propellor braking bolly vs mejzlik

[davidcaymus]

I have recently replaced a broken Bolly 28 x 10 carbon fiber prop with the equivalent Mejzlik. The Mejzlik is gorgeous when compared, all that shiny carbon fiber cloth. Anyhows, the finish is slick as compared to the bolly which looks as if it has been sanded with 220 grit and the bolly is 20 to 25% heavier. Performance on the other hand is very different. Idle speed was 300 rpm lower with the bolly without engine quitting but the mejzlik on top end was about 300 rpm better. making me wonder if the weight of the bolly created more centrifical energy allowing lower idle speed??? But really my question is this The bolly had much better braking on down lines and landing. I compare the remaining blade on the bolly to the mejzlik and they are the same excet for the last inch to the tip is 1/8 larger on the bolly all the way to the point. Is there a reason for the difference in braking or just my imagination..??

[SleepyC]

I have just switched from a Mejzlik CF 23 - 8 to a wood Bolly 23 - 8.
And I have to say the Bolly still did the same things as you describe?!
Also the bolly seemed to give the plane more torque and pull out and less speed than the Mejzlik.
I like both, but i just ordered another few Bollys!

[dick hanson]

The numbers on the props ar just that --
numbers
They really do not give you an accurate idea of the effective pitch.
measuring width of blade also means little in trying to figur out which pulls hardest or brakes most effectively

The prop which turns fastest on the ground --is usually the one with least effective pitch ----not always tho as some blades simply load up differently
Bollys are among the heavier props and also -Inall of the examples I have run - have effectively lower pitch than others stamped with same numbers
Does not mean they are not good or anyone is trying to lie to you
run what works best for you and ignore the numbers
I run a 22x12 on my 50 - (A ZM ) works great and extremely quiet
on my 160 I run a 30x14 - ZM also extremely quiet and pulls 40 lbs easily from a hover. The number on these props looks high - effectively they act as lower pitched competitors' props - just much more quiet.

[Ronbo]

Dick,
any suggestions on a good pulling prop for a DA150 with mufflers on a H9 Ultimate? looking for more thrust but as quiet as my Mejlik 32x10 for IMAC. Looking at wood, unless a carbon will as well. talked to a gent who used a mej 30x12 for 3D on his Ultimate and loves it.

[dick hanson]

the DA150 -on the Mejzlic 30x10 --is about the most power compatible setup -
At the last TOC this was the most power makin setup there -I was Line Chief and saw everybodys' setups . Noise meant nothing -
adding larger props reduces power -every time . I snicker when I see talk about how some engines supposedly pull extremely large props --
Unless you are puling well into the 6000 rpm range - you are making less power on the 150.
The only big engines I have seen which make big power in the 5000 rpm range? the ZDZ 210.
That is simply because it is BIG.
Maybe you can whittle on some 30x12's and narrow them carefully but for the Ultimate - you are faced with a very big plane that really soaks up power .
Full length pipes on 30x10 will make more power but that is a $$orta hard way to go .

[adrian]

interesting - i have been running a h9 ulti for a long time - DA150, stock pipes - i have tested so many props i cant remember - i seem to come back to bolly wood 32x10 everytime - i am at sea level - also 30x12 is great but less pull out but greater speed

[Jon]

I've got a wood NX 23x8 to try on my ZDZ 50, but was thinking of trying a Mejzlik 23x8 asweel. Any thoughts?

[RustyTumbles]

I thinks it depend on what you want to do for prop selection. I have only really tried bolly wood props. They are a good all round prop (3d and IMAC) I think. But from what I have seen the mejzlik are the prop to have from IMAC work.

[dick hanson]

the best prop -is the one you like best .
once you make stipulations - such as "best power BUT low noise" etc., the selection changes .
I like the 30x14 ZM on my 160 -big pig 42% Radiocraft. quiet and very good power other stuff blatts like crazy-or- does not pull as well at low speed.

[davidcaymus]

just stopped in to check up on my original thread about braking. Had an interesting experience. I tried a zinger 22x10 on a da 50 on an aerotech yak 54. flew ok but I landed and replaced the zinger with my favorite bolly wood 22x 10 the performance difference is unbeleivable. the zinger would barely pull the plane out of a hover but the bolly pulled unlimited at 2/3 throttle. Also the bolly gets the plane airborne in about 12 feet (no up elevator required) the zinger takes about 40 feet to reach same airspeed. I talked to bolly rep who believes the difference is not only in the pitch coeffiecient??? but also in the stiffness of the wood the bolly being considerably thicker and therefore will not flex nearly as much as the zinger when throttling up. I tried to get him to explain coefficient of pitch but never really understood what he meant,, has something to do with design of blade width at greatest angle of attack and blade thickness on leading edge tapering evenly to tip of prop..

[davidcaymus]

what size engine would you put on a turkey da 50 or 100?? and are they IMAC legal if there to scale..??

[dick hanson]

co efficient of pitch?
strange -------------
The efficiency of a prop is a tricky thing to measure --because the airplane is included
Here is a rather basic explanation:
a prop -throttled up to full rpm on the ground--- will accelerate until the drag of the plane stops it from going any faster .
If there were no airplane -- then the prop and engine would accelerate till the engine could no longer turn the prop faster AND -- the prop was no longer accelerating any air thu it.
Think that over --
Now --lets try a big heavy but clean aerodynamically airplane and a very narrow high pitch prop - likely the plane would take forever to get going but once in the air may reach a pretty high speed.
Start over -- same plane use a low pitch prop designed pull hard at low airspeeds
The same plane will likely take off much faster and quickly reach top speed -- that is - as fast as the engine can turn it against the prop load.
this top speed may be much lower tho -than when using th skinny high pitched prop.
You can calculate all you want to -but you really have to match the engine/prop and airrplane through experimentation

[davidcaymus]

Co-efficient of pitch?? strange was my impression too. Ive never heard this term and wondered if I misunderstood the explanantion that I got. Has anyone ever heard the term co-efficient of pitch I tried to look it up in aerospace terminology treatices but can find nothing.. I cant see where the thicknes of the leading edge would make a differnece either. why does the bolly work so much better than the zinger???I can understand some differnece just in quality difference of the two but not the real difference I am experiencing. Makes me think prop selection is much more important than pitch diameter and brand considerations alone, and experimentation is probably the only way to determine ideal set up which may vary with individual taste and flying style..

[dick hanson]

just looking at the props ---- makes selection difficult.
best props are very stiff
blade shape and thickness? well they are just part of it
the progression of the pitch counts too.
props which are made from thin blanks are typically a bit too flexible
wobble or flex is a no no .
there are full scale prop designs which are supposed to change pitch at various airloads (or unloading)
our stuff is not like those designs.

[Jon]

The thickness of the leading edge makes a difference as it changes the distribution of pressure over the aerofoil, and affects the lift generated. Easy way to put it is reno racer=thin wing, funfly=thick wing.