Official Black Horse 1724mm Dornier DO335 Pfeil ("Arrow") Thread

[Oxotnik]

I’ve had a couple PM’s asking about balancing with the 6S-8AH battery pack. I went the route of purchasing two 3S-8AH batts (CNHL 3S-8AH-30C) and wiring them in series, to get 6S voltage and 8AH capacity. I’m parallel-feeding both 5055 motors from this pack. To balance at the manufacturer’s suggested CG location of 175mm aft of the leading edge, I had to push the battery pack as far back as it’d go in the battery compartment. I’m still about 5mm nose heavy, but plan to maiden with this slight nose heaviness.

I ‘ve got her loaded and ready to deploy. Once I get to the field, I’ll do a thorough range check, recheck the wiring and kick the tires. If no problems are encountered, I should have her in the air in a few hours. :-)

I’m a getting a bit nervous, I have to admit. Maddening small stuff doesn’t phase me anymore, but maidening large, complex warbirds still turns my stomach in knots.

[Twowingtj]

Oxotnik Good luck on the maiden. Glad the hear that it did CG with the 8k lipos. Do you have any idea what the AUW on it is?

I was planning in the future to put nose gear doors on it and have the landing light operate with the gear. I thought that the cicuit board from the FW A-10 would suit the purpose to do that. I did find out that the XWave retracts work on the opposite signal than the Freewing A-10 retracts. I had to reverse the channel in the transmitter. So when the gear are up, the light comes on. Goes out when extended.

[Oxotnik]

Maiden Flight Report

I successfully maidened my Do-335 today. Upon arriving at the field, I carefully checked the alignment of the ailerons, elevators, rudders, and flaps. Did a thorough range check with the engines at full throttle, with no problems. Did a taxi test to get the nose-wheel steering trimmed. One of the Main Struts rotated in the trunion. Several grub screws were loose on the Mains and were vigorously retightened. After tightening the screws, the 335 taxxied just fine (and later took off and landed just fine, too). I know that I’ve described my setup in other posts (and some of it multiple times), but for the completeness of a maidened flight repot, I’ll describe my setup again.

Radio: JumperT16
Receiver: FrSky X8R (two), running on 8.4v from a 2S LiPo receiver battery.
Motor (tractor and pusher): Freewing 5055-390Kv (Flightline Spitfire), with prop adapter from Flightline 1.6m Corsair)
Prop: MAS 16x10x3 (tractor and pusher)
ESC: Hobywing 60A ESC, BEC power disconnected
Battery: 6S. Two CNHL 3S-8AH-30C batteries wired in series.
Flight Weight: 15.6 lbs
Wing Loading: 37.8 oz/Ft^2
Wing Cube Loading: 14.7
Power: 2690 Watts
Power/Weight: 172.4 Watts/lb

Weather: 70°F, winds 5 – 10 mph, clear skies and sunshine.

Although I didn’t put a wattmeter on the motors at the field, I had done that at home and the motors, each pulled around 55 Amps and 1340 Watts. When I did the first power-on range test, the 335 moved the stand, to the amazement of those watching. The guys all really impressed with the output of the inline 5055 motor and 16x10 props.

Take off was incredibly easy. I’d previously done taxi tests and had the nose-wheel steering trimmed in nicely. The takeoff roll and climbout was straight as an arrow. The climb out was much steeper than I would’ve liked, but she had a lot of up trim, that I had trim back out.

Flying was easy, too. She was very predictable and flew like she was on rails. I was not aggressive with her on this first flight (didn’t even roll or Immelmann), but I could tell that she’d easily be up that. The only surprise that I experienced during the entire flight was when I decided to do a WOT pass down the runway. I can in on shallow dive as I brought throttle to full. Almost instantly, the 335 started wagging her tail like a fish. I eased back on the throttle and she resumed easy predictable flight again. (more on this in my final thoughts and recommendations)

Landing was very predictable, as well. I came in a bit high and fast, as often when landing from the North on this field, due to the trees lining both sides of the runway. I’d misjudged the throttle input a bit as I was turning onto final. She was high and fast; so, I chopped throttle and came in on a rather steep approach and brought power back up as I neared the ground. I was a little doing that, though, and the 335 plopped down a bit harder than I would’ve liked. I’d actually half expected her to bounce. Because she didn’t tells me that the suspension in the gear is well engineered. I flew for almost 5 minutes. After the flight my 6S-8AH battery had about 75% of the capacity left (about 3.85 v/cell).

