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Aft CG

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chenoweth(at)gwi.net
Guest

Posted: Sat May 20, 2006 2:45 pm Post subject: Aft CG

This is a question for any of you with a completed tailwheel 9.  I'm in 

the tail cone and mid section construction part of one and wonder about 

CG problems.  I'm hoping to use a wooden prop and worry that I'll end up 

with a very aft CG if I do.  That is leading me to wonder if ELT and 

strobe power supply placement should be other than behind bulkhead 706 

(which is where Van's strongly recommends I put them).  

Any comments and suggestions on this will be gratefully received.

Bill

Albion, Maine

aurbo(at)ak.net
Guest

Posted: Sun May 21, 2006 6:54 am Post subject: Aft CG

Bill,



I have the same concerns. I do plan on installing a larger tailwheel 

assembly. Although I am not planning on using a wooden prop I do plan on 

installing the elt and the strobe power packs farther forward.



It would be interesting to see what others think or have done?



An answer to your concerns would be to insulate both the firewall and front 

floor heavily.



Mike Ice

Anchorage, Alaska

RV-9 Fuselage, installing wings for the first time

---

bill(at)repucci.com
Guest

Posted: Sun May 21, 2006 11:13 am Post subject: Aft CG

Bill,



Check with Van's to verify what I'm about to say.



 	  Quote: 	
		  From what I have read the RV-9 does not seem to have the same aft CG

issues as the -7A.  I have played around with sample loadings while
	


moving the CG for and aft as much as 2" on the -9 and found everything

is good.



I suspect this is because of the RV-9's wing.  Meaning that it is longer

and thus more of it is forward of the CG.



Also, on TW RV's there is less weight aft of the CG than on the A

models.  A's have the main gear and steps aft of the CG where we only

have the TW, granted it is WAY back there but it still doesn't seem to

be an issue as it is offset by the heaver engine mount (two gear legs

mounts) and the gear legs and wheels them self way in front of the CG.



Van's also compensates a bit with a slightly longer engine mount for the

-9's.  I know the one I have and the cowling are sized (extended) for

the O-235.  This will help out with the Catto wooden prop I have sitting

on my shelf.



That is what I am hoping for as I'm putting a lighter engine in my -9

(O-290-D2).  As a side note, I exchanged some emails with a gentleman

out West who has the same set up and he simply said not to worry about

the CG as it isn't a problem.



To verify this, check Dan C's site (www.rvproject.com) and play around

with his CG calculator.  Granted, there are no -9's on the list, only

-9A's but you will get an idea of how the CG comes out.



Hope that helps.

Bill R.

www.repucci.com/bill/baf.html



--

chenoweth(at)gwi.net
Guest

Posted: Sun May 21, 2006 2:29 pm Post subject: Aft CG

Bill,

Great info and thank you very much.

The fellow I asked at Van's was singularly un-helpful with this.  His

response was to not worry about the CG and if it came out too far aft use a

metal propeller.  Sort of missed my point about wanting to use a wooden one

and provided absolutely no ideas about where/how to locate things like ELT.

strobe power supply, etc, farther forward.  Was pretty adamant about not

making the baggage area floor removable, though.

I conclude from what you said that I should have no problem if I go ahead

and mount the ELT and all just behind the 706 bulkhead and, absent anyone

commenting to the contrary, I think that's what I'll do.

Bill C.



---

bill(at)repucci.com
Guest

Posted: Sun May 21, 2006 5:43 pm Post subject: Aft CG

Bill,



As for the placement of items behind the 706 bulkhead, I would still be

careful.  I put both the strobe power supply and ELT under the baggage

compartment floor using access doors.  This will allow me to rivet the

floor in place.



I suspect the reason Van's wants both the baggage floor and seat pans

riveted in place is to make them act like a box structure as there is a

lot of loads going through those items.  However, there are a good

number of planes flying with them screwed in place.



