Interesting discoveries there, Matt!!

The only thing I can think of to ask, Any change in throttle linearity with the pipe?

I am going to fly today and the only thing I will fool around with is the throttle curve. Straight expo ain't gettin' it done.

Not really Bob, the longer pipe did not improve the non-linearity much. I played with throttle curve a little yesterday too. My curve starts out practically flat to around 40% and then goes straight up. I am using the expo function on the JR TX. There's a very small region around 1/3 throttle where the throttle delta is just too high. Needs to be tailored more. I will also try some different things today to get this closer to what I prefer

BTW where did you get your Saber Pro?

Matt, [link=https://www.amsoil.com/a/synthetic-2-cycle-oil]AMSoil Saber pro[/link]

Comes in a box of 48 1.5-0z premix packets. Very handy.

Got in 5 more flights today, with 2 of them under the able coaching of Anthony R who is getting me in the groove for the Intermediate sequence. A couple of times I actually kept a good line at a good pace, and Anthony is getting me to use space and speed a little better. It felt really great when I listened to him and pulled out of a maneuver on the correct heading!

Back to the SAP 180... didn't really work on the throttle curve because of other things going on, and the plane and engine were doing so well otherwise that I didn't want to interrupt the rhythm. Anyway, the engine is really coming into stride and the throttle curve isn't exactly horrible, quite flyable in fact. The vertical pull is good enough that Anthony told me I needed to throttle back on the verticals a couple of times![8D]

The turbo hose coupler is working quite well, for a total of 11 very full flights now, and I think it is safe to say this is our answer for the coupler enigma. I like this stuff because of its flexibility, which takes stress off the header and the pipe.

Matt, the Advanced Auto Parts store on Salem St. at the Randolph/Dover border is an Amsoil dealer. I'll pick up some oil for you if you want.

Just a quick word on couplers before you close the book though, try to keep the gap between the header and the pipe as small as possible to reduce the exposed area of the silicon. I also use a slightly larger coupler than i need, so if I'm in a rush I can just slide the coupler over so the charred bit of silcon is now safely behind the header or the pipe. Also I like to flare the ends of my pipes by stuffing an appropriate sized socket into the hole and rapping it lightly with a hammer. this stops them coming off so easily.

Actually the button head screw idea Ed Skorepa suggested is a good one. I've changed the teflon coupler several times in the past few days because I was playing around with pipe length. Teflon (PTFE, not FEP or PFA) coupler is a keeper too. Don't expect any problems with teflon...temp rating is higher than most plastics.

Duly noted.

Since I have now got a solid 2 hours of run time on the turbo hose coupler - with a one inch gap - tomorrow I will remove it for inspection. The weather is going to be crappy anyway.

I have the one-inch aluminum spacer still handy from the previous coupler arrangement which I will figure out a way to insert into the gap when I reinstall with a fresh piece of turbo hose. This will keep the exposed portion to less than 1/32" in total.

In a way, for testing purposes it is probably good to have had the one inch gap to better judge how the hose is handling the gasoline exhaust residue and heat.

Turbo hose autopsy

The photos below show the inside of the turbo hose coupler after a bit more than 2 hours of vigorous flying.

A couple of cracks can be seen, but these occurred as a result of my having to spread the casing open to see the inner surface. The cracks appeared only in the section that was exposed to hot exhaust gases - which means the heat did degrade the material somewhat - however it can be seen in the cross-section photo that there was little if any penetration of the inner surface. Also, the hose was equally firm-but-supple in the "burned" area as in the end areas covered by the header and pipe. I have no doubts that this coupler would last 60 flights (Rendegade's conservative estimate) and perhaps even 100, as is, with zero modification. However, the JB Weld lip on the ES pipe is mandatory to eliminate slippage.

