Today's Message Index:
----------------------
1. 05:13 AM - yaw rates, correction (Gary Casey)
2. 05:40 AM - Re: yaw rates, correction (James R. Cunningham)
3. 09:12 AM - Re: yaw rates, correction (Tedd McHenry)
4. 02:20 PM - Re: yaw rates, correction (Archie)
5. 04:38 PM - Re: yaw rates, correction (James R. Cunningham)
6. 05:31 PM - Re: yaw rates, correction (Edward Chmielewski)
7. 06:57 PM - Re: yaw rates, correction (steve korney)
8. 07:30 PM - Re: yaw rates, correction (Fergus Kyle)
9. 07:31 PM - Fw: yaw rates, correction (Fergus Kyle)
Message 1
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| Subject: | yaw rates, correction |
--> Engines-List message posted by: "Gary Casey" <glcasey@adelphia.net>
<<Good analysis, and I agree with your comments. I'll be meeting this
weekend
with friend who's an engineer for a CART team. I'll ask him his thoughts on
yaw and pitch rates.
The only place I disagree with you is the significance of roll rates. If
the
car has a transverse engine installation the roll rates are also a factor.>>
Yes, my comment on roll rates not being important apply to aircraft, since
lots of aerobatic aircraft have published roll rate capability, which means
nothing in this case since those aircraft have longitudinal engines. My
estimate of 20 degrees in 20 milliseconds comes from air bag design issues.
A frontal collision can easily result in 100 G's of acceleration near the
cowl and the crash is mostly over in 20 milliseconds. I assume the yaw rate
is also. However, I can imagine the car changing axis by way more than 20
degrees in that time. Also, most race cars have the engine bolted rigidly
to the chassis so it will see whatever the rest of the car sees. I still
have sort of an educated suspicion that you can bolt a light (non-aluminum)
prop to a car engine crank in a non-aerobatic aircraft and have no problem.
More analysis needs to be done before I would bet on an "educated suspicion"
to keep my prop on my plane. Experience doesn't count for much in this case
as I don't think there has been enough combined experience to provide
statistical evidence that it works.
Also, I need to make a correction: In my previous E-mail I notice that the
"squared" term disappeared - I'm assuming the carrot didn't come through.
The polar moment should read pound inches squared, not "lb-in" as it reads.
In other words square the radius of gyration and multiply it times the
weight in pounds.
Finally, a couple of other comments: There was a comment about "car engines
producing peak power at high rpm." Yes, but that isn't because they are car
engines, but because the valve timing and other design features allow it to
breath effectively at high rpm. Change the cam profile and you can put the
peak power anywhere you want it. The typical aircraft engine also has a
peak power considerable higher than its rated rpm as well. Since in an
aircraft engine you really only care about max power output at rated rpm
(not lower) the idea is to tune everything to have maximum torque at the
rated rpm, thus maximizing power at that speed. Most large 2-valve V-8s
produce their peak torque at about 2800 or so - very close to where you want
it for a direct drive application. The whole direct-drive argument centers
around durability and weight. Which has better durability, an engine
running naturally aspirated at high rpm, or one running under boost at lower
rpm? Experience shows that rpm is the killer as far as durability goes.
Boost doesn't help either, but the problem is mostly heat dissipation and
peak cylinder pressure, not mechanical durability. I maintain that you can
get the same power with better reliability and lower weight with a
crank-mounted direct drive turbocharged engine than with a PSRU-equipped
naturally aspirated engine running at higher rpm. And the boost levels
don't have to be really high to do the trick - I estimate that the manifold
pressure would be about 1.5 atmospheres, maybe a little more. And remember,
we mostly care about power at altitude, where the turbocharged engine really
shines. I would spend my money on an aluminum block and a turbocharger, not
a PSRU. Some anecdotal evidence: Top fuel dragsters have no limits on
anything and what rpm do they run? About 5,000 under LOTS of boost, not
lots of rpm.
Gary Casey
Message 2
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| Subject: | Re: yaw rates, correction |
--> Engines-List message posted by: "James R. Cunningham" <jrccea@bellsouth.net>
I agree with this, with the minor exceptions that I'd use an extra
bearing to unload the crank, and I'd probably use a supercharger rather
than a turbocharger.
Jim
Gary Casey wrote:
> I would spend my money on an aluminum block and a turbocharger, not a PSRU.
Message 3
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| Subject: | Re: yaw rates, correction |
--> Engines-List message posted by: Tedd McHenry <tedd@vansairforce.org>
Gary:
Interesting comments. I'm also a fan of direct drive (as opposed to reduction
drives). For one thing, the re-drive adds a lot of cost to the project,
thereby offsetting a lot of the cost advantage of an auto conversion. Some of
the re-drives cost more than a timed-out Lycoming, which makes the prospect of
saving money with a roll-your-own engine pretty doubtful!
