To all,
>From testing with the Airmaster AP420 vs 332 a couple of notes on prop
vibration/noise.
I do not intend to comment on the different brands, only the differences
between a three and two blade prop both designed for and tested on the
Europa..
A two blade AP420 with Sensenich Blades vs. three blade AP332 with Warp
Drive Blades non tapered. Engine 914, Aircraft Europa XS Trigear.
First, at cruise the Rotax only turns nominally 2050 RPM prop speed and
the prop length is limited to 64 inches, so the tip compression or mach
whack noises are minimized. The limited cruise RPM really degrades the
performance of a propeller. The gear box limit of 2.43 reduction
imposes a problem in cruise, but allows longer blades and the ability to
deliver more torque to a prop. In essence, the slow prop shaft RPM and
limited length means the prop angle at cruise must be increased to
absorb the torque of the engine. The higher angle of attack of the
blade makes for some interesting problems for the blade designer.
Takeoff, vs. climb performance vs. cruise performance will be
significantly different conditions and design criteria for the blades
and the downwash off the blades as they pass the cowl are different.
The next thing is that the area of the blades must be near equal for
proper comparisons.
Finally, the Europa thrust line has a near zero angle at cruise, but
nearly 8 degrees during initial climb at max climb speeds of 65 and 75
for angle and rate.
Comment: Quality propeller blade manufacturers have very consistent
mass balance and airfoil sections blade to blade, so vibrations due to
balance are minimal. Hand cut or custom props, or defective props (yes
we had one Sensenich go out of balance due to an internal balloon
failure) must be sorted out. The slightest profile difference makes a
difference in both noise and vibration.
The two blade pulses, due to AOA during climb, does give a change in
sound outside the aircraft as well as inside. The power pulses of each
blade passing through the windshield arc allows the two blade to make an
audible (somewhat irritating) pulse across the windshield and cowl face.
The three blade prop increases the frequency of the power pulses and
smooths out the pulses affects and although the decibels aren't terribly
different, the noise (what is irritating to the ear) is less for the
three blade. Tapered tips are less noisy than square tips. Cutoff tips
give a sharp tip sound when compared to a swept tip. Swept tips have
lower initial inertia and lower tip drag at higher prop speeds.
At or near cruise, this pulsing noise is diminished significantly at the
shorter blade lengths. Long blade lengths tend to be noisier due to
their effect on more of the aircraft, most noticeably is the windscreen
pulsing noise transferred into the cockpit and to your ears.
On tests with the 76 inch long blades, the two blade is very loud in
comparison, diminishing with a shortening of the blade length.
The 76 inch long two blade requires ANR headsets for comfort, and the
windscreen in the Rans and Kitfox actually moves like a drum as the
blade passes. The two blade at the long lengths is faster on top end as
I approached the aircraft's VNE. High altitude performance was a bit
better with the two blade also. This is, in my opinion, not not due to
the differences in two vs three blade as much as the difference in blade
areas, thickness and taper plus the slight advantage in efficiency of
any two blade over a three blade (remembering the most efficient prop is
a single blade). The Sensenich blades are thicker and wider of chord on
the longer blades. The Warp Drive blades of that length were tapered
tips because of the very long length and the difference in rotational
inertia. We went to the wide chord blade on the 332 at 76 inches (not
good for the sprag clutch on the Rotax with its higher inertia on start)
but it still was a bit slower at top end and had only a tiny decrease in
static thrust than the 76 inch long Sensenich blades on the 420.
Tip design also has an effect. A swept tip tends to be quieter on the
very long props, but is less effective on the shorter props. A number
of designers have toyed with better blade designs but the problem is
each experimental is different. What works on a Vari Eze is not going
to work for a Ran's or Europa even with the same engine...
I talked with Steve and Mike at Sensenich about the 64 inch two blade,
but they had to admit, it isn't working as well as they would like. The
twist, area profile, taper and airfoil section have got to be tweaked to
get the most out of the Europa/914 combo. How many blades will we sell
to pay for all the tweaking and testing that comes into the blade
manufacture equation. Yes, mass produced blades must operate
efficiently but also sell. Right now the Sensenich market is in the LSA
market which doesn't need all that tweaking because they only go 120
Knots. We in the Europa commuity are looking for 150 Knots at 10,000,
which is a totally different blade design. Not that the casual observer
would notice the difference, but to those of us flying efficient glass
aircraft, we notice the difference. Again, I am not getting into whose
manufactured prop is better, because tests have to be done on the same
aircraft, same CG, same conditions to be valid. My Europa is
significantly faster (15 knots) than another XS in the shop. Same
airplane, landing gear, engine, and prop, just different in oh so many
little ways... CG, wheel pants, cowl seals, door fit, trim of the
aircraft, flap droop, wing gap seals, engine isolation mount age, etc.
