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moving the firewall back on a CG Ultimate..?

Old 02-05-2003, 08:34 AM
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punkey71
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Default moving the firewall back on a CG Ultimate..?

Hi Guys,

I'm building a CG ultimate. It's only my second kit (first was a 4* - wow what a difference) and i'm being challenged to say the least. I'm using a Saito 150 and need to move the firewall back a 1/2" in order to keep the thrust washer in the correct spot per plans. So......How the heck to I do that?!?!?!?

I would think it would be fairly easy if the fuse was a perfect square....just lop off 1/2" of the front of all sides. The problem is the fuse bottom actually comes up as it goes forward (not a perfect square).

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<----front

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Ok...that's the worlds worst attempt at a diagram, but I think you get the point!


My inexperience is probably showing here and I bet dollars to donuts there is an easy answer...unfortunately, I have no idea what that answer is!

Any help would be greatly appreciated.

Thanks in advance,
Harold
Old 02-05-2003, 08:36 AM
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punkey71
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Default ???

for whatever reason, my pathetic diagram didn't show up the way i tried to make it look...those slashes should make a 45 degree down angle to the right...

sorry...Harold
Old 02-05-2003, 01:47 PM
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rusgmil
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Default CG

I have built two CB ultimates with OS 120s (just finishing the second one now) and I just moved the cowl forward about 3/8 in. Frist one had the battery behind the cockpit and the new one has the elevators servos in the tail and battery forward. Don't know what the weight difference is between the engines but I hope the helps. BTW the frist one weighed 9 1/2 lbs, by using carbon fiber gear, light weight tires and other changes, this one will be about 8 3/4 lbs.
Old 02-05-2003, 02:13 PM
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Default moving the firewall back on a CG Ultimate..?

I agree.

Don't move the fire wall, move the cowl.

I am almost at the covering stage on mine. It will use the OS 120.
I will fit the cowl to the motor before I start to cover.

You might also look to see if you can move the motor back on the motor mount. The carb. on my OS clears the fire wall with only about 1/4 inch of space. Thats plenty of room. All else is cut to fit so that the end result looks good.

I am also building a second Ultimate 15% larger than the CG Ultimate. All I did was Xerox copy the rib pattern at 115% magnification and increased the span to be about 62 inches.
The cowl for this Ultimate will be the old Ohio RC Ultimate. I will modify the fuse of the airplane to fit the cowl. A little wider than plan, but it will look good when finished.

Once its done no one will know that you changed anything.

good luck

tonyc

tonyc
Old 02-05-2003, 08:21 PM
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ilikeplanes
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Default moving the firewall back on a CG Ultimate..?

I moved the firewall back on mine (Saito 120, same case as 150). It's not a good modification for only your second kit. I changed the cut-outs in the top and bottom lite-ply fuselage pieces. I also added a little right thrust while I was at it. Routing the exhaust was a little tricky too. I mounted my engine down 20 degrees to give the stack more room.

My experience with my current project (second CGM Ultimate) is that you will be nose heavy unless you move you battery behind the lower wing or mount servos in the tail. When I put everything in the locations indicated by the plans, I had to add 4 oz of weight in the tail. I added a hatch behind the wing and moved earthing back to the adjacent former and got it to balance with no lead (including moving the firewall back 1/2"). I do not have the servos in the tail.

I have done some more mods which you can find by doing a search on "CGM Ultimate".

I'm almost done with mine. I'll post pictures soon.

Good luck.
Old 02-05-2003, 10:20 PM
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GaryM
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Default CG Ultimate

The previous post pretty much covered the pros and and cons of moving the firewall. There is another mod you really should consider if you haven't built the wings. Get you some 5-ply 1/8 plywood and duplicate the four ribs which are the attachment points for the outer cabanes. The light ply ones in the kit will not take very much abuse. If you put a couple of lightening holes in the new ones you really want pick up that much weight. Then after you build the cabane add a short piece of wood dowel to the location where the 4-40 bolt goes thru the cabane. This will keep the cabane from being crushed.

You might even want to consider replacing the light ply on the firewall with the 5-ply, just a thought.

Also just so you will be thinking about it. If you want the muffler to be inside the cowl, you will have to do one of two things. Cut a half moon shaped tunnel in the bottom of the firewall and chinblock. Then face it off with some 1/64 ply that you can easily bend to the curve of this area. Your second choice is to cut a small v in the exhaust header, bend it to a greater angle then mig it (weld) it back together.

I've had 120s and 150s in mine and I have shortened the firewalls, added two degrees right thrust and put small servos under the horizontal.


Good Luck
Gary
Old 02-06-2003, 12:54 AM
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ilikeplanes
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Default moving the firewall back on a CG Ultimate..?