My -9 will have them riveted in place for two reasons.  1st, I'm lazy

and that is a lot of plate nuts.  2nd, I'm trying to make my -9 as light

as possible and those plate nuts and screws add a good bit of weight.



The reason for putting the ELT and transponder under the floor is also

twofold.  1st, it gets more weight out of the tail so I can avoid any

potential CG problems. (Even though I doubt I will have any.)  2nd, an

airplane with all the weight in the center handles better.



Here is a picture of where I put my ELT:

http://www.repucci.com/bill/images/elt%20with%20door.jpg



And here is the location of my strobe power supply:

http://www.repucci.com/bill/images/strobe%20power%20pack.jpg



Good luck,

Bill



--

kerrjohna(at)comcast.net
Guest

Posted: Mon May 22, 2006 6:42 am Post subject: Aft CG

You won't know until you know......



My w/b with x320 and metal prop, and the elt and power supply behind the baggage bulkhead; would allow for over 100# of baggage so intuitively it suggests that a lighter prop would be accommodate that location for the elt and power supply.



I went through all of the various loadings on the computer, and could not get close to the edge of the envelope.



The 9 is a fine flying machine, lands just like a kitfox.



John Kerr

n927BJ, 56 hours



-------------- Original message -------------- 

From: "Chenoweth" <chenoweth(at)gwi.net> 



[quote] 

 

 Bill, 

 Great info and thank you very much. 

 The fellow I asked at Van's was singularly un-helpful with this. His 

 response was to not worry about the CG and if it came out too far aft use a 

 metal propeller. Sort of missed my point about wanting to use a wooden one 

 and provided absolutely no ideas about where/how to locate things like ELT. 

 strobe power supply, etc, farther forward. Was pretty adamant about not 

 making the baggage area floor removable, though. 

 I conclude from what you said that I should have no problem if I go ahead 

 and mount the ELT and all just behind the 706 bulkhead and, absent anyone 

 commenting to the contrary, I think that's what I'll do. 

 Bill C. 

 

 ---

jdisher(at)intergate.com
Guest

Posted: Mon May 22, 2006 1:10 pm Post subject: Aft CG

Now you've dampened my enthusiasm. After 1200 hours in a V-tail Bonanza, 

I

built a Kitfox IV Speedster about 10 years ago. Sweetest flying plane in 

the

world, at least until I tried to put it on the ground on an asphalt runwa

y.

I'm sure a lot of it was me, but I found it to be the squirrelliest thing

 in

the world with variable winds on the ground. Only plane I ever ground-loo

ped

and now here I am about 95% finished with a 9A. Tell me your Kitfox

comparison was for a 9. 

 

----

kerrjohna(at)comcast.net
Guest

Posted: Mon May 22, 2006 2:08 pm Post subject: Aft CG

My frame of reference is that in 700 hours and 2000+ landings on asphalt and high altitude mountain strips I have yet to experience any difficulty landing the Kitfox.  The rest of my education is still to come.



I found the 9 easier to land than the RV7 that I was in for transition training.  I typically cross the fence at 60-65 mph IAS compared to 85 mph IAS in the RV7.



Don't be disheartened.  The Gear on the RV9 is much more reliable than the bungy gear of the 'Fox.



John Kerr



-------------- Original message -------------- 

From: "John Disher" <jdisher(at)intergate.com> 



[quote] 

 

 Now you've dampened my enthusiasm. After 1200 hours in a V-tail Bonanza, 

 I 

 built a Kitfox IV Speedster about 10 years ago. Sweetest flying plane in 

 the 

 world, at least until I tried to put it on the ground on an asphalt runwa 

 y. 

 I'm sure a lot of it was me, but I found it to be the squirrelliest thing 

 in 

 the world with variable winds on the ground. Only plane I ever ground-loo 

 ped 

 and now here I am about 95% finished with a 9A. Tell me your Kitfox 

 comparison was for a 9. 