A fresh piece of turbo hose was installed, using the aluminum spacer that I mentioned earlier, which is simply a 1-inch long piece of 7/8" OD wing tube. The entire coupler assembly weighs 48 grams. It was easy to get the aluminum spacer into the hose by wetting the inside of the hose with isopropyl (rubbing) alcohol and using the remainder of the wing tube as a ramrod to push the spacer into position.

I am fairly confident that this arrangement will last for an entire season of flying, and possibly a lot more.

The polyester reinforcement is intact. I had a concern about this material because it has a temp rating lower than the silicone does. It appears to be of no cosequence.
The weight is to be expected. This is a fairly thick hose.

Teflon is pretty heavy too. I haven't weighed it but Teflon is about as dense a plastic as we know.

Bob, BTW, the cracks are the typical failure mode for a the highest temp rated silicone. This material is probably of that variety.

Matt,

Yep, it's a bit on the heavy side, but it works so well in the harsh environment of heat and vibration that it is worth a few extra grams.

For me, that's the last bit of futzing I am going to do with the turbo hose - this one is the keeper. My next encounter with it will be when it fails or after 200 flights, whichever comes first!

Looking forward to your observations about the Teflon coupler.

In my previous experience with gas engines for pattern, the trick is to build the final copy of the header with metal material as light as possible (be creative in this aspect, the key is to find thin-walled metal pipe). Use a piece of Teflon coupler that exposes minimally to the exhaust heat (e.g., about 1/8"). You will be saving weight greatly and have a long lasting exhaust system.

Thanks for the advice.

In a round-about way, that's where we are ending up. The aluminum header is pretty light. It's the Macs header for the OS 1.40RX.

With the use of the aluminum spacer (which acts as an inner sleeve) the inside of the turbo hose will have no more than a total of 1/32" exposure (1/64" on either end of the spacer) to the direct exhaust gases. This set-up should be quite durable, and along with the Teflon coupler Matt is using it appears we now have a couple of options.

My Focus II weighs 10 lb 9 oz so it is lighter than many glow and certainly electric versions.

With which pattern plane and gas engines have you had experience? I am hoping later this year to get another SAP-180 and a bit more modern pattern design.

Bad Brad has some graphics for the Syssa now. Check em' out.
at BadBradgraphics.com

ZDZ40 with the scratch-built gas pattern (ama plan). I recall the plan calls for light tube used for heli tail boom. It worked pretty well. If you have the flange for the exhaust port, find some mop or broom with steel tube handles. At some point of time, I examined one such tube and found it is extremely light and can be map gas soldered to the flange. The coupler I used is pretty short (1" or less and no metal insert).

I am using a home-made soft mount for the engine, and there is a 2-1/4" rise also needed for the header, which means it isn't just as simple as running the header straight from the exhaust. So simplicity is best with the exhaust header. It is working well now and it took a fair amount of effort to get to this point, therefore the old adage applies, "If it ain't broke..."

Do you have a build thread link for this, or another thread in which it can be found?

Always looking to see how others approach things. Tracked down the turbo hose because I remembered seeing a coupler in the corner of a photo of Rendegade's pattern ship with a MVVS 26.

[link=http://www.rcuniverse.com/forum/fb.asp?m=6366809]Found it.[/link]

Yesterday it rained all day so I decided to build a new soft mount for the SAP such that I can adapt it into my old trusty pattern plane, Temptress. It was a simple retrofit and if anything, I built the donut a bit too narrow. Need to extend the stand offs by about 1/8" which won't hurt anything. The engine fit great although Temptress is fairly narrow. Still need to install the CDI and route the ignition cable around the chin cowl.

The fuse is a Temptation fuse. The pipe tunnel is adequate for the piped set-up.

Matt, sounds as if this one will be ready to fly very soon.

Are you using the newer engine or the first one? Which header?

I am going to make another soft mount soon, in anticipation of getting a back-up plane/engine in the not-too-distant future. Hard to believe how well the first mount is holding up. The nose ring is also doing well, but I think I am going to have to line the inside of it with some smoke tube because it appears to be a rather significant source of noise. Although there's a fairly tight tolerance between the wood and metal, it doesn't take much to create a rattle when the engine is running.

