RCFlyerDan

My Feedback: (54)

This is the way that I have solved the issue. My F-4 had the worst issue. I don't care for the male plug in for the overflow. It's always difficult to pull out, especially if it has new O-rings. I prefer a tube outside. I just plug the Tygon tubing onto it. It also makes it easy for new spotters to pull the tank. Then on the leading edge of the tube, I file a bevel. It does solve the Venturi affect of the overflow. Instead, as with full scale, it puts a light head pressure on the fuel system. In my mind, it helps, and has solved my issue. My Viper doesn't have the bevel, and I only have a 160 in it

Faces into the relative wind. I run a 180 on this overflow.

This is my F-4. I run a 220 on this overflow. No issues or fuel starvation due to head pressure. I think it is only 6mm. I worried about having too small of overflow the first flight. Now I don't worry about it.

Skunkwrks

Thanks, RCDan on how you prevented the syphoning effect, I appreciate your input from the real world of aviation on this.

sewbusy

There are different ways that pilots tackle that issue. Several of us who are flying in Jet Aerobatics competition, use a method that we learned when we flew Scale Aerobatics and brought it over into the Jet world. It has worked perfectly for me during the many vertical up and down lines that we fly, during our various sequences. It may be to your advantage to at least look into it. There is absolutely no fuel loss at all during the entire flight.

Hopefully, it will work for you. The photo below will show the method.
Safe flying.
Wayne

Skunkwrks

Thanks, Wayne for weighing in on how you have dealt with this issue of syphoning from the vent line. Learned from flying Scale Aerobatics.

Russ

BlueBus320

My Feedback: (57)

Does this jet knife edge well? I’ve looked at countless videos of this Viperjet & it seems most people fly them very scale like. I must have looked at 50 videos & am very surprised to not see anyone knife edging this plane.
thanks, Jay

Dave Wilshere

If you balance as the manual no…it hardly holds a KE at full power. As I balance it you can fly KE circuits, it’s just not that type of Jet normally.

BlueBus320

My Feedback: (57)

Thanks Dave

RCFlyerDan

My Feedback: (54)

I have mine neutral balance in the air. It will do a nice, straight, at speed knife edge without coupling. And that is with a 160.

Dave Wilshere

Should climb in KE with a 160…

Skunkwrks

At sea level, a lot harder at 3300ft to do........

Dave Wilshere

Yep, never flown at those altitudes, but know the physics.

sven1906

Hello to all Viper Pilots,
maidened my Viper (McLaren scheme) two days ago, after getting into jets on Xcalibur and Avanti XS before. Mine is powered with a KT160G4, Savöx SA-1256TG all around, except SV-1230 for flaps, Powerbox Mercury, stock tank and thrust tube. All settings are in line with the recommendations given in this thread, thanks to everyone contributing with experience and advice.
T/O and flight was flawless, no issues and only a few trim clicks required. However, on short final I switched to full flaps (70 - 80°) and in the same moment she got pretty unstable. This took my totally by surprise. I applied power and made a go around. The second approach was not much better and I hardly brought her back to the ground. It was an ugly landing (way too fast) and finally she jumped and came down on the nose first. Luckily, only the nose gear pin sheared off, no damage to the airframe thanks to the robust design! My impression was that speed is ok, but it looked like I was pretty close to stall.
I should have checked stall speeds first, but I have to admit that I missed that so I appreciate any feedback on your thrust settings with full flaps before I take her back in the air.
Thank you & regards from Hannover
Sven

DUCMOZ

Sven, from what you are describing, you might have too much flap. That plane comes to a crawl and still does not do funny stuff. I would say either CG or Flap needs to be checked. Dave can pinpoint the issue better.