ALL the cabane mounting points need to be beefed up. I learned this on my first one. It's very easy if you simply put a small patch of 1/32 ply on both sides of the mount point. This includes the ply ribs and the fuselage. I also added a short piece of triangle stock under the fuselage points and omitted the lightening holes in the ply ribs. For a 150, it would not be a bad idea to beef up the firewall attachment. I used a 1/2" wide strip of lite-ply to double the fuselage sides where the firewall attaches. Do not use CA to attach the firewall. Use a nice sloppy layer of epoxy and scrape off the excess. You can also run a layer of glass all around the firewall/fuselage joint. That's what I did on my Sukhoi. I also omitted the firewall lightening holes for strength and to better accommodate my engine mounting system.

Later
Old 02-06-2003, 01:37 AM
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Default thanks

Thanks for all the suggestions thus far (keep em coming! )

Here's what i've done so far...

first, I'm using Higley's Bipes as a guide (excellent)....but doesn't address the moving of the firewall if needed...

I'm using 5 ply aircraft for firewall and 1/4" spruce stringers as opposed to smaller balsa ones in kit....I'm gonna glass the joint as suggested...thanks!

reinforced the interplane struts with light ply...

Used all of Higleys suggestions for top wing mounting (5 ply for wing wire mount blocks...etc...

leaving aft fuse punch outs in sides for mounting dual elevator servos in tail....Hitec 225MG mini's

Dual aileron servos...Hitec 77 low profile's (having trouble deciding/figuring out how to build servo mounts in the wing)

1650ma NiMh will be towards the back to balance the big Saito 150...

I guess I'll just leave the firewall where it is and have the engine about 1/2" forward of plans...with the servos in the tail and battery aft, I should be ok...right?

4-40 all around (or maybe carbon 2-56). Can't decide!

Any body have a better than plans suggestion for the pull-pull system on the rudder? Also, Hitec 645MG ok?

Anything else you guys might wanna suggest...I'm hope i'm not too much of a bother. I am doing my own research and trying learn (not just ask someone to do it for me). This forum just has so much good info, I have to ask for suggestions from those who know....

I really do appreciate it..thanks!

Best,
Harold
Old 02-06-2003, 07:51 PM
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ilikeplanes
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Default moving the firewall back on a CG Ultimate..?

I'm using 5 ply aircraft for firewall and 1/4" spruce stringers as opposed to smaller balsa ones in kit....I'm gonna glass the joint as suggested...thanks! I would not use spruce stringers. If you feel the need to stiffen the deck, add a couple of balsa formers. It will be much more effective and light weight.

leaving aft fuse punch outs in sides for mounting dual elevator servos in tail....Hitec 225MG mini's Good plan. Keep the push rods as short as practical.

Dual aileron servos...Hitec 77 low profile's (having trouble deciding/figuring out how to build servo mounts in the wing) Also a good plan. I used standards on their sides and it was a huge PITA. I would make a recessed tray to minimize the amount of servo hanging out of the wing. Pretty standard set-up.

1650ma NiMh will be toward the back to balance the big Saito 150...
Yowza, your tx will not last that long. 1100 would be fine.

I guess I'll just leave the firewall where it is and have the engine about 1/2" forward of plans...with the servos in the tail and battery aft, I should be ok...right? Yea, no big drama here.

4-40 all around (or maybe carbon 2-56). Can't decide! I use 2-56 unless the rod will be too long so that it can buckle (the aileron interconnecting rod, for example, needs to be 4-40). In most cases, 4-40 hardware is way more beefy than anything it's attached to.

Any body have a better than plans suggestion for the pull-pull system on the rudder? Also, Hitec 645MG ok? I don't like metal gear servos too much. I'm using a 605. I like the CGM pull-pull hardware. It's simple and effective. If you want to go "hi-tech", try a kevlar system.
Old 02-07-2003, 08:17 AM
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ILIKEPLANES...thanks..

I appreciate your help. I'll be back with more questions soon i'm sure!

Thanks again,
Harold
Old 02-08-2003, 11:13 AM
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Default moving the firewall back on a CG Ultimate..?

Another mod to consider. The undercarriage needs to be strengthened. I eventually gave up on the wire legs, and moulded a kevlar/carbon undercarriage that's been going great. If you use the wire legs, the inside of the ply plate and the torsion box should be strengthened. I used kevlar heavy cloth and some 1/2" tri stock. Honestly though, throw the wire legs away, they bend on the lightest landings. Invest in a good light composite undercarriage.

steve
Old 02-08-2003, 02:30 PM
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Default moving the firewall back on a CG Ultimate..?

Thanks Steve...I've actually been looking for carbon fiber gear to save a little weight since my mods are going to put on a few ounces here and there. I haven't had any luck finding composite gear for the CG Ultimate. Any ideas out there?

