Wright Stuff C

[klastyioer]

Me neither, originally thought it might be a school filtering policy though that still might be the case.

I'm seeing them alright. Did you refresh your page after you got off school wifi? My school blocks the images but after I get off and refresh they show up.

i like only use my school laptop soooo can you like pm the images to me or something

[xiangyu]

Me neither, originally thought it might be a school filtering policy though that still might be the case.

I'm seeing them alright. Did you refresh your page after you got off school wifi? My school blocks the images but after I get off and refresh they show up.

i like only use my school laptop soooo can you like pm the images to me or something

Sure, I'll try to pm you on here if that doesn't work pm me your email and I can send them to you that way

[lechassin]

You guys all quoted the pics so now I can see them everywhere, lol.

I tossed the 2 blade props in favor of a series of 3 blade props with the tips at 30, 40, and 50 degrees. The 50 degree runs the longest but there's just a lot of drag so IDK if it's any good.

The 30 degree prop:


The jig to get it running true:

[lechassin]

We tweaked the design and now have a pretty good protocol for those inclined to go without a kit:

1) The previous 8.0 g plane can still climb well at 10g flying weight, so it can lift a 2 g 24" motor. To maintain a 1.5 ratio of the motor to hook distance we started with a 16+" 1/4" x 3/32" motor stick.
2) Taper the top of the stick to 1/8" at the ends and position the hooks not more than 1/4" from the stick, minimizing that while being sure a fully wound motor doesn't rub. Test run the stick at full power to be sure it doesn't bow under load. We have no down thrust or right/left thrust and we temporarily used a long piece of wire in the bearing to align the hub along the motor stick perfectly. Our motor stick with hub and hooks weighs 1.8 grams, and our hub is threaded to allow easy prop changes without removing the hub and tweaking it in the process.
3) Mark the motor stick at 50% and keep the CG there so you can tweak the motor size without adjusting much. We marked where the CG needs to be on our wing stack and therefore just glued the wing to the motor stick, at zero+ incidence. I guess that means this protocol only works if you have a known set of wings, lol, but 40% from the leading edge seems close.
4) We moved the rudder forward again so its trailing edge is now even with the stab. We went back to super light 1/8"x1/8" for the tail boom, which is now OK because the boom is short enough to be stable (the motor stick is so much longer now). The tail is built of light 1/16" x 1/32" and is frail but we haven't broken one yet even in the house. This is important so the tail moment can be as long as possible and still maintain CG.
5) With prop installed (ours weigh 1.1 grams), tack the boom into position and check the CG, repeatedly shortening the boom until the plane juuuuust balances. Then glue the boom with a little negative incidence in the stab ("up"). The angle is small and isn't critical; you can bend the boom is easily to trim and it keeps its setting nicely (our plane sits in a cradle we tape to the bottom of a Tupperware container, so the plane won't deform while sitting). The distance from the CG to the leading edge of the stab came out to 30 cm, which is enough to keep the plane stable with 3 large prop blades and the 24" motor at 2250 turns (85% for our lubed/stretched rubber).
6) Our rudder needs a little more left than right for whatever reason, but we started with a 1/32" cube glued to the rear of the boom. The 1/32" thickness of the rudder causes enough deflection on which ever side of the block it sits, and a shim can easily be added if necessary. The rudder is surprisingly small (about 1" chord x 1.25" tall) otherwise tiny changes are too much. The hinge is a 1/32" x 1/32" post with a 3/32" x 3/32" piece of thin plastic sheet and is stiff enough that the rudder presses against both sides of the block and holds its setting. Bending the rudder allows it to pop over the block to the other side without damaging it.

We'll try to get to the gym Sunday and video some time trials, but the thing climbs nicely in the house and has a gentle descent angle when it's almost out of knots.

[klastyioer]

You guys all quoted the pics so now I can see them everywhere, lol.

I tossed the 2 blade props in favor of a series of 3 blade props with the tips at 30, 40, and 50 degrees. The 50 degree runs the longest but there's just a lot of drag so IDK if it's any good.

