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Old Mar 10, 2011, 10:00 PM
Drifting off the reservation..
JumpySticks's Avatar
USA, LA, Broussard
Joined Jan 2011
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Oh, and I just remembered. The FPV fellow (Morpheus?) in England, flying in the fog, experienced a similar loss of control in a dive and planted his plane. Most likely moisture on the electronics, but also maybe all the camera gear hanging out caused forward cg and/or turbulence on the stab.
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Old Mar 10, 2011, 10:25 PM
The "Foaminator"
mikeruth's Avatar
United States, CA, Los Angeles
Joined Mar 2007
2,134 Posts
Quote:
Originally Posted by JumpySticks View Post
There have been real (and probably some model) planes which have had to be redesigned because the elevator tended to be involved in turbulence at certain speeds and angles of attack. The turbulence is generated by the wing, and results in the loss of laminar flow across the stabilizer....a stall of the stabilizer. That's another possiblility. Been a long time but I thought that it was seen more in T-tail planes, with the stab mounted atop the vertical fin.

Looking at the RP, the camber of the wing, it seems likely that the normal flow of air behind the wing is downward enough that tubulence in normal flight would pass below the stab. The turbulence may pass above the stab too, but it does not matter. At some angle of attack, the turbulent section will pass over the stab. At higher speeds, and at a certain angle of attack the deflection of turbulence may be cancelled enough by the airspeed to allow the turbulent section of air to flow directly across the Stab and stall it. If such a condition is bad enough, neither up or down elevator has an effect and the stab gets trapped in the "vacuum". I can imagine how a roll might result in enough twist in the turbulent flow to allow the stab contact with some non-turbulent flow, allowing for a recovery.

May be worth testing with some brightly colored streamers and a fly-by to see where the airflow is.

This example of stab stall was due to flap turbulence.

Edit: This article says that stabilizer stall may be caused by a CG too far forward (look about halfway down the page for "Operations At Forward CGs...
").

I'm just speculating of course, offering another possible explanation.
Always impressed with your knowledge and research.

the turbulance strikes me as a real possibilty. And the Down elevator attempt mentioned also interest me.

Next time I have an EZ out I'll give it a try.

Mike R
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Old Mar 10, 2011, 10:54 PM
Drifting off the reservation..
JumpySticks's Avatar
USA, LA, Broussard
Joined Jan 2011
2,296 Posts
Thanks Mike.

These forums are a great place to share experiences and to learn from others around the world.

Off topic, but events in the world lead me to believe we are really at a crossroads, and will never again be satisfied with what I call "the one way media". "Communication" is by definition two way.

I believe this "communication revolution" will lead many people to freedom.....a brave new world, and it's a great thing!
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Old Mar 10, 2011, 11:17 PM
Drifting off the reservation..
JumpySticks's Avatar
USA, LA, Broussard
Joined Jan 2011
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Duplicate post...wasted electrons.
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Old Mar 10, 2011, 11:18 PM
Drifting off the reservation..
JumpySticks's Avatar
USA, LA, Broussard
Joined Jan 2011
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It seems that stab stall is a hot topic among airline pilots.
The most common causes I can see there are icing, flaps or CG too far forward. The main recommendation is to retract flaps.
Perhaps folks are deploying flaps at high speed, either intentionally or by accident? I know I accidentally hit the crow switch on about every fifth launch.:
Anyway, if interested in the subject, check out this airline pilot forum discussion. And while there, check out the avitar of this guy..rickair7777 near the bottom of the first page.
A long video, mainly dealing with icing but lots of info about tailplane stalls and recovery.
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Old Mar 11, 2011, 12:54 AM
Gravity is patient............
Joined Mar 2006
1,908 Posts
I'm never going to remember all of these glider functions in my radio. lol

Who knew that flying something unpowered was so darn complicated? I've got a V22 Osprey that was easier to set up lol.
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Old Mar 11, 2011, 02:23 AM
Dixie Normious
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Can A da....Ehh!!
Joined May 2010
5,396 Posts
Quote:
Originally Posted by harrye View Post
Guys,

Just finished my "scratch built" RP so I'd thought I'd post a few pics.

