So i got a Phoenix Extra off Tower for $109 WOW!...would do again in a heart beat. The quality is very nice, with out without the cheap price tag. I already had an 0.S. .46 AX, which is the recommended motor in the user reviews section of RCU.
See Pix
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So I have it all built, but have a problem... The motor is mounted on its side, so the pbox muffler runs down the bottom. With the motor mounted at the recommended distance from the firewall, the pbox runs into the fuselage. Right where the muffler hits the fuselage there is a lightening hole with covering over it. What should I do? How do accomidate the pbox, but keep the fuse closed so slag and fuel won't get inside. All of this will be under the cowl once installed.

Looks to me as you have it mounted as they intended?

Only thing is that its going to get pretty hot where the muffler is closest to the firewall. Might put some insulation there? It'll burn out the covering there if you dont.

Enjoy,

Jim

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What about cutting the covering and building a balsa box inside the nose and then coat it with epoxy or some other fuel proof compound (polyurethane)? Balsa isn't that expensive and it wouldn't take much thickness - say 3/32" to do the job.

remove the stock muffler and replace a BCM pitts pipe, issue resolved

Dubro makes a 1/2" extension for that engine. Put it on and the muffler will no longer "run into the fuselage". However, I'd suggest....

If the lightening hole is right where the muffler hits, I'd go inside and epoxy a sheet of lightply or strong balsa over the hole. Trim the covering, fuelproof whatever is still raw wood, and you've got an instant clearance of however thick the fuselage is right there. It's easy and quick.

If the lightening hole isn't exactly where you need the clearance, I'd still use the hole as the starting point to remove a bit of fuselage "skin" to provide the clearances needed. Placing a sheet of thin plywood or thicker lightply over whatever fuselage side you remove is going to actually improve the nose of the model right where it could probably use some improvement.

It's sort of interesting to hear that there is a lightening hole right down where the landing gear is supported and immediately behind where they expect many people to have their mufflers. Your uploaded picture that indicates where the hole is is amazing. Just having balsa there would have strengthened the gear a fair amount. It's amazing they'd have felt the need to lighten the model up in an area that is usually strengthened. It's also amazing that they think an oracote skin is going to keep all the crud and fuel that's blowing around behind the engine wouldn't defeat a thin film of covering. After seeing the insides of a couple of Phoenix models, and seeing a bunch of them with really heavy construction in fuselages that were built with components that Phoenix hid with 2.5 ounce lead weights in the nose.......... It's amazing they have a design they think they will build with the need for lightness in the nose.

I'd check the balance of the model to see if adding a sheet of ply inside that hole is going to have any affect that can't be easily worked out. If it was my model, I'd rather not have a hole there that is only covered by oracoat. And a thin sheet of ply won't add much weight anyway. The area actually is relatively close to the CG anyway.

How heavy is the model going to be when it's done? Do you already know that it's going to be nose heavy?

Boy, I just checked out the Phoenix Extra model in the Tower listing. Phoenix says that sucker is only 3.5lbs and that's sort of amazing. I just stuck together one of their Sukhoi's and it was nearly 6lbs. It is a slightly smaller model than their Extra too. They had some things in the Sukhoi that suggested they really aren't using lighter stuff. The pilot figure is HEAVY for what could be and should be a thin, almost weightless item, yet is made from really thick, heavy plastic. I saved way over an ounce just swapping out the wheel bolts. Yeah, just the bolts/nuts. I'd go weigh them, but I'm using them on some farm machinery. And they used such heavy wood in the fuse and the tail feathers that they saw the need to hide a 2.5oz lead slug in the nose.

If I had that Extra, I really would close off that lightening hole with something that'd stand up to wear and tear lots better. If your muffler ever loosens up, it's exhaust could quickly and easily defeat that single layer of oracote. And what's behind that plastic film? All your radio stuff. And none of the insides of the fuse where that exhaust is going to go is fuelproofed is it?

It ought to be easy to keep the balance of the model with that "extra" wood added. Just move the battery back some.

BTW, my Sukhoi flew good and that's the bottom line on these ARFs. I think we really need to consider that a bunch of the ARFs aren't actually being "designed" by modelers, they're being put together by toy mfgs who've discovered an easy market. We've always been the last word, and with some of the ARF mfgs that's more clearly obvious than ever.

