Today's Message Index:
----------------------
1. 03:05 AM - Re: Gross Weight (cgalley)
2. 06:10 AM - (Andy Smith)
3. 06:46 AM - Re: Gross Weight (Larry)
4. 07:03 AM - Re: Gross Weight (familie chesterman)
5. 08:02 AM - Re: Fw: Zeniyh-List: Re: CH601 XL nose wheel fork (Jack Russell)
6. 08:04 AM - Re: Gross weight (Brandon Tucker)
7. 08:55 AM - Jeff Paden: Big-a$$ engine installation (James Brigman)
8. 10:21 AM - Re: Zenith-List Digest: 20 Msgs - 10/30/04 (Grant Corriveau)
9. 10:39 AM - Re: Re: Zenith-List Digest: 20 Msgs - 10/30/04 (Cdngoose)
10. 10:46 AM - Re: Zenith-List Digest: 20 Msgs - 10/30/04 (Grant Corriveau)
11. 11:50 AM - RE; Gross Weight (roy vickski)
12. 02:21 PM - Re: Jeff Paden: Big-a$$ engine installation (cgalley)
13. 03:33 PM - Re: Jeff Paden: Big-a$$ engine installation (Larry McFarland)
14. 04:57 PM - Re: RE; Gross Weight (Jeff Paden)
15. 05:01 PM - Re: Re: Zenith-List Digest: 20 Msgs - 10/30/04 (Jeff Paden)
16. 05:07 PM - Re: Re: Gross weight (Jeff Paden)
17. 05:13 PM - Re: Gross Weight (Jeff Paden)
18. 06:46 PM - Canopy build order (Bill Steer)
19. 11:38 PM - Re: Jeff Paden: Big-a$$ engine installation (cgalley)
Message 1
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| Subject: | Re: Gross Weight |
--> Zenith-List message posted by: "cgalley" <cgalley@qcbc.org>
Hate to burst your bubble. The stall speed is probably much higher even
though you airspeed says 45 mph. Most airspeeds are very inaccurate at low
speed due to positional errors of the pitot. Using my Bellanca 14-13-2 the
listed speed is 48 MPH but I see an indicated airspeed of 38 MPH before the
break. You might want to get out the GPS and see what it says by trying
several directions to cancel out the wind. This is what the Test period is
all about.
Flutter is not the only problem at higher speeds. There are some strength
considerations. The FAA establishes the red-line by demonstrating flight to
a number and then making the red-line at 90% of this demonstrated figure.
The faster you go, the stronger the airframe has to be to withstand air
loads and turbulence. That is why the safe maneuvering speed is much less
than the red line.
The VNE for your plane you say is 167. That is designed into the airframe
by the designer. You probably don't have an margin of error for gust
loading above that point unless you have redesigned the airframe. Just one
bout of clear air turbulence could ruin your day. Or you could do the damage
yourself by full rapid control inputs.
I hate to say this but your plane is every designer's worse nightmare. When
you make the modifications then all the careful calculations of the designer
are gone.
I hope that you understand that due to liability considerations, the factory
probably will not give advice. Remember it is no longer a Zenith design, it
is yours and yours alone due to the deviations from the design parameters.
Right now there is a move underfoot to ground a certified airplane via an
AD. Why? Because these airplanes have been re-engined not even with greater
weight but just added horsepower.
I hope you can get some structural analysis done. All airplanes fly better
when they are lighter.
Cy Galley
EAA Safety Programs Editor
Always looking for ideas and articles for EAA Sport Pilot
----- Original Message -----
From: "Jeff Paden" <jeffpaden@madbbs.com>
Subject: Re: Zenith-List: Gross Weight
> --> Zenith-List message posted by: "Jeff Paden" <jeffpaden@madbbs.com>
>
>
> I have had many members of the list point out the fact that I have
installed
> a 260 hp engine. However this is not the problem as is easy to see when
you
> do the calculations. The engine I installed is only 110 lbs heavier than
> the 180 hp engine that the aircraft was tested with. This also keeps me
> within the max installed power plant weight as I had checked this before
> installing the engine.
> My aircraft is 1560 lbs empty and the proto was 1147 lbs empty. This
means
> that some how I have added over 400 lbs and the engine only accounts for
110
> lbs of that. If I had the other 300 lbs to play with then I would not
have
> a problem at all.
>
> As for swapping out the engine for a smaller one, that just simply is not
an
> option. Everything was built around this engine and if needed then I will
> simply have a very nice two place aircraft or only carry 20 gal of fuel
with
> four.
> So far I have found that almost every aspect of the figures on the web
site
> are WAY off and I am just looking for answers as to why.
>
> For example, the Vne is published at 167 mph however I have done flutter
> testing up to 190 mph with no sign of any problems as of yet and that is
> still only at 75% power. I will post to the list once I figure out what
the
> real Vne is. By the way, I do NOT recommend to anyone on the list that
you
> perform flutter testing unless you really know what you are doing. I have
a
> friend who is a test pilot and he is the one that is helping me with this
> test. Do the test wrong and you will destroy the aircraft and probably
not
> survive the test.
>
> With that said, I have also found that my stall speed is 45 mph with full
> flaps so the fact that the aircraft is heavy has not increased that number
> as we expected it to do. Also my take off roll is only about 500 feet but
> that is probably because of the extra power.
>
> Once I have all the numbers confirmed then I will post them all to the
list.
>
> I guess my next job is to try to find a way to make the aircraf lighter
but
> I really can't think of anything that is going to make that happen.
