Logo
Builders' Plan Gallery  |  Hip Pocket Web Site  |  Contact Forum Admin (Account/Technical Issues)  |  Contact Global Moderator
October 23, 2020, 04:56:36 AM *
Welcome, Guest. Please login or register.
Did you miss your activation email?

Login with email, password and session length
 
Home Help Search Login Register
Pages: [1]   Go Down
Print
Author Topic: Anybody coached, or competed in, the Science Olympiad "Helicopters" event?  (Read 523 times)
0 Members and 1 Guest are viewing this topic.
Little-Acorn
Silver Member
****

Kudos: 5
Offline Offline

United States United States

Posts: 153

Topic starter


Ignore
« on: September 03, 2020, 10:46:12 PM »

For some unknown reason I agreed to coach Helicopters at the local High School Science Olympiad this year. Due to Covid they want it done "virtually", on computer screens maybe using Zoom, emails etc. Being an old diabetic fat guy, that's about the only way I could do it too. Even the coming tournament will be virtual - students will fly their helicopters and report the results. Pretty good chance I'll never meet the students face to face, even through the tournament.

Two flies in the ointment: Though I've done model planes since age 6, and having recently coached Wright Stuff, Elastic Launched Gliders, and Electric Wright Stuff, I've never had anything to do with rotary-wing craft, outside of studying them in college. No practical experience, no real interest till now, and frankly no clue.

Rules include 20cm cm rotor diameter (dinky), min weight of 2.5g without motor, unlimited motor mass, up to three rotors, unlimited blade count. Average ceiling height of about 8 feet, which is typical for the inside of an ordinary house's living room or bedroom. BUNCHES of unpleasant restrictions there.

The other fly in the ointment: I just found out about doing this day before yesterday, and the tournament is Oct. 10, 2020. Five weeks.

Setting up a jig to build rotors now, already ordered a bunch of stuff from Freedom Flight and the local hobby shops. That 2.5g min weight will be providential. These will simply be really little copters, but proportionately somewhat balanced. Flying in people's houses, not in a gym.

Will start with somewhat-balanced rotors, prototype will have ground-adjustable pitch though contest models probably won't (for weight purposes), once the prototype gets us into the ballpark. Building pitch twist into the blade might be the toughest part, I hear some folks simply make flat-blade rotors with constant spanwise pitch angle. That might be lighter, and may be the way to go, though it sounds inefficient. An extra month or two would certainly be welcome, but ain't gonna happen.

This tournament is supposed to be an experiment to see if a "virtual" tournament (or season) is even possible. That's why it's so early. I seem to have stupidly signed up for the most difficult event to do that in, they tell me it will be the only flying event.

Anybody got any guesses about how thick the rubber motor should be for something like this? I don't want to spend the flight bouncing off the ceiling, at least not very hard. That says to me that I'd be wasting energy. But getting a constant flow of power, enough to simply hover for a long time without hitting anything, might be impossible for a rubber motor.

Sigh.

Any suggestion or words of wisdom? Other than "Quit Now", I've already heard that one.
Logged
Indoorflyer
Platinum Member
******

Kudos: 23
Offline Offline

United States United States

Posts: 1,292



Ignore
« Reply #1 on: September 03, 2020, 11:22:16 PM »

When is a helicopter not a helicopter any longer?  Could you use an "airplane" type contraption with angled thrustlines/opposite rotation "rotors"--thinking V22 Osprey layout.  Flaring blades, or flapped blades could be helpful, if not prohibited...

Logged
ceandra
Silver Member
****

Kudos: 11
Offline Offline

United States United States

Posts: 244



Ignore
« Reply #2 on: September 04, 2020, 10:00:25 AM »

This must be a local thing only? National SO is supposedly a repeat of last year rules.

I would ask Dave at ffm if he had any non Chinook kits left. They are two rotors on one stick. This is typical indoor helicopter. Best if you can start with his kit.

They don't hover. We call them ceiling stickers.

Not too hard, but given your time a kit would help.

