Flight B/C

[randomdogonapc]

Thanks for the response. Do you happen to have an outline of the flaring Ikara planform? The only pictures that I have found are the ones on the freedom flight website and I’m not sure if tracing that would provide accurate results.

[bjt4888]

Thanks for the response. Do you happen to have an outline of the flaring Ikara planform? The only pictures that I have found are the ones on the freedom flight website and I’m not sure if tracing that would provide accurate results.

Random,

About eight posts back in this thread is a “hip pocket aero” link I posted. Reply #91 on that hip pocket thread has a drawing attached of the Ikara flaring prop blade. Most people cut off the portion of the blade aft of the spar, which reduced the blade wide point from 2” to 1.5”. Also, you might want to sand about .001” less than shown for this year. We’re finding that a slightly stiffer flaring and lower pitch is working. Probably the wide chord, inefficient wing need the extra touch of horsepower.

Brian T

[pumptato-cat]

Oooh thanks for all the useful information everyone!!! I have also been eyeing torque burners for quite a bit but that was enough to convince me to stay away, haha!
Here's a bit of a dumb question: After I dial in trim on my second plane, I understand that I'm supposed to test for optimal rubber density. But how do I dial in a prop and rubber combination? If I fly until I get the highest duration with rubber density, wouldn't changing prop pitch change the rubber again? And vice versa?
Or is the answer to just test until best duration comes out, with no particular order in what you do? I feel as if optimizing rubber for the Ikara, and then changing prop pitch, would be an inefficient method of testing.
Also, for those of you that prepare for a venue with AC(States is almost 100% guaranteed to have strong AC, this time blowing down at an angle...), how do you practice? I don't have access to the states flying site(it's a 2 hour drive). I understand the reasoning behind forward CG and higher incidence, but I'm not sure how to dial in those settings if I can't fly in AC similar to the site.
Any ideas? Thanks so much!!!

Without going to flaring props, the optimization is two-parameter (two adjustable, multiple observational). You adjust the prop static pitch, and then adjust the rubber to match. If you have flaring, there are several more parameters that you control. The things you observe include duration, altitude, perhaps first lap altitude, circle size, etc.

1. Change pitch. Make small changes, a couple degrees at a time
2. Fly and adjust launch torque to get to near ceiling
3. Observe remaining winds. If too much, go thicker rubber, if too little go thinner. Generally winds remaining = unwinds to get to launch torque (Fine tuning of rubber density can be by duration, as long as you are getting to the same altitude on each flight). You may need o adjust launch torque when changing rubber density.
4. Record time
5. Repeat flight in final configuration to confirm time
6. Repeat at another pitch and compare time AFTER optimizing rubber and torque for that pitch. Do a systematic search for an optimum. It will not be a straight line, probably something with a peak at the optimum, so a large adjustment may miss the optimum

This can be a substantial amount of flights! Add in a variety of props (if you are making your own) and the matrix gets large!

As far as AC being on, about all you can do is prepare by having a stable configuration (CG forward), and have some heavier rubber available to power through. The heavier rubber will keep it up in cruise, higher torque will help it get up during climb. The impact of the AC will be different for every site, so best thing is to have stable and powerful options ready, and observe other flights to "read the room". Get some testing in if the ES allows (before check in testing is at discretion of the ES, but none in the last half hour of the session)

Coach Chuck

Thank you so much!!! This was very helpful. Is it better to build props for every different pitch, or to build a couple of props and change the pitch on those by bending spars/hubs?
Also, how is the hub with the prop blades attached? I see pictures of F1Ds with pigtail bearings(I think that's what they're called), but I'm not sure if I'm able to add those on my current FF plane. Would simply replacing the Ikara prop with a dowel that has a hole drilled through it be okay(while keeping the plastic prop hook)? Wow, this is a lot harder than I thought it'd be.
Again, thank you!!!
I'm trimming this weekend and I think I'll be changing props in a couple of weeks. I only have a couple of weeks until states, but I'm pretty excited to start experimenting!

[coachchuckaahs]

Thanks for the response. Do you happen to have an outline of the flaring Ikara planform? The only pictures that I have found are the ones on the freedom flight website and I’m not sure if tracing that would provide accurate results.

See coach Brian's note. I have just moved and my prop template is still in a box, somewhere.

I don't think the exact shape is critical, but the general flavor of the Ikara had some thought put in as far as the chord at various radial stations.