>
> Thank you all for your help and don't worry, after putting one aircraft in
> the trees I don't have any plans of flying this one in any condition that
> would be unsafe. We just need to figure out what is "SAFE" for this
> aircraft and the published numbers simply do not seem to have anything to
do
> with my aircraft.
>
> Jeff Paden
> CH-640 Test flight stage.
>
>
> Jeff,
> The gross weight is defined by structure and hardware that's heavly
> calculated to provide
> a safe platform for weight, maneuvering and power loading. On the simple
> side, you can put an
> engine that weighs much more than the 180 to 220 HP engine, but you pay a
> price in safety and
> performance that should become obvious. Anytime you have more tail weight
> than the
> baggage you're able to carry, you've gotten outside of the fine art of a
> design specification
> that's initially intended to keep you and yours safe for a long period of
> time. The engine
> limits assure that the elevator will offer adequate resistance to pitching
> moments from turbulence
> and stalls so long as the plane is balanced within the envelope. The
limits
> also assure that the
> engine mounts and attachments will not crack prematurely from fatigue of
the
> engine torque and
> prop pulse. Both of these design elements are huge for the designer.
These
> are tested and
> designed with safety factors that assure a reasonable lifespan. When one
> exceeds the specification
> the first compromise is in wear and working fatigue life. Little else
will
> be noticable, but
> time becomes a bigger player as a few bad landings and weather work
against
> the airframe.
>
> I've tried to put my finger on the exactitude of your problem and it is
> this.
> It is much safer to consider the practical solution of trading engines to
> get within specification
> and resolve every problem you've had to deal with.
> Larry McFarland - 601HDS
>
>
Message 2
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0.00 FROM_HAS_MIXED_NUMS From": contains.numbers.mixed.in.with.letters.1.16.MISSING_SUBJECT.Missing.Subject:header@matronics.com
--> Zenith-List message posted by: Andy Smith <skyguy4you2001@yahoo.com>
help
=====
Sami Wegner
__________________________________
Message 3
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| Subject: | Re: Gross Weight |
--> Zenith-List message posted by: "Larry" <lrm@isp.com>
Jeff, even though I don't see eye to eye with Zenith on some items like
tires, they always respond to me. Sometimes I don't like the response but I
always get a response. Perhaps you should double check the address and
request a reply, if that doesn't work pick up the phone. I'm sure there is
some mix up, you haven't called them dirty names have you? kidding! Larry
N1345L
Do not archive.
----- Original Message -----
From: "Jeff Paden" <jeffpaden@madbbs.com>
Subject: Zenith-List: Gross Weight
> --> Zenith-List message posted by: "Jeff Paden" <jeffpaden@madbbs.com>
>
> I know I have asked this before but I am going to try one more time to see
> if anyone can point me in the correct direction.
>
> I need to know what limits the gross weight of an aircraft. How does the
> engineer calculate gross weight of an aircraft?
>
> I ask this because at this moment I have a VERY powerful CH-640 that I can
> only take one passenger in which does not seem logical at all.
>
> I know the aircraft will fly WAY over the published gross weight but I am
> trying to figure out what goes in to the calculations so that I can come
up
> with a logical gross weight for my aircraft. The 2200 lbs that is
published
> simply is not logical for an aircraft that has an empty weight of 1560
lbs.
>
> Before anyone says it, YES, I have asked ZAC for assistance but as of yet
I
> have not had any response from them. As a matter of fact I have not had
any
> response from them about any of my questions since I have completed the
> aircraft which is very upsetting for me but I guess I will just have to
> figure things out on my own. That is why I hope that someone on this list
> may be able to point me in the right direction.
>
> Thank you for any assistance you can offer.
>
> Jeff Paden
>
>
Message 4
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| Subject: | Re: Gross Weight |
--> Zenith-List message posted by: familie chesterman <chesterman@on.aibn.com>
This is likely a dumb question, but are you sure about the accuracy of your
scales when you did the weight and balance? 300lbs is a lot. Was your tool box
sitting in the fuselage?
dave c
> >
> > Jeff Paden
> >
> >
>
Message 5
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| Subject: | Re: Fw: Zeniyh-List: RE: CH601 XL nose wheel fork |
--> Zenith-List message posted by: Jack Russell <clojan@sbcglobal.net>
Buryl: I think the measurment between the forks should read 135mm not 35mm. Would
you check this please? I measured my XL fork and it is 140mm so I don't think
that the Hd doubler will work. Thanks Jack In Clovis CA
--> Zenith-List message posted by: "burylhill"
Jack: My 601 HD fork doubler measures 100mm deep X 150mm Down the side. 35mm between
the U. Drawings show 410mm Developed Length. I think the whole metal length
before the bend ( R15mm ) is 410mm X 100mm.
Jack Russell -Clovis CA
601 XL Jabiru 3300
Progress update at:
http://www.geocities.com/clojan@sbcglobal.net/zodiacbarn.html
Message 6
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| Subject: | RE: Gross weight |
--> Zenith-List message posted by: Brandon Tucker <btucke73@yahoo.com>
Jeff,
Maybe I am off base here, but I am much more
concerned about the extra 300lbs in the airframe than
the extra 110 lbs in the engine. Better than half the
list is using an engine that is considerably heavier
power plants than the engines that Chris had in mind.
There is a ton of documentation on compensating for
extra engine weights, from the Subaru in the 601, to
Ben's Ford in the 801. Jeff has stated that the
engine is within the max designed weight. We can't
say that for the 701 guys looking into Corvair, and
Subaru engine installations.
