Skymaster F18D Hornet twin build
03-28-2017, 07:55 PM
#229
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Earlier in the thread there was discussion about shielding the Hall effect sensors, Faraday cages, mu metal, and steel.
I'm not a jet guy.
I am a systems engineer at a major OEM that manufactures MRI scanners. I know a bit about ... magnets. And Faraday cages. I'll throw in my two cents here.
There are two Fields being discussed here ... the Electric Field and the Magnetic Field. Faraday cages block Electric Fields, and for them to work properly, you have to shield the object in a closed surface. In other words, you would need to wrap an object in something like copper foil, and solder all the seams. This depends a lot on what frequency range you are trying to shield - in MHz freqs, mesh screens work just fine (the operator of an MR scanner can look through a window at the scanner because the window has this mesh in it). So, if you were trying to shield the two engine sensors from the electric field ... well, that would be hard.
Fortunately, Hall effect sensors work on the Magnetic Field changing. In this case, you guys want to shield the sensor ... only the sensor ... from the other magnet. The objective then, is to reduce the magnetic field contribution from the engine #2 magnet at the engine #1 sensor. Someone earlier suggested using steel. That is correct, and I'd bet a small 1" square of sheet metal of the right gauge would work. There are obviously analysis packages that can calculate all this for you, but it is darn time consuming to do it. Even in our industry, we often wind up measuring the impact of shielding with magnetometers ... which RC folks probably do not have on the bench right now.
I would suggest, in any application where you have two Hall effect sensors in close proximity, to fabricate a connector to one of the Hall sensors itself and plug an small reference voltage source and voltmeter in to the leads that switch. You might need to look up the sensor part number for the pinout if it is not clear from the wire colors. Then rotate the turbine, (and magnet) by hand (I'm not a jet guy ... I assume you can do this) and see if you can detect the Hall switching on one engine. With no shielding, rotate the other engine and if the sensors are too close, you may pickup the switch on the "wrong sensor". If this works, then slip a 1/16 strip of steel that blocks the space between the Hall sensors. It doesn't have to be big ... it is line of sight between the magnet and the sensor that makes it switch. The gauge of the steel is important ... too thin and it does very little.
Keep trying different thicknesses until you cannot make the "wrong" sensor switch.
I think this only gets you in the ballpark. If it were me, I'd then double the thickness of the metal shield, then run one of the engines (can you spin them with compressed air?), again watching the wrong engine for Hall effect switching, which is no longer "on" and "off", but rather a small fluctuation of voltage - if you see any voltage change on the wrong sensor, then the shield is not working well enough. Unlike the Electric Field, blocking the Magnetic Field completely, is hard ... you can reduce it, but the best way to get away from it is distance. This is why rotating your sensors away from one another is working.
Mu metal ... horribly expensive, but a better magnetic shield with less weight.
I wish I were half the pilot the OP apparently is. I've had my share of twin fun with a P-82 that had periodic engine outs, the last flight an engine out on takeoff. To have flown that F18 two laps in a condition where the engines were fluctuating randomly ... sir, I stand in awe of your ability.
I'm not a jet guy.
I am a systems engineer at a major OEM that manufactures MRI scanners. I know a bit about ... magnets. And Faraday cages. I'll throw in my two cents here.
There are two Fields being discussed here ... the Electric Field and the Magnetic Field. Faraday cages block Electric Fields, and for them to work properly, you have to shield the object in a closed surface. In other words, you would need to wrap an object in something like copper foil, and solder all the seams. This depends a lot on what frequency range you are trying to shield - in MHz freqs, mesh screens work just fine (the operator of an MR scanner can look through a window at the scanner because the window has this mesh in it). So, if you were trying to shield the two engine sensors from the electric field ... well, that would be hard.
Fortunately, Hall effect sensors work on the Magnetic Field changing. In this case, you guys want to shield the sensor ... only the sensor ... from the other magnet. The objective then, is to reduce the magnetic field contribution from the engine #2 magnet at the engine #1 sensor. Someone earlier suggested using steel. That is correct, and I'd bet a small 1" square of sheet metal of the right gauge would work. There are obviously analysis packages that can calculate all this for you, but it is darn time consuming to do it. Even in our industry, we often wind up measuring the impact of shielding with magnetometers ... which RC folks probably do not have on the bench right now.
