Flight B/C

[bjt4888]

I was trying to use the rubber max turns calculator that was provided to me by coach Brian, the calculator gave me very bad results(I was getting 200 max winder turns when the tested max was 108).Later I was browsing the NFFS library of resources and I found another rubber calculator by Roger Willis when I used it I got almost perfect results (Predicted max winds 108 actual tested max was 110) https://docs.google.com/spreadsheets/d/ ... sp=sharing This sheet contains all the calculations I did, what did I do wrong?

Vjse,

Send me the rubber motor loop length and rubber motor weight. Don’t include the knot when measuring length and just pull the motor straight when measuring. Don’t stretch it when measuring. Also, what type of o-rings (ex. Two black rubber o-rings from the FF kit package). I’ll use the formula and explain it to you.

Brian T

[vjshe]

I was trying to use the rubber max turns calculator that was provided to me by coach Brian, the calculator gave me very bad results(I was getting 200 max winder turns when the tested max was 108).Later I was browsing the NFFS library of resources and I found another rubber calculator by Roger Willis when I used it I got almost perfect results (Predicted max winds 108 actual tested max was 110) https://docs.google.com/spreadsheets/d/ ... sp=sharing This sheet contains all the calculations I did, what did I do wrong?

Vjse,

Send me the rubber motor loop length and rubber motor weight. Don’t include the knot when measuring length and just pull the motor straight when measuring. Don’t stretch it when measuring. Also, what type of o-rings (ex. Two black rubber o-rings from the FF kit package). I’ll use the formula and explain it to you.

Brian T

Here are the rubber parameters

Length 16.25
Strands 1
Thickness 0.04
Width 0.09375
Weight 1.98 grams
O-rings I got them from J&H aerospace, they are #4 Nylon O-rings: https://jhaerospace.com/product/4-o-rings-25ct/


Thanks for the help!

[WetUnicorn]

Hi, I'm in division C and I have some questions about CG and other things.

I’ve got a FF kit, and I had a question about my CG/ballast placement. Here are my current plane settings first: got 1.26g of total ballast and instructions say all at the nose but i got 0.55g at nose and 0.71 g 4 1/8" (~10.5cm) from the back of the plane. Is this optimal? Cg is at 2 1/8" back from TE, and wing position is 1/4" behind the kit recommendations. Front wing post/le is raised 3mm up for incidence. Prop pitch hasn't been changed (idk how to change anyways). Left wing washin I want to say is about 1/8" but I don't know if I'm doing it right…It flew at the birds invitational for about 1;30 mins, so I want to say it is reasonably trimmed. My question though, is that is it ok to have clay at the nose and clay towards the back of the plane? How will it affect my plane performance? Also what is the reason for putting all the clay at the nose? I haven’t tried moving the clay yet because I just got done with the invitational and I didn't want to change any settings in case it messed up my plane. I also don’t get a lot of gym practice (like 30mins a week) and I don't want to waste time experimenting with ballast/CG because what I have works (I mean at least right now that's what I want to know). I think my next step in trimming should be putting more winds in, I haven’t been winding to max and backing off as I should (discovery requires experimentation and I think also trying different rubber and stuff but I just wanted to confirm the trim settings I have now aren’t going to haunt me later I do have a video if it helps…

For CG I got a little confused while reading some posts. Just to clarify, moving the wings backward will move the CG forward in relation to the TE but move more mass towards the back of the plane, while moving the wings forward will move the CG backwards in relation to the TE while moving more mass to the front of the plane? So moving the CG forward and the wings backward will get you a more stable plane?

Also another question (sorry) but what are anyone’s opinions on flying outside? Like I said, I don't get a lot of gym time and there is literally no where else for me to fly (even a classroom) except my own house. So I’ve resorted to flying outside and that's where I get a lot of my data for my flight logs. Just wanted to ask how reliable is this/is it a good idea? I know lots of external factors (like wind arghh) and really influence how the plane flies and stuff, but just wondering. Thank you so much anyone willing to help me out here!!

The stability is where the CG is relative to the center of lift, essentially. For our purposes we can say it is where the CG is relative to the primary lifting surface, or the wing. Since these planes have the CG for stability close to the rear of the wing, we often use that for reference.

So, moving clay toward the front of the plane increased stability by moving the CG forward. Moving the wing back moved the CL back a bit, but also moves the CG FORWARD relative to the primary lifting surface (wing), since the wing is only about 1/3 of your mass.

