250 HK250 wont lift off

[Mda1701d]

Hello all,

Not posted for a while, as we have been so busy relocationg our workshop.
Anyway, been building the little 250 on the odd occasional evening, and its now just about done.
Tried a test flight this afternoon, full battery, align motor and 15t pinion. I have 11 deg of pitch either way, with 0 deg at the centre. Head speed seems realy fast, but the heli will only just lift off at full stick. I do have training gear on, but its still not all that heavy.
One curious thing, during the build, I notices the blades, and the flybar paddles have a 'B' marked in the plastic. You may assume this is for 'bottom' but this would be upside down compared to my 450's. Rotation of the head is clockwise.
Anyone have any ideas about my lack of lift??
Thanks in advance, Mark

 

[Smoggie]

It can really only be either lack of pitch or lack of RPM.. if you have both those things then it cant fail to at least lift off the ground.

If you are 100% sure that you have enough positive pitch then it can only be RPM.

 

[Lee]

A quick little video will give us a good idea whats going on,
but as Smoggie said, if you really do have 11º positive pitch, then it can only be RPM.
Lets have a look at it

 

[Mda1701d]

Thanks for the replies!!
This is really puzzling me......
Just checked the pitch again, 11deg pos, and 10.9 neg.
Just spooled it up here in the house, went idle up 2, set at 100% throttle, head speed looked very fast. Full pos stick made it light on the skids, but did not lift, full neg blew the light shade above all over the place. I wonder if the blades are the problem. They are the ones the HK kit came with, and are very bendy indeed. The blade tracking looks good, and there is no vibration, but I wonder if there is not enough stiffness in them to lift off.
In the yard yesterday, the heli would lift about a foot of the ground with a fully charged lipo, its an 850 3 cell, but only for a few seconds.
Has anyone else noticed the 'B' on the blades? Also on the flybar paddles, but I'm sure they should be as I have fitted them!
I'll try and post some pics, and a vid.
Thanks all.

 

[Lee]

Photos and video will help a lot.
When you set you set your blade pitch, did you have a linear pitch curve?

 

[Mda1701d]

Hi Lee, yep, pitch curve set linker on throttle hold. Done that one before
Really got me stumped this one.......

 

[Stambo]

Perhaps no pitch on normal flight modes only on throttle hold?
Maybe try disconnecting motor wires and check the pitch curve in normal and idle up modes.

 

[Mda1701d]

Hi stambo, thanks, looked at this one! Also, I tried both idle ups.
Hopefully here's some pics of the pitch and a video. Don't know what happened to the first attempt at posting this so sorry if it appears twice.
Also, note as I hit throttle hold, therefore neg pitch, it pins the heli down hard.

[video=youtube_share;nsmMzNYFGTs]http://youtu.be/nsmMzNYFGTs[/video]

- - - Updated - - -

Uploaded the same pic twice I think, hopefully here's the right one!

- - - Updated - - -

Ok, so that's the positive pitch pic three times! And I don't know why it's upside down. Last try now to upload negative pitch pic.

 

[Lee]

What radio are you using.
Can you tell me what your pitch curves are for all your Flight modes.

 

[Mda1701d]

Hi lee,
It's a dx9, pitch curves are 0 50 100 on idle 1, 2, and hold, and 15, 50 100 on flight mode.
Throttle curve on idle 2 is 100 90 100 as tried on video.
Thanks for looking!

 

[Lee]

Ok so let me go through the set up so we are both on the same page.
Blades removed or motor leads unplugged.
Set all flight modes to linear pitch, 0-100%
Check that at mid stick you have all cyclic servo arms at 90º
If this is correct, and your head is set up correctly, you should have approx low stick -11º, Mid 0º, High +11º

On the DX9 you have Norm, 1, 2, and Hold, correct?
Lets just forget 1 and 2 for the moment, and set up Norm mode.
Set Pitch curve to have 5 points, I think you have the option of 3,5 or 7.
Set pitch % to 45,48,50,75,100
This should give you a range of around -2º to +11º. We don't want huge amounts of negative pitch at this stage. Just enough to be able to bring the heli down in windy conditions.

Set the throttle to 0,45,70,70,70, this will give a smooth rpm above mid stick.
For Throttle Hold, Set pitch to same as Norm, but obviously Throttle curve is a flat 0% across the board.

Now try to run it up in Norm mode, and see how it reacts.
If all the above is correct, then there should be no issues.
I hope I'm not trying to teach you to suck eggs, bt I just want to make sure we are 100% talking the same language.

I'm of to bed. Its an hour later here in Spain, and I work early.
Let me know How it goes.
If it still does't work, then start over with a new model in the radio, just incase you have change a mix or something somewhere, that you are not aware of.

Good luck.

 

[trainrider06]

Sometimes having the blade grips upside down can do that....ask me how I know!

