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Author Topic: Boston Beagle  (Read 2958 times)
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Yak 52
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« Reply #25 on: December 11, 2012, 11:36:07 AM »

Well the Beagle is now finished. The final weight of the airframe is 9.1 grams excluding the prop and shaft (which with a slightly scraped Peck prop and shaft gives an AUW of 11.35g) Glides over the bed look promising, the glide was flatter than expected with the model hitting the wall on the far side of the bed!  Roll Eyes So the drag looks good. The undercambered wing has been a success so far, it’s light and stiff with no warps except for the wash in I’ve added to the left wing. Covering was with unshrunk esaki, steamed and then banana oiled.

So have I met my design goals? Not quite. It looks like it’s going to need tail weight Sad 0.8g to be precise, with the 2g Peck prop on the nose and the predicted 4g motor weight. This means that the design is still not optimal. The nose is slightly too long or the motor could be run further back into the rear fuselage (necessitating a re-design of the tail.) In other words I could have had either a longer tail moment arm (better stability) or a longer motor (HtP).

This is partly because I’ve built lighter than expected, I over-estimated the weight of the empennage in my point mass calculations. A heavier build might be balanced without tail weight. I could use a lighter prop (the BD5 laminated prop was under a gram), but since I need to add 2.65g of ballast anyway I probably won’t bother, the only advantage would be reduced inertia. In fact, rather than putting 0.8g on the tail I will put the whole 2.65g just aft of the wing, which will be better for inertia.

I have already learnt some lessons from this design however. Firstly I’m encouraged by the weight (a concerted effort could see this as a 7g design) Being so underweight also shows that a full length motor set against nose weight in a conventional layout should be possible. This is where the next one will be headed. Obviously when a motor is part of the CG equation (ie it doesn't balance on the overall CG) then some fine tuning with nose or tail weight will be needed as you change motors during trimming. This is another good reason for building underweight. I now have better notes on the weights of the various components so my CG estimates should improve.

The other thing is that noses can be too long. It’s a fine balance, especially when using a heavy stock prop. I’ve come up against this in another of my designs but this has really made the point for me. I will look more carefully at this in future designs. It does mean that you can move the wing forward a little and the tail moment can be lengthened slightly.

Of course this fine tuning is what Bostonian is all about: competing design factors and building to a minimum weight forces compromises that wouldn’t be applicable to a general model with different limits and where lighter is better.


Now I just have to fly the thing  Smiley


Jon
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Russ Lister
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« Reply #26 on: December 11, 2012, 02:35:26 PM »

Jon,

Have you considered using a 'Clem' style prop? If you can keep the weight of this down below that of the Peck you may be able to lose that tailweight at least in part.
A flying friend of mine got an immediate 10 second improvement in times using a copy of the prop I used on my SortaSenator (The original being sent to me by the late Al Backstrom)
... his times being greater than I have yet to achieve myself! (wish I hadn't told him  Roll Eyes)
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« Reply #27 on: December 12, 2012, 09:48:37 PM »

Jon,

Have you considered using a 'Clem' style prop? If you can keep the weight of this down below that of the Peck you may be able to lose that tailweight at least in part.
A flying friend of mine got an immediate 10 second improvement in times using a copy of the prop I used on my SortaSenator (The original being sent to me by the late Al Backstrom)
... his times being greater than I have yet to achieve myself! (wish I hadn't told him  Roll Eyes)

The Clem prop is in the plans gallery.
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Yak 52
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« Reply #28 on: December 13, 2012, 11:26:32 AM »

Have you considered using a 'Clem' style prop? If you can keep the weight of this down below that of the Peck you may be able to lose that tailweight at least in part.

Russ, I did consider doing a laminated version like on my BD5, but since I have the weight available I have continued with a Peck prop scraped slightly to improve the shape and balance. I will see how it goes with that and switch to a clem style later perhaps.

