Paul,
Thank you for providing feedback on the Hush power we have contacted
Flowmaster to start a testing program and they further indicated they would
work with us on a muffler solution for our engines. We will send you the
results after testing.
As it relates to your question what sort of fuel burn are you seeing at 5500
to 6000 RPM in terms of gallons per hour?
RotaMax Answer: This is an area where we see a potential to misrepresent
facts especially in the aviation industry. We burn fuel at an air ratio of
13:1-13:4 at the higher RPM ranges of our engine. As you are well aware fuel
usage is based on Lbs/hp/hr IE BSFC. Below I have copied results of engine
testing at an engineering school who is building an LSA with our single
rotor engine.
I also want to comment that fuel burn in aviation is a very important
calculation with many variables, Aircraft, Prop, Wind speed, Air Speed,
Temperature Etc. We would caution individuals that these calculations are
very critical when making flight plans and can vary greatly based on the
stated conditions above.
Our engine produces very flat torque and we believe more testing will
validate these tests below that show proper use of torque can and will lower
the required HP thus fuel consumption in an aircraft. We also only run the
engine to 6000 RPM Max as the operating range as it relates to max thrust
shown below is 5000 RPM Max. At the end of the day we would like to take off
at 5500 and cruise at 5000. Depending on the application take off at 5000
and cruise at 4500 provides very manageable engine program as it relates to
EGT, noise, cooling Etc this is a great range as the torque is flat
throughout this range.
Test results from engineering students using a 650cc normally aspirated
single rotor with a belt PSRU and a Kiev prop:
Eric,
At first glance, pitch setting #7 looks like a good choice. Of course, this
pitch setting is almost certainly too shallow for a decent cruise speed, but
there is no denying that the engine seems to like this setting - it runs
effortlessly at 4000 RPM, and spools up to 5000 RPM easily. However, I
expect that the #9 setting is probably closer to what we would want to
actually use. As you know, static tests are limited in predicting actual
performance in the air, and we won't be able to find the optimum pitch
setting until we can do flight tests, but these results are very
encouraging, particularly with regard to the low fuel consumption results -
I was expecting it to use more fuel at these power settings. With the new
fuel consumption measuring method, the numbers were not only lower but much
more consistent.
Here are the latest test results:
Pitch Thrust GPH Max Max
setting 4000 4000 thrust RPM
6........ 215... 2.50... 370... 5500...
7........ 250... 2.42... 400... 5220...
8........ 255... 2.56... 380... 5060...
9........ 250... 2.75... 350... 4870...
10....... 250... 3.30... 335... 4630...
11....... 260... 4.00... 300... 4330...
Notes:
1) The pitch setting is an arbitrary number on a protractor provided by the
manufacturer, and represents neither blade angle nor inches of pitch.
Larger numbers mean more pitch.
2) Thrust 4000 is the thrust at 4000 RPMs, averaged over about a two minute
period.
3) GPH 4000 is the average fuel consumption over the same period, while
holding the speed at 4000 RPM.
4) Max thrust is the maximum thrust possible at this pitch setting.
5) Max RPM is the maximum engine speed possible at this pitch setting.
I think we have learned about as much as we are going to from the current
setup, and I suggest that we next turn our attention to the reduction ratio.
The 2.5 to 1 ratio we are currently using was an educated guess made back
before we had any engine or prop test data, and I am quite sure that we can
do better. I wish I could say that I have a mathematical model that will
predict the effect of changing the ratio, but without test data from other
ratios, this is not easy to do. So, I think the next step is to cut some
additional sprockets and run the tests again with the different ratios.
With more data, I believe we can draw some conclusions with regard to
matching the optimum prop speed with the best compromise in engine power and
fuel consumption. When we designed the reduction drive, we chose sprockets
with a simple semi-circular tooth profile so that we could easily CNC
machine additional sprockets to achieve various ratios. While we are
capable of making sprockets here, I am under the impression that your
machining capabilities are superior to ours, and I wonder if it might be
quicker and easier for you to make the new sprockets. If so, I would be
very happy to send some drawings and suggest some ratios to try.
Again, we are very pleased with these results, and we think with some
additional work, the combination of the RotaMax engine and the Kiev prop is
going to be an excellent power source for light sport aircraft. With the
bugs worked out of our test stand and a group of enthusiastic students
returning to campus in a few weeks, I think we are in an excellent position
to work together with you to complete the work required to take this design
from prototype to product.
Don
Eric Barger, President
Phone 419-694-3000 x 222
RotaMax Inc.
15152 Twp Rd 190
Arlington, OH 45814
Fax 419-694-1401
www.rotamax.net
Don't put too much emphasis on static thrust. People have died doing that
with airplanes.
The actual pitch required is higher than that required for max static
thrust. The prop is always stalled up to about 60 MPH where it starts to "bite".
The engine RPM will start to increase around 60 MPH and on up. At static the
engine RPM is loaded down due to the stalled prop so static RPM may be as little as
75% of max power RPM. The bottom line is max thrust at the top speed of
the aircraft or max thrust at the climb speed. Cruise prop verses climb
prop.
BTW airplanes fly on HP and not torque. Drag times speed is HP.
200 pounds of drag at 200 FPS (136 MPH) is 40,000 pound foot per second HP.
One HP is 550 pound foot per second so that is 40,000/550 or 73 net thrust
HP out of the prop. The engine HP required is 73/.8 or 91 HP. This is because props
are only about 80% efficient.
The gear ratio you use has nothing to do with the HP except you
can not run a prop tip above about .8 to .9 Mach. The idea is select
a gear ratio that will allow your engine to reach its peak HP RPM when
the prop tips are going about .8 Mach. About 800 feet per second.
My suggestion is a gear ratio of 2.5:1 so at 6000 RPM and 90 HP the prop is
turning at 2400 RPM during climb out which is about right for a 72 inch prop
and an LSA airplane. You will need to cruise around 5000 RPM. Where the
power will be down to about 75 HP. Larger dia. prop for better climb use
a 2.8:1 gear ratio. If you have a short landing gear problem and need a
smaller dia prop go with a lower ratio such as 2.3:1.
Consequently from the above table you cannot calculate the BSFC or the HP as
you don't know how fast the airplane would go with these RPM's and these prop pitches.
My guess is your engine will have a BSFC of around .6 +/- .05 so 90 HP
will burn roughly 54 pounds per hour or 9 gallons and hour. At 65 HP it will
burn roughly 6.5 gallons per hour.
The only way to determine the HP and the BSFC under static
conditions is measure the torque. The easy way and cheap way is to build a
prop load dyno as in these dwgs. Cut the diameter of the test prop or club down
until the engine will achive 6000 RPM static. Then measure the torque. Ignore the
static thrust.
HP is then (RPM x Torque)/5252. Of course you can then measure the fuel burn
directly in gallons per hour. Multiply by 6 to get pounds per hour
and then divide by the HP to get BSFC in pounds of fuel burned per HP per
hour.
Paul Lamar ...No rotor no motor.
Paul,
Thank you for the input we will provide you results of our testing.
Eric Barger, President
Phone 419-694-3000 x 222
RotaMax Inc.
15152 Twp Rd 190
Arlington, OH 45814
Fax 419-694-1401
www.rotamax.net
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