I have just got a new thunder tiger 46 d i need to know what prop gives the
best perf i have a 11X7 on it now and it seems to turn a lot of RPM's with
this prop is there something i can get more air speed out of and less RPM's
What do you guy run on your 46 size engine i guess is what i am trying to
say. Sorry i am new to the airplane stuff and need to ask stuped Q like this
"George Thomas " wrote in
Based on my 2 .46's (one Magnum Pro, which is now TT, the other an OS FX),
I'd say you're overpropping it a bit with that 11x7.
The "more air speed and less RPMs" doesn't quite work that way. If you
want to go fast, you generally want a relatively small-diameter prop with
high pitch and big RPMs. For static thrust, big low-pitched props win. If
you want to hover your plane, go with an 11x4 or 12.25x3.75 (they need a
shorter name for that prop).
The brand makes a difference, too, especially if it's APC.
Depends on your plane. A plane with a lot of drag, like a biplane or Cub, will
not fly well on a small diameter/high pitch prop. However, a sleek, sport-type
plane will fly well on this prop.
GIVEN THE SAME RPM: Small diameter/high pitch gives more speed (high gear in a
car). Large diameter/ low pitch gives more pull (low gear in a car).
Too much pitch or diameter can overload your engine. It won't make the RPM to
generate either thrust or speed.
"There's a Hun in the sun!"
Thunder Tiger know their engines better than supposed "winnable known as an
expert" flyers who advise without knowledge of your plane and the drag
TT operating instructions recommend:
Pattern Aerobatic 10 X 6.5, 10.5 X 6 and 11 X 5.
Sport Scale 11 X 6 & 10.5 X 6.
These have all been well tested with several TT Pro.46 and except for a 3D
model which has a 12.25 X 3.75 [and one must be very careful not to over rev
with this prop], I believe the recommendations should be adhered to. Buy one
of each to suit your type of model and try it.
An 11 X 7 is a Pro.61 and .61 FX standard size and will lead to short engine
life and in all probability rear bearing failure on any brand of .46
especially if less than 5% castor content in the oil. There is a wealth of
information to be gained under engines, props and fuel on my web page.
Alan's Hobby, Model & RC Web Links
I have this engine on a Worlds Model T-34. For speed I use a 10x8. I like
this prop because it lets me generate enough RPMs to be in the power zone
yet will not overspeed in a shallow dive (WOT in shallow dive). For
unlimited climbs and short take offs I use a 11x6. This prop generates more
static thrust. The 12.25x3.75 take the concept a step ferther. The best
way to determine which is the best prop for you is to first understand why
and how different props affect performance and then go out and buy a bunch
and try them out. Also get this program
It will help
you better understand prop selection. Like someone said earlier props are
like gears on a car. If you have a 3D plane you may want to fly in 1st
gear. If you have a pattern plane you may want to fly in 5th gear.
Something in between and you may want 3rd or you may mke your prop selection
on the type of field you're flying at. No matter which prop you select you
will be making a compromise. Remember you can only fly in one gear at a
time (alas a variable pich prop would be nice) but you can always land and
"shift gears" if needed.
If you want to experiment get this muffler
It will allow
the engine to generate more power than the stock muffler.
An 11X7 is on the high end of the range for just about any sport .46. The
TT does not turn props any faster than the OS FX and is a good mid pack
performer. For most sport applications where all out vertical isn't
important, I would use an 11X6. Keeps the RPMs down a bit and also the
I'm new to this, and trying to sort things out. Barry's program shows a
simple linear relationship between RPM and speed. The thrust curve is a
simple parabolic. (He doesn't graph these values; I printed them to a file
and imported into Excel to plot a graph.)
Can that be right? Is it as simple as that? Without crunching any numbers, I
expect speed/RPM can be linear only if we treat the propeller as an air
screw. One turn moves it forward some fixed fraction of its pitch distance.
Also without crunching numbers, I can only guess where the thrust figure
comes from. I suspect he's looking at the mass of air a simple airscrew
would move at the given RPM, and expressing that as thrust.
Help me out here. I'm new to fixed wing, but not new to flight or
aerodynamics. My background is rotary wing; I recognize the airscrew model
as a simplified version of a helis' actuator disk, the simplest of the
simple, without the niceties of spillage and vortex loss.
