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C.G. point of my Retlas Spitfire

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C.G. point of my Retlas Spitfire

Old 07-29-2005, 07:36 AM
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Tjen il-vec
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Default C.G. point of my Retlas Spitfire

Hi There,


I'm new here and I first would like to take this oppertunity to compliment those responsible for this superb site! [8D]

However, I have a bit of a problem; I've been searching for the build instructions for my Retlas Spitfire 69". The kit is ready, well... apart from pinpointing the exact place for the center of gravity. I've been told that the C.G. is quite critical as far as this model Spitfire goes so I have to get it just right!

But due to the fact that I moved to another city I found out that I apparently lost the build instructions [:@] wich contains the exact info according to this center of gravity....

PLEASE HELP

I would be very very greatful to the poerson who is able to give me this information !!

Thanks!

Tjen il-Vec

Old 07-29-2005, 10:18 AM
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dicknadine
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Default RE: C.G. point of my Retlas Spitfire

have you contacted the kit manufacturer? he is the best one for the info. dick
Old 07-30-2005, 02:38 PM
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smck
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Default RE: C.G. point of my Retlas Spitfire

Manufacturer no longer in business. CG should be 105mm (4 1/8") from LE at centre section.
Keep control throws small, particularly elevator, recommended 12mm (1/2") each surface.
Good luck.

Stuart
Old 07-31-2005, 02:18 PM
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Tjen il-vec
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Default RE: C.G. point of my Retlas Spitfire

That's exactly right SMCK! I purchased this kit by reading an, now old, edition of the 'FMT' magazine back in 1996 I guess (I don't remember exactly when) and saw this short article and review about the !QUOT!Retlas Spitfire Mk-Vb!QUOT! The illustration that came with the article immediately drawed my attention according to the 'scale' features and quick build options. So I bought the kit... took me over 2 years to get it resembling the Mk-V (LF) EP120 Spitfire that is based on Duxford in Britain. But the instructions that came with the kit were quite poor. Just one piece 'a paper and a, what I think it was, a pat on the back and good luck. So unfortunately I lost this instruction over the years and, after some configuration changes, I'm planning to fly this beauty this summer but the C.G. is difficult to get right caused by the short nose of the MK-V and I was told that this C.G. for a Spitfire can be very very critical to get your Spit to fly well. But nowhere on the Internet could I find anything pointing to Retlas whatsoever.


Anyways, I would like to thank you SMCK for this valuable information about the C.G.!!! thanks!!


Tjen il-Vec [8D]
Old 08-01-2005, 02:17 PM
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smck
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Default RE: C.G. point of my Retlas Spitfire

I had/have a booklet of instructions which were reasonably comprehensive. I finished up with 13 1/2 oz of brass, (carefully turned and trued) in the spinner.

Stuart
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Old 08-02-2005, 04:21 AM
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Tjen il-vec
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Default RE: C.G. point of my Retlas Spitfire

13 1/2 oz? that's sounds quite a lot to me... well it seems to be obvious given the fact that this version is equipped with this short nose unfortunately. It has the Merlin 46/47 harboured in the MK-V with a Single Stage, single speed supercharger.

Stuart, how does this Retlas MkV fly with this extra weight in the nose that evidently adds up to the total weight of the model? And do you have flaps installed on your MK-V?

My Retlas has no flaps installed (yet) and I have to add the weight in the nose and I'm planning to fly it with a 20cc Saito and to cope with the impactforce that comes with a landing I have a set of damped oleo legs installed, manufactured custom bij Unitract... what is your opinion about this configuration?


Thank!

Etienne

(my apologies for the poor English my friend )
Old 08-02-2005, 03:18 PM
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smck
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Default RE: C.G. point of my Retlas Spitfire

No Flaps, no problems slowing up to land. Did not fancy carving up the foam wing. Once I got used to the idea of flying with some down elevator as per the fullsize, it flies very well. I too use the Unitracts with oleo legs, engine is a Laser 120. Believe your set-up will be very suitable. As I said earlier, just be careful of the elevator movement.
Hope all goes well.

Stuart

(Your English is extremely good)
Old 08-03-2005, 03:21 PM
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Tjen il-vec
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Default RE: C.G. point of my Retlas Spitfire

Hi Stuart,

Thank you for your friendly reply ;-)

What I'll do is take a few pictures of my Spit to show you what my efforts did to the looks of this MK-V if only I knew how to upload a photo... I'll figure it out hopefully (I'm not a PC expert unfortunately [])

I'll keep in mind the sensitive elevator settings and try a few configurations in the air according to ailerons C.G. and elevator.

I did a couple of test runs with the engine FA120S yesterday and I found out that the way I fitted the engine, inverted, gives me some problems due to the fact that unburnt fuel with priming builds up in the glow plug causing improper firing of the mixture which again causing the propeller to fly off and end up at the other side of the field ...... after 3 attempts it gets quite frustrating believe me! However, I tried firing up the engine with the model upside-down... no problem. Only you have to pick up the model, turn it upside-down, have it supported by a stand (I don't know the word for it [&:]) That's the only thing I forgot to give it a thought before installing it.... but OK, I can live with it. Basically, I have the same problem with my inverted-engined FW190D9 but fitted with a 2 stroke and somehow that give me less problems to fire up if you only keep in mind that it isn't primed to much.

I'll keep you informed on the photo's I'll place soon OK?

Regards,

Etienne

Old 02-25-2006, 09:12 PM
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Tjen il-vec
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Default RE: C.G. point of my Retlas Spitfire

Hi There,

Well, new update. The Spitfire hasn't flown yet because I'm still working on getting the C.G. right...... []. I kept in mind the suggestion of adding about 13 1/2 oz of weight in the nose but it didn't seem te be enough. Along with the SAITO FA120 I had to add another 21.2 oz to the nose to get the C.G. at its required 105mm point from L.E.

That seems a lot to me given the weight of the Saito 31.7 oz. and for a Laser 120 27.7 oz. That would be a total of.....

21.2oz + 37.7oz = 58.9oz total nose weight for the Saito configuration
13.5oz + 27.7oz = 41.2oz total nose weight for the Laser configuration

That's a weight difference of 17.7oz!

I finished up with 13 1/2 oz of brass, (carefully turned and trued) in the spinner.
Maybe it is caused by my method of the adding of weight in the engine cowling instead of the spinner? (closer to the C.G. so to speak?)

regards,

Tjen


By the way.... the engine starting problems have been solved. Using the right priming method and mixture setting works wonders!
Old 06-20-2006, 02:58 AM
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Tjen il-vec
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Default RE: C.G. point of my Retlas Spitfire

UPDATE!

I understood that the total weight of the Spit may not be more that about 10.5 lbs. Now with my C.G. at the right position the Spit's weight is exactly 12.1 lbs. Is that an affordable weight to fly the spit?

Tjen il-Vec

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