All the paint is rattle-can Krylon Fusion. AUW with 1350mAh battery is 31.55oz.

Might consider plug-in wing connectors in the future after I see how long it really takes to rig her in the field.

Components: 4X HTX 900 Servos, Turnigy Plush 30A ESC, 2x HT65's, Turnigy 35-36C 1100KV motor with Sotog motor mount, Orange RX rcvr with remote satellite, .375"OD hollow carbon spar from ACP.

Haven't put the watt meter on the motor yet, but I'm guessing about 20 amps with the stock prop.

I was going to use my Futaba 9C, but decided to try the DX7 programming..not too bad as far a basic "full house" functionality goes. Thanks to Chuck T for his excellent DX7 programming vid!

Maiden in a few day as the WX improves.

:harry
Nice build .
So how much was the total?
Im running the OrangeRX Plus Satellite as well No complaints yet!! No Brownouts,No Loose plane in a horror dives. I have went too a Alt of ...Ahhh i cant see/pick out which way im going!!! (Its not the greatest feeling)

I would stretch that Satellite out too the nose/Esc area. The further a Satellite is from the RX the better. If you look in-under where your Battery sits,there is a little tunnel/gap. I ran my throttle lead from the ESC to RX plus the Satellite wire.
Also mount your Satellite so the wires are perpendicular to your RX wires.
Like this.

http://www.spektrumrc.com/Content/Im...eflection2.png

Also i cut this little block out of the Wing area for the extra wire/s form the servos extensions.Make is a hell of alot easier to get the extra wires in there.
If i had too try and get all my servo wires down that little hole. it pushes my RX around and puts pressure on my bay door!!


http://www.rcgroups.com/forums/showthread.php?t=1358342
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Old Mar 11, 2011, 02:41 AM
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Woodstock 1's Avatar
Ireland, County Kerry, Kerry
Joined Dec 2005
6,923 Posts
Accept it for what it is.

We have to accept these airframes for what they are: reasonably-priced, foam, light-wind sailplanes. High-speed dives, etc. are simply not in their design performance window. It's pointless trying to make these into "all-round" glders.

Chris
Had 2 EasyGliders, currently has a factory-stock Radian Pro, and loves it.
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Old Mar 11, 2011, 04:13 AM
Never trust laughing dolphins
Joined Feb 2011
2,095 Posts
Quote:
Originally Posted by JumpySticks View Post
EDIT: It is more common in T-tail planes due to angle of attack.[
I know you're speculating as far as the cause goes, but the above is certainly not the issue considering the design of the RP. It's most likely either a CG issue or more likely just a simple elevator deflection issue.

Mine do not fully deflect both downwards and upwards. I've set servo limits, because it really doesn't need a huge elevator range and actually can be pretty pitchy when not limited.

Perhaps full elevator up only distorts the airflow (ie. like air brakes) but doesn't actual steer the plane at the highest dive speeds? A little less elevator in such case might make it controllable again.

I've never ever had issues pulling out of a seriously fast dive, whether on purpose or not and that's with a Radian Pro, 1300mah lipo with proper CG and no reinforcements on the tail or control surfaces.

The tail might not look that strong, but being a little bit more flexible is a pretty good thing actually for as long as the control surfaces will still move correctly.

Quote:
The most common causes I can see there are icing, flaps or CG too far forward.
Depending on the battery weight it could also be not forward enough. My 1300 mah lipo can sit right on top of or slightly against the ESC as far as the CG goes. It's still in the stock lipo hook and loop, but not exactly where the CG is (meaning it then has little or no nose weight and you don't want that).

You'll have to see what works best in practice, but I'd say it's fine to have a little nose heavy Radian Pro. Not too much, but it will fly better.

Mine used to fly great the one day and bad the next and it turned out the lipo wasn't forward enough (instead of backwards) to give the Radian Pro some healthy nose weight and therefore it used to behave differently depending on the wind a lot. Obviously more weight in the nose will make it fly a whole lot nicer in stronger winds, but it also had that issue when using the motor so I knew the CG was off.

