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-   -   Scratch Built Avro Arrow (http://www.Wattflyer.com/forums/showthread.php?t=74402)

CDN71 08-31-2014 12:59 AM

Scratch Built Avro Arrow
 
HI everyone I am new to this forum so this is my first post, I am looking for some advice/ideas as to why my scratch built pusher Avro Arrow would immediately bank to the left and into the ground. This was on my maiden flight, I managed to come out of this crash with slight damage to the left wing. I am using a Turnigy1450KV motor with a 8x4 prop and a 1000mAh battery 3 cell. I am guessing that it torqued into the ground, but would love to hear some of your opinions. I am considering putting in a 2700KV motor with a 6x4 or 5x5 prop as an alternative.

Thanks in advance:confused:

Wrongway-Feldman 08-31-2014 04:57 AM

Is your scratchbuilt from plans or your own design. I have one that I built from dollar tree foam board from some plans I found. It has the same tendency as what you describe. Leading cause of this is hand launching with too much throttle. I launch mine at 50% till it is moving nicely then open her up.
I run mine on 3s with a power up 400 zoom 2200kv spinning a 5x5.
Also make sure that your wings are perfectly flat without twisting as that can also cause your symptoms.

CDN71 08-31-2014 06:50 AM

Thanks for the reply Wrongway-Feldman, yes I did as well find my plans online except the guy that made the plans used a Gearbox motor, dont know alot about these so I am trial and erroring my motors. I will try the 50% throttle on the next round, I think I am still going to ditch my 1450 KV motor for the 2700KV that should help reduce the torque if that was the problem. I would post some pic but at the moment I am still trying to figure things out on this forum, so it may take some time. I also have a very short video of my maiden flight, maybe I will upload soon.

Wrongway-Feldman 08-31-2014 03:47 PM

Here's a link to the plans for the one I built.
http://www.rcpowers.com/community/th...e-plans.14626/
Easy build and looks great in the air.
For a simple way to post video here just upload to YouTube and attach the link to your post.
Look forward to seeing yours.

CDN71 08-31-2014 10:31 PM

Thanks for link to the plans, if things don't work out with my avro
after I try a new motor I will retry a build with those plans.
As far as pictures go I have tried three times to upload them
but get an error message.

CDN71 09-04-2014 01:36 AM

I pulled a newbie blunder for my avro arrow I had the motor rotation going the proper direction for the pusher but didnt flip the prop on the correct way( with the size facing the front, I had it facing the rear). Just did the correction now & did a test on the plane seems like I have 10x's the thrust I had before. Not sure if this is the reason the arrow banked left and into the ground on take off, but at leady I am headed in the right direction this time.:). Waiting for a calm day now to test fly it again.

quorneng 09-07-2014 03:42 AM

CDN71
Having the prop the wrong way round would certainly make thing worse as you have all the torque but much less thrust.
To make matters worse a delta has a relatively short wing span so the ailerons have to work that much harder to overcome motor torque.

A delta is also a bit sensitive to a rearward CofG. With a delta when the nose rises the centre of lift does not move much so the plane continues to try to fly but the drag rises very rapidly. The end result is the nose rises until it virtually stops flying. It is then likely to roll right over from the motor torque before the nose drops and the speed builds up again but it will need a lot of height to recover!

CDN71 09-07-2014 03:51 AM

Thanks for the interesting reply, you said the plane would nose up and roll right but on my take off it nosed up and rolled left. Would this be because didn't have the prop on correctly or something else????

quorneng 09-08-2014 12:17 AM

"Roll right over"
What I meant was a fully stalled delta will not just 'drop a wing' but will roll (and will continue to do so) under the influence of motor torque until the speed builds up sufficiently for the wing aerodynamics to recover.

