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Dawn flyer; C of G


Basil
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Hi, at long last have finished my Dawn flyer, or so I thought. As a newbie I found installing the battery/tx/BEC/ safety plug all a bit if a minefield hence the long time to finish, I have had a lot of distractions and other builds. However I have installed a 2200 Lipo up against the rear of the engine bulkhead, the BEC alongside. RX as far forward as possible.The servos are as far forward as possible. When trying to check the cog I find that in order to obtain the cog under the mainspar, as per article, (about the end of the LE sheeted area), I need about 300grams  in the nose to obtain this. This seems a bit much I thought.What have other builders found, and is this the correct position??? What have I done wrong? My AUW is 1.26kg including everthing.

I feel very perplexed as I have followed the build without deviation.  I would really welcome some advise/comments. I've checked BEB's thread and Biggles brother said it was spot on!!!!

Bas

Edited by Basil
addition of Biggles elder brother's comments
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I used Oratex Antique.Mini plastic bowden cable for Elevator.Wire push pull Rudder.The rest according to plan.Andy & Early bird, have you built this?. I'll check the COG wieght again later to day, along with some other checks including the position of the 2 servos.

Bas

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The plan, as far as I can see does not detail the positioning of the servos. My MG16R are mounted just in front of the 'Wing bolt fixing plate'.They wiegh app 19grm each(Plus the woodem mount and fixing screws) and could be moved forward at best app 2", to a position between the U/C legs. Bringing them under the COG.However the RX would then have to be moved to the rear of the servos(wieghs 8grm)  This would undoubltly improve the COG.Where has you servos been mounted. Does any body know the loaded AUW of their model.?

Bas

Edited by Basil
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1 hour ago, john stones 1 - Moderator said:

My servos went in well forward,everything as far forward as possible, some had 6oz, hard to believe yours requires 21 oz Bas.

21oz??? 300grms is app 300/28 =10.7(oz)!!!

Have found BEB Dawn Flyer entries, so moving servos to the front.

I would be very interested to hear other members AUW of Dawn Flyer.By the way I am a newbie/returnee so have a lot to learn!!

Bas

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1 hour ago, Denis Watkins said:

Just got replies from 2 Dawn Flyer builders at my club Bas.

Both within design AUW of 2lb 12oz 1270grams

All gear forward Leads to 3oz and 4oz added for C of G.

These builders are like others on this site who select the wood for tail feathers very carefully.

Thanks Denis, I am not so far out at 1.26kgs !!, a bit comforting then!!!. I am moving the servos forward nearer the COG, getting rid of the snake in favour of a small dowel. Then I will have a quick check to see if it improves. I found a thread that gives some detail on servo mountings, Biggles brother again.

Bas

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To answer your question Basil, no I have not built the Dawn Flyer but I have built similar models.

 

If you used Oratex on the tail surfaces then that is quite likely where your extra weight requirement has come from. Oratex is very heavy compared to film / tissue / Airspan covering. On a plane like the Dawn Flyer it is likely that the weight ratio is 4 to 1 or 5 to 1. By that I mean 10 grams of weight on the tail  will require 40 - 50 grams on the nose, so if we work this backwards - 300g in the nose could be due to 60g at the tail. Is the skid you have fitted made from heavy components?

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6 hours ago, Andy Gates said:

To answer your question Basil, no I have not built the Dawn Flyer but I have built similar models.

The same here Andy and I also wondered why use heavy Oratex on a small model like this. Basil the key is to build the tail light, but not a lot you can do about it now. I had the same issue with my Ohmen build and was advised to add the lead and go fly. Moving the servos forward will help and I will be interested to know by how much. Your AUW of 1.26 kg did this include the 300g?

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2 hours ago, EarlyBird said:

The same here Andy and I also wondered why use heavy Oratex on a small model like this. Basil the key is to build the tail light, but not a lot you can do about it now. I had the same issue with my Ohmen build and was advised to add the lead and go fly. Moving the servos forward will help and I will be interested to know by how much. Your AUW of 1.26 kg did this include the 300g?