 

[Heliman450]

Hi Mark, just a few points regarding your pictures. I use Photoscape as per Tony's recommendation, simple editing is quick and easy including rotating them

The blade should be at right angles to tail when you measure the pitch i.e. not in line with the heli. I can't actually see the little arrow on the pitch gauge but it should be pointing upwards. Of note is that my pitch gauge sits with the screen underneath the blade, not on top. I've never tried placing it that way up so maybe it doesn't matter anyway. I'll test that out next time for curiosity. Don't forget to zero the gauge on the same plane as the heli. I rest it on the skid. Remove the training gear from the heli as you want the heli as near to perfectly level as you can get.

Can you take some photos, close and in focus on the gauge readout. Then take a couple of photos above the rotor looking down at it so we can see the blades.

Good luck!

 

[Mda1701d]

Hello all,
Thanks for all this help!
Thanks Lee, been through all the settings again, can't see anything wrong. All is set very close to your recommendations.
I checked the blade grips train, they are the right way up, as the useless stripped threads are underneath lol, lock nuts fitted instead. Heli man, I think you may have something. As I was laying in the bath last night, I remembered something about using the foam blade keep to hold the flybar on my old blade 400 while setting it up, I've been messing around with Fbl too much recently! Looks like my pitch gauge can be used either way up, got the same reading, but checking the pitch at right angles has given some new clues. Meg pitch reads minus 15, and pos only about 6, so this could be why it will only get light on the skids, the swash isn't in the middle. If I check with the blades in line with the boom, I get the readings I set it up with, ie 11deg pos and neg, and 0 in the middle. Most annoying making this mistake! I guess it's back to the drawing board and set it up again at the weekend! Thanks agin all, I'll report back after head set up again!

 

[Heliman450]

Hi Mark, sounds like there could be some light at the end of the tunnel.

Which gyro is fitted?



Here's your photo the right way up

 

[holtneil]

I second that good luck this week end , I feel a flying 250 coming to this forum very soon

 

[Heliman450]

Hi Mark, now that I've looked at the picture a bit longer, I can also see the flybar. The gyro doesn't matter much in that case.

Attached below is a pdf of a graph I produced showing the curves, which are set in my transmitter for use on the simulator. As you can see, I don't use very much of the available pitch limiting it to a maximum of 72%. This gives me around 3.5 degrees at a stick position of 67%. At this point the heli comes up nice and steady into a hover at 0.8m and doesn't zoom off into orbit with increased collective input. I've also found some settings in the simulator to give an almost perfectly steady hover without any stick input.

I also want to limit the cyclic input, so I use 60% D/R and 30% Expo on both the aileron and elevator settings. This way the heli has less tendency to tip over when the cyclic stick input is a bit uncertain as per novices or the heli is newly put together. For the real heli, the exact numbers vary according to conditions or size but the basic principles are the same.

When you finally get yours set-up correctly give the curves a try and fine tune them for your model.

May the force be with you!

View attachment Heli Settings 04.02.16.xlsx.pdf

 

[Mda1701d]

Hello again all,
Mr heli a, you are a genius! After a bit of resetting, with the blades in the right place lol, I have what looks like a flying model. Set the pitch with 11 either way and 0 at mid stick again, I had loads of neg as it was, and not much pos. Just shows how far out its possible to get with a mistake in setup. Anyway, quick blade track, then a test here in the room, and it seems to have loads of lift! I'm taking it to work tomorrow, shift some cars out the way and do a hover test. Weather looks awfull outside! Thanks for the advice on the settings, I'll be giving them a try as well. I'll report back tomorrow! Thanks again for all the help and advice from everyone. Cheers, Mark.

 

[Lee]

Glad you got it sorted out.
Heliman, can you explain why the blades need to be at right angles to the tail to measure collective pitch?
If the swashplate is level, then the pitch will be the same at any position in the rotation of the blades.
Now, if you are measuring cyclic pitch, the orientation of the blades makes a difference.
Maybe I missed something
But at least its all working now.

 

[Heliman450]

Glad you got it sorted out.
Heliman, can you explain why the blades need to be at right angles to the tail to measure collective pitch?
If the swashplate is level, then the pitch will be the same at any position in the rotation of the blades.
Now, if you are measuring cyclic pitch, the orientation of the blades makes a difference.
Maybe I missed something
But at least its all working now.

Hi Lee, just one of those things I picked up and kept with. It's mentioned in various instructions I've followed. Can't disagree with your logic though. Without being there alongside Mike I can't really say if there was something else. Most important is that he seems to be confident that it's fixed and ready to test with some help from his friends here on the Forum.

P.S. Just checked out my bible (Ray Hostetler's Shop and Field Companion) and Chapter 21 "Collectivfe Pitch Setup" page 159 is where my Guru says it. He refers to his recommended slight tilt to the swashplate to compensate for translating tendency as the reason for doing the pitch check at right angles. I suppose when one doesn't do this then it won't matter anyway. He also recommends always using a flybar lock, which helps with the sighting of the gauge he uses in the procedure and stops everything flopping around whilst doing it. For my thinking it also helps with using my digital gauge under the blade, not on top (as per Mike's photo). I also use a pair of cut-off blades until everything is set up in the workshop as they take up less room and are a bit safer if one makes an error and the heli spins up unexpectedly (it happened to me once and it was a bit scary).

Bye now!