Hi! Again all.
At the expense of being unpopular with those who are further on into their
constructions and choices of Propellers and Engines I am taking the liberty
of publishing this on the forum in an attempt to reduce the number of
messages required of me since I chose the MT Propeller and the Jabiru 3300.
I must apologise to the Rotax /Wilksch buffs accordingly!
Perhaps it may be usefull to place this info. on the FAQ section somewhere ?
Many of the pictures concerning my mods are to be seen at the support webb
site :-
http://www.crix.org.uk
Under "Bob Harrison's Europa G-PTAG new"
AND/OR
"Modifications"
Scroll down to "Stabilators"
Then click on the word "here" for pictures of the torque tube clamp mod.
Regards
Bob Harrison G-PTAG Europa 337 MKI /Jabiru 3300
Question:- Why did you choose the Jabiru 3300 ? and would you again?
I didn't want a very high revving engine in a highly stresssed mode running
close to its extended design limits needing a reduction gear box to make
prop speeds attainable in front of me!
especially I didn't wish to have a climb out max. power time limit
applicable to my power pack.
The Jabiru 3300 is both clear of these problems
I would go the Jabiru way again but I "paid the price" of being the first
"through the mill" which has not been a totally pleasing experience,
although now rewarding. I do feel that there is still an absence of Jabiru
willingness to give written commitment with regards any installation
problems.
___________
Question:
Why did you choose the MT CS Prop and are you completely happy with it? I
think
it has the Warp Drive blades doesn't it? Was the Airmaster available at that
time, the time that you made your choice? If so, what in your opinion is the
benefit of your prop?
__________
I chose MT because Europa had just bought one for G-KITS and I wanted one to
a professional standard, tried and tested to save PFA Hassle(but I still got
hassle because the Germans refused to use the Jabiru flange saying that it
is a fatigue "waiting to happen"!) However they ,the Germans, put their
money where their mouth was because when Jabiru got their statement and the
"s......" went in the fan and Jabiru refused to supply an improved flange
the Germans made one for free, I call it "my flywheel". However it turned up
a can of worms about the very limited PMI of the Jabiru crank, resulting in
my having to design the new shank cap bolts and modify the crankshaft end.
Jabiru were ultimately prepared to provide the engine warranty but NOT THE
METHOD OF FIXING THE NEW PROP FLANGE (which was perhaps understandable!).
The MT is very expensive but within the price was a very professional stress
and balance analysis which has identified a stress resonance between crank
shaft and prop in the range 2150 rpm and 2400 rpm , so I have a restriction
band of 300 rpm for continuous running . I was disappointed originally since
I had always cruised at 2300 rpm (110 kts) with about 6 gallons per hour but
now am down to 5.3 galls per hour at 120 kts. This power resonnance problem
would not have shown without the analysis and I believe that there is
insufficient attention paid to this phenomenon by other prop suppliers.
No the Airmaster wasn't available at the time but if you choose the
Airmaster way you must:-
a) ensure the blades have an ultra short shank with a considerable pitch at
the spinner, otherwise there will be little air getting into the ram air
ducts when on departure delays and ground running. G-PTAG prop has MT
blades with about 5" chord at 45 deg pitch at the spinner tapering to about
1 3/4" chord at the tip. Very low Polar Moment of Inertia in spite of the
overall weight of 32lbs. but more than Jabiru authorise.
b) ensure that the spinner diameter doesn't interfere with the ram air duct
intakes (see my cowl intake eyelids, top and bottom, to catch ground running
air with no forward dynamic intake air available.
__________
Quote:
I've had to supply cold air through a cowl top duct to the No. 5 and No 6
>cylinders to supplement the ram air from the existing ducts.
>Question:
Is there some cowl work that they should do on the form of your cowl that I
should expect on mine if I buy one, and if so, what shape do you think it
should take i.e. bigger air intakes etc.
I think it is conceivable that the MT Prop spinner being larger diameter
than the Jabiru spinner
(But not as grotesque as the MK I Europa spinner!) may be deflecting the
dynamic air from entering the ram air ducts, it is very necessary to keep
airspeed above 80kts on climb out to ensure adequate cooling. It would have
helped if the spinner was sharp pointed instead of "rounded". I originally
started with a 2200 cowl supplied by ST Aviation and fared to their Europa
"Plug" and I agreed to open up the intake ducts as necessary. It would have
been better to
be even larger and particularly wider (because of the spinner diameter) I
also increased the size of the oil/sump cooler intake hole far too much and
have only just achieved higher oil temps
by fitting a removable mask to restrict the intake size during Winter months
at least.
I have also reasoned that, since the No.5 and 6 heads are getting pre warmed
air from the forward
heads, it makes sense to get some cold air directly into No.5 and 6 hence I
have another ram air duct now on top of the cowl squeezing air into No.5 and
6 cylinder heads directly.
I was intending removing it for winter running but have decided to keep it
in place throughout,
besides it makes the "rig" look " souped up" !
__________
>I wish I had an extra inch clearance from the Europa Foot wells ,especially
>3" if you have the XS extended foot wells. The carb and distributors are
>much too close the firewall on mine.
This is purely for maintenance access ,since I have to remove the top engine
mount bolts and allow the engine to droop to access the distributors and
carb. However the movement of the whole engine forward would dramatically
affect the C of G limitations. (BUT since I now have a Long Range tank (9
Gallons) fitted behind the original rear tank bulkhead my a/c would have
enjoyed the engine to be a couple of inches forward.)
________
I have the standard short footwells, but am only 175 cm (5'9") tall. Are you
saying you would want the longer ones, and if so I haven't got the picture
re
the carb and distributors. When I reread it, I think you are saying that I
would be best with the shorter ones anyway?
Standard footwells are better for the access problems I mean, you "re-read
correctly" We are about the same height.
___________
In your opinion "does the actual shape need to be anything special, or
simply
eyepleasing?"]
I guess you mean wing tips now?:-
I think "eye pleasing" is the buzz, however I believe that the turned up
factor must improve the departing vortex drag by having it more organised
and I am amused that the new Home Built MAVERICK Jet in the current Flyer
magazine has "copied" mine !!!!!!!!!! ( I wonder if I could claim
Intellectual Property rights? but then the SYCO chap would start to "dance
to the piper!")
With regards to control I don't have any adverse effects from this anyway.
However from the "donkey torque" at 120 kts 2700 Rpm I ought to have a 6"
trim fitted to the top of the port aileron also one to the bottom of the
starboard side .
___________
Thank you for your ideas. I hope I can put the tips to good effect.
___________
>Concerning the wing tips ,..... Originally an aircraft G-SYCO had them (a
>most UN helpful guy you could ever call on ) I copied his near enough ,
>PFA said just a letter would suffice since it isn't a control surface and
>unlikely to affect control performance. I think there is also pics of the
>wing tips during construction on the web site.
__________
>Hope this helps...
>
It's just a pain having to type it out so many times to so many folks ,I
wish Jabiru would copy it out to their respective punters! Perhaps you could
suggest it to them?
I flew to Old Sarum near the South coast 1hr 20minutes each way from
Wickenby , yesterday worked out at 5.30Imp gallons per hour at 120kts
cruise.
Best regards
Bob Harrison G-PTAG Europa 337 MKI /Jabiru 3300
|