A full stall with my EDF Fairey Delta 2 means it is flying in an almost vertical attitude and is almost stationary. Even the limited EDF motor torque causes it to roll as the nose begins to drop. It recovers easily enough but in which direction it will be flying is anybodies guess!
I had the CofG just a bit too far aft on its maiden and it did exactly this about a second after the launch and just 10' from the ground. There was nothing I could do about it.
Moving the battery forward by about 1" made all the difference and it flies very well, however trying to find out how slowly you can get it to fly at full power is best done at considerable height!

CDN71 09-08-2014 12:38 AM

Ok now that I read your post again I hear ya now. Guess I read it too fast. How do I counter the motor torque until I gain enough speed. Do I shim the motor to one side??

quorneng 09-08-2014 01:52 AM

As a delta pusher adding side thrust may not work that well. It will rather depend on how the delta responds to a sideways force.
All my Scale hand launched deltas do tend to an initial roll so it pays to give them a firm shove into wind to get some aileron control as quickly as possible.
I fly mode 2 so the aileron is under my right thumb but I launch with my left hand (one advantage of being a lefty!) so I can 'catch' any roll tendency early.

On this day there was virtually no wind so the launch was pretty marginal!
YouTube Video
ERROR: If you can see this, then YouTube is down or you don't have Flash installed.

As always it rolled to the left from the launch!

nuteman 09-13-2014 10:13 PM

I strongly suspect you're dealing with asymmetrical lift due to build imperfection (warped foam, whatever). One way to tell is to remove the motor torque from the equation by doing a glide test. If it rolls violently with no power, then it has nothing to do with motor torque.
As others have mentioned, too far aft CG will exacerbate any problems at speeds near stall even more.
The plane I built in the video below was terribly asymmetrical (very warped foam), but I was able to compensate with trim setting.

https://www.youtube.com/watch?v=i-x2Zr1J5no

Siberianhusky 09-14-2014 12:57 PM

Cool project! Used to know the test pilot Janusz Zurakowski. He flew with my grandfather in the Polish RAF during WW2. He delivered his eulogy.

CDN71 09-14-2014 05:24 PM

Now that's cool, so whats the truth, did an Arrow get away before the Canadian Gov could cut it up? I havnt had a chance to fly the arrow a second time as the weather has been crappy. I wish I could share a photo of my project but i keep getting errors every time I have tried. I have reduced the size of the file as well, but that didn't change.

Siberianhusky 09-14-2014 07:40 PM

I don't think so, I also know of an engineer that worked for A.V Roe on the Arrow. If Jan or the other guy know anything they either took it to the grave or aren't talking. The engineer is the neighbor of a close friend.
Some day when I have the flying skills one of my goals is a largish scale EDF Arrow.
I also want to do a Hurricane with my grandfathers markings from the Battle of Britain, he also flew a Spit but really liked the Hurricane more.
Another family member I know nothing about flew some kind of twin engined night fighters against German bombers during the blitz.

CDN71 09-14-2014 11:18 PM

Quote:

Originally Posted by nuteman (Post 957079)
I strongly suspect you're dealing with asymmetrical lift due to build imperfection (warped foam, whatever). One way to tell is to remove the motor torque from the equation by doing a glide test. If it rolls violently with no power, then it has nothing to do with motor torque.
As others have mentioned, too far aft CG will exacerbate any problems at speeds near stall even more.
The plane I built in the video below was terribly asymmetrical (very warped foam), but I was able to compensate with trim setting.

https://www.youtube.com/watch?v=i-x2Zr1J5no

I have tried throwing as a glider already it it flew actually quite well, so like I said I had the prop on the wrong way, that didnt help and the second thing I am going to try is reduce the throttle on takeoff to 3/4. Will also give it a harder throw, maybe this will help. If this does not work I am switching motors to a high KV maybe a 2700KV and 5x5 prop.
Thanks for your imput.:)

solentlife 09-15-2014 02:00 PM

OK ... lot of sense here and I will add my bit -

1. An 8x4 prop will generate a lot of torque but a lot less thrust. On a 1400 motor - you are in the low thrust region that does not suit pusher and delta.
2. Throttle will be ultra sensitive with such setup and would lead to the left torque roll near every time.