 

 ----

chenoweth(at)gwi.net
Guest

Posted: Tue May 23, 2006 5:11 am Post subject: Aft CG

John,

That's comforting but I think I've been persuaded to do the door in the

floor thing.  I'm really wary of aft CG's since I've been living with one

for 220 hours with my Kitfox.  It's a IV-1200  with the Grove spring gear.

As for landings I wouldn't mind if the tailwheel 9 is a bit easier.  In the

Kitfox I've found that, for me at least, reasonable landings are fairly easy

to come by and good ones are not.

Bill

---

chenoweth(at)gwi.net
Guest

Posted: Tue May 23, 2006 5:11 am Post subject: Aft CG

Bill,

That's very persuasive so I guess I'll head in that direction.  I had a look

at your pictures - nice job.  A few questions:  Was there any particular

reason you hinged the doors?  Did you feel it necessary to consider the G

loads the ELT would suffer in a crash and beef up its mounting accordingly?

It doesn't look like the Ameri-King ELT?  Is it 406 MHz Artex?  If not, did

you make any provision for switching when the time comes?  Could you

describe the way the sides of each bay are done - material and attachment?

And again, thanks for the help.

Bill C.



---

bill(at)repucci.com
Guest

Posted: Tue May 23, 2006 6:48 am Post subject: Aft CG

Bill,



Regarding the G loads, I did not give it any consideration.  The ACK ELT

(http://www.aircraftspruce.com/catalog/avpages/ack_tech.php) that I am

using is bolted to the baggage compartment rib, not the bottom skin.

The idea was to keep it from vibrating on the bottom skin.  I don't know

if this will work or not, time will tell.  My tech advisor did want me

to move it to on top of the baggage compartment floor so it is

accessible in the case of an accident.  I have elected to leave it under

the floor but will use thumb screws so I can access it in the event of

an accident.



 	  Quote: 	
		  From what I've been reading, most of the accidents that trigger the ELT

are such that the passengers don't survive so I'm not really too worried
	


about it's placement.  One thing nice about having it under the floor,

if I do get into an accident, it will most likely not become a

projectile.



A side note to this, after placing it there and running the phone line

and antenna wire through the other floor ribs it was pointed out to me

that certified aircraft try not to run these wires through ribs because

in the event of an accident the rib can cut the wires.  Just another

thing to consider when you select your placement.  I'm not sure if the

phone wire that goes to the control switch is that critical but I

suspect it could be cut in such a way so as to deactivate the ELT,

again, I'm not really sure about this.



If I had to do this over again, I doubt I would include the hinges, just

use the screws to hold the tops in place.  I had extra hinge laying

around and used it, which is just like me to make it more difficult to

build.



As I said above, the ELT tray is bolted to the side of the floor rib

with 8-32 plate nuts.  The lids were made from an extra tank skin I had

laying around (don't ask).



The strobe light power supply was similar in construction, only I bolted

it to the lid itself.  Again, in an effort to keep from mounting

anything directly to an outside skin.  Someone once told me not to mount

anything to an outside skin because the flexing of the skins could cause

stress cracks.  This may be an old wives tail, I don't really know.



Bill



--

chenoweth(at)gwi.net
Guest

Posted: Wed May 24, 2006 3:35 pm Post subject: Aft CG

Bill,

I appreciate the info and your time in providing it.  I'm going to order the

ELT and Strobe 6 from Van's soon and will follow your example.

Bill C.

do not archive

---

bill(at)repucci.com
Guest

Posted: Wed May 24, 2006 5:49 pm Post subject: Aft CG

Careful on the strobe you order, some of the strobe packs are so large

they will not fit under the floor.  The one I have is from these guys:

http://www.airplanegear.com/skybright.htm.  It is basically an

automotive unit.  Small, light, and simple.



Bill



--

chenoweth(at)gwi.net
Guest

Posted: Thu May 25, 2006 1:03 pm Post subject: Aft CG

I'm planning to get the strobe from Van's and I think it's the same power

supply I have in the Kitfox.  I'm expecting it will fit since my 7A neighbor

has one in about the same place.



---

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