Sounds like rules from 2017 if I am counting right.

Coco
Logged
Little-Acorn
Silver Member
****

Kudos: 5
Offline Offline

United States United States

Posts: 153

Topic starter


Ignore
« Reply #3 on: September 04, 2020, 01:51:31 PM »

Yup, they are very similar to 2017 rules. Dave is already making up some kits for me, and also sending some other parts I asked for. He described the Chinook style (two non-coaxial rotors), as well as the coaxial type, I'm going with the coaxial due to time pressure and my own inexperience. Got some rotor blades cut out for my own prototype from 1/32" sheet, 5 pounds per square inch balsa, they're soaking in water now. Built a jig to produce 1/r spanwise blade angle distribution, slightly cambered.

I chickened out of putting covering on them due to the compound curves they'll have, mine will be quicker to build though maybe heavier, hmm. I have never trusted the crumple-it-up-in-your-hands method of covering, but it looks like it would be mandatory for helicopter blades.

In 2017 you could get a huge bonus for building a copter with non-coaxial rotors, that's why Dave came up with the Chinook design. But that bonus doesn't exist in the rules I've seen for 2020-2021. TPTB have already told me, several times, that this year's rules are not necessarily final, there could be changes before Sept. 8.

Onward and upward.
Logged
bjt4888
Gold Member
*****

Kudos: 6
Offline Offline

United States United States

Posts: 253



Ignore
« Reply #4 on: September 04, 2020, 08:31:20 PM »

LA,

Congrats on volunteering for the heli event. Chuck and I have lots of experience in this event and we both (and other on the forum) can help with questions. I would recommend x-rotors as opposed to rotor blades that look like “propeller” blades. The propeller shaped blade does not provide much inherent lateral stabilizing force. You can stabilize a Heli with this blade shape by adding lateral area that takes the appearance of vertically oriented “stabilizers” but it’s much easier to build x-rotors that have built in lateral stabilizing effect (this is what Dave uses in all his kits). Also, the x-rotors (with proper pitch, pitch distribution and blade area/chord) perform great.

Also, Chuck and I (and others) wrote a lot of info into the Scioly.org forum for helicopter a couple of years ago. Your teams will advance rapidly if they take a couple of hours to read this material.

Enjoy,

Brian T
Logged
Little-Acorn
Silver Member
****

Kudos: 5
Offline Offline

United States United States

Posts: 153

Topic starter


Ignore
« Reply #5 on: September 05, 2020, 06:48:42 PM »

I used to build Wright Stuff planes with small tip plates on the wings. The wing is horizontal, the tip plates were 90 degrees from that (vertical).

Is that what an X-rotor is?

Got any photos of one of these? I'm an information sponge!

The jig I built has two half-inch dowels, about 10" long each, bolted together in the center with a small spacer between them. You can pivot them against each other to form a sort of X shape. When you do, it looks sort of propeller-ish, except the dowels are way too thick.

And this "propeller" has pitch you can see. High angle near the root (propeller hub), lower angle near the tip. For you geometers out there, the tangent of the pitch angle is proportion to 1/r, where r is the distance from the root. I'm building rotor blades on it, starting with a tip angle of 30 degrees. We'll see how that comes out.
Logged
calgoddard
Gold Member
*****

Kudos: 26
Offline Offline

United States United States

Posts: 999


AMA, NFFS & FAC Member



Ignore
« Reply #6 on: September 05, 2020, 07:24:09 PM »

Little-Acorn -

I think Brian's reference to X-rotors is exemplified by the rotor in the attached picture.

Two spars are axially spaced and connected by ribs before being covered with Ultrafilm.

Early on in the history of the Helicopters event, I experimented with sheet balsa wood rotors. They are far too heavy for a competitive helicopter in this event.

The rubber band powered co-axial helicopters have rotors that spin in opposite directions. The winning helicopters rocket to the ceiling and stay engaged with the ceiling, and stationary, if you are lucky.  Then they come down rapidly when the turns are almost gone in the rubber motor.