Yes ... swap the prop first for high pitch low diameter. Make the 1400 work before you swap out. You could take a 7x6 prop ... chop it back to 6x6 .... or find online a 6x6 or greater pitch (pitch is the second number, first is diameter).

One thing you never mentioned - weight, length and span. Those factors would help us a lot to advise better.

Nigel

CDN71 09-16-2014 02:55 PM

Quote:

Originally Posted by solentlife (Post 957204)
OK ... lot of sense here and I will add my bit -

1. An 8x4 prop will generate a lot of torque but a lot less thrust. On a 1400 motor - you are in the low thrust region that does not suit pusher and delta.
2. Throttle will be ultra sensitive with such setup and would lead to the left torque roll near every time.

Yes ... swap the prop first for high pitch low diameter. Make the 1400 work before you swap out. You could take a 7x6 prop ... chop it back to 6x6 .... or find online a 6x6 or greater pitch (pitch is the second number, first is diameter).

One thing you never mentioned - weight, length and span. Those factors would help us a lot to advise better.

Nigel

Thanks Nigel, I will try the 7x6 cut down to 6x6 prop, but I always have been under the impression that the pitch dictates the torque; higher the pitch the higher the torque, is this incorrect???????
Also I will get those specs on the forum as you suggested in the near future.

Thanks again.

CDN71 09-17-2014 06:09 AM

OK here are the specs for my arrow. 527Grams with battery, motor and all electronics Length is from nose tip to motor spinner tip at the rear 35.5" Wing span is 24"

nuteman 09-17-2014 09:51 AM

Quote:

Originally Posted by CDN71 (Post 957351)
OK here are the specs for my arrow. 527Grams with battery, motor and all electronics Length is from nose tip to motor spinner tip at the rear 35.5" Wing span is 24"

Ohhhh, only 24" span with 8 x 4 prop :concern: No wonder you were torquing with power.

CHELLIE 09-17-2014 11:08 AM

Yep, Way to big of a prop, a High kv motor of about 2500kv and a 5x4 - 5x5 Apc prop will Take care of that problem :)

solentlife 09-17-2014 02:16 PM

24" span !! Thats less than my all-up T45 ex 50mm EDF and I put a 3700kv + 4.1x4.1 in her ... gives me about 2 mins but over 190kph. NOT something for the faint-hearted ...

I suggest MAX 5x5 ... on a 2500 -> 3000kv. In fact 5x5 on a 2400, and 4.1x4.1 on 3000 and more kv

My Tupolev on twin 2190KV 2208 Floater Jets is overpropped on 5.5x5.5 ... she's now carrying 5x5's. I may even go less if I think need.
Tu144 is 1200mm long, 650mm span, 860gr incl. flight batts twin 3S 1750 35C's

Nigel

CDN71 09-17-2014 02:52 PM

OK like I said I was experimenting, originally I had a 1950KV motor in this plane and it seemed like it was lacking thrust, kind of the reason I flipped it to a 1450, but hearing all this I will change it to a 2700kv motor I have with a 5x5 prop and give that a try. One more question on a high KV motor I am assuming a prop saver would be out of the question??

solentlife 09-17-2014 09:39 PM

Quote:

Originally Posted by CDN71 (Post 957380)
OK like I said I was experimenting, originally I had a 1950KV motor in this plane and it seemed like it was lacking thrust, kind of the reason I flipped it to a 1450, but hearing all this I will change it to a 2700kv motor I have with a 5x5 prop and give that a try. One more question on a high KV motor I am assuming a prop saver would be out of the question??

I use prop savers on my Tu144 but avoid them usually ... I'm not a lover of them.

On high kv - I agree - do not use. I prefer the tapered collet adaptors ... I usually replace the dome nut with a standard hex nut.

Nigel

CHELLIE 09-17-2014 11:13 PM

A Bungee cord would be best to use for launching the plane, that will give you more air speed on taking off.


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