Thanks again.

Best,
Harold
Old 02-09-2003, 05:39 PM
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Default A LOT OF GREAT TIPS...HERE"S MORE

Hello,
I am too constructing a CG Ultimate as my off season project. I have like the rest of you made some mod's to the kit along the construction process. They go as follows. I thought one of the most important mod's was beefing up the fuse top frame where the 4 mounting bolts hold the top wing supports brackets. I used 1/2 balsa triangle stock to beef that up. I also used tri stock around the firewall as well. In addition to the tri stock on the firewall I plan to use Kevlar instead of glass (air bag from any autobody shop) to coat the inside for strength. I put the 225's in the tail for elevator, Using 605 for the pull pull. I used the Sullivan Kevlar kit. I used the 77's in the wings for aieleron's. I did construct recessed tray's for them to make them neat. I also used the Klett (C.G. product) tail wheel instead of using the rudder to mount stock wire system in place. I sheeted the sides of the fuse with 1/32 6x48 in sheets for torque twisting. I am using a Saito 120 with a Slimline smoke muffler 4006US . I will be using a TME smoke pump and 16 Oz tank for smoke oil (this will be my C.G. balancing items). I am installing a 20 Oz fuel tank for longer flight times. Covering is Ultra Kote. NOW... to see if this bird will fly with all of this weight????? I am covering the bottom wing now (last part)and I wish I found this forum earlier since I didnt think to beef up the cabanes and the appropriate ribs. I used the cutout from the fuse (the one in front of the cockpit) as a servo tray instead of using the 2 spruce strips provided. Throttle and rudder are mounted here. I'll stop here, if any comments or suggestions please e-mail [email protected].

ISO of better landing gear.
Old 02-09-2003, 05:49 PM
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Default moving the firewall back on a CG Ultimate..?

Got my gear from Moose Carbon Fiber (A type landing gear). $23+$5 S&H
Old 02-09-2003, 07:29 PM
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Default moving the firewall back on a CG Ultimate..?

Robelander, interesting mods. Dito on the tri stock for cabane mounting. I also added 1/32 ply on each side of the screw pad.

I hope your all-up weight is not too high. I'm thinking of starting another but going the ultra-light route. I would like it to be no more than 7 lb with a 90 four stroke. That suits my close-in slow flying style. I would actually be removing more wood from the structure. One possibility is an all balsa fuselage (truss frame style). I think I could get away with fewer ribs and wider spacing on the wing. The tail sheeting was very heavy in my kit. I would go 4-6 lb contest grade balsa for this project. I would change the gear and lower wing mounting too. All that hardwood adds a lot of weight. Maybe some carbon doublers in key areas.

Later
Old 02-09-2003, 07:42 PM
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Default moving the firewall back on a CG Ultimate..?

Where do I find Moose Carbon Fiber landing gear?
Old 02-09-2003, 10:38 PM
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Default moving the firewall back on a CG Ultimate..?

Here's the address....

http://moosecarbonfiber.tripod.com/

Rusgmil,

How is the fit with the Type A gear from moose? Do you have any pics you can send me (or post) of the construction of the mounting block and the finished product. I'm going to go the same route and I'd appreciate any help/advice you can offer.

Thanks!

Best,
Harold
Old 02-10-2003, 12:07 AM
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Default moving the firewall back on a CG Ultimate..?

Sorry, should have included their web address.
www.moosecarbonfiber.tripod.com
Old 02-10-2003, 04:14 AM
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Default moving the firewall back on a CG Ultimate..?

The type "A" CF landing gear is rated for a 7lb. plane. I am sure I will be in the 10 pound range. Any other source for CF landing gear?
Old 02-11-2003, 06:51 PM
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Default moving the firewall back on a CG Ultimate..?

Robelander;

I ordered the "A" gear from Moose for the Ultimate that I am building. I did the recomended Harry Higley mods to the Ultimate. I hope to come in at around 8.5 lbs and the "A" gear should do just fine. That gear is strong.

On two other projects I used Moose gear and ordered two sets of gear "beefed up". He did this for a $5 up charge per set. I used these on a scratch built Hots, 84 inches, and a scratch built Edge 540, 80 inches. The Moose gear was advertised for 10 lbs but when I asked him to beef it up I told him that I needed at least 14 lbs of "bad landing" heavy duty gear. The gear has worked great. The Hots has had the gear tore out 3 times, bad landings, the gear has held up. I repaired and you would never know it. The gear still looks new.

For this Goldberg Ultimate I will use stock A gear, for a scratch built 62 inch Ultimate that I am building I will use Moose stock H9 Edge gear.

tonyc

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