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Aug 14, 2005, 02:01 PM
Registered User
julianb's Avatar

Crow brakes on a Voltij


I've been playing with the Voltij today, and have been scratching my head trying to decide if flap or 'spoilerons' work best at slowing the Voltij down for landing.

Airbrakes (up ailerons), seems to need lots of UP elevator - weird huh? If I use down elevator compensation, the darn thing bunts like a demon. Any idea why? If I use up elevator compensation, the model parachutes down quite nicely.

If I use large amounts of flap instead, roll control is severely diminished, but the model can be driven at the ground quite a steep angle with very little forward speed.

Which do you prefer?


Ju.
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Aug 14, 2005, 03:18 PM
Piscine Promulgator
surfimp's Avatar
Well, with respect to the Voltij, I'll have to wait to pass judgment till later... but in general I think both can be useful. The thing I don't particularly care for sometimes is spoilerons. Our mountain flying site requires that we set down gently atop a fairly narrow A-frame peak. Normal approach involves a crabbing climb up a side hill into the wind, then plopping it on top in a patch of scraggly grass about 20' long x 10' or so feet wide. Not quite spot landing, but darn close.

When we come in too hot, it's pretty easy to just go around for another try, but having flaperons allows you to really get the ground speed slowed down without making the plane fall out of the air. For that particular approach, they can be really nice. They're also great for hover plop landings; i.e. pop up into the wind, then drop flaperons (once wings are level) and gently sink it onto the ground.

Spoilerons tend to seem like they require a more traditional final approach, i.e. you get high, then deploy spoilerons and keep a nose-high attitude to control speed/sink. I tend to come in faster with spoilerons, but I'm not an expert in their use so it may just be that I don't have enough experience. They certainly don't do much good unless you keep the nose up--making them seem a bit trickier to use, to me.

However, I plan to test both extensively with the Voltij and will be more than happy to report back when my ideas on the above change

Steve
Aug 14, 2005, 03:55 PM
Registered User
julianb's Avatar
Cool,

I'm having similar thoughts, the flapperons really do seem to offer the best results. Interested to hear your thoughts post flight.

regards


Ju
Aug 14, 2005, 04:22 PM
Registered User
motorhead's Avatar
As for the pitch change when deploying spoilers or flaps. You are effectively changing the wings angle of attack with respect to the horizontal stab. Spoilers as you found out require up elevator and flaps require down. If you have a computer radio you can program in elevator compensation. With either it is a good idea to set it so the glider keeps a slight nose down attitude so you do not slow it down too much.
Mike
Aug 14, 2005, 04:56 PM
Registered User
julianb's Avatar
Quote:
Originally Posted by motorhead
As for the pitch change when deploying spoilers or flaps. You are effectively changing the wings angle of attack with respect to the horizontal stab. Spoilers as you found out require up elevator and flaps require down. If you have a computer radio you can program in elevator compensation. With either it is a good idea to set it so the glider keeps a slight nose down attitude so you do not slow it down too much.
Mike
So, it follows that the flaps on my F3F ship offer more aerodynamic force than the ailerons whilst crow braking, because the elevator compensation is 'down'.

This is what had me scratching my head in the first place, i.e. why was there a difference? Of course, the Voltij has no flaps. QED.

And yes, I have a computer radio, it's called a 14MZ or something like that..


:-)
Aug 14, 2005, 08:02 PM
antipodean recalcitrant
AntonL's Avatar
Quote:
Originally Posted by motorhead
As for the pitch change when deploying spoilers or flaps. You are effectively changing the wings angle of attack with respect to the horizontal stab. Spoilers as you found out require up elevator and flaps require down.
Isn't this model-specific? I.e., some models pitch up with flaperons down and some pitch down (and vice versa for spoilerons), thereby requiring either up or down elevator compensation depending on their behaviour? According to Martin Simon's book on model aerodynamics, the wash from the wing can hit the tailplane and consequently affect pitch stability. The wash is, of course, modified by TE adjustment. It could be that different planes are affected by this mechanism in varying degrees depending on their wing and tailplane configuration/geometry?

Julian - are you able to reverse aileron differential (not just cancel it but actually reverse it) progressively as spoilerons are applied? In my limited experience, I've found that this can really help with maintaining better roll control as the ailerons are raised.

Anton
Aug 15, 2005, 12:21 PM
Registered User
julianb's Avatar
Hi Anton,

I usually disable diff under crow as a matter of course with F3F ships, but I've never tried reversing it. Might be worth having a play with.

I tend to agree with you about different planforms needing different pitch compensation.

