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Jun 30, 2018, 11:15 PM
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Dirty Birdy ARF


I bought a Dirty Birdy Arf back in 2012 and started to put it together. I sort of got stuck when I got to the nose gear retract and never seemed to get around to finishing it. A couple weeks back I finaly got back to it and got it finished this week. The engine is a Lee modified K+B .61. A friend put it in the air for the first time today and got it trimmed out. On the landing the front wheel came off. I had forgotten to loctite the wheel collar! We found both the wheel and the collar, and did no damage to the plane. I flew it next and it really is a good flier. After about five minutes the engine quit when I throttled back after a loop. I think I was too lean on the needle. I managed to get the plane turned back at low altitude and it glided all the way down our runway and made a very good dead stick landing. It is still a little nose heavy, and needs a little more control throw, but I am impressed so far.

The engine seems plenty powerful with an 11/8 prop. I bought it from Mr. Lee back in 2012. I ran it a few times on a test bench then. I was so impressed with how it ran that I bought two more. It revs to about 11800 with a master airscrew 11/8 prop. It ran perfecty on the first flight except that the idle was a little too fast and the plane didn't want to slow down to land. It was a couple of hours later when I flew it and the air temp had gone way up. The next time I fly it I will back the needle out a little more.
Last edited by CE Taylor; Jun 30, 2018 at 11:21 PM.
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Jul 01, 2018, 01:42 AM
Registered User
Dirty Birdys are good airplanes, whether kit or arf built. I have both. Its good nothing major happened either with the lost wheel incident nor the deadstick landing. But I have to ask... why a master airscrew? Please... anything but... first photo shows an APC prop. Stick with that...
Jul 01, 2018, 02:10 AM
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Thread OP
We broke the tips on the APC on the first landing when the wheel came off. I had a master airscrew in my box, so that's what went on.
Jul 01, 2018, 01:00 PM
Registered User
I agree. APC only. Never a MA.

On other topic: Try to balance correctly before you adjust the throws. It will be more responsive after removing the excess nose weight.

One more: Always have dual rates programmed when you adjust the CG.

Great plane!
Jul 01, 2018, 01:33 PM
A man with too many toys
I have one of those and it is one of the heaviest DB's I have seen. My wings are very heavy, maybe I just got a set with heavy wood. A K+B .61 is not a very powerful engine so it will be under powered. I agree at MA props age less efficient that APC props.

I have fixed gear but may install retracts this winter.

.
Jul 01, 2018, 01:51 PM
Registered User
edh13's Avatar
Yay another Dirty Birdy in the flock!

Hey, PM me your address and I'll send you a set of these. I got a new little vinyl cutter I've been playing around with. I know the decals that come with the ARF are black
Let me know...
Eric
Jul 01, 2018, 02:06 PM
Registered User
Quote:
Originally Posted by RC Man
I have one of those and it is one of the heaviest DB's I have seen. My wings are very heavy, maybe I just got a set with heavy wood. A K+B .61 is not a very powerful engine so it will be under powered. I agree at MA props age less efficient that APC props.

I have fixed gear but may install retracts this winter.

.
Totally agree. I actually fly mine with a piped Novarossi 91, APC 11x11 turning 13,500 static. It flies sick fast though, measured GPS speed around 150 mph
Jul 01, 2018, 02:27 PM
AMA 46133
SeismicCWave's Avatar
>>But I have to ask... why a master airscrew? Please... anything but... first photo shows an APC prop. Stick with that... <<

