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Mini Arrow doesn't fly

Mode 1

Active member
#1
Hi All,

Ran into a problem today that may have multiple reasons why my Mini Arrow didn't fly. I've flown for years so it's not a thumbs issue, it could be a "don't know what I don't know" issue... maybe the launch needs to be more forceful. No idea.

Symptoms - Multiple launch attempts that saw the plane nose down almost immediately after launch.

All preflight checks were fine.

Motor - Emax RS2205 S - 2600kv Max Thurst - 1021G

Prop - Standard 2 blade APC 6x4. installed numbers facing forward.. plenty of thrust in the right direction.

ESC - Emax 30a

CG - Was good after moving the battery as far foward as possible.

My gut is the prop or thrust angle... I'm leaning towards the prop as thrust angle looked to be fine. Another option could be the fact that as i've never flown or configured a pusher, I did something wrong. There was little to no response from the control surfaces as there was hardly any airspeed and being a pusher, no air from a prop in the nose to help.

Do pushers need special props? As I've never installed a prop "backwards" the prop blade was pretty much touching the motor.


As always, any help would be greatly appreciated.

~ Dave

Link to video of one of the launches. This was the last attempt but the previous 3 attempts ended the same way.




Pic of Prop on motor.

motor.jpg
 

Hai-Lee

Old and Bold RC PILOT
#4
The video was less than informative but I can give you a few things that you could test or do to at least get it airborne.

Firstly I cannot see the elevon deflection or throw but as a rule you will need plenty of deflection especially at low speed.
The motor thrust angle is not easy to discern but ideally it should be angled slightly upwards by a degree or two only, DEFINITELY NEVER DOWN THRUST!!!

Try launching with half or less throttle to see if it dives equally as fast or if the dive is less abrupt. If less abrupt then thrust angle is indicated.

Apart from the obvious CG/balance issues the only other thing I would recommend is to launch with a fair amount of up elevator/elevon which you can quickly lessen if required once in the air.

I re-maidened my wing today, (after replacing dodgy HK plastic servos), and it was tail heavy and the elevon settings needed to be reset but as I had the proper thrust angle it was no major issue and I flew and landed without incident. Mind you I cheat a little as I use a bungee launch system so I do not even need motor thrust to get airborne!

Just what works for me.

Have fun!
 

Arcfyre

Well-known member
#5
I had the same exact problem with my arrow. You need a little more reflex (up elevon at the neutral control position). I have much better luck with an almost vertical launch at high power. The Arrow was much more twitchy and less forgiving than the pusher Versas I've had. Heres a video of what I mean by "vertical launch". Basically grab it by the nose and throw it almost straight up, with a touch of back at the top of the throw.

 

Mode 1

Active member
#6
Hai-Lee: Thank you for the response. One of the previous launches was actually a bit less violent from a dive perspective and may have been at a lower throttle. At the end I was going all in on the throttle which may have been a mistake. However, it never once came close to "flying"

I just dug up the box the engine came in and it recommends a 4-5 inch prop.
 

Merv

Well-known member
#7

Looks to me like you don’t have enough reflex. You don’t want your elevator set at neutral, you need to have a bit of up elevator, that is reflex. Lay your wing on a table, adjusting your push rods to allow for a piece of FB to just fit under the control surfaces. I don’t know how much reflex the Arrow needs 1 layer of FB may be too much or not enough.
 

Mode 1

Active member
#8
Could a bit of reflex make that much difference? It's not like this flew "sketchy" or was hard to control once airborne. This did nothing, there was minimal, if any, response from the control surfaces. It was pretty much like tossing a horseshoe, only the horseshoe would go farther :)
 

Arcfyre

Well-known member
#9
Some reflex, and then a much more powerful launch, should really help you out. In your video you seem to almost drop it instead of giving it forward momentum. Wings need a little speed before they do anything useful.
 

Merv

Well-known member
#10
Could a bit of reflex make that much difference? It's not like this flew "sketchy" or was hard to control once airborne. This did nothing, there was minimal, if any, response from the control surfaces. It was pretty much like tossing a horseshoe, only the horseshoe would go farther :)
Yes, too little reflex can do that. It’s like having you plane way out of trim.
 

Mode 1

Active member
#11
I had the same exact problem with my arrow. You need a little more reflex (up elevon at the neutral control position). I have much better luck with an almost vertical launch at high power. The Arrow was much more twitchy and less forgiving than the pusher Versas I've had. Heres a video of what I mean by "vertical launch". Basically grab it by the nose and throw it almost straight up, with a touch of back at the top of the throw.

That's interesting. What is your engine / prop combo?
 

Mode 1

Active member
#16
Looks a little strange touching the motor bell, but as long as it all spins, I don't really see an issue.
That's what I thought too, but I've never configured a pusher so I didn't know. The first two attempts I had a spacer in there but on the first flight the prop came off during the crash. I've never had that happen before. I've broken plenty, but never had one just fall off at impact.
 

rockyboy

Skill Collector
Mentor
#17
In my experience wings need a lot more launch speed, and arrows like to have a little reflex set in the control surfaces (make the bottom of the control surfaces level with the top of the foam board at the back of the elevon).
 

Mode 1

Active member
#18
In my experience wings need a lot more launch speed, and arrows like to have a little reflex set in the control surfaces (make the bottom of the control surfaces level with the top of the foam board at the back of the elevon).
Rockboy - Thanks for the suggestion on launch speed. I thought we were ok, but it's starting to make sense we need to give it a bit of motivation.
 

SlingShot

Maneuvering With Purpose
#19
In my experience wings need a lot more launch speed, and arrows like to have a little reflex set in the control surfaces (make the bottom of the control surfaces level with the top of the foam board at the back of the elevon).
That's interesting. When I wing tip launch wings, I don't impart anything with my hand. I just guide the arc with my hand as the motor pushes through the arc.

You definitely need reflex. That's a no brainer. Also verify your cg to assure that you are not excessively nose heavy.

Are the control surfaces moving in the correct direction? Up for up.
 

lrussi750

Rogue Pilot
Mentor
#20
As others have said, you need up reflex in the control surfaces. That prop is not installed correctly. You have a quad style motor and the APC props do not fit well, the arch in the prop should not touch the motor bell. And it cannot be tightened down properly. That prop is going to fail in your current setup. I use the rs2205 2300kv motors with HQ 5x4.5 Blunt Nose props on 4s. Your arrow will be a rocket with the proper setup.
 
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