Author Topic: Nakke flight test problems (Read 3412 times)

walterbro · « **on:** April 30, 2008, 03:05:01 PM »

Hi Gang -

I am looking for some help on my next step on my Classic "Nakke" model. I am using
AXI2826/10,CC-45 ESC, JMP timer set to 9180 -9150 RPM, Evo-lite 14.8v 4270 mah
battery. APCe props 11.2"x6, 11"x6, 11"X5.5. I ran bench tests before my First 3
flights today and all looked well. My ESC was set similar to Dean Pappas/Hunt parameters. except Throttle response was low (2), Gov gain was custom 40,and
spool up speed was Med(5) These changes were made because there was surging at top RPM on 11.2"X6 prop during my bench runs.
Today I flew my first GOV MODE flights,using 64' 4" .018"Dia lines. my first flight used 11.2"x6 prop and Evo lite battery. WOW! was I surprised at the 4.6 sec lap speed . IT was consistent all of the flight. Needless to say I decided to change to a
11"x5.5 prop and check the rpm before releasing the stooge. Lap times were way too
slow for manuevers at 6.1 seconds per lap. My last flight used an 11"x6 prop and
flight speed was 4.97 second laps. That was a little too fast for me but there was
plenty of power for all the manuevers. I am not sure what my next step should be to be able to use a larger dia. prop and reduce lap speed to 5.1-5.2 seconds.
My first change was to reduce the JMP timer 1 step and then plan to fly again with
the 11.2"x6 prop. I want to get near to 12"x 6 prop without burning up my motor or battery. My initial bench test drew 47.7amps with a 12x6. I cut it off as soon as I
saw that number. I would like some help in taking the next steps to safely get to
my maximum dia with 6" pitch. I use a Prather pitch gauge to make sure of the pitch.
Since the change in static to flying amps is 25% or more I can't run up prop on the bench to get my info verified.

Looking for help,
Walt

Dennis Toth · « **Reply #1 on:** April 30, 2008, 03:37:39 PM »

Walt,

I have been running a test setup with a AXI 2820/8 and an A123 10V 4600mah battery, CC45 ESC , Ztron II timer. I have the ESC set for governor mode and have settled on 8800 rpm using a cut down and repitched APC-E 12x6 to and 11 3/4 x 4 3/4. I also found that the APC E 11x5.5 was a dog. I had similar lap time of 5.97 sec on 64' lines. The APC E 12x6 prop is a great place to start just cut it down and repitch as needed the thrust is unbelievable. I originally use one set to 11 1/2 x 4 and the lap time jumped to 5.25 this is the prop. I also tried one of the Rev-up 11 1/2 x 5 we used on the ST 46 and it was worst than the APC E 11x 5.5 with a lap time of 6.1. One thing about electric with the governor set is that it holds the rpm and doesn't unload like an IC engine. It is an interesting way to test prop efficiency.

Best, Dennis

Alan Hahn · « **Reply #2 on:** April 30, 2008, 04:17:29 PM »

Walt,
I am running an APC12-6E prop on my E-Nobler, using a Scorpion 3020_12 motor (similar to the AXI 2820 series one that has a kV in the 1100 range), also with a 4s battery (2100 FMA in my case). Anyway I am running now with an rpm in the 8100 range to get lap speeds close to 5.0 on 60 foot handle to plane center lines. My currents are maxing out in the 32A range during the vertical maneuvers. Level flying is in the 20A range. Your motor, the AXI2826, can handle more power than mine, so I don't think you will have a problem,as long as you reduce the rpm setting from your currrent 9000 rpm range.

I would think you should drop your rpm down to this 8000-8200 range and see how it goes with the 12-6 prop, if that is the prop you want to use.

Crist Rigotti · « **Reply #3 on:** April 30, 2008, 06:05:04 PM »

Hey Alan,
How come you're getting away with using about 1/2 the battery capacity that Walt and Dennis are using? Are you flying twice as fast?

Alan Hahn · « **Reply #4 on:** April 30, 2008, 06:58:23 PM »

Crist,

I just like living on the edge!

