First off, I finished the model and have put 2 flights on it. It was “too” windy but I flew it anyway. A few aborted landings but I waited for a break int he wind and lands very nicely. For FYI, I balanced the model at 3.75” at the wing tips. I assembled the model and balanced before installing batteries (two A123’s), rudder servo, ignition module, optical kill, voltage regulator, pull-pull, etc. Then I moved everything around until it balanced. It was at perfect CG when completed and required no additional weight at all. Also to my great surprise, after the plane was airborne it required ZERO clicks of trim on ANY channel. I have never had this happen before on a new model. This is my first large scale/gasoline model so excuse what may be obvious. My questions are as follows and I thank you all in advance for any input you provide:

1. I am running a DL-50, the engine runs fine on the ground at all RPM ranges and tranisions fine, but seems to run less that optimum in the air. I have heard that some people put some sort of plate over the carb to prevent forced air from entering into the mixture control. Have your heard this? Is it neccesary? Would question #2 cause this?

2. Please review the attached photos, does it appear that I have sufficient clearance/air exit around the engine? Or is it too tight?

3. I am using ball links for the throttle. This seems to transfer a lot of vibration to the throttle servo. At full RPM I can see the rod vibrate substantially, and if I touch it, I can feel a lot of vibration being transfered. Should I be using something less rigid? Should I be using ny-rod and standard clevises with a little more “slop” to release some of this energy? I balanced the prop and hub both. (see hardware photo of the throttle servo)

4. Should the wiring be tightly secured or left somewhat loose when “zip-tied”? (see photo of my receiver)

5. Question on the cowling: It was extremly difficult and time consuming to install the two screws for the lower cowling (from inside of the cowl to the firewall) with the engine/muffler installed. Given the "hook" type mechanism at the bottom, are these screws necessary?

I'll try to answer the best I can- I am wondering what is going on with question #1, because I thought that this engine (dl 50) had a rear carb, and would not be directly in the airflow... I run the toc 53 that Tom sells, and I have had some troubles along the way with airflow- I think possibly what might be happening is that there may be a low pressure situation in the cowl due to the prop disc covering the intake opening on the front of the cowl, and due to the fact that the bottom of your cowl is pretty closed up.. I would DEFINITELY open it up quite a bit more if I were flying it out where I am... (Palm Springs area, 120+* in the summer) I actually cut a hole in the side of the cowl where my carb was, and that helped, but didn't act the same way as when the cowl was off completely. I cupped my hand as to scoop air into the opening I had cut for the carb, and presto- it worked..... ...for me- this is quite odd, as I have never heard any other mention of this happening with this airplane.

The answer to question 2 is NO, it is too tight. the general rule is you want three times the exit area as the the intake area. ie; if you have a 1" square opening in the front, you want no less than a 1.5" square opening for the air to exit- 1" sq. = 1sq. inch- 1.5" sq. = 3 sq inch. etc etc.

For #3, I have a similar installation for the throttle servo, and have had no issue in 60 or 70 flights with that servo/linkage.

I would leave some slack in everything- You have to take in to account the G-forces that this plane can see- I would imagine it could be upwards of 10 or 15 G's
Just think, your 6oz battery could possibly weigh 3 to 4 pounds in a wall or snap roll. you know things will flex and move around a bit.

once again, I have 60 or 70 flights on this bird, and well, WHAT SCREWS? lol- They are not needed- at least I have not needed them, and even after a terrible crash, they are still quite solid!


hope this helps!

Re:the DL50, check out the DL 50 Engine thread and yu will get more than enough information on setting up your DL50. Your Extra set up looks very clean and organized.
NEDYOB

On question #2. If there is no extra cutout exists other than the one on the cowl, then probably yes, you need to open it up more. It should be at least the same size as the current cut-out.

On #3. you can install an sleeve tube over the nylon rod and anchor the sleeve tube somewhere inside the engine box of front of fuse with a piece of 1/8 plywood. The rod should slide freely inside the sleeve tube.