I would suggest, in any application where you have two Hall effect sensors in close proximity, to fabricate a connector to one of the Hall sensors itself and plug an small reference voltage source and voltmeter in to the leads that switch. You might need to look up the sensor part number for the pinout if it is not clear from the wire colors. Then rotate the turbine, (and magnet) by hand (I'm not a jet guy ... I assume you can do this) and see if you can detect the Hall switching on one engine. With no shielding, rotate the other engine and if the sensors are too close, you may pickup the switch on the "wrong sensor". If this works, then slip a 1/16 strip of steel that blocks the space between the Hall sensors. It doesn't have to be big ... it is line of sight between the magnet and the sensor that makes it switch. The gauge of the steel is important ... too thin and it does very little.
Keep trying different thicknesses until you cannot make the "wrong" sensor switch.
I think this only gets you in the ballpark. If it were me, I'd then double the thickness of the metal shield, then run one of the engines (can you spin them with compressed air?), again watching the wrong engine for Hall effect switching, which is no longer "on" and "off", but rather a small fluctuation of voltage - if you see any voltage change on the wrong sensor, then the shield is not working well enough. Unlike the Electric Field, blocking the Magnetic Field completely, is hard ... you can reduce it, but the best way to get away from it is distance. This is why rotating your sensors away from one another is working.
Mu metal ... horribly expensive, but a better magnetic shield with less weight.
I wish I were half the pilot the OP apparently is. I've had my share of twin fun with a P-82 that had periodic engine outs, the last flight an engine out on takeoff. To have flown that F18 two laps in a condition where the engines were fluctuating randomly ... sir, I stand in awe of your ability.
03-29-2017, 08:15 AM
#232
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Hi Guys;
Your the man of the day
Very nice plane . One of my all time greats. Maybe when my son grows up he will engage in a project like that.
My input on the gear issue, as an engineer, I tested my Albatross l-39 gear fuse tilting on the ground after landing roll out.
If you add more OIL with a moderate air pressure, you will get a stiffer strut sitting at a low stance.
Too much air will have your plane bouncing around.
Replace the missing air with OIL. Try it and you will see the difference.
Large full scale aircraft deal with the same issue and the conclusion is always the same. OIL to air ratio.
Not enough OIL in the strut.
Air is to absorb the shock of ground maneuvers and oil is for the transfer of weight to slow the landing shock
compression down from full extension to collapse.
The orifice in the Skymaster gear is maid for the same purpose.
Not telling you what to do,
Just a thought you might be interested in.
Art
Your the man of the day
Very nice plane . One of my all time greats. Maybe when my son grows up he will engage in a project like that.
My input on the gear issue, as an engineer, I tested my Albatross l-39 gear fuse tilting on the ground after landing roll out.
If you add more OIL with a moderate air pressure, you will get a stiffer strut sitting at a low stance.
Too much air will have your plane bouncing around.
Replace the missing air with OIL. Try it and you will see the difference.
Large full scale aircraft deal with the same issue and the conclusion is always the same. OIL to air ratio.
Not enough OIL in the strut.
Air is to absorb the shock of ground maneuvers and oil is for the transfer of weight to slow the landing shock
compression down from full extension to collapse.
The orifice in the Skymaster gear is maid for the same purpose.
Not telling you what to do,
Just a thought you might be interested in.
Art
04-01-2017, 03:05 AM
#236
what a shame., No matter the reason. i do have a question though... With the engines so close together,would you really get such a hard yaw if you lost one or if if you lost power in one? IMO that was a very hard yaw to be able to roll it over that fast. i commend you on keeping it in the air that long .No question on your piloting skills
04-01-2017, 04:29 AM
#237
what a shame., No matter the reason. i do have a question though... With the engines so close together,would you really get such a hard yaw if you lost one or if if you lost power in one? IMO that was a very hard yaw to be able to roll it over that fast. i commend you on keeping it in the air that long .No question on your piloting skills
The hard yaw was because of where the engines are mounted. Normally in our planes with twins the engines are much closer to the aircraft CG. This means a yaw caused by one engine does not have a huge effect just like adding a pound of weight to the middle of the plane does not effect CG. Even though the thrust on our jets comes out the back of the plane the engines are mounted in the middle and thats where the center of thrust is not the back of the plane.
