Author Topic: takeoff rpm with inside tank (Read 872 times)

Steve Glass · « **on:** August 05, 2020, 06:19:50 AM »

Hi Guys,

My first post here so be gentle. I've been lurking for a while now trying to soak up some wisdom.

Anyway, I've made a doodleized flite streak with a FP20 and a 9x4 APC. The tank has a fixed uniflow with muffler pressure.

What might be sensible takeoff RPM's? Don't want to damage the FP20 as is only just been ran in.

Steve

Brett Buck · « **Reply #1 on:** August 05, 2020, 07:28:18 AM »

Quote from: Steve Glass on August 05, 2020, 06:19:50 AM

Hi Guys,

My first post here so be gentle. I've been lurking for a while now trying to soak up some wisdom.

Anyway, I've made a doodleized flite streak with a FP20 and a 9x4 APC. The tank has a fixed uniflow with muffler pressure.

What might be sensible takeoff RPM's? Don't want to damage the FP20 as is only just been ran in.

You are very unlikely to damage it no matter what you do, but particularly not with an inboard tank. I can't give you specific RPM ranges, but what I would do is peak it out lean on the ground (that is, as lean as it can get without sagging), then let it go. It *should* richen up considerably in the air. If so, then adjust the needle to give you a medium-rich setting in level flight, regardless of what it is doing on the ground.

Brett

Steve Glass · « **Reply #2 on:** August 05, 2020, 07:53:38 AM »

Thanks Brett, I'm hoping to maiden tomorrow if the wind drops.

One more question, what might be a sensible lap time? I'm using 60ft eyelet to eyelet lines.

Steve

Brett Buck · « **Reply #3 on:** August 05, 2020, 09:49:13 AM »

Quote from: Steve Glass on August 05, 2020, 07:53:38 AM

Thanks Brett, I'm hoping to maiden tomorrow if the wind drops.

One more question, what might be a sensible lap time? I'm using 60ft eyelet to eyelet lines.

Steve

4.5-4.6 is about what you will get when it is working correctly unless there is something unusual going on. It will seem like slow motion in the maneuvers.

Having it run in a medium 2-stroke in level flight is more important than the lap speed or the RPM, so you get the right amount of boost in the maneuvers. Get that right and even this fast, it's still easy to fly.

The inboard tank will tend to make it go rich after launch, so it will probably have to be set leaner than normal to get the right in-flight setting.

Brett

Steve Glass · « **Reply #4 on:** August 05, 2020, 01:31:14 PM »

Thanks Brett,

I'll report on how I get on.

Steve

Dennis Toth · « **Reply #5 on:** August 05, 2020, 02:58:18 PM »

Question: Assuming this ship is being flown on 60' lines C to C which for a 4-2-4 ship would be a lap time around 4.9 sec. Once the engine run is pretty much set if he wants to reduce the lap time can he simply add line length? As I remember adding 1 foot increase lap time by about 0.1 sec. So going from 4.6 to 4.9 add three feet to the lines.

Best, DennisT

Tim Wescott · « **Reply #6 on:** August 05, 2020, 04:28:59 PM »

Quote from: Dennis Toth on August 05, 2020, 02:58:18 PM

Question: Assuming this ship is being flown on 60' lines C to C which for a 4-2-4 ship would be a lap time around 4.9 sec. Once the engine run is pretty much set if he wants to reduce the lap time can he simply add line length? As I remember adding 1 foot increase lap time by about 0.1 sec. So going from 4.6 to 4.9 add three feet to the lines.

Best, DennisT

You mean either "reduce radial speed" or "increase lap time" -- yes. The plane's airspeed speed will stay pretty much the same, the lap time will go up.

Tim Wescott · « **Reply #7 on:** August 05, 2020, 04:31:04 PM »

Nice plane! I wish I'd known about inboard tanks when I was using a Flight Streak for stunt -- I ended up making a weird tall short tank to fit between the engine and the wing -- mounting a plain ol' tank inboard would have been much nicer.

John Leidle · « **Reply #8 on:** August 05, 2020, 05:08:15 PM »

If we reread Ted's article on the Imitation he has a cutout in the fuse to fit a tank . So I used to slide the tank inboard or outboard to achieve desired engine run.
That was a real nice feature he put in that plane.
John L.

