Re: KR> Pitch sensitivity

[Jeff Scott via KRnet]

What Chris describes is not at all unusual.  A number of aircraft fly better in 
an aft CG as the elevator gets too heavy with a forward CG.  A C-182 is a good 
example.  A 200 horse Muskateer is another.  It flies better and is easier to 
land if your CG is a bit aft simply because the elevator gets so heavy during 
landing when the CG is forward even though both configurations are still within 
the acceptable CG range.  Flying with a forward CG in these planes requires so 
much aft trim that the down force on the tail and trim drag is enough that the 
plane flies slower in a forward CG. 

The stock KR has so little stabilizer that an aft CG configuration can get very 
pitchy.  I flew my KR with the small tail for 500 hours before cutting it off 
and building a larger tail.  I've flown it another 650 hours since with the 
larger tail, so I think I can comment on this from a position of first hand 
experience.  After building a larger horizontal stabilizer and elevator, I 
really don't notice much difference in handling between a forward and aft CG in 
my KR as long as I stay within the 6" CG range as recommended by most builders.

I built the new stab and elevator to an 8' span using the templates Mark 
provides on his web site.

-Jeff Scott
Los Alamos, NM

 
---
 
> Could you go into further detail about "how" it flew better with a forward
> CG than an aft CG?

Sure, the plane under normal conditions (no baggage) would require
significant up trim to unload the stick, and when pulling power, would
drop the nose unless you held onto the stick. "Lawn dart"is a
description used more than once.

Conversely, with plenty of stuff in the baggage compartment (at or
near aft CG limit), the plane seemed to "float" in balance and handled
much better and was faster to boot. A pure dream to fly.

This was discussed often. It was considered by some to be good
practice to ignore the front half of the CG envelope.

It is possible that the CG envelope was shifted a bit forward than it
should have been and in fact I spoke with someone in good authority
that the aft limit was quite conservative and flying AT the published
aft limit would in fact produce good results, and it did.



> See http://www.n56ml.com/wb/index.html for more on the KR aft CG, which I'm
> pretty sure is common to most aircraft. This story should scare you...it
> certainly scared me!

I actually had read that last year, another well written piece and in
fact I am sure I saved it to PDF as well in my KR own knowlege base.


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Re: KR> Pitch sensitivity

[Kayak Chris via KRnet]

> Could you go into further detail about "how" it flew better with a forward
> CG than an aft CG?

Sure, the plane under normal conditions (no baggage) would require
significant up trim to unload the stick, and when pulling power, would
drop the nose unless you held onto the stick. "Lawn dart"is a
description used more than once.

Conversely, with plenty of stuff in the baggage compartment (at or
near aft CG limit), the plane seemed to "float" in balance and handled
much better and was faster to boot. A pure dream to fly.

This was discussed often. It was considered by some to be good
practice to ignore the front half of the CG envelope.

It is possible that the CG envelope was shifted a bit forward than it
should have been and in fact I spoke with someone in good authority
that the aft limit was quite conservative and flying AT the published
aft limit would in fact produce good results, and it did.



> See http://www.n56ml.com/wb/index.html for more on the KR aft CG, which I'm
> pretty sure is common to most aircraft.  This story should scare you...it
> certainly scared me!

I actually had read that last year, another well written piece and in
fact I am sure I saved it to PDF as well in my KR own knowlege base.

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Re: KR> Pitch sensitivity

[Mark Langford via KRnet]

Kayak Chris wrote:

> with all this talk about pitch sensitivity, one common mention is
> using forward CG. What is up with that? My last plane really liked aft
> CG (within the envelope obviously) and flew MUCH better there. What
> happens to a KR at aft CG?

You had an odd bird if it flew better with an aft CG than a forward CG. 
Could you go into further detail about "how" it flew better with a 
forward CG than an aft CG?


See http://www.n56ml.com/wb/index.html for more on the KR aft CG, which 
I'm pretty sure is common to most aircraft.  This story should scare 
you...it certainly scared me!


