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Old Feb 17, 2013, 05:34 AM
222 km/hr Parkjet flyer
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Latvia, Ventspils pilsēta, Ventspils
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Discussion
Thoughts on flight behaviour after changes

Take a 53" wingspan biplane ... traditional balsa rib construction with tex covering..... fibreglass fuselage ..... designed for a standard 61 (10cc) glow 2st motor ... 11x6 - 12x6 prop .....

On the standard config is a dream to fly with typical AA size Rx pack and a 10oz tank up front .... balances nicely.

We move on 20yrs and another kit of exact same machine (been on shelf for all that time) appears and I build her just the same.

But instead of a 61 Glow motor - I elect for a 15cc gasoline motor that has an ignition box, extra AA cell ignition pack as well as the normal Rx AA pack etc. same 10oz tank, same position.

I fit all this ... reckon the motor must be a good amount more than the original 61 ..

The extra AA pack goes just in front of servo tray ... about on CoG ... Ignition box is just ahead of undercarraige so about in line with LE of top wing (the two wings are staggered about half chord).
I add no weight or adjustments to tail at all ... she appears to balance on CoG ...

In flight she is fine ... bit slower in rolls ... but loops fine ... so general flight ... take-off are fine. Shut the throttle and she rears up like a Rodeo stallion ! This makes landing a challenge ... in fact only nice landing was on the very first maiden when engine cut short way into flight ... and she exhibited NO signs of this trait then ... she dead-sticked in beautifully ...

Here's maiden flight ....

Skymaster maiden 29 oct 2011.wmv (12 min 6 sec)


So the question for all to consider is why she rears up as she does ? Is it because she has so much more weight in her ? As far as I can tell all wing incidences etc. are as should be ... in fact it would be difficult to change those as the cabanes are prebent by factory, mount holes pre-marked, tailplane slots are pre-moulded ... and my 1980's one built as per plan flew for years without any of this ....

Is it the extra weight ? Should I distribute the weight more ? is it the CoG is harder to determine as being a large biplane - could actually be off from where I found it ?

This model is nearing rebuild completion and i have to make choice - fit the new 15cc motor I bought or order a 61 and fit out as my original one / designed ?

Over to you guys !!

Nigel
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Old Feb 17, 2013, 05:57 AM
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Nigell,

Main problem tail heavy visible also as sensitive on the elevator.
You can see it right after the second take off.
Because you continue the flight the problems become even worse as fuel is consumed by the engine.
Observing the plane you better could have shortened the second flight, now you were very lucky to have it back on the ground without much damage

Cees
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Last edited by Taurus Flyer; Feb 17, 2013 at 06:03 AM.
Old Feb 17, 2013, 09:24 AM
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If as. you say it is balanced correctly could the angle on the firewall be incorrect causing you trim for level flight. Then as you pull off power the airplane balloons up
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Old Feb 17, 2013, 11:11 AM
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Looks tail heavy to me. Looked like you were fighting the elevator to keep it at level flight. At faster speeds the elevator trim is keeping the tail up. When you back off the tail wants to drop.

Most people balance their planes for level flight at 1/2 to 3/4 throttle, depending on their style of flying. Usually these planes will rise when the throttle is increasd.
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Old Feb 17, 2013, 02:09 PM
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I'd guess that it was balanced ok when the tank was full, but after the tank emptied it was too tail heavy and that is why it got worse over time.
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Old Feb 17, 2013, 09:00 PM
222 km/hr Parkjet flyer
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Latvia, Ventspils pilsēta, Ventspils
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Quote:
Originally Posted by Taurus Flyer View Post
Nigell,

Main problem tail heavy visible also as sensitive on the elevator.
This reply surprises me .... as the model is checked for CoG with empty tank and was spot on design point. having had one of these models before and flown for 100's of flights over years - the design CoG point is good.

Quote:
You can see it right after the second take off.
My style with such models that even with stock power are over-powered is to haul of instead of rise of ground ... The servos used also are very slow compared to todays ... they are the same 1980's JR NE101's from my original model. I also, as I intended to use for display work - as I did with my original - have a lot of movement on the surfaces ..

Quote:
Because you continue the flight the problems become even worse as fuel is consumed by the engine.
The RCGF 15cc is actually underpropped significantly and fuel consumption is way less than a 61 glow ... after a 7 min flight I still had near 2/3 a tank left .... The model is also balanced with empty tank as I've always done for over 40 yrs.

