Belt 6HV FBL conversion

[DominicD]

No need to dump any build up if it can never build up.

[Tomstoy2]

Good point!

[jperkosk]

The cracked front skid repaired with CA and dried overnight:



Then this morning I applied Belt v2 landing skid mod, no reason it shouldn't work on v6 :



It should be perfectly dry and usable for tomorrow, it's blowing gale today anyway, easily 60-70kph gusts, so no flying of any kind today .

[sutty]

Well that landing was a little hard Jerry, but I am very surprised it broke the skid. Never had much success with repairing skids, or any other plastic parts, but the technique you've employed there looks like it should do the trick at least in the short term. Done all sorts of makeshift repairs on the 250 including not even bothering with the landing gear and simply hand launching, but I don't suppose that would work with the 6HV, lol. My 250 has actually been without skid pipes for about 2 months now. Makes no difference, and saves a little weight.

Cheers

Sutty

[Bugster]

Originally Posted by sutty

... My 250 has actually been without skid pipes for about 2 months now. Makes no difference, and saves a little weight....

I reckon that could just be Mancunian thrift

[jperkosk]

Grounded ! Thanks, Dominic ! Figured a 1.5 mm hole drilled in the boom wasn't going to weaken it, screwed a PC motherboard 2 mm stand-off screw into it:

[DominicD]

Strange, your kit came with the plastic gyro mount.

[Tomstoy2]

Jerry, curious what your vib readings were?

[jperkosk]

Yep, didn't realize it should be a metal mount , got the kit slightly used, after all, originally it was a FB kit and it's probably how it came a couple of years ago...

Vibs are next to nothing compared to 700N , two flight logs from maiden:




Had problems with RPM sensor not showing up in the 2nd log (it reads on DX8 telemetry, though), investigating the cause.

[jperkosk]

OK, so couldn't wait any more and went to the club's field with 6HV to do a couple of more test flights. After yesterday's gale force the wind has calmed down a bit and settled to 40-50kph, so I thought "what the heck, it's a FBL 600 after all"

Bumped the headspeed up to 2000RPM (so Tom couldn't say I didn't listen to him), increased cyclic response in SK720, and the thing felt like welded in the air, strong wind or not . I did one full battery pack, 8 min total in the air @ 2000RPM, split into five short hops, posting the videos of the first and the last hops. In the first video I still have some tail issues, but by the last test hop they're sorted out.

Now, I was aware of the repaired skids, so I was waiting out stronger gusts up in the air before landing, and there might've been a couple of "oh shiite" moments; apologies for the "R" rated language but the damn gusts almost moved ME a couple of times, I'm serious.

In the first video after the landing I flipped the idle-up to off and brought the throttle stick down. The heli shook violently and popped the fancy Compass headlink off. So I thought it might've been related to ramp-down of the ESC and maybe I should use TH on landing. Next 3 hops seemed to have confirmed it until the last short hop, landed in idle-up, hit TH, and a couple of seconds later 6HV gets a death shake and tips over. The vids:

First out of 5 short test hops:

[ame]http://www.youtube.com/watch?v=JabVNmGHMsA[/ame]

Last test hop, the tail is very much sorted out, a death shake at the end:

[ame]http://www.youtube.com/watch?v=vctB1uRmSvI[/ame]

The heli tipped over, the horizontal fin moved around 90° and snapped the 2 boom support end off, otherwise no damage at all, some very minor scratches on the blades, the head speed was very low by then:



So the question is, WTF ??? Looked into the Compass forum and there is a thread on the death shake on spool down, have to read it carefully tomorrow. For now, CA on support ends and tomorrow some black color matched thread with CA. The damn bird starts looking like a VA patient .

Any ideas on the death shake will be greatly appreciated.

[DominicD]

Looks like you are using a TON of negative pitch on your landings. I usually land with only a degree or two of negative pitch. Using negative pitch means you are trying to drive the heli into the ground, which will get those skids a shaking.

[jperkosk]

Not really, Dom. First vid landing was in normal mode, I have something like 4-5° neg pitch on full down stick. The last was in idle-up, landed gently, hit TH, and I don't think I moved throttle stick at all afterwards. Few seconds later at some point during the spool down 6HV becomes violently resonant, looking into it on Compass forum...

[DominicD]

The 6HV doesn't like landing and taking off of hard surfaces if you are using the lower head setting on the FBL head.

[jperkosk]

I am, and I'm beginning to gather that from Compass forum... Still sucks. Maybe I should adapt Align skids, they're a bit taller and would raise blades-to-ground distance, would probably have the same or better effect as rising the head 5mm, wouldn't it?

[DominicD]

Anything but stock should work

[ragge1]

Originally Posted by DominicD

The 6HV doesn't like landing and taking off of hard surfaces if you are using the lower head setting on the FBL head.

hmmm you mean the the upper hole of the head , got mine on the upper hole and never had this issue

[Ah Clem]

"Maybe I should adapt Align skids, they're a bit taller and would raise blades-to-ground distance, would probably have the same or better effect as rising the head 5mm, wouldn't it?"

No, it is not so much the proximity of the head to the ground, as it is the proximity of the head to the vertical center of gravity. Raising the head changes its distance from the vertical center of gravity.

Two things I learned from Mr. Ketelhut:
(supporting what the Capibara said)

1) Using the lower hole in the head will raise it by 5mm. This will really help to eliminate the ground resonance issue. The TracX Delrin Drive tubes are 5mm longer, so you can raise the head without modifying any of the linkage below the swashplate. (I have not experienced ground resonance since I did this).

2) Adding just a hair of positive collective when spooling down will also dramatically reduce the ground resonance.

By the way, there are two different landing gear struts for the 6HV. The later ones are made from a different material that is much sturdier than the originals. The lettering on the package for the new ones is blue, if memory serves.

[DominicD]

Richard the new struts are the ones we are having problems with, one side is proving to be super flexable, and the other side brittle.

[sutty]

Forgive me for making a suggestion with no knowledge of the heli itself, but it looks to me like the blades are too loose. I think, and I do say think, I can see them collapse significantly on spool up. Sudden deceleration might have a similar if smaller reverse effect, but it could perhaps put it well out of balance. As I say, don't have experience of the heli, and I follow the logic of the wobbly skids argument, but as I say the blades did look particularly loose to me.

Cheers

Sutty

[jperkosk]

Thanks guys, will raise the head to the lower hole and readjust the Delrin links, that's easy enough.

Ragge, have you been landing on paved surface? I was doing the tuning flights yesterday with 40kph winds with much stronger gusts, the total of 5 landings. Three of them no major issues, but a first and last landings caused death shakes, I'm almost sure the wind was calming down at those. So maybe high winds help kill the resonance? Portable industrial blower into the LZ?