I am thinking of a different approach to the carb noise and will say more about it here... IF it works.

[/quote]

Matt, sounds as if this one will be ready to fly very soon.

Are you using the newer engine or the first one? Which header?

I am going to make another soft mount soon, in anticipation of getting a back-up plane/engine in the not-too-distant future. Hard to believe how well the first mount is holding up. The nose ring is also doing well, but I think I am going to have to line the inside of it with some smoke tube because it appears to be a rather significant source of noise. Although there's a fairly tight tolerance between the wood and metal, it doesn't take much to create a rattle when the engine is running.

I am thinking of a different approach to the carb noise and will say more about it here... IF it works.
[/quote]


Hopefully weather permitting, this weekend. It's the new engine.... has run super; and just picked up the OS header so I'll use that. This time I will put a hole in the firewall and get the carb intake inside the plane.

Never was able to get the one flip starts everyone else is experiencing until this past weekend. That's really cool. Just like flipping a well tuned Webra against compression in warm weather.....I need to learn to do that every time

On the soft mount, I took the old mount I was using in Temptress apart last night just see what the damage was after 1500-1700 flights with the Webra 145 and 160 up front. I was pleasantly surprised too. I still had rubber tearing adhesion on the bands, which is as good as you can have. The mount essentially entered its 7th year of service this spring. It is practically identical construction

I guess I am confused how the anti vibration mount works.  I thought their would be a layer of rubber between the posterior portion of the mount and  the fire wall.  But from looking through the pictures their is not.  And, what is the function of the outer side layer of rubber?  If the outer ring is solid wood, guess I don't see were the flex is coming from to take up the vibration.  Sounds like  you guys are getting good results with it thou.  I am just curious how the thing works.  From my untrained eye is appears that most of the vibration is reduced from the flex of the anterior ring mounts and then disappated through and to  the outer ring.   I tried the dubro anti vibration mount with my MT-35 but I don't think it was holding on to my right thrust in higher powered up lines.   I needed to do something with the MT-35 because the vibration was horrible.

Thank you for your help... this thread is packed full of great information and very little babble.  Awesome! I just wish I had the patience to sit down and read it thoroughly.  I know my question is probably answered somewhere in the thread... My AADD usually kicks in and I miss it.

Picture two separate plates, one over the other. Place a thin rubber sheet between them to separate them. Then place a rubber ring, like a rubber band, over their respective edges, capturing both plates. Voila!

The rear plate mounts to the firewall and the front plate to the engine. The two plates a connected to each other via the rubber band and are separated by the rubber sheet. The rubber band is the isolator and the rubber sheet between the two plates is the bumper that keeps the two plates from slapping each other and making noise

Hope that helps; I have a complete thread here on RCU that describes how to do it....but it requires some study to understand how the parst fit and how it works. Several have built one from that thread. Search under MTK

tele1974,

I used a photo posted earlier by FlyEng of the soft mount he constructed to make this illustration.

The photos show how it looks when attached to the motor box, and installed on the model.

Should help clarify things.

Take the time to read through [link=http://www.rcuniverse.com/forum/m_6285026/tm.htm]Matt's thread[/link]. I had a lot of questions as well.

I got... it makes complete sense now! Thank you!

As I was cutting of the the firewall of my motor box...I wondering if I could do the same thing with the motor box instead of the ring. I cut off the firewall and a 1/2 inch back and I am just going to replace it with another one that I have. Thanks to your encouragement cmoulder. I just needed a push in the right direction.

Instead of gluing the new firewall on could I leave a 1/16 inch space and do the same thing with the rubber and in effect maybe a similar result. It probably wouldn't last as long as the current design. I don't know much about it but I would think it would probably prematurely break down at the corners of the box.

Your comments would be much appreciated. Hopefully before I glue it.