Bushwacker Questions

Chelonian

New member
Hi, new here. I have a few questions regarding the FT Bushwacker I'm currently scratchbuilding.

Specifically, I'm wondering about exactly what "right thrust" means in context of mitigating P-factor. Does this mean the motor and prop should be facing to the right a little bit? Does it matter if I use CW or CCW props in this case?

Thanks!:)
 

Hai-Lee

Old and Bold RC PILOT
The right thrust angle is to reduce the roll effects due to "P" factor and the right is related to CCW props ONLY. If you choose to use a CW prop you MUST use a left thrust angle of the same magnitude as would be used if the angle was to the right.

A little trick if you are not sure what prop you are going to use is to have the motor mount without any side thrust and use washers or other material as spacers to ensure that the motor has the correct degree of side thrust when it is fitted. A simple advantage is that if you break a prop and the only spare you have is for the opposite rotation you can reverse the motor direction by swapping 2 wires and then swap the spacers around to give the opposite thrust angle as well.

Have fun!
 

Chelonian

New member
Well, another thing came up that I'm not quite sure about, and that is battery placement. I checked the CG using the backs of two chairs, and it seems as though to achieve the required 1.75" back from LE, I will need to place the battery rather far forward, slightly in front of the canopy. Is it normal to need the battery so far forward? The battery is 1800mah.
P6170173.JPG

If you see anything else in the photo that might be a problem, don't hesitate to mention it. Thanks!
 

Hai-Lee

Old and Bold RC PILOT
It should fly as it is but I would have a further concern based upon the supplied picture.
The wiring is external and not properly secured.

Normally the wires are not visible but this in itself is not the problem.

My concern is about increased repair bill if you crash into a tree or bush as the wires could be caught on a branch or twig and ripped out thereby require the purchase of a replacement servo or Rx.

Similarly crashing on wet or muddy ground could fill the Rx with water or mud basically ruining the Rx and requiring a replacement.

Here we do suffer from the odd bird strike or attack on our models but with the exposed wires it is possible for a bird to break a wire or even unplug a servo which is always going to give a bad result. Rather than a dent or even a hole in the FB you could end up with a major repair bill.

Finally apart from the risk of wiring damage in transport there is the simple fact that flapping wires can and do break over time due to metal fatigue and properly secured wires do not.

Just a heads up!

have fun!
 

Chelonian

New member
It should fly as it is but I would have a further concern based upon the supplied picture.
The wiring is external and not properly secured.

Normally the wires are not visible but this in itself is not the problem.

My concern is about increased repair bill if you crash into a tree or bush as the wires could be caught on a branch or twig and ripped out thereby require the purchase of a replacement servo or Rx.

Similarly crashing on wet or muddy ground could fill the Rx with water or mud basically ruining the Rx and requiring a replacement.

Here we do suffer from the odd bird strike or attack on our models but with the exposed wires it is possible for a bird to break a wire or even unplug a servo which is always going to give a bad result. Rather than a dent or even a hole in the FB you could end up with a major repair bill.

Finally apart from the risk of wiring damage in transport there is the simple fact that flapping wires can and do break over time due to metal fatigue and properly secured wires do not.

Just a heads up!

have fun!
The wires are taped down in a few places along the length of them, but I could completely cover them with packing tape if that would be helpful. The place I fly at dosen't have any water close by, but there are small puddles sometimes. The reason the wires are not inside the fuselage is because the planes I build have a rather low success rate, and I like to be able to remove the electronics easily after one fails. I'll see if I can find something that I can put over the Rx which will protect it, while remaining somewhat easily removable. I'm also really hoping that this plane works, because I have spent about 15 hours building it trying to do a good job.
 

Hai-Lee

Old and Bold RC PILOT
When I built mine I did not have any dihedral and made my wing a single piece with full span ailerons of course.
At take off I found it was a little disappointing for the wing area and it had a somewhat nose down attitude when flying. I then increased the main wing incidence by placing a "Paddle pop" stick under the wing LE, now it takes of at half throttle and at full throttle it is definitely STOL with a bit of "P" factor. Just make sure that you use around 30% expo, (Minus expo on the radio your plane seems to have installed), and you will have a nice cruiser in the trainer class.

As for the wires I just push them all inside and let them flop around inside. My servos are pushed into the holes in the fuselage and held in place with a touch of hotmelt glue. Getting my electrics out for fitting to a new plane or to replace them in the event of their failure is just a matter of removing the dab of glue and then pull them out. My Rx floats around in the fuselage under the wing. I tape the ends of my antenna leads to get the required 90 degree separation, clear of other wires. Finally I fit my 1300 3S battery in the Power pod, (against the motor mount).

Have fun!
 

Chelonian

New member
I do have some of those sticks, I think I will try adding one before I fly it. The reason I didn't want to put the battery in the power pod behind the motor was because, one, I thought that would wanted to keep the CG as low as possible with this type of plane, and two, because I feel in a crash the battery would slam forward into the motor, possibly damaging either the motor or the battery.
 

