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Old Nov 27, 2011, 11:24 PM
Electric Coolhunter
Thomas B's Avatar
United States, TX, Fort Worth
Joined Jun 2000
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Making good progress at last on my much delayed Sparrowhawk! All that is left to do is the motor installation and part of the landing gear installation. Have already built a nice heavy duty ply box to correctly position the motor. Might get it in the air next weekend, weather and time permitting.

Successfully moved the two elevator servos to the area next to the rudder servos...hated the exposed elevator servos on a nice looking scale model. Used 4/40 steel pushrod assemblies in plastic tubes and it was a pretty easy modification.

Servos are Spektrum DS-821 throughout. Had considered using a Hyperion motor earlier, but decided to use a Tacon Bigfoot 110 from hobbypartz.com instead, on 8s 4400-5000 cells and an 18x10 prop. RX will be an AR8000. Still considering ESC options.

Have a nice aluminum spinner and am drilling and tapping the aluminum bolt on prop adapter to accept the spinner retaining bolt.
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Old Nov 28, 2011, 01:18 AM
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Peter M's Avatar
Newcastle, New South Wales, Australia
Joined Sep 2007
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Quote:
Originally Posted by wuest3141 View Post
I have the 71" Sparrow Hawk waiting for assembly. A few queries...

1. How many mAh are you pulling out of your batteries, when you fly?
2. How may amps is your system pulling?
3. Do you know how many watts to the prop your system is putting out?
4. Approximately what is the stalling speed of your plane?
1. Aim for not more than 3200mAh and generally more like 2800ish.
2. About 56 amps static
3. About 2100 watts
4. Not really slow but not fast either! Faster than a 40 sized trainer but definitely not bad mannered or difficul. If the CG is correct, it is very nice to fly.

If you haven't skimmed the first 6 pages of this thread - before the thread got weird - I suggest you may find these pages useful.

Regards
Peter
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Last edited by Peter M; Nov 28, 2011 at 01:40 AM.
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Old Nov 28, 2011, 01:43 AM
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Peter M's Avatar
Newcastle, New South Wales, Australia
Joined Sep 2007
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Quote:
Originally Posted by Thomas B View Post
Making good progress at last on my much delayed Sparrowhawk!
Thomas,
Didn't you start this conversion when Nixon was still President????


I'm pleased you're nearly there and really really want to see some photos please!

Regards
Peter
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Old Nov 29, 2011, 10:00 PM
Pullin' G's Man
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Ossining, NY
Joined Dec 2005
1,005 Posts
The model arrived today (a day earlier than originally projected) on the big brown truck and was no worse for the trip from California. The covering could use a touch fro the heat gun here and there, but no cracked wood or plastic anywhere.

Thankfully, the cowl fits. The wings felt a little heavy, but then I remembered that they also have to support the landing gear.

I think I will be able to use only long stand-offs to mount the motor, but that isn't certain yet.

Will have to look back through Peter's earlier photos to see what to Dremel out to make room for the batteries, and where exactly to cut the hatch and how to size the battery cradle.

The elevators aren't as huge as they appeared to be in the photos, so I think I will use the Hitec mini servos that I have on hand, the 5245's. I would use 225's if I had them. Plenty of torque and way more speed than necessary, and they will fit under the stabs easily. There isn't as much space back there as I thought. However, if I use the mini's I don't think they will need to be offset.

Rudder will remain pull-pull. The way they have it set up will make installation a snap. Glad I don't have to figure out the cable exit holes.

As usual, looks like another great product from Seagull. The general quality level of ARFs is incredible these days. Recently assembled a 3DHS Osiris and it was superb as well.

-- Bob
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Last edited by cmoulder; Nov 30, 2011 at 07:47 AM. Reason: servo model # 5245, not 5425
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Old Nov 29, 2011, 10:14 PM
Pullin' G's Man
cmoulder's Avatar
Ossining, NY
Joined Dec 2005
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Quote:
Originally Posted by Peter M View Post
1. Aim for not more than 3200mAh and generally more like 2800ish.
2. About 56 amps static
3. About 2100 watts
4. Not really slow but not fast either! Faster than a 40 sized trainer but definitely not bad mannered or difficul. If the CG is correct, it is very nice to fly.

If you haven't skimmed the first 6 pages of this thread - before the thread got weird - I suggest you may find these pages useful.

Regards
Peter
Peter, I should be able to stay aloft for about a half hour with the 5000 10s.

I test fit them in the fuse and don't think there will be a problem with having enough space.

-- Bob
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Old Nov 30, 2011, 08:27 PM
Pullin' G's Man
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Ossining, NY
Joined Dec 2005
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I got a little work done today, getting the elevator servos installed in their modified locations, as well as marking out the battery hatch where it is to be cut on the top of the fuselage.

