Adjusting prop pitch

[BalsaFerret]

BJT will give you very good and detailed feedback. If I remember, those props are either 35 degrees or 40. Not sure. I think it's 40 by default?

Yeah, bjt is actually amazing in his knowledge of flying
Thanks for the prop info, but I still don't know how to measure them or utilize them greatly, so knowing these numbers are kinda out of my reach and don't mean that much to me, ya get me? My understanding is the greater the pitch, the greater the distance per revolution it travels.

I strongly urge you to get a pitch gauge. They're the best way to measure pitch for your props. The greater the pitch, typically, the more efficient the prop is. It just scoops up more air, and should be slower (I think). But yeah, get some sort of pitch gauge (Like one on freedom flight models, only 5 bucks I think) and start testing!

I agree, but I have a comp this weekend so it might not come in time for that. I would def buy after comp tho.

[jander14indoor]

You are thinking wrong direction on controlling speed. Your plane MUST fly in equilibrium. Lift = mass. At any trim condition, that happens at ONLY one speed, and you must fly near that speed or you'll either auger into the ceiling or dive.

There are two ways to slow your plane. Lose weight (I don't see you mention your planes weight in its description) so you don't need as much lift and can fly slower, or change the trim condition (wing and stab angles of attack, center of gravity) to generate more lift at slower speeds. If your plane has to fly faster than others just to climb steadily to ceiling and descend, you need to address those things FIRST.

Once you have an efficiently trimmed plane, its time to work on matching prop & rubber to fly that plane efficiently at the slower speed. What you are trying to do is match the prop/rubber to efficiently use the stored energy from winding AT the speed required to maintain steady flight.


Gages, there is NO need to buy, they are VERY easy to make. Multiple plans on the web.

Jeff Anderson
Livonia, MI

[BalsaFerret]

You are thinking wrong direction on controlling speed. Your plane MUST fly in equilibrium. Lift = mass. At any trim condition, that happens at ONLY one speed, and you must fly near that speed or you'll either auger into the ceiling or dive.

There are two ways to slow your plane. Lose weight (I don't see you mention your planes weight in its description) so you don't need as much lift and can fly slower, or change the trim condition (wing and stab angles of attack, center of gravity) to generate more lift at slower speeds. If your plane has to fly faster than others just to climb steadily to ceiling and descend, you need to address those things FIRST.

Once you have an efficiently trimmed plane, its time to work on matching prop & rubber to fly that plane efficiently at the slower speed. What you are trying to do is match the prop/rubber to efficiently use the stored energy from winding AT the speed required to maintain steady flight.


Gages, there is NO need to buy, they are VERY easy to make. Multiple plans on the web.

Jeff Anderson
Livonia, MI

I kinda understand what you mean. However, with thick rubber right now it most likely always flies at a fast speed with the pitch rubber combo rn (plane also weighs 8.3g as of now, can sand to reduce a bit). I also think that my trim now is pretty good; the only problem is that when I try to change the angle of incidence or stab, it doesn't lift as much as previous trims. It also lifts pretty fast (5ft/ circle) in about 20 seconds, but descends pretty normally (1-2 ft/circle) if that helps.

I still don't know how to measure pitch with a protractor but I'll plan on making a gauge

[bjt4888]

Balsa,

Crayola, Polar and Jeff Anderson have all given you good info.

Quick notes based upon our experiences this year: don’t increase your wing incidence; your airplane may look like it is flying faster than others you have watched because your turn circle is quite small; you can leave it as is if you need to if your flying sites are smallish rooms or reduce rudder offset to about 1/8” to open the circle to about 25 ft; buy several extra propellers so that you can bend each of them to different pitch angles for testing; with extra props you won’t be concerned If you ruin one while bending; see the picture in the FF kit instructions related to bending pitch into the Ikara and just go for it. (Sorry for the punctuation)

The rest of the story. The first thing to do is to start winding to a full 80% to 90% of breaking turns and backing off to launch torque for every flight. Your turns remaining of 40% is not a “real” data point as you are not winding full. 17.8” loop of .102” should take about 149x15 turns before breaking (after breaking, properly stretch wound and lubed). So, 125x15 should be a safe full wind. This should correspond to a torque of over 1.0 in oz. Backoff to about .35 in oz and fly. Hopefully this winding will fly a little over halfway to the ceiling. Reduce backoff and increase launch torque on subsequent flights till you are just under the ceiling. After you have full wind and full altitude flights, you can get valuable info from the turns remaining, pitch changes and rubber thickness (actually, density; see my earlier comments about this).

I agree with Jeff Anderson. You can make your own pitch gauge using a small protractor and a piece of wood and a Method to hold the nose button still (small piece of tubing form the hardware store. I would measure pitch at the 3” prop radius if using the 24 cm prop. We have an extendable pitch measuring tool that measures at every radius (home made).

If you have the time and inclination, read the 2015 WS forum posts on winding, trimming, propeller sanding and design. This will advance your knowledge of the WS event rapidly.

Good luck with your competition.

Brian T

[bjt4888]

S.b. ...after breaking in ... not “after breaking”; sorry typo

[bjt4888]

Balsa,

Sorry, not enough positive feedback in my message above. Great job building the FF kit and adjusting so well.

