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Ripmax Chris Foss trainer help please

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andy paterson10/04/2017 09:08:50
60 forum posts
I have the above plane with irvine 53 engine, really having problems controlling throttle, plane keeps ballooning up with throttle increase , c of g correct , if i put a sc 46 engine in would it stop the ballooning
Engine Doctor10/04/2017 09:21:58
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2467 forum posts
39 photos

You are sure the CG is correct ? Changing to a smaller engine won't cure problem Can you trim out the ballooning with the elevator trim? If not it could be either engine thrust line is wrong or the wing incidence is wrong. Without seeing the model it's difficult to diagnose . Do you belong to a club ? If you do I'd get an experienced builder/ flyer to look at it as it could be a combination of faults .We did have a member who bought one a couple of years ago and the fitting of the wings was so bad due to poor manufacture that it kept ballooning , he returned it and got a replacement . That was totally different and flew fine. Let us know how you get on .

ken anderson.10/04/2017 10:22:11
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8634 forum posts
779 photos

hello andy......i would reckon either the thrust line is wrong for the motor or the incidence of the tail plane is wrong...changing the motor wont stop it....make sure it hasn't been put together incorrect....

ken Anderson...ne...1.... incorrect dept.

andy paterson10/04/2017 10:31:40
60 forum posts
I don't know were the thrust line should be as i don't have a plane of model only the instructions for fitting together, how do i find thrust line
ken anderson.10/04/2017 10:39:25
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8634 forum posts
779 photos

andy-i don't have the model -I've seen one flying...the 53 is a pretty powerful motor for the model also..i may need the motor mount packed to give some down thrust-or the tail plane packed to remove the tendency to climb....wait until a owner of the model comes on to the forum with some info for you or try - Google..there may be some advice about the model etc...

ken Anderson...ne....1..... ballooning dept.

andy paterson10/04/2017 10:42:00
60 forum posts
I have added some down thrust by packing but i can't check the thrust line , would it be straight line with tail stab
TIM Shaw10/04/2017 11:01:03
166 forum posts
41 photos

I don't know the model either, but how is the wing held on?

I do know that the UnoWot - which was an earlier version of a trainer from Chris Foss - (and a very good one, IMHO), had the wing held on with rubber bands.

More than once I saw beginners turn up with just 2 crossed bands to hold the wings on, and they exhibited a similarly bad behaviour...

If it is a banded on wing, make sue you have 2 crossed, then 2 parallel, then another 2 crossed.

Otherwise I would think the Irvine 53 is a tad too big for the model - I have one in a DSM Contact 140, which is a serious, old school pattern plane, around 56" span, and that goes unlimited vertical on an 11x9 prop - not what you want on a trainer!

Jon - Laser Engines10/04/2017 11:03:45
5418 forum posts
263 photos

I fly many of these as i am responsible for training at my club and they do have a large pitch change with airspeed. the 53 is much too powerful for the model and frankly a decent 36 would do it as they are just big old gliders at the end of it.

The best one i have flown so far is 52 4 stroke powered and has a ton of lead on the tail for c/g. the additional weight helps settle the model and its quite nice to fly now.

andy paterson10/04/2017 17:03:49
60 forum posts
Just had a look at the engine mount, and they have been put on below the original mount points, would this give me the ballooning effect when throttle is increased
iqon10/04/2017 17:16:06
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1481 forum posts
239 photos

Andy, its a long time since i had one, cant remember anything about engine except it floats forever when landing. but engine fitting should be same as any other. Try this place a spirit level on vertical stab at tail and lift tail up until its level, then look at front of plane - point the prop towards the ground and you should be able to see if it has any down thrust. " yes there should be some....

..10/04/2017 17:22:50
974 forum posts
1 photos
Posted by Jon Harper - Laser Engines on 10/04/2017 11:03:45:

I fly many of these as i am responsible for training at my club and they do have a large pitch change with airspeed. the 53 is much too powerful for the model and frankly a decent 36 would do it as they are just big old gliders at the end of it.

The best one i have flown so far is 52 4 stroke powered and has a ton of lead on the tail for c/g. the additional weight helps settle the model and its quite nice to fly now.

I would echo this , my least favourite model to train people on. The Irvine 53 is a gutsy performer for a small two stroke, I too would dowsize it to a 52 size four stroke.

