They have good traction. Little deformation to increase speed in comparison with other propellers (PT or Brenner propeller with nucleus with nothing, Mejlink propeller with nucleus of foaming Agent. The foaming agent is very good to avoid deformation of the propellers).
Brenner-Mejlink 22*18 Front EL- 22*20 Rear EL (Hacker C50 Brenner ContraDrive 3500-4000 Rpm) 22*18 Front EL (Brenner 48'5gr, Mejlink (1) 45gr, Mejlink (2) 48gr. 22*20 Rear EL (Brenner 53'1gr, Mejlink (1) 48gr, Mejlink (2) 50gr. The Mejlink slows down more than the Brenner, in descents. In traction and straight flight operation is similar. PT Model-Mejlink 22*10 EL - 22*12 EL -21*14 EL- 20*13 EL 3Bladed (Plettemberg Advance 30-10 and Plettemberg Xtra 30-09) 22*10 EL (PT 40gr, Mejlink 44gr) 22*12 EL (PT 40gr, Mejlink 45gr) 21*14 EL (PT 41gr, Mejlink 46gr) 20*13 EL 3Bladed (PT 47gr, Mejlink 55gr) The PT propeller is deformed by increasing the speed more than the Mejlink propeller.etween this prop and 30x13 3-blade is noiselevel and the slower speed.
See comments below. This is an F3A application.
I was curious about the newly available Mejzlik Contra Props, mainly because with the increasing popularity of the Contras, the demand for props can exceed the supply sometimes, and I thought it would be good to explore an option. I put my plane over weight with the APC's so that was not an option for me.
There was a picture of them floating around last summer out of Czech Rep, but the Mejzlik folks said that production runs would happen this winter, and they put me on the list of shipments in February. A friend of mine who flies F3A out of Vienna with his son was involved in the development of the props and he was feeding me some info in January when I met him in Madrid. Reportedly, the Mejzlik props were to be better from two perspectives…first the Mejzlik people were able to shave a few grams from the props and second, the props provided more downline braking (as if more was needed!) than the Brenner props.
Cost of the props including shipping was almost identical, although they come via registered mail from Czech Rep, and that process took 4 weeks, so you need to plan ahead.
So, I opened the box last night and took a first look. They look like every other Mejzlik I've seen…the finish is mirror-like and all the edges are nicely done. Each blade is carefully sealed in a plastic sleeve, and the shipping box is well-padded. The leading and trailing edges are still "raw carbon" flat finish, so the finish is still not as good as a Falcon blade, but still very good. The hubs are smooth and show no tool marks.
In the end, the Mejzlik blades are better looking from an esthetic perspective than the Brenner props.
It's deep freeze here in Kansas City, so the flight test will need to wait, but here is my static pro/con assessment. Overall, the executive summary prior to flight test says that Brenner might win the static round, so read on...
Quality of workmanship - Fit & Finish
Brenner's props are hand-made and individually trimmed and shaped, so the blade-to blade variation will exist. In 2013, I had to send Brenner back a few blades due to a flat leading edge on one specimen, and a separating trailing edge on another, but they were always promptly replaced with perfect items. Brenner's support of his products is absolutely amazing. The Brenner props show many tool marks, especially around the hubs and a few small occlusions in the resin, but never anything that would affect safety or function.
The Mejzlik looks like it was made in a production-line mold series that required a very minimum of trimming and apparently no post-mold shaping. This accounts for the smoothness and virtual absence of tool marks. On the other hand, if you hold the blade up to the light so the light shines along the blade, the Mejzlik shows a number of very minor "waves" in the surface, so the reflection of a window frame on the blade is bent and warped…doing the same test with Brenner's blade shows fewer such waves or variations. (The pics show a bit of this, difficult to get the full effect via camera) So, Brenner's mold is virtually flawless while the Mejzlik's is maybe less so. Having said that, the surface variations in the Mejzlik are consistent from blade-to-blade, so whether this is intentional or not, the blades are still very well-executed against the mold.
Finally, the Mejzlik blades fit onto the Contra hubs with no play or rattle on the hubs, while the Brenners have a very small amount of rattle on the hubs. I wiped the inside of the Mejzlik hubs with some 600 grit to make sure there was no fab remnants, and this condition did not change. The rear prop fit perfectly, but the front prop was slightly "fat" at the hub so the Contra nose cone barely fits over it. It fits, but very tricky and tight.
