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*Unofficial* FT Goblin

CapnBry

Well-known member
Took a lot of reflex to get it to stop dropping. The bottom of my Elevon is about a foam board width's above the top of the wing.
Oh, we've all had our fun with needing to add more reflex.

Did you end up with any good mods for reorganizing the insides? My biggest (minor) complaint with the design is how it splits all the free space inside in half, with some on top of the nose area and some on the bottom, then there's some space above the wing and some below.
 
Just took mine out for its maiden (after waiting impatiently for it to be delivered from the US). Damn was it squirrelly, bobbing about all over the place. Brought it down, added D/R and expo, didn't help at all, now it's in three pieces (counting the nose peice). Anyone had similar experience? Will some reflex sort it out?
 
Just took mine out for its maiden (after waiting impatiently for it to be delivered from the US). Damn was it squirrelly, bobbing about all over the place. Brought it down, added D/R and expo, didn't help at all, now it's in three pieces (counting the nose peice). Anyone had similar experience? Will some reflex sort it out?
How squirrelly was it? If it kept wanting to pitch down then it probably needs more reflex. If it was pitching up or all over the place then it may be your CG. I will say that I run mine with a cheap Omnibus flight controller running iNAV and it does fly a ton better with a little stabilization.
 

Hai-Lee

Old and Bold RC PILOT
Just took mine out for its maiden (after waiting impatiently for it to be delivered from the US). Damn was it squirrelly, bobbing about all over the place. Brought it down, added D/R and expo, didn't help at all, now it's in three pieces (counting the nose peice). Anyone had similar experience? Will some reflex sort it out?
The one thing hardly ever mentioned is how to properly set up a flying wing for optimum performance and stability. Just doing an Elevon mix and adding some reflex may help get it in the air but it could still be far from a pleasant experience.

After balancing the plane as per the instructions and implementing the mix there are a few further steps that will improve your flight experience. For a plank type flying wing the standard mix does not allow for the short coupled nature of the elevator function and so you either have a bird that maneuvers well in pitch and poorly in roll or good in roll and far too sensitive in pitch. If this is part of your problem then you will need to alter the standard elevon mix ration from 50:50 to something like 60:40 where the lower proportion is the elevator function.

Expo is recommended strongly with around 30% a good starting point though if a relative beginner then perhaps 40% may be a better starting point.

After setting up the mix ration you will need to fly the bird, (high enough for safety), and do a stall test by cutting the throttle and bringing the elevator input to maximum. If at stall the bird becomes directionally unstable and even drops a wing and dives then the CG is too tail heavy, whereas if the bird starts to drop its nose and then the nose suddenly rises only to fall and rise again in a rapid nodding fashion the bird is too nose heavy. Ideally the bird should settle into a flat and slow decent with full roll control maintained.

After fine tuning the balance point then you can adjust your reflex to obtain stable level flight. If it nose dives when you centre the controls you need more reflex and if it noses up or climbs you require to reduce the reflex . Do all adjustments finely. NO sudden and massive adjustments.

When you have finished fine tuning the set up you will find that you end up with a very nimble and stable bird which can really perform and yet is almost impossible to stall on landing.

IF you increase the weight of the bird, (fit larger batteries or add FPV gear) then you may need to adjust the reflex to compensate or it will tend to drop its nose or sink when you centre the controls in level flight. (More reflex means greater AoA and therefore greater lift).

I hope the brief outline of a decent setup helps in taming its performance for you!

Have fun!
 
Hai-Lee,
Great info, I didn't see your response before sending mine.

dogflight,
1. D/R and Expo helped. My rates were too large to start with. I normally like a lot of elevon movement in the event I need it during slower flight; however, my Goblin flew a lot better with less roll rate.
2. I needed more reflex than the template had in the plans. I almost hit the ground on maiden.
3. I was able to move the CG back about 1 cm. My Goblin flies better this way. I was also able to reduce the reflex slightly.

If it was squirrelly and bobbing that sounds like the CG may be too far aft making it pitch sensative.

Good luck, the Goblin has been one of my favorite planes to easily chuck in the car and fly a couple batteries. It is really fun on light wind FPV missions or flying with other planes.
 
The one thing hardly ever mentioned is how to properly set up a flying wing for optimum performance and stability. Just doing an Elevon mix and adding some reflex may help get it in the air but it could still be far from a pleasant experience.

After balancing the plane as per the instructions and implementing the mix there are a few further steps that will improve your flight experience. For a plank type flying wing the standard mix does not allow for the short coupled nature of the elevator function and so you either have a bird that maneuvers well in pitch and poorly in roll or good in roll and far too sensitive in pitch. If this is part of your problem then you will need to alter the standard elevon mix ration from 50:50 to something like 60:40 where the lower proportion is the elevator function.

Expo is recommended strongly with around 30% a good starting point though if a relative beginner then perhaps 40% may be a better starting point.

