gunradd

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Skymaster did not test the F18 on single engine because I talked to Anton and Li-Kai at FLjets. After mine went in they talked about possibly doing some tests but as of this time none have been done. The issue came up because of the thrust line that comes pre mounted in the airframe. The left and right sides are not even done at the same angles. Shimming is required to get the engines at the same angles.

Jim has not flown the F18 single yet. I talked to him also. I hope he never has too. But he has mid mounted engines and I predict a much better flying airplane with the mids.

FenderBean

Thanks for the info, that clears up a lot. I think people who own one or plan to own one like myself should get some proper testing done from Skymaster. I assumed after seeing all the testing on the f-14 they would put that into all thier models but I guess that was them making sure people didn't look at their f-14 like fejs. Guess I'm lucky my email to Dirk with my order keeps getting lost in Internet land, the file size is too big even being under 25 megs lol. Anyway I will shut up but if the crashed was caused from a design flaw they should hook you up on replacement. I'm not giving up on the tail mounts just yet since that's my attraction to this model, plus the Internet mounted option makes the the engines even closer together than the tail.

Thanks for your continued trouble shooting, may save some folks a loss as well!

mr_matt

My Feedback: (10)

MAybe a true aero engineer can chime in (Bob Parks, Oli?), but in my experience, the whole point of having these thrust angles is to have the thrust line intercept the 3D center of gravity, so you minimize the torque reaction in a single engine mode.

With the turbines in the rear, if you are not careful, you can adjust the turbine angles all day long and still have the thrust line (extended forward) no where near intercepting the center of mass.


When you have the turbines near the center of mass, it is harder to mess this up when you angle the pipes. The pipes will always be pointing somewhat near the center as that is where the turbines are to begin with.

YMMV, sorry for the loss

zdsh13

Even the full size F-18 suffers from yaw on a single engine at low speed.

https://youtu.be/0HDIxzSMp-0

gunradd

My Feedback: (9)

My point is with our typical set ups our turbine nozzle where the thrust is being generated is not at the rear of the pipe its at the turbine itself. In full scale its at the rear of the pipe because that is the turbine nozzle.

So our typical RC jet is pushing its thrust out from near the center of gravity of the plane. The pipe is simply taking that thrust to the outside of the plane. The pipe does not have a nozzle on it in our models. So the thrust is being generated at the rear of the turbine itself. Now like Matt says angle the pipes towards the CG and now its even more stable.

For the record I did do my best to align the engines to the aircraft CG. On the maiden flight the plane behaved the same way with the opposite engine out because the angle then was to much.

I am not trying to assign blame here. Bottom line is I was pilot in control and it crashed. I just want others to not suffer the same fate. Like most air craft incidents their was a trail of problems and not just one single thing.

>I did not catch the RPM problem on the ground by running one engine at a time. Granted I have never herd of this problem before but still I missed it... Also problem was intermittent to add to it.
>Engine angle still not good enough for single engine flight. Maybe I could have spent more time on the ground testing engine angles.
>Rear mounted engines... This was a first and a last time I choose that installation method. I am very confidant she will fly single engine just fine with a conventional engine set up with engine out.
>My single biggest regret... I should have landed the dam plane on the first lap around and ignored the traffic on the runway.... I had confidence flying on one engine already from the maiden flight and thought I could go around one more time for runway to clear.
>Should have stayed in the power more during the turn to final where I ended up loosing it. Every time I added power the yaw overcame the rudder and it was trying to flip out of the turn onto its back. I should have rolled the aircraft more like on the previous turn and went slight inverted and pulled it around. this would have kept the speed up some.
>Should have left the gear in until I was on final for landing.
>after the snap when it was heading for the ground.... I should have cut the remaining engine and gave it a softer pull and it would have probably came out of the dive. I panicked and pulled up to hard and it snapped. I then gave it a softer pull and it did respond to that but it was already to close to the ground.

My day job is Director of Maintenance for an aviation unit. I am a licensed A&P and a FAA licensed IA inspector. My goal at this point is to help others and learn from from my mistakes.

IFLYBVM2

My Feedback: (360)

We should all thank Gunradd for sharing all this info with us, especially considering a heart breaking loss like he had. Most guys are very reluctant to even talk about a crash, let alone have a discussion about what happened, in hopes of preventing it happening to someone else.
My hat is off to you-
Mike O.

skunkwurk

My Feedback: (18)

+1

EDFJim

My Feedback: (2)

The way your plane was yawning looked good and very controllable if one engine simply shut down . The new angle you mounted the engines looked very stable. But no one could handle an engine randomly going from idle to pump limit and everywhere in between! From the video looked like you had everything stable for single engine then the yaw totally reversed on you and rolled you over second time on downwind. Single engine flight on the F-18 should be a non event. I'm sure skymaster will look at the aft mounted engines angle and do some testing to find the zero yaw angle.