Seriously, I am not sure. I originally chose the Nobler because it has a relatively thin airfoil so I was thinking it might be less draggy than the modern Fat airfoil stunter. I think to some extent, the fat airfoil is a development of having mucho power in the modern CL engine, and actually it helps hold back the engine in level flight. When the plane goes vertical, the airspeed drops a bit but the drag drops faster so it is a way to get some self regulation with the modern glow engine. With electric, I'm flying with a governor, so I don't really need the fatter airfoil. Of course I may be giving something up in square turns (more chance of stalling), but that depends on wing loading (low wing loadings need a lower angle of attack, so stalling is less probable). So my battery pack weighs in at 6.7 oz, not a lot more than stunt tank and 4 oz of fuel. Considering my motor only weighs 5.4 oz, and my speed control another 0.9oz, you can see my power package is pretty competitive (weight wise anyway) with a modern 35 sized engine and fuel setup. The entire ENobler weighs in a little less than 44 oz (and that is with the battery charged!).

Anyway in the end we will see if my batteries die a faster death than others, but I try to keep them at the 20% reserve level at the end of the pattern. Another reason are my batteries are a lot cheaper than most others ($62.25 a pack and now 10% off that), and probably that is the main reason!

Crist Rigotti · « **Reply #5 on:** May 01, 2008, 06:43:08 AM »

Thanks Alan. See you in Polk City?

Dean Pappas · « **Reply #6 on:** May 01, 2008, 08:23:42 AM »

Hi Walt,
Okay, you have me confused. You got two very different lap times with two props that have the same pitch and only 0.2" difference in diameter?
Then you change to a 5.5" pitch (only a ~10% change) and you get more than a 20% rise in lap time?
I'm betting that you are not "on" the governor. This may explain why you felt you needed to knock down the loop gain, too.
If the combination is falling out of the range of controllability, its behavior will be erratic.

When you say that the JMP is set for 9150 RPM, how did you set that? Was the ESC in governor mode, or was it in regular mode?
What is the pulse width coming out of the ESC? Is it about 1.3 milliseconds, or is it much greater?
Try setting the JMP so that you get 9,000 RPM with an 8-6 or 9-6 prop. Then change to the 11-6 and the RPM had better still be 9000.

Look for a PM,
Dean

Alan Hahn · « **Reply #7 on:** May 01, 2008, 10:09:27 AM »

Quote from: Crist Rigotti on May 01, 2008, 06:43:08 AM

Thanks Alan. See you in Polk City?

No sadly I am saving my pennies to make it to Sig this year (plus Russ may have cooled off by then!). I do plan to fly at the Windy City Contest Memorial Day Weekend.

I made the mistake of buying a Ford Explorer just before gas took off from the $1 range into the hypersphere! And now it's paid up, so I need to keep it a few more years--its in pretty good shape. However the next car is going to be more frugal on the gas.

Crist Rigotti · « **Reply #8 on:** May 01, 2008, 10:41:43 AM »

OK Alan, I understand. It is supposed to rain on Saturday at Polk City and I wouldn't want to see you get electrocuted.

I'll see you at Mike's contest.

walterbro · « **Reply #9 on:** May 02, 2008, 11:21:05 AM »

HI Dean and ALL- I made some real headway this morning. I changed motors and set
up for some Bench testing suggested by Dean. I put on a 12x6 APCe prop and used an ESC set for airplane mode. My JMP timer was set for 93% power to see if my motor battery combo was OK. I used a 14.8 v, 4270mah EVO-lite battery. I was really pleased as the prop turned at 9870 RPm and only pulled 43.5 amps. Then I used a
new ESC set for heli -high gov. mode,and a JMP set for 9120 rpm with same battery and prop. the actual RPM was 9120 and 36.1 AMPs. then I set the JMP to 9200 RPM
and ran again. Rpm was 9150-9180 with 39.8 AMPS. This means I should be able to fly with this set-up in my NAKKE.

THANKS !! TO ALL
Walt

Dean Pappas · « **Reply #10 on:** May 02, 2008, 02:24:09 PM »

Great!
36 or 37A for static conditions at 9K sounds right for that prop.
Dean

NED-088 · « **Reply #11 on:** May 21, 2008, 08:03:14 AM »

Try a Graupner CAM prop, 12,5 x 6, lower the revs another bit and be in for a surprise!

Dean Pappas · « **Reply #12 on:** May 21, 2008, 08:09:59 AM »

Bruno!
Are you suggesting that diameter is king?
I agree,

say hello to Erik for me,
Dean

NED-088 · « **Reply #13 on:** May 21, 2008, 08:21:15 AM »

That's what I found sofar. Of course other things get more critical, and you should know your electric basics to spot things ahead of possibly going sour, but on a plane like a Nakke, the 2826-10 should not blink once....