The CG is still somewhere around 70mm from the wing though, so it's not an extreme difference as far as lipo placement goes. It makes all the difference in flying, so I think I might eventually buy a bigger lipo for this plane.

( Also... as far as no elevator control goes, when diving towards the ground basically right above the transmitter, your transmitter might have issues sending a signal your plane can catch because of the donut shaped transmission. )
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Old Mar 11, 2011, 09:51 AM
Registered User
United States, CA, Pleasanton
Joined Apr 2002
455 Posts
Cost of Scratch Built RP

I've had a few questions about the cost of my scratch built Radian Pro, so here's the breakdown:

PZ Airframe parts incl. prop and sotog's custom motor mount: $105.74

HK Components: T35-36C, 4xHXT 900's, Plush 30A ESC,
Orx and sat. $68.64

The HT65's were junque box resurections and I have lots of batteries.

Paint was on hand from a previous project. I figure $30 for pro-rated shipping and my BNF comperable RP totals out at $204.38.

So not a big savings over the stock PZ BNF offering, but a nice little project.

:harry
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Old Mar 11, 2011, 11:26 AM
cuz real planes cost too much
USA, CO, Frederick
Joined Jan 2011
823 Posts
regarding the possible stab-stall, when considering it, i don't think this is/was it. here's why...
.
before i had elevator to flap mixing (elev only), i could do nice big loops with no problem. i also flew the plane quite a bit in various conditions without incident. when the plane dove straight down, i reacted immediately with elev, without response. i held the stick for full up elev and it didn't react (pull out of dive) for quite some time, and the speed was high. i had no flaps deployed.
.
next time (yesterday) i had elev mixed with flaps (snapflaps). this gives extra pitch in the direction of the elev control. it was windy, i was flying fine both before and afterwards. when the dive happened, i was facing into the wind to come back from a good thermal lift, and had a good attitude. been there many times before. just after the 'extra' wind passed us, the plane nosed straight down. i responded (with snapflaps on) and it took an excessive amount to get the plane to curve out of the dive, but it snapped straight back down as soon as i started to ease up on the elev stick. it was a fight like that the whole way down. i tried to get the nose up, but it wouldn't go until close to the ground.
.
my CG is definately not too far fwd, and not too far back (i was flying with the 1800 battery). i think it's around 76-78 with this setup. but, like i said, i've flown this way a lot now, and i know how the plane handles - pretty well.
.
my situation yesterday was VERY similar to chuck's. open area, plowed fields, stiff wind, good thermals, heading=into wind. i tend to think the wall of strong sink, maybe compressed by the wind, hit hard and fast. if so, the plane's wing immediately non-functional and the sink dropped it. maybe the elev doesn't work well, in such a situation, because the airspeed isn't high enough (vs too high)? with only elev (no flap mix), the plane pulled out at very high gnd speed and would bow the wings at the bottom of the dive/arc - as if it escaped the sink and was arcing into 'regular' air.
.
maybe other cases are different (morpheus)?
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Old Mar 11, 2011, 11:37 AM
Klutzsquatch
mgroves's Avatar
Columbus, Ohio
Joined Oct 2006
390 Posts
check servos

Check your control horns on the servos. Especially the elevator one. I have found the spline on the control arms slip pretty easy. Or could be a gear tooth missing on the servo gearing casuing it to ratchet out of position. Abrupt and severe force on the control surface could be causing the slip then recovery from adverse attitude by jockeying the controls gets it back inplace.

I had an alieron control arm slip on the spline. Made groove in the foam, next to the servo recess, in the wing with dremel tool, so i could get screwdriver into the screw and rest the position and tighten her back down.