My question is what in the !#@* happened with the
airframe weight? I know that you double and triple
checked your numbers when weighing your aircraft, but
something is way (weigh) off! :) That is the first
place I would be looking into. You built from kit
right? I don't think it is even possible to add 300
lbs of weight unless you skinned it with .050
stainless! Maybe I missed a post that explained this,
but I don't think so.
Let's not lecture on engine weights and weight in
the tail when many of the Subaru guys have been
putting batteries behind the passenger compartment to
compensate for engine weight.
Respectfully,
Brandon Tucker
601 HDS wings, tail complete
do not archive
__________________________________
Message 7
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| Subject: | Jeff Paden: Big-a$$ engine installation |
--> Zenith-List message posted by: "James Brigman" <jbrigman@nc.rr.com>
> From: "Jeff Paden" <jeffpaden@madbbs.com>
> Subject: Zenith-List: Gross Weight
...
> I need to know what limits the gross weight of an aircraft. How does
the
> engineer calculate gross weight of an aircraft?
> I ask this because at this moment I have a VERY powerful CH-640 that I
can
> only take one passenger in which does not seem logical at all.
...
> what goes in to the
> calculations so that I can come up with a logical gross
> weight for my aircraft. The 2200 lbs that is published
> simply is not logical for an aircraft that has an empty
> weight of 1560 lbs.
...
> installed a 260 hp engine. However this is not the problem
> The engine I installed is only 110 lbs heavier than the
> 180 hp engine the aircraft was tested with.
> This also keeps me within the max installed power
> plant weight as I had checked this before installing the engine.
> My aircraft is 1560 lbs empty and the proto was 1147 lbs empty.
> This means that some how I have added over 400 lbs and
> the engine only accounts for 110 lbs of that. If I had
> the other 300 lbs to play with then I would not have
> a problem at all.
Jeff;
First: congratulations are in order for your completing a CH-640 and
installing such a nice engine. I see from your website where you went
with an O-540 instead of the usual O-360. Thanks for the fresh update to
your builder page on the ZAC website - your plane looks beautiful. I
have complete lust for your aircraft...I'm hoping that a 640 will be "my
next airplane". :-)
Now: I'm not gonna tell you HOW on anything. From your website, you seem
to know what kind of plane you want to end up with. You are right that
basic weight does not determine useful load capacity. In fact, for many
certified GA planes, there are STC's for engine upgrades that actually
increase gross weight a bit, not decrease it. However, there's more to
it than just gross weight: Structural load design, empennage sizes CG
and weight distribution are as important as gross weight. I don't have
the answers, but here's where I would look if I were in your shoes.
1) Be clear about one thing: you went 20hp over the powerplant design
for this aircraft, per http://www.zenair.com/specifications.html. I'm
sure all us builders routinely tax the patience of our fathers at ZAC. I
know I have ;-) Reading between the lines at
http://www.zenair.com/engine.html, it almost looks like Chris
purposefully excluded the O-540 as an engine choice.
2) There's got to be both a Weight & Balance table as well as a POH for
the CH-640. These are the base documents which will precisely answer
your questions about how to calculate gross weight. The CH-640 has a
certified GA brother, so there ought to be a W&B template and a POH
template for it. Although they are not available online from ZAC (for
good reason) the versions for the 601 are available at
http://www.zenithair.com/zodiac/6-up-bldr.html
3) Aircraft engine weights are published as optimistically as possible.
This means "DRY" (no engine oil, coolants or fuel) and WITHOUT starter,
alternator, carb/intake or even magnetos. This could account for as much
as 100lbs of the extra weight you're seeing. Here's a great webpage for
engine reference: http://www.wanttaja.com/avlinks/engines.htm Ron has an
interesting link on "structural efficiency" which shows how widely the
gross weight of aircraft can vary with their various engines and
airframes.
4) How much heavier is your panel than the "stock" ZAC panel for the
640? I remember when I sat in the ZAC CH-640 at Sun 'n Fun, it had the
typical 6-pack, a couple radios, a transponder and a small assortment of
engine instruments (I think six or eight small gauges?). Chris likes to
keep his panels simple, it really helps with the CG.
5) Did you go with the stock fuel tanks to feed that bit O-540, or did
you beef those up a bit too? For reference between yours and several GA
planes, see http://www.zenair.com/performance-comparison.htm. You could
have picked up 80lbs of weight there easily.
6) Where's your battery placement? Is it on the firewall or back behind
in the rear of the plane? Don't you have to use a bigger battery to
start that 540? If so, how much weight did that add?
7) You've clearly been flying the aircraft to generate test data. How's
it handle in the flare? What happens in the stall? What about landing
speed? I know from past history that some guys who built 601's with
bigger engines in the UK had to beef-up their HS attach points and
install larger HS's to get PFA certification. (that might still be in
the archives here)
Message 8
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| Subject: | Re: Zenith-List Digest: 20 Msgs - 10/30/04 |
--> Zenith-List message posted by: Grant Corriveau <grantc@ca.inter.net>
> Concerning roll trim I found an interesting article in
> contact magazine #77, the author who is a lancair235
> driver states that any lateral imbalance should be
> countered with a constant force (spring)
If you are interested in a simple and easy to install spring/bungee chord
aileron trim system, there are at least 2 ideas that have been proposed by
listers -- I can't find them on my computer right now... should be in the
matronics archives, or the www.ch601.org website.
do not archive
Grant
Message 9
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| Subject: | Re: Zenith-List Digest: 20 Msgs - 10/30/04 |
--> Zenith-List message posted by: "Cdngoose" <601xl@sympatico.ca>
Here is one Idea that Grant referred to
http://www.ch601.org/resources/trim/bungee_trim.htm
Mark Townsend
Alma, Ontario
Zodiac 601XL EJ 2.2L
Osprey 2 serial # 751
www.ch601.org
www.Osprey2.com
-----Original Message-----
If you are interested in a simple and easy to install spring/bungee
chord
aileron trim system, there are at least 2 ideas that have been proposed
by
listers -- I can't find them on my computer right now... should be in
the
matronics archives, or the www.ch601.org website.