Here's a couple of final pics (tissue a bit saggy in the damp). AUW before rubber or ballast is 11.35g. And one final attempt to convince Russ  Wink
Attached files Thumbnail(s):
Re: Boston Beagle
Re: Boston Beagle
Re: Boston Beagle
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« Reply #29 on: December 13, 2012, 11:40:28 AM »

The Beagle is obviously begging for a bone Roll Eyes
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« Reply #30 on: December 13, 2012, 12:03:30 PM »

I thought it was VTO (Vertical TakeOff)

Looks great Grin Wink Cool

Tom
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« Reply #31 on: December 13, 2012, 02:43:02 PM »

Jon,

A traditional ROG is all that is required   Roll Eyes ..... ok, ok, ok, I admit defeat!
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« Reply #32 on: December 13, 2012, 06:14:45 PM »

I'm with PT - defnitely Grin It will never get the bone with a ROG  Grin
That will be a nice flying model Jon.
John
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Yak 52
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« Reply #33 on: January 19, 2013, 04:51:48 AM »

Managed to maiden the Beagle last night. It did need a tad of tail weight. I just wanted to get it trimmed so I wasn't trying too hard. It's still under weight so it will need ballast for Impington rules.

http://youtu.be/0VanjjBsmuw


Unfortunately the fluorescent green trim tabs have compromised the stealth abilities of the aircraft. The ground crew should be court-marshalled...
« Last Edit: January 19, 2013, 05:18:36 AM by Yak52 » Logged
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« Reply #34 on: January 19, 2013, 05:45:53 AM »

Looks very promising Jon  Smiley
The only thing that struck me was that the final descent looked a little quick?
Only watching on an iPod so couldn't see any clues as to why this might be?
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Yak 52
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« Reply #35 on: January 19, 2013, 06:06:06 AM »

Thanks Russ. At about 0:20 it flies through the downdraft from one of the ventilators and drops the left wing a little. Not sure if that's what you mean, or after that?

It's far from sorted yet - the motor was just one I grabbed from my box (not even sure what size it was  Undecided 3/32 I think) and that flight was about 700 turns (perhaps the descent rate was it running out?) I haven't touched the thrustline yet. I'm hoping that with the ballast and more turns 3/32 will still be about right.
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« Reply #36 on: January 19, 2013, 11:46:09 AM »

Very good to be showing potential like that on a 3/32" motor ... though as you say, the model is still underweight.
I should have explained what I was thinking when I mentioned the descent. I was wondering if the CG was still too far forward and a bit of downthrust was required.
Hence the slight power stall (with quite a light motor as it turns out) and then a more nose down descent.
Whatever it is, things still point to the model being a good'un!
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Yak 52
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« Reply #37 on: January 19, 2013, 01:28:20 PM »

Very good to be showing potential like that on a 3/32" motor ...

It might be 7/64!  Embarrassed

I think you're probably right on that - I didn't get as far as downthrust and the CG is dead sensitive to tiny changes in the tail weight. This was supposed to be a trim flight so I was quite surprised it did 30 seconds...
« Last Edit: January 19, 2013, 02:51:22 PM by Yak52 » Logged
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« Reply #38 on: January 19, 2013, 01:54:44 PM »

I'd put money on it going through a minute before long ... past 70 seconds at that venue and I'm bringing a sonic 'bazooka' to the next Impington.
I've wondered before how these would 'deal' with flying models .... excuse me? ... not sporting you say?
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Yak 52
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« Reply #39 on: January 19, 2013, 02:09:11 PM »

Or a vortex cannon  Grin

http://www.youtube.com/watch?v=nsBuoBi-whU

I was thinking: how about a Gyminnie Cricket combat competition - last one down wins  Wink
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« Reply #40 on: January 19, 2013, 02:14:07 PM »

That's more what I had in mind Jon  Grin .... I think what I said is a product by 'nerf'
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Yak 52
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« Reply #41 on: January 20, 2013, 03:46:34 AM »

Very good to be showing potential like that on a 3/32" motor ...

It might be 7/64!  Embarrassed

I've checked and it was 18" of 3/32  Smiley Yay!
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« Reply #42 on: March 10, 2013, 02:45:09 PM »

Started trimming the Beagle with ballast (14g) at Oundle on Friday. I was using long motors of 7/64 but still getting too much climb. I didn't have any 3/32 to try, although it might not give enough oomph anyway.

Comfortably doing a minute at the moment with 2200 turns on a 33" motor. Russ, can you remember what time the winning flight was at the last Impington? I think it was 70+ seconds?

Hit the rafters and dinged the LE but it's all repaired now...