Also see
http://www.askacfi.com/5222/forward-cg-vs-aft-cg-which-is-better-and-why.htm 
as a starting point.


With the CG at the absolute front of the limit, my KR2 does require a 
trim tab on the elevator or it'll dive pretty quickly.  I didn't set it 
up that way, but that's the way it is.  Almost everything I installed 
after I bought it was to move it aft, but it wasn't enough to move it 
very far.


My KR2S is usually flown right in the middle of the range, maybe 
slightly aft, but even with heavy passengers there was not a huge 
difference.  Go really aft though, and you are living very dangerously, 
as discussed at http://www.n56ml.com/wb/index.html ...


Mark Langford
m...@n56ml.com
http://www.n56ml.com



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Re: KR> Pitch sensitivity

[Kayak Chris via KRnet]

with all this talk about pitch sensitivity, one common mention is
using forward CG. What is up with that? My last plane really liked aft
CG (within the envelope obviously) and flew MUCH better there. What
happens to a KR at aft CG?

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KR> Pitch sensitivity

[Larry Flesner via KRnet]

At 03:45 PM 1/12/2017, you wrote:


Pitch sensitivity is an overblown item, Virg

++

Pitch sensitivity is NOT overblown but it also SHOULD NOT be an issue 
for the knowing pilot.  It is easily accommodated on the first flight 
and actually makes for a nice flying sports car type aircraft.  I 
once saw a chart that listed the KR2 (original plans built I assume) 
as close to the F86 in stability based on physical dimension and wing 
and tail surface area.  The closest thing I can relate my KR to (24 
inch longer fuselage, standard KR2 tail dimensions) is driving my 
Buick or Toyota down the interstate at 70 miles per hour.  I can 
change lanes with very little movement of the wheel (much larger than 
my control stick) with the KR having much lighter control surface 
push back.  If you can drive an automobile at moderate speeds then 
you can fly a KR and enjoy it, given acceptable C.G. location of course.


There is a reason the 2S was lengthened and given more tail 
area.  Mark Langford might be the best authority given his many hours 
in both the 2s and then the 2.  Jeff Scott reported on the difference 
after enlarging the tail surfaces in his KR and I'm guessing Mike 
Sylvester can enlighten us on switching from a Cessna 150 to the KR2s 
on his recent first flight.


Keep the C.G. in the correct location, anticipate the sensitivity, 
and enjoy flying your KR...


Larry Flesner





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KR> pitch sensitivity relationship to wing length

[Mark Langford]

Doran Jaffas wrote:

> Do the wing extensions add significantly to the pitch sensitivity?

Wing extensions do degrade pitch sensitivity slightly, all other things kept 
equal, but the biggest factors are aft CG and "horizontal tail volume 
coefficient".   Look that up on Google and you'll see the relationships.

 I added wing extensions and saw no real difference in pitch sensitivity, 
but climb and glide rates improved, with a slight speed increase...call it a 
"free lunch plus"!   A lot of that was the Hoerner tips, however.

Speaking of such things, I'm the "hoaky spar" guy.  I built mine by simply 
sanding a foam block to shape and putting 2 layers of carbon fiber all over 
it.  Using packing tape and nut-serts, I could have made them removable and 
removed the foam when finished to save weight.  That structure is plenty 
strong enough for the loads at the tip.  See http://www.n56ml.com/900hour/ 
for some details of how that was done.

By the way, please refrain from quoting an entire issue of the Digest. 
It's a repeat of an entire day's email, and just clutters up the archive and 
subscriber mailboxes...

Mark Langford
ML at N56ML.com
website at http://www.N56ML.com
 

KR> Pitch sensitivity

[Dan Heath]

This has been a major topic of discussion over the years.  My first KR was 
pitch sensitive", however this KR is no more "pitch sensitive" than the RVs
that I was able to fly, prior to my first flight in this KR.  I really think
it has A LOT to do with getting the WB forward enough to keep you off the
teeter totter.  But then, maybe it is just because I had some prior
experience.  But I don't think so.

