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CookiePie1 wrote: ↑February 19th, 2020, 6:22 pm

coachchuckaahs wrote: ↑February 19th, 2020, 6:07 pm On an Ikara prop, you carefully twist the spar inboard of the blades. Best with two needle nose pliers.

However, if anything more than small changes, it will break after 2-3 adjustments. So pitch them initially to get them the same, and pitch them to a range of pitches (separate prop for each pitch) rather than plan on adjusting multiple times to find an optimum.

Coach Chuck

what do you mean by twist? Are you rotating the spar along its own axis or bending it?

I will answer for him: rotate (twist) the spar along its own axis.


Strange, we need to dramatically reduce the prop pitch to match with the rubber came with the kits. Maybe the other extreme end also work? We will see after we receive the new prop.

CookiePie1 wrote: ↑February 19th, 2020, 6:22 pm

coachchuckaahs wrote: ↑February 19th, 2020, 6:07 pm On an Ikara prop, you carefully twist the spar inboard of the blades. Best with two needle nose pliers.

However, if anything more than small changes, it will break after 2-3 adjustments. So pitch them initially to get them the same, and pitch them to a range of pitches (separate prop for each pitch) rather than plan on adjusting multiple times to find an optimum.

Coach Chuck

what do you mean by twist? Are you rotating the spar along its own axis or bending it?

You are changing the pitch. You need to rotate the spar about its axis to change the pitch. You need a pitch gage to do this accurately. A few degrees difference between blades can really impact at the speeds we are turning this year. Could vibrate, or just unevenly load (less efficient)

Coach Chuck

jinhusong wrote: ↑February 19th, 2020, 7:54 pm

CookiePie1 wrote: ↑February 19th, 2020, 6:22 pm

coachchuckaahs wrote: ↑February 19th, 2020, 6:07 pm On an Ikara prop, you carefully twist the spar inboard of the blades. Best with two needle nose pliers.

However, if anything more than small changes, it will break after 2-3 adjustments. So pitch them initially to get them the same, and pitch them to a range of pitches (separate prop for each pitch) rather than plan on adjusting multiple times to find an optimum.

Coach Chuck

what do you mean by twist? Are you rotating the spar along its own axis or bending it?

I will answer for him: rotate (twist) the spar along its own axis.


Strange, we need to dramatically reduce the prop pitch to match with the rubber came with the kits. Maybe the other extreme end also work? We will see after we receive the new prop.

Generally, as you increase pitch it will increase load, which for a given torque (given rubber width) will slow the prop down. Somewhere in this thread someone referred to "torque" as "power". It is not. Power is torque x RPM. The torque is driven by the rubber width (and the launch torque is set by backoff). The torque remains the same (with same rubber) regardless of prop pitch. So pitching up will slow the prop, which will reduce power, which may help limit initial climb.

If you over-pitch the prop, you may reach the point where you do not have enough power to climb. You may also over-pitch the prop and stall the blades, resulting in very poor power transfer, and no significant thrust.

In either case, more likely the first, you will find there is an optimum pitch for a given prop and rubber, where optimum in this case is the rate of climb or the total attainable climb. There will also be an optimum for duration (again, assuming same rubber). It is not necessary that the optimal pitch for climb also is optimal for duration. So, to merge these, you need another variable, which would be rubber width (or linear density, g/in). Now by adjusting both pitch and rubber linear density, you should be able to bring these two optimums together, so that you maximize altitude within the confines of your contest venue, AND maximize time aloft. Of course, this optimum will change for different venue heights. This does not even touch on prop planform, number of blades, etc.

The short of it is pitching up may help control initial zoom, but may be detrimental to duration if the rubber is not thick enough to provide enough power during letdown. The kit-supplied rubber is not necessarily optimal, it is a starting point.

Coach Chuck

Power vs torque was me

IMO the explanation above is Wright Stuff in one paragraph Coach Chuck and others have posted this in various forms many times and I keep having to re-read it again and again to grasp even a portion of the core concepts....

Off topic a bit, I'm stunned by the success of monoplanes. The high wing loading does appear to be largely offset by the reduced drag. Amazing.

