Maiden flight last night, sorry no video. It was a little sketchy at first until I was able to trim. It needed a lot of up and right trim. Bad combination for a fast plane but barely kept it in the air until I could trim. I'm sure it's a build flaw on my part. I used 10x10 prop on 3s and it was fast, I couldn't resist and threw in 4s for second flight. WOW it's fast, I'm going to have to catch up to it and program some more expo and lower rates. It can slow down beautifully and landing is a breeze. If you want speed this one is it. Great job Nic.
nnChipmunk v2
- Thread starter nerdnic
- Start date
Awesome! What motor are you running again?
BridgeInspector
Flite Test Groupie
Wow! I had a maiden on my yesterday too! Mine also needed up trim(60 clicks), and I had the CG on the tail heavy side by about a third an inch from the mark. Wonder what might be going on there?
60 clicks!? Can you adjust your trim so that each click has more weight?
The requirement for up trim is sadly a side effect of me trying to correct ballooning at full throttle. I talk about it in this post.
I made improvements on my nnKi-61 and may go back and update the v2 chip once I'm happy with the results.
The requirement for up trim is sadly a side effect of me trying to correct ballooning at full throttle. I talk about it in this post.
I made improvements on my nnKi-61 and may go back and update the v2 chip once I'm happy with the results.
nerdnic said:What you're touching on is something I haven't talked about yet. So I'd like to dig in a little to talk about the flight behavior you're describing.
Ever since I started playing around with higher performance foam airplanes there was something very annoying that I noticed about ALL of them. They all climb or balloon, some dramatically, at high speeds. This is seen in every FT plane, and most of my designs, even the speed planes.
I hate this tendency.
The nnChipmunk v2 was my first real attempt to combat this behavior. I've waited until this latest design to try and 'fix' this issue mainly because I didn't fully understand the problem.
A plane that dramatically rises under different throttle settings is a sign of bad engineering, in my opinion. The goal here is to design a plane that feels and performs the same throughout its speed envelope. In a model plane this can be challenging since this envelope can cover such a huge range. Also the size of the plane plays a large roll here as well.
Some of the factors in how a plane will perform at a given throttle setting include:
-Airfoil
-Angle of attach on wing
-Angle of attach on hstab
-Thrust angle
-Size of plane
-Presence/degree of washout
-Trim
The bolded items are ones I have played around with in previous design to combat ballooning.
AIRFOIL
The airfoil design of FT planes is the main reason they all have such awful ballooning tendencies. They are flat bottom airfoils with relatively thick camber. This creates a high lift wing which tendencies are exponentially seen as speed increases. Another thing to note is that FT planes all have 0 incidence surfaces.
I've been playing around with airfoil in my last few designs, each one has had a different airfoil. I've been attempting to craft a wing that has enough lift for our scale yet perform really well at high speed.
For my v3 speedwing (which the v2 chip has) I am using a new airfoil that is based off a Clark Y. Its thickness, camber height, etc etc all were designed to try and produce a high speed, medium lift airfoil. Something that's good at all speed/throttle settings but with a slant toward speed. My designs aren't the fastest planes possible, but they sure have a wide speed envelope and cater to a wide audience.
THRUST ANGLE
This is the easiest way to mask the ballooning behavior and it's one I used with my Sonic Series nnP-39. I love this design but it balloons something terrible at the small scale. The 1000mm full size version nnP-39 doesn't have this issue as severely so this was lesson for me on how scale impacts behavior. I plan to revisit this design and fix this issue at some point.
The issue with using thrust angle is that at slow speeds the motor can overpower the planes natural trajectory because not enough air is moving over the wings. This leaves you with a plane that will pitch down on launch until it gets up to speed. Using thrust angle simply sets level flight at a given speed, but doesn't do anything to fix level flight overall.
TRIM
The on the fly adjustment of trim is one that's been used by many to correct ballooning without even realizing it. The flight impact here is similar to thrust angle except you don't get the overpower tendencies. So while it might drive a little on launch, it's not nearly as apparent as thrust angle induced dive. Others will set trim settings based on throttle input. The trade off here (at least I have noticed) is that you get a higher drag penalty. This will ultimately slow you down and rob you of hitting potential top speed.