Final Thoughts and Recommendations:

If you’re planning to run a power train as aggressive as the 6S, 5055-390kv, MAS 16x10x3, be careful at high speed. After the flight, I checked the elevator and rudder pushrods and discovered that by manually pushing on the rudder and elevator that the stock pushrods will flex inside the fuselage. I’m suspecting that the heavy propwash was causing the elevator and/or elevator to flutter.

Recommendation: Stiffen the rudder and elevator pushrods. Either add addition supports within the fuselage or replace the pushrods with 4-40 pushrods.

My Do-335 flew better than expected. Even though it was a maiden flight and I more tense than usual, I still enjoyed the flight. She was very well behaved during takeoff, flight, and landing. If the Do-335s aerosurfaces are visually trimmed, there should be no surprises during the takeoff and climbout.

She’s a real keeper. I can’t wait to fly her again, now the maiden-flight pressure is off!!!

[downwind3zero]

Awesome job man! Congratulations! I've been up waiting for this post. Thank you for your documentation.

[OV10]

Oxotnik CONGRATS
I can hardly wait for ya to reinforce the rear control surface pushrods on that Chuck and then give the WOT treatment to that power system and tell us what ya think then.
Can the ol' Warbird spec out a power system

[Oxotnik]

Oxotnik CONGRATS
I can hardly wait for ya to reinforce the rear control surface pushrods on that Chuck and then give the WOT treatment to that power system and tell us what ya think then.
Can the ol' Warbird spec out a power system

I'm flying a FrSky GPS in my 335. I flew at half throttle for almost the entire flight. The GPS recored a peak ground speed of 93 mph (maybe 5mph wind during the flight). I bet that if the 335 can be opened up, she'd do every bit of a Buck 10.

When I had the 335 on a prep bench for the range check, when I opened up the throttle during the range check, the 335 was making the prep bench roll. At 2690W total, she's a friggin freight train for sure. LOL

[MrSmoothie]

I successfully maidened my Do-335 today

Congratulations Chuck!! The best news I've had today, and very encouraging for me going forward with my Do335. I really appreciate all the details.

[Oxotnik]

Congratulations Chuck!! The best news I've had today, and very encouraging for me going forward with my Do335. I really appreciate all the details.

Thanks, Nick. While you’re modding you’re 335, look carefully at the elevator and rudder pushrods, since you’re also planning to run the freight train 6S/5055/16x10x3 setup.

[Twowingtj]

Congrats on the maiden Chuck. Good job! I suspect it will be closer to factory CG when you get the Tru-turn hung on the back end.

I don't know if you can, but I'd be curious what she weighs in at with the lipos loaded. And if it's close to spec or much above. I'm just wondering if she's a bit beefy and loading up the surfaces causing the rod flex.

[Oxotnik]

I was also thinking that when I replace the plastic Corsair spinner with the aluminum TruTurn spinner, that the moment arm of the additional mass would bring the CG back a tad.

I’see if I can cone up with a way to get an AUW. Unfortunately, my small scale only goes up to 10-lbs and a bathroom scale would be grossly inaccurate on that low end of the scale. A few months ago, I’d done a little online searching for an economical 20-25 lb scale, but nothing jumped out at me. The Post Office would probably frown on me asking them to weigh a 68” warbird on one of their scales. LOL

I’ll see if I can come up with a clever way to get an accurate AUW.

[Twowingtj]

I just use a couple of loops of 1/8" braided nylon cord, padded if needed, and a digital fish scale. Most are pretty accurate for our needs.

I use a Vanessa rig to CG most of bigger birds. The fish scale is part of it as well. That way I get AUW at the same time.

[OV10]

I was also thinking that when I replace the plastic Corsair spinner with the aluminum TruTurn spinner, that the moment arm of the additional mass would bring the CG back a tad.

I’see if I can cone up with a way to get an AUW. Unfortunately, my small scale only goes up to 10-lbs and a bathroom scale would be grossly inaccurate on that low end of the scale. A few months ago, I’d done a little online searching for an economical 20-25 lb scale, but nothing jumped out at me. The Post Office would probably frown on me asking them to weigh a 68” warbird on one of their scales. LOL

I’ll see if I can come up with a clever way to get an accurate AUW.

Oxotnik Chuck...…..What I do that has been very reliable and pretty much spot on is to weigh myself on the digital bathroom scale and then re-weigh myself while holding the model and take the difference.

[Oxotnik]

Dang! So simple.

