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Old Mar 09, 2013, 02:51 PM
222 km/hr Parkjet flyer
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Latvia, Ventspils pilsēta, Ventspils
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Replacing Glow with Gasoline power and size.

I'm posting this here in the general section and not Engines or Pattern / Aertobatic sections because I think this brokers a question that others consider whatever the model :

I used to fly many years ago Prettners CURARE pattern machine. It's 64" span and 61 powered.

So lets take this as the foundation model ... plans attached below for people to study and reference to help answer my question.

I'm proposing to build this again in modern materials mixed with traditional. In Latvia Balsa and Lite Ply are expensive IF you can find them ! So my idea is to sandwich foam with balsa sheet to provide main forms with pine spines / spars etc. Strength will not be an issue ... Weight should hopefully be slightly less than original .. lets say -10%.

Power plant is the main question. Standard high power 61 is norm for this model - with or without pipe. But my proposed power is from an RCGF 15CC gasoline engine .... a heavy equivalent to what I reckon is about a 75 ...

Given the model - my question is :

Would you increase the size overall of the model for this engine or leave as is at 64" span ....

If you would increase - what would be your factor increase ? 10%... 20% ... 30% ??

Me ? I'm hovering between leaving at original size (I'm not proposing any tuning additions to standard motor) ... up to +25% overall ... at 80" span.

??

Nigel
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Old Mar 09, 2013, 03:53 PM
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Why don't you size the engine as the electric fliers would -- pick pounds of thrust.

For vertical aerobatics you need 150 watts per pound, or just over 1 pound of thrust per pound of plane. Figure out what the Curare weighs, then pick an engine with 30% more thrust in pounds.
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Old Mar 09, 2013, 04:41 PM
222 km/hr Parkjet flyer
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Quote:
Originally Posted by wuest3141 View Post
Why don't you size the engine as the electric fliers would -- pick pounds of thrust.

For vertical aerobatics you need 150 watts per pound, or just over 1 pound of thrust per pound of plane. Figure out what the Curare weighs, then pick an engine with 30% more thrust in pounds.
I'm already an Electric Flier as well as Wet Fuel .... but that's beside the point.

Please re-read my original post - I am not asking what engine .......... I am asking IF anyone thinks to INCREASE model size to take the 15cc Gasoline engine or to leave as original 64" span.

For anyone interested - I've already identified suitable electric conversion for it - but would like to fit my RCGF 15cc ...

Nigel
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Old Mar 09, 2013, 08:52 PM
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a 15CC equals a 90 2 stroke...so you'd be ok with the 64 in span
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Old Mar 10, 2013, 05:28 AM
222 km/hr Parkjet flyer
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Quote:
Originally Posted by jetmech05 View Post
a 15CC equals a 90 2 stroke...so you'd be ok with the 64 in span
I know technically it does ... but in practice is really about a 75 equivalent ... This is second RCGF I have.

The other thing is whether the RCGF will fit in the nose .. as the Curare nose is quite tight even for a 61 glow.

Nigel
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Old Mar 10, 2013, 09:15 AM
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At the time the classic pattern planes were designed for 10cc or .61 size two stroke engines. They didn't have gasoline engines or even four stroke engines yet. Then streamlining for speed was very important too. So yeah they did make the engine compartment and nose of the plane really tight fitting for .61 engines.

You may be able to squeeze in a rear carb, beam mount 15cc or 17cc engine OK. But it may be pretty tricky, as you may have to move the firewall back. Another option is to use a NGH 17cc gas engine, which is a front carb, beam mount engine. With the more conventional engine design the NGH 17cc engine would be easier to fit into the tight engine compartment.
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Old Mar 10, 2013, 09:44 AM
222 km/hr Parkjet flyer
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Originally Posted by earlwb View Post
At the time the classic pattern planes were designed for 10cc or .61 size two stroke engines. They didn't have gasoline engines or even four stroke engines yet. Then streamlining for speed was very important too. So yeah they did make the engine compartment and nose of the plane really tight fitting for .61 engines.

You may be able to squeeze in a rear carb, beam mount 15cc or 17cc engine OK. But it may be pretty tricky, as you may have to move the firewall back. Another option is to use a NGH 17cc gas engine, which is a front carb, beam mount engine. With the more conventional engine design the NGH 17cc engine would be easier to fit into the tight engine compartment.
I had the Curare many years ago when Hanno was flying it at championships ... we all followed guys like him ... mate of mine had a Magic ... I had the Curare etc.

I have the RCGF 15cc - which has standoff tube mounts at rear with rear carb - so I'm hoping that with minimal changes - she will go in. If not then I see a 61 going on order !!

Nigel
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Old Mar 10, 2013, 10:07 AM
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Quote:
Originally Posted by solentlife View Post
I had the Curare many years ago when Hanno was flying it at championships ... we all followed guys like him ... mate of mine had a Magic ... I had the Curare etc.