Coach Chuck

[bjt4888]

Oooh thanks for all the useful information everyone!!! I have also been eyeing torque burners for quite a bit but that was enough to convince me to stay away, haha!
Here's a bit of a dumb question: After I dial in trim on my second plane, I understand that I'm supposed to test for optimal rubber density. But how do I dial in a prop and rubber combination? If I fly until I get the highest duration with rubber density, wouldn't changing prop pitch change the rubber again? And vice versa?
Or is the answer to just test until best duration comes out, with no particular order in what you do? I feel as if optimizing rubber for the Ikara, and then changing prop pitch, would be an inefficient method of testing.
Also, for those of you that prepare for a venue with AC(States is almost 100% guaranteed to have strong AC, this time blowing down at an angle...), how do you practice? I don't have access to the states flying site(it's a 2 hour drive). I understand the reasoning behind forward CG and higher incidence, but I'm not sure how to dial in those settings if I can't fly in AC similar to the site.
Any ideas? Thanks so much!!!

Without going to flaring props, the optimization is two-parameter (two adjustable, multiple observational). You adjust the prop static pitch, and then adjust the rubber to match. If you have flaring, there are several more parameters that you control. The things you observe include duration, altitude, perhaps first lap altitude, circle size, etc.

1. Change pitch. Make small changes, a couple degrees at a time
2. Fly and adjust launch torque to get to near ceiling
3. Observe remaining winds. If too much, go thicker rubber, if too little go thinner. Generally winds remaining = unwinds to get to launch torque (Fine tuning of rubber density can be by duration, as long as you are getting to the same altitude on each flight). You may need o adjust launch torque when changing rubber density.
4. Record time
5. Repeat flight in final configuration to confirm time
6. Repeat at another pitch and compare time AFTER optimizing rubber and torque for that pitch. Do a systematic search for an optimum. It will not be a straight line, probably something with a peak at the optimum, so a large adjustment may miss the optimum

This can be a substantial amount of flights! Add in a variety of props (if you are making your own) and the matrix gets large!

As far as AC being on, about all you can do is prepare by having a stable configuration (CG forward), and have some heavier rubber available to power through. The heavier rubber will keep it up in cruise, higher torque will help it get up during climb. The impact of the AC will be different for every site, so best thing is to have stable and powerful options ready, and observe other flights to "read the room". Get some testing in if the ES allows (before check in testing is at discretion of the ES, but none in the last half hour of the session)

Coach Chuck

Thank you so much!!! This was very helpful. Is it better to build props for every different pitch, or to build a couple of props and change the pitch on those by bending spars/hubs?
Also, how is the hub with the prop blades attached? I see pictures of F1Ds with pigtail bearings(I think that's what they're called), but I'm not sure if I'm able to add those on my current FF plane. Would simply replacing the Ikara prop with a dowel that has a hole drilled through it be okay(while keeping the plastic prop hook)? Wow, this is a lot harder than I thought it'd be.
Again, thank you!!!
I'm trimming this weekend and I think I'll be changing props in a couple of weeks. I only have a couple of weeks until states, but I'm pretty excited to start experimenting!

Cat,

See pictures of our pigtail bearing and prop hook on page eight of this 2015 forum thread. A couple of ikara props that you can bend to various pitches is enough. Bend the diamond shaped hook that you see pictured. You can use this hook with the Ikara plastic nose button and the stock plastic prop hanger too.

https://scioly.org/forums/viewtopic.php?t=6085&start=70

Only two weeks to test props is a very short amount of time. But, try it if you’re inclined to. You might hit a good setup quickly of extra pitch (or, reduced pitch) and different rubber density. We’ve been testing props, pitches and rubber density since November. We gained an extra 10 seconds with the modified flaring Ikara prop and another 10 seconds with a custom built flaring prop (Division C). It’s fun science.

Brian T

[coachchuckaahs]

Thank you so much!!! This was very helpful. Is it better to build props for every different pitch, or to build a couple of props and change the pitch on those by bending spars/hubs?
Also, how is the hub with the prop blades attached? I see pictures of F1Ds with pigtail bearings(I think that's what they're called), but I'm not sure if I'm able to add those on my current FF plane. Would simply replacing the Ikara prop with a dowel that has a hole drilled through it be okay(while keeping the plastic prop hook)? Wow, this is a lot harder than I thought it'd be.
Again, thank you!!!
I'm trimming this weekend and I think I'll be changing props in a couple of weeks. I only have a couple of weeks until states, but I'm pretty excited to start experimenting!

You can re-use the Ikara button, and make a new shaft form 0.020" music wire. You should be able to find that at a local hobby shop, or possibly Ace hardware. Otherwise, a guitar string at something close to 0.020 should work, but that is pretty thick for guitar strings. You could straighten the Ikara shaft and re-bend it, but that is risky, and may have funny bends.

