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Fat Avid weight and balance

95 posts in this topic

Posted

Hi Willis,

 

Your plane is looking GREAT and coming in a 733 lbs is amazing!

 

My empty CG is 9.17.  With the forward CG limit at 11.185 and rear at 16.5 my solution was to just keep a minimum of 10 pounds of survival gear in the rear most baggage area  (No problem, my survival bag is about 50 lbs).  With my baggage area I am able to place this survival duffle bag at 66" behind the datum of the wing leading edge.  I also have my battery and ELT back there.  This keeps me within CG range with all possible loadings.  It also helps keep you from nosing it over when you get on the brakes.  I have had no issues with the way it handles in flight or landing, and it is much easier to wheel land than the regular Avid.

 

Look forward to hearing your test flights reports.

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Posted

What is / was the EW of the SuberAvid?

EDMO

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Posted

Hi Willis,

 

Your plane is looking GREAT and coming in a 733 lbs is amazing!

 

My empty CG is 9.17.  With the forward CG limit at 11.185 and rear at 16.5 my solution was to just keep a minimum of 10 pounds of survival gear in the rear most baggage area 

 

Look forward to hearing your test flights reports.

I'm not sure that it matters what your empty CG is. It wont fly without you in it (hopefully) so I would think that what really matters is forward CG with the lightest pilot and lowest amount of fuel being inside the CG envelope. Maybe I'm misunderstanding what you mean by empty CG?.... Wing tank fuel is figured at 15" and people are at 16", so both of those move the CG back. Jim

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Posted

Jim on some airplanes especially bigger tricycle ones it's important to know the empty CG so they don't tip over on their ass when they are sitting there empty on the ramp. On our little planes it's not a factor. Mine is forward of 11.185 empty as well. All my calculations with me and fuel in it put it in the 12 range. I'd like to have it closer to 14-15. Hoping getting rid of my side radiator will shave some more weight off the nose.

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Posted

I'm not sure that it matters what your empty CG is. It wont fly without you in it (hopefully) so I would think that what really matters is forward CG with the lightest pilot and lowest amount of fuel being inside the CG envelope. Maybe I'm misunderstanding what you mean by empty CG?.... Wing tank fuel is figured at 15" and people are at 16", so both of those move the CG back. Jim

Empty CG was for the plane only.  Not to worry, I didn't fly it as a UAV.  The most forward CG was with pilot only and min. fuel.  With the 10lb in the rear cargo area the CG was 11.39 in this configuration.  It took the 10lb in the cargo area to get it within the forward CG limit.  In the Avid+ the wing tank arm is at 15" but the seats have an 18" arm which helps.

 

Ed, my empty weight is 830 lb.

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Posted (edited)

Empty CG was for the plane only.  Not to worry, I didn't fly it as a UAV.  The most forward CG was with pilot only and min. fuel.  With the 10lb in the rear cargo area the CG was 11.39 in this configuration.  It took the 10lb in the cargo area to get it within the forward CG limit.  In the Avid+ the wing tank arm is at 15" but the seats have an 18" arm which helps.

 

Ed, my empty weight is 830 lb.

Randy,

Thanks for the weight comparisons - I guess 733 would be light for the Soob - I am hoping that mine comes in at 800, but have to wait until it is finished to know that - Maybe I'll go on a diet.

With my 4"extended leading edge, cutting off 1 1/2" of rear of rib by doing the Riblett conversion, and making 15" ailerons and flaps, I am figuring a CG range of 13.2 Forward, and 20.4 Aft - using same % as Avid.

I hope my calculations are right for 60" instead of 51" standard chord. I need to go measure the chord again.

The 13.2" forward would be maybe 7 to 8" if I had standard wing, and would not be in the approved range of 11.185 to 17.

These are all just calculations - Someday I will have the real numbers.

I should have about 160 square feet of wings.

EDMO

Edited by Ed In Missouri

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Posted

Empty CG was for the plane only.  Not to worry, I didn't fly it as a UAV.  The most forward CG was with pilot only and min. fuel.  With the 10lb in the rear cargo area the CG was 11.39 in this configuration.  It took the 10lb in the cargo area to get it within the forward CG limit.  In the Avid+ the wing tank arm is at 15" but the seats have an 18" arm which helps

That does make it a bit clearer. The way I read your first post was that the empty plane CG needed to be within the 11.185 and 16.5" CG envelope. That of course is not the case. That was the point I was trying to make. Also, I do realize that it's important to know the empty CG, as all other CG calculations can be figured from there by knowing weight and length from datum. This kind of points out the limit or negative aspects of typing messages verses conversations. In a conversation, questions can come immediately, and false impressions get straightened out right then (hopefully) :) Jim

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Posted (edited)

Jim,
I've got the short fuselage, and don't have the big baggage compartment like the Fat Avids, so it is taking a lot more mods to get mine in trim with the Soob and nosegear.
EDMO
I looked at my Kitfox 4 manual tonight, and their CG range is 10.2 - 16, for the same 51" chord. I don't know what would make the difference unless it is the Riblett ribs.
Can anyone explain this?
ED

edit:  so, if I use Kitfox 20% Forward and 30% Aft, I get 12" Forward and 18" Aft CG with 60" Chord.