Quote:
Observing the plane you better could have shortened the second flight, now you were very lucky to have it back on the ground without much damage
A later flight - the elevator servo failed ... model inverted turned to come past in a semi low pass ... she then dived for the deck.

Skymaster 5 nov 2011 crash.wmv (5 min 11 sec)


Initially as in the video - I believed I'd done the typical wrong way while inverted ... in these cases - its very difficult to really truly remember what you do ... so you assume. On studying the video - you see that the model stayed straight as a die into the tarmac, with no hint of deviation even though I was giving elevator commands ... suggesting that elevator servo had failed. At home later checks indicated an intermittent problem with the servo. This also could be part of the overall problem as well ... but I think the failure is a later act and not part of the slow speed ballooning.

There were lots of discussions with other in my flight group as to possible reasons for the ballooning ...

Wrong thrust line ? altered that significantly to see if any change ... none.

Wing incidence wrong ? shimmed that + and - ... no change

The only thing I did not do was to alter the distribution of gear. Checking the CoG indicated that all was fine ... but I always had a nagging thought in back of mind that something was wrong. How can you add a much a heavier motor, two NiMH AA packs instead of 1 - in same place as original and still balance same ? In fact the original also had a tuned pipe mounted along the fuselage side !!

One guy suggested that too much weight was in one place ... making her more violent in pitch. This is actually a common problem on boats, I sail boats as well ... fulll size ! There you spread out weight to reduce violent pitching.
This prompted my starting this thread to get opinions on causes / solutions to the ballooning.

I don't say tail heavy is wrong - what I say is comparing my 1980's and present models, the only changes are significantly MORE weight up front. The kit is same ... no additional items at tail etc.

There is the matter of too forward a CoG that flies OK ... but when power is taken off particularly in a nose down dive - that model pitches up ... so could that be it ?

I'm rebuilding the model ... near to completion and want to make decision to either fit the new RCGF 15cc engine, spread out the weight more ... or go for original set-up by ordering a 61 glow motor ... (I chose the gasoline engine for running costs ... glow fuel is difficult to get here in Latvia and expensive .. only 1 supplier and that is via order only ... but gasoline is 5 mins down the road).

Nigel
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Old Feb 18, 2013, 09:40 AM
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Main problem seems to be the position of CoG but............... weakness of the structure does have the same result.
Was the mounting of the wing rigid? And an even more important question were shear webs mounted in the wing!!!
When the wings deforming under load the result also can be instability over the pitch axis as we see!!

General , can't you fly one straight meter with that plane, what is your goal of such a flight, full power, above concrete??????

Cees
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Old Feb 18, 2013, 01:48 PM
222 km/hr Parkjet flyer
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Quote:
Originally Posted by Taurus Flyer View Post
Main problem seems to be the position of CoG but............... weakness of the structure does have the same result.
Was the mounting of the wing rigid? And an even more important question were shear webs mounted in the wing!!!
When the wings deforming under load the result also can be instability over the pitch axis as we see!!
Wing is built same as my previous and designed by one the UK's best - Chris Foss and Phil Ramsay along with Kenny Binks - the model was designed for Skyleader radio Display ... In fact I changed balsa spars in both mine for pine after chatting with Phil Ramsay.

Quote:
General , can't you fly one straight meter with that plane, what is your goal of such a flight, full power, above concrete??????

Cees
In fact the motor was never full throttle as it was still running in ... and anyway - what is the point of your statement .... which has no relevance to the thread.

The flight site is Ventspils Airport Runway ... so ?

I've been flying such models for displays and other for many years ... along with WOT4's and other ...

Nigel
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Old Feb 18, 2013, 03:32 PM
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Double post deleted.
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Old Feb 18, 2013, 03:38 PM
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Now I see this all was an old story, 2011!!

2012:
http://www.wattflyer.com/forums/showthread.php?t=67517

I also did find this thread, about repairÁ 2012.
http://www.rcgroups.com/forums/showt...d#post23458571

When I observe photographs, internals of the top wing and the cabana, I doubt very much the structural stifness. Of course this is the repair after the crash but, how did the structure look like before, because the RCGF15 gas is 2.4 HP, much more than the 0.60 standard engine the plane is designed for in 1980.

