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From: "Tracy Crook" <lors01@msn.com>
To: "Rotary motors in aircraft" <flyrotary@lancaironline.net>
References: <list-868589@logan.com>
Subject: Re: [FlyRotary] Re: Rx-8 Rotors
Date: Fri, 15 Apr 2005 22:33:28 -0400
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Here's my take (FWIW as usual). Ed's answer is essentially correct. =
But there is another reason for the greater depth of the 2nd - 3rd gen =
apex seals. The increased contact area in the groove is needed to =
transfer heat from seal to rotor. So no milling down the RA seals to =
fit RX-8 rotors in RX-7 engines. (but hell, it might work anyway). =20
Also, the center of mass of the rotor DOES rotate in a perfect circle. =
No monkey motion is ever involved. =20
Another question was about why counter weights were required if the =
rotors ballanced each other out. They are not in the same plane of =
rotation which creates what is known as a "rocking couple". The =
counterweights make another rocking couple (out of phase) to cancel out =
that of the rotors.
Tracy (still at SnF)
Hi Doug,
Some good thoughts and questions, of which I would like to know the =
answers to as well. I believe the reason the experts are recommending =
milling the RX-8 rotors for the older seals (when used in the older =
rotor housings with peripheral exhausts) is that the RX-8 seal was not =
designed to withstand the forces of crossing the exhaust port (in the =
Peripheral wall) opening unsupported. Its rather skinny and long. =
Mazdatrix reported the RX-8 seals warped as a consequence of the the hot =
exhaust gas blowing over them and primarily the lack of wall support at =
the exhaust opening(on the older housings). The combination of the =
additional heat and lack of wall support appears to be more than the 8 =
seal can take.
However, I am in basic agreement with you why machine the rotor when =
perhaps a new/modified seal is the answer. I want to check with Tracy =
Crook since his seals are reportedly 800% stronger than stock apex seals =
to see whether the seals could be machined down/created so that they fit =
in the RX-8 rotor standard apex slot and still be strong enough - say =
300% stronger than stock {:>). Since they are not made of typical "gray =
iron" alloy that the stock and most other seals are made and chill/case =
hardened, they may be amenable to machining.
Yes, having airports scattered around in just about every county and =
sometimes three or more in a county, the geography is much kinder to =
engine-out excursions here on the east coast. Fly High, Glide long! =
Better yet, keep running on both rotors.
Ed A
----- Original Message -----=20
From: Shearbond@aol.com<mailto:Shearbond@aol.com>=20
To: Rotary motors in aircraft<mailto:flyrotary@lancaironline.net>=20
Sent: Thursday, April 14, 2005 10:10 AM
Subject: [FlyRotary] Rx-8 Rotors
So.....since the rotors weigh the same within measurement error, the =
ability to rev to the 9,000s range vs. 7,000s range is not related to =
the orbiting mass of the rotor. (Note: the motion is NOT truly =
circular, it is an epicycloid path that the center of mass of the rotor =
takes. That 10 lb. rotor flops around plenty (technical term) and 10 =
lb. is lots heavier than an aluminum piston!
It is apparent from an article on the "other" site, that the wall =
thicknesses and casting detail are lots more refined on the RX8 rotors =
than on earlier models...for more uniform and desirable heat transfer =
and uniformity.....oil cooling the rotor, etc.
The mass being basically the same, it becomes a high probability =
that since centripetal force is F =3D (Mass x rotational velocity =
squared)/radius of rotation, {F=3D(m x w^2)/r}, it must be the weight of =
the seals themselves that are the critical element? The force at 8,500 =
vx. 6,500 is (8.5/6.5) squared or 1.71 times greater. Might this be why =
seal wear on the original seals goes up substantially at around 6,500 =
rpm?
Tell me....why would one increase the depth of the seal groove of an =
RX8 rotor to allow a heavier seal???? On the RX8, 3.25mm/9.5mm =3D> =
approx. 34% reduction in apex seal mass!! A lighter seal means a whole =
lot less force of the seal against the housing at 8,500 rpm!! Anyone =
want to go back to old seals and rev to 8,500 rpm? =20
Note: the seal force against the housing at 8,500 rpm on the RX8 is =
still higher than the old seal at 6,500.... (.66 x 1.71 =3D 1.129). Not =
much more, but there are probably even more very small details that we =
are not at first glance able to know and understand? Seal =
material/housing material compatability is probably one significant =
factor?? (I used 9,000 vs. 7,000 and the numbers still come out about =
10% higher seal force on the RX8, even with the lighter seals.) =20
Having been an R&D engineer at FoMoCo, it is hard to explain to most =
persons the creativity, detail, imagination, trial and testing and =
testing and testing and testing and ...... which goes into making an =
engine acceptable for production in quantities of XXX,XXX's and higher. =
(One simply can't be wrong...it could bankrupt even the largest OEM.) =
And....those Mazda engineers have done what many OEM's gave up on many =
years ago. How? Through their persistence and incredible insight into =
the issues.
