Elevator decay in FFFF

[Mercuriell]

This thread culls talk of pitch problems during FFFF from TB's #18 thread.

I too am having doubts about my 451s, I think they are on the edge of the envelope in the DS and I wondered if some of my nose up,pitching tendency wasn't the elevator servos being overcome! I see some 172s in my near future!

The smaller tail blades would be ok for speed runs but the tail would feel soft in other flight so I Think 95s are a good compromise!

I'd be pleased to put up,your vid on the HF server, you could send it to me by a Dropbox link maybe ...

[Mercuriell]

Originally Posted by wblombard

Thanks John! Once a have another video i will sure send it to you. The BLS 451's have really been around a long time and proven them selves over the years. DT has a serious dolphin effect on his DS...we trying to sort that out with the head gain.

Might be worth starting a thread to swap experience as I am having same problem. What is annoying is that this has developed since I started flying the DS. How is DT's CofG?

[wblombard]

[quote=Mercuriell;6119281]

Originally Posted by wblombard

Thanks John! Once a have another video i will sure send it to you. The BLS 451's have really been around a long time and proven them selves over the years. DT has a serious dolphin effect on his DS...we trying to sort that out with the head gain.

/QUOTE]

Might be worth starting a thread to swap experience as I am having same problem. What is annoying is that this has developed since I started flying the DS. How is DT's CofG?

DT is a perfectionist of note and guarantee his CG is correct. However we reduced the head gain from 70% to 55% yesterday and the dolphin effect got worse much worse. Unfortunately that was his last set of batteries for the day but I do know he has upped it to 80% thinking to increase the head gain because it became worse.

If that does not work then honestly I'm lost to figure out what else he needs to change.

I'm sure he will be commenting here pretty soon, so lets wait and see what he says.

[Mercuriell]

I bumped my head gain too from 55-75 (HC3) and it improved but still there. If it isn't a servo or CG problem it must be a feedback loop in the cyclic control in which case have to look at P and I values. Can't remember if they're accessible in HC/BD software ...

[wblombard]

Which servos you running John?

I can send you my BD3X file...maybe you can compare settings. My head gain is set at 50% and she is a smooth as silk no pitch ups or dolphin effects.

Must say its very strange to me why he has that. I used Miles's BD3X file combined with my TDR settings. Working very very well for me.

[Mercuriell]

I have 451s, yes would be interested in seeing your BD file

[wblombard]

Originally Posted by Mercuriell

I have 451s, yes would be interested in seeing your BD file

Email sent

[wadders248]

Wouldn't you normally run nose-heavy for speed?

Originally Posted by wblombard

DT is a perfectionist of note and guarantee his CG is correct.

[TommyBear]

Originally Posted by wadders248

Wouldn't you normally run nose-heavy for speed?

Yes.

Well done William. [emoji122]

John, have you tried the 5000mAH 7S packs to get a heavier nose?

[tgiencke]

What blades are being used?

Bavarian Demon tuning might solve the issue.

I’ll put out another idea. The heli at that RPM & forward speed is playing with the edge of a retreating blade stall. When the blade stalls and the nose pitches up, the forward speed decreases just enough that the retreating blade cyclic pitch can be decreased just enough to un-stall the blade, and the FBL can command back to original orientation.

Try decreasing the RPM by 50RPM and see if the “dolphining” goes away. If it does I think you are dealing with a retreating blade stall; and if not already using XBlade X713s blades, their increased tip chord could solve the problem at the original RPM, or just use a RPM that the retreating blade doesn’t stall.

Forward Speed – RPM – Retreating Blade Stall is a balancing act.

[Mercuriell]

Thanks for your input. Use Speed-X blades as I found right from the get-go that they were superior to Rails & DH. CG only just tips in level with the 4400 packs, haven't tried the 5000 yet which should just tip her nose heavy and maybe improve stability.. Phenomenon present at 2050 and 2600, maybe tinkering around with HS a little may help. Looks like k have a few things to try

[wadders248]

Although I'm not at the limits that you are with a Diabolo S, the stretched Kasama Dune that I've built for speed is using a BD 3x and to get the weight forward I run two 5000 6s packs and a separate 5000 2s pack on the front position. This feels very nose heavy, but in a good run I'm almost hands-off. Without such a forward CoG, I'm fighting to hold the nose down.

Out of curiosity, what decay rate setting have you got on the rigid settings?

[Mercuriell]

Have the decay at 5 currently, might try and drop it to 3. Elevator filter nearly off at 3.

Think we should make a new thread for this discussion !

