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Acrowot takeoff & landing

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Down to Earth

Down to Earth

Putting a model into the air and keeping it there is relatively easy, it's the landing stage where things can come unstuck!

PeD18/09/2013 22:47:10
28 forum posts

I have recently aquired a Kit built Acrowot and finding that it takes a fair length to unstick from Mother Earth. (Grass bumpy)

The Acro. does not have the original undercarriage but is fitted with a heavier thicker "plastic" type and the wheels look to be further forward and lower than pictures of the ARTF version.

The height of the center of the spinner from ground level is 200mm

undercarriage measured at the fixing bolts 105mm

and the tail measured at the hinge line of the rudder 65mm.

Is it too low or too parallel to the ground?

Engine is a SuperTiger 61, running on Southern Modelcraft 10% nitro

with synthetic and castor oil. 11*71/2 prop.

Elevator and aileron settings I've set from the ARTF manual.

In the sky it tracks perfect with very little trim reqd. At just less than 1/2 throttle it "bats" along quite quick.

Being more used to heli. flying, I also find it lands at a fair lick as well and needs all the available runway we've got. This could of course be my inexperience in landing this type of plane and fearing a low speed stall. An experienced colleague has flown it and he also brought it in very quick. I was advised to turn the tickover down a tad which I've done. But it still seems very fast to me to land.

Are the above symptoms normal for this plane or is there something slightly out of kilter in the setup?

Regards

Peter

Dean B18/09/2013 22:59:12
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131 forum posts
32 photos

Hi PeD

I have just maidened my Acrowot this last weekend. I did notice that it goes a lot further than my Wot 4 when taking off but once its in the air it is superb. It is the ARTF version with an SC91 pulling it. My Wot 4 will take all of in two feet of runway on full throttle at take off. Not very scale but fun all the same.

I found that running a smaller pitch prop helps when landing. I have a 14 X 6 on my acrowot and it lands nicely within the boundrys of the pitch. I run a 13 X 4 on my wot 4 as it is quite hard to get down in the space available when there is little head wind to help slow the model down. The smaller pitch creates less waft when the engine is at idle allowing the model to come in slower.

hope this helps

Dean

Martin Whybrow18/09/2013 23:48:26
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884 forum posts
33 photos
Posted by PeD on 18/09/2013 22:47:10:

and the tail measured at the hinge line of the rudder 65mm.

Is it too low or too parallel to the ground?

Do you mean the bottom of the rudder hinge line? If so, that sounds very high and would mean that the angle of attack of the wings is very low which would indeed, result in a high take off speed.

Biggles' Elder Brother - Moderator19/09/2013 00:05:27
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15748 forum posts
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PeD - you say it takes a long time to unstick - are you waiting until it decides to become airborne on its own? This is OK as a take off technique - but depending on the model it can indeed lead to very long take off runs. Some aircraft need to be "rotated" to get up.

All other things being equal lift depends on two things; speed and angle of attack. If the model naturally sits with a small angle of attack, or if you are letting the tail come up so it sits horizontally (which is the "correct" method), then you will need a lot of speed to get enough lift to become airborne. The problem with this is that models experience a lot of drag when on the ground - remember a model going along a typical grass strip will be like a full size aircraft trying to take off in 3 foot high undergrowth!

If you "rotate" by squeezing in a bit of up-elevator once the speed has built to a reasonable level, you should become airborne fairly easily. The increased AoA giving you a bit of extra lift. Once in the air, and free of the drag of the grass, the model will build speed more rapidly and you can feed out the elevator. Obviously it's important to exercise some judgement with this! Put in the elevator too early and the model will be too slow to fly! Overdo the elevator and you run the risk of stalling the wing. But its easy enough to develop the feel of when and how much!

BEB

David Davis19/09/2013 05:54:15
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3865 forum posts
741 photos

I find that an Acrowot can fly pretty slowly without stalling and need not be brought in at speed. Why not try taking it to altitude next time and reducing the power to test the stall speed? Then you'll know how slowly it can fly. A smaller pitch prop as Dean suggests might help. Try a 12x6 or13x6.

