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Gavinm9805
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Quick Question

Post by Gavinm9805 »

Short version: What is a reasonable weight for a plane with the standard 9cm x 45cm wing with a 7cm x 30cm horizontal stabilizer?

Long version: I've been trying to get a plane to fly for over a year know and I just don't seem to be able to make it work. The rules specify 8g but I have never been able to get my plane under 10g. Is the weight of my plane the issue or should I be focusing more on the design aspects?

(Also please let me know if this is not the correct place to ask this question)
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Re: Quick Question

Post by bjt4888 »

Gavin,

Weight of the plane is important, but you should be able to fly a 10 g airplane over a minute. Properly winding the motor is the most important thing to learn. I’ll post a detailed description of motor winding in a little bit.

What design are you building that comes out to 10 grams?

Brian T
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Re: Quick Question

Post by bjt4888 »

Gavin,

I was the Event Supervisor for one of the larger virtual tournaments last month hosted by Boyceville HS, Wisconsin. At the completion of the tournament, I created and distributed this description of rubber motor winding for Wright Stuff 2022:

https://drive.google.com/file/d/1-syZZF ... sp=sharing

The link above describes proper rubber motor winding and also has a number of helpful links built in and a video of me winding the motor for and launching a Science Olympiad Helicopter last year. The state of Michigan had Helicopter as the HS event as it can be easily flown at home.

Brian T
Last edited by bjt4888 on January 21st, 2022, 6:54 pm, edited 1 time in total.
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Re: Quick Question

Post by coachchuckaahs »

In addition to Brian's input, the thing I have seem most at issue is the basic trim of the plane. A plane will not climb and get reasonable times if the trim is not properly set.

This is an area in which Coach Brian and I will work on a video soon. However, initial setup and tuning information can be seen in https://youtu.be/knuH8DdhL3w, which wan an online WS discussion earlier this year. This video does not have in-gym flying, but does walk through initial plane setup.

We recognize this as an area where much assistance is needed. We have had a few seminars at various events around the country, but this is hit or miss as far as covering the need. If you are going to a large in-person invite and would like to help arrange an in-person seminar, please let us know EARLY so we can see if it is possible. These seminars have really helped bring planes from unflyable to flyable, and from flyable to competitive.

If you would like to set up a zoom session while in gym, I can do that on a limited basis, PM me and we can see if it is feasible.

Finally, if you are having trouble with your plane not flying well, a more complete description is useful for diagnostics. Among other things, it should include:
  • What plane (kit, home built) are you flying?
  • What are your decalage measurements (incidence of wing and stab, as measured form motorstick to leading and trailing edges)
  • Where is your CG, relative to the trailing edge of the wing or the rear wingpost?
  • What is the mass of your plane
  • What propeller are you using, and if adjusted, what pitch?
  • What mass of rubber are you using (should be 1.5g)
  • What "width" of rubber are you using. While much pre-cut rubber is sold by a measured "width", it is more helpful to either express in terms of grams/inch or the loop length before using (once used it gets stretched, sometimes permanently)
  • How many winds and unwinds are you using?
  • What torque did you wind to, and what torque at launch
  • A complete description of the planes path in the air (dives, climbs then suddenly drops, dips, won't circle, etc. )
Coach Chuck
Last edited by coachchuckaahs on January 22nd, 2022, 10:34 am, edited 1 time in total.
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Gavinm9805 (January 22nd, 2022, 11:30 am)
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Re: Quick Question

Post by Gavinm9805 »

Hello Brian and Coach Chuck,

The design I am using is based on the Stinger 2022 from J&H aerospace. The extra weight comes from material differences from the actual design (I'm having to use basswood for the ribs). When walking with the plane, the plane will generate enough lift to fly. However, when trying to make the plane fly with the rubber motor, the propeller doesn't generate enough thrust to make the plane fly, so I'll try using the tips in the document you posted. I am using an unadjusted "9.5″ S/O Ikara Prop Assembly" from FAI model supply with a 1/16" super sport rubber. I have some new, better building materials coming in a few days that will allow me to build some other designs (most likely the "Finny") so I will be able to give a more complete description once I build a more finalized design. I'd love to have a zoom meeting if the time may allow it. I will give an update on the plane soon. Thank you so much for your help, I really appreciate it.

Regards,
Gavin M
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Re: Quick Question

Post by coachchuckaahs »

What is missing from that update is how you are winding, mass of rubber, loop length, number of turns at launch, and torque if you have it.

Based on what you are telling us, the following thoughts certainly jump out:

1. The rubber is probably WAY too thin. With that prop, and especially with the excess weight, you will need something a bit over 3/32 as a starting point
2. I suspect in addition to too thin rubber, you are likely severely under-winding. Even with the 1/16 rubber, you should be able to launch at a torque high enough to initially climb, though the flight will not last long and a lot of turns will remain on the rubber.

