George,

Do the mods, because the first time you experience it might be the last, if not it will scare the heck out of you. I know and have been there and when I build the new one, I will definitely do the mods and upgrade the servos. Never hurts to have a little extra under the hood.

Sung

Thanks for your input to my question guys. Do you think that two 9411's will be enough to fix the problem??? I know that 8411's will fix the problem but I'm concerned with the amount of modifications that are necessary to install them.

Kevin

Has anybody talked to BV or Tom about this. I wonder what they have to say. Do they think there is a probem and what is it and what can be done to fix it. Shuleman I know you are reading this.


Doug A

Doug
Myself and two others up here in MN are just about done with Bobcats. This will be my second. I have not called Bob on this issue but the other two have. They were told that the 3301's were fine and that they have over 300 flights with no problems. However I have talked to a BV rep. and he recommended the 9411 conversion. My first Bobcat had a Mercury only pushing about 14-15lb. of thrust. My new one will have a JC p-80 plus at about 20lb. of thrust, so this thread is making me a little nervous. I'd really prefer not to have a servo hanging out of the stab. But it seems better than no plane.
Good Luck!
Scott

Take a look at BV's website or CLICK HERE. It just got updated.

I was looking at the BobCat Stab plan last night, and was wondering if there is too much room for interpretation on the elevator travel.

It reads
"Elevator Travel:
1 3/4" up and down."

I was wondering if some people were thinking that this meant that the elevator was to have 1 3/4" total travel. Instead of 1 3/4" up and 1 3/4" down.

Looking at everyone's ATV settings was what lead me to think this.

I did a little drawing and would like to know if this is what everyone's elevator looks like at full deflection. And as I said before it has been my experience that 140-150% ATV is necessary to achieve what is shown in my drawing.

Mine was set up the same way you show in the picture. Just bought two 9411's. Going to install them just to give a little extra safety margin.

Mike Jensen

Mike,

sent you a pm

David,

I was not there friday in Austin when you lost your bobcat, I showed up 2 hours later, but 2 guys I work with were there and they were watching your flight very closely. They said indeed you low pass was very fast and the pull to vertical was pretty agressive. As the plane went vertical they both said they saw something fly off the airplane. Never really looked for the piece due to the aftermath of the crash, everyone was busy.
Don't know if this info will help or add more confusion.

Regards,

Dan M.

but they will only add confusion on here.

If you want them PM me.

As for the technical issues, I think BV has hit it on the head, namely the power supply to the servos. Imagine if you are using a 4 cell pack, and it is somewhat run down, and you have small gauge extensions (or too many extensions), slightly corroded connectors, etc. You could have 20% less torque than other Bobcats with 5 cell packs, regulators, 22 gauge gold plated extensions, hi quality extensions etc.

Also BV mentioned 200 mph, if you enter a dive, split S or enter the backside of a loop already at 200 mph you are going to go way over 200 on the downside if you do not get out of the throttle fast.

215 mph requires almost 15% more servo torque than 200 mph

So like most things it adds up. 4 cell pack, somewhat depleted, numerous small gauge extensions, corroded connectors, 215 MPH vs 200 and now you might have a problem

Just my thoughts

PS I just noticed the Vne for the Bobcat is 175, so the torque required for full deflection at 215 mph is 34% greater than 175 mph!

I had an Isobar Rudder servo start to fail on me, where
it would worked fine but it only had ~30 oz of torque...

I changed the servo to a brand new one with over 100 oz
and still very week.. say ~30 oz of torque..

I traced the problem back to the Y harness used for the
steering servo and rudder..

You would never know it because everything worked fine
on the ground just no power...

My point is, my Y harness acted like it had a resistor in
it, limiting the current and the output torque.

Any wiring / battery problem will not show up until
its too late..

I think bob cat owners should just measure there elev
torque by hanging weights on the end of them and
compare theirs to all the other bob cat at the field that day...
This could tell a lot and save a plane... !!!

I can bring my scale to Miss Afterburner... and set it up..
Won't take but a sec... If any one will use it...