Starting with the basics, it doesn't seem reasonable to expect the propeller
to act as an air screw. I would think you would need the Cd, wetted surface
area, and model weight to reasonably predict how the plane will fly. So, how
would I use these two numbers, one representing (apparently) the no load
speed, and one representing (apparently) static thrust? Are they enough for
the knowledgable to select a good prop for a particular airframe?
No stupid questions, but if you are really keen to lean, buy a book on
aerodynamics so that you can properly come to understand the
inter-relationships which exist between engine characteristics,
propeller choice and airframe type. Undoubtedly still one of the best
and yet an easy read for the layman is Air Vice Marshall AC Kermode's
"Mechanics of Flight". Been in (re)-print for many, many years.
A concise no brainer recommendation without the why?
Sport_Pilot's sizing suggestions for your engine are spot on, and as
close to no brainer perfect as you're gonna' get from the "Dummies
Guide to Propeller Selection" for the TT46Pro.
You might also *pay close attention* to the erudite A.T.'s comments.
Optimum propeller choice for any (& that) engine is dependent upon the
airframe and intended flight envelope. Noise restrictions
notwithstanding, you want to choose a propeller diameter or pitch
combo (you can't have both) which will keep that engine turning within
its optimum power curve.
A problem with marketing vs sport flyer need or reality, is that
engines today are marketed as "most powerful" to outsell the
opposition, but which is diametrically opposed to most R/C sport flyer
mid-range power and noise restriction requirements. To achieve
anything near these manufacturer hp claims, you have to operate these
hotly timed Schnuerled two strokes at the top end of their RPM range
which means high RPM and more noise. If you don't, then most of the
time, you're only achieving about 65% of their potential or claimed
So to come back to your question, your best propeller choice is
entirely dependent upon what you want to do, and into what model
(type) you installed your TT, and how much potential excess power you
have available and are willing to sacrifice in that compromise for
Further, an 11x7 is a big ask for the TT46Pro IME&O. It certainly
won't operate anywhere near in the band, and will be a shitty
performer indeed unless married within a quite narrow choice of
airframe. If you have an aerodynamically clean model with a moderate
to high wing loading and want speed as well as great vertical, then go
with an aerodynamically efficient 10x7 (APC). If it's vertical you
want but at a slower pace and have more wing area and lower loading,
choose an APC 11x5 or Bolly 11x5.5. For pure 3D with big surfaces,
slow speed flight, you want more diameter again and even less pitch.
The key to all contemporary Schnuerled 46's is that they are virtually
all highly timed and oversquare, designed to develop their claimed
potential hp outputs over 15k. If you aren't at 14k or >, then you're
losing heaps of hp as that hp curve isn't anywhere near linear.
Even more importantly, power be it potential or developed is only
proportional to thrust, and depends upon propeller efficiency for the
constant (x). Choose intelligently and wisely, because with the
limitations of a fixed pitch, you can't have it all over a wide
So, if you want more speed, you need to choose the maximum pitch and
minimum diameter prop which will still offer you efficient *thrust*
with your particular airframe. With such a fixed pitch combo,
acceleration will of course usually be quite poor unless you have a
very light *and* low drag model. If it's a large draggy airframe, form
drag will be so high at speed, propping for speed becomes a pointless
exercise. And of course, propping for speed unavoidably means more
NOISE, both from engine and propeller RPM.
There is an excellent article in the October RCM that addresses just
this type of question. Also the September MA has a similar article as
well. However, both are really saying exactly what has been pointed out
by the kind folks here in the NG.
All these prograns will do is get you close. You cannot rely on them for
absolutes. The key here is to experiment with different combinations to
find what works best for YOUR engine and airframe.
That also takes more horsepower. The larger prop gains efficiency
through a smaller tip loss percentage, and also (as I should have
mentioned) through a lower drag. It's more efficient to accelerate a
larger column of air to a low speed than a small column to a high
speed, if the net thrusts are the same. The faster, smaller prop loses
much more to drag, as drag also increases by the square of the
increase in speed.
have tried them all and find that these people make a 10.5 x 8 that is
perfect for this engine. So much so that I have sold over 8 people at the
flying field on this including our biggest die hard. They are also a cheap