We use a 1/16" square basswood for the spar. We sand it thinner in one dimension on each side of center, so it is 0.045 x 0.062. Sanding is done 90 degrees apart for the two sides. The flatter part goes against the blade, and the blade is glued to this. To change pitch, we rub some water onto the spar where it is exposed between the shaft and the blade, and then apply the needed twist, in the pitch gage, while drying the spar with a heat gun. to change flare stiffness, we either sand the exposed spar, or trim the inner end of the blade to expose more spar.

The spar sits on the diagonal, so that the prop shaft goes through the 0.062 x 0.062 center on the diagonal. We drill a tight hole with a scrap of the music wire. We then pass the prop shaft through from the back side, bend it sharply 90 degrees, and then tack it in place with a bit of glue. The bent part should only be about 1/8" long, and runs parallel to the spar. We then wrap with 3-4 wraps of sewing thread, and soak this with thin CA to lock it all down. If using the Ikara button, be sure to install that and the beads before installing and bending the shaft. You can buy extra Ikara buttons, I think from FAI model supply. We use the pigtail hangers, or make our own from wire, and we make our own shafts.

See my video on the NFFS YouTube channel, on prop making. It is a smaller prop but same process.

You COULD also make a hub like F1D, where the center hub is a tissue tube, and each prop spar plugs in to that. This makes changing pitch easy, but it takes away the torsion member that allows flaring.

Coach Chuck

[pumptato-cat]

bjt4888,
Thanks for the link!! That clears it up a lot. If I'm understanding it correctly(I read Coach Chuck's explanation earlier but I'm not sure if I fully understood), is there a hole in the front "pin' sticking down that the shaft goes through, and then a "v" sort of shape on the second part sticking out that the shaft is pulled through from the rubber's force? Hopefully that makes sense.
I guess I could try cutting the plastic hook off, but maybe that'll wait until after States! I don't want to break the plane so close to competition...
Also, I only have around 5 weeks until states, but I do plan on continuing flying after states. I want to see if I can compare to nationals times. And besides, like you said-it's "fun science", so why not? Also good practice for next season. Gosh, Flight's fun!
coachchuckaahs,
That's actually very convenient, I have a whole tube of 1/16" bass from my bridge-building days! How do you "drill" a hole with the music wire? Do you actually stick it into a drill and use it as a drill bit? And would a hair dryer work for a "heat gun"?
Thank you so much for your help bjt4888 and coachchuckaahs!!

[coachchuckaahs]

We make a small drill with a price of mucic wire. Snap the end to be sharp, but like a chisel more than a point. Glue the other end into a scrap of 1/8" square balsa as a handle. Twist back and forth it will go right through. See the video.

The hair dryer may work but will take some time. We used this: https://a.co/d/66WHNm6

It is also handy to make tail boom adjustments, again wet the boom, bend and twist, apply heat.

The rubber does not pull the shaft through the rear pigtail. You droop through the angled part of the shaft, then slide it back so the straight part sits in the rear slot? The rubber keeps it there when it pulls back

Coach Chuck

[pumptato-cat]

Okay, thank you so much!!! That cleared everything up!

[pumptato-cat]

I'm back again with my second plane!
So, I had everything set to default(by eyeball) and on the first flight, my modified FF kit(with the tailboom) was flying happy little circles perfectly. The best flights I've ever had--smooth and stable.
Fast forward two weeks to today. Flew it, and well... no changes whatsoever and it starts turning right. RIGHT. It goes straight in the beginning, and then gradually turns right. I read somewhere that this is due to excessive washin, but I only have 1/4". This also occurs during glide tests, if that helps.
I wasn't sure what had changed, because all I did was add some weight to the nose during regionals(I flew it once at regionals and it crashed. Does that matter? Not sure.). I only flew it during regionals and made some very minor changes(added ~.07g ballast to the nose, flew on .26oz torque, and it dived to the floor).
I tried cutting off and regluing the tailboom at an increased angle, which didn't help. Seemed to make things worse.
STATS:
rudder tilt: left side is around 1/8" higher
stab tilt: left side 1/8" higher than the right(might be a bit off, I couldn't measure it in my flying site)
washin: around 1/4", 1/2" makes the plane roll nastily to the right and crash.
Everything else is FF default--might be a mistake because the tailboom makes things different? Either way, glide tests look okay.
I will PM videos to bjt4888 tomorrow morning, and anyone else who requests them.
Any ideas on what in the world happened? No loose joints before I reglued the tailboom, no AC, no all trim settings suggest a left turn, propeller has left thrust, and I'm at a complete loss as to what is wrong. I'm 100% sure that the CG/incidence i was the only thing that changed in between regionals and today.

Thanks!