> However, I can imagine the car changing axis by way more than 20
> degrees in that time. Also, most race cars have the engine bolted rigidly
> to the chassis so it will see whatever the rest of the car sees.
No question about it. Anyone who's spent much time watching both car races and
aerobatic airplanes wouldn't question that race cars see higher rates of
crankwhaft-axis rotation during crashes than airplane engines see in aerobatic
flight. But the race car engine isn't likely to be exposed to those rates more
than a handful of times in its life. The angular rates experienced in "normal"
use are important, too, as fatigue could be a factor. However, I agree
completely that auto engines used in racing have demonstrated that their
ultimate gyroscopic load capability is up to the tast of handling a FP prop.
> Experience doesn't count for much in this case as I don't think there has
> been enough combined experience to provide statistical evidence that it
> works.
I'm not so sure. There are an awful lot of airplanes out there flying around
with props bolted directly to the crankshaft of an auto engine. At one time
this was a common--if not the most common--way of doing VW and Corvair
installations. I've never heard of a case of the output flange failing. There
may have been some, but certainly not conspicuously many. And, as someone here
pointed it, it's not unknown with Lycomings and Continentals, so even if there
were a few such cases with auto engines it would not be damning evidence.
> Experience shows that rpm is the killer as far as durability goes. Boost
> doesn't help either, but the problem is mostly heat dissipation and peak
> cylinder pressure, not mechanical durability.
The auto engine has some advantages over a Lycoming or Continental in these
areas.
Because they are designed to run at higher RPMs (and for other reasons), auto
engines typically have more cylinders per unit displacement than airplane
engines. So they have shorter strokes, resulting in lower piston speeds. A
comparison of RPMs between different engines needs to take that into account.
For example, an Eggenfellner Subaru cruising at 4,000 RPM has about the same
piston speed as an O-360 cruising at 2,400 RPM.
Auto engines typcially have smaller diameter but wider journal bearings, making
their bearing wear index lower at the same RPM (or the same at a higher RPM)
than that of a Lycoming or Continental.
Water cooling also means that auto engines are more durable at a given BMEP
than a Lycoming or Continental. A reduction-drive auto conversion will often
have a lower BMEP at cruise than a Lyc or Cont, giving it a distinct durability
advantage.
I'm not trying to sell the higher-RPM approach, though. I agree with you that
the direct-drive approach has a lot of merit. It's possible to build a V6
Chevy of about 321 in
3 with off-the shelf components. At that displacement,
there's no need to turn more than 2,700 RPM to make good power. Such an engine
would have a huge durability advantage over a Lycoming by virtue of having a
lower bearing wear index, similar BMEP but with better cylinder cooling and
control of cylinder dimensions, and much lower pistion speeds.
> Some anecdotal evidence: Top fuel dragsters have no limits on anything and
> what rpm do they run? About 5,000 under LOTS of boost, not lots of rpm.
Very interesting. I had always assumed that they ran around 8,000 RPM like
other big-block racing engines. But then drag racing engines are not
necessarily the best example when durability is important!
Tedd McHenry
Surrey, BC
Message 4
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| Subject: | Re: yaw rates, correction |
--> Engines-List message posted by: "Archie" <archie97@earthlink.net>
> > Some anecdotal evidence: Top fuel dragsters have no limits on anything
and
> > what rpm do they run? About 5,000 under LOTS of boost, not lots of
rpm.
>
> Very interesting. I had always assumed that they ran around 8,000 RPM
like
> other big-block racing engines. But then drag racing engines are not
> necessarily the best example when durability is important!
===========================================================
Archie's interesting nitro burning dragster facts:
* One dragster's 500-inch Hemi makes more horsepower
than the first 8 rows at Daytona.
* Under full throttle, a dragster engine consumes 1 1/2 gallons of nitro
per second,
the same rate of fuel consumption as a fully loaded 747 but with 4
times the energy
volume.
* The supercharger takes more power to drive then a stock hemi makes.
* Even with nearly 3000 CFM of air being rammed in by the supercharger on
overdrive, the fuel mixture is compressed into nearly-solid form before
ignition.
Cylinders run on the verge of hydraulic lock.
* Dual electronic magnetos apply 44 amps to each spark plug.
This is the output of an arc welder in each cylinder.
* At stoichiometric (exact) 1.7:1 air/fuel mixture
(for nitro), the flame front of nitromethane measures 7050 degrees F.