Andy Blackburn19/09/2013 08:26:38
515 forum posts
487 photos
1 articles

I have one with an OS 55AX running on a 12 x 7, and it sounds as though the c.g. on yours is maybe a bit too far forward; I can't tell you where it should be (just looked for the instruction manual, couldn't find it) but maybe someone else has one. Try moving the c.g back a bit...

ken anderson.19/09/2013 09:10:39
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8864 forum posts
820 photos

hello peter...change the prop as suggested and give it a bit more umph...in the take off...it should really jump off the ground.......landing-if the tickover is too high the aircraft will want to fly-and no amount of stick twiddling will make it land.....so back off all together on the power once the aircraft is straight and level on the landing appproach....have a try at some dead stick landings-this will help in your power on landings......you should find the A/Wot has no nasty tendencies.......and will float in....

ken anderson....ne....1 ......umph dept....

Phil 919/09/2013 09:19:20
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4287 forum posts
257 photos

I think people are used to seeing models leap into the air after putting the throttle to max and two feet of rolling then throwing the model up at 45 degs

horrible

models used to fly with a lot less power than most people use nowadays meaning a longer roll out was needed.

I try to deliberately make my take off roll out long and climb up at more scale like angles. Controlling a tail dragger along the floor with the tail flying can be very satisfying

PeD19/09/2013 09:23:49
28 forum posts

Thanyou for all the replies :

"Martin"

The measurement is at the rudder vertical hinge. The Acro. came to me without a tailwheel just a non original aluminium bkt without the tail wheel. The original mount fixing holes look as though the tail would have been lower. So perhaps me adding a wheel assembly to the bkt. has compounded the problem.

"Dean"

I see in the Super Tiger 61 manual it will go too 12*6 or 7. So that maybe worth a try.

"Beb"

I've not tried a "shorter" takeoff as it just does not feel like it wants to lift off until I've almost run out of runway. The speed accross the grass seems adequate for it to lift.

I'll try giving it a bit more "welly" accross the grass. The Acro. came from club with a lot longer runway than mine, so maybe not a problem for them and a long takeoff was normal. I'll make enquires re-that.

"David" I will take it up higher next time out to see where the stall is.

"Andy" The c.g is slightly forward (3 1/4 +- 1/4) .This probably down to the non standard undercarriage. I thought I'd leave the c.g forward initially to make sure it was at least flyable.

Will test some of the replies on the next outing, weather permitting.

Thanks again

Peter

Djay19/09/2013 09:30:21
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562 forum posts
557 photos

With my kit built acro powered with an OS AX 55 and 12x6 prop I fly it so slow it actually stops flying and just sits there before going into a flat spin, it is virtually impossible to stall this plane so on landings it should come in at a fast walking pace, I do flat turns using full rudder and opposite aileron at virtually zero airspeed, much more fun then full throttle flying.

This plane has a massive flight envelope, explore it and have fun.

Darryl

Edited By Djay on 19/09/2013 09:30:52

Glyn R19/09/2013 09:40:31
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443 forum posts
179 photos

I always flew my glow Acro with a 12x5 on an Irvine 53. My Electric Acro flies with a 13x6.5 on 1100 watts. thes are both built as the chris foss kit. I find an Acrowot has to be flown in so it will have more speed than a Wot4 for example.

Edited By Glyn R on 19/09/2013 09:41:03

Stephen Grigg19/09/2013 09:40:39
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8691 forum posts
1128 photos

I recently acquired an ARTF Acrowot.It has a short take off distance and Ive practised its landing and find by coming in from a long way out ,you can loose the height and speed and land at a reasonably slow speed very stabily.Love the model with a passion,given me bundles of confidence.

00119/09/2013 11:15:28
2212 forum posts
1 photos

The first AcroWot I had, years ago, was fitted with a Enya 50 helicopter engine, not the largest in the recommended range. Never had any problem taking off at all. But I did think at first that I couldn't land it satisfactorily, probably because I was not letting it slow down enough. As a result I kept knocking the undercarriage off.

I then learned to slow it down before the final approach!face 1

If it is set up correctly it will be easy to land if you give it a chance to settle.

My second, electrified AcroWot takes off in about ten feet, probably because of the greater torque available from rest...................face 23

Bob Cotsford19/09/2013 11:53:05
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8948 forum posts
498 photos

Is the tail coming up on the take-off run? My kit-built Acro needs a little up held in to stop it nosing over because the tail comes up almost as soon as it starts to roll, and then it needs a touch more up to unstick.

Martin Harris - Moderator19/09/2013 14:11:25
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9808 forum posts
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The take off technique has been outlined pretty well above but regarding your floaty landings, the Acrowot is a slippery model with a relatively high wing loading so it will respond poorly to the all too common "cut the throttle and point the nose at the runway" technique.