In my opinion the many disadvantages of utilizing a biplane configuration in the WS 2020 competition far outweigh any potential advantage of its theoretical lower wing loading. See my December 10, 2019 post explaining this in detail.

Apparently, most students competing in the WS 2020 event who build a biplane do so because they have a kit for a biplane, and not based on any analysis of a biplane configuration versus a monoplane configuration.

The teams I coached in WS only flew monoplanes when biplanes were allowed in a previous WS season. They easily beat all the biplanes, in extremely competitive regional and state WS competitions.

If you are already regularly flying 105+ seconds each direction with a monoplane under the WS 2020 rules in a typical high school gym, it might be worth experimenting with a biplane, but probably only after your team qualifies for Nationals.

lechassin - your son has achieved excellent results with the more challenging biplane configuration due to his dedication, use of the scientific method, and extensive practice. Congratulations!

calgoddard wrote: ↑February 20th, 2020, 10:42 am lechassin - your son has achieved excellent results with the more challenging biplane configuration due to his dedication, use of the scientific method, and extensive practice. Congratulations!

Well, I hope that's the prevailing perception, anyways... I've gotten some grief over the course of the season for the extent of my involvement, even though I've posted DIYs for everything including the faster winder, the prop build, the torque meter, and exact airplane specs for all to judge and copy if desired. IMO that's no different, and possibly better than buying all of these things.

Luke admittedly did not work alone with only Google and the money he earns at work, but I'm very happy with where he's at. He converses intelligently, flies planes he made, on motors he makes and winds, and he understands the rudder and decalage trimming to suit a particular venue.

Hello everyone,

I just got back from the invite. Here's how it went:

Took 1st overall with a combined flight time of 2:45 under 30 ft. First flight was good, to the right 1:41 no touch. The second flight...uhhhhh.... This is where things got wonky. I'm still not sure what exactly happened. Even though I went to the same torque as I tested before in my gym, the plane only went up to about 10 ft. It may be a weird rubber piece (I used a different strand of rubber than the first flight, although all the specs are the same...), or it might've been a weird wind? Annnyyyways, we only got 1:05 for this flight but combined it was enough to take 1st.

Has anyone purchased those new propellers that just came out? Any successes with them? I am considering buying them but I wanna get an idea of how effective they are.

Thank you again to all of you in the forums for your help and advice!

Xiangyu

Does anyone know Penn placing times?

xiangyu wrote: ↑February 22nd, 2020, 5:32 pm Hello everyone,

I just got back from the invite. Here's how it went:

Took 1st overall with a combined flight time of 2:45 under 30 ft. First flight was good, to the right 1:41 no touch. The second flight...uhhhhh.... This is where things got wonky. I'm still not sure what exactly happened. Even though I went to the same torque as I tested before in my gym, the plane only went up to about 10 ft. It may be a weird rubber piece (I used a different strand of rubber than the first flight, although all the specs are the same...), or it might've been a weird wind? Annnyyyways, we only got 1:05 for this flight but combined it was enough to take 1st.

Has anyone purchased those new propellers that just came out? Any successes with them? I am considering buying them but I wanna get an idea of how effective they are.

Thank you again to all of you in the forums for your help and advice!

Xiangyu

Xiangyu,

Congratulations. Don’t feel bad about the second flight this is a very good result.

We have the new propellers, but have others to test before them in the next sessions. So might be a week or so till we test.

Keep up the good work.

Brian T

golden Gate Invitation:

This year, same location but bigger (2 basketball courts). The center is further from all the AC. Also once in many years, a clear day, no rain, looks bright.

You still can see clearly the AC blows down the planes but all top flyers got pretty reasonable results:
Besides ours, I was just luck being there when both TroyA and TroyB flying.

Raw time:

First (Milpitas Blue): 1:14 (left, height ~15) + 1:37(right, height 25?) Biplane.
Second (Troy A): 1:18 + 1:27. (not sure the height, ~20). Monoplane.
Third (Troy B): 1:01+1:20. Monoplane.

Many flyers are good at one direction.

Tiger