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Old Sep 23, 2009, 04:37 PM
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Build Log
Dirty Bird-E for SPA competition

After the loss of my Curare, I was forced to use may backup plane (last year's Intruder) at the Asheville, NC SPA contest in July. While I was at that contest, I noticed an "in the bones" Dirty Birdy that Vic Koenig had for sale. Seems he builds a few of these for sale, and this one had been set up to use an OS 91FS engine. After looking it over carefully, I decided it would make a great .... and very light weight (thanks to Vic's careful balsa selection and building expertise) 5S SPA plane. My goal was a 5S (Zippy Rhino 3700) powered plane with an AUW of 6.0 lbs. I had a Hacker C50 11S+6.7:1 collecting dust, and thought this would be a good way to use it.
Here are a few shots of one of Vic's Dirty Birdy's. The one I bought was identical ..... except it has built up wings.
Ed
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Old Sep 23, 2009, 04:46 PM
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I worked out a deal with fellow club member Jim Andrews to apply a Monokote covering scheme while I sorted out the conversion details to get it from a 4 stroke 91 to electric power.
Jim does a wonderful job with Monokote .... and his expertise really made the model stand out.
Here are a couple shots of his work:
Ed
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Old Sep 23, 2009, 04:51 PM
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I worked out a nose mount for the C50 and it looks like this installed.
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Old Sep 23, 2009, 05:04 PM
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The good news .... I was able to achieve 6.25 lbs AUW with the 5S C50 setup.
The bad news .... It was way tail heavy (had been built for that heavy OS 91FS up front) .... and I had to add 9 oz of lead to the nose to get the CG where it needed to be.

Now my 6 lb 1200 watt plane had become a 7 lb 1200 watt plane.

I propped it up to 1400 watts .... and it flew great ! But .... flight times with the 5S 3700's pulling higher amps (75 at WOT) resulted in 5-6 minute flight times.

It looked great for those 5 minutes though .
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Old Sep 23, 2009, 06:20 PM
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Here are a couple more shots showing the elevator and rudder setup.
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Old Sep 23, 2009, 06:40 PM
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I decided to replace the 9 oz of lead weight in the nose with a heavier motor ( Hacker A50 12S outrunner ) and a 6S pack of Zippy Rhino 3700's.

This will give me 1400 watts ... but at 63 amps .... so my flight times are back to 7-8 minutes.

With an adapter ring the A50 drops right in to the mount I have in place.
Here's what it looks like:
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Old Sep 23, 2009, 06:53 PM
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Prop testing disaster

After I bolted the A50 in place, I wanted to try several props to see where I wanted to start. The A50 (mounted by the nose) has a collet type prop adapter that pinches down to secure it to the 6mm motor shaft when you tighten the prop. Evidently I did not get the prop nut tightened enough as during my tests the prop adapter (and prop) slipped forward. When the adapter and prop reached the end of the motor shaft a violent wobble resulted. This wobble literally ripped the nose off my brand new DB-E and sent the motor flailing into my back yard.
I just stood there with my mouth open.
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Old Sep 23, 2009, 07:12 PM
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The good news was that the broken balsa was neither fuel soaked, nor caked with dirt ..... so it fit back together rather easily.
After tacking it back together with CA, I reinforced the nose with 2 oz fiberglass and epoxy.
A call to my buddy Jim Andrews with hat in hand secured his assistance in reworking the Monokote on the repaired nose.
I thought I was home free until I bolted the motor in place and started to resume my prop tests. Seems the motor shaft was slightly bent ..... either from the violent wobble or from hitting the concrete below my test bench when it flew off.
I had a spare A50 10S ..... and little time ..... since I wanted to have this plane flying in the SPA contest in Andersonville, GA in less than a week. I contacted MicroDan ( Daniel Sny ) at gobrushless.com and asked him for his help. Dan lives only 30 minutes from me, and generously agreed to swap out the shaft in my A50 10S for the bent one in the A50 12S. Dan graciously agreed to do this on Sunday afternoon following my Saturday night emergency call.
So .... thanks to the help from Dan and Jim, I was at the field practicing with my new DB-E on Tuesday .... before leaving on Thursday for the SPA contest .
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Old Sep 24, 2009, 09:11 AM
jrb
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Looks like you'll be swapping some of the lead with glue Ed!

Keep the photos and reports coming.

Jim
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Old Sep 24, 2009, 07:57 PM
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By the time I substituted the heavier A50 and the 6S pack for the 5S pack (and after the fiberglass/epoxy repair) I only needed 3 oz of lead in the nose.
I can't seem to let well enough alone though ..... as I've fitted a C50 13S+6.7:1 for further trials.
One thing I miss about the geared inrunners is the finite throttle control .....especially from 25% to 100% throttle. Seems no matter how I tweak the throttle curves with outrunners .... I always get the whole throttle range stuffed in the 20% to 70% range.
It is really hard to get finite throttle increases in the 40% to 60% range. You end up getting a burst of power all at once, which plays havoc with your pattern smoothness.
4 flights today convinced me that further testing with this motor is warranted .
Ed
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Old Sep 25, 2009, 08:06 AM
jrb
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Quote:
Originally Posted by Ed Lyerly

One thing I miss about the geared inrunners is the finite throttle control .....especially from 25% to 100% throttle.