Chelonian

New member
I never knew that! I'll definitely be using that rubbing alcohol method in the future.

I do have a bit of a CG problem at the moment. I tried to put the battery as far forward as I could, but the CG is still at 2 2/3" from the LE. Do I need to add weights to the nose, or is there some way to lighten the tail?
 

Hai-Lee

Old and Bold RC PILOT
You could do any of the suggestions you have made but on mine I went and fitted big heavy wheels of a commercial variety and then a heavy spinner. Gave the plane a great look, more low down weight, (pendulum stability), more forward CG point, and allow the use of a smaller battery.

Another thing which can be done easily to bring the CG forward is to fit a spacer between the motor and the powerpod. This pushes the motor forward and improves the balance, I sometimes use a double firewall or even steel washers behind the motor to help with this. Often a little extra weight added to the prop adapter can make a large difference and to this end I have even used thick steel washers under the prop on a large and heavy prop adapter. The further forward the weight is added the more effect it has on balance. 1 ounce added to the prop adapter can be the same as adding up to 3 ounces in the powerpod.

When you lighten the tail you may suffer from more "Nosing in" but then bigger wheels help with that.

You can always move the tail servos forward, (use the cutout from the new servo position to plug the hole from the previous servo position), or even provide under fuselage cutouts in the tail boom to decrease the rear weight. You can always cover the hole made with tape to keep water and the like out!. Similarly you can cut some lightening holes in the vertical and horizontal fins and cover the holes with tape BUT be careful as the weight saved is not going to be great and the fins can be fatally weakened if you have a crash or make the holes too large.

Just a few things you can try without adding a huge amount of lead somewhere!

Have fun!
 

Chelonian

New member
I finally got the CG about right. I added another layer of duct tape on the wheels, and reinforced the nose with popsicle sticks and skewers. I then covered that in gorilla tape, and that made the CG almost perfect. The AUW is now 700 grams. Hopefully that isn't too much?
 

Hai-Lee

Old and Bold RC PILOT
A little weighty but not excessive. Actually a bit of weight is good for handling in those slightly windy conditions.

Post how your maiden goes!

Have fun!
 

Chelonian

New member
Just got back from flying it, things overall could have gone worse I think.

Because of course none of my flights can be without their signature issues, the motor decided for no reason to just not spin. It made the little startup beeping noises as per usual, but when throttle was applied, it did nothing. I had tested everything right before I left the house, and it was working fine. I unplugged and re-plugged the battery, and this time it worked. This made me a little worried that it would shut off in midair, but I chose to proceed anyways.

It taxied nicely, and since I had never had a plane with landing gear before, I had a bit of fun driving it around. I then decided to take off, and it jumped up off the ground VERY easily, so that was a nice surprise. In the air, the plane flew, but not exceptionally well, In fact, it flew rather badly. It still seemed tail heavy to me, but I don't really have enough experience to know for sure. I don't entirely know how to describe the way it turned, but if I had to sum it into a few words, they would be "lazy, jerky, lumbering". The thing that made me think it was tail heavy was that whenever I gave it more than about 70% throttle, the nose would pitch up sharply. The thing that made me think it's NOT tail heavy is the fact that if I tried to glide it, the nose would pitch down significantly.

I then attempted to land it before anything went wrong, and it did land fairly gently, but the landing gear still broke. This I'm guessing was because because I used aluminum chain-link fencing ties instead of music wire, simply since that was what I had on hand. It wasn't completely broken, just a little bent, so I wanted to try flying it again. It had just taken off, when all of a sudden the motor died again. The plane landed roughly, finishing off the landing gear. Why is the motor doing this? It's an almost brand new Gforce E400 1250KV motor in case that helps. I then had someone hold the plane (with the prop away from them of course) while I tried giving it throttle. I tried giving it 100% throttle, and the speed of the motor was in no way constant. It was sort of pulsing in a rhythmic fashion. It seemed like whenever it got to 100% throttle it would drop back down to about 50%. I lowered the throttle, then returned it to 100%, and this time around, it seemed fine. I really don't understand what would be going on here.

While writing the part about the pitch instability being seemingly linked the the throttle input, I thought of another possibility. Could it be that the motor's thrust angle is too high? Should I make it point down a little?

I'm unsure if I should attempt another flight until the motor issue is resolved.
 

Hai-Lee

Old and Bold RC PILOT
Where do I start?

Firstly a good cheap source of spring wire that you can use for landing gear is the wire used to hold the cheap plastic hubcaps on the wheels of cars, (normally they litter the side of busy roads here). Just straighten it before you bend it.

the Flying tail heavy might be CG related so bring the CG a little further forward before the next flight.
The rearing up on throttle could be thrust angle related, (need more down angle).

Another cause of an apparent tail heavy with throttle and nose heavy without throttle can be the incidence angle of the main wing. Try fitting a spacer, (paddle pop stick), under the rear of the wing where it mounts on the fuselage. With a wing pointing slightly upwards the extra lift generated when you open the throttle will cause the plane to climb and without throttle it will want to glide with a slightly nose down attitude for less drag. With the CG correct there is a tendency for the plane to drop its nose if you fly too slow, when the wing is pointed upwards it slows the wing down, drops the nose slightly and builds up a bit of speed to maintain this attitude.