Grant
Message 10
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| Subject: | Re: Zenith-List Digest: 20 Msgs - 10/30/04 |
--> Zenith-List message posted by: Grant Corriveau <grantc@ca.inter.net>
> For example, the Vne is published at 167 mph however I have done flutter
> testing up to 190 mph ... you will destroy the aircraft and probably not
> survive the test.
Jeff,
If ZAC published a vne of 167 mph, it doesn't mean that they encountered
flutter at 168 mph. It's probably because that's as fast as they dared /
cared to take the airframe. I'm glad you mentioned that you have a test
pilot friend working this for you - are you parachute equipped too? He
should be able to help answer these questions ... you will find textbooks
written about this stuff. It's complicated...
Beyond the aerodynamic issues there are all the issues that others have
mentioned regarding wear and tear on the landing gear, wing spar, engine
mounts, and all the stress points over time. FWIW this is true of all size
aircraft. The airliner I used to fly was eventually certified to a higher
MTOW, but we weren't able to make use of it until the landing gear had been
reinforced -- and along with that all the paperwork and performance numbers
had to be recomputed. But this was only allowed AFTER the aircraft had been
in service a significant number of hours, and the airframe had proven itself
under constant monitoring, etcc... You're facing the same task on a smaller
scale.
Your plane will become a test plane and maybe your future passengers need to
be forewarned?
Again, the best source for any allowance to the Max TOW is the designer.
Also you seem to have a HUGE increase in empty weight compared to the
prototype - over 30%? Are you sure this is so? That's an awful lot of
weight. Besides the engine, where did it all come from? Did you make other
modifications/imrovements? Have you ever added it all up? I'd be very
uncomfortable not knowing why my aircraft is so much heavier...
Good luck -- be careful!
--
Grant Corriveau
C-GHTF / HDS / CAM100
Message 11
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| Subject: | RE; Gross Weight |
--> Zenith-List message posted by: roy vickski <rvickski@yahoo.com>
Hello Jeff and regards to the group,
> I need to know what limits the gross weight of an
aircraft. How does
the
> engineer calculate gross weight of an aircraft?
Sand bags. Lots of them.
I guess engineers can make all the calculations on a
supercomputor and come up with a very close
theoretical approximation of performance but I think
the real test is real weight.
Gross weight is related to g force and load factor.
The (ultimate?)load limit factor for an airframe is
based on the maximum ammount of g force (weight)it can
withstand before damage occurs.
So a 2200# gross weight airframe rated for 6 g's
ultimate load shouldn't be damaged up to a weight of
13,200 pounds. But subject a 2500# gross weight to 6
g's and get 15,000 pounds
Angle of attack and g force have a near linear
relationship.
In level flight double triple,or quadruple the angle
of attack and the g force (weight) doubles,triples, or
quadruples.
If at 150mph un-accelerated flight with an angle of
attack of 3 degrees, a gust or stick deflection
increases the angle of attack to 18 degrees the
airframe would be subjected to 6 g's(18/3=6).
Angle of attack and airspeed also have a relationship.
The same airframe at 180mph could have an angle of
attack of 2 degrees and would experience 6 g's at 12
degrees aoa, well below critical aoa, and 7 g's at 14
degrees aoa. If the load limit factor of the airframe
was 6 g's damage could result.
On page 3 of my 701 plans there is a warning about the
decrease in load factor if opereating overweight,
there is also a formula.
The 701 sp has an ultimate load factor of 6 g's pos.
"g" overgross = 6 x design gross weight/actual gross
weight, then divide this by 1.5(saftey factor)to get
the load limit factor.
I believe the load limit factor of the airframe
defines which catagory the aircraft qualifies for
under the design standards of FAR23.
I invite any and all corrections and clarifications as
I am also learning.
What is interesting about the CH640 is it is based on
the CH2000 certified which has a saftey factor of 2.
Which may or maynot mean anything to the 640.
>For example, the Vne is published at 167 mph however
I have done flutter testing up to 190 mph with no sign
of any problems ...
Vne is 90% of the speed that flutter occurs,
190x.9=171
171mph-167mph = 4mph. This seems close enough to be
inside the margin of error of the gauge, pitot, static
system.
Has the question of gauge accuracy and calibration to
TAS been adressed?
As Larry mentioned, and I respect his knowledge and
opinion, many things need to be considered for "safe"
operation. And I think what Jeff wants to know is how
far he can crowd or exceed the published Vne, Vc (Vno)
and weight limitations "safely".
William Wynne has a sobering and realistic grasp on
the concept of risk versus saftey on page 7 of his
corvair conversion manual, personally I can say that
his common sense philosophy has adjusted my attitude
toward my hobby in a positive direction. Also what I
know about maneuvering speed, load limits, and angle
of attack, I learned from Rod Machado's Private Pilot
Handbook which explains these relationships very well.