The servo modification was pretty straightforward... just cut some ply doublers, CA them in and cut the openings for the servos.


Figuring out where to cut for the battery hatch was somewhat tricky. I used the thick balsa "ledges" on the inside of the fuse as a guide and stuck some T pins from the inside out to get a starting guide, then worked from there to try to square everything up, with some rubber bands then stretched around the outside curves to help make a guide for marking. I will do the Big Cut tomorrow.
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Old Dec 01, 2011, 12:08 AM
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Peter M's Avatar
Newcastle, New South Wales, Australia
Joined Sep 2007
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Bob,
Good luck with your cut!

(Probably the most nerve wracking part of the conversion!)

Regards
Peter
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Old Dec 01, 2011, 05:51 AM
Pullin' G's Man
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Ossining, NY
Joined Dec 2005
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Quote:
Originally Posted by Peter M View Post
Bob,
Good luck with your cut!

(Probably the most nerve wracking part of the conversion!)

Regards
Peter
Peter,

I hope it comes out half as nice as yours!

I will content myself with the fact that a multitude of sins can be absolved with a good sanding bar and some Oracover, of which I happen to have the exact color on hand.

Haven't yet decided a latch method. Perhaps some magnets and some small ply guide tabs will do since the model will not see a lot of negative aerobatic G forces.

-- Bob
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Old Dec 02, 2011, 01:43 PM
Pullin' G's Man
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Ossining, NY
Joined Dec 2005
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Peter, what down thrust angle are you using?

I got the hatch finished and magnets hold it on very well.

On to the motor mount which should be the last tricky bit. I am going to wait until almost done to put in the battery cradle so that I have the CG figured out and know better how far forward or aft it needs to be. With heavier motor and batteries, I am guessing the batteries will end up farther aft than yours.

-- Bob
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Old Dec 02, 2011, 02:27 PM
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Peter M's Avatar
Newcastle, New South Wales, Australia
Joined Sep 2007
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Bob,
You're a go getter!

I've used between 1 and 2 degrees of right and down thrust on mine and have never any cause to revise this even though I used tube standoffs that are very easily adjusted.

With the battery box I just made it as long as I reasonably could and just use foam spacers front and rear of batteries to maintain the CG in the correct location.

I also find that the foam spacers protect the batteries very well when I crash and are very easy to adjust if you try different motors, batteries or even as the weight distribution changes as repairs are made. Consequently I've taken this approach on all my conversions.

Keep at it! And post some more photos please!

Regards
Peter
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Old Dec 02, 2011, 02:57 PM
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bicyclemonkey's Avatar
Fayetteville, AR
Joined Jan 2010
471 Posts
Quote:
Originally Posted by cmoulder View Post
Peter, what down thrust angle are you using?
I'm glad to see this thread seeing some action again. I've had mine for a couple months and I'm thinking about starting to build...

Doesn't the firewall already have the thrust angle built in already?
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Old Dec 02, 2011, 03:16 PM
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Peter M's Avatar
Newcastle, New South Wales, Australia
Joined Sep 2007
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That's good to hear, another completed conversion would be great!

My recollection is that the standard firewall is square to both axis. I build my false firewall square (which is just one end of a very long battery box) as well and just built in the side and down thrust by using different length standoffs for the motor mount.

LOL, I'm sure Bob will correct me if I'm wrong!
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Old Dec 02, 2011, 04:15 PM
Pullin' G's Man
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Ossining, NY
Joined Dec 2005
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Mine has some right thrust built in. Looking at it from the side, it appears to have a bit of up thrust.

However, this is subjective because I don't know what exactly is the base line for the measurement. I am going to eyeball it and give it what appears to be a bit of down thrust owing to the facts that the thrust line isn't all that far above the wing, and the wing itself has a semi-symmetrical airfoil.
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Old Dec 02, 2011, 09:12 PM
Pullin' G's Man
cmoulder's Avatar
Ossining, NY
Joined Dec 2005
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Keep at it! And post some more photos please!

Some pix from today's work.

I forgot to get some photos of the covered hatch by itself but will do some more later.

The magnets were glued in with copious amounts of CA and were covered with Oracover. They hold the hatch very well and the hatch is centered without the need for some additional guide tabs. It will likely need a small "lift tab" on the edge of the hatch on one side near the magnets to assist in removal, such is the power of the magnets. This hatch is not going to come off in flight, I am absolutely sure.
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Old Dec 03, 2011, 12:01 AM
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Peter M's Avatar
Newcastle, New South Wales, Australia
Joined Sep 2007
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That looks magificent!

Great work Bob.
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