I will.

Alan Hahn · « **Reply #14 on:** May 21, 2008, 08:26:13 AM »

Quote from: Dean Pappas on May 21, 2008, 08:09:59 AM

Bruno!
Are you suggesting that diameter is king?
I agree,

say hello to Erik for me,
Dean

Diameter may be king, but the ground level trumps them all! Right now I mow a nice strip with the 12-6 APC, and with the weather, the darn grass is growing pretty fast! I did go to larger wheels to get some ground clearance. And I'm holding up elevator during the entire ground roll. Doesn't help my takeoff and transition into level flight much either. Need to do something in the long run--probably extend the gear another inch higher. This Nobler is going to look a little weird!

NED-088 · « **Reply #15 on:** May 21, 2008, 08:32:47 AM »

Quote from: Alan Hahn on May 21, 2008, 08:26:13 AM

This Nobler is going to look a little weird!

Shure, but who worries when it outperforms all it's IC predecessors?

Igor Burger · « **Reply #16 on:** May 21, 2008, 08:36:04 AM »

Hi Bruno .. what rpm you need for APC 12x6 and what rpm for CAM 12,5x6 for the same lap times?

Dean Pappas · « **Reply #17 on:** May 21, 2008, 08:40:36 AM »

Quote from: Alan Hahn on May 21, 2008, 08:26:13 AM

Diameter may be king, but the ground level trumps them all! Right now I mow a nice strip with the 12-6 APC, and with the weather, the darn grass is growing pretty fast! I did go to larger wheels to get some ground clearance. And I'm holding up elevator during the entire ground roll. Doesn't help my takeoff and transition into level flight much either. Need to do something in the long run--probably extend the gear another inch higher. This Nobler is going to look a little weird!

Hi Alan,
Yeah, this tug toward bigger diameters will require a slight (ground) attitude adjustment.
Retracts anyone?

take care,
Dean

NED-088 · « **Reply #18 on:** May 21, 2008, 08:49:12 AM »

I haven't tried the APC 12x6 in the same configuration as the CAM, so I can't say.
Maybe Erik has some data, I'll have to ask.
But may I ask, what's important about laptimes? It's the speed in the figures that matters to me.

The MGM controller you got me last year was a big improvement and I think I'm beginning to understand why.....
Erik and I are working on this matter but we don't want to shout out opinions, that appear to be wrong in the end, so give us some time.

Alan Hahn · « **Reply #19 on:** May 21, 2008, 01:52:20 PM »

Quote from: Dean Pappas on May 21, 2008, 08:40:36 AM

Hi Alan,
Yeah, this tug toward bigger diameters will require a slight (ground) attitude adjustment.
Retracts anyone?
take care,
Dean

Here by the way what happens when 12-6 prop contacts Terra Firma on takeoff roll and digs in. It was my fault actually for thinking I didn't need to use a stooge (animate or inanimate). The long slow takeoff roll gives too much opportunity for bumps etc. So I (re)learned something. It is amazing what can happen as long as the electrons are flowing into the motor. My data recorder says I hit about 80 Amps during the episode.

Motor, prop, ESC, and battery survived just fine (can't say the same about my pride!). Plane is now back together and ready for the Windy City Classic this Saturday.

Mark Scarborough · « **Reply #20 on:** May 21, 2008, 02:43:57 PM »

bummers!
but look at the bright side, no soaked in glo fuel to try to drain out of the balsa! Should make repairs a lot easier right? I know you can use corn starch or K2R to pull fuel out of the balsa, what do you use to soak the electrons out of the exposed wood?

Alan Hahn · « **Reply #21 on:** May 21, 2008, 03:42:15 PM »

Quote from: Mark Scarborough on May 21, 2008, 02:43:57 PM

bummers!
but look at the bright side, no soaked in glo fuel to try to drain out of the balsa! Should make repairs a lot easier right? I know you can use corn starch or K2R to pull fuel out of the balsa, what do you use to soak the electrons out of the exposed wood?

Well of course I use one of those "Bounce" Anti-Static Dryer sheets to pull out those pesky electrons.

