (and yeah,
> all
> of this could be wrong too)
> You might need a super computer to do the full blown flight
simulation..
> but the big factors (I believe) are the following:
>
> You have the engine thrust vector.. how much it is pitched up or down.
> Considering its location, I doubt that is the primary contributor, if
> changes are slight.
> You have the drag of the wing, as profile AND the dynamic drag (due to
> producing lift, which changes with speed and angle of attack).. AND
> there
> is a pitching moment caused by how different airfoils react at
different
> angles of attack.
> You have the total aircraft profile drag, which is WELL BELOW the wing,
> engine, and thrust vectors.. ie, all of the drag from the fuse, pilot,
> landing gear. And all of that changes with the square of the airspeed.
>
> But I would suspect it doesnt change much with the attitude of the
> aircraft, (if right side up).
> You have the center of mass, which may be only slightly higher than the
> center of drag.. considering again, undercarriage, pilot weight, fuel
> (in
> most, behind the pilot but low), and the mass of the fuse
> And you have the mass distribution over the whole of the air-frame. If
> all the heavy stuff is close in to the center of mass, its different
> than
> if it is further out. (See ice skaters spinning.. arms in = faster,
> etc).
> Well HOPE thats not changing while we fly.. but it does have an effect
> on
> how easily the plane pitches, with power changes applied.
>
> Aircraft designs can use a lifting stab.. such that with increased
> airspeed, (producing more lift).. the flying stab tends towards keeping
> it
> level, but still climbing. (HP above what is required for level
> flight,
> produces ROC). A positive angle of attack on the flat stab of the Kolb
> has
> a similar, but reduced effect. And the size of the tail area * tail
> arm
> the amount of control authority. Kolb tail feathers are really small
> in my
> opinion, esp compared to those of my Drifter for example.
>
> But the one thing which comes to my mind, is that by having the engine
> mounted above and behind both the cg and center of drag and mass, is
> that
> if near stalling, the quick application of power, will A) pull more air
> across the wing, reducing the stall point, and forcing the nose down,
> reducing the angle of attack. Both good things. But none of the Kolbs
> are
> designed by aero-space engineers (or that I am aware of).. so it may
> well
> have some characteristics which require trim, or human reaction to huge
> power change inputs. Flying with my dad (old hat pilot).. and knowing
> a
> little bit about engines in general.. huge/fast power changes are not
> ideal, if they can be avoided.. either to accelerate or decelerate! And
> with our non-certified engines, if they are running, may be more
> important
> than anything else.
>
> Making changes to a EXP? No problem there, if done carefully and with
> some research. And yeah, engine placement is rather easy to edit. If
> you
> are going to re-engineer it, there are a lot of factors, and just as
> many
> things which could benefit from being revised. But its not a simple
> puzzle.
>
> On Mon, 5 Apr 2021 10:30:07 -0600, B Young
> wrote:
> > Rick said and it got me thinking....The CG is forward of the position
> of
> > the prop but
> > also fairly close to the CG. Press down on the prop and the plane
> pitches
> > up, lift and it pitches down. .
> >
> > Still trying to get this figured out in my mind. So ive gone to
> the
> > extreme. Ive seen a photo of a low wing plane with the engine
> mounted
> > on top of the rudder... The prop is mounted 7 feet behind and
> above
> > the cg and center of drag (cdrag) much like the kolb but much
> further
> > back, in my mind the physics remains the same but on a larger scale
> than
> > the kolb. Because the thrust is higher than the cg /c drag there
> will
> > still be some nose down tendancy with increased power. The
> > following examples may (i hope) shed some light on how to neturalize
> it.
> > Now this is where i am taking a good size leap, and if i am wrong Ill
> > apologize in advance.
> >
> > Now in the following examples if the angle changes dont register in
> your
> > mind the pressure changes to the aircraft... Draw 2 pictures. One
> of
> > the aircraft ive described, and one of an engine and prop. Place the
> > second pic on top of the first, and if needed over exaggerate the
> thrust
> > angle even more,,, say 15 and 30 deg. If you ask why i suggested
> > this, ive done it.
> >
> > Lets assume that the aircraft is flying straight and level, and the
> > engine thrust line is parallel to the direction of travel. The
> thrust
> > is above the cg/cdrag so there will be an amount of nose down
> > tendancy that can be compensated for with a small amount of up
> > elevator. When the power is cut, the nose down tendancy (forces) go
> > away and the nose of the plane goes up.
> >
> > I will exaggerate to make a point....If we raise the front of the
> engine
> > 2 deg. The thrust above the cg/cdrag will have a tendancy to
> push
> > the nose down adding the up pressure from the prop thrust angle on
> the
> > tail will require even more up elevator. When the power from
> cruise
> > is cut the higher than cg/cdrag is removed also the 2 deg. uplift on
> > the tail is removed. This should cause a much greater nose up
> > situation.
> > If we lower the front of the engine 2 deg the majority of thrust is
> still
> > above the cg/cdrag and the nose down tendancy is countered by down
> > pressure on the tail from the prop pushing down 2 deg. No
> elevator
> > is needed and when we cut power there should be no tendancy for the
> nose
> > to drop or raise.
> > Try again with 4 deg of down angle ln the engine.(lower the front of
> the
> > engine).. The thrust line is still above the cg/cdrag so a small
> nose
> > down moment is still present, but now there is much more down
> force
> > from the prop thrust angle. This additional down force to the rear
> of
> > cg(tail) should require down elevator to compensate. If we remove
> > power. The nose drops.
