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Old Jul 07, 2004, 03:11 AM
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London Heathrow, Great Britain (UK)
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Difficulty in Thermalling!

Hi Guys,

I have the Swift Vee electric glider, which i've had for approx 2 months now, but i really struggle to maintain any lift.

I fly in perfect lift conditions like the other weekend, we have a full size glider club nr where we fly RC, and these full size gliders get lift in seconds up to 1000's of Ft.

I just can't seem to maintain lift.....should i be constantly turing/circling? should my turns be tighter?...i've been told also that the Swift Vee should be flown as it's natural cruising speed which is relatively fast and that i should'nt hogg the elevator...

I know about the principle's how thermals work and where i should be looking for thermals but hooking the two up is seeming impossable...

I'm sure these tips have been asked before....appologies in advanced.

Simon
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Old Jul 07, 2004, 04:39 AM
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Johannesburg SA
Joined May 2004
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Hi Simon,

Who ever told you that you need to fly relatively fast was right. Determining that ideal speed is another thing altogether. The method I have used, which seems to work for me, is to trim out so that the plane maintains a level flight path. I normally start with some up trim which is inclined to make the plane porpoise gently. A few clicks of down trim sorts this out and should give a reasonable glide angle which is what you want for duration. I'm assuming you have set up the balance correctly.

Observation is the key to finding lift. Watch your plane carefully as you fly around your field. Any sign of a wing lifting or the nose lifting, depending on the plane, is an indicator that you have found lift. If the right wing lifts, turn right and visa versa. Watch to see if you are gaining altitude. Narrow down the diameter of your circles closer to the ground and expand them as you gain height. Turns should ideally be as flat as possible and try to avoid sudden and harsh control movements to preserve energy. Dont forget that thermals move with the wind so don't go overboard trying to circle in one spot but rather be guided by the wind strength and direction.

Constant hooking into thermals is to me a bit of a 'black art' which only improves through experience. You will find that on occasion you can go for some time without any significant lift and then just as you start becoming despondent, you land up in a boomer and only land because either your neck is too stiff or you are worried about the Rx battery pack.

Hope this helps.

Soarbird
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Old Jul 07, 2004, 08:13 AM
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London Heathrow, Great Britain (UK)
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Hi Soarbird, thanks for your information,
My Swift seems to be ballanced fine, although off the power the nose seems to dip down slightly, which means i'm always putting small amounts of elevator to bring the nose up to level flight. When i re-trim the elevater even marginally on the transmitter it has a tendency to stall on turning...which i'm quite confused about....because i'm talking about just a few clicks of elevater trim adjustment!!

On the power the glider climbs well....it's just when gliding as the nose is pointing down marginally it looses altitude fairly quick....

CofG seems to be in the recommended place.....i don't get porpoising and in general it fly's ok...its just in glider mode that confuses me...

It may be the fact it prefers the nose to be slightly down...

Any idea's?

Simon
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Old Jul 07, 2004, 09:37 AM
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Martini's Avatar
USA, ID
Joined Jun 2004
254 Posts
Sounds like you may have a slightly nose heavy glider. If high speeds make the nose rise (similar to having the motor on) this may indicate a forward CG. If the nose is a little heavy the elevator will be trimmed to keep it up at average speeds. The higher speeds then cause the elevator to push the tail down even more causing the nose up condition.

The best thing you can do for a thermal glider is get the CG back as far as is comfortable for you. It will make the plane signal the rising air better, and it will make your controls more sensitive - which also helps efficiency since the control surfaces don't have to move too much which causes drag.

Try removing some weight at the nose (or add a little tail weight) a little at a time. Do this in SMALL steps and you will know when the plane is becoming too tail heavy because it will start requiring a lot of attention to fly smoothly. The manufacturers "CG setting" is just a starting point and is often a little nose heavy since this is a very stable setting for first flights. You probably already know this...

Good Luck with your thermalling and also, as Soarbird says here, it is an art and it will become easier for you as you get more experience.

Cheers
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Old Jul 07, 2004, 10:56 AM
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Thanks Martini,

yeah there is a lot of added weight in the nose area, as this Glider has a tendency to allways come out tail heavy, infact i have 84grams of extra weight (nearly 3oz) but this appaeantly is the norm with the Swift Vee...i guess i just need to play around a bit more with the CofG.....but if the Cof G is moved back more this would just add to the tip stalling!! or am i wrong?

