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Old Feb 17, 2012, 09:51 AM
R.C. Aviation Fanatic
Razors edge 29's Avatar
Canada
Joined Aug 2009
21,039 Posts
If the plane is pitching up for no reason without TX imputs then something is definately wrong!

I'm not liking this

I will be using DX6i which I know you do as well Bob; what TX are others using whom are having issues?

If the plane was loosing speed or going to slow and stalling, would the nose not go down and then into a dive or flat spin maybe? That's what my F86 Jpower POS did!


Are the fan units good and secure, thrust angle not off?

Bob

For a test

Somehow afix the aircraft on a desk, run the unit as if you were flying and record what the RX unit is doing

Perhaps do this; but also as a range test as well!
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Old Feb 17, 2012, 10:20 AM
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livonia bob's Avatar
United States, MI, Livonia
Joined Apr 2009
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Quote:
Originally Posted by Razors edge 29 View Post
If the plane is pitching up for no reason without TX imputs then something is definately wrong!

I'm not liking this

I will be using DX6i which I know you do as well Bob; what TX are others using whom are having issues?

If the plane was loosing speed or going to slow and stalling, would the nose not go down and then into a dive or flat spin maybe? That's what my F86 Jpower POS did!


Are the fan units good and secure, thrust angle not off?

Bob

For a test

Somehow afix the aircraft on a desk, run the unit as if you were flying and record what the RX unit is doing

Perhaps do this; but also as a range test as well!
As this is my first swept wing EDF model,, I don't know, I would like it to do this but if the wing tips are stalling first it may very well pitch up and not down. I think the first Sabers had slots in the wings to stop this.

My worry now is that to many of us are seeing this flight problem, whether it's the pilot or the plane it still is not good to have so many crashing for what looks like the same reason.. Now to me I think the odds of the pilot not knowing how to fly this plane might be more likely to be the cause than this many bad radios coming out at once..

So leaves us with coming up with a solution to make the plane not do this. If this is going to take changing the CG location or maybe a little washout on the tips. For me I'll be waiting for some calm weather so I can try to make the plane do what it does on it's own. Like that flip, if I can make it do it at will then maybe some how I did make it do it.. But I had the elevator set on low rate which for that flight was 75% and the elevator barely moves at this setting. I feel that if the plane was able to do that with this little travel even if I had pulled the stick back all the way,, Which seems funny that I would do that as I had just turned around and was planning on making a diving high speed pass down wind for the camera just before this happened.

How I know from flying my F-18 one time I had a bad battery that quit just minutes into a flight that should of been 4.5 minutes long that it completely fooled me as there also I was down at that end of the field making a wing over type turn around and the plane went funny on me flattened out and was then doing the wing rocking nose high descent right over a lady walking her dog. As I do sometimes make landing approaches doing this with it I just held it in this to lessen forward speed in case I was to hit them. As it was it landed right in front of her on the grass with no damage.

So if the F-86 was shutting down the motor for some reason than that could be the cause of the pitch up,, but I didn't hear that while flying it nor on the video..

When am I going to learn to test cells before making them up into battery packs?? The one that came with the plane is useless will not even charge up enough to kick off on any of my chargers one cell is really bad.. Of the two new from package Hyperion's I made up neither of them will balance out right either as both have a low cell but they will go to full 8.4v charge and then one cell drops back down.. Is this causing the RX to say low voltage stop motor and then after a fraction of a second right after the nose has pointed upwards the battery bounces back up high enough without me resetting the throttle stick and this pushes the plane into the climbing stall?? Testing here it works as it should and shuts down and stays down unless I cycle the throttle..

I don't know about most people but I wanted this plane as a windy day flier for when it's not fun to fly the Fokker or Champ or any of my other planes.. And it might of been aimed more for inside flying..

I think I'll go ahead and make up a 400mAh pack and try it,, as my worry that I wouldn't be able to hold the nose up at low speeds with the added weight seems to be wrong..
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Old Feb 17, 2012, 11:12 AM
R.C. Aviation Fanatic
Razors edge 29's Avatar
Canada
Joined Aug 2009
21,039 Posts
I hope mine isnt like this or I'll be pissed right off

I thought this was supposed to be a good flyer even without as3x? You would think that the claim of "slow flying ability" would mean it has a low and not high stall rate

I really hope these are isolated incidents
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Old Feb 17, 2012, 11:21 AM
Team Futaba
Devin McGRath's Avatar
Rochester New York
Joined Oct 2004
952 Posts
Hey guys,

From watching your videos and reading everyone's flight descriptions I believe you are encountering an issue I had while trying to low speed Harrier the F86. What I believe was happening is the wing is blanking out the elevator at a specific speed and angle of attack. To correct this I have added some ventral fins to the bottom of the fuse. RJ gritter and myself added these to our F86s at efest while exploring the flight envolope

I attached some pictures to better explain what we did. Give them a shot and take it up high to play with the low speed characteristics to get a better feel for it. I will try to take some video of mine soon.


Devin McGrath

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Old Feb 17, 2012, 11:25 AM
LiPo-Sucker & Airframe EMT
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Charlottesville, Virginia, USA
Joined Aug 2010
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Originally Posted by Devin McGRath View Post
.....To correct this I have added some ventral fins to the bottom of the fuse.
Brilliant if it works!