ROFLMAO, you are a true pattern flyer. A bit jaded maybe but a aficionado none the less. I have not looked at a Master Airscrew since APC came out. Before APC it was all wood props. Oh I do use a Master Airscrew for stirring paint and that's not a figure of speech. I cut one down chuck it on an electric prop hub with a piece of piano wire as shaft and use an electric drill to stir paint.
Jul 01, 2018, 04:11 PM
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For all you MA haters I did find a couple more 11/8 APC props in my shop. I have added a little more throw to both my low and high rates, with about 1/2 oz more lead on the tail. As far as the K+B, it has 800 more rpm than an OS .61 that I have on the same prop, and seems to have better throttle response. The plane is no rocket, as I am using the stock sport K+B muffler. I don't like flying too far out as my eyes are not the greatest so absolute speed is not all that important to me. The plane is very sleek, and once you build up speed it doesn't slow down easily, which saved me when I had to make the dead stick. It may be a week or two before I get to fly it again.
Jul 01, 2018, 05:02 PM
I just want to go fly!
walter3rd's Avatar
150 sounds really fast. Wow
Jul 01, 2018, 05:54 PM
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I ran the K+B with three different props a few minutes ago. It is 99 degrees here, so pretty warm. The fuel is Omega 15% nitro.

Master Airscrew 11/8 11900 (It was 12500 until the engine got warm.)

APC 11/8 11100 (Was only 10600 until I richened the needle a quarter turn.)

APC 11/7 11900

Head temp was 230 degrees after about 6 minutes of running. The engine doesn't want to start hot. I think that it needs a lot more run time to get the ring seated in properly. I suspect after running a gallon or so flying I may see 11800 with the 11/8 APC. I was definitely running too lean on both flights, and the hotter air temp on the second flight was enough to cause the flame out.
Jul 01, 2018, 06:09 PM
I just want to go fly!
walter3rd's Avatar
Is a flame mean dead stick happens?
Jul 01, 2018, 06:13 PM
A man with too many toys
Quote:
Originally Posted by CE Taylor
I ran the K+B with three different props a few minutes ago. It is 99 degrees here, so pretty warm. The fuel is Omega 15% nitro.

Master Airscrew 11/8 11900 (It was 12500 until the engine got warm.)

APC 11/8 11100 (Was only 10600 until I richened the needle a quarter turn.)

APC 11/7 11900

Head temp was 230 degrees after about 6 minutes of running. The engine doesn't want to start hot. I think that it needs a lot more run time to get the ring seated in properly. I suspect after running a gallon or so flying I may see 11800 with the 11/8 APC. I was definitely running too lean on both flights, and the hotter air temp on the second flight was enough to cause the flame out.
You really can't predict flight performance form ground RPM. Different props perform differently at flying speed. You just have to fly with a few different props to find out what works best.


.
Jul 01, 2018, 10:36 PM
AMA 46133
SeismicCWave's Avatar
>>I ran the K+B with three different props a few minutes ago. It is 99 degrees here, so pretty warm. The fuel is Omega 15% nitro.

Master Airscrew 11/8 11900 (It was 12500 until the engine got warm.)

APC 11/8 11100 (Was only 10600 until I richened the needle a quarter turn.)

APC 11/7 11900<<

Those numbers are not really that useful since you really don't know the actual pitch of the propellers. The APC may be loading up the engine more than the Master Airscrew. Then again statically does not tell you what the engine will do. The static RPM only gives you some reference about the engine while running on the ground. It will be nice to have a way to actually measure performance of the propellers while the plane is flying. You can do that by flying the setup and seeing if the performance is up to your expectations.

>>Head temp was 230 degrees after about 6 minutes of running.<<

That's a nice temperature if that is after 6 minutes of WOT running. Engine will cool off a bit after idling for a while.

>>The engine doesn't want to start hot. I think that it needs a lot more run time to get the ring seated in properly.<<

Yes probably or the compression ratio in the engine is just too low for the 15 percent nitro fuel.

>> I suspect after running a gallon or so flying I may see 11800 with the 11/8 APC.<<

Again use the number only for reference.

>> I was definitely running too lean on both flights, and the hotter air temp on the second flight was enough to cause the flame out.<<

Time to try a lower pitch and let the engine unwind a bit.
Jul 02, 2018, 06:19 AM
Registered User
Thread OP
I have a Tower Kaos with a AX .46 and a tuned pipe. I have flown it with Master Airscrew and APC props. In the air the MA definitely revs higher and makes a hell of a lot of noise, but the APC actually pulls harder and the plane is faster, so rpm is not the be all and end all of performance. I know that rpm on the ground is only a relative measure. APC props generally seem to perform the best, although Zoar wooden props do very well on some of my larger engines.


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