Increasing Flight Times

[coachchuckaahs]

Use the top of the motor stick as a reference, measure height to the bottom of the spats at laying edges and trailing edge of each surface. This assumes you aligned the top of the motor stick and tail boom. Could use bottom of those are aligned. You can then easily convert to angles using a little trig. We just stay in mm, compare le and te height.

Coach Chuck

[jinhusong]

Use a caliber to measure heights of leading edge and tail edge poles in mm.

Then the sin(angle)=(height difference in mm) / 70mm.

70 mm is the wind/stab chord.

Jinhu

[xiangyu]

Thanks everyone, that sounds like a great method!

[xiangyu]

I want to thank everyone again for your help so far, over the weekend, I was able to break our record and make a flight at 2:40. (See video below). As you can see in the video, my plane bumped the ceiling several times causing it to lose altitude. I am wondering if anyone knows how I can decease the rate of climb and over a longer time. I am also wondering if my rate of descend is too fast. Any help will be greatly appreciated!

I have already altered the pitch of my prop in order to get this result. The current pitch is sitting at 35 degrees. I'm guessing increasing the pitch will make the plane climb slower but over a longer period of time, am I right?

Just in case these might be helpful:

Winds Forward with (~2.5 g? - 1.5 times length between prop and back hook, using .109 width): 128
Winds Back: 25
Torque: ~.39
Pitch: 35 degrees
Winds left: 21
Mass of plane; (~8 g) - my scale measures 8 g but I think it is a little under weight so probably around 8.1 realistically

Video: https://www.youtube.com/watch?v=3T8t8Ds ... e=youtu.be

Thanks again everyone

[coachchuckaahs]

Your video did not show the initial part of your flight, the part that you are most concerned about.

There are three primary phases of the flight:
1. Initial climb (first lap or two), driven by launch torque
2. Late climb and cruise, usually less than a foot per lap, driven by rubber width vs. prop pitch
3. Letdown, driven by rubber width

You do not report the winds remaining. The letdown does not look too bad, but does drop more rapidly at the end. If you are just about out of winds, that may be why. Reducing the rubber thickness a few thousandths will reduce the late climb and may help the letdown hang in there, leaving you with a little more winds in the end (assuming you keep constant mass, so narrower rubber leads to longer rubber).

You can reduce initial zoom with lower launch torque, or more flare on your prop, or both.

It is a bit hard also to judge your trim, though it looks fairly good. This year the trim is more subtle with the tandem wing arrangement. It appears you have low decalage, which is fine. You will want to experiment with moving CG forward and back for a given decalage. Only the stopwatch will tell. You could also count RPM of the prop as you move CG, that can be indicative, but the stopwatch is the end goal.

Note: On our recent LPP adventure, we had a 10" motor stick (front of prop hanger to hook, so about 9.25" hook to hook), and we ran rubber as long as 22", though over 20" started to get tough to manage bunching.

Keep testing, and play with those variables. you will find that when you are close, very small changes in rubber width will move the stopwatch, good or bad.

Coach Chuck

[xiangyu]

Your video did not show the initial part of your flight, the part that you are most concerned about.

There are three primary phases of the flight:
1. Initial climb (first lap or two), driven by launch torque
2. Late climb and cruise, usually less than a foot per lap, driven by rubber width vs. prop pitch
3. Letdown, driven by rubber width

You do not report the winds remaining. The letdown does not look too bad, but does drop more rapidly at the end. If you are just about out of winds, that may be why. Reducing the rubber thickness a few thousandths will reduce the late climb and may help the letdown hang in there, leaving you with a little more winds in the end (assuming you keep constant mass, so narrower rubber leads to longer rubber).

You can reduce initial zoom with lower launch torque, or more flare on your prop, or both.

It is a bit hard also to judge your trim, though it looks fairly good. This year the trim is more subtle with the tandem wing arrangement. It appears you have low decalage, which is fine. You will want to experiment with moving CG forward and back for a given decalage. Only the stopwatch will tell. You could also count RPM of the prop as you move CG, that can be indicative, but the stopwatch is the end goal.

Note: On our recent LPP adventure, we had a 10" motor stick (front of prop hanger to hook, so about 9.25" hook to hook), and we ran rubber as long as 22", though over 20" started to get tough to manage bunching.

Keep testing, and play with those variables. you will find that when you are close, very small changes in rubber width will move the stopwatch, good or bad.