I did not like this event as getting a competitive time was far too dependent on luck. There is no trimming involved.

Consider using a rolled sheet balsa wood motor stick. It will save you a lot of weight over a solid balsa wood motor stick.

Attached files Thumbnail(s):
Re: Anybody coached, or competed in, the Science Olympiad "Helicopters" event?
Logged
Little-Acorn
Silver Member
****

Kudos: 5
Offline Offline

United States United States

Posts: 153

Topic starter


Ignore
« Reply #7 on: September 05, 2020, 09:47:19 PM »

bjt4888 and calgoddard, thank you! Great information!

Yeah, I was pretty sure that sheet-balsa rotor blades would cause the copter to exceed minimum-weight. Worried about it too for the motor stick. I put it together to finish quickly, so I'd have something to "find out the problems". The jig can be used to built built-up rotors too. I'm nervous about putting covering on these compound-curve rotors. Got enough blades for two rotors (one three-blade, one two-blade), will see how it goes from there.
Logged
ceandra
Silver Member
****

Kudos: 11
Offline Offline

United States United States

Posts: 244



Ignore
« Reply #8 on: September 06, 2020, 12:26:39 PM »

2018 had Chinook bonus, 2017 was standard coaxial helicopter.

Weight is everything. Any weight over minimum costs time substantially.

If rubber mass is not limited, you will spend time finding optional rubber width vs length.

Variables include blade pitch, blade flex, cg. CG had important impacts on stability, taking "luck" out of the launch phase. Assuming you are not in a girdered gym. I think you said home. In that case you can almost place the heli on the ceiling, eliminating the climb.

We learned a lot about stability, and could get very repeatable climbs compared to initial.

Dave had a novel to plate that helped the heli stay in one spot. Adds a bit of weight, but still possible to build to weight.

Dave's carbon blades are simple to build and strong. Motor stock balls selection is important. May not have time to learn rolled motor sticks.

Chuck
Logged
calgoddard
Gold Member
*****

Kudos: 26
Offline Offline

United States United States

Posts: 999


AMA, NFFS & FAC Member



Ignore
« Reply #9 on: September 06, 2020, 02:49:36 PM »

Little-Acorn -

I have attached a picture of a typical SciOly co-axial helicopter that met the 2013 rules.  Note the dime-sized disc on the left (upper end) of the helicopter which was require under the 2013 rules. It engages the ceiling.

Don’t be tempted to build rotors with more than two blades.  They are much harder to build and make it much more difficult to build a rubber powered helicopter to minimum weight under the SciOly rules. Moreover, if you research the subject you will find that each additional blade on a propeller decreases its efficiency. The most efficient propeller has a single blade, because that lone blade travels through undisturbed air as the airplane flies forwardly.

If I am not mistaken, the reasons for using three or four blades on the prop of most WWII fighter airplanes had to do with one or more of the following.  The prop diameter had to be less than a certain limit to avoid the need for excessively long landing gear.  The prop RPM had to be limited to prevent the blade tips from exceeding the speed of sound.  The engines, both in-line and radial, were extremely powerful and that power had to be translated into thrust by more than two blades.

In the 1940’s the Everel Propeller Corporation of Baltimore, Maryland, commercially manufactured the counterbalance single blade wooden propeller that was designed for use with full-sized lightweight aircraft. For a variety of reasons, the single blade propeller never caught on in either civil or military aviation.  See the attached picture of an actual aircraft equipped with a single blade Everel propeller.

Also attached is a picture of a SciOly helicopter I built with two single blade rotors.  As was popular in rubber powered free flight in the 1930’s each blade has a counterweight.  The counterweight arm is bent rearwardly to offset the thrust generated by the lone blade opposite the counterweight.  Note that this design used CF composite spars, a rolled motor tube, and a sheet balsa wood blade on the lower rotor.  This design can be built to minimum weight and was legal under previous SciOly rules, but turned out not to be competitive with the FFM kit helicopters. It was also harder to build.  If I had thought the design through I would have realized that most of the flight time of a SciOly helicopter is stationary, so the lone blade of a single blade rotor is not passing through undisturbed air and the efficiency advantage of a single blade rotor or propeller is therefore largely lost in the SciOly Helicopters event.
 