I would also replace the airframe with a Seagull Boomerang whilst I was at it😉.

Edited By Justin K. on 10/04/2017 17:24:39

Denis Watkins10/04/2017 17:45:14
4326 forum posts
104 photos

Andy, the whole tail bolts on, so check this out, as it can easily be out of scew or loose

Nevertheless, your model is way overpowered

On a .40 Irvine, our club trainer, ( this model ) is akin to a powered glider, and is very stable

Martin Harris10/04/2017 18:30:59
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9262 forum posts
245 photos
Posted by andy paterson on 10/04/2017 17:03:49:
Just had a look at the engine mount, and they have been put on below the original mount points, would this give me the ballooning effect when throttle is increased

A low crankshaft centre line would increase pitch up with power - the resulting elevator trim for level flight at cruise power will then drop the nose excessively with power reduction. More downthrust would reduce this effect...but it wouldn't hurt to put the engine where Chris specified.

andy paterson10/04/2017 18:43:41
60 forum posts
Thanks all for the replies, have put engine at correct place now ,will be interesting to see the next flight
Martin Harris10/04/2017 18:51:35
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9262 forum posts
245 photos

Jon's observation that all of these models pitch up with power would suggest to me that a little downthrust wouldn't go amiss with your powerful engine - if the engine is upright or inverted, you can buy sets of various angled plastic wedges that fit between the mount and the bearers.

Don Fry10/04/2017 19:11:42
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4557 forum posts
54 photos

If you limit the servo throw to about 60 percent of an open full throttle position most of the ballooning will go away, i.e. You will have less power. And when it balloons, ease in a bit of down elevator, to keep the nose from rising, the excess speed will bleed away, and as it slows, ease off the down elevator.

I would not be too quick to blame the tools, that is a fine, if overlarge motor, and a well respected trainer. But it flies in real air, it has its quirks, as they all do, and a thousand circuits cures your inability to fly it, as long as you address your problems. You fly it, it does not dictate what it does.

I wish my dogs would learn that lesson. Had one timid creature in the river this afternoon.

Jonathan M11/04/2017 20:49:41
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722 forum posts
289 photos

Surely any badly set-up model is going to add greatly to the pilot workload and make flying - especially if you're still a learner - so much harder.

From my free flight scale experience (as well as setting up DLG gliders and most recently my Acrowot, which certainly had a few ARTF issues!) I'd suggest that, in addition to considering downsizing the engine or at least limiting its throttle, I'd assume nothing and:

1. Ensure the centre of gravity is in the correct place (say the mid-point of the suggested range). Its possible that the extra weight of your big engine the CG is putting this too far forward. Thus, to achieve normal level flight you might have elevator up-trim dialled in, so any blast of power will then cause ballooning. A dive-test will soon tell whether the CG is correct.

2. Have a good look at sorting out down-thrust and possibly side-thrust. The greater the power, the greater the need for this. The possibility of this being a culprit is increased as the design/factory-setting for side and down thrusts will assume a smaller motor is being used. Washers, correctly sized to your mounting screws, can be inserted between the bulkhead and the engine-mount (or between the engine and the bearers) to increase these.

2. Take a close look at whether the tailplane (horizontal stabiliser) is parallel to the datum line (assume this, for your purposes, to the mid line between the tailplane leading-edge and the engine) and also what incidence the wing is set to. If the incidence of the tailplane is negative relative to the datum line, then you've got built-in up-elevator. If the incidence of the wing is excessively positive, then you're going to have similar issues.

Hope this helps,

Jon

PS I've just realised that this all repeats various bits of advice above.  But I'd reiterate my advice to assume nothing and check everything.  My Chris Foss Ripmax Acrowot ARTF came out of its box missing its elevator completely and I then discovered the wing had a 1deg NEGATIVE incidence.

Edited By Jonathan M on 11/04/2017 20:56:36

onetenor11/04/2017 23:44:58
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1901 forum posts

HORIZONTAL STAB you mean

Jonathan M12/04/2017 08:35:07
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722 forum posts
289 photos

I always understood 'stab' to be an abbreviation of 'stabiliser', its usage originating in America.

andy paterson12/04/2017 08:41:10
60 forum posts

thanks all for the replies, interesting results well check all, if I cant get it sort out will go for a seagull boomerang,

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