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

[Alpha]

I'll throw in another dimension to your [wise] musings, Oxotnik: We should also consider the ampacity of the wire being used. Not only will your system not pull nearly as much current as the battery itself is rated to provide, but even if the system did pull 180A continuous, parts of a Power System run into the bottleneck caused by fusing current.

Industrial batteries (12Ah is getting there!) flown in agricultural drones for example, don't need exotic 50c batteries, because their systems don't pull 500+ amps, and even if they did, the wiring would melt!

Power System design is about optimizing everything in a SYSTEM. Prop, motor, ESC, wire gauge and type, battery ampacity (peak, burst, sustained, average unloaded), etc. In the context of an airplane we're also adding Dimensions, Weight, and CG-ability into the equation. If anything in that system changes, the equation outputs differently.

It is best to consider all factors at once to find the best balance of all factors that meets your target.

[Oxotnik]

I like the idea of this Lipo! Depending on if you can get the CG right with it, the Amp draw of your motors (55A x2) would be OK with 12C from this battery.

Yeah, last night as I was lying in bed, it dawned on me that I was thinking about the C rating wrong. I was hung up on the absolute value of the C rating, but not thinking about it in terms of current push. 12AH batt at 15C can provide 180A. As you noted, my 5055's only pull 55A (max, static), each. So, the battery could easily provide the power to both motors. I'll do some measuring today, to see if the battery would fit in the battery bay. I also saw a 10AH 6S battery, too, which I'm assuming would be a bit smaller.

[downwind3zero]

I like the idea of this Lipo! Depending on if you can get the CG right with it, the Amp draw of your motors (55A x2) would be OK with 12C from this battery.

[Oxotnik]

Having gotten an email this morning about a sale on HobbyKing batteries, i went to look. I spotted this 6S-12AH battery, but it's only 12C. I've never actually used a graphene battery, but I thought that their chemistry allowed them dump energy with less resistence. So, the 15C discharge rating (30c burst) confuses me a it. I also haven't checked dimensions to see of this 12AH Graphene would fit in the battery bay of the 335.

Any thoughts on the battery, relative to its use in the Do-335?

[Oxotnik]

Thank you, can hardly wait for your feedback on power vs weight performance with the motors you are using. Good luck with your maiden.

I believe that I have already reported the wattmeter test results. Spitty 5055-390kv, MAS 16x10x3 (tractor), CHNL 6S 70C battery. 1345 W, 55A, for 2690W total. If the final flight weight of the 335 is 3.5 lbs, then the power-to-weight will be 199 Watts/lb. I'm expecting the Pfeil to perform very nicely with this power train.

BTW, when I had my Flightine Spit IX at the field this past weekend, I stuck a wattmeter on it. With the stock 16x10x4 prop, it pulled 59A and 1376 Watts, which is only 30W more than the motor pulls with the 3-bladed MAS 16x10.

[MANFRED]

Thank you, can hardly wait for your feedback on power vs weight performance with the motors you are using. Good luck with your maiden.

[Oxotnik]

Did you get your rear spinner yet? If so, what size prop and motor did you ask for with the tractor cut?

I have not received my aft spinner yet. The TruTurn tractor spinner I found at my LHS. It’s 3 1/2”, Ultimate shape, and has wide cuts. It’s a little larger than scale, but looks fine. I special ordered a 3 1/4” Ultimate Shape with pusher slots for the MAS 16x10x3, for the rear. I’m really hoping that my pusher spinner arrives in the next day or so. I’d love to get my Pfeil in the air this weekend.

[MrSmoothie]

I received my much-anticipated Do-335 book today. I flipped through the variants and I never saw an instance of the tractor and pusher motors/props being different in any of the variants. The motor was always a variant of the DB603, and the tractor and pusher props were both 3300mm diameter.

That's a little scary. I ordered and received the very same book today. Excellent reference! But Chuck, refer to the chart on page 25. It lines up with the chart below -- 3.5m and 3.3m.

I'll post the chart from Monogram No. 9 and highlight "fore" and "aft" showing different props. Motor was the same except for one letter designation to indicate opposite rotation. Also, every good scale drawing I've collected shows the prop diameter difference.

[MANFRED]

Did you get your rear spinner yet? If so, what size prop and motor did you ask for with the tractor cut?

[Oxotnik]

I received my much-anticipated Do-335 book today. I flipped through the variants and I never saw an instance of the tractor and pusher motors/props being different in any of the variants. The motor was always a variant of the DB603, and the tractor and pusher props were both 3300mm diameter.

[Twowingtj]

Ah blimey, just boldly go where others haven't and hope that you don't run into any power issues
I know you remember the power issues with the D8 :astonished:

Awwww buddy, you just had to go there didn't ya. Power wasn't really the problem with the D8. It was clearly the absence of a tail.

[OV10]

Two examples for prop difference is first hand observation of the full scale at the Udvar-Hazy museum and a plastic scale model that my bride built and we still have.

While in no way an expert on aerodynamic hysteresis, the higher rpm and lower pitch(angle of attack) should reduce the likelyhood of stalling the rear prop. Might have to build a wind tunnel .

Ah blimey, just boldly go where others haven't and hope that you don't run into any power issues
I know you remember the power issues with the D8 :astonished:

[Twowingtj]

TJ, is this a visual you are observing from pics??