Off the top of my head, with 1.5g of 1/16" rubber, you should probably be getting 2500-3000 turns into the rubber, then back off to launch torque

Coach Chuck
Last edited by coachchuckaahs on January 22nd, 2022, 1:01 pm, edited 1 time in total.
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2018 C Heli Champion
2019 B ELG 3rd place
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Re: Quick Question

Post by jander14indoor »

Hope this isn't too late, but why are you using bass for the ribs? These are the lightest loaded parts on the plane. Low density balsa is MORE than adequate.

Let me emphasize this, WEIGHT is the first, most important thing when building your plane. Over weight means faster flying, more drag, shorter flights, harder crashes (MORE damage, not less) harder to trim (things happen too fast). It is hard to lighten a plane, much better to build light from the start!

To do this you need a plan, called a bill of materials. Basically list every part, weight what you have for parts, add them up, and without glue you want to be below 8.0 gm, maybe 8.5 gm max. You'll get to weight with the glue and a little clay ballast. Easier to add weight than remove it.
If your list of parts adds up to more than your target, start replacing parts with lighter parts. Smaller parts, lower density balsa, etc. Balsa density is the thing you have most control over in these planes, so be very conscious of what you are using. Fit the balsa density to the strength needed for that part. Example, wing post MUST be strong, deserve denser balsa, wing ribs don't take much stress at all, can be VERY low density. Spars somewhere in between. You also need to be conscious WHERE you put the weight. Weight in the tail has to be offset with essentially dead weight in the nose. Keep your tail parts LIGHT.

Jeff Anderson
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Re: Quick Question

Post by Gavinm9805 »

I have switched to balsa and have reduced the weight to 8g. Things have made a complete turnaround thanks to all of your help, and I cannot express my gratitude enough for all your help. I have built a second plane that follows the same design as the Stinger from J&H Aerospace but uses a wideband propeller and microfilm winglets. Using a 1.5g propeller with 3/32" rubber and Teflon o-rings, I typically wind to about 1000 turns. However, when I release (after unwinding for optimizing launch torque) the plane will not fly, and rather falls in a controlled glide. I think the extra weight on the wideband prop and reduced weight on the wings and tail (due to microfilm wing covering) has made the plane too front-heavy. I have tried adjusting the wings but it doesn't seem to help, and I'm hesitant to add a ballast due to the plane already being overweight. If anyone has a recommendation to help fix this issue it would be greatly appreciated. Thank you again for all the help you guys have given me.

Gavin

edit: the propeller is the "9.5″ FLARING PROPELLER FOR INDOOR FLYING" from J and H Areospace
Last edited by Gavinm9805 on April 22nd, 2022, 5:27 am, edited 1 time in total.
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Re: Quick Question

Post by bjt4888 »

Gavinm9805 wrote: April 22nd, 2022, 5:23 am I have switched to balsa and have reduced the weight to 8g. Things have made a complete turnaround thanks to all of your help, and I cannot express my gratitude enough for all your help. I have built a second plane that follows the same design as the Stinger from J&H Aerospace but uses a wideband propeller and microfilm winglets. Using a 1.5g propeller with 3/32" rubber and Teflon o-rings, I typically wind to about 1000 turns. However, when I release (after unwinding for optimizing launch torque) the plane will not fly, and rather falls in a controlled glide. I think the extra weight on the wideband prop and reduced weight on the wings and tail (due to microfilm wing covering) has made the plane too front-heavy. I have tried adjusting the wings but it doesn't seem to help, and I'm hesitant to add a ballast due to the plane already being overweight. If anyone has a recommendation to help fix this issue it would be greatly appreciated. Thank you again for all the help you guys have given me.

Gavin

edit: the propeller is the "9.5″ FLARING PROPELLER FOR INDOOR FLYING" from J and H Areospace
Gavin,

Good job building to weight. We need the following to help you diagnose:

1. Wing incidence
2. CG location
3. Left wing washin measurement
4. Rudder or tailboom offset
5. Launch torque
6. Is the airplane built and adjusted exactly per the kit instructions?
7. Does the airplane circle? Which direction?

If you are nose heavy, slide the wing saddle forward about 1/4” at a time for each test flight. What do you mean by “1.5 gram propeller”? Did you mean 1.5 gram motor? By wide propeller, do you mean you are using the “Ikara Flaring” propeller? This propeller is about 0.5 grams heavier than the symmetrical 24 cm Ikara and is actually not a better propeller unless you modify it.

A flight video would be very helpful.

Brian T
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