The 30 degree prop:


The jig to get it running true:

lol i still cant see them you should totally just post the photos.google link

[lechassin]

Well, don't let anyone tell you they won't climb high with a tiny prop

There was zero wind today so we tried it outside. After a bunch of trimming flights both ways and with different props, we wound a 24" motor to 2400 turns and used the 40 degree prop. It circled waaay up and on its way down it settled onto a tree high enough that three 8 foot sections of PVC pipe won't reach it . Hard to say how long a flight it would have been, but we're cautiously optimistic.

We built another plane with an 18" motor stick. We'll start with a longer (heavier) 27" motor to reduce the climb. It needed 0.3 grams of lead to reach the 8.0 gram rule (it's right in front of the trailing edge):


We'll be more careful with this one, it came out nice...

[lechassin]

We built a second identical plane and they store in a Tupperware bin, one hanging from the lid:

The piece of PVC pipe has a long section of music wire in it that acts as a very precise torque meter, which we need because these planes absolutely will climb to the rafters even with the small prop.

Here are two typical flights from today, one to the right and one to the left:
https://www.youtube.com/watch?v=hMacn95xoYo
https://www.youtube.com/watch?v=u77yWYz5yow
Routinely between 60 and 70 seconds, for now were using a 32" motor at 3000 final turns and a 30 degree helical prop with 3 blades. We have to aim for a maximum height below the lowest obstacle to avoid losing a plane on an HVAC unit.

The planes are durable enough: multiple hits, a few times getting poked out of the basketball rigs, and a few nose dives into the floor without any damage at all.

Which leads me to my question: the planes do not recover quickly (or at all) from a hit like I see in others' videos. The CG seems conservative at 26mm from the leading edge, with some "up" trim needed for good flights. What causes that?

[bjt4888]

Lechassin,

Congrats on the good results.

We're finding with our design that a minimum static stability margin of 25% is needed to recover well from ceiling hits.

My teams uses the Bernie Hunt design spreadsheet (with tweaks based upon past experience) to ballpark SSM and estimate possible good CG range.

I think that Coach Chuck posted this spreadsheet in the forum.

Brian T

[lechassin]

Thanks for the response. I didn't find the spread sheet but I think we're past the point where we could use it (for example: we can't know the exact weight of the tail boom because we make it intentionally too long so that with the tail mounted we can progressively shorten the boom until the plane balances on the prototype's CG.

Our decalage is 2 degrees. I suspect that to increase the stability margin, we need to go towards 3 degrees of decalage and adjust the CG forward to achieve the best flight path.

However, to compensate for the small [inefficient] prop, we compromised the plane in the following manner: we know the plane can easily carry 0.3 grams of ballast placed on the CG even with 32" (2 grams) of rubber. The 32" motor does not fall off of an 18" motor stick, but it's close, especially if we use a low-pitch [3 bladed] prop that allows the knots to run out. Because we want as long a motor as possible, the longest and lightest possible motor stick is the single driving feature of the design beyond what the rules specify, ergo the motor stick is shaved just shy of the point of bowing under load, we omitted all hardware to adjust incidence(s), and we adjust the length of the tail boom to achieve the CG without any ballast. Any tenth of a gram we could spare was allocated to the length of the motor stick.

Sadly, this means that changing the static stability is only possible for us by giving up something else, i.e.: add incidence and nose weight but go over the 8.0 gram target, or shorten the tail boom to move the CG forward but lose tail moment/tail authority.

I suspect the latter option will be best, we will see in testing.

[klastyioer]

lechassin
i have a few questions for you, if its okay to ask here
you can pm me if youd rather not say over to forums or just not answer them at all
what material is your prop blade made out of? it seems to be something other than wood but i dont know what it is
curious to know why your vertical stabilizing devices are so tiny (referring to wing tips and rudder)
any particular reason why you arent using wing posts for the stab or the wings, rather just having them flat on the motor stick
nice approach to the torque meter, sounds quite interesting
how did you make your prop hub?? i cant quite tell from the picture