ameyam

I am refitting a Phoenix Extra 60-90 with a DLE20. Earlier having flown it with a FS91and nose weights for balance, the DLE20 including everything is lighter than the lot, so i am OK there. I just have one concern. I was thinking that the firewall on this model is 10+mm thick but while working with it, I notced its closer to 6-7mm. Its got tristock bots inside and outside along with fibreglassing. I was wondering whether there could be a problem with this thickness. A fellow flier has the Phoenix Yak (which is essentially the same airplane) but he has a 120ax in it and the firewall connection to the fuse is even worse in that airplane. But he hasnt had any problems with it. My engine is not going to fall off the airplane- 4mm blindnuts + locknuts inside the fuse and a GP 120-180 adjustable mount are standard. I havent finished drilling the mount, but I have filled the stock firewall holes and drilles two new ones for the GP mount, so you could say I am at the point of no return

So is the firewall thickness sufficient?

Ameyam

Tired Old Man

My Feedback: (1)

1/4" with reinforced corners minimum. 5/8" reinforced would be better.

a1pcfixer

My Feedback: (7)

That will be fine.
Many firewalls that range of models are 1/4" thick (.250 in/6.35mm)

Don't drill the holes for the blind nuts too big. You just want the hole barely big enough to start the blind nut.
I then take and put a stack of washers over a mounting bolt, and use that to draw the blind nut into the new holes.
An allen head socket screw will be easier to do such with if available.

a1pcfixer

My Feedback: (7)

How about as is, but pin the firewall instead of making it thicker?
That'd be easier for him to do.

captinjohn

Sometimes it is not how thick a firewall is, but how many plys the piece has and how well it is tied into the rest of the airframe. Also pins are very good. Capt,n

spaceworm

I'm guessing you mean 3/8" reinforced would be better?

Sincerely, Richard/Club Saito #635

Rcpilot

My Feedback: (78)

I would consider the type of wood used.

If it's cheap china card board - then I would cut it out and replace with HARD aircraft ply.

I would never build a firewall out of lite ply, but thats just me.

If it's hard plywood, I'd say 1/4" minimum and tri-stock the corners and pin the sides with bamboo kabob skewers soaked with CA. But thats a minimum. I'd rather have a 3/8" hard ply firewall behind a 20cc engine. I'd pin that and back it up with tri-stock as well.

Tired Old Man

My Feedback: (1)

Uhh, yea. It's been a REAL unusual day. Just a little distracted in a great many areas.

apalsson

My Feedback: (1)

If I realised I had a plane built to that kind of a standard, I'd replace the plane but keep the engine
Imagine how the rest of that plane wouild be built!

ameyam

Hold on, Phoenix is usually (or was usually) well built. I can count about 6 plys. It isint cheap board, this seems to be wood similar to GP's airplanes. Its has tristock all round inside and outside. I have the outside already fibreglassed, thinking I will epoxy inside for more strength. Its a icky job, you need to put your entire forearm in but lets see

I am making the bling holes witha a drill one size larger than 4mm (its not 5mm) and the blind nuts sat ok. I had issue with one that slipped in the wood and kept rotating but I got that out somehow and then applied epoxy with 50% microballoon filler in that area. The engine sits inside the cowl but I will cut the access hole anyway. The cown sits about an inch ahead of where it would sit with the 91 (marked by the rear blue line) but fit and centering seems to be ok

Ameyam

Tired Old Man

My Feedback: (1)

If you have glassed the full outside already, including a wrap onto the sides at the corners, mount the engine. Engines pull out so 95% of what you do inside is a waste of time and effort. A good glass job is worth 1/8" of wood any day.

a1pcfixer

My Feedback: (7)

Indeed!
That firewall is already better reinforced than a lot of other models.
There's the fuse sides, top, and bottom, then there's two side formers, and the floor for fuel tank, PLUS you say it has tri-stock.

You'll be just fine as is!

ameyam

Ok, I epoxyed the inside anyway (let me be the first to say that that is the most icky-est job I have ever done) Now the issue of throttle pushrod is still left. The pushrod route clears the tank, so that isint a problem. I had planned to go for 4-40 pushrods with z-bend one side and ball link on the other but the 12" pushrods are too short for the servo location. The LHS has only cables, no pushrods. so I am stuck here

Also, I wish the ignition modules would come with lugs for screwing into the firewall or fuse. Strapping it in means looking for a place to put the ply to do that plus holes for the strap and cable ties

The cowl fits over the engine just fine but I will still need to make the cooling holes. It sits an inch front of where it would sit with the 91 so I will need to look at the CG again

Hope I am not adding too much weight for 3D

Ameyam

ameyam

Its become quite nose heavy. Dont know exactly how much bcoz I need to put in everything- may be some other day. I need longer screws on the firewall- 40 or45mm and larger washers. Putting in double washers + spring washer on the mount side and blind nuts on the inside. I will also need to move the tank all the way back to the wingtube to adjust the CG

Made a pilot hole (1mm) just to check the clearance for the throttle pushrod and it lines up ok, no tank interefence. I needs to be a pushrod though, the spring return causes a thinner wire to lock and bend. Should I look at a turnbuckle for a 4-40 rod?

