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Mini Arrow Too Far Aft CG

#21
Update.... I just got back this evening from a business trip and went right to my 3D printer and printed a flush motor mount. I installed it, checked the weight and balance, and now instead of needing 50g of weight in the nose, I now only need 48g :(:(. The 3D printed motor mounts eliminate the foam board power pod, and weighs 13g. The other motor mount that stuck out a bit weighed 15g. Both probably weigh a bit more than the 3/16 recommended piece of wood. The only other thing different is that I'm using 9g metal gear servos weighing 13g each vs. the recommended 5g servos weighing 4g each each. I can understand adding maybe 20-25g in the nose but just can't understand why each time I build one it's so blasted tail heavy. With 6 other real airplanes to fly, getting this one to fly right is now just a matter of principle. LOL.
 
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Keno

Well-known member
#22
Update.... I just got back this evening from a business trip and went right to my 3D printer and printed a flush motor mount. I installed it, checked the weight and balance, and now instead of needing 50g of weight in the nose, I now only need 48g :(:(. The 3D printed motor mounts eliminate the foam board power pod, and weighs 13g. The other motor mount that stuck out a bit weighed 15g. Both probably weigh a bit more than the 3/16 recommended piece of wood, so I can understand adding maybe 20-25g in the nose but just can't understand why each time I build one it's so blasted tail heavy. With 6 other real airplanes to fly, getting this one to fly right is now just a matter of principle. LOL.
Hey, you joined the world of model R/C plane building. Tail heavy is our worst friend. Don't forget that on the Mini Arrow the CG and elevon reflex set is related. Once you have these two in "balance" you will be rewarded. This assumes that the wing is not warped or constructed incorrectly. On wings always be ready for UP elevon on first launch otherwise an immediate hard landing could necessitate repairs or rebuild. Like to see a pix of your 3D flush motor mount. Happy flying.
 
#23
Hey, you joined the world of model R/C plane building. Tail heavy is our worst friend. Don't forget that on the Mini Arrow the CG and elevon reflex set is related. Once you have these two in "balance" you will be rewarded. This assumes that the wing is not warped or constructed incorrectly. On wings always be ready for UP elevon on first launch otherwise an immediate hard landing could necessitate repairs or rebuild. Like to see a pix of your 3D flush motor mount. Happy flying.
Thanks Keno! I plan to go out to the field tomorrow morning and give it a shot. Here is the link for the flush motor mount https://www.thingiverse.com/thing:2060678
 

Bricks

Master member
#24
I have not built the Arrow but have built a few of the Blunt Nose Versa`s and even with keeping everything as far forward as possible each one I have had to add at least 2 ounces of weight to the nose, Just the way wings are.
 

Merv

Legendary member
#25
just can't understand why each time I build one it's so blasted tail heavy.
A nose heavy plane flys poorly, a tail heavy plane fly’s only once. Flying wings are very sensitive to CG. Like @Bricks, I have not built an Arrow, I have build many Versa’s, which also struggle with CG. I have found that you have to move everything as far forward as possible to get the CG correct. I don’t use any nose weight but I have moved my motor forward about 3 inches from the stock position.
 

SlingShot

Maneuvering With Purpose
#26
Update.... I just got back this evening from a business trip and went right to my 3D printer and printed a flush motor mount. I installed it, checked the weight and balance, and now instead of needing 50g of weight in the nose, I now only need 48g :(:(. The 3D printed motor mounts eliminate the foam board power pod, and weighs 13g. The other motor mount that stuck out a bit weighed 15g. Both probably weigh a bit more than the 3/16 recommended piece of wood. The only other thing different is that I'm using 9g metal gear servos weighing 13g each vs. the recommended 5g servos weighing 4g each each. I can understand adding maybe 20-25g in the nose but just can't understand why each time I build one it's so blasted tail heavy. With 6 other real airplanes to fly, getting this one to fly right is now just a matter of principle. LOL.
I'm betting that you surprise yourself. The Mini Arrow is a great flyer, and for a foamy has nice mass.
 

Hai-Lee

Old and Bold RC PILOT
#27
I totally disagree with the statement that the CG/Balance point and the setting of the reflex setting are related.

With a wing which is properly balanced the reflex is applied to provide a balance of forces so that the wing will fly in a stable and predictable manner. The pressures to be balanced are wing lift, weight, and the positive pressure generated by the reflexed elevons.

The acid test of the proper setup of your wing is at stall, (with full up elevon)l. If your wing is nose heavy it will drop the nose, pick up speed and then raise the nose again, (I call it nodding). Properly balanced the wing will maintain level attitude and sink in a controlled manner at a uniform rate. If it is tail heavy the wing wing lose its directional stability and it will wander from side to side before one wing just drops and the wing heads towards the ground vertically.

Sure you can use Excess reflex to counteract poor balance settings but the performance will be adversely affected. A properly balanced wing is a beautiful handling machine but can be a little sensitive in pitch for the Newbie. I have supplied wings to all of my local club members and showed them how to balance them as well as set up the radio systems. We even have newbies flying wings setup as I described above and all LOVE THEM now they can set them up properly. Heck we even have massive melees/dogfights on a regular basis!