If the motor is undamaged and you have calibrated the ESC correctly it might be, (and sounds like) either you have a timing issue with the ESC or even possibly a winding issue with the motor.

As for the Lazy, jerky, and lumbering it will tend to be if the glide can only be maintained at low speed and if the throttle has an effect on the flying attitude. With a SF prop there will always be control and acceleration from slow flight but do not expect a rocket because the SF prop runs out of thrust as the speed gets higher.

Perhaps try altering the wing incidence and try again!

Have fun!
 

Chelonian

New member
I have tried calibrating the ESC a few times, and I'm never really sure if I'm doing it right. It just keeps on making beeping noises, and it seems like it just keeps looping around forever. I'll see if I can find a guide for how to do it properly somewhere.


I'll try changing the incidence angle of the wing, if that dosen't work I'll go from there. Thanks!
 

Chelonian

New member
I added a paddle pop stick under the wing, and tried flying it again.

I decided to do some more troubleshooting with the electronics by bringing it to the baseball field to have a nice open space in case anything went wrong. I did a whole bunch of taxi runs up and down the basepath, and it seemed to be working perfectly. And since I was already at the field, I chose to give it a little test flight since the electronics were working pretty well. It still didn't fly great, so I landed it pretty quickly before anything bad happened.

I then decided to remove the small amount of uptrim I had on the elevator. I took off again, and the difference was immense. It now did not fly with a nose up attitude at all, in fact it seemed just about right. Then I got a little disoriented, and landed to plane to avoid a crash. I decided to try one more flight, and this time right before I took off, the motor began to make a short beep about every second. I wasn't sure what this was, but it stopped after about 20 beeps or so. I probably should have seen this as a warning, but I didn't, and tried to take off anyways. This time, before it even left the ground, the motor speed dropped significantly.(I I had to guess, I'd say I was about at 70% throttle, and it dropped down to about 30) I immediately cut the throttle when I realized it had slowed down, but the motor didn't stop. It kept on driving down the basepath. It wasn't going that fast, so I ran after it, picked it up, and unplugged it. I haven't tried turning it back on yet, but I certainly won't have the prop on when I do.

Having the motor randomly turn off is one thing, as long as I'm somewhat high up, I can glide it in for a reasonable landing, but having it not turn off? That does not sound fun to me. I can think of a lot of cases where that could be very bad.

Since the short frequent beeps kind of sounded like an error message, I looked up the manual for the ESC I use and I found some things that seem like possibilities for what is going wrong.

From the ESC's manual (under "protection features"):

"Over-heat protection: When the temperature of the ESC is over about 110 Celsius degrees, the ESC will reduce the output power:

^This seems possible, but I think if it had become that hot, I would have been able to smell it. It also does not explain why I was unable to stop the motor.

This excerpt from the manual seems more likely:

"Throttle signal loss protection: The ESC will reduce the output power if throttle signal is lost for 1 second, further loss for 2 seconds will cause the output to be cut-off completely"

^This one does seem a lot more likely, but the throttle was certainly stuck for more than two seconds, so I'm not sure why it didn't stop the motor after the two seconds went by. Also, why would I have lost signal? I was <20' away from the plane when it happened, and I had recently done a range test, and it worked fine at the 400' that I tested it at. The radio system I'm using is the fs-i6.

Also, the ESC's manual does have a section on calibrating, I'll try to do it, but it looks pretty complicated.

Here's the link to the instruction manual if you want to take a look at it:
https://www.valuehobby.com//media/wy...PDF/GFORCE.pdf
 

sprzout

Knower of useless information
Mentor
I'm not sure about your motor wiring, because I can't see how it is, but let me throw something at you that happened to me with my first soldering job on my MiG-3.

When I soldered on the 3.5mm connectors from the motor to the ESC, I left gaps in the shrink tube. What I should have done was taken it all the way up to the top of the female port, and to the base of the male port. That way, there was no metal exposed when the connectors were plugged in.

When we first maidened the plane, I got about 2 feet off the runway and lost all power. The plane came down pretty quick; fortunately nothing broke. When we got over to it to see what happened, the plane was jerking and making beeping noises at the ESC. We took a look to see if something had gotten fried, and that's when we noticed that the connectors for the ESC and the motor were making contact. Disco'd the battery, brought it home, and re-covered the ends, leaving no further spots of metal exposed. No problems with that ESC and motor after that...Not sure if that's going on, but I'd definitely check your solder points and make sure there's nothing where there could be a possible connection for a short, either at the ESC/battery join, or the motor/ESC connectors. It may be completely fine, but I'd want to check just to eliminate it as a possibility...Also, wiggle the battery connector at the ESC. You may find one of the battery pins for the connector is "funky" and something's not working at certain connection points, exacerbated by wires shifting around.