To be competitive in this event the helicopter must be at or very near to minimum weight.  Then you only need to determine the optimum rubber motor length and weight. Unlike winding indoor duration model airplanes when flying in low ceiling heights, with rubber powered SciOly helicopters you do not back-off turns after winding the rubber motor to near breaking.
Attached files Thumbnail(s):
Re: Anybody coached, or competed in, the Science Olympiad "Helicopters" event?
Re: Anybody coached, or competed in, the Science Olympiad "Helicopters" event?
Re: Anybody coached, or competed in, the Science Olympiad "Helicopters" event?
Logged
Little-Acorn
Silver Member
****

Kudos: 5
Offline Offline

United States United States

Posts: 153

Topic starter


Ignore
« Reply #10 on: September 06, 2020, 10:31:12 PM »

Quote
In the 1940’s the Everel Propeller Corporation of Baltimore, Maryland, commercially manufactured the counterbalance single blade wooden propeller that was designed for use with full-sized lightweight aircraft. For a variety of reasons, the single blade propeller never caught on in either civil or military aviation.  See the attached picture of an actual aircraft equipped with a single blade Everel propeller.

Yep. A single-blade propeller like that is theoretically more efficient than a two-blade (or more) propeller, aerodynamically speaking. And the counterweight on the stub makes it statically balanced.

But.... as the prop spins, when the blade is pointing straight to the right, it is applying full thrust forward, on the right side of the plane. One-half of a revolution later, it's applying full thrust forward, on the LEFT side of the plane. This would result in a harsh, left-right shimmy as the plane flew straight ahead, like a SEVERELY unbalanced prop. Ditto for up-down. Actually the prop would oscillate in a circular way, like a flipped coin that lands on a table and rolls around its edge, becoming flatter and flatter to the table just before it stops.

BTW, another reason for the 4-blade propeller, is that on a long-nosed plane (think Spitfire, F4U Corsair) with conventional landing gear, the gear had to be even taller to avoid the pilot digging in the propeller tips when he lifted the tail during takeoff.

When the Limeys put an even larger Rolls/Royce Griffon engine into the Spitfire Mk. 14, they had to go to a FIVE-bladed propeller because there was no more room for a longer-blade 4-blade prop. Ditto for the Hawker Sea Fury with its 2,480 HP radial engine. One of the Sea Fury's prototypes had a six-blade counter-rotating prop, really two coaxial three-blade props turning in opposite directions.
Logged
Little-Acorn
Silver Member
****

Kudos: 5
Offline Offline

United States United States

Posts: 153

Topic starter


Ignore
« Reply #11 on: September 13, 2020, 12:04:46 AM »

Well, so far so good. This my first-ever attempt at a SciOly Helicopter, and the results show it. 1/32" sheet balsa rotor blades, soaked in water and formed on a jig (two 1/2" spruce dowels and a bolt with a wingnut. pitch and dowel spacing are adjustable). Both rotors are 20cm diameter, three-blade one goes on top. Solid motor stick 3/16" x 3/8". The stick and the sheet balsa were both 6 pounds/sq in. The whole thing came out 4.14 grams without motor.

Folks here and elsewhere told me that such materials would weigh a lot more than the minimum allowed 2-1/2 grams without motor, and they were right. And that's without the required ceiling bumper on top. Well, this was my quick-and-easy version. The good news is, it flew surprisingly well, despite being too heavy.

Put an .094" thick, 10" hook-to-hook motor on it, 1.45g with two O-rings. Wound it up to 600 turns and let it go in my living room (It's a 2-floor house, 18" vaulted ceiling, might be illegal this virtual year). It ROCKETED to the ceiling, hit hard (no damage!?), bounced off several times, went skittering around the ceiling and then across one wall, finally coming to rest on my 14yo son's supercomputer, to his surprise. What he gets for wearing headphones. Will get the ceiling bumper on it and try an .079" motor next.

