Flight B/C

[coachchuckaahs]

How does the prop shaft get supported at the pigtail? Is there a slot for it in the middle of the two tails?

There is a hole drilled through a vertical piece of aluminum. Then this is slit with a fine saw down to the hole, and the two sides of the split are bent to make the pigtail. The wire drops in on the angle, then you pull the wire propshaft back (rubber load) and so the straight part is in the remnants of the hole,, and cannot escape unless the wire pulls forward to the angled portion.

Coach Chuck

[randomdogonapc]

Another unrelated question. I’ve been looking at forums with mentions of torque burners, and I’ve got a pretty good idea of what the concept is, but I’m confused at how the wire assembly works. In Brett Sanborn’s old posts on hippocketaeronautics, he has some diagrams, but how does the wire prevent part of the motor from unwinding. A picture or video of a torque burner in action would be helpful. Thanks in advance.

[bjt4888]

https://www.hippocketaeronautics.com/hp ... c=17412.75

Look at reply 95 in this thread for torque burner info

[coachchuckaahs]

Another unrelated question. I’ve been looking at forums with mentions of torque burners, and I’ve got a pretty good idea of what the concept is, but I’m confused at how the wire assembly works. In Brett Sanborn’s old posts on hippocketaeronautics, he has some diagrams, but how does the wire prevent part of the motor from unwinding. A picture or video of a torque burner in action would be helpful. Thanks in advance.

Don't get me started on Torque Burners! Bad memories!

We did try TB's I believe it was 2017 or 2018. We spent a LOT of our test flying on them, and I believe those hundreds of flights would have better served us in optimizing our basic plane.

Torque burners can be magical, and a notable help in a low ceiling. However, in SO you only get two flights. Torque burners can be temperamental, and even when they do work they may not be consistent. In AMA flying you get 5 flights to get one good one, and plenty of time between flights to adjust things. A TB adds 3-4 new variables. IMHO, you are better off perfecting a flaring prop.

A TB consists of a wire extending down from the motorstick. The rubber motor is wound with a straw or tube of some sort at some midpoint. As you install the rubber, you slip the tube over the wire, and carefully pull the tube out, leaving the wire in between two winds of the motor. As the front half unwinds, the back half still pulls, until it pulls hard enough to flex the wire and the rubber motor slips off the wire, releasing the rest of the winds. There can be a (substantial) shift in CG toward the back (since the back half is still tightly wound), a bunching of the rubber, etc. The timing of the release is determined by the length, angle, and stiffness of said wire. IN addition to those variables, the torque behind the wire can be different than the torque in front. You can probably come up with a number of variations of winds/dewinds before and after locking down the rubber onto the wire.

The intent is to limit the climb without substantial dewinds. In a perfect world, either upon the second release the plane climbs again, or it extends cruise, depending on how you set the release timing.

Look on Hip Pocket, and in old INAV publications.

While doing your research, also look at variations of flaring props.

While each approach adds more variables, the flaring prop is usually more consistent that the TB, and in SO having a predictable two flights is paramount.

IMHO

BUT, it was fun to explore!

Coach Chuck

[jander14indoor]

As someone who watched/measured Brett's Torque Burner at the state tournament, let me reinforce what Coach Chuck said! Unless you already have a perfected plane capable of 3 minute plus flights in a normal gym, you have MUCH more profitable places to spend your time!
The time Brett did that, he was already one of the top junior flyers in the country! He could beat almost anyone flying Wright Stuff at the time. The one or two flyers who could compete on an even basis all went on to be top adult flyers (and if you aren't aware, Brett is a multi time world champion F1D flyer!).
At that time, the MI state tournament was flown in a ridiculuosly low site. He would have won that year without the TB, had already won MI state previously. I think it became a personal challenge for him to get high ceiling times in that low site. Plus a challenge to the other good flyers across the country. In taller site, it wouldn't have paid off.

Again, unless you can already fly nationally competitive times in your sleep, don't go there! Much better places to spend your time. Now, if you are that person, think about trying out for the junior F1D team!! Heck, even if you aren't, but want a challenge...

Jeff Anderson
Livonia, MI

[randomdogonapc]

Thanks for all of the advice. I was only looking at torque burners sort of from a distance, to measure how viable one could be. If I can get a few flaring props to perfection, I might start experimenting, but I’ll probably use all of that time that I spent learning the basics of indoor free flight this year to experiment next season.

[pumptato-cat]

Oooh thanks for all the useful information everyone!!! I have also been eyeing torque burners for quite a bit but that was enough to convince me to stay away, haha!
Here's a bit of a dumb question: After I dial in trim on my second plane, I understand that I'm supposed to test for optimal rubber density. But how do I dial in a prop and rubber combination? If I fly until I get the highest duration with rubber density, wouldn't changing prop pitch change the rubber again? And vice versa?
Or is the answer to just test until best duration comes out, with no particular order in what you do? I feel as if optimizing rubber for the Ikara, and then changing prop pitch, would be an inefficient method of testing.
Also, for those of you that prepare for a venue with AC(States is almost 100% guaranteed to have strong AC, this time blowing down at an angle...), how do you practice? I don't have access to the states flying site(it's a 2 hour drive). I understand the reasoning behind forward CG and higher incidence, but I'm not sure how to dial in those settings if I can't fly in AC similar to the site.
Any ideas? Thanks so much!!! :)