Before one gets the wire EDM out and starts going counter to what =
Mazda no doubt spent many $$$$ (more than all of our annual incomes put =
together??) on how to increase HP in an RX8, more information is needed =
before we start mixing and matching just because the parts will fit. I =
know we are experimenters here, but lives of some who may not understand =
the "physics" limitations will ultimately be at stake.
Above all: Just because something works for 100 miles in a sprint =
race DOES NOT mean it will work while hummmming along for 5 hours at a =
crack at 75-80% max. HP on a cross-country over and over and over =
again....hopefully. So far, my Lyc is a piece of 30's era design and =
materials...but it has run for 2,000 hours (350,000 miles) at 75-100% =
without fail!!
Most of us aren't as lucky as Ed and his "on airport" emergency =
landings. Perhaps it is that his green carpet (Carolina's) is lots more =
friendly than our granite peaks out here?
Doug in Colorado
------=_NextPart_000_02BA_01C5420B.2529D860
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<DIV style=3D"FONT-SIZE: 10pt; COLOR: #000000; FONT-FAMILY: Arial">
<DIV>Here's my take (FWIW as usual). Ed's answer is essentially=20
correct. But there is another reason for the greater depth of the =
2nd -=20
3rd gen apex seals. The increased contact area in the groove is =
needed to=20
transfer heat from seal to rotor. So no milling down the RA seals =
to fit=20
RX-8 rotors in RX-7 engines. (but hell, it might work =
anyway). =20
</DIV>
<DIV> </DIV>
<DIV>Also, the center of mass of the rotor DOES rotate in a perfect=20
circle. No monkey motion is ever involved. </DIV>
<DIV> </DIV>
<DIV>Another question was about why counter weights were required if the =
rotors=20
ballanced each other out. They are not in the same plane of =
rotation which=20
creates what is known as a "rocking couple". The counterweights =
make=20
another rocking couple (out of phase) to cancel out that of the =
rotors.</DIV>
<DIV> </DIV>
<DIV>Tracy (still at SnF)<BR></DIV>
<BLOCKQUOTE dir=3Dltr=20
style=3D"PADDING-RIGHT: 0px; PADDING-LEFT: 5px; MARGIN-LEFT: 5px; =
BORDER-LEFT: #000000 2px solid; MARGIN-RIGHT: 0px">
<DIV>Hi Doug,</DIV>
<DIV> </DIV>
<DIV>Some good thoughts and questions, of which I would like to know =
the=20
answers to as well. I believe the reason the experts are =
recommending=20
milling the RX-8 rotors for the older seals (when used in the older =
rotor=20
housings with peripheral exhausts) is that the RX-8 seal was not =
designed to=20
withstand the forces of crossing the exhaust port (in the Peripheral =
wall)=20
opening unsupported. Its rather skinny and long. Mazdatrix =
reported=20
the RX-8 seals warped as a consequence of the the hot exhaust gas =
blowing over=20
them and primarily the lack of wall support at the exhaust opening(on =
the=20
older housings). The combination of the additional heat and lack =
of wall=20
support appears to be more than the 8 seal can take.</DIV>
<DIV> </DIV>
<DIV>However, I am in basic agreement with you why machine the =
rotor=20
when perhaps a new/modified seal is the answer. I want to check =
with=20
Tracy Crook since his seals are reportedly 800% stronger than stock =
apex seals=20
to see whether the seals could be machined down/created so that they =
fit in=20
the RX-8 rotor standard apex slot and still be strong enough - =
say 300%=20
stronger than stock {:>). Since they are not made of typical =
"gray=20
iron" alloy that the stock and most other seals are made and =
chill/case=20
hardened, they may be amenable to machining.</DIV>
<DIV> </DIV>
<DIV>Yes, having airports scattered around in just about every county =
and=20
sometimes three or more in a county, the geography is much kinder to=20
engine-out excursions here on the east coast. Fly High, Glide=20
long! Better yet, keep running on both rotors.</DIV>
<DIV> </DIV>
<DIV>Ed A</DIV>
<DIV> </DIV>
<DIV> </DIV>
<BLOCKQUOTE dir=3Dltr=20
style=3D"PADDING-RIGHT: 0px; PADDING-LEFT: 5px; MARGIN-LEFT: 5px; =
BORDER-LEFT: #000000 2px solid; MARGIN-RIGHT: 0px">
<DIV style=3D"FONT: 10pt arial">----- Original Message ----- </DIV>
<DIV=20
style=3D"BACKGROUND: #e4e4e4; FONT: 10pt arial; font-color: =
black"><B>From:</B>=20
<A title=3Dmailto:Shearbond@aol.com=20
href=3D"mailto:Shearbond@aol.com">Shearbond@aol.com</A> </DIV>
