ptulmer

My Feedback: (5)

Ok, there's not much to tell. Flyswatter weenie'd out on me. Something about now being able to get his engine to run....[>:]

The DNU! made about eight flights today. Several with a streamer attached. Of course there were some in the club that just COULDN'T stand to see a streamer zooming around the sky. So I got chased all over the place. The DNU! really showed it's abilities. I could turn WAY quicker than the "Barnstormer" could. I'm not sure what it really is. It a low wing sport plane that is already a very agile plane. So the fact that I could Split S and be across the sky before he came out of a turn was pretty funny. My streamer was never cut!
The one ounce tank gives plenty of flight time, but the product engine started giving me trouble after a couple of runs. A 6x3 is too much for the product engine without upgrading to a Galbreath head. So Wilson ordered one too. Now I gotta get him to actually fly....

ProBroJoe

Patrick, that's a great report, and hey.... that's a pretty sweet trim scheme on your DNU!

So, what'd you really think of the DNU! - isn't it everything I said it was (and more)?

Too bad flyswatter's engine wasn't cooperating... I wonder what was up with that? I can get 'em to fire off on the first flick by slightly pressurizing the tank through the vent. After filling the tank, I just hook my filler bottle to the vent line and apply pressure until I see the fuel line fill with fuel, prime through a closed exhaust, hook up my glow battery and give 'er a flick. (I read about that one here.) It seems a good "starting" position for the needle on these is right around 3 turns out. FWIW, my engine (with the hop-ups) really likes the Cox 5x3 and will run out a whole tank without as much as a hiccup. (Along with sounding great in the air!)

Your flight report really makes me wish I would have gone out and flown today... I'm goin' through DNU! withdrawl.


BTW, I think it's ironic that flyswatter was the one givin' YOU a hard time... turnabout is fair play, right?

-Joe

flyswatter

Actually, pt did put in more flights than I did. The max rpm I could get out of the 6X3 and a stock product engine was about 11k.[] This was not even sufficient for a test flight - so I changed to a 5X3 rubber ducky. I got about 14.5 to 15krpm with the prop change. This was more like it! The DN2U handled nice and was about as fast as pt's DNU! with the Galbreath head and a 6X3. Interestingly, my DN2U has "stock" ailerons and these were very effective with about 3/16" throws. I have ordered a Galbreath head and it should be here this week. PT and I will begin streamer chasing as soon as "he appears" at the field next week. However, as was the case for pt today - we will probably have to dodge all the 0.25-0.40 size planes at the field who will be chasing both of us! From what I saw today with pt, these little planes can get way inside of the "big boys" - they have no chance!

Larry Driskill

A week?

Gosh, it shipped on Friday and I will be a bit disappointed if the good ole US Mail does not have it to you by Tuesday.

ptulmer

My Feedback: (5)

Joe, I really wish I could take credit for the design, but it really was very close to the original. It is one heck of alot of fun. I lost count of how many times it went up, and the delta stayed in the trunk all day. Flyswatter's "engine trouble" had better be fixed by the weekend or he will get a real load of cr*p about it. Steady needle settings were nearly impossible, so the spring will get replaced by a piece of fuel tubing. It started out running through a whole tank of fuel and quickly started cutting out about 1/3 of the way through a tank.
Using a MAS 6x3 and a Galbreath head on 35% was getting me about 14k static. That could improve and make me happy. Vertical was nice, it would shoot up about a hundred feet before falling off. Rolling with the torque (right?) was axial, but going against it could get ugly quick. The turn radius is freakin' AMAZING!

combatpigg

My Feedback: (3)

Glad to hear about your DNU tearing up the sky! It doesn't take much to make these planes come to life. 14000 with a 6x3 isn't terrible. I'm going to work my DNU over for flat spins, I think it will do them with more power, some flap / elevator mixing and of course a lot of rudder.

ptulmer

My Feedback: (5)

Wilson will be running the galbreath head also, so we will probably stick with the 6x3. "Tacking" 14k it would move out nicely, but I'd like to see more vertical.

flyswatter

I wonder if we went to a 6X4 would give us more vertical?

ptulmer

My Feedback: (5)

Maybe a 6x2. More rpm, same diameter= more thrust. Just like the degree/inch throw arguement we had at the field....I'm right!

flyswatter

Not exactly - By your definition, if I mount a 6" popsicle stick on the front of the engine (which will give me more rpm), then I must have more thrust. Nope!

I'm still not sure what you were saying about the ailerons (sizes, degrees & throws). I thought you were saying that small chord ailerons are more effective than large chord ailerons for the same throw. If that is what you meant, then I don't think I can (or will ever) agree with you. On the other hand, you could have been saying something else. The flying field is hard place to carry-on "civilized" conversations.

ptulmer

My Feedback: (5)

Ok, I'm banging my head on my desk. 'Had that one coming after all the cr@p I've given you about your "engine trouble"
Now, within reason if you reduce the pitch and increase rpm it will gain thrust. How do I know that? I've got an friend that's an AE and he told me so.... Of course static thrust ain't the end of the world. You remember how the Cox 5x3 "lit up" the delta, but the 6x3 would barely get it in the air.
I'd like to try the Cox 5x3 and 6x3 props next weekend. The Cox 6x3 was getting about 16k on another product engine. That may be the answer. Flexible props are great, ain't they?

combatpigg

My Feedback: (3)

I did a fair amount of thrust testing last year and none of the engines tested could handle a 6x4 as well as a 6x3. The best use I found for a 6x4 is to cut it down to 4x4 and mount it on a racer type plane.