Probably you won’t have time to do all of the above before competing this weekend, so, if I were you, I’d fly using the strategy that you already know gives best results.

Using the methods above, you should be able to fly closer to 2:30 (and maybe better).

Brian T

[CrayolaCrayon]

We have an extendable pitch measuring tool that measures at every radius (home made).

Brian T

Holy guacamole. How do you make something like that?

[bjt4888]

Crayola,

It’s built in the style of the deflection meter in the Hobby Shopper EZB article which is available on the Indoor News and Views webpage. See starting on page 34 here:

https://indoornewsandviews.files.wordpr ... f-inav.pdf

Protractor measuring part of pitch gauge slides along rails.

Brian T

[BalsaFerret]

Balsa,

Crayola, Polar and Jeff Anderson have all given you good info.

Quick notes based upon our experiences this year: don’t increase your wing incidence; your airplane may look like it is flying faster than others you have watched because your turn circle is quite small; you can leave it as is if you need to if your flying sites are smallish rooms or reduce rudder offset to about 1/8” to open the circle to about 25 ft; buy several extra propellers so that you can bend each of them to different pitch angles for testing; with extra props you won’t be concerned If you ruin one while bending; see the picture in the FF kit instructions related to bending pitch into the Ikara and just go for it. (Sorry for the punctuation)

The rest of the story. The first thing to do is to start winding to a full 80% to 90% of breaking turns and backing off to launch torque for every flight. Your turns remaining of 40% is not a “real” data point as you are not winding full. 17.8” loop of .102” should take about 149x15 turns before breaking (after breaking, properly stretch wound and lubed). So, 125x15 should be a safe full wind. This should correspond to a torque of over 1.0 in oz. Backoff to about .35 in oz and fly. Hopefully this winding will fly a little over halfway to the ceiling. Reduce backoff and increase launch torque on subsequent flights till you are just under the ceiling. After you have full wind and full altitude flights, you can get valuable info from the turns remaining, pitch changes and rubber thickness (actually, density; see my earlier comments about this).

I agree with Jeff Anderson. You can make your own pitch gauge using a small protractor and a piece of wood and a Method to hold the nose button still (small piece of tubing form the hardware store. I would measure pitch at the 3” prop radius if using the 24 cm prop. We have an extendable pitch measuring tool that measures at every radius (home made).

If you have the time and inclination, read the 2015 WS forum posts on winding, trimming, propeller sanding and design. This will advance your knowledge of the WS event rapidly.

Good luck with your competition.

Brian T

Thanks so much for your reply, I got into some of your advice today. However, I snapped my the 90 cm rubber at 125 winds today, even after breaking it in a bit. That leaves me to ask how broken in is broken in? Also, is rubber length proportional to # max winds? Say, I have the 90 cm 0.102 at 125 safe winds. Would an 80 cm be 125*8/9 = ~111 safe winds? Along with winding, is Dave's winding instructions how I'm supposed to wind? He says that I should 4x the rubber length for 70% winds, then come in slowly for last 30%. But, in the inav pdf winding section, it says that I should do 4x for 50%, 9x and then 4x and walk in for last few winds (that's from my memory, may be different). Which one should I follow for the best winding?

I feel that 2:30+ is still a bit low for higher standards. Do you have anymore general/ long term advice for later on in the season so that higher times may be achievable (3:30+)?

Lastly, sorry for still talking about this, but Dave's instructions on changing pitch are still a bit vague to me. Could someone find a diagram, or even explain thoroughly, to show me how to change the pitch for the ikara prop? I just don't think I have the best grasp on pitch.

[bjt4888]

Balsa,

Good job trying new things. I should have more detailed in describing the winding to max procedure. Breaking in can be done by winding to 80% max a couple of times or by hooking the rubber over a smooth door knob and holding stretched at 7x relaxed length for about two minutes.

When winding to 80%, or so, maximum the number of turns is a theoretical target. The actual stopping point is measured by torque. Between 1.0 and 1.2 in oz is a pretty good stopping point. Tan SS breaks at between 1.4 and 1.9 in oz. How many turns you get into the rubber is dependent upon technique and feel; difficult to communicate this in writing. We stretch more than 4x during winding and wind 60 to 70% of “target” turns at full stretch and the remaining turns till we get to the max torque of between 1.0 and 1.2 (go farther if your technique is good).

For twisting more pitch into the Ikara propeller, look at the picture on page 19 of the FF kit instructions. You’ll see that the pliers are gripping the propeller shaft so that the pliers jaws are just barely away from the root of the blade (root is the blade edge closest to the propeller center). The left hand in the picture is gripping the barrel-shaped prop center that the shaft goes through. The right hand will push the pliers in a twisting motion down in the picture to increase the pitch.

After winding to max, you’ll probably find that it will take about 18x15 backoff winds to get down to 0.35-0.38 in oz for a first full power test flight. Max turns as a function of rubber length and width is a quadratic equation. I posted the equation we use in the 2014 or 2015 forum. Sorry, I don’t have time right now to look for it.

It would be difficult to describe the directions to test to get more duration without revealing my team’s strategies. So, sorry about that. A couple of experienced coaches have given good hints in earlier posts though.

Brian T