> > Now I have used a high tail mounted engine in the example. But would
> > imagine that the same principals apply to the kolbs. The moment arms
> > are much smaller on a kolb, and because of the shorter moment arms,
> > some of the angles would be greater.
> > Burt Rutan is reported to have said that on a bird, every feather
> makes
> a
> > difference in how it flies.. not accounted for in my
> explanation
> > is relationship between cg and c lift, Moving cg with fuel burn,
> > changes in attitude at different flight speeds, climbing or
> descending,
> > the exact relationship (arm)between cg/cdrag and the thrust line of
> the
> > engine prop. I did however assume the thrust line stayed above the
> > cg/cdrag.
> > Please remember that the large angle changes in the narration were
> used
> > to induce thought, not to be used in real life trials.
> > Again if i have it wrong, please , someone HELP me understand.
> > Boyd Young mkiii UtahSorry this got overly longDo not archive
> ==========
> -List" rel="noreferrer"
> target="_blank">http://www.matronics.com/Navigator?Kolb-List
> ==========
> FORUMS -
> eferrer" target="_blank">http://forums.matronics.com
> ==========
> WIKI -
> errer" target="_blank">http://wiki.matronics.com
> ==========
> b Site -
> -Matt Dralle, List Admin.
> rel="noreferrer" target="_blank">http://www.matronics.com/contribution
> ==========
>
>
>
> Links:
> ------
> [1] mailto:1957grnchev@bluemarble.net
> [2] mailto:1957grnchev@bluemarble.net
> [3] mailto:byoungplumbing@gmail.com
Message 10
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| Subject: | Re: Kolb-List Digest: 3 Msgs - 04/04/21 |
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Message 11
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| Subject: | Re: Kolb-List Digest: 3 Msgs - 04/04/21 |
Larry
This maybe this is where real world smacks theory. Ok so put that
protractor on the wing in flight at cruise. If you have around 4 degrees of
pitch on the wing to maintain level flight then you have your thrust line
pushing down and that would explain why you aren't getting pitch trim
changes with power changes. I would think that you would need more than 4
degrees upthrust to get there but what do I know.
I set my pitch trim so my MKIIIC will cruise with just a bit of down pitch
because I like it that way. Full power requires a bit of back pressure.
When I pull power to land I need to push to get the nose down till I add a
notch of flaps then it is neutral again. It is the way it is and feels
normal to me. My thrust line is app. 4 degrees flatter or up from my wing.
My motor mount is welded at 4 degrees with no way to change it.
Ok so what is the best thrust line? It would seem that a thrust line that
pushes down on the plane would require a bit more pitch up and more drag
and maybe some wasted thrust but what do I know?? If you get no pitch
changes with power changes that is a good thing too. Theory vs real world?
I think John H is out playing on his boat doing the 2nd great loop.
Rick Neilsen
Redrive VW Powered MKIIIC
On Mon, Apr 5, 2021 at 3:07 PM Larry Cottrell <lcottrell1020@gmail.com>
wrote:
> I've followed this thread through all the different replies, and I once
> rode in a Mark three that dived for the ground when full power was pushed.
> Didn't like it at all, and didn't feel that it was airworthy either. Anyway
> I was curious about the difference in my HKS on my firestar. So I stuck the
> ?protractor? on the bottom of the wing as it sat in my hanger and found
> that the bottom of the wing measured 38 degrees, I then stuck it on the
> engine plate and found that it read 30 degrees. So my 60 horse engine is 8
> degrees flatter than the wing.
>
> With this configuration and trimmed for straight and level flight at 5400
> rpm's. Max sustained cruise is 5800 for the HKS. If I go to full throttle
> of 6100 rpms the plane climbs, rather than nosing down. In other words I
> can climb at neutral input from the stick.
>
> Not real sure if any of this answers your question or not, but it seems to
> me that a difference of 8 degrees flatter compared to the wing should get
> one to where the plane operates best.
>
> for what its worth.
>
> Larry
>
Message 12
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On Mon, Apr 5, 2021 at 1:44 PM <1957grnchev@bluemarble.net> wrote:
>
> Hi Larry!
> When you are at cruise is the wing 6-8=C2=B0 positive? That would put th
e
> engine thrust at 0. What's the stab angle, as compared to your wing/engi
ne
> measurements. I'd guess it's less than the engine, to produce some tail
> down to balance the engine push over effects.
>
Since the plane is just out in the hangar, I decided to quit fooling around
and just use my ?smart phone? to do the job for me. Since I manage to fool
myself oftener than I would like.
Larry
> -
--
*The older I get, the less tolerant I am of those who are intolerant of
others.*
*If you forward this email, or any part of it, please remove my email
address before sending.*
Message 13
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The list wouldn't take all four pictures even though I had reduced them by
2/3 so here are the other two pictures.
--
*The older I get, the less tolerant I am of those who are intolerant of
others.*
*If you forward this email, or any part of it, please remove my email
address before sending.*
Message 14
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| Subject: | Re: Kolb-List Digest: 3 Msgs - 04/04/21 |
Perhaps a bit better measurement of the angles will tell us what we need to
know. One gets used to what ever we use often enough, I just like the fact
that when I input throttle the only thing that happens is I go faster or
slower depending on which way I push it. At my age simple things are better.
John is back on the Great Loop and moored close to the intercoastal
waterway on the East side of Florida at the moment enjoying life to the
fullest.
Larry
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