Alan Hahn · « **Reply #22 on:** May 21, 2008, 03:52:00 PM »

Sorry to perhaps hijacking this thread.

Out of curiosity, what size is a Nakke?

With my Nobler, I am running an APC E 12-6 prop at 8100 rpm to get 5.0 s laps on 60.5 ft handle to plane center lines, whereas most others with larger planes are using the same prop at 9k rpm values to get the plane flying the way they like it. I haven't calculated their lapspeeds, but if pitch were the only determinant of lap speed, their planes would be flying roughly 12-13% faster than me. I believe their lines are longer than mine (65 feet? or ~10% longer), so maybe that is true.

Igor Burger · « **Reply #23 on:** May 22, 2008, 12:16:18 AM »

Right Bruno ... the speed in figures matters, my question was because of true pitch and lap time shows it clear. Just wanted to know what means 6" for graupner and what for APC

walterbro · « **Reply #24 on:** May 22, 2008, 04:41:39 PM »

HI Alan - The Nakke is a classic design that used a .35 cu.in. motor. It has a wing area of 605 sq. in. wing span is 56.5" I think. Tom Dixon sells plans for the model.
I have used Graupner CAM props since 2005 on my electric models. I like them very
much but, the actual pitch is less than stated. For example an 11x6 is actually
a DIA of 11.2 in. and a pitch of 4.2 inches. They are well made GR/EP so when you repitch them they hold the new pitch for good. I found that the APCe 12 x6 prop
is actually 12"dia by 5.7 -5.8" pitch. I would like to know what is the true pitch of
the CAM 12.5x6 prop used in Europe?

Walt

Alan Hahn · « **Reply #25 on:** May 22, 2008, 08:06:29 PM »

Walt,

Thanks for the info on the Nakke. So it is about 10% bigger than the Nobler I think.

I've learned to be careful about what pitch really means. Naively people talk about pitch speed. If I calculate the pitch speed for the APC12-6 Prop at my 8100 rpm (assuming 6" for pitch), I get an airspeed speed of 46mph. I note that my Nobler is flying about 5.0s laps with a radius of ~63.5 feet (counting for my outstretched arm). This equates to a "real" average airspeed of ~54mph. So I am overflying my "pitch speed" by 10 mph! If I use your measured pitch (which I think is just measured with a Prather-like pitch gauge on the underside of the prop), then I am overflying by even more.

So pitch, in the way we measure it, doesn't seem to have much use in an absolute sense (to me at least). Obviously my APC E 12-6 is generating thrust on my level lap, whereas the pitch would indicate it should be pushing the plane backwards (slowing it down).

If I were to switch to the Graupner Cam (I think I have one around somewhere--I could almost open a prop shop!), I would expect to have to find another rpm to get to 5s laps. However the real question I have is whether it takes less watts to give me a 5 s lap than the APC. Another question (more important I think) is whether it has a steeper (negative) thrust vs airspeed slope than the APC.

Ah, paraphrasing Fred K., "so many props, so little time!"

walterbro · « **Reply #26 on:** May 28, 2008, 08:07:18 AM »

Well my flight tests on NAKKE are finished and I can start on trim and practice flights.
I managed to get in 3 flights yesterday (in between the raindrops). All flights held their
constant rpm for the entire flight.I used 2 props 12x6/5.6 and 12x5.5/5.4 both were
APCe 12x6 props repitched. I used two JMP timers set for 1.254ms and 1.264ms. My
lap speed were 5.06, 5.25 and 5.35 sec. This range was good for the light winds(2-3mph). After the flights I repitched 2 more 12x6 props so that I now have steps which should cover all wind conditions . I just have to log some flight time and find my best combo.RAIN RAIN GO AWAY---! All flights were on 62'x0.018"lines eye to eye.

Walt

Dean Pappas · « **Reply #27 on:** May 28, 2008, 08:10:50 AM »

Hi Walt,
So you have decided to "lock down" the timer setting and change props for lap time/weather?
We need a timer with a needle valve! Doesn't the new Z-tron have one?
later,
Dean

walterbro · « **Reply #28 on:** May 28, 2008, 11:24:37 AM »

Dean
yes I am doing what I can right now. I have ordered the new Zigras timer but have not received it yet. My rpms are running at 8700 on 1.264ms and 8640 on 1.254ms.
I think that I may boost up my upper limit to 1.270ms just for higher wind conditions.
Walt