flyswatter

Hey pt:

Are you using the standard Cox plug shim with the Galbreath head? [sm=confused.gif] Oh, by the way, my Galbreath head was delivered yesterday (Tuesday) with the plugs, etc (Thanks Larry for getting them to me so fast).[sm=thumbup.gif]

ptulmer

My Feedback: (5)

Yeah, I think I had two of'em in there. A little experimentation could be in order to get the best performance.

combatpigg

My Feedback: (3)

With the NELSON set up, pull all the shims out. Your product engines, if they are worked in right should feel like PATRICKs' KB, the prop should flick with a POP and the prop should bounce back and forth a few times after being flicked. The KB has had the main journal relieved and polished. The needle valves need to be sealed better and stabilized if you want consistant runs. It would be good to show up with a plan B engine, like a BIG MIG if you guys want more combat time, because coming up with a fix for a stubborn COX at the field is usually about as fruitfull as looking for money in pay phone slots.

ptulmer

My Feedback: (5)

CP, using the Nelson setup on a BigMig it was burning a plug every run. They would still glow, but not light the engine off. Replace the plug and all was well. I figured that it was being overcompressed, so I started adding shims and there was little to no difference in the RPM. I may not be doing something right...

combatpigg

My Feedback: (3)

Well, these engines are like finger prints, no two are identical. I had a problem with a AME at 28,000 fracturing glow plug elements. The rod had a twist. I replaced the rod and the new rod twisted, which meant that the crank pin could have been out of whack. Anyway, the engine was going through plugs due to vibration. If you are pulling out plugs where the element is totally cooked, or detonated away, then your set up has too much compression. I wonder what this engines' deck height is compared to others? .001" is probably equal to a compression ratio point. I have found with the engines that I use the NELSON set up on, whether it be COX, AP or NORVEL. that zero shims and up to 30% nitro works well. The thing for all users of these engines to do is experiment with shimming, if you make a change that forces you to open up the needle, then you have done good. Keep working in that direction until the needle setting needs to be leaned, then go back to where the compression setting allowed the most fuel to be burned. I'll bet most of the guys who are using these engines haven't taken the 15 minutes that it takes to see to it that they are getting their moneys worth out of these engines, and that's a shame because there isn't that much power to be wasted! Castor oil will retard the spark and delay detonation too, in a way you could think of it as an octane boost.

flyswatter

cp-

In your experience, have you tried the 5X3 3-bladed Cox prop. If so, how did it perform?

combatpigg

My Feedback: (3)

I don't have any experience with 3 bladed props, they must do OK or COX wouldn't include them in their stock. The 5x3 two blade prop performs well, it is the standard hot rod prop. You can get more use out of a tired engine with a 5x3, than with a 6x3. Less load, easier to needle. The draw back for combat, especially if you are flying 30" wings instead of 36" or greater, is the models' speed goes way up, which has obvious draw backs for good, low impact fun. I would rather see you guys try running running 6x2s. This way you can keep the planes in the box easier too. The DNUs are small enough to fly well with 6x2s. I should give it a try too,[on a DNU]. Our 36" planes don't perform well with the 6x2s, they really pull well with 5.7x3s or 6x3s.

flyswatter

It does as you say when you remove the shim. It "pops" and rocks when you flip the prop through. You know, when I used a standard Nelson and the shim, there was very little compression - much less than with the shim and a standard Cox plug.

If you take the prop and turn it through slowly, then you can feel the strong topside compression cycle. Almost like it is not going to go through - then bang-o it is through. It feels very similar to the Rossi 40 (except no "bump" at the top) when you do the same thing.

Andrew

Flyswatter --

Unless your engine is well broken in, the resistance at the top is not likely due to compression, but rather the classic NORVEL "pinch". NORVEL's are fitted very tight at the top end and while the engine will flip thru easily, turning slowly will be met with a lot of resistance, enough so that you cannot turn the crank without a prop installed. A simple test is to remove the plug and/or head and turn slowly again. If it remains tight, then resistance is "pinch" and not compression. If have a couple of .15's that squeak at the top, much like the Q40 ABC engines. After sufficient running, the pinch will ease up, but not go away completely.

ptulmer

My Feedback: (5)

Andrew, we've confused the issue a little. Mine's the Norvel, Flyswatter's is the Cox Surestart.

Andrew

Ka-Whack !! Apparently it wasn't the issue that was confused -- OK, it's not my fault, my brain's done in from old age and butyrate fumes. I'm headin' for the easy chair now.

combatpigg

My Feedback: (3)

So far all the surestarts that I've run need all the compression they can get. I'm going to make a piston swelling tool like JMs' and see if a little more life can be pumped into them.

flyswatter

cp-

What do you do to fill that big old shaft hole on the APC 5.7X3s. Even with the smallest filler bushing that came with the props, I have still got a 1/8 to 3/16 inch dia mounting hole - way to big for the screw of a product engine!??[:@] Are metal or composite fillers available on the market?

Now, in the past when pt and I had this problem at the field (Problems always happen at the field - right?), I do not want to tell you the things we have used. Necessity being the Mother of some pretty stupid ideas, we have tried about everything and lord knows what the prop-engine balance looked like for some of those "fixes".![X(]

Meanwhile, as I am typing this, I am saying to myself; "I just bet when cp had this problem, he just machined himself some fillers". Anyway, I still need some of your "Guru" suggestions - if you would be so kind!