Brett Buck · « **Reply #9 on:** August 05, 2020, 05:12:39 PM »

Quote from: Dennis Toth on August 05, 2020, 02:58:18 PM

Question: Assuming this ship is being flown on 60' lines C to C which for a 4-2-4 ship would be a lap time around 4.9 sec. Once the engine run is pretty much set if he wants to reduce the lap time can he simply add line length? As I remember adding 1 foot increase lap time by about 0.1 sec. So going from 4.6 to 4.9 add three feet to the lines.

Best, DennisT

The numbers are about right, but 3 feet of line is a HUGE change that also greatly affects the precision and control response. 60-62 is the normal range for these sorts of models but I wouldn't change it solely to adjust the lap time. 4.5-4.6 is not too fast if you get the engine response correct. I have had airplanes were I felt rushed at time at nearly 6 seconds/lap, and others where I felt comfortable with 4.2, depending on how the engine was acting.

The reason I am so hard over about the 20FP and 25LA is that those tend to have that slow-motion feeling without any special effort or even knowing what you are trying to accomplish. A lot of the other engines in the "small engine experiments" were fine and flew the airplane pretty well, but did NOT have the same effect, like the 25FP, Brat 28, K&B 3.5, etc, or at least not without being able to evaluate the problem and do something to correct it.

Brett

Brett Buck · « **Reply #10 on:** August 05, 2020, 05:17:03 PM »

Quote from: John Leidle on August 05, 2020, 05:08:15 PM

If we reread Ted's article on the Imitation he has a cutout in the fuse to fit a tank . So I used to slide the tank inboard or outboard to achieve desired engine run.
That was a real nice feature he put in that plane.
John L.

Unfortunately, with some engines, it also made it very prone to vibration issues. Basically all the 4-2 break engines tried on the Doctor had some sort of funny engine run issue we traced to vibration, and some of the 4-strokes may have also had a problem. We ended up changing the way it ran by adding stick-on weights to the *tank*. You could do the same thing and maybe overcome the problem by using 3/8x5/8 or 3/8 x 3/4 mounts.

But of course the real answer was run smoother engines much faster, it solved the vibration issue AND the airplane flew much better and more predictably.

Brett

John Leidle · « **Reply #11 on:** August 05, 2020, 05:42:06 PM »

Hey Brett,
I see where a 4 stroke would maybe been a problem another example of that plane serving the stunt people well testing the 4 stroke I mean . Ted reenforced the nose area with balsa to maybe over an inch thick. It was 30 years ago some things slip by little brain .. my choice of power was an OS Max .46SF when I was still running a low pitch prop. Vibration didn't trouble my plane.
John L.

John Leidle · « **Reply #12 on:** August 05, 2020, 08:27:25 PM »

My OS .46 engines were mounted inverted I used the RC radial mount.
John L.

Steve Glass · « **Reply #13 on:** August 06, 2020, 01:20:49 PM »

Today's flying went well, it was very easy to get an acceptable engine run. Indeed, the FP20 ran like clockwork and my only criticism is that there was no warning when it was about to quit.

I'm at the stage now where I can fly inverted and perform a few basic manoeuvres and not crashing so often. I'm sure this model will help me to progress.

Very happy

Steve

Ken Culbertson · « **Reply #14 on:** August 06, 2020, 01:57:01 PM »

Quote from: Steve Glass on August 06, 2020, 01:20:49 PM

Today's flying went well, it was very easy to get an acceptable engine run. Indeed, the FP20 ran like clockwork and my only criticism is that there was no warning when it was about to quit.

I'm at the stage now where I can fly inverted and perform a few basic manoeuvres and not crashing so often. I'm sure this model will help me to progress.

Very happy

Steve

I learned what you are progressing through on a Streak Jr. My mentor told me to just keep stretching out lazy eights until I didn't have to repair the Flight Streak. Great sport ship.

Ken

Author Topic: takeoff rpm with inside tank (Read 872 times)

Steve Glass

takeoff rpm with inside tank

Brett Buck

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