Simon
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Old Jul 07, 2004, 02:43 PM
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The 'Wack, BC, Canada
Joined Oct 2002
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Simon, would it be possible with this model to use a heat iron to warp in a bit of washout? I'm not familiar with that one.
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Old Jul 07, 2004, 05:30 PM
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Quote:
Originally Posted by BMatthews
Simon, would it be possible with this model to use a heat iron to warp in a bit of washout? I'm not familiar with that one.

I spoke to the company that I purchased the model from who are a specialist in the Swift.....and they told me to do the exact same thing.......

I've never heard of this before....can you explain what i need to do and what does it do to the flying characteristics......

Also they told me to add in 2 degrees of down thrust........

What do you think?

Simon
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Old Jul 07, 2004, 07:54 PM
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Zwolle, Netherlands
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Hi Simonbryant,

From your observations I would also say your Swift Vee is nose heavy and that putting in more washout would improve it's turning behaviour. You can add washout by gently twisting the wing from the tip "nose-down" and then using a heatgun in order to take away the wrinkles in the wing covering and fixating the new shape. Multiple small twists are more effective and safer than trying to introduce one large twist. If possible ask someone to help you as this is a typical "three-hand job". I'd start with small amounts, and watch out that the end result is equal on both wings.

Although putting in more down thrust would help I suggest you first mix in some elevator with throttle (if your transmitter allows for this) to see if you can overcome the zooming up in powered flight. You may find that you'll actualy need very little elevator to prevent zooming up, which would add little drag and might not justify extended nose surgery. Although in theory mixing in elevator introduces drag IMHO the real-life drawbacks are almost non-existent.

Do you have rudder control with your V-tail?? Learning to use the rudder is very important for thermal flying. The rudder enables you to make relatively tight turns without banking in too much. When you're flying circles it helps to use the rudder to control the diameter, and ailerons to keep your banking angle constant. Most gliders will bank inwards on rudder-induced turns, which can be counterd with small amounts of opposite aileron input (and maybe some elevator). I learned this by practising in no-wind conditions, and found it very awkward in the beginning, but after some time it became more natural.

Another great learning experience for me were the buzzards that will thermal around our flying field. I learned a lot by just chasing them and trying to stay with them while they're circling in lift. Apart from finding lift they also show which way the thermal is heading. Once I started hitting thermals this way I became more sensitive to the way my glider responds to it, which made it easier to recognise lift by eye without the immidiate assistance of my feathered friends.

In general it takes time and experience!! Although I got the basics down by now I am still regularly struggeling to remain properly centered (even when assisted with a vario) and judging wind conditions, especially when flying at a distance. Just keep at it and you will get it down!

Good luck, hope this helps,
Martijn
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Old Jul 08, 2004, 02:11 AM
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Johannesburg SA
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Hi Simon,

Some very good advice in these postings. Here is a link to a calculator for determining the neutral point of your plane and the range of CG points to work within.

http://home.germany.net/100-173822/schwerp.htm

The closer your CG is to the neutral point, the more sensitive it will be. Experiment with these settings until you are comfortable with the flight performance. BTW the best time to do this is very early in the morning or late afternoon when there is no wind.

For flying in varying wind conditions, I use my battery pack as a variable load to move my CG forward when needed.

Martijn has some very good points regarding washout. I have found though that over time the washout seems to dissapate so check it regularly.

There is no substitute for a properly aligned and balanced airframe. Have you checked that both wings are exactly the same weight and that the plane balances along the fuselage centreline? One wing heavier than the other can play havoc with trimming it out effectively. When all your control surfaces are centred and the model flies straight and true, then the airframe is right.

There are two schools of thought regarding thrust angles for motors. I have tried both and prefer to mount everything 100% straight and true and use a little elevator down trim during the power cycle. Link this to your throttle stick and the down trim is proportional to the speed in level flight.

Good luck and may the lift be with you.

Soarbird
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Old Jul 08, 2004, 03:07 AM
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Thanks Guys for all help....i' believe the Glider/Airframe is balanced fine...the Swift Vee does like a heavy nose i've been told, on this particular model the Elevator/Elevon is all controlled from the V tail, so i don't have a T-tail style Rudder nor do I have Aileron's on the wing....all the pitch/Roll come purely from the V-Tail.