So now with tail mounted engines they are probably 3 or 4 feet away from the center of gravity. This acts like a large arm and any asymmetric thrust gets amplified. I spent allot of time aligning the engines. On the maiden flight I used the stock engine mounts and when I lost a motor I almost crashed it because they had to much angle and the left and right mounts didn't even have the same angles. So after that flight I decided to change the thrust lines and I did everything I could to try and have the engines point to the aircraft CG. This still didn't help much and you see the end result.
From what I hear skymaster is now going to do testing to try and get the correct engine angle. The instruction manual does not cover engine installation at all with no instructions n how to even install them much less then setting the correct angle........... IMO mid mounted engine option is best and the plane will fly fine on one motor with mid mounts. But none of this helps me at this point. beta testing at its finest.
04-01-2017, 10:25 AM
#239
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Matters how its done, some single engine installs have to have a double take
https://www.youtube.com/watch?v=ebA2Y8nfZvQ
https://www.youtube.com/watch?v=ebA2Y8nfZvQ
Last edited by erh7771; 04-01-2017 at 10:35 AM.
04-01-2017, 01:20 PM
#240
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Matters how its done, some single engine installs have to have a double take
https://www.youtube.com/watch?v=ebA2Y8nfZvQ
https://www.youtube.com/watch?v=ebA2Y8nfZvQ
04-02-2017, 02:34 AM
#241
Crappamjoke or whatever you call yourself, I think YOU need to look at keeping it real ya pelican.
Erh7771 thanks for sharing that video. Probably the most realistic looking RC Hornet display I've seen. Great pilot.
Gunradd I'm sorry for your situation. Someone has to be the pioneer on these large new models and you have saved many other people from suffering the same failure by sharing your info.
Levi
Last edited by Levi Wags; 04-02-2017 at 03:04 AM.
04-02-2017, 04:47 AM
#242
The hard yaw was because of where the engines are mounted. Normally in our planes with twins the engines are much closer to the aircraft CG. This means a yaw caused by one engine does not have a huge effect just like adding a pound of weight to the middle of the plane does not effect CG. Even though the thrust on our jets comes out the back of the plane the engines are mounted in the middle and thats where the center of thrust is not the back of the plane.
So now with tail mounted engines they are probably 3 or 4 feet away from the center of gravity. This acts like a large arm and any asymmetric thrust gets amplified. I spent allot of time aligning the engines. On the maiden flight I used the stock engine mounts and when I lost a motor I almost crashed it because they had to much angle and the left and right mounts didn't even have the same angles. So after that flight I decided to change the thrust lines and I did everything I could to try and have the engines point to the aircraft CG. This still didn't help much and you see the end result.
From what I hear skymaster is now going to do testing to try and get the correct engine angle. The instruction manual does not cover engine installation at all with no instructions n how to even install them much less then setting the correct angle........... IMO mid mounted engine option is best and the plane will fly fine on one motor with mid mounts. But none of this helps me at this point. beta testing at its finest.
So now with tail mounted engines they are probably 3 or 4 feet away from the center of gravity. This acts like a large arm and any asymmetric thrust gets amplified. I spent allot of time aligning the engines. On the maiden flight I used the stock engine mounts and when I lost a motor I almost crashed it because they had to much angle and the left and right mounts didn't even have the same angles. So after that flight I decided to change the thrust lines and I did everything I could to try and have the engines point to the aircraft CG. This still didn't help much and you see the end result.
From what I hear skymaster is now going to do testing to try and get the correct engine angle. The instruction manual does not cover engine installation at all with no instructions n how to even install them much less then setting the correct angle........... IMO mid mounted engine option is best and the plane will fly fine on one motor with mid mounts. But none of this helps me at this point. beta testing at its finest.
I wish you well on the mental healing of the loss, now it is time to recover the financial loss, and I think the jet community needs to know how, or if these companies are standing behind their products. Because, I think the average r/c jet pilot wouldn't have known what really happened and just blamed themselves as a bad pilot. But, I think because of your Professional Aviation background, you were able to determine the causes that attributed to the loss of the jet.
