Re: Bellying up to the bar

David J. Gall


The "superq.pdf" file on the YahooGroups website is an older version. There
is a two-year newer version that has a lot more information, including
propeller information and performance. Unfortunately, the YahooGroups
website doesn't have enough space left for me to upload the newer version
and my own website building tools are broken so I can't post to my own
website.... Therefore, I'm sending the zipped file to you directly as an
attachment. I hope this helps you select a prop. Feel free to share the
zipped file, as Hawks and McCaman had intended.

For my money, I think the Powerfin prop is the best on the market right now
for such an application. The Hawks/McCaman Super Quickies used Craig Catto
props, and the Powerfin blade profile is a copy of the old Catto ground
adjustable props, I believe. The Super Quickie report refers to props from
48 to 44 inch diameter on Rotax 503's (SC and DC) with the 2.238:1
reduction, and prop pitch in the range of 52 to 56 inches. Using 6250 rpm as
the 503SC (46hp single carb) redline, that works out to a prop speed of just
under 2800 rpm for the 46D x 52P prop Jinx McCaman used.

I'll assume that the Hexadyne only puts out about 45hp to the prop at
redline (losses to the alternator, oil pump, and other accessories). Since
you're only turning the prop at 2300 rpm you'll need a slightly larger
diameter and much more pitch than the 503SC. You should have good results
with a 48 to 50 inch diameter to absorb the horsepower, and a blade pitch
somewhere around 70 inches (beta angle of about 30.5 degrees measured at
0.75 radius)to anticipate a max level flight speed of about 140 mph.

Since the above prop diameter is a bit too much for your ground clearance
requirements, I would recommend that you use the Powerfin B blade profile
with the wider blade chord than the E. Also ask the manufacturer how much is
the maximum you can trim off the blade diameter without ruining the
structural integrity of the blade, since you may find yourself cutting the
diameter down slightly and increasing the pitch as you discover that the
engine has more oomph or the airframe has less drag (Yeah! Go fast!) than
you anticipated. Then, too, you might just find that the blade chord is too
much for your engine and need to trim the diameter for that reason (which is
a good thing since it corresponds with why you chose the B-blade in the
first place).

You could probably get a similar (and more trustworthy) quote directly from
Craig Catto or one of the other "homebuilt" prop makers. I would avoid the
advice offered by manufacturers of propellers for ultralight airplanes,
since they never see the airspeeds obtained by the likes of a Super Quickie,
with the possible exception of Powerfin, Inc.

Heck, call Powerfin! Their website says this: "These recommendations are for
the largest possible prop that is aerodynamically suitable for the engine
and re-drive combination listed. The largest possible choice will generally
give you the best performance in the static and climb mode of operation.
Most ultralights fit into this category. If you have an airplane that goes
faster than the average ultralight, you might want to run a smaller diameter
than this list recommends. It would be best to call us if you have the
slightest question about this."

Good luck,

David J. Gall, BSAE

-----Original Message-----
From: Q-LIST@... [mailto:Q-LIST@...]
On Behalf Of davedrosen
Sent: Tuesday, August 09, 2005 1:56 PM
To: Q-LIST@...
Subject: [Q-LIST] Bellying up to the bar

Probably by the end of next week I'll be buying my engine
and prop. I just wanted to know what size and pitch prop
others are using with a Q1. It seems 48 to 52 inches is
popular. The Jinx/Brock paper does not mention props at all.
I think when I allow 9" clearance with the firewall
perpendicular to earth, I would be 48 or 50". I am intested
in Powerfin props (but not committed, open mind). Does anyone
have experience with them on a Q1? I was thinking a 3 blade.
The engine is the hexadyne P60,50 hp at 2300 rpm (prop rpm).
Any advice about props would be appreciated. Adding blades,
advantages/disadvantages, etc. Do I need lots of pitch,
because I can't get the rpm's. If I'm pitchy, will I have
crappy climb performance but great cruse? etc. If anyone is
familiar with powerfin would the E or B blade be better.

Thanks in advance,
Dave R.

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