Cees
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Old Feb 18, 2013, 06:31 PM
222 km/hr Parkjet flyer
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Quote:
Originally Posted by Taurus Flyer View Post
Now I see this all was an old story, 2011!!

2012:
http://www.wattflyer.com/forums/showthread.php?t=67517

I also did find this thread, about repairÁ 2012.
http://www.rcgroups.com/forums/showt...d#post23458571
So ? The repairs are still ongoing as I haven't finished ... the fueslage is only part that is apart from fitting the new motor.

Quote:
When I observe photographs, internals of the top wing and the cabana, I doubt very much the structural stifness.
The wing is still to be finished - only the ribs have been repaired ... webs, LE, spars etc. are still to be done. If you doubt the design capability of such as Phil Ramsay and Chris Foss - then you must be a "God" .... I am sure "Fossy" would be interested to hear your advice !!
You can believe or not believe - but that model was designed for serious display work by 4 of the top RC guys in UK in the 80's ...

Quote:
Of course this is the repair after the crash but, how did the structure look like before, because the RCGF15 gas is 2.4 HP, much more than the 0.60 standard engine the plane is designed for in 1980.
You really do not give up do you ....
The display machine was powered by Irvine and OS FSR engines ... which if you'd like to check were nigh on 2HP in those days and HIGH rpm. My 1980's model was fitted with Supre Tigre 61 ABC with tuned pipe ... rated to EXCEED 2HP with the pipe ...
The model was not usually powered with 'cooking motors' or 'plodders' - it was often found with high power AAC / ABC 61's and was more than capable of taking it. There were some who fitted 90 4 Strokes to it ...

Before making statements about a model that you obviously have little knowledge of - I suggest you read the following ....

http://www.philramseymodels.freeserv...roduct%201.htm

This is the Mk 2 version with the Foam veneer wings, but still same essentially as the Mk 1 that I had and have now. Designed for 60 2 str or 90 4 str ....

Nigel
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Old Feb 18, 2013, 06:41 PM
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Quote:
Originally Posted by solentlife View Post
So ?


Message shortened by TF


This is the Mk 2 version with the Foam veneer wings, but still same essentially as the Mk 1 that I had and have now. Designed for 60 2 str or 90 4 str ....

Nigel
This is my point and that cabana!!

This very pretty bi-plane has a new wing section and four ailerons to combine excellent low speed handling with its outstanding aerobatic capability, even in limited flying space. The Skymaster is equally suited for training or sport flying as it is extremely smooth to fly, as well as possessing unlimited scope in manoeuvrability. It is especially proficient at Touch and Goís. The Mk II version also makes use of moulded outer wing struts to add to the modelís strength in the air. The all-up weight of the Skymaster is 7lbs approximately.

Cees
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Old Feb 18, 2013, 07:44 PM
222 km/hr Parkjet flyer
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Latvia, Ventspils pilsēta, Ventspils
Joined Jan 2010
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Quote:
Originally Posted by Taurus Flyer View Post
This is my point and that cabana!!

This very pretty bi-plane has a new wing section and four ailerons to combine excellent low speed handling with its outstanding aerobatic capability, even in limited flying space. The Skymaster is equally suited for training or sport flying as it is extremely smooth to fly, as well as possessing unlimited scope in manoeuvrability. It is especially proficient at Touch and Goís. The Mk II version also makes use of moulded outer wing struts to add to the modelís strength in the air. The all-up weight of the Skymaster is 7lbs approximately.

Cees
Cees ......... with all due respect - you really do not know the model and you are flogging a dead horse with me over it. I know the model ... I know the guys who designed it ... I've been flying them for years ...
The struts were added later more for cosmetics and also that being banded on wings - it was not unusual to see the wing tips near clap in violent manouevres.

The cabanes are extremely stiff in heavy gauge piano wire ...... so really do not understand your comment about those ...

I would like to get back to the whole point of the thread - and that's weight distribution of the model and its ballooning on shutting throttle.
My point in ressurecting the model issue was because I am near the decision point of what to do with gear in it or to return to a 61 motor etc. etc. I was looking for dialogue to help decide ....... seems it's not to be ... so I shall wander off and decide on my own.

Nigel
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