Eddie Weeks

Just install 8411(s) check your leads and never think twice about it
I have the Utmost respect for BV but I dont think a servo who's torque rating is that close to max flight load values should be the "Recommended" servo. Sure, the 3301's are probably sufficient for a BC on 500 power but I dont trust them on 20+ lbs. I prefer to have twice what I calculate the surface would need and know I'm never coming close to stalling a servo....
Todd

Well....

Actually, you can't really 'just install 8411's' as they don't FIT, and the resulting buldge could cause a buffet or flutter. We are talking about 200+ mph here. Granted, it likely would not, but I don't really want to test that theory (and it is ugly).
I would say, that I have flown BV's personal BC with a P120 on it, and that plane gets wrung out with no issues. It never feels soft!
All of this does make me think twice as I am finishing my Bobcat... and I have always liked the simplicity of the 4.8 v system.
BV runs a regulator at 5.2v I think. Most of the '4.8' packs I have tested seem to hold 5.0-5.1v with a pretty good load.... Still, I think I may be ordering a 6v pack and regulator.
My Atv's are up arround 130% to get the 1-3/4" throw, and this is good. Seems to have a lot of torque even on 4.8v.
Anyone running 110% or lower ATV to get the throw should think hard about getting in there and changing the linkage to get a better mechanical advantage, and more torque at the elevator. (use more servo rotation) Also, because the wheel is rotating, the further you rotate it, the 'shorter' the perpendicular moment arm is getting, so the guys using higher ATV's are getting a double advantage at higher elevator deflections! This is really evident on mine.
D

>Sadly you can't really 'just install 8411's' as they don't FIT, and >the resulting buldge could cause a buffet or flutter. We are >talking about 200+ mph here. Granted, it likely would not, but I >don't really want to test that theory (and it is ugly).

The Isobar has 6 full size servos sticking out to the mounts
and its been clock at over 210 mph for many years now.... Buffeting or flutter is not caused by a servo sticking out a plane...
It only produces parasite draw witch is very stabilizing that
far behind the CG

Eddie Weeks
http://www.corpcomp.com/weeks1/

Ok, I give in, what is "Parasite Draw". I looked it up on yahoo and the closest match was some type of card game where if "you get a 'parasite, draw' a card..........LOL

Parasite draw is where it attracts people that don't have their own airplane but ask to fly yours..

Hey.. wait.. that sounds like ME!!

Er.. nevermind.

"Parasitic drag", which everyone knows is when someone tries to DRESS like you. It's a sad, sad psychosis...

Sorry to make an ongoing joke, that was not my intent. I have a really high opinion of Eddie's comments, I've gone through his site extensively and my opinion is that this guy thinks outside the box better in this hobby than anyone. If he says there is "parasite draw" and it's not an official term, my bet is that it's there, I just don' t know what it is. My Isobar is about three weeks from being ready and I was just hoping to get a better understanding of this term.

Ok Eddie is parasite draw an official aerodynamic phenomenon or is it something some of those south Louisiana women get that makes penicillin run for the hills.


Doug A

I think its when a turbine wannabe AMA EC member dresses up as a woman!

I saw him at the corner of the stage at Regina's one year, the term "parasitic draw" come to mind, I think it works this way....

The "parasitic draw" is directly proportional to the number of dollars on the rail. Is that how it works?

Just blowing off steam-I also have respect for the man. I do think he meant parasitic drag as it pertains to miscellaneous items hanging in the breeze off your airframe, but let's let him comment.

And as far as Louisiana women; well never mind that's another "story". Let's just say I appreciate my Texas "belle".

Matt has it correct. I've seen it live (except it was Regina II)!

David, with the 109% ATV, are you acheiving the 1 3/4" travel? I thought I had read in some very early BC post, that some people were going with a little less throw initially.

I've gone back and looked at my set-up and it was no where near correct (bought used). I have corrected the linkage and ATV settings and am very close. I'm also going back to a 5-cell pack and regulator.

Also, does anybody know what throws specified in inches converts to degrees? Is there a formula or chart.


Thanks in advance,
George

Yeah, me three,,,,,,, I spent two weeks in there one night........ Two weeks pay that is .... Ha Ha