Acrowot Foam E - CoG

[IanR]

Has anybody noticed any differences between the "identical" Ripmax and Flyzone Acrowots?

The Ripmax instructions position the CoG 75mm from the leading edge. Flyzone's instructions quote 62mm - adding that, for later flights, the CoG can be moved plus/minus 10mm to change the flight characteristics.

Additionally, Flyzone provide or recommend an 1800 mAh lipo whereas Ripmax recommend heavier 2100 to 2500 mAh.

If the Ripmax Acrowots' CoG was aimed at 62mm, would this obviate the need for weight on the tail which I note some people have had to add? What effect does this have on the need for down elevator for straight and level flight?

I'm just putting my Acrowot together and wondered if anybody has any comments re this difference.

Incidentally, the two sets of instructions also vary considerably on the recommended control throws and Flyzone's instructions recommend balancing laterally which Ripmax don't mention.

Ian

PS All the Acrowot's servos centre poorly but the rudder servo is particularly bad. I intend to swop this one. Does any body else have this - does it affect flying?

Edited By IanR on 04/07/2014 12:07:32

[Colin Carpenter]

Hi Ian. I have just replaced the fus on my Acrowot after second ding . I stuck it together and checked cg which needed lead at the rear to balance. When chucking out the packaging noticed the weights which I missed originally.

Checked the original kit and no weight in rear of that.

Replacement flies better inverted than original kit. A tad of for forward stick only needed.

Does the white Chinese glue explain this ?

No problems with servos at all.

Still my favourite plane though !!

Colin

[Andrew767]

Hi Ian

I've had 3 Ripmax AcroWots and all required different amounts of lead to balance......all were nose heavy. As for iffy servos, all have been ok except for an aileron servo on the second one which tested ok on the ground but on the maiden the plane would not trim out of turning left and went in!! I thought it may have been a twisted wing but on investigation it was found that the left aileron servo would centre from down but not from up. Still like the plane which is why i bought a third.

Andrew

[IanR]

Thanks for the replies gents. I was also interested in hearing from someone who had contributed to earlier threads about the Acrowot zooming under power and the need to trim in down elevator to achieve satisfactory level flight.

It seems strange to me that here, in the UK, we are all setting the CoG at 75mm whereas in the USA they are all setting it at 62mm. Not forgetting that Flyzone suggest that, in subsequent flights it could be set at 52mm. If we were to apply this plus/minus 10mm to our Ripmax Acrowots this could amount to a whopping difference of (85 - 52 =) 33mm !!!

I am not up on aerodynamic theory so I'm not commenting - just wondering why the difference, who is right and how does it affect the flight characteristics.

I'm reminded of the Parkzone T28, another very popular model. From what I've read on various forums, its CoG seems to be all over the place. Many people were cutting bits off the underside of the canopy in order to push the lipo further back and yet, in his review, David Ashby (my hero) added weight to the nose to get it to fly to his satisfaction.

Is it simply that, with some models, the exact position of the CoG is not all that critical and more a case of personal preference and the manufacturer's suggestion is just a safe starting point?

I'll bet the Flyzone boys were offered the Acrowot for sale in the USA and, after test flying it said, "OK, we'll sell it but we'll use a different set of decals and fix the CoG at 62mm instead of 75mm"

Ian

Edited By IanR on 05/07/2014 14:56:27

[IanR]

Well, I carefully set the Acrowot's CoG at 75mm, per the instructions, with my Multiplex balancer, adding 20 grams of lead at the rear. As soon as it took off on its maiden it just ballooned upwards. I put in all available down trim on my DX7 and it would just about glide normally with zero throttle. As soon as I applied the tiniest bit of throttle I had to put in down elevator to stop it zooming again. I managed to land safely and went home.

There's a lad at the club who flies the pants off his Acrowot, which is why I bought mine, and its been suggested to me that I should make side by side comparisons with that. So hopefully I'll be able to arrange that in the next few days.

In the meantime, Colin, what are the weights you refer to on your replacement fus? This is the first I've heard of any "official" additional weights.

Ian

[Colin Carpenter]

Hi Ian. Coincidence or what ? Just switched laptop on !!

The replacement fus comes with 6 square white metal weights and some web pictures show these. I missed them in packaging until it was too late to insert whilst joining the halves. Now got a of lead lump inserted by tailwheel in gap cut in join line and taped over .

Coincidentally, another club member needed a new fus and I warned him about weights and he inserted all 6 in tail before joining but could not have checked properly cos now got 2 great lumps of lead on nose to balance .

I tested it for him today and whilst it flew ok, when power cut it nosed dived significantly !! it needs some downthrust I feel and rebalancing.

As for yours, if balanced ok, I would add a washer on top motor screw and than retry straight line power test. I am sure this will sort it as mine accelerates more or less straight on power and doesn't need any real managing .

They really do fly well for the money,

Colin

[IanR]

Thanks for the reply Colin. Could you please confirm that you are balancing at 75mm.

I'm a bit unhappy about having to add downthrust and feel that this should be incorporated into the design. I'm not much of a modelling engineer (or flyer, for that matter!) but I can understand the need for the user to set the balance since this would be affected by his choice of battery, but needing to faff with thrust angles is not a good thing in my opinion.

I was hoping that moving the CoG forward to, say, 65mm - closer to Flyzone's 62mm - might solve my problem on the basis of rather slightly nose heavy than nose light. I certainly don't want a repeat of the maiden!

Any thoughts, Colin? Anyone?

Ian

[Colin Carpenter]

Hi Ian.

Yes I balance as per instructions 75mm.

I use both Turnigy and Gens Eco batteries and they are not identical in size or weight but it flies the same on either. Try balancing further forward and see if it flies to your taste but I like my models to carry on in a straight line when the throttle is chopped and will adjust thrust line till they do - foam or wooden.

Getting the factory screws out is a real pain. 3 will move but 1 wont - guaranteed - I know !!

Persevere. Regards Colin

[IanR]

Cheers, Colin. Right then - I've got a plan of action. First, make some comparisons with my clubmates Acrowot and, if there's nothing glaringly obvious - like, for instance, I haven't got my tailplane screwed down properly - then move the CoG forward and try again.

I'm feeling more optimistic already! Thank you very much for taking the trouble to reply, yet again.

Regards, Ian.

[Stuart Z]

Just found the same challenge on my foam e. I'll do some more research before sending skyward, I used an Overlander 2200mah btw.

[John Roberts 9]

I have my AcroWot set at 75mm (no tail weight required). However, I use 4 different makes of 2200 LIPO which are all slightly different weights. Having just checked on my balancer I can see that the CoG varies from 71mm up to 75mm depending on which make of LIPO is installed. There is no discernible difference between the batteries in flight.