Just my two cents
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Old Mar 11, 2011, 12:22 PM
Drifting off the reservation..
JumpySticks's Avatar
USA, LA, Broussard
Joined Jan 2011
2,296 Posts
One more "stab stall" idea. The stiffener for the stab is not flush with the stab surface. Maybe at high speeds it creates a separation of airflow from the lower surface of the stab at high speed, causing a pitch down.
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Old Mar 11, 2011, 12:23 PM
Drifting off the reservation..
JumpySticks's Avatar
USA, LA, Broussard
Joined Jan 2011
2,296 Posts
Quote:
Originally Posted by harrye View Post
I've had a few questions about the cost of my scratch built Radian Pro, so here's the breakdown:

PZ Airframe parts incl. prop and sotog's custom motor mount: $105.74

HK Components: T35-36C, 4xHXT 900's, Plush 30A ESC,
Orx and sat. $68.64

The HT65's were junque box resurections and I have lots of batteries.

Paint was on hand from a previous project. I figure $30 for pro-rated shipping and my BNF comperable RP totals out at $204.38.

So not a big savings over the stock PZ BNF offering, but a nice little project.

:harry
I forget, did you purchase the RP fuelage or use a radian fuse?
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Old Mar 11, 2011, 12:47 PM
Drifting off the reservation..
JumpySticks's Avatar
USA, LA, Broussard
Joined Jan 2011
2,296 Posts
Quote:
Originally Posted by PHMX View Post
I know you're speculating as far as the cause goes, but the above is certainly not the issue considering the design of the RP. It's most likely either a CG issue or more likely just a simple elevator deflection issue.

Mine do not fully deflect both downwards and upwards. I've set servo limits, because it really doesn't need a huge elevator range and actually can be pretty pitchy when not limited.

Perhaps full elevator up only distorts the airflow (ie. like air brakes) but doesn't actual steer the plane at the highest dive speeds? A little less elevator in such case might make it controllable again.

I've never ever had issues pulling out of a seriously fast dive, whether on purpose or not and that's with a Radian Pro, 1300mah lipo with proper CG and no reinforcements on the tail or control surfaces.

The tail might not look that strong, but being a little bit more flexible is a pretty good thing actually for as long as the control surfaces will still move correctly.



Depending on the battery weight it could also be not forward enough. My 1300 mah lipo can sit right on top of or slightly against the ESC as far as the CG goes. It's still in the stock lipo hook and loop, but not exactly where the CG is (meaning it then has little or no nose weight and you don't want that).

You'll have to see what works best in practice, but I'd say it's fine to have a little nose heavy Radian Pro. Not too much, but it will fly better.

Mine used to fly great the one day and bad the next and it turned out the lipo wasn't forward enough (instead of backwards) to give the Radian Pro some healthy nose weight and therefore it used to behave differently depending on the wind a lot. Obviously more weight in the nose will make it fly a whole lot nicer in stronger winds, but it also had that issue when using the motor so I knew the CG was off.

The CG is still somewhere around 70mm from the wing though, so it's not an extreme difference as far as lipo placement goes. It makes all the difference in flying, so I think I might eventually buy a bigger lipo for this plane.

( Also... as far as no elevator control goes, when diving towards the ground basically right above the transmitter, your transmitter might have issues sending a signal your plane can catch because of the donut shaped transmission. )
I watched that long video and learned that as airspeed increases the center of lift of a wing moves toward the rear of the wing. That in turn shifts the cg to a nose heavy state. This cannot be avoided, and it puts an additional load on the elevator to counteract with a sufficient downforce. So a stab stall is always more likely with high speed.

As for the arguments about spline jumps or linkage problems, it seems that if that much force were being exerted on the elevator, the attitude of the plane would change due to that force before the splines would strip or control rods bend. When balanced, it takes only a touch of the finger on the tailplane to tip the plane up or down.

Based upon the film, even NASA has not determined why this happens and how to rectify the issue. Pilots are being asked to increase power and pull hard on the stick, which seems contrary to the idea of lessening the load on the elevator. The only instruction that does make sense is to retract flaps. Pretty hard to not pull back when the plane is careening toward the ground though. I'll bet that a quick roll manuver is a good tactic and will probably try that if it happens to me. Second option might be to push an inverted loop as was suggested above.

I have had "hints" of this control issue with my RP, but never enough for a full scale panic.
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