Bad day flying today. What went wrong?

[frank mccune]

         Hi All:

         Today I had a very bad time getting two planes to stay out on the end of the lines for enough tension to do stunts.

         PLANE 1

         Ron Burns P-51 Profile 36" span slightly smaller than the Sterling P-51.  Weight 1.1Kg ready to fly.

         ENCINE Fox .25 Circa 1955 ?

         PROPS  9-4, 9-5, 9-6 Wood

         FUEL Fox 29% castor 5% nitro

         LINES .015x57 Lap time 6.0 sec

        PLANE 2

        Sterling  P-51 weight 1.1Kg ready to fly.

       ENGINE Brodak .25

       PROPS As above.

       FUEL 12,12, 10

       LINES and lap time as above

       I this normal output for these engine/plane combinations?

      Solutions other than shortening the lines to 45-50 feet?  I could mount a Fox .35 to replace the Fox .25 as s the mounting holes are the same.  More nose weight on a small airplane!
   
      Any suggestions

                                                                                                                                      Tia,

                                                                                                                                      Frank

[Dan Berry]

Too slow.

[FLOYD CARTER]

Your 36" span  and a .25 cuin engine with 50'+ lines is all wrong

Too under powered for that power and long lines.

1.1 KG =2.42 lb=38.72 oz

too heavy
.

[Carl Cisneros]

agreed, way to slow.

[Dave_Trible]

Yeah Frank you’ll need to get that crate going 5.2 or faster- maybe below 5 sec. to do much.  .35 territory.

Dave

[Dennis Toth]

Frank,
With both ships you need to GO FASTER!  For your line length get the lap time around 4.85 sec, don't set the engines for a 4-2-4. For the Fox 25 I would use the 9x6 prop (RSM 9x6 is a great prop). Set the engine to a rich 2 with the nose level. For the Brodak use an APC 9x4 and set again for a little leaner 2 cycle with the nose up at about 30 deg. I am assuming you have a uniflow tank and have the uniflow vent up in the free air stream (not just off the tank). This keeps the pressure constant (at least more than off the tank top).

Best,    DennisT

[Tim Wescott]

In math land, the outward acceleration is equal to the circle radius times a constant divided by the lap time squared.

Someone can disagree with me, but theoretically, if you run 5.5 second laps with 70' lines, you should run:

5.5s laps with 70' lines
5.3s laps with 65' lines
5.1s laps with 60' lines
4.9s laps with 55' lines
4.7s laps with 50' lines
4.5s laps with 45' lines
4.2s laps with 40' lines
4.0s laps with 35' lines

This is just a purely theoretical exercise (assuming 3G acceleration and that you add about 3' to the line length).  Your mileage may vary.  In particular, as the planes get smaller and harder to trim, you may need shorter lap times to compensate.

[Phil Spillman]

Hi Frank, Try 10% Nitro fuel with 9::9 oil mixture. Brodak engines run much better on "thinner" oil content than what you're using. Run your .25's at about 9200 to 11,000 rpm at release and see what happens! If not broken in too well leave the  muffler off until you've got 10 to 20 runs on it! More even better!

Phil Spillman

[Brett Buck]

       
         LINES .015x57 Lap time 6.0 sec

 

  As everyone else notes, WAY too slow!  The lines are probably fine, maybe a bit much, but not way out of bounds. Either of those prop/engine combinations, although pretty weak, should be able to get in the 4.5-5.0 second range on these small airplane, which will give you enough line tension. If not, speed it up some more.

      Brett

[Gary Dowler]

My Ringmaster (42") flies well on a older Fox 25, with 5.2sec laps on 62' lines, but it's also a lot lighter at about 28oz compared to your 38.

Gary

[frank mccune]

          Hello All:

          Thanks very much for the prompt replies!

           One thing that I must acknowledge is. that my scales were very inaccurate.  One and a half Kg. was way off base.  I was caught not paying attention to what I had typed.

            The actual weight of the Ron Burns plane is 12 oz. rtf. and the Sterling Mustang is 16 oz. rtf. 

            I did not tach my engines as frustration had set in to add to a joyous day. Lol  Read my comments on starting problems I had with the Fox .25 in the Engine section.     The last time I tached the Brodak .25 I tested it against a ST G-20 .23.  The ST .23 had a bit more rpms with the same fuel and props.   The Brodak .25 seemed to run very well with a black plastic 9-4 prop in the past.  However, I stopped using plastic props due to health reasons. Lol

            Hi Phil, I will try your suggestion re. fuel.  I am using a mix of 20% synthetic oil and no nitro in my HP .40 with the Gardner p&c and it appears to run very well.  I have noticed a trend to get away from using "thick" fuels in some of the more modern engines.  Perhaps you know this engine.  It once belonged to Gill Reedy and it was mounted on a Super Clown.  I have no idea as to how much or how it has been run.  It did come with a chip muffler that I am using.  It was a real dog on the Super Clown! I an going to take some time to see what your fuel will do for it.  It is a sweet engine as far as starting and adjusting is concerned but is down on power. 

                                                                                                                                                                        Be well my friends,

                                                                                                                                                                        Frank McCune

[Brett Buck]

          Hello All:

          Thanks very much for the prompt replies!

           One thing that I must acknowledge is. that my scales were very inaccurate.  One and a half Kg. was way off base.  I was caught not paying attention to what I had typed.

            The actual weight of the Ron Burns plane is 12 oz. rtf. and the Sterling Mustang is 16 oz. rtf. 

            I did not tach my engines as frustration had set in to add to a joyous day. Lol  Read my comments on starting problems I had with the Fox .25 in the Engine section.     The last time I tached the Brodak .25 I tested it against a ST G-20 .23.  The ST .23 had a bit more rpms with the same fuel and props.   The Brodak .25 seemed to run very well with a black plastic 9-4 prop in the past.  However, I stopped using plastic props due to health reasons. Lol

   Both of these engines should probably fly with a 9-6, not a 9-4. They may run OK, but not likely to get adequate performance with a 9-4.  Neither is intended to run like a 20/25FP (which would darn near rip the wings off of either of these tiny models - I have flown 12 ounce models through many competent stunt patterns with a Medallion 049). A G20/23 is a much stronger engine than the Fox, and at least a match for the Brodak (which used to have all sorts of descriptions telling you it was a traditional "stunt engine" and not to expect it to run like a 25 FSR, etc).

   But, very fundamentally, if you do not have enough line tension, *speed up the airplane*. There may be trim issues causing it, but more speed will cover that to first approximation. If, when you have sufficient line tension, you find trim issues, then fix those, then slow it down again.

    Brett

[Dennis Moritz]

Brodak 25s can run hard. They’ve won in Foxberg. 9x6 should help.


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[john e. holliday]

Ignore all the above.   Just lean the engine out more and put about 4 washers under the front engine lugs.

[Steve Helmick]

I would ask what sort of wood props they are? I've never been impressed with the thrust of a TF Paddle Blade or Power Prop. Sadly, there was no 9-4 TF Speed series prop. Although I understand the "health issues", try APC's in those sizes. I think the Fox .25 would run well on a 9-5 APC and probably the B.25 also. Also would change to .012" lines and 10% vitamin N. I'd start at .012" x 55' eye to eye lines and be prepared to cut them to 52'.    Steve 

[C.T. Schaefer]

12-14 oz.   Really??    I would invest in a new scale.   TS

[FLOYD CARTER]

14 oz. vs 38 oz.  Big difference.  Other suggestions seem reasonable.  Get lap times down with more power.