You can use an OS muffler extension so the muffler will clear. I have used them on several different size engines without a problem.
[link=http://www2.towerhobbies.com/cgi-bin/wti0001p?&I=LXCA81&P=0]Muffler extension[/link]

they also make a 90 degree muffler adapter so the stock muffler sits sideways.
[link=http://www2.towerhobbies.com/cgi-bin/wti0001p?&I=LXCA81&P=0]90 deg. adapter[/link]

WOW! RCU rocks!....you guys are really the best. Where else can a guy post a problem, and get 7 responses in less than 12 hours.

Thanks a ton to each of you that took the time to respond. I have ordered the extension from tower.

Keep um flying!
~Tip

Darock,
I do not know how much the plane weighs yet, and have not started to try and balance yet either. I will definitely keep your suggestion in mind moving forward. it would be simple enough to add that ply sheeting to not only provide extra tortional strength, but also make sure the fuse is adequately sealed.

I did pick the extra because it was so much lighter, and seemed to be better match with my .46 ax. I did have my eye on the sukhoi though, and it will probably be my next model.

Thanks again for your reply and ideas!

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Which is probably what the model was designed for to begin with.

I have the same plane with OS46FX. I used a Slimeline Pitts Muffler. It worked out very well. I have about 40 flights on her now. I did have to use longer servo arms on the aileron servos to prevent the clevis' and control rods from hitting the wing. If you do this, make sure you limit your EPA. I mixed some expo in on aileron and elevator about 10% on low and 20% on high rates. Used throws recommended on all surfaces except the rudder. I had to increase the rudder throw to get it to knife edge. The plane is fairly fast. Clocked it at 80 MPH two weeks ago with a radar gun at full throttle and in a dive. Got a little whistle but no flutter. I originally had the wheel pants on it but then removed them and installed larger wheels because I fly from a grass field. Probably would have got 85 MPH with the wheel pants but takeoffs were getting hairy with the pants on. Good luck with it!

The Sukoi also flys nice and is nicely finished - we have had two at our field and both pilots liked them alot.

steinericj,
Thanks for the great insight. I am hoping the muff extension will do the trick. How does it balance? DId you have to add any wieght?

...also great to hear on the Sukhoi. First hand knowledge is worth its weight in gold.

Cheers!
~Tip

Sorry for the late reply. Only lateral balance with a small amount of lead on one wing tip. I think the battery (600ma flat pack) is mounted just behind the fuel tank in the normal position. Had her out about 3 weeks ago and got another 5 flights on the plane. Flys great! Don't put to much throw into your ailerons and elevator. Use recommended throws with a little expo and work your way up from there. Rudder needs more than recommended if you want to knife edge. Good flying!

What kind of ready to fly weights are you guys coming in at on the Extra with the 46FX/AX? Towers site is lacking the correct info on the weight. My Seabee came in at 5-1/2 lbs. with an OS .52 four stroke and it flew real nice.
dawg

When it comes to heat problems in the engine compartment I use 3 inch aluminum tape on the firewall and inside the cowl. Two or three layers works great as a heat barrier and the stuff is very light. If you'd like to know a little more about the Phoenix SU-31 check out the user reviews as I did a full review on the plane. My neighbor flys the extra with a Saito Golden Knight in it (.62 I think) and he loves it. We put a 13x4W prop on it yesterday and it flies great with it. Good luck with yours. If you'd like to look at another great deal check out the World Models CAP 232-46R. It's $119.00 and just an awesome ARF. I also reviewed that plane and have videos on Members Videos of it flying.

R/CDawg: I have not weighed it yet. I have no means to do so at home, and keep forgetting to borrow the mail scale from work. However when I do get around to it, I will be sure to post the results. I have say though that I am very doubtful that it will come out even close to the 3.5lbs stated on Tower. Great ARF!, well built!...but heavier than the description.

Lou: Thanks for the great tip on using that tape, I will remember that for future. I have already put a thin peice of balsa sheeting over the hole, and with the muffler extension I bought, the problem is fixed. I will also be sure to check out the SU-31 review.

Keep um flyin!
~Tip