Something rarely appreciated is that a model flies fastest - and essentially slowest - with full throttle. Before you dismiss this as a ridiculous statement, think of a 3D model in the hover or a harrier - the airspeed is close to zero but the throttle will be close to or actually wide open unless the model has a more than 1:1 power to weight ratio.

Translate this to a more normal landing approach and you'll find that the most manageable condition is with the nose somewhat higher than in a power off glide and enough throttle to maintain a steady descent, balancing the increased drag from the higher angle of attack. This will mean in practice that you either have to hold in a little back pressure on the elevator - or you could adopt full size practice and re-trim for the correct attitude.

If you find that you're beginning to undershoot, don't pull back on the elevator - nudge the throttle open a little. The airspeed won't increase significantly but the sink rate will decrease. If you're overshooting, close the throttle a bit (see why we aim to approach with a little power?) and the sink rate will increase BUT not the airspeed, which, as long as you hold the approach attitude will stay almost static until you go into the flare and landing hold off.

The chop and glide method does work relatively successfully with lightweight models and typical trainers but once you move on to the likes of Acrowots and WW2 scale models you'll find that the technique above will give you much more rewarding approaches and landings. There's an almost magical feel when you have a model "locked in" to an approach and you adjust the glide angle with use of the throttle, almost like there's a physical connection with an invisible string suspending the model...

Edited By Martin Harris on 19/09/2013 14:26:31

ken anderson.19/09/2013 14:48:41
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8864 forum posts
820 photos

of course my comments re- the flying of the A/Wots was of my experience's with the kit build versions......i should imagine that the artf imposter's ....... will have their own tendencies etc......

 

ken anderson ne..1 ........ imposters dept...

Edited By ken anderson. on 19/09/2013 14:49:05

Bob Cotsford19/09/2013 16:04:49
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8948 forum posts
498 photos

Ken, I recently had the chance to fly the ARTF at the RC Hotel in Corfu, and it really made me feel at home. It may be a bit bigger but it flies very much like the kit built version.

PeD19/09/2013 17:39:48
28 forum posts
Posted by Bob Cotsford on 19/09/2013 11:53:05:

Is the tail coming up on the take-off run? My kit-built Acro needs a little up held in to stop it nosing over because the tail comes up almost as soon as it starts to roll, and then it needs a touch more up to unstick.

The tail has not come up on any takeoffs so far. Again this maybe I've not given it enough "ummph" to start with.

"Martin" thank you for this type of landing approach. I'll try this at height along with the stall and find out more what it's going to do.

I've been a bit cautious, as I've had to do a couple of dead engine landings with it. The last 2 flights out, after another carb. clean (nothing found) it flew as on rails with no engine probs. All the electrics,tank and tubing were changed before it's first flight.

It is the heaviest plane I've flown so far and flying helis' as I normally do doesn't help in the take off and landing of planes, it only helps when it's up there.

Lots more practise with it (weather permitting)

Again thanks for the replies.

Peter

Jon Laughton20/09/2013 08:49:15
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1241 forum posts
72 photos

HI Peter

My old kit built Acrowot with an OS 55 didn't suffer from any of the problems described above...and whilst Martin's explanation on landing with power on is first class & correct I have to say that my model was quite happy on a cut and glide landing pattern and we have loads of trees to get over at our patch so it had to be quite steep at times...

Perhaps the C of G does need moving back slightly..but be careful not to go to far.

Enjoy!

Jon

Braddock, VC20/09/2013 09:14:01
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1688 forum posts
52 photos

I've watched this thread with interest, my original acrowot (brown printed instructions!!) had several engines before I settled on a saito 82 with a 14x6 prop.

Dead stick you could hear it whistling as it flashed up the strip but with the saito on tickover it flew very slowly indeed.

Getting the angle of attack right took some time as I wasn't sure what attitude to hold. After several sessions I found that if I held the model in an attitude that resembled that of a three point landing then I could perform the landings as Martin Harris described but it took me a while to become comfortable with it.

This paid dividends as I then practised that on a WM midget Mustang that previously tried to fly into the next county on landing but became a real pussycat with practice.

As always practice a little high until you've got the hang of it and also check out the stall speed at that attitude.

The other thing that makes for a fast landing is excess weight coupled with a forward c of g. I have heard that the artf weighs 6 pounds up, dependent on engine. I'm pretty sure mine weighed around 5 lbs with the saito in and I used a heavy alloy spinner but the c of g was at the rearmost point recommended and may even have been a few mm behind that, CF certainly gave a safe and useable range for that point. Anyhow I certainly had no problem getting it to spin.

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