Flight B/C

[bjt4888]

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!

Cat,

Ideas: Is propeller hanger slightly broken away from fuselage allowing it to move to right thrust under motor tension? I saw this with my one student with the FF kit propeller setup. It looked good till we tried to wiggle it and then we saw it was loose. His loose prop hanger caused additional left thrust and too tight circles.

Other things that might have broken with Regionals dive to floor: Propeller blade might be split where it attaches to spar or split away from spar. You have to very slightly flex the blade as if trying to pry it from spar to see these cracks/splits. A split can cause the prop to over pitch during flight and then with blade stall the airplane will “wander” and/or refuse to climb instead of flying/climbing. I’ve seen this before after even a medium level floor hit. We check the props often through the season. I usually see three or four with blade splitting from spar (usually near hub) out of my 16 to 20 students each year.

Let’s see the video too.

Brian T

[coachchuckaahs]

Based on the anecdotal evidence, I have to agree with coach Brian, something is cracked.

After checking over the prop, carefully flex every part, and every joint, on the plane.

This assumes the plane still passes the static eyeball test, which you seem to indicate, that nothing is visibly out of sorts.

Being that the glue has changed too, it may be something that does not take a lot of flex to be apparent. Check for loose covering as well.

Did the glider actually change? Often the planes will not turn deadstick. I don't put a lot into glide testing, we never do it, except maybe a new plane design to get initial trim, but even then we use low winds.

The fact that it changed after a crash is important

Coach Chuck

[pumptato-cat]

Thanks everyone!!
Here are the videos(please PM for access-I'm currently sharing with Coach Brian and Coach Chuck only). Hopefully they help some.
finalglide: video of final glide test after adding ~.1g to the tail because it was nose-heavy. Drops quick-ish and turns to the right. Can provide details for ballast if needed.
lowpowerflight: plane does a weird straight-right-turn thing when it flies on low torque/winds.
fullcirclestraight: hopefully this video "processes" by the time you open the folder--this is what the plane does on 0.3oz, 66 turns. Not sure why it does the weird "straight" thing in the beginning, but it appears to have a VERY large radius? This is also with reasonable rudder offset and stab tilt. More wash-in makes it dive nastily and curve to the right.
Pictures of the plane are also attached.
I've checked the joints over several times, and I've noticed that the tailboom has a slight flex to it if you push. I don't think that's the issue, though. Prop looks fine--note that without the propeller it still likes to turn right.... No visible cracks, wing looks fine, stabilizer looks fine too, and I'm, well--flabbergasted is the only word..
EDIT: Coach Chuck, I never did glide tests with the plane before yesterday. It definitely turns right though, without rubber or the prop attacked.
I think that with high enough torque, it will make a very large-diameter left circle, but on anything lower than .3oz, it seems to wiggle and turn randomly.

[coachchuckaahs]

Cat:

Can you try with less wash in? Wash in does two things, it rolls to the right to counter prop torque, and creates drag to the left. Our design is quite different and does not use any wash, so this looks like a lot of wash to me, but I understand the short-coupled C plane requires a lot this year. I would try it with less.

It is possible, a little hard to tell, that the wing may be sitting on the MS with a slight angle to the right. This in effect gives left thrust, which is fine. Some designs, such as Bill Gowen's, incorporate this in routinely. However, it has the effect of cancelling some of the rudder offset and tail tile.

Your tail tilt appears to be minimal, I would maybe try a bit more of that too.

Check the wing tips and stab tips for straightness, that is hard to evaluate form your images.

Generally, the path the plane takes it appears something is "fighting", and the only thing that jumps out at me is the amount of wing wash. You should ONLY have enough to keep it from rolling in sharply on highest torque. Since adding more made it worse, I would reduce to see the impact on the low power circle. Then introduce just enough to keep it climbing or at least not diving at high torque.

Coach Chuck

[pumptato-cat]

Ooh, that's a good idea. I considered decreasing wash-in, but I ran out of practice time... I think at one point I did remove some shims and fly with almost no wash-in. I might be wrong, as I'm going off of memory right now, but it seemed okay--except it had trouble climbing. Any more wash-in would cause it to turn right or roll and dive. I can't fly until next Saturday(ughhh) but I'll try some glide tests at home. Thanks!!
EDIT: The odd thing is that it was flying perfectly two weeks ago with very similar settings to FF default—and with 1/2”. Not sure what happened...

[coachchuckaahs]

I have found that a well-trimmed plane under power may go in a straight line gliding or dead stick. It looked like you were accomplishing a circle with low power, though large.

I think work on tail tilt and maybe rudder offset, perhaps with less wash. Then increase power. Watch for rolling in as torque increases. If it rolls in, add wash, otherwise don't.

Be sure your cruise, low power flight, is optimally trimmed. Increase decalage until a slight stall, then back off a half mm or so. If cruise is not optimal, climb can be impacted. Any change you make, always go back to basic decalage and cg optimization for cruise before fighting climb

Coach Chuck

[Frost0125]

HI!

Is there anyway to fix small rips in mylar covering on the plane? I realized I had glued something on my plane wrong, and made the mistake of trying to detach the piece and re glue it, instead I ripped the mylar covering and was unable to detach the piece (yay!).