Edited by Ed In Missouri

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Posted

Well today was the  day did the maiden flight on my fat avid and im still here  :bugeyes:  , wasn't a very long one  but all went well. I do have a problem to fix and we figure its probably a problem with the angle of the prop. What happens is the more throttle I give the more pressure I need to pull back on the elevator, was a weird feeling  but when I brought  back the throttle  to 3000 rpm or so to land the plane flew nicely, I was told I need to shim up the bottom motor mounts and it kinda makes sense to me. We re weighed the plane after moving the battery to directly under the back of the turtle deck and finally weight was 763 lbs , i think we missed the battery on the first weight for some reason. The soob seems to have alot of power and engine is running well and the new skis we built preformed great.

post-282-0-03077200-1388985876_thumb.jpg

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Posted

Awsome!!!!    Congratulations Willis!  :bday:

 

 

I think the angle of the motor/prop (thrust line) makes a big difference.  I used an Avid factory mount for the Stratus subaru to the Avid MKIV and Steve Windner modified it to fit my Avid+ when he was building the fusalage so everything was already pretty much established prior to me flying it but if you built your own mount then you may need to do some tweaking to get it right.  Hopefully it won't require much cowl modification.

 

Keep a thread posted on your flight testing and numbers.

 

Way to go!  Plane looks great and so do the skis.  Did you put plastic bottoms on them?  How big are they?

 

Randy

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Posted

Thanks Randy and thanks again for all the help,i'll get some numbers once we get the bugs out of it, The Skis do have that hard white plastic under neath( forget the name of the stuff) and weigh about 15 lbs each with the rigging I'll have to measure the lenght and width ,there my flying buddys design and these were the first ones he  made

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Posted (edited)

It could be Teflon, nylon, or less expensive PVC.

A C-130 Hercules has one inch thick Teflon on the bottom of the skis - It is good for ONE Landing on bare concrete!

EDMO

Edited by Ed In Missouri

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Posted

Congrats on the maiden flight! I echo the view of the others, nice looking plane and paint.

 

Did you do the stretch? If so do you have pictures of the process? I'm very interested in how it is done.

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Posted

Hi Kenneth ,thanks,this is the avid plus that was lengthen 18" longer and 10' wider from the factory to accomindate the heavier engines

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Posted

way to go man! nothing  like a brand new plane ,just looks clean.I don't know much about the thrust line problem ,but there is people on here that could probably help. keep us posted

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Posted

Willis, what great way to start the New Year and she sure is purty! Seems like just yesterday I responded to your 'Fat Avid' post on the TKF forums. Hope you feel you made the right decision and receive many years of enjoyment for your efforts. -Doug

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Posted

Thanks alot Doug, thanks for all the help also was about 2 years ago you directed me over to the dark side, :buttrock: I think its going to be fine once we adjust the thrust line up a bit , it felt really good on the skis and soob seems strong. It worked out pretty well since we just sold the kitfox  about a week ago.

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Posted

Willis,

      Congrats on the success.

Hope the 2-strokers don't read this:  I have seen so many Subaru cars go 300-400K miles, that I got my calculator out and did some figuring.  If we take the conservative figure of 250,000 miles at average of 2000 rpm and a speed of 40 mph for a car, then it would last 6250 hours of running time.  A Soob conversion in a plane turning 4000 rpm should last at least 3125 hours before overhaul - probably more, since we do more oil changes and maintenance.

Good Flying!

EDMO

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Posted

I figured if I put a new engine in at 1000 hrs, my tbo costs would be $2.20 per hr.so I fly a lot!!

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Posted

I've got a $1000 spare engine, so that should cut the costs even more.

GF

EDMO

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Posted

That is some serious cheap MX costs on the Subaru. I guess I never sat down and put the pencil to paper to do the math on it.

Ed, thanks for the figures. Makes me want to get my Subaru engine and redrive hung on something that is flyable instead of sitting on a plane that I wouldn't even consider flying due to it's weight and the way it was built.

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Posted

Willis is that the KF cowl I sent you? Sure looks good on the plane! Your plane looks awesome. Maybe I need to adapt a KF cowl to my Fat Avid! I didn't have a Fat Avid or need a cowl for one when I sent it to you. Now I am desperately looking for a cowl! Crazy world!

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Posted

I was wondering about the cowl too ,I like how rounded it looks. so what cowling is it?

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Posted

Hey Chris , yes it is the kitfox 5 cowl you sent me ,had to do some modifying , toughest part was shaping around the windsheild. I know how you feel looking for a cowl was just about the hardest part of the build, im  really greatful for you sending it but dont feel good about you needing one now.If you end up gong with a kitfox 5 cowl let me know and maybe I could chip in for it

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Posted

Keep in mind there are different cowl versions available from Kitfox, ie. round and/or smooth cowls for Rotax 912 FWF and round and/or smooth cowls for Sube/Cont/Lyc FWF. The 912 versions have a narrower, sleeker profile because the engines are not as wide. Pretty sure the one Willis got was not for a 912 FWF, one of the reasons I opted not to use it. All my research suggested the least amount of modification to a KF cowl on a Avid+ w/ 912 FWF was with the model 5/6 smooth cowl for 912 option. Due to aesthetics, I had originally hoped to make the KF7/SS 3-pc cowl for Rotax FWF work and, like the KF 5/6 cowl, it was pretty close. However, because KF lengthened the Model 7's 912 engine mount so much, I concluded it would take too much work to fit due in part to the Avid+ W&B considerations. I'll put pics of the KF7/912 smooth cowl test fit to my Avid+ on Chris' 'Still looking for a cowl' thread if you're interested.

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