ww2birds

My Feedback: (14)

Hi Gang,

I've just started building a Fei Bao F-15E. So far, Global Jet Club (Jose) has been a pleasure to deal with, and the factory was very accommodating in doing a custom paint job (Japanese F-15D "camo" scheme .. so yes, it's technically a fantasy scheme .. a D-model paintjob on an E-model airframe), not doing clearcoat at the factory so I could apply additional markings, doing a twin turbine mount setup and a few other things.

The plane looks good, not perfect .. but appears structurally sound and generally solid .. and overall is a great value for the dollar.

I've read the build threads posted here, and noted a lot of discussions about the landing gear, including the challenge of the rotating gear coming up given the large surface area they present on retraction, plus concerns about the robustness of the early main gear designs. My main LG look pretty robust, and even come with an extra aluminum part to "catch" the gear in the down position, much like Mick15 has shown as his own add-on. It looks like it's been improved a lot since the early designs, based on what I read. I'll be using the Hausl hydraulic system in the hope that the more positive nature of hydraulics will work better against the air loads of the rotating gear.

I am going to do it as a two-turbine setup, which I have not done before. I'd be interested to get the collective wisdom on fuel systems for twin turbines.

The factory tanks consist of a pair of side tanks that sit along the wing root, I measure approx 96 oz each. There is also a main tank that sits in the "Y" shape of the intake ducting .. it's 150 oz. For the 140-class motors I am planning for, the 96 oz is probably a little shy of what I need, but the whole 150 oz is too much. I see some others have used an additional 32 oz Dubro tank for each side. I am considering a custom tank, same size as the factory main tank, but split into two or three chambers .. that will give a total of 60-80 oz fuel (maybe as one tank, maybe split into two) and some space for smoke oil.

Any thoughts on the tank setup for twins? Is it best to plumb as two totally independent tanks, or back up the two side tanks with a shared center tank with two clunks?

Also, any clever ideas on how to handle radio setups that permit convenient startup with two motors?

thanks in advance for the thinking,

Dave McQ

Lance Campbell

Dave,

On my SR-71, I'm running total of about 275 ounces, on a pair of 120's and wish I had a little bit more. That works out to just over 2 gallons, and I'm landing with just over a half gallon (25%), with flight times of just over 6 minutes from brake release to timer going off to setup for a gear pass, prior to landing. Most of the flight is 2/3 throttle, with most passes up the runway, getting kicked up to full tilt.

Mine sounds similar to your setup.... I've got two tanks in the wings, that each feed one large center tank. In that center tank (that's got about 140 ounces in it), I have 2 lines with 2 clunks. Each line goes to it's own air trap tank, and from that point onward it's like 2 separate fuel systems.

So.. entire system: 2 fuel tanks, feeding 1 central tank, feeding 2 air trap tanks.

It's worked well for several years now.

Hope it helps and good luck with the bird,
Lance

FenderBean

My 1/7 F-15 has two saddle(mains), two forward and two uat. Because the forward tanks are a bit forward of the cg I have them empty first. Just something to think about since your main tank is about the same location of my two forward tanks, that is a lot of weight well forward of the CG so it will be a bit nose heavy on take-off. I have the forward empty first since the saddle tanks are right on the CG it makes the landing balance pretty much the same as when I balanced it.

bidrseed2

My Feedback: (2)

If you're using a Futaba 18mz, get in touch via pm and I'll send you the model file for a twin turbine model that allows you to start each engine separately or together.

ww2birds

My Feedback: (14)

thanks for the good thoughts so far! Lance, yes, your system is pretty much what I had in mind, glad to hear it works well, and interesting about fuel burn and quantity.

FB, yes, agreed, I'd burn the center first for exactly this reason.

Bidr .. PM sent .. thx!

Dave

George

My Feedback: (57)

I've had two twins, and both had separate fuels systems. I think it depends on what kind of room is available, but the system you are proposing will work as Lance has proven.

Jgwright

I have made a number of multi engine planes. I found it easier to have separate systems for each engine but that is a matter of choice and what tanks you can fit in. Starting 2 engines is not difficult. you do not need any special programs for the radio. I simply fit a switch on the negative wire each of the lines leading to the ECU to the radio. It does not matter if you have a jet cat or a Xicoy based set up. The switches can be used to control the start so you can start them together or one at a time.

Remember starting more than one engine can be more trouble than starting one. You should always fit the EDTs to monitor what is going on with both engines. If you have the separate switch you can turn off an engine that is refusing to start properly leaving the other running. The second can be started with the first running as the throttle is advanced up and down quickly
to initiate the start without making the first engine rev up hardly at all. With kero start I would always have a y lead on the batteries for the ECU so you can add a second battery to aid a reluctant starting engine especially in colder weather.

I have 6 turbines to start in the Arado and that can be a real pain as they are all started manually. It is amazing how often a wire is not correctly connected or some other problem comes up before they are all running.

John

ww2birds

My Feedback: (14)

thank you John. It's amazing to think about starting 6 turbines!

Appreciate the advice on the hardware approach to separating the engines. I've thought about some mix-based setups to perhaps place each throttle on a knob and some switches to connect/disconnect to the throttle stick but understand this is not really required .. just nice to have. Some of the guys are sending me their versions of this and I am looking forward to examining them .. but the simplicity of the switch on the black wire is good.

Re: EDT, yes, I have a personal rule that I follow .. every start with the EDT so for sure I'd do that with twins, where I presume it's even more critical since it's probably hard to hear what each motor is doing.

Dave

CraigG

My Feedback: (40)

Great points John and ones I have learned during the many years I have been flying my twin MIBO A-10. I strongly endorse the method of starting the engines one at a time and closely monitoring them on EDT's during start and to confirm both are responding to the throttle after start. In the event of a bad start on one engine, you need to be able to de-power it independently of the other, so as to reset the ECU and avoid shutting down the other unnecessarily.

Keeping the two engines as independent from each other as possible (fuel, electrics and even grounding) is preferable.

Good luck with the project!

Craig