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Infinity 90 Build

How good is it ?

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Peter Jenkins07/02/2019 00:08:54
1193 forum posts
132 photos

How accurate have you found that calculator to be in the past Cymaz?

cymaz07/02/2019 05:19:11
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8441 forum posts
1160 photos

Very accurate. The static margin can be adjusted, as I understand it this changes the position of the CG point forward. I’ve used it 4/5 times as in the past I’ve been given airframes to renovate with no plans or CG range. The latest one was my Dragon Lady....10% static marginal the CG spot on and correct from the start.

Peter Jenkins07/02/2019 10:18:12
1193 forum posts
132 photos

It's moving the CG that changes the static margin. However, the only real way to check correct CG position is to fly the aircraft and then adjust the CG to suit how you wish to fly. A calculated CG is helpful to avoid a woopsie on the maiden though.

Bruce Collinson07/02/2019 20:41:25
338 forum posts

Turnbuckles also by Kavan, M 2.5, from LMS. Or mail order from Modelshop Leeds.

BTC

cymaz08/02/2019 19:18:17
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8441 forum posts
1160 photos

 

Just a quick update...

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Need some help here. Who knows where the datum line is supposed to be so I can measure off. Tonight I assumed it was the cockpit floor. If this is correct then there is +2* on the tail and +2.5* on the wing. And therefore +0.5* declage. And a further 1* on the engine shaft. The UC is on the way from Hobbyking. I’m now going off to measure all the dimensions and put them into the CG spreadsheet. I will report back in a while. I should have done it earlier but tea was callingtea

Edited By cymaz on 08/02/2019 19:18:51

cymaz08/02/2019 20:33:21
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8441 forum posts
1160 photos

Reporting back..

The manual states the cg is 147mm

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The cg calculator says..

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Interesting to see that the the calc puts the aerodynamic centre at 147mm. At 10% static margin the cg is 185mm

cymaz09/02/2019 08:14:32
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8441 forum posts
1160 photos

 

Just weighed everything and it totals 4.1kg. In English that is 9lb exactly. I hope this to reduce a small amount when the new UC is fitted, according to Hobbyking its 53g / 2oz.

The wing cubic loading is 8. 

Edited By cymaz on 09/02/2019 08:21:25

cymaz10/02/2019 09:05:34
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8441 forum posts
1160 photos

This covering is a jokeface 8

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cymaz10/02/2019 12:49:44
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8441 forum posts
1160 photos

Peter ( my aerobatic coach) came over today. We talked about where the datum line could/should be. We agreed that the ply spar that runs down the length of the fuselage would be as good a place as any. Having set up the plane level and plumb the incidents where re -measured.

As it turns out the cockpit floor is not where the datum is. Using the ply spars the wing and tail are both at 0* and the engine has 2* of down. Now, I can continue with trying to get this frustrating and infuriating build finished. Just as well the weather has been poor of late. If the weather had been good the Infinity might have gone into the corner of the workshop for a bit while I regain my sanity.

Edited By cymaz on 10/02/2019 12:50:10

Peter Jenkins10/02/2019 14:17:55
1193 forum posts
132 photos

Does the manual give any geometry? Current aerobatic machines tend to carry engine at 0, wing at +0.5 and tail at 0. The old way was wing 0 tail 0 engine 0.

I would be inclined to reduce the engine downthrust to -0.5 as I suspect you could have a marked pitch down on opening the throttle with the set up you have. Mind you, best is to try it first and then adjust down and side thrust. You may also need to play with wing incidence to get close to a vertical down and up line. Takes time to get these beasts dialled in but well worth the effort. I reckon on around 10 - 15 flights to get really close and after that there can still be more tweaking before it becomes just so! But, you always need to keep checking as structures twist with time, heat, humidity etc.

cymaz10/02/2019 14:49:24
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8441 forum posts
1160 photos

PJ, the manual only gives the info posted through the thread..the rest of the photocopied sheets is for a slightly different airframe in parts. There is no room to adjust the side thrust as the engine mount sits tight up against the ply brackets. There will be only just enough room for a few washers to adjust down thrust if required. I must read a thread on RCUniverse about the Fliton Infinity 90 from around 2004/5. It’s 95% identical.