After setting up the mix ration you will need to fly the bird, (high enough for safety), and do a stall test by cutting the throttle and bringing the elevator input to maximum. If at stall the bird becomes directionally unstable and even drops a wing and dives then the CG is too tail heavy, whereas if the bird starts to drop its nose and then the nose suddenly rises only to fall and rise again in a rapid nodding fashion the bird is too nose heavy. Ideally the bird should settle into a flat and slow decent with full roll control maintained.

After fine tuning the balance point then you can adjust your reflex to obtain stable level flight. If it nose dives when you centre the controls you need more reflex and if it noses up or climbs you require to reduce the reflex . Do all adjustments finely. NO sudden and massive adjustments.

When you have finished fine tuning the set up you will find that you end up with a very nimble and stable bird which can really perform and yet is almost impossible to stall on landing.

IF you increase the weight of the bird, (fit larger batteries or add FPV gear) then you may need to adjust the reflex to compensate or it will tend to drop its nose or sink when you centre the controls in level flight. (More reflex means greater AoA and therefore greater lift).

I hope the brief outline of a decent setup helps in taming its performance for you!

Have fun!
Hai-Lee, great info thanks, had no idea about mix ratios, will definitely give it a go. This is the first flying wing I've made that I've had issues with and I suspect, on reflection, that the CG marked on the plans is quite close to the centre of lift, not leaving much room for error. I'll repair it this weekend and have another go with mix ratios, reflex and cg.
 

Hai-Lee

Old and Bold RC PILOT
Hai-Lee, great info thanks, had no idea about mix ratios, will definitely give it a go. This is the first flying wing I've made that I've had issues with and I suspect, on reflection, that the CG marked on the plans is quite close to the centre of lift, not leaving much room for error. I'll repair it this weekend and have another go with mix ratios, reflex and cg.
Please do not forget the fine tuning of the balance point/CG or even the most careful build might end up with a flying pig due to small weight variations in the FB and the amount of glue you use!

Have fun!
 
This is my second goblin I wanted to try a larger span this one is a full meter. I also added vortex generators. This will fly with a 2205 redbottom motor and a 2200 3s battery. I am hoping for some longer flights with the added wing area
Did you just scale up the plans x% until the wingspan was about a meter?
 
New FT Forum member. I’ve been flying the Nano Goblin and loving it, but not liking the issues I have with INAV. It flies wonderful with just my thumbs. Anyway, I’m about to order an FT Goblin for “extended” flight times. Let me know if I’m crazy here... thinking about using twin prop 2204/2300kv motors with an RMRC 3s li ion 3200 (18650 battery), 200mw or 400mw vtx with mad mushroom. My 2204s draw max 9 amps with an apc 5x3 bullnose. Per RMRC the Li ion packs can handle max continuous current of 10 amps. Might even be able to fit a second battery pack in parallel for stupid time. My 2s li ions seem to work fine with those motors and esc’s. Of course motors on wings, place vtx/antenna where motor mounts to offset weight. This would be a gentle flyer, no stunts. Then get a second one and use my Red Bottom 2205 for a rocket. Thoughts? What issues do you see with props in front of the wings?
 

donalson

Active member
what issues are you having with INAV?... honestly the NG is one of the most efficient flying planes around... I don't know how going to the FT goblin is going to help things for long flight times compared to what you've already got...

for the motors setup are you thinking of doing nacells or something and mounting them on the wing? if so it sounds like fun... but I'd be more likely to do that with the VAS ghost 22"

for the goblin I say 100% build one as a screamer... but I know that mine is just balancing (no FPV gear) with a 3s 2200mah and a 2205 motor
 
Donaldson, I should have clarifies why the FT vs the Nano Goblin. Here in North Texas we average 14-15 mph winds. With the Nano, I just get blown around a little too much especially when flying higher than 50-75 feet. When flying into the wind it sometimes struggles pretty bad. I was thinking that a little heavier plane I might cut the wind better. I have a fully functioning large Sky Hunter but it’s hard to move around. A medium size/weight plane would be easier to take in the car. That was a big reason for going with the Nano. Funny, I did actually look at the VAS Ghost but not sure it can handle the weight of a 1.3 system and handle the wind. I have a couple of VAS planes and love them.
As far as INAV, the issue is likely the board, mini f405, even though it’s calibrated and all shows proper working when hooked up to the computer, rth and horizon send it straight to the ground. I just downloaded the new firmware and hope to get a retest flight this weekend.
 
Well, I have won’t connect to th board. Tried several times through the day. Even restarted the computer/firmware. Think the board is bad. Grrr
 
Back to INAV, on INITIAL setup, you will need to ensure that all your channels are are towards the right when in the receiver tab, with the sticks both up and to the right. If that is not the case, as it was not for me, I has to reverse two channels in my transmitter. That is step number three in the Github INAV wing instruction. I did not do that when I first setup INAV. I reversed the channels in INAV only to get the controls surfaces to move correctly in manual mode. When I would switch to Acro the controls were reversed.
 

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