Fine-tuning a Weasel
By Steve Lange
The purpose of this document is to help people get their Weasel-pro and miniWeasel set up for optimum performance.
If the plane is built to the specs in the instructions, it should fly fine. However, as is often the case with plank-style
flying wings, small fine tuning adjustments can transform a plane that flies "Good" into a plane that flies "Great!" It takes
very little effort and is well worth it.
First, let's review the recommended CG and throws for the Weasel-pro and miniWeasel.
||Low Rates (Beginner)
||High Rates (Expert)
+3/16" / -3/16"
(+5mm / -5mm)
+1/2" / -1/2"
(+12.5mm / -12.5mm)
+11/32" / -11/32"
(+9mm / -9mm)
+7/8" / -7/8"
(+22.5mm / -22.5mm)
+3/16" / -3/16"
(+5mm / -5mm)
+3/8" / -3/8"
(+10mm / -10mm)
+5/16" / -5/16"
(+8mm / -8mm)
+11/16" / -11/16"
(+17.5mm / -17.5mm)
PLEASE NOTE: CGs are measured from the foam subtrailing edge (elevon hinge line) forward.
OK, let's get started!
- Dial in the CG: Climb to altitude, trim the plane for straight & level flight, and then put the plane in a 45* dive. Let the plane dive "hands off" and see what happens.
Repeat the above steps until the plane remains in a straight 45* angle dive hands-off, and then the CG will be pretty much perfect. This holds true for all airplanes, not just Weasels.
- If it quickly pulls out of the dive without any elevator input on your part, the plane is noseheavy. Remove noseweight or add tailweight.
- If the plane increases steepness of dive (aka "tucks under") then it is tailheavy. Add noseweight or remove tailweight.
- Confirm CG Location: You can confirm the CG location via the roll test and the inverted flight test.
- Roll test: Assuming fairly high aileron rates (so that you can do at least one full roll in less than a second), try rolling the airplane. If the CG is right and you've built the plane reasonably straight, a Weasel Pro at decent airspeed with medium to high aileron rates should do a perfectly axial roll (or very, very close to perfectly axial). If it wants to barrel roll, it's probably noseheavy.
- Inverted flight test: roll inverted and see how the plane flies. A perfectly balanced Weasel Pro should fly inverted with very little forward (down) stick, assuming good lift and reasonable airspeed. If it takes NO forward stick, then the plane is probably tailheavy, and if it takes more than 1/3 forward stick the plane is probably a bit noseheavy. How much this bothers you should be dictated by the two CG tests above, and how much you like/want to fly inverted. Some people prefer their planes to be a bit more noseheavy as they tend to be more stable and predictable. I like mine really, really neutral if not a touch tailheavy. Makes things more exciting that way
- Adjust Elevator Rates: At the same time you are working on the CG, you'll probably find that your elevator rates need adjusting. This is especially so if you move the CG back a bit; this will make your plane more sensitive, and it will require less elevator throw in order to get the same response that it had when it was more noseheavy.
The easiest way to test elevator rates is the loop test:
- In decent lift, a Weasel Pro with proper CG and elevator rates should be able to do a nice, reasonably tight loop after building airspeed in a dive. If the plane has too much elevator rates, when you pull up it will nose up quickly and then hesitate, perhaps not finishing the top of the loop or doing so only slowly. That is too much elevator rates, and the hesitation is a type of stall caused by too much control surface movement. If you see this you need to reduce your elevator rates.
- Likewise, if the loop gets huge and it seems like the plane could be turning harder than it is, you need to increase the elevator rates slightly. If the CG is close to right on, you won't need to do much--I suggest increasing the rates by 1% at a time (assuming Hitec radio here) until you get a nice loop from a reasonable entry speed. I like my elevators relatively insensitive, so I don't usually get my elevator rates as high as other people (I find it makes the elevator too sensitive and thus makes the plane harder to fly smooth). Play with it until you get it "dialed in" exactly the way you like. There will be some iterative feedback tweaking related to the CG setting here.
A final note: if, when flying, you pull back the stick and see that the plane "porpoises" or "headbangs" (aka hyperstalls), i.e. you pull back and the plane's nose bobs up and down very rapidly, then you've got way too much elevator throw. This is often seen with first-time builders of the miniWeasel but is seen with the Weasel Pro as well from time to time. If you have your elevon throws set to what's recommended in the instructions and you have your CG correct, YOU WILL NOT SEE THIS. However, if you are seeing it, it's a sure sign your throws are too high.