SIZE OF PLANE
This is where airfoil kinda meets reality in most cases. A given airfoil will perform differently at different sizes. I don't know the math behind all this but I'm sure there is a some complicated equation to explain how all this works.
From my experience I've learned that the camber height of an airfoil matters a lot as you scale the wing size. I think this is something you're seeing with the enlarged v2. Though I don't think this is the main issue, I'll explain why.
For the nnChipmunk v2 I did something new. I didn't just change the airfoil, I changed the angle of attach of the wing. It actually sits at negative incidence. This is why you had to add extra up trim and ultimately 2deg adjustment on the hstab. At the 1100mm size the issues you've described are present, but not nearly as noticeable. The measurements I used were based around the design of a 1100mm size plane, not a 2200mm. What you're seeing with the sink on idle is the result of the angle of attack of the wing.
What I was hoping to achieve was a plane that needed minimal trim, little dive tendencies, and level flight at high speeds. While I feel I've gotten closer to this goal with the v2, I'm still not quite there yet. The v2 has a gradual dive on launch that requires some up trim but it doesn't balloon between 30-120 mph.
This will be something I continue to tweak and adjust as a I release future designs
BridgeInspector
Flite Test Groupie
Perhaps, it is a Spektrum DX6 and not a feature I have looked closely at changing before, but I don't think it may be necessary. I can mechanically adjust it to it's new "neutral" flight position and get my Rx trim back to zero. I can photo and measure what up elevator position I ended up with for level flight on my build and report back. Once trimmed, there was no noticeable ballooning all along the throttle range on my light-ish setup (310 watts on 4s), so I say that is a win.
This is my experience also, even at 1000w. So I am happy with the performance overall, I'm working now to reduce the amount of trim needed by building this into the hstab attack angle.
Good, this is a great motor for the money. I usually run the Tacon because it has a little more top end but it's been discontinued. I'm looking for an alternative replacement but the NTM 3548 is what I'll be suggesting in the meantime.
BridgeInspector
Flite Test Groupie
My Chipmunk v2 paint scheme in real life
Hey these planes look familiar!
Hey these planes look familiar!
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BridgeInspector
Flite Test Groupie
Great editing! I'm glad you're enjoying the v2. I'm packing up to take mine out to the field right now. Haven't flown since FF so I'm excited!
Now we can LAND!
View attachment 73795
I bought the struts for about $3,50 each at banggood.
I found that the size should be at least per strut about 1.5 x the weight of the plane. As an example, plane is ~5.5 Kg struts ar 80 Newton each but better more than less!
Hinges are beach wood in copper tube strap
3.50 is a steal for those. Looking at the page they are being used on cabinets and stuff so I'm impressed they are strong enough to hold up your bird.
BridgeInspector
Flite Test Groupie
My elevator is up about 4mm from center after trimming during maiden.
BridgeInspector
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Little more flight time and fun with the Chip!
The camera on the horizontal stabilizer was not a good idea. I checked CG but the plane did not like being on there. I was lucky to get it down safely with only a bit of pod damage to the skewer holes.
The camera on the horizontal stabilizer was not a good idea. I checked CG but the plane did not like being on there. I was lucky to get it down safely with only a bit of pod damage to the skewer holes.
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BridgeInspector
Flite Test Groupie
Thoughts on RCtimer motors?
BC3548-4 1100KV Outrunner Brushless Motor
http://rctimer.com/product-134.html
Model: BC3548-4
Motor size: Ф35*48mm
Shaft size: Ф5.0*65.5mm
Weight: 156g
KV(rpm/v): 1100
Max Power: 911W
Battery: 3-5Li-Po
Prop: 12x6/11x8
Ri(MΩ: 0.023
ESC: 70A
The motor with the mount
KV value and motor size can make to order!
BC3548-4 1100KV Outrunner Brushless Motor
http://rctimer.com/product-134.html
Model: BC3548-4
Motor size: Ф35*48mm
Shaft size: Ф5.0*65.5mm
Weight: 156g
KV(rpm/v): 1100
Max Power: 911W
Battery: 3-5Li-Po
Prop: 12x6/11x8
Ri(MΩ
: 0.023ESC: 70A
The motor with the mount
KV value and motor size can make to order!
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