[coachchuckaahs]

Oooh thanks for all the useful information everyone!!! I have also been eyeing torque burners for quite a bit but that was enough to convince me to stay away, haha!
Here's a bit of a dumb question: After I dial in trim on my second plane, I understand that I'm supposed to test for optimal rubber density. But how do I dial in a prop and rubber combination? If I fly until I get the highest duration with rubber density, wouldn't changing prop pitch change the rubber again? And vice versa?
Or is the answer to just test until best duration comes out, with no particular order in what you do? I feel as if optimizing rubber for the Ikara, and then changing prop pitch, would be an inefficient method of testing.
Also, for those of you that prepare for a venue with AC(States is almost 100% guaranteed to have strong AC, this time blowing down at an angle...), how do you practice? I don't have access to the states flying site(it's a 2 hour drive). I understand the reasoning behind forward CG and higher incidence, but I'm not sure how to dial in those settings if I can't fly in AC similar to the site.
Any ideas? Thanks so much!!!

Without going to flaring props, the optimization is two-parameter (two adjustable, multiple observational). You adjust the prop static pitch, and then adjust the rubber to match. If you have flaring, there are several more parameters that you control. The things you observe include duration, altitude, perhaps first lap altitude, circle size, etc.

1. Change pitch. Make small changes, a couple degrees at a time
2. Fly and adjust launch torque to get to near ceiling
3. Observe remaining winds. If too much, go thicker rubber, if too little go thinner. Generally winds remaining = unwinds to get to launch torque (Fine tuning of rubber density can be by duration, as long as you are getting to the same altitude on each flight). You may need o adjust launch torque when changing rubber density.
4. Record time
5. Repeat flight in final configuration to confirm time
6. Repeat at another pitch and compare time AFTER optimizing rubber and torque for that pitch. Do a systematic search for an optimum. It will not be a straight line, probably something with a peak at the optimum, so a large adjustment may miss the optimum

This can be a substantial amount of flights! Add in a variety of props (if you are making your own) and the matrix gets large!

As far as AC being on, about all you can do is prepare by having a stable configuration (CG forward), and have some heavier rubber available to power through. The heavier rubber will keep it up in cruise, higher torque will help it get up during climb. The impact of the AC will be different for every site, so best thing is to have stable and powerful options ready, and observe other flights to "read the room". Get some testing in if the ES allows (before check in testing is at discretion of the ES, but none in the last half hour of the session)

Coach Chuck

[randomdogonapc]

Regarding the optimization of flaring propellers, what variables can be controlled there? Is it just how much the pitch changes? If so, is the only way to adjust flare % to thin the blades?

Also, how do different aspects of prop design affect flight? More specifically, what does making a prop with more blade area or a longer diameter change?

Sorry for all the questions, I’m just having a hard time leafing through forums and articles about propeller design to find the answers to all of my questions.

[coachchuckaahs]

Regarding the optimization of flaring propellers, what variables can be controlled there? Is it just how much the pitch changes? If so, is the only way to adjust flare % to thin the blades?

Also, how do different aspects of prop design affect flight? More specifically, what does making a prop with more blade area or a longer diameter change?

Sorry for all the questions, I’m just having a hard time leafing through forums and articles about propeller design to find the answers to all of my questions.

The flaring prop can be adjusted for static pitch and flare stiffness. Stiffness depends on the flaring member, whether that is a thinned blade or a torsionally flexible spar.. A thinned blade actually changes the airfoil as it flexes, so the deflected blade may no longer be a good airfoil. If the flaring stiffness is softened, the static pitch probably needs lowering to compensate.

Other parameters (that you already mention) include prop diameter and prop planform. Generally indoor planes fly better with larger diameter props, but there are limits. The SO planes are rather heavy, so they fly fast, and so that limit may be smaller than other planes. What is the limit? That takes some experimentation to find. One part of the limit is when the torque on a large prop overcomes the plane's ability to resist the torque. The balance between climb and cruise is also affected. I think the planform impacts are even more subtle, and may not show up well on a SO prop. Since the prop is turning, a really wide planform on a small prop may start to have angle-of-attack issues. We have usually used some scaling of the Ikara flaring prop as a starting point for planform. It may be scaled uniformly, or just scaled in diameter.

Each part of the prop is an airfoil, but each part is moving at a different linear speed based on the radius to that part. Therefore, a different airfoil may be needed along the prop. In addition, the inner end subtends a larger angle for a given chord, and this could impact performance.

I don't think there is a lot of good data available for our specific weight and speed that would drive me away from the Ikara planform, scaled. We have tried some other planforms in particular situations, but our best props have followed this layout. But we have played with a range of diameters on years that allow it. This year, while the prop diameter is not limited, the fit in the box does impact the maximum prop diameter, especially if you have a longer wing that sits diagonally in the box. With our wing shape, the C prop was limited to about 9.5", and B around 10.5-11. I suspect the C plane, and maybe the B, could see some improvement with a larger prop, but it would not fit the box without further compromising the wing size and/or location.

Coach Chuck