Coach Chuck

Hi Coach Chuck,

Thanks for the helpful feedback! The inial climb took about 20 seconds to get to the height (probably around 28 ft) when I started filming. I had 21 winds left after the plane came down. Is that too many?

Also, people keep talking about flare propellers, what exactly does it refer to? Is it the same thing as increasing prop pitch?

Also if I use a thinner rubber band I can wind even more turns in?

Thanks again for your help!

[coachchuckaahs]

If your 21 winds is 21 turns of the rubber, this is probably too few. If it is 21 turns of the crank, then it is either 210 or 315 (10:1 or 15:1 winder) turns of the rubber, and probably about right. In general, some have claimed that the number of remaining turns should be about the same as the number of unwinds to get to launch torque. We often see 200-500 winds remaining, as the torque is very low in the final row of knots.

The flaring prop is a "poor man's" variable pitch prop. More accurately, it is a way of getting variable pitch without a "mechanism", and thus fitting the rules of SO (and many AMA events). The flaring prop has most or all of it's area ahead of the spar. Either the spar or the blade (or both) flex with increasing load, effectively increasing pitch under load. This serves to slow the prop under high load, instead of releasing the high energy quickly and inefficiently. The best example is the Ikara 24cm "Flaring" prop. This has been a starting point for years. However, the flare is rather stiff, and the prop takes some modification, such as sanding or a new hub, to be effective. Of course, a flaring prop adds new variables such as flaring stiffness and blade shape to the mix of consideration. It takes a good amount of experimentation to perfect the flaring prop. Too much flare and the plane will not climb under high torque.

Yes, with a thinner rubber you can get more turns. But, your torque is lower, so these turns will not be effective if the torque is lower than the prop needs to climb and later, descend slowly. It is a balancing act, and this is what we talk about when optimizing the rubber/prop combination. Not only does the rubber width matter, but you will find that the number of uses on the loop of rubber may impact your time, positively or negatively. Is your log sheet getting wider?!

Coach Chuck

[xiangyu]

If your 21 winds is 21 turns of the rubber, this is probably too few. If it is 21 turns of the crank, then it is either 210 or 315 (10:1 or 15:1 winder) turns of the rubber, and probably about right. In general, some have claimed that the number of remaining turns should be about the same as the number of unwinds to get to launch torque. We often see 200-500 winds remaining, as the torque is very low in the final row of knots.

The flaring prop is a "poor man's" variable pitch prop. More accurately, it is a way of getting variable pitch without a "mechanism", and thus fitting the rules of SO (and many AMA events). The flaring prop has most or all of it's area ahead of the spar. Either the spar or the blade (or both) flex with increasing load, effectively increasing pitch under load. This serves to slow the prop under high load, instead of releasing the high energy quickly and inefficiently. The best example is the Ikara 24cm "Flaring" prop. This has been a starting point for years. However, the flare is rather stiff, and the prop takes some modification, such as sanding or a new hub, to be effective. Of course, a flaring prop adds new variables such as flaring stiffness and blade shape to the mix of consideration. It takes a good amount of experimentation to perfect the flaring prop. Too much flare and the plane will not climb under high torque.

Yes, with a thinner rubber you can get more turns. But, your torque is lower, so these turns will not be effective if the torque is lower than the prop needs to climb and later, descend slowly. It is a balancing act, and this is what we talk about when optimizing the rubber/prop combination. Not only does the rubber width matter, but you will find that the number of uses on the loop of rubber may impact your time, positively or negatively. Is your log sheet getting wider?!

Coach Chuck

Thank you so much!

I will be able to try all of these modifications tomorrow afternoon and we'll see how that goes.

Just to be sure, are the flaring props you are mentioning the broad blade flaring style prop freedomflight sells on their site? (The second propeller)

Also what torque do you suggest for the flaring prop?

Thanks!

Xiangyu

[coachchuckaahs]

Yes, the "broad flaring style".

The torque is going to depend on the amount of flare. If you use the prop as-is, you will want to sand the blade, especially just in front of the spar, to allow more flex (softer flare). You will find that at some point you get too soft, and it won't climb no matter the torque. Torque will likely be between 0.4 and 0.6, though it needs to be matched to your prop.

There are plenty of past conversations on the flaring prop on here and on HipPocket.

You probably do not need massive flaring as the Nationals ceiling is fairly high at about 38 feet to lights. But some degree of flaring will help. For the LPP's with a 100' ceiling we still used flaring props!

Coach Chuck