* Nitromethane burns yellow. The spectacular white
flame seen above the stacks at night is raw burning hydrogen,
dissociated from atmospheric water vapor by the searing exhaust gases.
* Spark plug electrodes are totally consumed during a pass. After 1/2
way,
the engine is dieseling from compression-plus the glow of exhaust
valves
at 1400 degrees F. The engine can only be shut down by cutting of it's
fuel
flow.
* if spark momentarily fails early in the run, unburned nitro builds up in
those cylinders and then explodes with a force that can blow cylinder
heads off the block in pieces or blow the block in half.
* Dragsters twist the crank (torsionally) so far (20 degrees in the big
end of the track) that sometimes cam lobes are ground offset from front
to
rear to re-phase the valve timing somewhere closer to synchronization
with the
pistons.
* To exceed 300mph in 4.5 seconds dragsters must accelerate at an average
of over 4G's. But in reaching 250 mph well before 1/2 track, launch
acceleration is closer to 8G's.
* Drivers shut off before the finish line, or even dual parachutes will
not stop the car.
* If all the equipment is paid off, the crew worked for free, and for once
NOTHING BLOWS UP, each run costs $1000.00 per second.
* Dragsters reach over 300 miles per hour before you read this
last sentence.
Message 5
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| Subject: | Re: yaw rates, correction |
--> Engines-List message posted by: "James R. Cunningham" <jrccea@bellsouth.net>
Archie wrote:
> * Even with nearly 3000 CFM of air being rammed in by the supercharger on
> overdrive, the fuel mixture is compressed into nearly-solid form before
> ignition.
Interesting. What's the density and by how much does it miss the phase
change?
> * At stoichiometric (exact) 1.7:1 air/fuel mixture
> (for nitro), the flame front of nitromethane measures 7050 degrees F.
Is that about the same as the surface temperature of a 'F' type star?
> * Nitromethane burns yellow.
About the same as a 'G' star (similar to our sun)?
> * To exceed 300mph in 4.5 seconds dragsters must accelerate at an average
> of over 4G's. But in reaching 250 mph well before 1/2 track, launch
> acceleration is closer to 8G's.
At 8 g's, it makes 250 mph in an elapsed time of 1.42 seconds at a
distance down the track of 261 feet. That would indeed be well before
1/2 track.
> * Dragsters reach over 300 miles per hour before you read this
> last sentence.
Wouldn't that be a reading speed of 173 words/minute? I thought 800
words/minute was about average, and 3500 words/minute was typical of a
really fast reader. :-)
Message 6
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| Subject: | Re: yaw rates, correction |
--> Engines-List message posted by: "Edward Chmielewski" <edchmiel@mindspring.com>
----- Original Message -----
From: "Archie" <archie97@earthlink.net>
Subject: Re: Engines-List: yaw rates, correction
Great post, Archie, except:
> * Dragsters reach over 300 miles per hour before you read this
> last sentence.
Remember, this is the Engines List. My mouth can't go that quick. ;
)
Ed in JXN
Kolb MkII/503
Do not archive.
Message 7
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| Subject: | Re: yaw rates, correction |
--> Engines-List message posted by: "steve korney" <s_korney@hotmail.com>
It will be a great post as soon as Archie verifies some of what he
says...James R. Cunningham has some good points that should be addressed and
verified...I suppose we all exaggerate a little...
Best... Steve
Enter for your chance to IM with Bon Jovi, Seal, Bow Wow, or Mary J Blige
Message 8
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| Subject: | Re: yaw rates, correction |
--> Engines-List message posted by: "Fergus Kyle" <VE3LVO@rac.ca>
| * Under full throttle, a dragster engine consumes 1 1/2 gallons of
nitro
| per second, the same rate of fuel consumption as a fully loaded 747 but
with 4 times the energy volume.
I'll admit dragsters are fascinating but I don't know. That's a
dragster at full throtlle and a 747 at 39,000 pulling 30% fuelflow. An
L-1011 at sealevel on takeoff costs about $1000 an inch.
Ferg
Message 9
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| Subject: | yaw rates, correction |
--> Engines-List message posted by: "Fergus Kyle" <VE3LVO@rac.ca>
Subject: Re: Engines-List: yaw rates, correction
|
| | * Under full throttle, a dragster engine consumes 1 1/2 gallons of
| nitro
| | per second, the same rate of fuel consumption as a fully loaded 747 but
| with 4 times the energy volume.
| I'll admit dragsters are fascinating but I don't know. That's
a
| dragster at full throtlle and a 747 at 39,000 pulling 30% fuelflow. An
| L-1011 at sealevel on takeoff costs about $1000 an inch.
| Ferg
SORRY THAT SHOULD HAVE BEEN $100/INCH
Ferg
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