My Do-335, as outfitted in the Maiden Flight post weighs 15.6 lbs (that's two pounds more than I'd estimated). The 6S-8AH battery pack (pair of 3S batts, plus heavy duty serial cable) weighs 2.6 lbs (this weigh is included in the 15.6 lb AUW). Based on that, here're the updated performance calcs for my Do-335:

AUW: 15.6 lbs
Wing Loading: 37.8 oz/ft^2
Wing Cube Loading: 14.7

Power total: 2690 Watts
Power/weight: 172.4 Watts/lb

[Twowingtj]

Oxotnik Thanks for the AUW Chuck. Interesting.... even if you went with the Motion recommended batteries, it would still be in the 14lbs+ range. The stock spinners are quite light vs. the Tru-turns. Plus the 3-blade vs. 2-blade props, and the pilot you added is likely more weight than the stock one. It adds up quick.

Looks like it flew well enough at that weight.

[Oxotnik]

Oxotnik Thanks for the AUW Chuck. Interesting.... even if you went with the Motion recommended batteries, it would still be in the 14lbs+ range. The stock spinners are quite light vs. the Tru-turns. Plus the 3-blade vs. 2-blade props, and the pilot you added is likely more weight than the stock one. It adds up quick.

Looks like it flew well enough at that weight.

TJ, the warbirds pilot is very light. Negligibly heavier, if any, than the stock plastic cartoon pilot. With the 5055/6S power train, she doesn't feel heavy. Over on RCG, Nick had asked me about a comparison between the Phoenix Model A-26 and the Black Horse Do-335, as they both had the same wing area. My A-26 (which was packing a pair of Aerodrive SK3 5055-430 motors and MAS 15x9x3 counterrotating props) had plenty of power, but she felt heavy in the air. My A-26 weighed 17.5 lbs, had a wing loading of 41.8 oz/ft^2, and a power/weight ratio of 127.5 Watts/lb. I've only rolled her once and I was thankful that I had plenty of altitude to trade for that maneuver. Although I flew my Do-335 very sedately during its maiden flight, I could tell that she is nimble. She feels light and quick, but not so light that the wind will blow her around, as her wing loading is still pretty high. Knowing that her AUW is 2 lbs heavier than I'd expected doesnt' bother me. With the 5055, 16x10x3 power train, her weight isn't noticeable, other than when you chop power, she comes down quickly.

[Twowingtj]

Oxotnik All things considered, I don't think your 335 is too heavy at all. As little as 10 years ago trying to put together a twin engine heavy metal warbird this size under 20lbs would have been near impossible. Especially powered with motors that can turn two near scale 16" 3-blade props.

Being able to get a nice Do-335 as light and structurally strong as this one, not to mention covered and cosmetically detailed, is outstanding. Especially at this price point. Having the efficient power system available at an affordable price that has the grunt to move this bird with thrust to spare is great. These are good times indeed my friend, good times indeed.

Thanks for being the "proving grounds" for testing to see if the Pfiel will handle an 8k lipo. I was planning on going large lipos for the 12S BH Glimore, but didn't want batteries that only worked in one plane. Now both the Gilmore and Do-335 can share the 8k 6S packs.

Most of us that fly the "heavy metal" warbirds don't fly them like an Extra 300 anyway, or shouldn't.

[Oxotnik]

Oxotnik All things considered, I don't think your 335 is too heavy at all. As little as 10 years ago trying to put together a twin engine heavy metal warbird this size under 20lbs would have been near impossible. Especially powered with motors that can turn two near scale 16" 3-blade props.

Being able to get a nice Do-335 as light and structurally strong as this one, not to mention covered and cosmetically detailed, is outstanding. Especially at this price point. Having the efficient power system available at an affordable price that has the grunt to move this bird with thrust to spare is great. These are good times indeed my friend, good times indeed.

Thanks for being the "proving grounds" for testing to see if the Pfiel will handle an 8k lipo. I was planning on going large lipos for the 12S BH Glimore, but didn't want batteries that only worked in one plane. Now both the Gilmore and Do-335 can share the 8k 6S packs.

Most of us that fly the "heavy metal" warbirds don't fly them like an Extra 300 anyway, or shouldn't.

I agree with you, TJ. I don't think she's heavy at all. When I was flying her, she felt nimble and quick, without being quirkly. Of course, I was flying low rates for the maiden. But, she was locked in, and rock steady, except the second or two that open up her throttles and her tail got squirrelly. I'm really pleased with her. I'm glad that I found a work-around for the aft spinning (painted a Flightline Corsair spinner black). I think that I was the only guy at the field that knew that the aft spinner was wrong. If any of the guys noticed that it looked odd, they probably didn't say anything because they probably thought that with me being the warbird nut that I am, I'd never a fly a warbird that was outfitted incorrectly. :-)

[downwind3zero]

I contacted Wendy at TruTurn today. She said that my aft spinner has been cut (she thinks) and is waiting to be shipped. They just have to be allowed to get back into the building to do the packing and shipping. I'd try printing one, but my 3D printer is down (plugged hot head); so, I can't even print one to get me by. I'm thinking about doing a bare prop for the aft. I just cringe, though, at the thought of flying it with a horribly wrong spinner. I'm such a dork... :-/

Happy to print you one and send it if you like. You would need to use the original back plate modified as I did. Let me know.