By going with 2 different sized kV motors turning different size/pitched props, I'm concerned that you are going to run smack into a possible engineering issue known as aerodynamic hysteresis.

Two examples for prop difference is first hand observation of the full scale at the Udvar-Hazy museum and a plastic scale model that my bride built and we still have.

While in no way an expert on aerodynamic hysteresis, the higher rpm and lower pitch(angle of attack) should reduce the likelyhood of stalling the rear prop. Might have to build a wind tunnel .

[MrSmoothie]

J, is this a visual you are observing from pics?? From multiple sources I've researched (including Wikipedia's Pfeil) the engines were the same and the props are the same diameter/pitch other than being tractor/pushers.
The props are 3.5m(11.5 ft) in diameter whereas the scale of this model as noted in the first post has the prop at 17 but most seem to think that the MAS 16x10x3 is the best bet to go with.
By going with 2 different sized kV motors turning different size/pitched props, I'm concerned that you are going to run smack into a possible engineering issue known as aerodynamic hysteresis.
Every inline tractor/pusher airframe made (Pfeil, Skymaster, Moynet Jupiter, Rutan, ect) had the same size engines and props fore/aft probably for real aerodynamic reason.

Interesting -- I'd already scaled a couple of different better quality scale drawings which show the front prop being larger than the rear. I just checked the specifications chart in "Monogram Close-Up 21: Do335" and it indicates the front prop as being 3.5m dia., and the rear prop being 3.3m dia.

Another source indicates that in single engine tests, the plane flew faster with just the rear engine. Either it comes down to greater efficiency of the pusher prop (using smaller diameter), or perhaps the stress on the drive shaft which was apparently under-strength and problematic throughout testing...

I too had wondered how it would fly with a slightly smaller motor on the back with a one-inch smaller prop (16" front, 15" rear). Regardless, I'm now on the course of identical motors/props front/back.

[handyman220]

OK Gang, here's the link to my RCGroups Build Log: https://www.rcgroups.com/forums/show...k-Horse-Models

There hasn't been much interest to start. I guess there are two dozen of us with the plane and we all know who we are!

Making good progress in the shop today but what I've posted is a few days behind where I actually am in the process.

Thanks for the building log link. Will be awhile before I start building/assembling mine so more options are better in my opinion. Did not notice the prop on motions site until you mentioned it! Duh! Very nice repair work by the way. I have yet to unwrap mine to check for damage, have to get off my butt, too many other projects.:rolling_eyes:

[downwind3zero]

Thanks for confirming, that's an option I was contemplating.

[Oxotnik]

Oxotnik How did you secure the aft motor (I am using the same as you are), ie how did you get locknuts in behind the panel or did you use another method? trying to figure this out before I go for it. Thanks

I drilled new holes, just a few small fractions of an inch outboard of the existing 3mm tee nuts and used #4 sheet metal screws to secure the motor to the bulkhead. I’m very comfortable with the strength of this setup.

[OV10]

I'm thinking of trying something a little different power wise on mine. Going to use the Flightline 5055-390kv with the MAS 16x10-3 up front. In the rear I'm going to try an Extreme Flight Torque 4016T/500kv with either a 15x7-3 pusher or 14x7-3 pusher. The choice for the rear was driven by the fact that I already had the motor and it needed a home. This will all be powered by 6S.

The Torque motor is the same one that powers the 84" Turbo Bushmaster very effectively. The concern with using the 15" prop is that it may overpower the front end. Swapping ends in flight might not end well.

On the full scale, there is a noticable diameter difference between the front and rear props. This set-up will allow that without sacrificing overall power.

Anyone know of any potential problems running different motors might cause in a pull / push configuration?

TJ, is this a visual you are observing from pics?? From multiple sources I've researched (including Wikipedia's Pfeil) the engines were the same and the props are the same diameter/pitch other than being tractor/pushers.
The props are 3.5m(11.5 ft) in diameter whereas the scale of this model as noted in the first post has the prop at 17 but most seem to think that the MAS 16x10x3 is the best bet to go with.
By going with 2 different sized kV motors turning different size/pitched props, I'm concerned that you are going to run smack into a possible engineering issue known as aerodynamic hysteresis.
Every inline tractor/pusher airframe made (Pfeil, Skymaster, Moynet Jupiter, Rutan, ect) had the same size engines and props fore/aft probably for real aerodynamic reason.

[downwind3zero]

Oxotnik How did you secure the aft motor (I am using the same as you are), ie how did you get locknuts in behind the panel or did you use another method? trying to figure this out before I go for it. Thanks

[Twowingtj]

I'm thinking of trying something a little different power wise on mine. Going to use the Flightline 5055-390kv with the MAS 16x10-3 up front. In the rear I'm going to try an Extreme Flight Torque 4016T/500kv with either a 15x7-3 pusher or 14x7-3 pusher. The choice for the rear was driven by the fact that I already had the motor and it needed a home. This will all be powered by 6S.

The Torque motor is the same one that powers the 84" Turbo Bushmaster very effectively. The concern with using the 15" prop is that it may overpower the front end. Swapping ends in flight might not end well.

On the full scale, there is a noticable diameter difference between the front and rear props. This set-up will allow that without sacrificing overall power.

Anyone know of any potential problems running different motors might cause in a pull / push configuration?