[wadders248]

I think you'll notice a big difference with 3, that's exactly what I use. You just have to be careful whilst on the floor that it can cause the heli to tip more easily if you make any stick movements.

I run BD's on all my helis and have been going through each one, increasing the gains until I get the wobbles, then backing-off. Usually I get wobbles first on the elevator, so I'm running offset gains. The elevator wobbles also tend to be higher speed shivers, so I've got quite a lot lower P-Gain than default.

Then if the heli feels a bit too robotic, I reduce the initial response. This process has made them all feel much better, even my basher 550 is really 'locked'.

Obviously I run really low tail gains for speed.

Originally Posted by Mercuriell

Have the decay at 5 currently, might try and drop it to 3. Elevator filter nearly off at 3.

Think we should make a new thread for this discussion !

[crash at 42]

5 is too high of decay rate 3 I found to work great

[darryltarr]

Hey Guys,

My DS was flying great with absolutely no issues (BD3SX / Futaba BLS156HV rated at 21Kg / Rail 696).

Then one afternoon - during a high speed run, I got too close to one of our obstructions (stadium flood lights), and needed to pull up. It was NOT a huge "yank" on the cyclic (I know better than that), but about 20% of UP was applied quickly. However, the reaction from the DS was an aggressive pitch up like I have never seen before, like the fastest STOP ever with the HELI, now almost vertical. I thought it was all over and the DS would need repairs from the stress.

Anyway after a close inspection the DS appeared normal although it became very pitch sensitive after that event and started to dolphin. I'm sure the head dampeners do need replacing as they may have become soft with the G loading. But I tried almost everything else (including Rail 716 / Head Gain / Agility / Expo, etc), and the dolphin remained. So yesterday I decided to go back to basics and re-boot the firmware of my BD3SX and load the latest version.

By the way my CG is forward (HELI tilts 5 degrees nose down when lifted by the mast), and after the update the DS now flies just like before, although my next step will be to re-build the entire head as my current one may have been stressed to the MAX.

I was going to email Gerd and ask for some advice/suggestions with regards to the head as I am sure this is not the first time the DS has been subjected to such maneuvers.

So despite all the issues I still managed (last weekend) to record a Max Speed of 289 Km/H even with the dolphin, but hopefully all has been resolved now.

Yesterday I had three great flights and was fastest with the Rail 695 but I can't say for sure weather the 696's are better than the 716's (running 2700 HS and 14 Deg Pitch).

Williams flights with the X713's are great. The DS looks locked in and I'm sure the extra weight of the 713's makes for a perfect loading (wing loading). During his last flight the DS was screaming - I took cover under my car, but it was great to witness. I'm glad he decided to upgrade his HELI.

[wblombard]

Originally Posted by darryltarr

Williams flights with the X713's are great. The DS looks locked in and I'm sure the extra weight of the 713's makes for a perfect loading (wing loading). During his last flight the DS was screaming - I took cover under my car, but it was great to witness. I'm glad he decided to upgrade his HELI.

DT you crack me up buddy, you forgot to mention how you guys were screaming like a bunch of cow boys....next week I will bring my hard hat....I think it is needed when the DS takes the sky.

Also glad you sorted out that dolphin effect...I just thought you were so baldy good that you do it intentionally and damn did you I think you have it under control nice and smooth and consistent up and downs...

I think the only items to replace in your head will be the spindle and dampers...the rest should be perfect...but a very good idea....oh...dont forget to to let me know when you place the order..I would like to get some spares as well....combining the order should save us both on shipping costs..let me know

[smsodhi]

Originally Posted by wblombard

I think the only items to replace in your head will be the spindle and dampers...the rest should be perfect...but a very good idea....oh...dont forget to to let me know when you place the order..I would like to get some spares as well....combining the order should save us both on shipping costs..let me know

I would add damping inserts to that also.

[wblombard]

I just sent my order to DT...for all bearings and dampers...I'm impressed that there are far less bearings in the DS compare to the TDR...well my cost is much less..heehee

Will tear her down after 50 flights to replace worn bearings....I think 50 flights should be the time to change them...damn coz the power that goes through this heli is just insane...thoughts?

[plankdriver]

I am using BLS451s at 8v and i am not having any nose up or down pitching issues.
The BD decay is set at 3. Head gain is at 65%

One thing that I KNOW is critical for very fast flight is the CG. I weighted my Diabolo S and Brian's until the tail had about 5 degrees up from horizontal. The tracking at high speed for #38 and #48 is literaly on rails. No bobbles, pitch up, or hesitation once you let of the stick at over 150mph.

S