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Old Feb 17, 2012, 11:25 AM
Heli collector
livonia bob's Avatar
United States, MI, Livonia
Joined Apr 2009
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Quote:
Originally Posted by Devin McGRath View Post
Hey guys,

From watching your videos and reading everyone's flight descriptions I believe you are encountering an issue I had while trying to low speed Harrier the F86. What I believe was happening is the wing is blanking out the elevator at a specific speed and angle of attack. To correct this I have added some ventral fins to the bottom of the fuse. RJ gritter and myself added these to our F86s at efest while exploring the flight envolope

I attached some pictures to better explain what we did. Give them a shot and take it up high to play with the low speed characteristics to get a better feel for it. I will try to take some video of mine soon.


Devin McGrath

Sent from my Android
Gee you think that the Mig 14 had this same problem so on the Mig 15 they stuck it up on the rudder???
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Old Feb 17, 2012, 11:31 AM
Registered User
Canada, ON, Muskoka
Joined Jul 2011
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Quote:
I hope mine isnt like this or I'll be pissed right off

I thought this was supposed to be a good flyer even without as3x? You would think that the claim of "slow flying ability" would mean it has a low and not high stall rate

I really hope these are isolated incidents
Ryan, you got yours yet? I want to be there for the maiden....let me know

Glen
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Old Feb 17, 2012, 11:34 AM
LiPo-Sucker & Airframe EMT
pugsam's Avatar
Charlottesville, Virginia, USA
Joined Aug 2010
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Originally Posted by livonia bob View Post
gee you think that the mig 14 had this same problem so on the mig 15 they stuck it up on the rudder???
roflmao!

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Old Feb 17, 2012, 12:03 PM
BVM Viper Fever
pdawg's Avatar
United States, OH, Dayton
Joined Apr 2004
5,540 Posts
Quote:
Originally Posted by Razors edge 29 View Post
I hope mine isnt like this or I'll be pissed right off....I really hope these are isolated incidents
Mine flew great from the first launch. Pay attention to airspeed and AOA when you fly and there won't be a problem. It's really a very gentle airplane overall. In some of these videos it's unclear to me whether the pilot is controlling the plane or whether the plane is controlling the pilot. If the pilot gets behind the plane you can't blame the plane since the pilot isn't on top of it. Maybe it's a CG issue....?
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Old Feb 17, 2012, 12:09 PM
Registered User
United States, TN, Jackson
Joined Mar 2007
4,019 Posts
Quote:
Originally Posted by Devin McGRath View Post
Hey guys,

From watching your videos and reading everyone's flight descriptions I believe you are encountering an issue I had while trying to low speed Harrier the F86. What I believe was happening is the wing is blanking out the elevator at a specific speed and angle of attack. To correct this I have added some ventral fins to the bottom of the fuse. RJ gritter and myself added these to our F86s at efest while exploring the flight envolope

I attached some pictures to better explain what we did. Give them a shot and take it up high to play with the low speed characteristics to get a better feel for it. I will try to take some video of mine soon.


Devin McGrath

Sent from my Android
How would ventral fins prevent the wing from still blanking out the elevator???......Ventral fins will help with directional yaw stability if the vertical stab is blanked out at high AOA but I don't see them doing anything for the horizontal stab/elevator...

The larger ducted fan versions of the Sabre that I've owned didn't have this problem...On landing the Sabre elevator was very responsive even with full flaps deployed...My guess for some of the issues described here is that the plane is stalling due to too much elevator combined with a slightly aft CG placement...

Kevin
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Old Feb 17, 2012, 12:37 PM
Registered User
Indianapolis, IN
Joined Oct 2010
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Flew mine and this is very easy to stall with elevator! I did not stall it flew fine but LVC came in around 2 minutes. It flew great, vertical stab broke as expected.
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Old Feb 17, 2012, 12:39 PM
Team Futaba
Devin McGRath's Avatar
Rochester New York
Joined Oct 2004
952 Posts
In this case they are adding to stability as well as adding a lifting surface to the tail when the elevator is not being fully effective.



Devin McGrath

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Old Feb 17, 2012, 12:49 PM
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United States, MI, Livonia
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I'm going to try this first,,, I don't care for planes that use the elevator to hold the nose down I like mine to be used to hold the nose up,, that way if the elevator gets blanked out by the wing the nose will drop and pick up speed lowing the AOA and regaining flying speed and not pitch up into a stall..

On my scale stock battery is 13.47g, Hyperion 240 is 16.08g and the HK 400 is 22.78g.

Yes the canopy still fits.. CG isn't really moved that much but I'm still checking it..
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Old Feb 17, 2012, 12:52 PM
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Quote:
Originally Posted by Devin McGRath View Post
In this case they are adding to stability as well as adding a lifting surface to the tail when the elevator is not being fully effective.



Devin McGrath

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If the plane needs more lifting from the rear end it's tail heavy..
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Old Feb 17, 2012, 01:16 PM
Team Futaba
Devin McGRath's Avatar
Rochester New York
Joined Oct 2004
952 Posts
That is correct but you have to look at why it is tail heavy at that point it is tail heavy because the elevator is no longer acting like a lifting surface. The center of lift is just as important as the center of gravity. You are changing the center of lift while in flight so drasticly that you would have to add a ton of nose weight to compensate and then you have another problem. You are flying around 99.9% of the time with an airplane that is unhappily nose heavy

Also The ventral fins because of there angle in relation to the direction of flight, help to push the airplane back into its normal AOA when you have gone to far.

Please excuse my poor explanation typeing on your phone never comes across correctly.


Devin McGrath

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