Behzad

sven1906

Hi Behzad,
thx for quick reply. I will certainly double check CG and eventually go a little fwd to the save side.
I am also thinking of changing flaps control from 3-way switch to knob so that I can extend them in small steps and see where the limit is.
Rgds, Sven

DUCMOZ

Use Dave's method for CG check. also, if i remember correctly, flap is about 60-65 degree range. all I know is that it does not disturb the plane.

clavin

My Feedback: (6)

Yep and here at 2200 feet its tough just to stay level with a 160

sailing1

My Feedback: (134)

Hi Sven, My guess is also that you have too much flap dialed in, at least for the way I fly mine. Have been flying mine for lots of years. Power is a 45lb Rhino and I fly mostly from a 400 ft hard surface strip. Can't remember my CG but its conservative. My flap control is via my left slider. Full flaps are set at 45 degrees with takeoff set at 22.5 degrees. At anything above takeoff flap setting I have crow mixed in at about 4mm up aileron and also have 2mm of up elevator. Flaps and mixes come on slowly. My landing procedure is to drop gear when plane gets even with me then go full flaps on the downwind wind and cut my throttle to 3 clicks off of idle. This leaves the plane at a slight nose high attitude which can be slowed way down without fear of snapping. Lots of ways to setup a Viper but this works for me.
Good luck. You will love your Viper

clavin

My Feedback: (6)

Dave where can I find your CG method?

Dave Wilshere

I don’t see how too much flap is the issue…IF it was too slow than it lacked power.
First question would be what is the weight?
Second, where is it balanced?

My method and position is in this thread in the last few pages.

My guys fly with plenty of flap. I’m sure there are photos in this thread showing angles.

Dave

clavin

My Feedback: (6)

This is my experience.. Not opinion .. Experience.. If you have too much flap the flap becomes the pivot point of control.. Sliding the CG back and making alpha eMORE responsive to elevator.. Just what I have experienced..

Dave Wilshere

I don’t see too much flap…maybe not enough power.
First question what flying weight?
Second Question what balance position?
My balance method is in this thread a few pages back.
This is not one of my guys, but the amount of flap we run….

Dave Wilshere

I have a little experience too. I think I have flown 12-15 Carf Vipers…you?

sven1906

Thx for all your feedback, much appreciated!
I did not put her on a scale yet, so I do not know the weight. But there is no unnecessary stuff in there, no smoke, no lead, small batteries. The only extra is the stock cockpit and a pilot. I balanced her acc. to Dave's recommendation, but as mentioned earlier will definitely double check before next flight.
I also first assumed that I had too much flap, as I was surely above the stall speeds reported here in this forum. There were no issues at all when I was on flaps 1. Also, I definitely had more than 3 clicks above idle when she started to dance. On the other hand, I have seen the pictures of several other Vipers with similar flap throw. This why I was asking for your thrust settings.
For the next test in safe altitude, I consider to put the flaps on a slider / knob so that I can adjust in case of any instability. I may also add crow mix, however this should not be needed on the 500 feet / 160m gras field where I usually fly. Elevator up / nose down was programmed.
It is truly a nice airplane and I am sure I will put many flights on her once I figured out the flap issue.
Again thank you & best regards,
Sven

sven1906

Hi Dave,
my flap throw looks pretty much as shown on the picture.I know it is difficult without knowing the weight, temperature, altitude but what would be your estimate for thrust setting in this configuration?
Referring to previous posts from Clavin and Skunkwrks, I forgot to mention that I was flying in 600+ m altitude. This will surely have an impact on max engine performance, but may it also have such a massive impact at landing config? During T/O and flight, I found performance was pretty ok.

Thx, Sven

Dave Wilshere

Sven

OK, yes, altitude will influence the wing performance a huge amount. We fly only 50m above sea level. CROW is going to reduce the wings lift, so I don’t see that helping you here.
Are you sure all your radio conditions are the same, you don’t have something changing at full flap? The way you seem to be describing the handling sounds more than stalling, normally even a tail heavy airframe is stable until pitched in someway by a control deflection

Balance was checked with everything in position, except wings removed and landing fuel in the main tank ( not full of fuel)

Dave