[Oxotnik]

Okay, sports fans, I have some more motor test data. I went to the field today with my 335, radio, a few 6S batteries, a couple wattmeters, and a tachometer. I ran five tests, each test lasting about 10 seconds. Single means that each motor was run alone. So, for Test Single1, the tractor or pusher motor was run individually, using the same battery, at close to the same starting voltage. Dual means that both motors were run concurrently, using the same battery, but separate wattmeters. For the Dual Tests, I could only tach one prop at a time; so, the Pusher Motor Dual Tach Reading was taken during a follow-on test (so the initial voltage, current, and power would've been a bit lower).




I'd wanted to run this test because I'd observed severe fish-tailing during the maiden flight, when I'd throttle up to WOT for a high-speed pass. I was wondering if, maybe, the flow fields from the tandem motors/props running at high speed were interacting with each other, possibly causing one of the motors to over spin. There was quite a bit of variability in the power and tach data. My take-away from this data is that each motor seems to drop about 100 watts when run in the tandem system, as opposed to running alone, and the prop speed seemed to drop about 100 rpm when running in the tandem system. This makes sense, since two motors are now pulling juice from that same battery at the same time; therefore, there'll be more voltage slump, which will lower the power and rpm. Test Dual4 seemed to be an abnormal test, as the current and power of the Tractor Motor seemed abnormally high. I ran Test Dual5 as a replacement test, and the data seemed more believable. Conclusion: I don't believe that there's significant interactions in the flow fields that caused my 335 to fish-tail at high throttle during the maiden.

Following my maiden flight, I did observe that by moving the rudder and elevator with my hand, the respective pushrod would bow. So, I replaced the stock pushrods with 4-40 pushrods. When I ran the Dual Tests, I did observe that rudders (both dorsal and ventral) angling a few degrees to the left. I believe that this is a P Factor effect, since the pusher prop is only an inch or two behind the rudders. The elevator did not move though. In flight, this may cause a slight left yaw at high throttle. I suspect that with the stock 2mm pushrods that both the split rudder and split elevator deflected significantly at high throttle, and that caused the observed fishtailing in flight. I'm okay with going back into flight, and high-throttle flight, too, with the stronger push rods. I'd encourage you all to check your rudder and elevator pushrods very carefully for stiffness, especially if you're planning to run as powerful a 6S motor system as I'm running.

Another observation from this test data is that the power trains are not putting out as much power as I'd originally posted that they would. I'd run two tests, a month or so ago, and observed 1345W/motor, for 2690W total. This test data indicates that the total power is more along the lines of 2400W. For my 16.5 lb Do-335, that'll give me a powers/weight ratio of 145.5 W/lb. Still very respectable for scale warbird. :-)

[OV10]

Oxotnik Oooohhhhhhhhhh, I luv tech data, thanx Chuck
I got to use some of my early years engineering skills in reviewing your PPP ( Pfeil Power Paper)
So it was hard to pour through the data and remain un-biased as I read your analysis at the same time of digesting the data but I think I was able to let the science prevail.
The long n short of it is I totally concur with you analysis that the WOT fishtailing was indicative of the control surface rod flexing than to an imbalance in thrust factors.
The only observation that I would make concerning your test set up is regarding the watt meters.
The slight variations between the tractor/pusher motors I would suggest are because you are using industry hobby meters that are:
1) of average standards and 2) not been calibrated to each other.
Lab power measurements that I did back in the day were with very expensive meters that got periodically calibrated.
Because of this I didn't even bat an eyebrow about the "dual 4" measurement and thought of it as just being a meter anomaly.
And lastly, I expected what you saw in the final paragraph because you are using a single power source versus a dedicated battery to each motor.
With separate dedicated power sources the additive sum of each motors power reading is going to be higher because the voltage slump as you mentioned
earlier is due to the motors running in tandem because of the single power source versus running in two singular modes with dedicated power supplies.
But as we both know all too well, separated power sources on twins is asking for trouble
Great stuff and at 150W/lb that Arrow is definitely in the fighter class.