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FT Bloody Wonder Question

Cabal_se

Junior Member
#1
Hi!

I have fallen for the Bloody Wonder and now built two of them, slightly modifying the second one in an attempt to get better performance, bigger motor, prop and battery.

Even if they have flown very nicely I have one problem. Both planes is pulling up when adding more thrust. So if I give full throttle and don't compensate with elevator the will do a loop. It's alright to fly as long as you counter it with down elevator.

The question is if there is a easy enough fix when building another Bloody Wonder like angling the engine downwards, or angling the whole body in comparison to the wing. Or if it's the tail section that might not be aligned perfectly with the wing. Any suggestions are welcome, thanks!

And yes, I need to build another one since my second one disintegrated on "landing" :) Totally a pilot-error, no excuses :)
 

eagle4

New member
#2
do you have a programable radio? if so you should be able to mix in a little down elevator when you punch up the thrust. that way you can have this work for your current planes, no need to wait for the next one ;)
 

Bolvon72

Senior Member
Mentor
#4
Be strict with your COG. If you add a larger motor and compensate the weight in slow flight with elevator, hitting the gas will pitch it up sharply.
 

jhitesma

Some guy in the desert
Mentor
#5
I noticed on mine that after a few "ungentle" landings the pod no longer sits in it quite the same and now gives the motor some up thrust as a result. May want to check that that hasn't happened with yours. I was able to correct this by adding a bit of popsicle stick between the two skewers that the pod mounts to.

Worked great until the foam of the pod ripped out around the rear skewer in mid-flight causing a spectacular disintegration of my pod. I was surprised at just how well it glided without a pod...except that that meant a longer walk to retrieve it :D
 

RoyBro

Senior Member
Mentor
#6
Because this only happens when you apply throttle, I would think that programming some mix in your transmitter would be the answer. If you change the thrust angle, that gets applied all the time, even at slower speeds.
 

jrbemis

Junior Member
#7
I have built two Bloody Wonders with a rudder servo. Plan is to maiden them both. Then see if there is an interest in flying them against each other. Where do I add the hook for the trailing plastic tape on the fuse?
 

Cabal_se

Junior Member
#8
@eagle4 and RoyBro: I have a Dx6i and never thought about that option (being new to it all) but I think thats the best bet. And as you say RoyBro, if changing the angle it always apply.

@Craftydan: Missed that clip, very informative, thanks!

@Bolvon72: Thanks! Took extra care, learned the hard way with the Old Fogley that is no more :( But will definitely keep it in mind for my version 3 :)

@jhitesma: I have the same with the first version. Totally wrecked it a couple of times but it still could fly but it wanted to rise on throttle do to powerpod being all screwed up. On one last "landing" I had to rebuild the powerpod, even cracked the firewall in middle there.

@jrbemis: Also built two so I can have a friend over the fly together :)

Thanks everyone for the input, good ideas and pointers, appreciated.

I will build v3 today and tomorrow and hopefully get it into the air on Sunday if weather permit. I will tell you how it went :)
 

Craftydan

Hostage Taker of Quads
Moderator
Mentor
#9
@RoyBro

If you change the thrust angle, that gets applied all the time, even at slower speeds.
Actually I think you've got this backwards. The motor is applying a wrench (the engineering definition of Force + Torque, not the mechanic's) to the Center of Mass, causing the plane to accelerate forward and twist. the accelration we like, not so much the twist.

The typical problem this causes is that the full throttle motor will twist the plane to roll with the motor and pitch up/down (depending in where the motor is mounted). The pilot compensates while the throttle is up, then must uncompensate when he chops it (yes, a mix will automate this). The FTBW just happens to have a strong wrench from the bigger motor/prop on a high wing airframe (motor mount is below CoM).

The goal is to balance the forces/torques back into alignment. Keep in mind, the wrench is proportional to the speed of the motor - any counterbalance shold be also. Thrust angle subtly moves the motors line of force in relation to the CoM, creating internal forces/torques on the CoM to self-adjust against the wrench. Up/down angle for pitch, left/right angle for roll. When the motor speeds up, it increases the wrench, and the off-CoM thrust angle creates an opposing internal wrench that also increases. When it's set right, it's all proportional.

Now, change the prop or motor, you've changed your torque and thrust per RPM, and your angle might need to change -- probably more in l/r than u/d.


When I first saw this clip, I knew the physics involved from school, but being new to the sport I wondered why FT was going over it . . . untill it clicked that we are scratch building, not flying pre-fab, pre-trimmed planes. It's not a detail that'll make a plane unflyable (usually), but it can turn an annoying plane into a trimmed pleasure.
 
#10
@RoyBro
Now, change the prop or motor, you've changed your torque and thrust per RPM, and your angle might need to change -- probably more in l/r than u/d.

When I first saw this clip, I knew the physics involved from school, but being new to the sport I wondered why FT was going over it . . . untill it clicked that we are scratch building, not flying pre-fab, pre-trimmed planes. It's not a detail that'll make a plane unflyable (usually), but it can turn an annoying plane into a trimmed pleasure.
Makes very much sense even for one that don't have the engineering background :) Nicely put Dan!
I agree, not a detail that make it unflyable but enough to be annoying.
So, since I don't know what angle I need I better try it like they suggested in the clip (see above). Maybe using washers in order to angle the engine-mount in different directions as needed. It will work unless it needs a very large change of angle. Maybe a combination of angle and mixing in elevator with throttle?
 
#11
I too put a large motor on my Bloody Wonder because I have a genetic speed sickness. I was having the same issue with the plane climbing steeply at full throttle. so being a mechanic not a rocket scientist i started adding washer behind the aluminum motor mount until I got the results I liked. ( I think I ended up with 5 washers on top and 2 on the left side) now full throttle to no throttle she flys straight as a bullet! I'm running a 2215 1200kv on 4s with an 8x8 apc. I'm pretty sure i'm going to rip the pod out pretty soon but man this thing hauls the mail now.
I had an original Sig Wonder back in the day, piped rossi .15 my foamy is almost as fast
 
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