Earlybird, no it did not. Sorry I reported it that way.The AUW reported was the model prior to my efforts to balance it.From memory the reason I used Oratex was that the article or subsequent threads indicated that was the 'Thing' to use. This was my first model since childhood, and I am well over the yardarm now, things have moved on a long way.I l have always had a practicle bent and love the building but have to learned by trail ,error or from these threads.You cant rely on your club due to isolation rules. So !!!!

I am in the middle of some mods, so we'll see what transpires.

Bas

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Thats not why I wanted to build it!!!. I wanted a nice majestic slow flyer, obviously in carmer weather, I'am still learning.There's a possibility that the 300grms can be improved upon- watch this space.Many thanks for your comments.

Bas

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Just did a quick COG check, a bit over eager so only a rough figure. A reduction to about 210grm from 300gr. The servos sit almost under the COG.Next problem is where to sits the RX.Its about 8grm but if its forward its by the side of the servos. Surely I cant sit it on the battery & BEC in the nose area???

Suggestions on a post card to .....................

Bas

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Hi Bas,

8g won't make much difference however far ahead of the CofG it isAs long as it is ahead, it's really not a big deal. bigger gains come from moving things from behind to ahead of the CG.

 

Spend the most time looking for weight to lose right at the back. 10g at the back is 50g at the front!

 

Do what you can, but then add lead and fly it. It's not heavy even with the ballast. And in the grand scheme of things 7.5Oz is going to mean a couple of Oz on your wing loading, which is not going to be a deal breaker. 

 

Graham

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Basil,

 

Not necessarily this time around, but maybe your next model of this ilk try using laminating film covered with tissue. Should be quite  a bit lighter.

 

Good luck with your first flight.

If you have just come back into RC flying, can I suggest you get an experienced flyer of this style of model to maiden this for you to get it all trimmed out.

That will reduce the pressure on you when you do fly her for your first time.

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15 hours ago, Andy Gates said:

Basil,

 

Not necessarily this time around, but maybe your next model of this ilk try using laminating film covered with tissue. Should be quite  a bit lighter.

 

Good luck with your first flight.

If you have just come back into RC flying, can I suggest you get an experienced flyer of this style of model to maiden this for you to get it all trimmed out.

That will reduce the pressure on you when you do fly her for your first time.

Andy, I would be my intention to get someone to maiden it, I am not experienced enough to try myself.I have bought some laminating film through these forums, I used it on an other model, like the way it goes on etc but it does not seem that strong.Why cover with tissue, assume it makes it stronger!!. Why not just used normal heat shrink covering like eg Easycoat?.

Bas

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Without wishing to be rude, why cover with Oratex?

For its finish, it looks like fabric.

Tissue will look a lot more period than plastic film would on a machine like this, but tissue is a bit too fragile. So the laminating film provides enough strength and the tissue gives the period finish - best of both worlds.

Alternatives may be out there, airspan used to be good for this but now not made.

 

I would personally avoid Easycoat - it is awful stuff, the glue / colour layer comes off the film way too easily and the film does not seem to last. I have some planes covered with Solafilm which has been on the planes for 16 / 17 years. Easycoat seems to start lifting off the airframes I have covered within 1 season, even my 2 year old glider looks like it has been flying for 20 years, very tatty.

 

Good decission and good luck with the maiden.

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On 21/01/2022 at 09:04, Basil said:

I have bought some laminating film through these forums, I used it on an other model, like the way it goes on etc but it does not seem that strong.Why cover with tissue, assume it makes it stronger!!. Why not just used normal heat shrink covering like eg Easycoat?.

In addition to the appearance tissue can also add rigidity to a structure that you don't get with just a heatshrink film.  While this isn't important on something like the Dawn Flyer, on more lightweight airframes it can help prevent "flutter".

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