Peter and I did a lot of work trimming out and manually trimming ( mechanical adjustments made to clevises etc) a Wot4xl. It did make a world of difference on the flight characteristics and improve the ease of flying. As you know this then reduces the work load of the pilot so they can concentrate on the pattern schedule.

Thanks for the input .......all useful stuff in the air yes

Peter Jenkins10/02/2019 23:40:21
1193 forum posts
132 photos

Cymaz, you may already be aware of the GBRCAA Trim chart but if not, you will find it here. The point to remember is that CG position is the single most powerful trimming tool we have and any change in CG needs to be followed by the full trimming process.

There is also a very powerful trimming tool by Bryan Hebert who has designed and produced for sale a number of 2 mtr F3A designs. He calls his trimming process, Triangulation Trimming. Many in the US and GB teams have used it to good effect. You can find it here.

Good luck.

cymaz11/02/2019 05:25:49
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8441 forum posts
1160 photos

Thankyou , I will read with interest.

Bruce Collinson11/02/2019 16:51:33
338 forum posts

News. Jeremy's maidened today with c of g per the "wrong" plan, 147mm, no geometry checks per the above, ASP 120; reportedly "flew like a dream" with minimal trim but low-ish rates/throws.

As I am about to change the rx in mine I will need the flying deflections/rates but it does sound to need very little to change to make it fly very well. I will post the settings in due course.

The coal-face sadly kept me away from what sounded like a very successful session. Hope it gives you enthusiasm to finish and fly yours!

BTC

cymaz11/02/2019 18:09:20
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8441 forum posts
1160 photos

yes

cymaz16/02/2019 17:56:13
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8441 forum posts
1160 photos

Glued the tail on today. Flying was, again , a washout. Pins were placed in the wing tips and these were the two measure off points. The rest of he measurements were written down a couple of days ago. Everything was glued using the standard methods of check, measure, check, measure. I sat there until the epoxy had gone off.....just in case the Pixies and Elves came in and moved the tail. Everything is cock-onyes. The the fuselage fitting hole was too long packing pieces were slipped in. These have wedged the tail up into the front, it can’t slide to the rear. The incidence is 0*. The next job is to cut new hinges and install the elevators.........what could possibly go wrong now frown. I might even have time to get the canopy cut and fixed.

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Edited By cymaz on 16/02/2019 17:57:34

Bruce Collinson17/02/2019 09:39:13
338 forum posts

The weather’s frustrating, isn’t it? We had mild often sunny, dry weather but a fresh blustery 10 to 20 mph wind at 45* to the strip so I only dared fly once with the Wot 4 which has been in A & E and felt odd. Good landing though.

ran up the Laser 100 in the Infinitelyprotracted to check the tank/carb position etc. What a sweetie. First turn when primed, held 9100 on its running in prop, apparently no issues with the plumbing generally so no more excuses. Rx and Li-ion going in, c of g to settle, loose trim to fix (now there’s a helpful patina of engine oil on it), rear hatch bolt, locknuts and Loctite on clevises etc. Then wait for a 7mph straight wind. Club mates helpfully fettled the throws and rates in the new radio.

BTC

cymaz17/02/2019 14:33:45
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8441 forum posts
1160 photos

Made a start with the elevators. Also,ade my own hinges up. I decided to use 3mm push rods, bolt the ball link onto the horn and use m3 clevises. It’s all slop free. However, I was going to attach the horn to the elevator but the bolts are TOO SHORT angry

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cymaz17/02/2019 15:46:32
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8441 forum posts
1160 photos

“And the Award for the worst painted canopy this year, goes to Ray Charles at Probuild !! “ yescool

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Edited By cymaz on 17/02/2019 15:50:19

Edited By cymaz on 17/02/2019 15:50:57

Bruce Collinson17/02/2019 15:59:30
338 forum posts

At least you have a canopy .......

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