<DIV style=3D"FONT: 10pt arial"><B>To:</B> <A=20
title=3Dmailto:flyrotary@lancaironline.net=20
href=3D"mailto:flyrotary@lancaironline.net">Rotary motors in =
aircraft</A>=20
</DIV>
<DIV style=3D"FONT: 10pt arial"><B>Sent:</B> Thursday, April 14, =
2005 10:10=20
AM</DIV>
<DIV style=3D"FONT: 10pt arial"><B>Subject:</B> [FlyRotary] Rx-8 =
Rotors</DIV>
<DIV><BR></DIV><FONT id=3Drole_document face=3DArial color=3D#000000 =
size=3D2>
<DIV>So.....since the rotors weigh the same within measurement =
error, the=20
ability to rev to the 9,000s range vs. 7,000s range is not related =
to the=20
orbiting mass of the rotor. (Note: the motion is NOT truly =
circular,=20
it is an epicycloid path that the center of mass of the rotor =
takes. =20
That 10 lb. rotor flops around plenty (technical term) and 10 lb. is =
lots=20
heavier than an aluminum piston!</DIV>
<DIV> </DIV>
<DIV>It is apparent from an article on the "other" site, that the =
wall=20
thicknesses and casting detail are lots more refined on the RX8=20
rotors than on earlier models...for more uniform and desirable =
heat=20
transfer and uniformity.....oil cooling the rotor, etc.</DIV>
<DIV> </DIV>
<DIV>The mass being basically the same, it becomes a high =
probability that=20
since centripetal force is F =3D (Mass x rotational velocity=20
squared)/radius of rotation, {F=3D(m x w^2)/r}, it must be =
the=20
weight of the <U><STRONG>seals</STRONG></U> themselves that are the =
critical=20
element? The force at 8,500 vx. 6,500 is (8.5/6.5) squared or =
1.71=20
times greater. Might this be why seal wear on the original =
seals goes=20
up substantially at around 6,500 rpm?</DIV>
<DIV> </DIV>
<DIV>Tell me....why would one increase the depth of the seal groove =
of an=20
RX8 rotor to allow a heavier seal???? On the RX8, =
3.25mm/9.5mm=20
=3D> approx. 34% reduction in apex seal mass!! A =
lighter=20
seal means a whole lot less force of the seal against the =
housing at=20
8,500 rpm!! Anyone want to go back to old seals and rev to =
8,500=20
rpm? </DIV>
<DIV> </DIV>
<DIV>Note: the seal force against the housing at 8,500 rpm on =
the RX8=20
is still higher than the old seal at 6,500.... (.66 x 1.71 =3D =
1.129). =20
Not much more, but there are probably even more very small =
details that=20
we are not at first glance able to know and understand? Seal=20
material/housing material compatability is probably one significant=20
factor?? (I used 9,000 vs. 7,000 and the numbers still come =
out about=20
10% higher seal force on the RX8, even with the lighter =
seals.) </DIV>
<DIV> </DIV>
<DIV>Having been an R&D engineer at FoMoCo, it is hard to =
explain to=20
most persons the creativity, detail, imagination, trial and testing =
and=20
testing and testing and testing and ...... which goes into =
making an=20
engine acceptable for production in quantities of XXX,XXX's and=20
higher. (One simply can't be wrong...it could bankrupt even =
the=20
largest OEM.) And....those Mazda engineers have done what many =
OEM's=20
gave up on many years ago. How? Through their =
persistence and=20
incredible insight into the issues.</DIV>
<DIV> </DIV>
<DIV>Before one gets the wire EDM out and starts going counter to =
what Mazda=20
no doubt spent many $$$$ (more than all of our annual incomes =
put=20
together??) on how to increase HP in an RX8, more information is =
needed=20
before we start mixing and matching just because the parts will =
fit. I know we are experimenters here, but lives of some who =
may not=20
understand the "physics" limitations will ultimately be at =
stake.</DIV>
<DIV> </DIV>
<DIV>Above all: Just because something works for 100 miles in =
a sprint=20
race <STRONG>DOES NOT</STRONG> mean it will work =
while hummmming along=20
for 5 hours at a crack at 75-80% max. HP on a cross-country over and =
over=20
and over again....hopefully. So far, my Lyc is a piece of 30's =
era=20
design and materials...but it has run for 2,000 hours (350,000=20
miles) at 75-100% without fail!!</DIV>
<DIV> </DIV>
<DIV>Most of us aren't as lucky as Ed and his "on airport" emergency =
landings. Perhaps it is that his green carpet =
(Carolina's) is=20
lots more friendly than our granite peaks out here?</DIV>
<DIV> </DIV>
<DIV>Doug in =
Colorado</DIV></BLOCKQUOTE></BLOCKQUOTE></FONT></DIV></BODY></HTML>
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