On #5. You can install two anchor points on the firewall (near the bottom with 1/4 plywood). Install two blind nuts on the plywood (facing down). drill two holes on the bottom of the cowl so that bolts can pass through the holes and screw on to the blind nuts. Another option would be to open up the cowl at the proper location so that you can directly pass the bolt through the cowl with a long hex allen ranch.

Hope this helps.

You don't want or need the two lower cowl screws. It just slips under the 2 ply "hooks", then lift it up and put the 2 upper screws in.

The blind nuts are only there for somebody who has to cut away the center of the cowl ring.

TF

Thanks to all for your input. I welcome anyone elses comments as well!

The ball link connections at the throttle servo are a good thing. Changing to a regular clevis would not change the amount of vibration, but it would permit a loose fitting clevis pin to enlarge the hole in the servo arm, reducing throttle response and accuracy over time. Gassers have strong combustion impulses, so vibration is a given. Glow engines have more but it's on a higher frequency and therefore not as visible. Just as damaging over time though.

Wide variations in engine performance in ground versus flight locations can be attributed to many different factors. The first two that usually come up are: Is the engine warmed up prior to take off? If not, the engine will always lean out to some level after take off, causing the appearance of a change in needle settings. They didn't change, the engine simply reached it's correct running temperature. The next is: Were the needles adjusted (tuned) for the best performance with the prop and fuel mix? If not, then poor flight performance should be expected. Another is: Was the carb tuned with a warm or cold engine? If it was tuned cold then the needle settings will be wrong for a warm engine. This happens much too frequently when an anxious owner gets in a hurry to set the engine tune and starts in on it immediately after starting the engine. Let the engine warm up for a minute or two before tweaking needles.

I secure any wires or group of wires that are "flight critical", which probably means all of them. "G" forces place increased loads on anything, including wire connectors, so increased load factors occur on connector pins and wires just as they do on anything else. It's always a tragedy when a wire pulls out of a receiver or elsewhere for an "unknown" reason. Things flopping around inside a fuselage place a lot of strain on themselves so securing them so they don't fly around is a good thing. They don't have to be rigidly mounted along their entire length but a cinch here and their to limit motion is good enough.

The lower blind nuts are not needed if the hook arrangement is still used.

My wire securing method matches Pat's words pretty closely. Secure everything but not so tight that the wire ties and/or wood cuts into the wires. Securing something too tight can actually transfer vibrations better than if you left it a little looser (ie velcro squeezing down an ignition module's foam padding against the motor box). Moderation is good. I never leave anything over a few inches without being secured. G forces will tug on the 2 ounce extension and make it a pound during a snap roll. And always go over the plane now and then to look for cut wire insulation and fuel lines. This is one of those "ask me how I know" experiences. The sharp edges of thin ply makes great gas engine powered mini saws.[X(]

Is it just the picture or is your muffler almost touching the cowling on the right side bottom?

PS Edit: And every time out, as a pre-check, always push down on your rx's servo/battery extension plugs to make sure they are bottomed in the sockets.

Thanks again to all. The photo of the muffler may not show the best detail. Their is about 3/8" of an inch clearance or thereabouts.

With the understanding that you prolly don't want to do so, it would be good if you opened up the bottom of the cowl behind the muffler a little. That muffler gets pretty hot and the extra area would vent some of it.

Those Deans connectors become pretty heavy during hard maneuvering. Though they are hard to disconnect, securing the wires a short distance behind them would be a good thing. Leave enough slack to enable "working" the connectors.

You might want to cut off some of that exhaust stack. It won'r effect engine performance either way. The first thing that happens in a nose over is the stack hits the ground and tears out of the muffler. A shorter stack is easier to work with when removing/installing the cowl and is no longer the second thing to hit the ground. The first is the prop....

Here is what I did on my 300/DA50 for air exit and it has worked out very well.

That looks like a good clean cuttout. Thanks for the photo!

FYI to everyone, this is a video of my 3rd flight. Nothing spectacular since this is my first large scale/Gas powered model:

[link]http://rcuvideos.com/video/WH-Extra-3002LQ2-wmv[/link]