There are companies that provide engineering and
testing services for experimental aircraft, they
advertise in the EAA publications under the heading of
"services". IMHO a qualified second and even third
opinion of the design with its subsequent
modifications would go far to understand the
limitations of this aircraft and minimize un-necessary
risks.
Respectfully
Roy Szarafinski
701 plans
__________________________________
Message 12
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| Subject: | Re: Jeff Paden: Big-a$$ engine installation |
--> Zenith-List message posted by: "cgalley" <cgalley@qcbc.org>
Strange you mention 601 motor mounts. I have pictures of FAILED 601 motor
mount attachment fittings. Fittings that failed with a Subaru engine.
I don't know if part of the additional weight is due to the addition of a
constant speed prop. It hangs about 60 to 80 pounds in itself as far forward
as one can get. It has a large moment arm working on the motor mount and
the attach points.
I don't know the weight of the approved engine but for sake of discussion
let's say the factory engine was 300 pounds and the motor mount was designed
to handle 6 gs. It means that it is designed to withstand an 1800 pound
load. Adding 100 pounds is a 33% increase in weight. Divide the original
design load by 400 pounds and the g loads that the structure can handle is
now only 4.5 gs To put it another way the structure with the lighter load
will break at 6 gs but now it only takes 4.5 gs. Now there is a safety
factor but you can see that increasing the weight over the designed loads
decreases even the safety factor by 25%. Another good reason to build as
designed and as light as possible. All the little extras do add up.
Cy Galley
EAA Safety Programs Editor
Always looking for ideas and articles for EAA Sport Pilot
----- Original Message -----
From: "James Brigman" <jbrigman@nc.rr.com>
Subject: Zenith-List: Jeff Paden: Big-a$$ engine installation
> --> Zenith-List message posted by: "James Brigman" <jbrigman@nc.rr.com>
>
> > From: "Jeff Paden" <jeffpaden@madbbs.com>
> > Subject: Zenith-List: Gross Weight
> ...
> > I need to know what limits the gross weight of an aircraft. How does
> the
> > engineer calculate gross weight of an aircraft?
> > I ask this because at this moment I have a VERY powerful CH-640 that I
> can
> > only take one passenger in which does not seem logical at all.
> ...
> > what goes in to the
> > calculations so that I can come up with a logical gross
> > weight for my aircraft. The 2200 lbs that is published
> > simply is not logical for an aircraft that has an empty
> > weight of 1560 lbs.
> ...
> > installed a 260 hp engine. However this is not the problem
> > The engine I installed is only 110 lbs heavier than the
> > 180 hp engine the aircraft was tested with.
> > This also keeps me within the max installed power
> > plant weight as I had checked this before installing the engine.
> > My aircraft is 1560 lbs empty and the proto was 1147 lbs empty.
> > This means that some how I have added over 400 lbs and
> > the engine only accounts for 110 lbs of that. If I had
> > the other 300 lbs to play with then I would not have
> > a problem at all.
>
> Jeff;
> First: congratulations are in order for your completing a CH-640 and
> installing such a nice engine. I see from your website where you went
> with an O-540 instead of the usual O-360. Thanks for the fresh update to
> your builder page on the ZAC website - your plane looks beautiful. I
> have complete lust for your aircraft...I'm hoping that a 640 will be "my
> next airplane". :-)
>
> Now: I'm not gonna tell you HOW on anything. From your website, you seem
> to know what kind of plane you want to end up with. You are right that
> basic weight does not determine useful load capacity. In fact, for many
> certified GA planes, there are STC's for engine upgrades that actually
> increase gross weight a bit, not decrease it. However, there's more to
> it than just gross weight: Structural load design, empennage sizes CG
> and weight distribution are as important as gross weight. I don't have
> the answers, but here's where I would look if I were in your shoes.
>
> 1) Be clear about one thing: you went 20hp over the powerplant design
> for this aircraft, per http://www.zenair.com/specifications.html. I'm
> sure all us builders routinely tax the patience of our fathers at ZAC. I
> know I have ;-) Reading between the lines at
> http://www.zenair.com/engine.html, it almost looks like Chris
> purposefully excluded the O-540 as an engine choice.
>
> 2) There's got to be both a Weight & Balance table as well as a POH for
> the CH-640. These are the base documents which will precisely answer
> your questions about how to calculate gross weight. The CH-640 has a
> certified GA brother, so there ought to be a W&B template and a POH
> template for it. Although they are not available online from ZAC (for
> good reason) the versions for the 601 are available at
> http://www.zenithair.com/zodiac/6-up-bldr.html
>
> 3) Aircraft engine weights are published as optimistically as possible.
> This means "DRY" (no engine oil, coolants or fuel) and WITHOUT starter,
> alternator, carb/intake or even magnetos. This could account for as much
> as 100lbs of the extra weight you're seeing. Here's a great webpage for
> engine reference: http://www.wanttaja.com/avlinks/engines.htm Ron has an
> interesting link on "structural efficiency" which shows how widely the
> gross weight of aircraft can vary with their various engines and
> airframes.
>
> 4) How much heavier is your panel than the "stock" ZAC panel for the
> 640? I remember when I sat in the ZAC CH-640 at Sun 'n Fun, it had the
> typical 6-pack, a couple radios, a transponder and a small assortment of
> engine instruments (I think six or eight small gauges?). Chris likes to
> keep his panels simple, it really helps with the CG.