Why put the clay all at the front? These planes, particularly C division, are very short-coupled (tail distance from wing is short), which makes it VERY sensitive to trim changes. Therefore, you want the wing as far forward as possible to maximize your tail moment. Moving the wing forward decreases stability (because the CG moves back relative to the wing). Therefore, if you put all, or most of the clay at the nose, you can put the wing as far forward as possible to maximize the tail moment and still have the needed stability. If you have a moveable wing, then put ALL of the clay at the nose and adjust the wing for CG location. If your wing is fixed, you may need to move a small amount of clay back for balance purposes.

You indicate that your CG is 2.125" BACK from the wing trailing edge? That sounds way back for this year's C div planes. Be sure you are balancing with rubber motor installed, and measuring from the rear wing post. Generally we have seen 1-2" in front of the rear of the wing

Coach Chuck

Whoops I mean to say that my CG is is 2.125" FRONT of the TE (per kit recommendation with the motor attached). I probably gave you a heart attack with that information (so sorry for the confusion). I keep mixing up wing position and CG position, but now the stability make sense. I'll put the rest of the clay in the front next time I get gym time and see how that goes...Thanks!!

[coachchuckaahs]

Here are the rubber parameters

Length 16.25
Strands 1
Thickness 0.04
Width 0.09375
Weight 1.98 grams
O-rings I got them from J&H aerospace, they are #4 Nylon O-rings: https://jhaerospace.com/product/4-o-rings-25ct/


Thanks for the help!

I believe coach Brian's calculator accommodate outdoor rubber motors which may include many strands. Therefore we have to understand what the strands parameter represents.

In your case,I believe you are using a loop, as most will do. A loop had a winding cross section of two strands.

This is likely the source of your discrepancy

Coach Chuck

[randomdogonapc]

I’m building a second plane and I have one thick carbon fiber spar and one thinner one; do you guys think that I can get away with having the thinner spar if I have support that’s similar to the support that are on wings? I know that stab twist is an important factor so I might just have to size down my stab to be able to use two thick spars.

[bjt4888]

I’m building a second plane and I have one thick carbon fiber spar and one thinner one; do you guys think that I can get away with having the thinner spar if I have support that’s similar to the support that are on wings? I know that stab twist is an important factor so I might just have to size down my stab to be able to use two thick spars.

We have used .030” thin carbon spars for stabilizer span up to 12” with no issues. The actual thickness of the spars you are referring to would be helpful information, as would the dimensions of the stabilizer you are planning to build.

Good job building additional airplanes!

Brian T

[randomdogonapc]

I’m using a .020” rod and a .030” rod. The stab that I want to make would be 30cm wingspan

[pumptato-cat]

Hey all, anyone using a Freedom Flight torque meter? I have one and the needle always starts in a different place when I wind. It seems to center around 0.03oz. I wouldn't care normally but I've been getting inconsistent flight heights(for anyone with access to my flight log, I will update winding logs later tonight).
Here's an example:
Rubber: 0.094", 1.95g
Flight 1: 1.1oz max torque, 0.49oz launch torque, 115 winds 1:15, 17 dewinds. Flight height(Estimated using a laser pointer) around 23ft?
Flight 2: same settings except 116 winds, less dewinds I think? Details in log. 13ft. Absolutely no clue what happened there
Flight 3: same settings, still climbing very strong around 23ft, hit ceiling and crashed.
What's going on? I've noticed as the rubber stretches after the first run, it takes less dewinds or more winds to reach the same torque value. That seems normal but I also think the torque meter itself is inconsistent--the needle never starts at 0oz. I tried tilting the meter face to match with the needle at 0oz for starting, but the needle keeps shifting to the right and I don't want to have the meter face at a 90deg angle.
There's a wire hook that hooks onto a screw at the back-it is bent slightly at an angle. Is that a problem? (will provide pictures if I have time)
Context: I fly in a small dome--peak height 30ft, but seats(Auditorium) and curved ceiling cut flight area down to around 23ft or so. Sometimes there are slight air currents blowing upwards.

[coachchuckaahs]

Cat

We're all the flights with the same loop of rubber? As you have noticed, the rubber will take more winds after each use. We primarily wind to torque, using a home made digital torque meter. The twisting wire meters should be repressible enough. However, it sounds like your drift is continuing in one direction.

I would suspect that with the high torque this year that you are plastically depending the sensor wire. You may need to recalibrate with a slightly larger wire.

Another possibility is that something is slipping, but I am not familiar with the details of the design.

Coach Chuck

[bjt4888]

I’m using a .020” rod and a .030” rod. The stab that I want to make would be 30cm wingspan

.020" rod is used for Limited Penny Plane stabilizers 12"span and 4" chord. They fly quite a bit slower than Science Olympiad planes though. You might get excess flexing during flight with spars this thin. You could reinforce with struts, but better would be to us .030" rod for your stab.

Brian T