Next version will have carbon-fiber LE and TE built on the same jig with tapered tips, covering might be produce bag from the nearby Walmart, and it might also have a hollow motor stick this time. I'm still leery of covering the compound curves in a cambered, 1/r spanwise pitch distribution rotor blade, but nothing ventured nothing gained.

Each rotor blade in this sheet-balsa version has ground-adjustable pitch courtesy of materials from FFM. Both rotors came out fairly well balanced. Might extend this over to the next lighter weight version, experimenting until I can find a combination of pitch and motor thickness that gives the best flight times. Then version 3 will probably have fixed pitch, for lighter weight.

Got to build a box for it, too, with a fuselage-holder inside. I don't want its weight resting on the rotor blade tips when it's bouncing around on the seat of the car.
Attached files Thumbnail(s):
Re: Anybody coached, or competed in, the Science Olympiad "Helicopters" event?
Re: Anybody coached, or competed in, the Science Olympiad "Helicopters" event?
Re: Anybody coached, or competed in, the Science Olympiad "Helicopters" event?
Re: Anybody coached, or competed in, the Science Olympiad "Helicopters" event?
Re: Anybody coached, or competed in, the Science Olympiad "Helicopters" event?
Re: Anybody coached, or competed in, the Science Olympiad "Helicopters" event?
Logged
Little-Acorn
Silver Member
****

Kudos: 5
Offline Offline

United States United States

Posts: 153

Topic starter


Ignore
« Reply #12 on: September 13, 2020, 12:46:12 PM »

Hmm, flew it again this morning with the skinnier motor, outdoors this time,and it barely flew, pretty lifelessly. Got maybe 20 feet high and started descending within maybe 7 seconds. Took the hint and went back to the .094" motor, and that didn't fly very well either, maybe 8 seconds. WTF?

Checked the blades and found that one blade on each rotor had pivoted so the tip pitch was basically flat. So much for my brilliant innovation. Turned them so the tip pitch was around 15 degrees on all blades, and rewound (750 turns, .094" motor), and found that pitch and an aerodynamically-balanced rotor made a world of difference, duh. It climbed to a height about half a football field in distance before it seemed to run out of climb and hovered. That took about 40 seconds. Indoors under an 8-foot ceiling, I figured as soon as it couldn't climb any more, the flight would be over a second or two later. No sense in counting any "descending" time after that.

This (outdoors) is very different from the contest conditions (8ft ceiling) of course, and it could be that in an indoor contest other things could come up that I'm not smart enough to predict now. An encouraging flight, nonetheless. I'm wondering how it would do with the skinnier (.079") motor. Have to wait till I get it down off the neighbor's shed to find out. Undecided

Now to put the ceiling bumper on it, and start in on the carbon-fiber blades.
Logged
Little-Acorn
Silver Member
****

Kudos: 5
Offline Offline

United States United States

Posts: 153

Topic starter


Ignore
« Reply #13 on: September 28, 2020, 02:20:13 AM »

Carbon fiber version prototyped, so far so good. 53sec flight under an 8' ceiling, .094" motor, 14" long. Weight of copter w/o motor, 3.2g. Rotors made from 0.5mm carbon fiber.

Covering compound curves with a produce bag from Walmart isn't easy. Wrinkles galore. Sloppy work by me, trimming the covering too. Might try crumpling up some Mylar real tight next.

Might also try 3- or 4-blade rotors next, mix-n-match.
Attached files Thumbnail(s):
Re: Anybody coached, or competed in, the Science Olympiad "Helicopters" event?
Re: Anybody coached, or competed in, the Science Olympiad "Helicopters" event?
Re: Anybody coached, or competed in, the Science Olympiad "Helicopters" event?
Logged
bjt4888
Gold Member
*****

Kudos: 6
Offline Offline

United States United States

Posts: 253



Ignore
« Reply #14 on: September 28, 2020, 12:07:41 PM »

LA,

Good job. Design has all the basics. Here's a design that was the result of a full school-year SO season of design and testing leading to copying elements of a competing school's design. 2.35 grams, 17.5" motor stick, kevlar thread lateral and vertical truss, deceivingly simple lower rotor design saves 5% weight (no .020" wire shaft, no pushrod tube "axle" housing, no bearing) and works better than it looks.