Another area of vibration is the wind angle during taxi, compression
braking with the prop at high speed, resonance effects, Rotax gearbox
(straight cut verses taped cut). There are certain aircraft where the
vibration of the prop in one, or all of the above is quite irritating.
The Warp Drive, does drive me nuts during taxi with a quartering tail
wind as my engine /prop combo sounds terrible during taxi and if I dive
into the pattern with the prop at cruise (5000) at 130 Knots and lower
the power setting further, I can feel the prop and gearbox lash and
rattling noise. Entering the pattern at "Takeoff" setting diminishes
that as does entering the pattern at lower speed.
Pusher designs have noticeable differences from the tractor types due to
air flow disturbance across the blades, especially if a tail boom is
below the prop. Even the addition of an augmenter exhaust to only one
side of the aircraft makes a difference in feel.
In my summary to Airmaster, I saw no difference in performance between
the AP332 vs the AP420 in the Europa (64 inch prop length) but a
noticeable difference in the longer 76 inch blades on the Kitfox / Rans
S6 aircraft. The two blade was lighter, easier to get the cowl off and
on, and a bit noisier on the Europa. Longevity of the blades depends on
how much grass you intend to mow.
Have a great weekend,
I'm off to the shop.
Bud Yerly
----- Original Message -----
From: GRAHAM SINGLETON<mailto:grahamsingleton@btinternet.com>
To: europa-list@matronics.com<mailto:europa-list@matronics.com>
Sent: Tuesday, June 26, 2012 2:27 PM
Subject: Re: Europa-List: Re: Contact detail & Help
Hi David
Yes it probably is, but it's at low speeds and high power on climb out
that the vibration is worst.
With multi blade props the problem isn't as bad. I'm not good enough
at maths to explain why
but I am just reiterating what Bruno Guimbal said years ago. He
designed a very attractive looking helicopter I once saw at
the RSA Rally years ago. He seems to have moved on, haven't heard
anything for years. Very experienced aerospace engineer
who built a Vari Eze around 1978 which he flew to Leicester when our
rally was there in 1979 I think.
Graham
-------------------------------------------------------------------------
-----
From: David Joyce <davidjoyce@doctors.org.uk>
To: europa-list@matronics.com
Sent: Tuesday, 26 June 2012, 18:35
Subject: Re: Europa-List: Re: Contact detail & Help
<davidjoyce@doctors.org.uk<mailto:davidjoyce@doctors.org.uk>>
Graham, In my innocence I thought that the plane was designed so that
in normal cruise attitude the engine axis was horizontal and the blades
at equal AOA
Regards, David Joyce, G-XSDJ
GRAHAM SINGLETON
<grahamsingleton@btinternet.com<mailto:grahamsingleton@btinternet.com>>
wrote:
> Karl
> 3 blades will always be smoother because when the 2 blades are
horizontal each blade sees a
> different AoA, especially with high angles of attack. This causes
different thrist on the blades resulting
> in yawing oscillation of the airplane.
> Graham
>
>
> ________________________________
> From: Karl Heindl <kheindl@msn.com<mailto:kheindl@msn.com>>
> To: europa-list@matronics.com<mailto:europa-list@matronics.com>
Sent: Tuesday, 26 June 2012, 14:57
> Subject: RE: Europa-List: Re: Contact detail & Help
>
>
>
> Hi Frans,
>
> Thank you for the additional information. I will follow your advice,
but probably not until next year.
> If you are going to publish in the flyer, then some good pictures
please of the radiator installations.
> Also, a source for the rads.
>
> You mentioned that the prop is not as smooth at lower rpm's. I have
the same prop and I discovered a long time ago that the carbs need to be
in sync 100% for a two-bladed prop. With three blades the carbs would
need to be out of sync quite a bit before you would notice. I know,
because I tried it by putting my original Warp Drive back on.
>
> Karl
>
>
>
>
>
>
>
>> Date: Mon, 25 Jun 2012 23:09:34 +0200
>> From: frans@privatepilots.nl<mailto:frans@privatepilots.nl>
>> To: europa-list@matronics.com<mailto:europa-list@matronics.com>
>> Subject: Re: Europa-List: Re: Contact detail & Help
>>
>> Hi Karl,
>>
>> > I have been following your developments with great interest and I
think
>> > that the end result is just plain amazing.