Ameyam

Tired Old Man

My Feedback: (1)

Moving the tank to be against the wing tube is something everyone should do at every opportunity. That's the one place (close to the C/G) that the addition or reduction of fuel weight will have the least impact on center of gravity. Any place alse and the C/G changes as fuel burns off. The plane becomes more and more tail heavy as the the fuel quantity reduces with more forward tank locations.

Gas engines by themselves are not always heavier than a glow, but the addition of the ignition can change that picture. Someone converting a plane from glow to gas needs to be prepared to relocate servos and batteries to offset the change in propulsion module weight. Often this will require modifying the plane to install elevator and rudder servos in the tail, while installing the flight battery aft of the canopy hatch.

Mounting lugs for ignitions have been treid before. Unless the ignition has a robust metal case mounting lugs will always break off. RC Excell cases had mounting lugs in the beginning with their plastic cases and all of them failed. Better to have a few extra small holes somewhere on the plane than an ignition that separates in flight.

apalsson

My Feedback: (1)

Looks like you will be more than OK with your setup and the firewall plenty strong.
My personal preference is not blind nuts for engine mounting but good quality steel bolts with a large washer on both sides of the firewall but sometimes you just cannot get the hands at the back of that firewall.
A set of extra long allen keys is very handy to have for those kind of setups

spaceworm

I make pushrods out of fiberglass or carbon fiber arrow shafts. A buck fifty each for a 31 inch arrow at Wally World. Epoxy fittings or wires into each end, or you can buy special arrow shaft end fittings. Or, Use Sullivan Goldenrod sleeves and inside rods. Buy the stiffest of the several offerings. 2-56 rods thread nicely into the inner rod and then your choice of end fittings as long as you don't have any metal to metal joints. I don't think you need 4-40 fittings for throttle applications.

Richard/Club Saito #635

Campgems

I ran into a bit of a problem using the #2 threaded rod into the golden rod center on my last two builds. There was enough difference between #2 rods that some would bite in the plastic center and some would not. Imust have aquired a batch of the would nots along the line. It's like the thread was only 30% or40% vs a more normal 60% to 70%height. If the threads screw into the golden rod easly you probably have a 30%er The good threads required me to use two nuts locked and then a wrench on them to put the threads home.


Don

a1pcfixer

My Feedback: (7)

I've got longer but they won't all fit in a good photo..........

MTK

Just as important is the type wood the firewall is glued onto. If it's bare balsa, it's better if the balsa was lined with 1/64" ply first, about 3/4" wide, all around. If its a ply box, the firewall doesn't need to be particularly thick. I use 1/8" aircraft ply for my 30 cc engines and double the thickness around the blind nuts with 1/2" wide squares. Triangle stock behind the firewall reinforces well. OR fiberglass around the box outside edges in lieu of triangle stock. The 20 cc puts out, what? 2 1/5 hp? 2 or 3 oz cloth is plenty

EF models are made in China and they use an excellent 2mm lite-ply for most of their construction. Wish this wood was offered in sheet form; obviously somebody makes it. The current lite ply offered to the US market is almost junk status comparatively speaking.

10 mm firewalls will work for 120-170 cc engines.

ameyam

I very much think the firewall issue is resolved, now I have weight problems

I have flown this airplane before with a FS91SII and that made it tail heavy. I didnt have weights at the time, so I put together all the heavy nuts, bolts etc I could find in my spares box and stached it against the firewall to get the CG. So, even before I touched the airplane, I weighed the lot with the 91 against the dle. It was 888g for the lot as against 878g for the DLE and everything. Remember, the other option was to go to 120ax which weighs similarly. I think the stouter mount and the fact that the DLE sits further front makes the difference. I havent weighed the model ord done the CG just yet fully. Yesterday, the ighition, tank and batteries were still not in place. Few questions

1) How large a tank?

2) Will 4c Eneloop be heavier than 4c NiMH or 2C 1300mAh LiFe? In any case, will this matter? All of these sit just under the wing tube

3) Should I put in foam wheels now? I had 3" rubber in earlier because foam absorbs glow fuel

There is no relocation of servos possible, the elevator servos are already in the tail. Only rudder is in the fuse. I also have to put a stiffer tail wheel assembly in which may help a bit

I think I should persist with this route. In the worst case, If its too nose heavy, I can still go back to glow, it only needs to redrill the old firewall holes (two are the same, two I had to close and make new ones due to the 120-180 dle mount). Though I do feel that would be taking a step backward

Ameyam

spaceworm

There are rolled threads and there are cut threads, and the base rod diameter should be determined by which method is to be used. Sometimes to get a certain rod diameter, like 1/16 diameter, a cut thread is not quite the outside diameter that a rolled thread would be, or not the proper diameter it should be. A rolled thread will be greater in diameter than a cut thread for a given rod size. Sounds like you got a cut thread on a 1/16 diameter rod. You could look up what a 2-56 thread outside diameter should be and see how that compares to that with which you had a problem. To help thread the good rod into the Goldenrod inners, I sometimes run a 2-56 tap into the Goldenrod. I also sometimes run a tap into nylon clevises or other plastic parts into which I need to run a 2-56 threaded rod.

Sincerely, Richard/Club Saito #635

eddieC

My Feedback: (2)

Hopefully thicker than at 1:57:

http://www.youtube.com/watch?v=lzUUdilYbSU

ameyam

Can someone point me to the Tower address of the nylon throttle linkage that I need and also explain how exactly they work and are to be setup? My mentor did explain but it bounced over- to many details in one go I guess

Ameyam