2:15 flight time for 8 ft ceiling with minimal testing. Looked capable of 5 - 10 seconds more with better motor matched to rotor. Saw a very similar design do 2:35 under a 22 ft ceiling winning Michigan SO States that year.

Test longer and longer and thinner and thinner rubber and play with rotor pitch and definitely build to minimum weight.

Have fun,

Brian T
Attached files Thumbnail(s):
Re: Anybody coached, or competed in, the Science Olympiad "Helicopters" event?
Re: Anybody coached, or competed in, the Science Olympiad "Helicopters" event?
Re: Anybody coached, or competed in, the Science Olympiad "Helicopters" event?
Logged
Little-Acorn
Silver Member
****

Kudos: 5
Offline Offline

United States United States

Posts: 153

Topic starter


Ignore
« Reply #15 on: September 28, 2020, 08:41:38 PM »

Thanks Brian! I'm learning tons of stuff here, but still have tons to go. (Will probably always be true.)

What size rubber motor did you finally use on it? Sounds like many different sizes were tried. And what was the pitch angle at the tip? Same for both top and bottom rotors?
Logged
bjt4888
Gold Member
*****

Kudos: 6
Offline Offline

United States United States

Posts: 253



Ignore
« Reply #16 on: September 28, 2020, 09:08:53 PM »

LA,

21” loop of .052 g/in 6/2016 Tan SS. Winding was 2,850 turns max to 1.4 in oz max torque, 30 backoff turns and launch torque of 0.9 in oz. turns remaining 750. High turns remaining number indicates a slightly thicker motor might be better; maybe .053 g/in. Also, this was the end of the season for my students and we never got around to testing longer motors. Plans were to test about 24” loop of .054 g/in.

Enjoy.

Brian T.
Logged
bjt4888
Gold Member
*****

Kudos: 6
Offline Offline

United States United States

Posts: 253



Ignore
« Reply #17 on: September 29, 2020, 02:00:21 PM »

LA,

Sorry, forgot to reply to tip pitch question. 17.5 degrees. Also, as is typical of most high aspect ratio wings, our rotors have slight  tip washout in order to reduce induced drag.

Brian T
Logged
Little-Acorn
Silver Member
****

Kudos: 5
Offline Offline

United States United States

Posts: 153

Topic starter


Ignore
« Reply #18 on: October 02, 2020, 06:47:40 PM »

Something like that?

Simplified rotor structure, still true 1/r, motor stick 15", way too skinny (3/16"x3/16", 5 pounds/cf) so I hope the guy wires (Kevlar) help. Bottom rotor is glued to the motor stick, so whole fuselage spins left as top rotor spins right. Tip pitch angle is 18 degrees, helical pitch distribution so it builds on the same jig.

Good news is, it weighs 2.38 grams without motor. Will need ballast, minimum by rule is 2.50 grams.

I may have borrowed one or two features from the design you showed me. Naah, hell, I stole it. Guess I'll find out if my constructions techniques are any good. Students won't have time to build their own, tournament is in eight days(!)

No flights yet, glue is still drying. Will use .067" motor at first, that may change quickly.

ON EDIT:
1st flight, 8' ceiling, living room. 1,050 winds, flew 37 sec, hit a radio speaker and fell. 600 winds left.
2nd flight, 1,275 winds, flew 47 sec, landed normally. 585 winds left.