Any help would be appreciated. I have the materials to rebuild the ripped section entirely (start from scratch), but if I remove the wing with the broken covering I may break the entire plane.

[bjt4888]

Thanks everyone!!
Here are the videos(please PM for access-I'm currently sharing with Coach Brian and Coach Chuck only). Hopefully they help some.
finalglide: video of final glide test after adding ~.1g to the tail because it was nose-heavy. Drops quick-ish and turns to the right. Can provide details for ballast if needed.
lowpowerflight: plane does a weird straight-right-turn thing when it flies on low torque/winds.
fullcirclestraight: hopefully this video "processes" by the time you open the folder--this is what the plane does on 0.3oz, 66 turns. Not sure why it does the weird "straight" thing in the beginning, but it appears to have a VERY large radius? This is also with reasonable rudder offset and stab tilt. More wash-in makes it dive nastily and curve to the right.
Pictures of the plane are also attached.
I've checked the joints over several times, and I've noticed that the tailboom has a slight flex to it if you push. I don't think that's the issue, though. Prop looks fine--note that without the propeller it still likes to turn right.... No visible cracks, wing looks fine, stabilizer looks fine too, and I'm, well--flabbergasted is the only word..
EDIT: Coach Chuck, I never did glide tests with the plane before yesterday. It definitely turns right though, without rubber or the prop attacked.
I think that with high enough torque, it will make a very large-diameter left circle, but on anything lower than .3oz, it seems to wiggle and turn randomly.

Cat,

Sorry, I was busy this afternoon flying with a couple of my teams and just now looked at your video of the airplane fighting to turn left and the glide test that turns right. I agree with Coach Chuck, this looks very much like too much washin. Also agree with Coach Chuck, that you want just enough washin to control the left rolling tendency (you don't need to remove all roll) and just enough to give a reasonable climb rate with the particular rubber density, launch torque and prop pitch.

It could be that the "right tendency" was not as noticeable in earlier flights if you had particularly energetic motors for those earlier flights. Another possibility is that the shim (or more likely the wing saddle) moved during the crash and increased the washin. The wing saddle has a tendency to move as it is only held in place with the dental rubber bands. I'm sure that you've seen that a 1 mm movement of the shim or the wing saddle can dramatically change the washin. Once you reduce washin and get the turn the way you want it, mark the location of the shim and mark the location of the front of the wing saddle. Then inspect these every time you fly. You can also glue both the saddle and the shim to the fuselage stick with just a small amount of Duco cement to make sure they don't move on you again. Just use Duco to affix the front edge of the wing saddle and just use a dot of duco to affix the shim. If you need to readjust the saddle or shim after it has been glued, you can split it away from the fuselage with a blade, or use acetone to loosen the Duco.

So, the washin setting is so critical on these wide wing short tail moment arm airplanes, we have had airplanes stop turning or climbing correctly as the wingpost fit in the tube starts to slightly loosen over the course of the year. We fixed this temporarily by taking a shallow wedge shaped sliver of soft 1/16" balsa and slipping it into the post tube and then slipping the post in for a snug fit; and presto, the airplane was climbing and turning correctly again. It's usually the rear wing post fit in the tube that is most critical.

I'm almost positive that washin reduction will fix your issue; adjust bit by bit to retain your desired climb rate.

Brian T

[pumptato-cat]

Thank you so much bjt4888 and coachchuckaahs! I'll try some glide testing to see if the right turn goes away. I think you're right about the shift--it wasn't exactly a crash landing at regionals(like, not a dive or anything), more like a very violent shove from AC into the ground? I do think it damaged something, as the landing was far from gentle. Wish I had a video of the landing...
Frost.

Is there anyway to fix small rips in mylar covering on the plane? I realized I had glued something on my plane wrong, and made the mistake of trying to detach the piece and re glue it, instead I ripped the mylar covering and was unable to detach the piece (yay!).

Hey Frost0125! I had the exact same issue on my old plane. I tried to tear off the stab(wow, so smart) and tore two ribs and the mylar covering along with it. Bjt4888 and coachchuckaahs provided in-depth responses in earlier forums on how to fix mylar tears.

The Mylar we use on these planes is fairly thick, and well behaved. Jeff's approach works well.

We often do a slightly more complex route. We use Vaseline (very little) to stick the scrap of covering to paper. Then we trim the paper and covering with sharp scissors, so there is no exposed paper on at least 3 sides. On the 4th side, the "handle", place another scrap of paper over the handle paper, with the covering face up. Now spritz a very light mist of 3M77 above the covering scrap, and let it fall down. It does not need much.

Now remove the extra scrap of paper, and place the patch over the tear. Work it lightly in place, then peal back the paper. If you used very minimal Vaseline, it will peal back easily.

That is what we do. But Jeff's approach is much easier!

In a contest, especially with these heavy planes, we will just use a small piece of scotch tape.

Coach Chuck

[poonda]

welp i went from having way too fast of a climb to struggling to get a good climb at all
plane suffered a major break but after fixing it (even with the same prop, cg, pretty much everything) its been kind of struggling to climb

on the kind of bright side, the plane maintains altitude strangely well. it gains maybe 2 meters but can stay at the same height for like 1:30
could be because under powered; i switched from .94" to 3/32" rubber, but I feel like that change is way too small for a major impact like this

if any of the coaches or anyone has theories to why this is happening thatd be great