I've explained the problem i'm having to a Swift Vee expert and he has made a diagnosis that the CofG is balanced correct and that i have the correct amount of added weight upfront....So on to the Washout Wings tips!!

If anyone would like to come over to England and help me with this one, i'll take you to the Pub.

Regards

Simon
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Old Jul 08, 2004, 07:53 AM
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Zwolle, Netherlands
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Quote:
Originally Posted by simonbryant
If anyone would like to come over to England and help me with this one, i'll take you to the Pub.
That's a tempting offer, I could use a nice pint
If you come over here I'll bake you some "pannenkoeken" and we could have a Grolsch or two

Good luck!

Martijn
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Old Jul 08, 2004, 09:05 AM
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Quote:
Originally Posted by Vinkie
That's a tempting offer, I could use a nice pint
If you come over here I'll bake you some "pannenkoeken" and we could have a Grolsch or two

Good luck!

Martijn
Or even a bottle of Pilsner should work.

I decided earlier that i would give it ago and try and twist the wing tips...so i removed the wingtips from the main Wing Chord position them on to a flat surface...and started to add in some washout (LE lower, TE higher direction) all i could hear was the balsa frame making nioses as if it was about to crack...so i gave up...the wing tip just pinged back in to it's normal position...if i would of gone anymore it would snapped for sure....

I guess i'm just to scared to risk a healthly wing tip, any suggestions......
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Old Jul 08, 2004, 10:41 AM
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Zwolle, Netherlands
Joined Sep 2003
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Hi Simon,

I'm glad you didn't push on when you felt the sounds were alarming. Wrecking a perfectly good wing isn't worth the effort! I just looked at your Glider at hobby-lobby.com to see how your wing is built up before answering this. Is it correct to assume that you have the version with 3-part wing w/ spoiler in the center piece? This would mean that you'd have to work on the outer wing panels (duh..). I'll try and talk you through:

Because of the open ribbed construction you should be able to twist the LE downwards from the tip (I'd do this by holding the tip and gently applying pressure to the LE right where it starts to curve towards the tip). Be sure to twist the entire wingpiece, not just the tip. We're not talking cm's here, I'd start with say 3-5mm. I'd be very surprised if this action would yield really alarming sounds. Off course releasing the wing at this point would make it spring back to the exact position it came from. Therefore the next step is to use the heatgun to tighten the covering on both sides (starting on top) around it's new position while still holding the wing in it's slightly twisted state (btw. this is where third hand I was referring to comes in, it's much easier and safer if some-one else applies the heat).

When your finished shrinking the covering and you release the twist you will find it bends back a bit, but probably not all the way to where it came from. This small difference might be enough to cure your tipstalling. If not repeat from step 1. Off course you should be careful and patient, and if even the slightest twist sounds scary then back out. However I can't imagine this type of wing to be so extremely rigid.

I hope this helps, Simon, let me know how it works out. I'll have a Grolsch ready to drink to your succes!

Martijn
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Old Jul 08, 2004, 01:14 PM
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Ohhh i see so by shrinking the solar film back while holding the twist will allow some of the twist to stay in shape.....im with ya now! all i need is a heat gun!!!

Would a demestic house hold iron on a low heat be sufficient??

thanks for the advice!!! keep the Grolsch in the chiller, i'll let ya know when to pop it open!!

simon
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Old Jul 08, 2004, 03:50 PM
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Quote:
Originally Posted by simonbryant
Ohhh i see so by shrinking the solar film back while holding the twist will allow some of the twist to stay in shape.....im with ya now! all i need is a heat gun!!!

Would a demestic house hold iron on a low heat be sufficient??

thanks for the advice!!! keep the Grolsch in the chiller, i'll let ya know when to pop it open!!

simon
Yep, you are with me now I'm sorry I maybe wasn't clear on this from the start.

Although it might be possible to use a household iron I prefer using a heatgun because it's easier to use and gives a more even result, especially on the arched top side of the wing. In general they are not expensive and many people have 'em so you might be able to loan one for a while.

Cheers (still on a tap water diet... )
Martijn
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