>>
>> Thanks!
>>
>> > Now, top speed is very useful for testing drag improvements, but
you
>> > don't cruise at those speeds, do you ? When you are touring, what
are
>> > your preferred settings regarding speed, MP, rpm etc., and
exactly what
>> > is your fuel consumption then.
>>
>> I found the sweet spot of the aircraft is with 27 inch MAP, where
it
>> usually cruises with a speed somewhere between 120 and 130 KIAS,
>> depending on C of G and some other obscure factors. Fuel
consumption
>> used to be 16 to 17 liters per hour, but I have observed this year
that
>> the fuel consumption has increased to 18 liters per hour. Maybe the
>> carbs need an overhaul or so.
>> RPM is usually between 4800 and 5000 RPM, this feels best for the
>> engine. I have a two blade prop and at lower RPM's it feels less
smooth.
>> Of course actual settings depend on various circumstances. With a
strong
>> head wind we usually advance the throttle a bit, with a tail wind
we
>> enjoy the lower fuel consumption of a lower power setting. We fly
90% of
>> our cruising with power between 26 and 28 inch.
>> With higher power settings the fuel consumption goes up faster than
the
>> gain in speed. Other than in a car, a higher speed doesn't give any
>> other feeling than a lower speed, it just gives the same sensation.
One
>> hour flying is still one hour flying. On a 3-hour trip I rather
enjoy an
>> additional 10 minutes flying and have a free meal than just
cranking up
>> the fuel consumption, paying more for less fun. AVGAS can be close
to 3
>> Euro's per liter over here, so saving 10 liters on a trip can save
>> enough money to have a dinner for two! ;-) I love telling friends
that
>> flying there isn't more expensive than getting there by car.
>>
>> > If the rest of us mortals wanted to implement some of your
changes
>> > without too much expense, what would you recommend ?
>>
>> There isn't much money involved actually. The radiator costs about
300
>> Euro's, the heat exchanger a bit less. You can do without the heat
>> exchanger, I have been flying one summer with the stock oil
radiator fed
>> by a 2" Scat tube via a wedge diffuser. Apart from the long warm up
time
>> it was quite an improvement over the tandem setup. Best thing to do
is
>> to scrap the stock coolant radiator, dog house, duct and associated
>> hardware and just install a thin radiator in a 45 degree angle in
front
>> of the exhaust and turbo.
>>
>> The main hurdle here is to shape a new underside of the cowling.
You
>> have to be brave enough to cut the dog house away, and then insert
a
>> block of blue foam and start cutting, rasping, sanding until you
have
>> the shape you desire. Anyone who wants to make a mold out of my
cowling
>> is welcome to do so, provided I'm allowed to use that mold to make
a new
>> light weight carbon cowling for myself. ;-)
>>
>> BTW I'm not the only one who devised something like this. See the
>> attached picture. This is another configuration with a thin
radiator in
>> a 45 degree angle, although it lacks a cowl flap and heat exchanger
for
>> the oil. (Oil is cooled by a radiator, fed by a NASA duct on the
port
>> side, you can see it on the picture). Also this owner claims very
good
>> results with his setup on his 914 engine. The key really is to use
a
>> thin radiator and mount it at the belly so the "used" air can take
the
>> heat of the exhaust with it, and enjoy the benefits of a very sleek
>> cowlng, excellent cooling, low pressure losses, and minimal cooling
drag.
>>
>> Anyway, my cooling design is not an exclusive invention of me but
the
>> combination of ideas and experiments of multiple Europa owners who
>> believed that the cooling of the Europa could be improved other
than by
>> using draggy brute force solutions.
>>
>> > What is the part number for the
>> > heat exchanger and exactly where did you install it ?
>>
>> See picture, taken from under the engine. The heat exchanger is
mounted
>> behind the engine. This was the first setup, with the stock coolant
>> radiator, hence the configuration of the coolant hoses pointing
>> downwards. In the current design the hose routing has been changed
to
>> accomodate for the thin belly radiator.
>> If you really want to go this way, contact me privately for more
info.
>> One caveat though: this heat exchanger has very thin canals and is
not
>> compatible with Evans coolant due to its viscosity. I use it with
50/50
>> without problems.
>>
>> > It also had a very
>> > small (8AH?) battery.
>>
>> I also have a small 8Ah battery, never needed anything more than
that.
>> But I have a second alternator (mounted on the vaccuum pad) so I
don't
>> ne//www.matronics.com/Navigator?Europa-List"
target="_blank">http://www.mat="http://forums.matronics.com/";
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