As for bringing the motor further forward you could try cutting away small length of the electronics housing/fuselage on top of the wing, raise the motor slightly to be above the wing bottom surface and design a new mount to allow the motor to be mounted with the entire motor CAN above the wing lower surface, Sure it will be noisier but the balance will be a little better!

Just my opinions of course!

Have fun!
 

Mode 1

Active member
#28
Hey, you joined the world of model R/C plane building. Tail heavy is our worst friend. Don't forget that on the Mini Arrow the CG and elevon reflex set is related. Once you have these two in "balance" you will be rewarded. This assumes that the wing is not warped or constructed incorrectly. On wings always be ready for UP elevon on first launch otherwise an immediate hard landing could necessitate repairs or rebuild. Like to see a pix of your 3D flush motor mount. Happy flying.
"Assumes the wing is not warped or built incorrectly" - I built my first arrow inside out (folded the wings the wrong way) and it flies incredibly well. It probably shouldn't, but i'm not complaining :)

Onboard my "not built correctly" Mini Arrow
 

Keno

Well-known member
#29
"Assumes the wing is not warped or built incorrectly" - I built my first arrow inside out (folded the wings the wrong way) and it flies incredibly well. It probably shouldn't, but i'm not complaining :)

Onboard my "not built correctly" Mini Arrow
I have seen worst flying fine. On the Mini Arrow and all of FT's flying wings I have found FT's placement of the CG well placed. Just make sure your plane is not tail heavy (Nose should slightly tend to drop). My experience with wings maiden is just be ready to apply a bit of up elevon or you may land early. It could be the guy who chuck it or the pilot not getting finger on the stick fast enough. A second launch can prove successful. If you build with care to minimize building mistakes, maidens flights have a better chance of success. Anything will fly if you can get into the air with enough power, time, and skill. Heck, I have seen Snoopy on his dog house , witch's on a broom, Harry Potter and somethings we will not speak of here fly. I think Denny H. now has a clear under standing of the issue, I just hope that Denny H. has found his reward in flight of his FT Mini Arrow. Fly happy.
 
#30
I brought the Arrow out to the field last week with all 48g of weight in the nose. It flew squirrely for about 15 seconds, then took a "dirt nap". I give up on FT designs that don't allow enough room to move the battery to adjust the CG. I have flying wings that fly great, so I know what to expect with them. I since built an Avro Vulcan Bomber and it flew perfect (and fast) on the maiden flight. I'm having a blast with it!! http://modelaviation.com/avrovulcan
 

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#31
I totally disagree with the statement that the CG/Balance point and the setting of the reflex setting are related.

With a wing which is properly balanced the reflex is applied to provide a balance of forces so that the wing will fly in a stable and predictable manner. The pressures to be balanced are wing lift, weight, and the positive pressure generated by the reflexed elevons.

The acid test of the proper setup of your wing is at stall, (with full up elevon)l. If your wing is nose heavy it will drop the nose, pick up speed and then raise the nose again, (I call it nodding). Properly balanced the wing will maintain level attitude and sink in a controlled manner at a uniform rate. If it is tail heavy the wing wing lose its directional stability and it will wander from side to side before one wing just drops and the wing heads towards the ground vertically.

Sure you can use Excess reflex to counteract poor balance settings but the performance will be adversely affected. A properly balanced wing is a beautiful handling machine but can be a little sensitive in pitch for the Newbie. I have supplied wings to all of my local club members and showed them how to balance them as well as set up the radio systems. We even have newbies flying wings setup as I described above and all LOVE THEM now they can set them up properly. Heck we even have massive melees/dogfights on a regular basis!

As for bringing the motor further forward you could try cutting away small length of the electronics housing/fuselage on top of the wing, raise the motor slightly to be above the wing bottom surface and design a new mount to allow the motor to be mounted with the entire motor CAN above the wing lower surface, Sure it will be noisier but the balance will be a little better!

Just my opinions of course!

Have fun!

Thanks Hai-Lee. That's some very good information that makes perfect sense!
 

SlingShot

Maneuvering With Purpose
#32
I brought the Arrow out to the field last week with all 48g of weight in the nose. It flew squirrely for about 15 seconds, then took a "dirt nap". I give up on FT designs that don't allow enough room to move the battery to adjust the CG. I have flying wings that fly great, so I know what to expect with them. I since built an Avro Vulcan Bomber and it flew perfect (and fast) on the maiden flight. I'm having a blast with it!! http://modelaviation.com/avrovulcan
Try a Goblin. Works with the same motor and has plenty of room. I added 14 gms of nose weight to make things easier for me. Flies great. Mine wanted more than a 6x3 prop though.
 

makattack

Winter is coming
Moderator
Mentor
#33
My mini arrow has fpv gear mounted (board cam in the nose and vtx and antenna in one of the equipment bays.) It balances out without additional nose weight. I also have a fairly light 2204 motor on it and the 5g servos.
 

Merv

Legendary member
#35
I give up on FT designs that don't allow enough room to move the battery to adjust the CG.
I'm glad you are having fun with your Avro Vulcan Bomber.
I would encourage you to not give up on FT designs. How much glue you use and the weight of your electronics have a large impact on how easy it is to balance a plane. Use FT plans as suggestions, mod them to fit your equipment and building style.