Jon
« Last Edit: March 10, 2013, 03:51:26 PM by Yak52 » Logged
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« Reply #43 on: March 10, 2013, 03:02:24 PM »

Jon,

I have a feeling that it was over 75 seconds on average? There were less entries last time and yet the times were noticeably longer than normal for some reason (possibly the clear hall when everyone is in the seminar?).

As I remember, the air at Oundle can be quite 'bouyant' (has it got underfloor heating?) ... might be different at Impington?
Good to be getting a consistent minute or so, but I have never got that many turns onto a Bostonian motor. Are many turns left on landing?


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Yak 52
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« Reply #44 on: March 10, 2013, 03:46:06 PM »

75 sounds about right  Undecided

As I remember, the air at Oundle can be quite 'bouyant' (has it got underfloor heating?) ... might be different at Impington?

Not noticed this myself, the heating is a ring of radiators at about 10 feet up. I only noticed 'cause they swallowed a hangar rat on Friday! I was getting quite a bit of turbulence off the radio models too.

Are many turns left on landing?

Not sure. It's still early days with it... Should get a lot more than that on the motor but the climb from adding turns was what ended my session with it (the ding)  Undecided



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« Reply #45 on: March 10, 2013, 03:58:13 PM »

It's a few years now since I used to travel to Oundle so the memory is a bit vague ... but I do seem to remember models finding the ceiling a little easier there than on subsequent flights elsewhere.

Only another week to find out anyway! I might be failing again ... but if all else fails I will put some times in with my old 'Oo La La'.
Interestingly, I have not had very good times with this since moving the rear peg forwards ... it has got heavier with glue since this time too though  Roll Eyes
Even at it's best, times were under a minute for this though ... not really built for all out duration. No other functioning Bostonians!
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« Reply #46 on: March 10, 2013, 04:44:06 PM »

Look forward to seeing it!
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Yak 52
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« Reply #47 on: March 19, 2013, 06:29:58 AM »

I flew the Beagle at Impington on Sunday. It's doing a minute ok but it didn't win. The winner did 65 seconds. I found that it has a spiral stability problem. It's ok with modest power but as you work up to more turns and more torque it reaches a critical angle of bank and rather than ROG it scoots around the floor like a car on a race track. I can get enough turns for longer flights but that's useless if it won't take off!

It had a big rudder tab giving too large a fin area so I cut that down a bit, but it really needs more dihedral. I might try winglets to give dihedral effect or re-build a smaller fin. I've realised that because the airfoil is more refined and the model is flying slower at a higher CL it has less spiral stability than a model with a worse airfoil! It also has a short vert tail moment compared to most Bostonians.

I tried it on 3/32 but decided to use 0.100 thou. Still a bit too much climb (handled by backing off the turns) but the cruise was about right.
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« Reply #48 on: March 19, 2013, 05:54:43 PM »

Good to see your Beagle flying at the weekend Jon  Smiley

I was watching it for a few flights, so I saw the problems that you refer to.
I might have gone down a slightly different road in an attempt for a 'cure' (any model doing a minute at Impington is doing well!)
My first NE14T had perhaps less dihedral than your Beagle ... I would have mine flying in larger circles than you had the Beagle flying .... running the gauntlet of the walls and those nicely placed basketball hoops though!
I also had mine slightly more nose heavy as the model tracks a circle more predictably in this manner with less tendency to nose into a slight stall ... the ceiling is that low there it helped to keep short of the rafters too.
Having said that, my model did have a longer tail moment that perhaps helps as you say.
65 seconds for the winner ... missed the times. Wish that my SortaSenator hadn't got trodden on!
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« Reply #49 on: March 19, 2013, 07:51:47 PM »

I've just measured the CG and it's quite far forward (more so than my Cub actually) I was using a very long motor (33") so perhaps that was shifting the CG around. I'm tempted to try a shortish 3/32 motor again. It was definitely squirrelly! I found that it was hard to get the correct turn radius. It was either too tight or opening up too much  Roll Eyes a bit of a knife edge. But on lower thrust later in the flights it was pretty steady.

I was wondering if the forward CG (for weight reasons) is keeping the inner wing stalled in 'race track mode', which would prevent the ROG quite nicely  Grin

It turns out that this isn't the Ultimate Bostonian but it's getting there and I have a few ideas and lessons to apply to the next one...
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