Seems no matter how I tweak the throttle curves with outrunners ....

I always get the whole throttle range stuffed in the 20% to 70% range.

It is really hard to get finite throttle increases in the 40% to 60% range.

You end up getting a burst of power all at once, which plays havoc with your pattern smoothness.

An interesting issue -- wonder if it has to do with the number of poles, and the calcs needed to be done by the ESC?

Way back when the Mega 6 poles came out we fould that the on Kontronik ECSs there was a 33,333 rpm (200,000 / 6) issue.

You need more poles to go slower/lower the Kv, or use a gearbox.

I'm having good luck so far with my outrunners and ESCs on A123-10S when flying mostly between 1/2 and 2/3s stick.

What's you typical throttle stick position Ed?
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Old Sep 25, 2009, 08:27 AM
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I guess I really don't understand the variables involved. I always hated the way the Jeti/geared Hacker combos wanted to start up at about 15%-20% throttle. They were very smooth and linear after that .... but things got dicey when you needed just a touch of throttle to extend you landing (can you say galloping landing approaches).
I just adopted the "power up and go around" approach if the landing approach glide did not look perfect. Early Aveox (and I think MaxCim motors) had "sensored" controllers .... and these worked very well and smoothly on startup.
I've tried Jeti, CC, and Turnigy ESC's on outrunners. They all want to give you a "burst" of power at some point around mid-throttle. Working with the throttle curve helps .... but IMHO, the power can be applied much more smoothly with these geared inrunners. It might be the fact that they are spinning 6.7 times as fast when you apply the request to speed up.
I move the throttle stick around a lot. This is a carry over from nicad days when capacity was limited and throttle management had a lot to do with the flight times you achieved. Basically, I just give it the throttle it needs to do the maneuver .... and no more.
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Old Sep 25, 2009, 10:34 AM
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My Jeti 77 opto & HiMaxx HC6320-250 (on A123-10S) act funny at start-up -- apply throtlle slowy and it won't, with quick snap to 1/2 it's burst. But they do seem to work well on approach -- able to make small power changes even from stop w/brake.

The 77 worked well with a Scorpion 4025-16 as well as with a geared Mega 22/30/2.

The HiMaxx HC6332-230 and Kontronik 3SL40-14-32 (on A123-10S2P) in my Cub has never showed any throttle issue.
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Old Sep 25, 2009, 11:19 AM
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McLean, VA
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Hi Ed,

Its been awhile hasn't it! Glad you are still tearing up the sky. Beautiful plane, by the way!

I need some power plant advice, and hope you can help. Last week, I lost my Short Fuse Sallee, a Model Tech P-51D. It was powered by a Hacker B50L 5.2:1, on a 5S-5000 mAh pack from XPS. Prop was a 14x10 APC-E. This is similar to Kelvin's notorious Spitfire. I began the plane many years ago after seeing jrb's great conversion of the same model. all up weight of mine was 8.2 lbs and the wing loading was 30 oz/sq.ft. The plane was very well powered with this setup and flew well. I had revised the color scheme and markings and fitted larger tires so it may not look like the original Sallee. (see pic)

After the crash (not rebuildable) I sent the motor to Hacker for a new output shaft and to have the Hacker/Jeti 77 Opto ESC checked. Hearing that others also experience the jerky power application from that combo, I think I will replace it, possibly with a CC 100 ICE. That assumes I find another P-51 airframe to put the motor in. The Model Tech P-51 was a 2001 vintage ARF and are now hard to find.

There is a new Hangar 9 P-51 that looks really nice.

http://www.horizonhobby.com/Products...ProdID=HAN2420

Its wing span is 8 inches greater and it is 2 lbs heavier than the Model Tech.

Here are the questions.

Do you think there is any way my B50-10L could power that plane? I can not tell whether the motor can be run on a 6S Lipo pack. There is ambiguous info on the Hacker sites about the max cell count. In one place 6S and all others, 5S. Goingto 6S would be the preferred approach.

If the B50 is not feasible, then what other Hacker geared in-runner would you suggest? I happen to be hooked on their sound and efficiency. For planes this size, I don't think the performance prediction computer models are reliable, so the real world experience of others is highly valued.

P.S. to jrb.....Thanks for blazing the trail on this conversion. I never got around to fitting a four blade prop. Maybe next time!

Thanks Ed,

Best Regards, Jim
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