>
> 5) Did you go with the stock fuel tanks to feed that bit O-540, or did
> you beef those up a bit too? For reference between yours and several GA
> planes, see http://www.zenair.com/performance-comparison.htm. You could
> have picked up 80lbs of weight there easily.
>
> 6) Where's your battery placement? Is it on the firewall or back behind
> in the rear of the plane? Don't you have to use a bigger battery to
> start that 540? If so, how much weight did that add?
>
> 7) You've clearly been flying the aircraft to generate test data. How's
> it handle in the flare? What happens in the stall? What about landing
> speed? I know from past history that some guys who built 601's with
> bigger engines in the UK had to beef-up their HS attach points and
> install larger HS's to get PFA certification. (that might still be in
> the archives here)
>
>
Message 13
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| Subject: | Re: Jeff Paden: Big-a$$ engine installation |
--> Zenith-List message posted by: "Larry McFarland" <larrymc@qconline.com>
Cy,
A correction is perhaps in order here.
The engine wasn't a Subaru, but a Rotax 912. I had to send drawings
of the 912 mount to permit one to be made to replace the one that had cracks
in addition to the broken attachment fittings. This was a 10-yr old plane
that
had seen some rough runways and was exposed to the damp ocean air
in the UK. The mount was 3/4"-.035 wall 4130 tube. I recommended .049
as replacement for durability and an easier welding job.
Larry
Do not archive
Subject: Re: Zenith-List: Jeff Paden: Big-a$$ engine installation
> --> Zenith-List message posted by: "cgalley" <cgalley@qcbc.org>
>
> Strange you mention 601 motor mounts. I have pictures of FAILED 601 motor
> mount attachment fittings. Fittings that failed with a Subaru engine.
Message 14
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does not designate any permitted senders)
| Subject: | Re: RE; Gross Weight |
--> Zenith-List message posted by: "Jeff Paden" <jeffpaden@madbbs.com>
Thank you VERY much. This was exactly the type of response I was looking
for. Now I have a few different directions I can go to learn more about
what goes in to the calculations. And you are correct, I am trying to
figure out what the aircraft will do safely and what ever that ends up being
is what I will stick to. The last thing I want to do is to push an aircraft
beyond safe operating limits.
Thank you again
Jeff Paden
Hello Jeff and regards to the group,
> I need to know what limits the gross weight of an
aircraft. How does
the
> engineer calculate gross weight of an aircraft?
Sand bags. Lots of them.
I guess engineers can make all the calculations on a
supercomputor and come up with a very close
theoretical approximation of performance but I think
the real test is real weight.
Gross weight is related to g force and load factor.
The (ultimate?)load limit factor for an airframe is
based on the maximum ammount of g force (weight)it can
withstand before damage occurs.
So a 2200# gross weight airframe rated for 6 g's
ultimate load shouldn't be damaged up to a weight of
13,200 pounds. But subject a 2500# gross weight to 6
g's and get 15,000 pounds
Angle of attack and g force have a near linear
relationship.
In level flight double triple,or quadruple the angle
of attack and the g force (weight) doubles,triples, or
quadruples.
If at 150mph un-accelerated flight with an angle of
attack of 3 degrees, a gust or stick deflection
increases the angle of attack to 18 degrees the
airframe would be subjected to 6 g's(18/36).
Angle of attack and airspeed also have a relationship.
The same airframe at 180mph could have an angle of
attack of 2 degrees and would experience 6 g's at 12
degrees aoa, well below critical aoa, and 7 g's at 14
degrees aoa. If the load limit factor of the airframe
was 6 g's damage could result.
On page 3 of my 701 plans there is a warning about the
decrease in load factor if opereating overweight,
there is also a formula.
The 701 sp has an ultimate load factor of 6 g's pos.
"g" overgross 6 x design gross weight/actual gross
weight, then divide this by 1.5(saftey factor)to get
the load limit factor.
I believe the load limit factor of the airframe
defines which catagory the aircraft qualifies for
under the design standards of FAR23.
I invite any and all corrections and clarifications as
I am also learning.
What is interesting about the CH640 is it is based on
the CH2000 certified which has a saftey factor of 2.
Which may or maynot mean anything to the 640.
>For example, the Vne is published at 167 mph however
I have done flutter testing up to 190 mph with no sign
of any problems ...
Vne is 90% of the speed that flutter occurs,
190x.9171
171mph-167mph 4mph. This seems close enough to be
inside the margin of error of the gauge, pitot, static
system.
Has the question of gauge accuracy and calibration to
TAS been adressed?
As Larry mentioned, and I respect his knowledge and
opinion, many things need to be considered for "safe"
operation. And I think what Jeff wants to know is how
far he can crowd or exceed the published Vne, Vc (Vno)
and weight limitations "safely".
William Wynne has a sobering and realistic grasp on
the concept of risk versus saftey on page 7 of his
corvair conversion manual, personally I can say that
his common sense philosophy has adjusted my attitude
toward my hobby in a positive direction. Also what I
know about maneuvering speed, load limits, and angle
of attack, I learned from Rod Machado's Private Pilot
Handbook which explains these relationships very well.
There are companies that provide engineering and
testing services for experimental aircraft, they
advertise in the EAA publications under the heading of
"services". IMHO a qualified second and even third
opinion of the design with its subsequent
modifications would go far to understand the
limitations of this aircraft and minimize un-necessary
risks.
Respectfully
Roy Szarafinski
701 plans
__________________________________
Message 15
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| Subject: | Re: Zenith-List Digest: 20 Msgs - 10/30/04 |
--> Zenith-List message posted by: "Jeff Paden" <jeffpaden@madbbs.com>
I agree, I was shocked when we did the weight and balance to find that the
aircraft was so darn heavy.