As stated before, the Mejzlik blades are very shiny and attractive, while the Brenner blades are a little more satin finish.
Weight of the Blades
Here was my biggest surprise…the Mejzlik blades are heavier than the Brenner. Not what I was expecting, and a bit surprising given the previews. Here is the data, taken on a 50g jewel scale (duplicated readings with a second Ohaus digital scale)...
Front prop… Brenner 46.23g Mejzlik 46.50g
Rear prop… Brenner 48.94g Mejzlik 49.96g
So, the Mejzlik set gives you a 1.29g penalty. This is not very much at all, but I was expecting lighter blades.
I also had a spare front blade from Brenner, so I weighed it to compare to the Brenner front blade I was currently flying. Two Brenner blades weighed 46.23g and 46.63g respectively, so almost a half gram variation between Brenner blades. I have only one set of Mejzliks, so not much Statistical Process Control conclusions to draw on here. Both Brenners are lighter than the Mejzliks, so I would assume that Brenner's process is centered at a lower weight than the Mejzliks.
Looking at balancing of the blades…also a different story. I don't trust prop balancers, so I use the balance beam method, with one tip on a fixed support, and the other tip resting on the scale. This shows me the full-blade variation when I swap ends. Perfect balance would show exactly half the total weight of the blade on the scale, even after swapping ends.
So, end-to-end variations were as follows...
Front prop… Brenner 0.17g Mejzlik 0.19g
Rear prop… Brenner 0.02g Mejzlik 0.12g
Bear in mind that neither prop needs to be re-balanced by the standards of even the most stringent modeler, but still…the Brenner wins.
Some aerodynamics differences…
If I look at the blades, the Mejzlik blades are slightly thicker near the roots and then thin out at a steeper rate than the Brenners. The Brenners have a more gradual taper from root to tip. The curvature of the leading and trailing edge profiles is virtually identical, however, the chord of the blades is slightly different. For example, the greatest chord of the rear prop blades on the Mejzlik is 1.77in versus 1.55in on the Brenner. Does this account for the downline braking? I don't know.
Finally, the leading edge radius of both props is almost identical, while the trailing edge radius is greater on the Mejzlik.
The Brenner blade just seems thinner, sharper, more physically refined, if not as shiny and pretty, as mentioned.
That's it for now…will fly them first chance I get and report further.
As far as I am concerned, I have found a very high quality alternate supplier that merits being in the same class as Brenner's props from a manufacturing point of view. As always, the flight test will be the ultimate measure of which props I will take to contests.
As I indicated, I did a flight test comparison today between Brenner and Mejzlik props.
First flight...the plane seemed to behave exactly the same as with the Brenner props. Maybe a bit better climb power, but it was very subtle if it was real at all. The most noticeable difference was the musical note of the props in flight. The Mejzliks have a higher tone to the buzz. None of this shows any real differences so I resorted to getting some data.
I did three flights with each set of props, but used the WattsUp meter in the circuit to see if there was any difference in amps or mAh used.
The data shows a difference. Under reasonably constant conditions, I flew the Masters pattern as exactly the same as possible (as usual). Batteries used were TP 5000 G6 and the motor is a Neu F3A.
I was surprised to find that the Mejzliks props showed a lower peak amps of 64 Amps versus the usual 67 Amps with the Brenner props. The power consumed was 150mAh less with the Mejzliks. Bear in mind this isn't much, but it is data collected on the same day, same plane, same pilot, same pattern, same batteries, so the difference maybe isn't exactly 150mAh, but it is consistently less and correlates with the lower peak amps.
So, as we saw that the Brenner was very slightly ahead on the static/manufacturing aspect (except for appearance), it appears that the Mejzliks may be a bit more efficient. Is this efficiency the reason I seemed to notice a bit better climb? I don't know.
The other difference I saw was at the test field, there were some irregular patches of grass and dirt. On one flight, the Mejzlik props tips hit the ground briefly. There was absolutely no damage. By experience, the Brenner props would have been damaged, even with very slight contact. This is a valuable feature.
In my opinion, all this shows that there is very little difference between the Mejzlik and Brenner props, so pilots can use them interchangeably without worrying too much about differences that will affect performance. Possibly, the Mejzliks can make a difference for pilots flying at the very edge of 4500mA packs and where a few mAhs can make the difference between finishing or not.
For now, I am going to keep the Mejzliks on the plane and continue to practice with them.
Soon I will send you some pictures of the last competiotions.