I have the RCGF 15cc - which has standoff tube mounts at rear with rear carb - so I'm hoping that with minimal changes - she will go in. If not then I see a 61 going on order !!

Nigel
As a heads up... there is rumor that Evolution might be releasing a 15cc similar to design of the 10GX next month at Toledo Show. The 10GX is a drop in for a .46 case and it might be that a possible 15GX is a drop in for a .61 size case.... we'll have to wait a month and see.
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Old Mar 10, 2013, 11:47 AM
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I can't speak for the 15cc, I wanna get one, I have the 20cc and the 50/55cc! "RCG"

I think, other then moving the firewall back, to accomedate the carb, is that it will need a longer prop, to get the thrust needed to equal a 60 2 stroke!

I think if you can prop it properly, it should be a great plane, as gassers are great tractors, as in will pull vertical hard!
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Old Mar 10, 2013, 01:24 PM
222 km/hr Parkjet flyer
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Quote:
Originally Posted by whiskykid View Post
I can't speak for the 15cc, I wanna get one, I have the 20cc and the 50/55cc! "RCG"

I think, other then moving the firewall back, to accomedate the carb, is that it will need a longer prop, to get the thrust needed to equal a 60 2 stroke!

I think if you can prop it properly, it should be a great plane, as gassers are great tractors, as in will pull vertical hard!
On my Skymaster Biplane ... a 1980's display biplane from UK used to display for Skyleader radio ... the RCGF 15cc was propped with a cut-back 14" to 12.5" ... beautiful smooth ... then I just fittted 12 x 6 and let her go with that ... definitely underpropped - but the engine throttled and ran smooth as anything. I was concerned that the smaller prop than recc'd may suffer lack of flywheel effect for the motor ... but no - she was fine.

What did happen - was the RCGF really pulled her round as she could rev up easier being lightly loaded - meaning rpm was higher than would have been on it's recc'd 14".
Original of the model was for 11x7 on 61 ... so my 12x6 basically was comparable.

Lets see when I get home and start measuring up ... it may mean just a simple widening of the forward frames to increase fuselage width ... along with moving firewall back a bit.

Nigel
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Old Mar 10, 2013, 02:16 PM
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although not personally interested in pattern ships, I will be keeping an eye on you, as I am interested in all facets of the hobby!

and this looks like an interesting subject!

and with the selections of props out there, you should have no problem finding the one you need!

if you could find a tuned pipe, now that would be awesome!
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Old Mar 10, 2013, 03:19 PM
222 km/hr Parkjet flyer
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Quote:
Originally Posted by whiskykid View Post
although not personally interested in pattern ships, I will be keeping an eye on you, as I am interested in all facets of the hobby!

and this looks like an interesting subject!

and with the selections of props out there, you should have no problem finding the one you need!

if you could find a tuned pipe, now that would be awesome!
I have passion in modelling ... whether it's EDF, Pusher, Glow, Gasoline, Biplane, Mono, .......... literally any !

I also post various in hope it will help others ... even to creating a topic ...

Nigel
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Old Mar 10, 2013, 03:59 PM
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Quote:
Originally Posted by solentlife View Post
On my Skymaster Biplane ... a 1980's display biplane from UK used to display for Skyleader radio ... the RCGF 15cc was propped with a cut-back 14" to 12.5" ... beautiful smooth ... then I just fittted 12 x 6 and let her go with that ... definitely underpropped - but the engine throttled and ran smooth as anything. I was concerned that the smaller prop than recc'd may suffer lack of flywheel effect for the motor ... but no - she was fine.

What did happen - was the RCGF really pulled her round as she could rev up easier being lightly loaded - meaning rpm was higher than would have been on it's recc'd 14".
Original of the model was for 11x7 on 61 ... so my 12x6 basically was comparable.

Lets see when I get home and start measuring up ... it may mean just a simple widening of the forward frames to increase fuselage width ... along with moving firewall back a bit.

Nigel
If there were an Evolution 15GX, then it would require a smaller diameter prop than a typical gas engine, as the construction is typical to glow and the rpms more similar to glow than traditional gas planes.
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Old Mar 10, 2013, 04:11 PM
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That is a good point, the gas engines behave more like four stroke engines in turning larger props at slower RPMs, they don't do well at higher RPMs like the .61 pattern engines do.
The next problem is if you have a large prop, do you have enough ground clearance for it? usually the pattern planes barely had enough prop clearance for a 11 inch prop and still have it possible to get in retracts and have them work too.
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Old Mar 11, 2013, 03:10 AM
222 km/hr Parkjet flyer
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I intend to fly both ways : No U/C and Fixed U/C ... have it removeable.

I make my own legs etc. - so ground clearance is not a problem.

Once I've printed of the plan ... stuck the A4's together - I'll measure up ...

I'm waiting for info on flights home ... so hopefully should be home tomorrow to start on this ... and all the other projects I have going !

Nigel
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