While building I was very careful to try to keep everything as light as
possible because I knew that my engine was going to add 110 lbs.
However we have used two different sets of scales and the fact is that the
aircraft is very heavy. I sure wish that I could get ZAC to answer some
email and then maybe I could rest a little better. However for some reason
they are ignoreing my email and I have no idea of why.
Maybe they are not getting the email because of some spam filter or
something. I plan on calling them on Monday to see what is going on.
Thank you all for your help
Jeff Paden
Also you seem to have a HUGE increase in empty weight compared to the
prototype - over 30%? Are you sure this is so? That's an awful lot of
weight. Besides the engine, where did it all come from? Did you make other
modifications/imrovements? Have you ever added it all up? I'd be very
uncomfortable not knowing why my aircraft is so much heavier...
Good luck -- be careful!
--
Grant Corriveau
C-GHTF / HDS / CAM100
Message 16
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does not designate any permitted senders)
| Subject: | Re: RE: Gross weight |
--> Zenith-List message posted by: "Jeff Paden" <jeffpaden@madbbs.com>
I agree with you on this one and that is what I want to know also. Where
the heck did all the weight come from!
That is why I said that I would like to see the prototype on scales because
I just can not believe that my aircraft
is that much heavier than it is supposed to be. I for one was SHOCKED.
Jeff Paden
Maybe I am off base here, but I am much more
concerned about the extra 300lbs in the airframe than
the extra 110 lbs in the engine. Better than half the
list is using an engine that is considerably heavier
power plants than the engines that Chris had in mind.
There is a ton of documentation on compensating for
extra engine weights, from the Subaru in the 601, to
Ben's Ford in the 801. Jeff has stated that the
engine is within the max designed weight. We can't
say that for the 701 guys looking into Corvair, and
Subaru engine installations.
My question is what in the !#@* happened with the
airframe weight? I know that you double and triple
checked your numbers when weighing your aircraft, but
something is way (weigh) off! :) That is the first
place I would be looking into. You built from kit
right? I don't think it is even possible to add 300
lbs of weight unless you skinned it with .050
stainless! Maybe I missed a post that explained this,
but I don't think so.
Let's not lecture on engine weights and weight in
the tail when many of the Subaru guys have been
putting batteries behind the passenger compartment to
compensate for engine weight.
Respectfully,
Brandon Tucker
601 HDS wings, tail complete
do not archive
Message 17
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| Subject: | Re: Gross Weight |
--> Zenith-List message posted by: "Jeff Paden" <jeffpaden@madbbs.com>
Actually I did not deviate from the design. The engine I installed is prop
limited to 240 hp which is the max allowed hp and the installed engine
weight is a few pounds below the published max. Also Chris approved the
installation of this engine before I even purchased it.
I made sure to check everything before putting the past two years into
building her and ZAC has always been very good at answering any questions I
had while building. We have actually helped each other out quite a bit over
the past two years. I am the one that fixed the CD they send to all
builders since the one they sent to me did not work at all and my business
at that time was web page design and the CD is nothing more than a web page
on CD. We have a good working relationship and I am sure that if I can ever
get ahold of them that they will be able to clear up most of my questions
Thank you for your input though
Jeff Paden
--> Zenith-List message posted by: "cgalley" <cgalley@qcbc.org>
Hate to burst your bubble. The stall speed is probably much higher even
though you airspeed says 45 mph. Most airspeeds are very inaccurate at low
speed due to positional errors of the pitot. Using my Bellanca 14-13-2 the
listed speed is 48 MPH but I see an indicated airspeed of 38 MPH before the
break. You might want to get out the GPS and see what it says by trying
several directions to cancel out the wind. This is what the Test period is
all about.
Flutter is not the only problem at higher speeds. There are some strength
considerations. The FAA establishes the red-line by demonstrating flight to
a number and then making the red-line at 90% of this demonstrated figure.
The faster you go, the stronger the airframe has to be to withstand air
loads and turbulence. That is why the safe maneuvering speed is much less
than the red line.
The VNE for your plane you say is 167. That is designed into the airframe
by the designer. You probably don't have an margin of error for gust
loading above that point unless you have redesigned the airframe. Just one
bout of clear air turbulence could ruin your day. Or you could do the damage
yourself by full rapid control inputs.
I hate to say this but your plane is every designer's worse nightmare. When
you make the modifications then all the careful calculations of the designer
are gone.
I hope that you understand that due to liability considerations, the factory
probably will not give advice. Remember it is no longer a Zenith design, it
is yours and yours alone due to the deviations from the design parameters
Right now there is a move underfoot to ground a certified airplane via an
AD. Why? Because these airplanes have been re-engined not even with greater
weight but just added horsepower.
I hope you can get some structural analysis done. All airplanes fly better
when they are lighter.
Cy Galley
EAA Safety Programs Editor
Always looking for ideas and articles for EAA Sport Pilot
----- Original Message -----
From: "Jeff Paden" <jeffpaden@madbbs.com>
Subject: Re: Zenith-List: Gross Weight
> --> Zenith-List message posted by: "Jeff Paden" <jeffpaden@madbbs.com>
>
>
> I have had many members of the list point out the fact that I have
installed
> a 260 hp engine. However this is not the problem as is easy to see when
you
> do the calculations. The engine I installed is only 110 lbs heavier than
> the 180 hp engine that the aircraft was tested with. This also keeps me
> within the max installed power plant weight as I had checked this before
> installing the engine.