This KR is rock solid, will fly hands off, and it is a stock KR2 with the
engine forward 2". 

See N64KR at http://KRBuilder.org - Then click on the pics 
See you at the 2007 - KR Gathering
There is a time for building and a time for FLYING and the time for Flying
has begun.
Daniel R. Heath - Lexington, SC
---Original Message---

My friend told ,me i would kill myself in this airplane because it would be
pitch sensivity and I sold it. 

he taxied it for 10 hours before he flew it to get the feel for pitch, its a 
good idea.  

KR> Pitch sensitivity

[Charles Burgoon]

Isn't stick height a factor as well?  I have a very tall non-tilting stick, 
with a chain drive pivoting handle.  It would seem to be less pichy feeling.  A 
lot more stick movement is required for the same control surface deflection in 
my case.  Better?  I do not know.  Different? Yes. Also it allows for more leg 
room, since the stick does not tilt, only the stick handle does.

> Date: Sun, 10 Dec 2006 10:37:58 -0500> From: da...@alltel.net> To: 
> kr...@mylist.net> Subject: KR> Pitch sensitivity> > This has been a major 
> topic of discussion over the years. My first KR was > pitch sensitive", 
> however this KR is no more "pitch sensitive" than the RVs> that I was able to 
> fly, prior to my first flight in this KR. I really think> it has A LOT to do 
> with getting the WB forward enough to keep you off the> teeter totter. But 
> then, maybe it is just because I had some prior> experience. But I don't 
> think so.> > This KR is rock solid, will fly hands off, and it is a stock KR2 
> with the> engine forward 2". > > See N64KR at http://KRBuilder.org - Then 
> click on the pics > See you at the 2007 - KR Gathering> There is a time for 
> building and a time for FLYING and the time for Flying> has begun.> Daniel R. 
> Heath - Lexington, SC> ---Original Message---> > My friend told ,me i 
> would kill myself in this airplane because it would be> pitch sensivity and I 
> sold it. > > he taxied it for 10 hours before he flew it to get the feel for 
> pitch, its a good idea. > ___> Search the 
> KRnet Archives at http://www.maddyhome.com/krsrch/index.jsp> to UNsubscribe 
> from KRnet, send a message to krnet-le...@mylist.net> please see other KRnet 
> info at http://www.krnet.org/info.html

KR> Pitch sensitivity

[Colin & Bev Rainey]

Jeff Scott just mentioned about increasing stability by making the horizontal 
stab longer but still having issues with the pitch sensitivity of the plane. I 
cannot say for other pilots, but I have flown more than 15 different models of 
aircraft and find that there are quite a few aircraft that could be considered 
to be pitch sensitive depending upon what part of the flight regime you are 
referring to.  ALL planes are sensitive at speeds above 120 mph or approx 105 
knots.  I think where the KR seems to get a bad rap is that by comparison to a 
basic trainer, i.e.: J3 Cub, or Cessna  152/172, the KR is much more sensitive. 
 However, there is a whole list of planes that display the same sensitivity and 
increased elevator authority that the KR has. The Extra 300, Pitts S1 & S2, 
Glasair I, Thorp T-18, Sidewinder, Mustang II, just to name a few.

Builders can dampen this tendency to over control by using what I have 
documented on my website, taken from illustrations on Adrian Carter's website.  
Between the 2 sites you can find how to de-tune the elevator to require more or 
larger inputs from the stick to get the same motion at the elevator. I have 
flown behind this arrangement for over 30 hours and love it.  It also has the 
effect of balancing the elevator response to the aileron response for better 
control harmony.  I also followed a suggestion from Larry Flesner and 
re-drilled the pivot locating hole in the aileron bell crank inboard by 1/2 an 
inch to get the full 20 degrees up and 10 degrees down deflection from the 
ailerons. By doing this and what Dan Heath suggested about spacing the pushrod 
down to make it level so that it is actuating in a straight line, accomplishes 
this.  By improving the aileron motion and de-tuning the elevator, I believe 
that our KR has excellent control authority and harmonizing. As good as any 
plane I have flown.  All these things can be accomplished by a builder at any 
stage of construction, and with very little extra effort over the original 
assembly, just changes.  Obviously use at your own risk as any suggestion found 
on the KR Net, but it is working for several builders.