AV8ATOR

My Feedback: (5)

+2

TonyBuilder

My Feedback: (11)

+3

tb

sysiek

My Feedback: (176)

+4

dubd

+5

ledesma45

+6

Levi Wags

Thanks Gunradd. I reckon you are spot on about the rear mounted turbine set up.
Look at a rear wheel drive car. Under hard acceleration the back is trying to overtake the front as its being pushed from the rear. I'm sure Dantley knows a lot about this hence oversteer. A front wheel drive car is getting pulled along from the front hence under steer.
With mid mounted turbines the plane is getting pushed along at the point where the turbine is bolted to the mounts of the plane which is close to the cg. That would have to provide a more stable aircraft.

Levi

tothemax

I'm not aeronautical engineer either but I suspect the gyroscopic effect of the engines being so from from the CG would add a different dynamic to the equation.

Dansy

My Feedback: (53)

+20

I'm sure everybody is aware, but while the full scale is perhaps a hand full on single engine low speed......its a handful for the flight computer (s) the pilot merely move the stick to get the plane to do what he want...the flight's computer move what ever surface it want and need to achieve the desire effect....at least thats what I remember from when I did some work on the F-18 back in the early 80's

RCFlyerDan

My Feedback: (54)

+7 I used to fly with Kris up at Ocala and he is an excellent pilot and that was 5+ years ago. I have watched him over the years and he has only improved. Due to his Professional Aviation background, he has been extremely stand up about the evaluation of the crash and after math. Crashes are unfortunately how we learn, just as in full scale. Do it once, you might get away with it, do it twice, and may not.
Kris, thank you for your professional evaluation of the situation. I truly don't think anyone else would have done any better.

yeahbaby

My Feedback: (21)

+100 #likeaboss

ravill

My Feedback: (11)

I am humbled by an engine out in twins.

It has been my experience with prop twins, that when one engine quits, I was way more likely to have an airplane to repair if I went to idle and never touched the throttle again versus any other maneuver and completely destroy my airplane.

Gunradd's painful loss reminds me of that as well, and I'm 1/1,000,000,000 the pilot he is.

philjac94

Seeing our tailpipes are more aligned with Exhaust Augmentation theory they must and do have role in thrustline alignment. Thrust vectoring is the most visible example. A bad engine alignment can be corrected by tailpipe correction...at the expense of the tailpipe.

gunradd

My Feedback: (9)

Thanks everyone.

As for warbirds.... I used to have a B25 and wow was it a handful on single engine. But I was able to get her home a few times on single engine by using full scale practices and always turning towards the good engine. With that plane one turn towards the dead engine and its gone.

gunradd

My Feedback: (9)

Kieth the more I think about this and the more I study everything I would not use tail mounted engines in anything but a single. Even on your F14 the center of thrust was in the middle of the plane near the CG. While yes the pipes redirect the airflow the center of thrust is still near the center. When your center of thrust is at the rear of the aircraft a very slight change in thrust will have a huge effect in yaw due to it being so far from the CG.

Having the proper angle set on the engines is critical but with power changes so will the yaw effect even if they are aligned with the CG. This will explain why the stock offset was to much at 5 degrees and then my corrected offset at 1 degrees also didn't work. The angle will only work at a specific throttle setting with the plane being so unstable due to the center of thrust being at the tail. Very much like flying a tail heavy aircraft.

I saw Scott bring back his twin YAK with an engine out no problem at all at FLjets. His engines are further apart then the F18s engines. The reason why its no problem for this airplane is because the center of thrust is near the CG. While yes the pipes come out the back the thrust pushing the plane is in the center of the aircraft. This is also why others with twins have said the only thing they notice is a reduction in power and that is on planes with engines much further apart then mine where.

BTW I have talked to several owners of this plane now and all have miss aligned rear engine mounts. Meaning they are not even glued in at the same angles.......... Tail mounted engines is a flawed design and anyone I can help talk out of doing it I will. If I had mid mounted engines it would still be here today.

Pylonracr

[QUOTE=gunradd;12320988]Thanks everyone.

As for warbirds.... I used to have a B25 and wow was it a handful on single engine. But I was able to get her home a few times on single engine by using full scale practices and always turning towards the good engine. With that plane one turn towards the dead engine and its gone.[/QUOTE



Unless I'm flying it, then it is gone either way>

Sorry about your loss, she was beautiful

Scott

FenderBean

From the sound of your explanation have 0 degrees would be best but will still yaw with throttle adjustment, which most twins will do regardless of turbine location. I guess I will wait and see what testing is done. The only worry with mid turbines in this jet is the fact they almost touch each there. Closer than the rear mounted. Keeping my fingers crossed on a fix, any idea if the F model would have the same results on a flame out?

gunradd

My Feedback: (9)

Kieth any plane with twins and rear mount engines is a recipe for disaster in my opinion. It will be fine unless one quits.