sysiek

My Feedback: (176)

I have a friend who told me to use two separate receivers and bind to same radio at once and use them separately for each turbine to prevent the signal walking through the y or the same rx .

afterburner

My Feedback: (18)

But isn't the problem really between the RPM sensors and the ECU's getting spurious info and just using throttle position as a reference to where the RPM should be?

rhklenke

My Feedback: (24)

Bob Wilcox told me way back when that two engines on a "Y" were not a problem with JetCat engines. I think that this would also be the case with Kingtech engines.

I think as Marty said, the issue is with the engines interfering with each other's RPM sensor readings - leading to faulty operation, as in one or both engines failing to respond to throttle inputs, or responding incorrectly to throttle inputs.

I believe that the engines use Hall effect sensors to read RPM and the magnet is in the rotating part (i.e. the compressor, nut, or shaft, I'm not sure which). The two spinning magnets next to each other create magnetic field interference that leads to faulty RPM readings.

BTW, I think that JetCats used to use optical RPM sensors...

Bob

mr_matt

My Feedback: (10)

JetCats used optical RPM sensing a long time ago but also switched to magnetic. I have no idea if this magnetic cross talk is a problem with JetCat or not. The only twin I have has turbines mounted much farther apart (MiG-29).

I will say I have used (in another life) a material commercially referred to as Mu metal for magnetic shielding of certain test enclosures, it might work in this case, who knows.

SECRET AGENT

My Feedback: (18)

I wonder if wrapping the bypass in copper mesh would create a type of Farady cage and shield the motors from each other?

sysiek

My Feedback: (176)

The recommended material to use it's a mumetal nikel permalloy,relatively easy to find on eBay little expensive but $100 for 30x45 cm it's not bad ,this will cover two turbines .

Bobneal1

My Feedback: (21)

Matt,

Which Mig 29 did you have and what engines? I am doing a Skymaster Mig 29 right now with Jet Central Cheetah 160's and was thinking that they were far enough apart that it wouldn't be a problem.

Thanks,

Bob Neal

sysiek

My Feedback: (176)

Will you please post some pictures with the turbines,I'm doing the same jet with two vt-80 and just want to see other jets skymaster build to be twin thanks.

Craig B.

I'm pretty sure Matt has the CARF mig29

mullerr

This issue is not a concern when using Jet Central engines, you will be fine

rhklenke

My Feedback: (24)

I thought I remembered my old P-80 from way back in the day having a hole in the Bendix/compressor nut and an optical sensor in front of the intake ring...

That does seem like a long time ago...

Bob

rcjetsaok

My Feedback: (7)

AMT is the only Mfg. That uses optical...

Dan

rhklenke

My Feedback: (24)

Matt is right though in that JetCat used to - not any more...

Bob

Airliner-rc

My Feedback: (1)

Somebody use telemetry on twin engines model? On both engines.
If yes, so what kind of telemetry and how it connected with receiver?

TonyBuilder

My Feedback: (11)

Maybe turbine manufactures should invest in testing this issue and come up with a factory matched set for those that want to use twine turbines.

TB

sysiek

My Feedback: (176)

+1

gunradd

My Feedback: (9)

After lots of thinking about the F18 and why it was so unstable on one engine even though they are close to the center line. What I have come up with is with the engines mounted in the tail so far from the aircraft CG the yaw has a much greater effect. Same way adding or removing weight far away from the CG has a large effect. After learning what I have learned on this plane I would not use tail mounted engines on twins.


On a few flights the plane flew fantastic and was really loving it .But if one engine fails you will be in deep trouble. If I had mid mounted engines I am sure my plane would still be here. Its a hard lesson learned and I hope others can learn before loosing a plane. In my opinion tail mounted engines should not even be an option.

Also it is very important to run your engines 1 at a time and double check for any issues between them. We already discussed the RPM issues with the close mounted engines. Also make sure your ECU wires are ran separately.

rcjetsaok

My Feedback: (7)

Kris,

Do the planes call for tail mounted engines or is that an option you chose? Is it an either or deal for the kit out of the box ??

Dan

gunradd

My Feedback: (9)

When ordering the plane you can pick tail mounted or mid mounted.

mauryr

Maybe mounting them in the tail makes it harder to evaluate the angle: a long pipe just a little off is very noticeable, whereas a short engine nozzle off by the same amount would seem pretty much straight?

Looking at this picture it seems like the engines were quite convergent:

gunradd

My Feedback: (9)

I feel with mid mounted engines the thrust angle would not be near as critical. Tail mounted engines just have a lot of leverage being so far from the CG just a slight yaw would have a huge effect.

Bobneal1

My Feedback: (21)

As far as the yaw effect of the engines being in the tail , the full scale has them back there , maybe not quite as far, but very close so that should not affect it. If they were misaligned that would have some effect, but the amount of misalignment would have to be large.

BlueBus320

My Feedback: (57)

I buy this theory. It seem like shooting with a rifle vs a snub nosed revolver. The moment created from the thrust exiting the rear should be the same in either config, but it's a lot harder to get the turbine cans exhausting the exact direction that you want, where as the pipes traveling through the fuse are much easier to aim where you want them.
Jay

skunkwurk

My Feedback: (18)

I wonder if zero degrees offset for tail mounted would be better, and possibly adding some level of thrust vectoring. Not something crazy like 3D vectoring, but something mild. This way the model does not end up with a static setting. If you lose a turbine you or a gyro would still have some control of the thrust angle. Just spit-balling here. These concepts are complicated, I believe the full scale jet has a million lines of code to help compensate for a lot of these contingencies.

FenderBean

I think some testing should be done, SM supposedly test these things single engines but unlike the f-14 they did not video prove their testing. Jim has had both one with tail mounted and now mid mounted, not sure if he went mid for thrust vectoring or something else. Maybe he could chime in on this, I think he lost an engine last year on his but that could have been the f-14.