> My aircraft is 1560 lbs empty and the proto was 1147 lbs empty. This
means
> that some how I have added over 400 lbs and the engine only accounts for
110
> lbs of that. If I had the other 300 lbs to play with then I would not
have
> a problem at all.
>
> As for swapping out the engine for a smaller one, that just simply is not
an
> option. Everything was built around this engine and if needed then I will
> simply have a very nice two place aircraft or only carry 20 gal of fuel
with
> four.
> So far I have found that almost every aspect of the figures on the web
site
> are WAY off and I am just looking for answers as to why.
>
> For example, the Vne is published at 167 mph however I have done flutter
> testing up to 190 mph with no sign of any problems as of yet and that is
> still only at 75% power. I will post to the list once I figure out what
the
> real Vne is. By the way, I do NOT recommend to anyone on the list that
you
> perform flutter testing unless you really know what you are doing. I have
a
> friend who is a test pilot and he is the one that is helping me with this
> test. Do the test wrong and you will destroy the aircraft and probably
not
> survive the test.
>
> With that said, I have also found that my stall speed is 45 mph with full
> flaps so the fact that the aircraft is heavy has not increased that number
> as we expected it to do. Also my take off roll is only about 500 feet but
> that is probably because of the extra power.
>
> Once I have all the numbers confirmed then I will post them all to the
list.
>
> I guess my next job is to try to find a way to make the aircraf lighter
but
> I really can't think of anything that is going to make that happen.
>
> Thank you all for your help and don't worry, after putting one aircraft in
> the trees I don't have any plans of flying this one in any condition that
> would be unsafe. We just need to figure out what is "SAFE" for this
> aircraft and the published numbers simply do not seem to have anything to
do
> with my aircraft.
>
> Jeff Paden
> CH-640 Test flight stage.
>
>
> Jeff,
> The gross weight is defined by structure and hardware that's heavly
> calculated to provide
> a safe platform for weight, maneuvering and power loading. On the simple
> side, you can put an
> engine that weighs much more than the 180 to 220 HP engine, but you pay a
> price in safety and
> performance that should become obvious. Anytime you have more tail weight
> than the
> baggage you're able to carry, you've gotten outside of the fine art of a
> design specification
> that's initially intended to keep you and yours safe for a long period of
> time. The engine
> limits assure that the elevator will offer adequate resistance to pitching
> moments from turbulence
> and stalls so long as the plane is balanced within the envelope. The
limits
> also assure that the
> engine mounts and attachments will not crack prematurely from fatigue of
the
> engine torque and
> prop pulse. Both of these design elements are huge for the designer.
These
> are tested and
> designed with safety factors that assure a reasonable lifespan. When one
> exceeds the specification
> the first compromise is in wear and working fatigue life. Little else
will
> be noticable, but
> time becomes a bigger player as a few bad landings and weather work
against
> the airframe.
>
> I've tried to put my finger on the exactitude of your problem and it is
> this.
> It is much safer to consider the practical solution of trading engines to
> get within specification
> and resolve every problem you've had to deal with.
> Larry McFarland - 601HDS
>
>
Message 18
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| Subject: | Canopy build order |
--> Zenith-List message posted by: "Bill Steer" <bsteer@gwi.net>
I've just started working on the canopy for my 601 HD and am wondering about the
build order (I'm using the side-tilt). The manual says to construct the frame
so it fits nicely on the fuselage and then to "fine tune" it to fit the canopy.
Does that mean the frames, parts 6E4-1 and 6E4-2, are cut to about the dimensions
shown in the plans, so it fits the fuselage, and then the canopy itself
is trimmed to fit that frame? That doesn't seem to allow for raising and
lowering the height of the canopy with dimension "h" shown on the plans. And
the frames and the other frame parts can obviously only be drilled once, so can't
be changed for fine tuning. Last, does "fine tune" refer to changing the
shape of the frames so they exactly fit the canopy?
Thanks very much for any help.
Bill
Message 19
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| Subject: | Re: Jeff Paden: Big-a$$ engine installation |
--> Zenith-List message posted by: "cgalley" <cgalley@qcbc.org>
Ah CRS strikes again.
Point is that the Attachment points can fail with even a lighter engine.
Better check carefully with a heavier engine.
I think a Rotax is even lighter than a Subaru.
----- Original Message -----
From: "Larry McFarland" <larrymc@qconline.com>
Subject: Re: Zenith-List: Jeff Paden: Big-a$$ engine installation
> --> Zenith-List message posted by: "Larry McFarland"
<larrymc@qconline.com>
>
> Cy,
> A correction is perhaps in order here.
> The engine wasn't a Subaru, but a Rotax 912. I had to send drawings
> of the 912 mount to permit one to be made to replace the one that had
cracks
> in addition to the broken attachment fittings. This was a 10-yr old plane
> that
> had seen some rough runways and was exposed to the damp ocean air
> in the UK. The mount was 3/4"-.035 wall 4130 tube. I recommended .049
> as replacement for durability and an easier welding job.
>
> Larry
> Do not archive
>
> Subject: Re: Zenith-List: Jeff Paden: Big-a$$ engine installation
>
>
> > --> Zenith-List message posted by: "cgalley" <cgalley@qcbc.org>
> >
> > Strange you mention 601 motor mounts. I have pictures of FAILED 601
motor
> > mount attachment fittings. Fittings that failed with a Subaru engine.
>
>
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