Bird of Time

[David Keil]

I have almost finished my Bird of Time and am now at the point of deciding on a motor to suit, hoping someone can advise me. The only physical restriction is I am limited to 28mm dia. The weight of the model will be about 60 ozs.

As an absolute beginner please make it as simple as possible

[will -0]

Hello can't help you with electrocuting your BOT, but when you say absolute beginner - is that to electrics or RC gliders in general? If the latter and your BOT is the full 3m one, I hope you have a big field to land in!

Oh and Pictures please!

[David Keil]

Will -0.... I have been flying for only a few months but do understand the difficulty in landing it. However to assist this I have included spoilers which I am told will help.

[ken anderson.]

welcome from david...I would look on some of the sites for a 400-450 watt motor to suit your model........also make sure that the wings are up to the job-I believe some were folding when people were stressing them in the air.....even more so with the power conversion one's.....

 

ken Anderson ne.....1 stress dept...

Edited By ken anderson. on 21/10/2013 18:10:10

[David Keil]

Erm wings folding doesn't sound good, any idea where the weak point could be

[pete taylor]

Hi David
If you've built your BoT from the original plan or the Dynaflight kit you'll have no worries about folding the wings..this was only a problem with the artf version. Dave Thornburg designed the BoT for f3b comes...a long time ago admittedly! She's still a thoroughbred though Pay attention to setting up as the plan suggests, esp the cg - resist any urge to move this forward of the suggested range, the rearmost position will allow you an amazing speed range and indicate the slightest lift.
As for motors, look for one that will swing a 12-14" prop. Have a look at the robotbirds or hobbyking glider motors.

[ken anderson.]

have a look on this site-they touch upon the wing failure....you may need to strengthen the centre section...

 

ken Anderson...ne...1 ...BOT dept...

 

 

and another by a forumite........use the search facility for more info .....

Edited By ken anderson. on 21/10/2013 19:26:20

[David Keil]

Thanks for the info on motors...thinking of these from hobbyking, any thoughts would be appreciated.

NTM Prop Drive 28-36 1200KV / 530W

NTM Prop Drive 28-36 1000KV / 400W Brushless

[pete taylor]

Ken, those links both refer to the artf version that was known to have issues with the centre section construction. The original BoT is built using 1/2 x 1/8 spruce top and bottom spar caps with 1/2 hard balsa vertical grained webs between and 1/16 ply doublers in the centre section and will withstand a sensible winch launch without modifications. Interestingly, Ray Hayes of Skybench Aerotech still uses exactly this spar structure for their range of soarers.

Edited By pete taylor on 21/10/2013 20:32:54

[David Keil]

Pete, just to change track a little having completed the stabilator and all setup on the fuselage, in the neutral position there appears to be little or no down elevator. Now as a newbie to this I am not sure if this is normal or maybe just an optical illusion.

[pete taylor]

The rigging angles depend on the exact cg position. Basically, with the cg at the rearward plan position the bottom surface of the wing and the centreline of the tailplane will be at 0/0 degrees. This is why the plan states that this cg is best for speed as it produces least drag.
If the cg is brought forward for greater stability the tailplane needs to be at a greater negative angle to stop the model from diving, producing more drag. That's a bit simplistic, but gets the idea over

[David Keil]

Thanks for that Pete,

I obviously have an awful lot to learn but getting there very slowly

[pete taylor]

You'll get there! Pm me.
Cheers

[David Germany]

David,

I assume you have built the fuselage exactly as plan with a tapered nose which is why you will be restricted to 28mm dia. On advice from other BOT builders I built mine with a parallel section forward of the wing which enabled the fitting of a 35mm dia motor and I have used a Turnigy 540L V-Spec Inrunner w/ Impeller 810kv from HobbyKing. With a 12 x 6 this pulls approx 300 Watt on 3 cells and gives a reasonable rate of climb, however on 4 cells the climb is very good and a 30 second motor run takes is plenty high enough for my aging eyes. I think the preferred motor is a MVVS 3.5 Outrunner, but these are very pricy (about £90)

Re the above comments on wings folding if you stick with the mild steel wing joiner you will not have a problem. I lost my joiner a few months ago and unable to locate any 1/4" bar I used 1/4" HT Ally instead, Worked fine for 6 or 7 flights until turning into wind for a landing at about 50 feet the wings folded up like a buzzard and promptly dived into the ground. Amazingly one wing panel was intact and the other suffered only a cracked root rib and minor leading edge damage, the ally bar was folded through 120 deg. The fuselage suffered only minor damage. I think maybe the higher stresses from using the 4 cell battery and the reduced strength of the ally were just too much. The joiner has now been replaced with steel as Dave Thornburg specified.

I also built spoilers into the wing panel and they do work, but you need to mix in some up elevator to counteract the pitching down and keep the model level. I also included a wire joining strap across the two stabilators as I found there was a tendancy for them to pull apart slightly in flight. I also have some down elevator mixed in with throttle to prevent the nose from pitching up to sharply, or you could hold in some down during the climb.

I have marked the fin with the position of the stabilators where they give a flat glide and I check this before each launch. not sure what the incidence is, I'll try to have a look tomorrow.

Get someone to give you a good strong level launch without power, preferably over some long grass, you can then have both hands on the tx ready to react and you can check the glide.

You'll love this model.

David

[David Keil]

Thanks for that David, some very helpful tips and suggestions.

Unfortunately I built exactly as per plan without even considering motor size. Unless I do some severe alteration to the fuselage I think I am stuck with the 28mm width.

[Tim Hooper]

David,

If money isn't too much of an issue, you should be able to find a 28mm inrunner fitted with a gearbox on the front. This well let you swing a huge (and efficient) prop. These are used quite often by the glider flyers.

tim

Edited By Tim Hooper on 22/10/2013 20:40:31

[David Keil]

Thanks Tim but having had a look they are really out of my price range at the moment. Think I am going for a Hyperion GS2213. Hopefully it will produce the required results.