A pal of mine set up his own Voltij with spoilerons and down elevator compensation a la every other model he owned. The first time he landed it, the model was left sticking out of the ground after bunting into the floor really viciously from about 8ft up.

I tried a flapperon approach today and it was much more comfortable. The model really got slowed down quick but still floated quite nicely - with spoilerons it just parachutes onto the floor like a brick.

Roll control was compromised quite a bit as you'd expect, but I think I might give the reverse diff a try - the model does have a powerful rudder if all else fails.

Let you know how I get on.

regards


Ju
Aug 15, 2005, 12:55 PM
ave
ave
Wind Junkie
ave's Avatar
On my 60" LEG cobra with dual aileron servos I find flaperon works better for landing in 15mph and less, the spoilerons bring it in too fast. Spoileron is the only way to land on 20mph+ days, but I don't keep them on, I just cycle them to drop altitude and keep control of the plane, drop it 10ft at a time until you're ready for final, then keep them on light until touch down. If the landing is getting hairy you can just go full spoileron to dump the plane where it's at... but that's a foamie, no harm done.

What I'd like to know is when you have separate flaps/ailerons and you're using crow, how do you know how much flap and how much aileron travel you should use? I'd imagine the flaps should be all the way down, but not sure about the ailerons? The suggested setup on my 2M mouldie only raises the ailerons maybe half or less of their travle for crow, while the flaps go full range. Maybe it's to retain roll control during landing... hmmm.

ave-
Aug 15, 2005, 01:10 PM
David Cairns
dcairns's Avatar
Are you talking about crow or just air-brake on the Voltij? Crow would require 4 servos and cutting the ailerons in half (this what I plan to do with mine). So for crow, the outer ailerons would go up, and the inner ailerons would go down.
Aug 15, 2005, 02:41 PM
PlaneCrazy
jdcook54's Avatar
spoilerons dont slow the model as much, but thats good due to once you slow it down and lose the altitude you want, it can be switched back off for landing with no ill effects due to your decreasing the lifting ability of the wing then swithing them off increases the lifting ability back to normal, plus better roll control, but with flaperons you are increasing the lifting ability, so you have to be carefull not to turn them off if you have slowed the wing down past the point where it can still generate lift with them turned off. and if you have to keep them on, there is always the chance of bending something or stripping a servo.
Aug 15, 2005, 05:44 PM
SlopeHead
jcosta's Avatar
Quote:
Originally Posted by AntonL
Isn't this model-specific? I.e., some models pitch up with flaperons down and some pitch down (and vice versa for spoilerons), thereby requiring either up or down elevator compensation depending on their behaviour?
Yes. A Mini Ellipse requires down compensation for spoilerons, a ProdiJ requires up compensation...
Aug 15, 2005, 06:13 PM
Registered User
julianb's Avatar
It sounds like having the ability to use both flapperon and spoilers in varying conditions is the hot ticket. At last, a use for another condition in my 14MZ!

The biggest problem is that I just don't get out and do enough slope soaring. Half the problems I ever have are usually related to not being positive or confident enough with approaches and landings - particularly with the hotter toys like the Zipper etc, that don't have any form of landing aids other than my thumbs.

Just gotta practice I guess. I shouldn't be relying on flapperons or spoilers or crow braking at all!!!


Ju
Aug 15, 2005, 06:16 PM
Registered User
julianb's Avatar
Quote:
Originally Posted by dcairns
Are you talking about crow or just air-brake on the Voltij? Crow would require 4 servos and cutting the ailerons in half (this what I plan to do with mine). So for crow, the outer ailerons would go up, and the inner ailerons would go down.

I'd thought about retro fitting mine with separate ailerons and flaps. That would solve all the problems, and give some nice options for further aerobatic mixing.

Problem is going to be getting a servo wire down that wing panel. Any ideas?
Aug 15, 2005, 07:45 PM
Registered User

Split flaps?


Ah well if you want to you can run a hot wire thru the wing and pull the wire thru the foam into the new servo well...

If you like flapperons go that route in landing mode just mix in a bit of rudder coupling to the ailerons and this will help with the slow speed landing.
The standard Voltji is a fiberglass wing skin and not the strongest wing in the business. Besides adding weight to the wrong end of the wing tips you might be weakening the wing as well...my guess anyway...Tom did a build on f3x on a carbon prodji with added flaps which you could copy. I would be cautious of the layup on the Voltji...ping Tom @f3x ask for his view...Tom?

Alan
Aug 15, 2005, 08:24 PM
Registered User
julianb's Avatar
Thanks for the wisdom T.

My Voltij flexes quite a bit anyways, so maybe best left alone!


cheers


J.


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