To throw out one more answer, Mark L already posted a more elaborate answer but 
suffice to say that a VW or Corvair will probably stop turning, not windmill.

crain...@cfl.rr.com
http://kr-builder.org/Colin/index.html
KR2(td) N96TA
Sanford, FL
Apex Lending, Inc.
407-323-6960 (p)
407-557-3260 (f)
crai...@apexlending.com

KR> Pitch sensitivity

[jscott.pi...@juno.com]

On Wed, 20 Apr 2005 15:50:09 -0400 "Colin & Bev Rainey"
 writes:
> Jeff Scott just mentioned about increasing stability by making the 
> horizontal stab longer but still having issues with the pitch 
> sensitivity of the plane. I cannot say for other pilots, but I have 
> flown more than 15 different models of aircraft and find that there 
> are quite a few aircraft that could be considered to be pitch 
> sensitive depending upon what part of the flight regime you are 
> referring to.  ALL planes are sensitive at speeds above 120 mph or 
> approx 105 knots.  I think where the KR seems to get a bad rap is 
> that by comparison to a basic trainer, i.e.: J3 Cub, or Cessna  
> 152/172, the KR is much more sensitive.  However, there is a whole 
> list of planes that display the same sensitivity and increased 
> elevator authority that the KR has. The Extra 300, Pitts S1 & S2, 
> Glasair I, Thorp T-18, Sidewinder, Mustang II, just to name a few.

Actually, that's not what I said.

While you have improvised a workaround that is serviceable for you, it is
not a fix for a pitch sensitive aircraft. Why do you suppose Troy and
Dana modified the tails on their KRs?  Why do you think these other guys
have gone to a larger tail?  Check the numbers on static margin and tail
volume.  Everyone that has flown both has nothing but good things to say
about the larger tail.  Check with Bill Clapp.  He's flown both, as has
Troy.

I have also flown most of the planes you listed above and a fair number
of other high and low performing aircraft.  The KR is one of the less
harmonious aircraft to fly.  If one is building the plane, why build in a
well known problem, then devise a work around for it?  If I was building
mine again, it would have substantially more horizontal stab.  Does that
mean I don't enjoy flying the plane or can't fly it safely?  Not in my
opinion.  But if I was going to let others start flying my KR, I would
want to make it handle better than it does.

-Jeff

KR> pitch sensitivity

[Colin & Bev Rainey]

Franco Negri & netters

It is very common for any aircraft to become more sensitive in all control axis 
when the CG moves rearward towards the aft limit.  This is because the CG is 
approaching the Center of Pressure (or lift as some know it) and so instead of 
the plane acting like you are balancing a see saw with one foot stretched out 
on each side of the hinge, it is like bringing your feet close together and 
still trying to balance the see saw.  It can be done but takes alot more 
concentration, and smaller deviations result in bigger movements of the see 
saw.  Same applies to the aircraft.  It is akin to trying to balance on one 
foot.  Larry's longer tail boom makes his less sensitive because he pry bar or 
leverage is better, and he is more stable with the greater keel effect of the 
aircraft.  Larry's also has a higher wing loading due to shorter wings, which 
will have a tendency to make his less sensitive as well.  Diehl wing skins 
should make it even more so as they have the additional wing panel outboard of 
the plans tip.


Colin & Bev Rainey
KR2(td) N96TA
Sanford, FL
crain...@cfl.rr.com
http://kr-builder.org/Colin/index.html