Thanks!
Last edited by RCFlyerDan; 04-02-2017 at 05:00 AM.
04-02-2017, 07:14 AM
#243
Kris, I know you are a rep for Kingtech, so I know or hope they are helping you on this financial loss, even with the airframe cost. After all, you are doing the R&D for both Kingtech for mounting twin engines, and definitely for SkyMaster. I hope they will come through and help you with the next airframe, should you decide to buy from them again. I was going to buy a SkyMaster, but so far; from watching one coming apart at my field on the third flight with no "G's", and then your poor experience with their product, I have decided to NOT purchase their products. I can't afford to be an R&D for a manufacturing company. I am not trying to bash here, like everyone did for FEJ, but I do know this has to be a huge financial loss for you. Especially with 6 kids going to college here soon.
I wish you well on the mental healing of the loss, now it is time to recover the financial loss, and I think the jet community needs to know how, or if these companies are standing behind their products. Because, I think the average r/c jet pilot wouldn't have known what really happened and just blamed themselves as a bad pilot. But, I think because of your Professional Aviation background, you were able to determine the causes that attributed to the loss of the jet.
Thanks!
I wish you well on the mental healing of the loss, now it is time to recover the financial loss, and I think the jet community needs to know how, or if these companies are standing behind their products. Because, I think the average r/c jet pilot wouldn't have known what really happened and just blamed themselves as a bad pilot. But, I think because of your Professional Aviation background, you were able to determine the causes that attributed to the loss of the jet.
Thanks!
Both manufacturer would benefit more by simply replacing the products even though they don't need to. It would go way further then not.
Good luck with your next build.
TB
04-02-2017, 07:29 AM
#244
Thnx guys it means allot!
Kingtech has always stood by me! Could not be happier with our relationship.
I am waiting to see the results of skymasters testing with engine out and rear mounting although not sure what to expect.. They will be able to turn the engine right back on in flight if they get the yaw I had and will be able to land and re adjust the angle until they get it right. Theoretically if the angle is perfect then the plane will fly ok. But if its off at all then it will have a huge affect on yaw and roll. Very much looking forward to see what they get. The above pic is about 5 or 6 seconds before the crash and shows all flight controls in the right spot and working fine. Its 100% and engine thrust issue with the mounting.
Kingtech has always stood by me! Could not be happier with our relationship.
I am waiting to see the results of skymasters testing with engine out and rear mounting although not sure what to expect.. They will be able to turn the engine right back on in flight if they get the yaw I had and will be able to land and re adjust the angle until they get it right. Theoretically if the angle is perfect then the plane will fly ok. But if its off at all then it will have a huge affect on yaw and roll. Very much looking forward to see what they get. The above pic is about 5 or 6 seconds before the crash and shows all flight controls in the right spot and working fine. Its 100% and engine thrust issue with the mounting.
04-02-2017, 07:57 AM
#245
If SM is making models that are "flying apart with no G's" and this crash from lack of testing then something needs to be done. The company should know it's not okay to sell something without proper testing. I would think if they do care as people say they do it would not be any hard feelings since that's the right thing to do.
04-02-2017, 08:08 AM
#246
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I'm not adding anything but I have a question. I know you need a turbine waiver at AMA sites so is it because of the speed of the jets or the operation of the turbine or both.Thanks in advance.
04-02-2017, 08:31 AM
#247
The way I look at it from reading it the main reason is safe operation of the turbine but it seems to have evolved into flight demo as well. I guess they want to make sure u can safely operate and fly the turbine powered aircraft.
Speed in my opinion is pointless since some electric jets can fly faster than turbines. We are limited to 200 regardless
Speed in my opinion is pointless since some electric jets can fly faster than turbines. We are limited to 200 regardless
04-02-2017, 12:43 PM
#248
Today, you can have never flown a jet, buy the same F18 as in this post, power one with turbines and the other with electric. The non turbine waiver pilot can fly the electric model and not the turbine, unless buddy box with an AMA Turbine Pilot. Even if the non-turbine pilot is better then the turbine waivered guy. The electric powered jet can also go over the 200 mph limit of the turbine jet.
But! The main reason is......insurance.
Last edited by RCFlyerDan; 04-02-2017 at 03:36 PM.