Well, it flies. Gotta balance the rotors and add ballast to get it up to the required 2.5 grams.
Attached files Thumbnail(s):
Re: Anybody coached, or competed in, the Science Olympiad "Helicopters" event?
Re: Anybody coached, or competed in, the Science Olympiad "Helicopters" event?
« Last Edit: October 02, 2020, 07:22:27 PM by Little-Acorn » Logged
Little-Acorn
Silver Member
****

Kudos: 5
Offline Offline

United States United States

Posts: 153

Topic starter


Ignore
« Reply #19 on: October 06, 2020, 11:11:31 PM »

Put two straight pins into the fuselage, bringing the weight up to 2.51 grams. Several flights, it seems to like the 1/16" (.067") motor. But doesn't like it very much. The fuselage leans over around 15 degrees, keeps corkscrewing around at that angle like a gyroscope or top running down. With the pins set next to the top rotor, seems slightly worse than when the pins are near the bottom rotor.

So, fore-and-aft weight distribution seems to make a slight difference, but not much.

A long, long time ago in a galaxy far, far away, I took a Sleek Streek fuselage (plane was $.25 complete back then) without wings, tail, and gear. Glued a couple of slats to the tail of the fuse, slightly angled like a sort-of propeller. Very crude, but it flew, mostly. Didn't take long to start breaking slats. I started gluing them with different pitch angles, and found it seemed to fly more stably if the bottom slats had less (flatter) pitch, and flew unstably if the slats had greater (coarser) pitch. Only tried this a few time, so it is hard to tell if it was really the difference in pitch between the top and bottom propellers.

It's a little harder today to change the pitch of either top or bottom rotor, so before beginning major surgery on it, thought I'd ask people with more experience than me (which is most people).

What have you all used in the past, to straighten out a helicopter that corkscrews around like this one does? Weight distribution from top to bottom rotor? Rotor-pitch distribution from top to bottom? A large hammer?

Inquiring minds want to know!

Thanx all!
Logged
Little-Acorn
Silver Member
****

Kudos: 5
Offline Offline

United States United States

Posts: 153

Topic starter


Ignore
« Reply #20 on: October 11, 2020, 12:14:27 AM »

Tournament day today. Done "virtually", with students videorecording their flights and sending in their videos and flight logs. All flights done at home, with an 8-foot ceiling, in this pandemic-restricted tourney. I've often wondered how much longer the flights would be in a gym with a 25-35-foot ceiling, giving that much more time to descend as the rubber motor slowly ran down.

One of my students got a 1 min 31 sec flight out of her helicopter, my first carbon-fiber design, see Post #13 above. .085" motor, 13 inches long, same Walmart produce-bag covering, 3.2 grams without motor. 1,400 winds. She's been higher than a kite ever since. Congrats to her!

https://youtu.be/gjazMvC3W7k
« Last Edit: October 11, 2020, 01:06:04 AM by Little-Acorn » Logged
bjt4888
Gold Member
*****

Kudos: 6
Offline Offline

United States United States

Posts: 253



Ignore
« Reply #21 on: October 11, 2020, 02:15:13 PM »

LA,

Sorry, didn't see posts from a few days ago. Design looks like it will do the job. Wandering can usually be fixed by CG location. Some wandering/oscillating is typical on descent for the teams I coached. My very faint memory was a descent rate after detach from ceiling for the last time of about 1 second/ft of ceiling height. So, a 10 ft. taller ceiling might add another 10 seconds to the flight.

Good job to your student. Good start. Much longer motors will give much longer flights. Get a torque meter (or make one) and wind the rubber motor all the way to 90+% of maximum (student can see the John Barker "turns equation" in last years Scioly.org Forum/Wiki for Wright Stuff on about page 15-20. The equation calculated projected number of turns for a particular density (or thickness) and particular length of rubber motor. In this Wiki there is a description and example of using the formula.

Student can also hold the helicopter higher above her head on launch to reduce the velocity and impact on the ceiling (this can sometimes bend the aluminum thrust bearing). For an 8 ft ceiling, my taller students would hold the helicopter about 1" from the ceiling to launch.

Brian T
Logged
Pages: [1]   Go Up
Print
Jump to:  

Powered by MySQL Powered by PHP Powered by SMF 1.1.21 | SMF © 2015, Simple Machines Valid XHTML 1.0! Valid CSS!