FB 1/7th F15 scale build
#302
My Feedback: (18)
A great builder friend of mine took the front tank and took 5" out of the middle and then put a divider from front to back and made two tanks out of one. Each engine will have two tanks to run off of. The front holds about 45 oz each and will drain first and then to the main tanks (saddle tanks). This will keep the fuel that is left close to the CG on the landing. I will have about 1.25 gal for each engine that will give me a good 6 mins. of flight with plenty of go around fuel for a landing.
I've been wondering what to do, I'm leaning on the side of going with three tanks and 2 UATs. Plumbing both UATs to the one center tank. Is there a reason not to do this? It seems it would be the best option as either motor would be able to use that center tank as a supply. I was thinking of adding two high-flow clunks to the main tank.
Also, in the case of a flame out, I would not have 1/2 my fuel supply stranded.
LMK.
sc
#303
Thread Starter
My Feedback: (9)
Thanks, Joe.
I've been wondering what to do, I'm leaning on the side of going with three tanks and 2 UATs. Plumbing both UATs to the one center tank. Is there a reason not to do this? It seems it would be the best option as either motor would be able to use that center tank as a supply. I was thinking of adding two high-flow clunks to the main tank.
Also, in the case of a flame out, I would not have 1/2 my fuel supply stranded.
LMK.
sc
I've been wondering what to do, I'm leaning on the side of going with three tanks and 2 UATs. Plumbing both UATs to the one center tank. Is there a reason not to do this? It seems it would be the best option as either motor would be able to use that center tank as a supply. I was thinking of adding two high-flow clunks to the main tank.
Also, in the case of a flame out, I would not have 1/2 my fuel supply stranded.
LMK.
sc
I would not do it this way with a twin. It defeats the whole purpose in having a twin for redundancy. You need to separate independent fuel systems IMO.
Also the center forward tank is way to big stock and shifts the CG so far forward. Joe plumbed his so he burns off the forward tank first so his CG will not change much the remainder of the flight since the saddles are close to the CG. DO NOT use that forward tank. I cut mine in half and its working great this way. My other friend with one Mike is using a jettech fuel cell in the front.
For a twin on this plane I would use 2 smaller tanks in the front or do as joe did and have the tank cut in half reduced and then slit whats left for separate sides. Also no need for high flow unless you are going single. Only reason I did high flow is because I will be dropping a K300 in when its ready also was having high PW issues that have since been resolved.
#306
My Feedback: (14)
Of course with the pilots it really looks quite a bit cooler :-)
Dave
#311
My Feedback: (18)
Hello SC
I would not do it this way with a twin. It defeats the whole purpose in having a twin for redundancy. You need to separate independent fuel systems IMO.
Also the center forward tank is way to big stock and shifts the CG so far forward. Joe plumbed his so he burns off the forward tank first so his CG will not change much the remainder of the flight since the saddles are close to the CG. DO NOT use that forward tank. I cut mine in half and its working great this way. My other friend with one Mike is using a jettech fuel cell in the front.
For a twin on this plane I would use 2 smaller tanks in the front or do as joe did and have the tank cut in half reduced and then slit whats left for separate sides. Also no need for high flow unless you are going single. Only reason I did high flow is because I will be dropping a K300 in when its ready also was having high PW issues that have since been resolved.
I would not do it this way with a twin. It defeats the whole purpose in having a twin for redundancy. You need to separate independent fuel systems IMO.
Also the center forward tank is way to big stock and shifts the CG so far forward. Joe plumbed his so he burns off the forward tank first so his CG will not change much the remainder of the flight since the saddles are close to the CG. DO NOT use that forward tank. I cut mine in half and its working great this way. My other friend with one Mike is using a jettech fuel cell in the front.
For a twin on this plane I would use 2 smaller tanks in the front or do as joe did and have the tank cut in half reduced and then slit whats left for separate sides. Also no need for high flow unless you are going single. Only reason I did high flow is because I will be dropping a K300 in when its ready also was having high PW issues that have since been resolved.
Thanks for the advice, I appreciate the help. The three tanks (1x4.6 & 2x2.7 liters) equal to about 246 oz of total capacity, I'm basing this off of their online manual. I'll measure the capacity once I have the tanks in hand. Each of the 180s burn ~20oz p/minute at full throttle, at 246 oz of total capacity that's about a 6 minute burn time. I don't plan on flying at full throttle the entire flight but I would like a 6-10minute flight plus spare fuel capacity. There doesn't seem to be a hugh margin, wouldn't reducing the fuel capacity work against me a little bit? What do you guys use as a rule of thumb on twins? I will be performing ground testing to help narrow this down, but any input is appreciated.
I'll look into splitting the center tank, I don't disagree with your logic regarding the two separate fuel systems.
Also, since we're on setup commentary. I see what you did with the air valves on the mains, which I'm considering as an option. I've also seen plenty of comments regarding hydraulic as well, but I'm wondering why no one is suggesting going electric. I've seen guys like Fenderbean build a nice install on a 1/7 Scale F15 using D&L's system, I like it. It's clean and looks reliable.
Is it cost, reliability or something else which is influencing folks not to suggest this, do you have an opinion by chance?
thanks in advance.
sc
Last edited by skunkwurk; 02-03-2016 at 01:28 PM.
#312
Thread Starter
My Feedback: (9)
Short video of what I have done so far on the pilots. Used a 19 dollar robot controller and old servos I had laying around.
https://youtu.be/iQp50CvS1kE
<iframe width="560" height="315" src="https://www.youtube.com/embed/iQp50CvS1kE" frameborder="0" allowfullscreen></iframe>
https://youtu.be/iQp50CvS1kE
<iframe width="560" height="315" src="https://www.youtube.com/embed/iQp50CvS1kE" frameborder="0" allowfullscreen></iframe>
Last edited by gunradd; 02-04-2016 at 04:20 AM.
#313
My Feedback: (3)
Nice job, Gun!
Short video of what I have done so far on the pilots. Used a 19 dollar robot controller and old servos I had laying around.
https://youtu.be/iQp50CvS1kE
https://youtu.be/iQp50CvS1kE
#314
Thread Starter
My Feedback: (9)
Hi Gunradd,
Thanks for the advice, I appreciate the help. The three tanks (1x4.6 & 2x2.7 liters) equal to about 246 oz of total capacity, I'm basing this off of their online manual. I'll measure the capacity once I have the tanks in hand. Each of the 180s burn ~20oz p/minute at full throttle, at 246 oz of total capacity that's about a 6 minute burn time. I don't plan on flying at full throttle the entire flight but I would like a 6-10minute flight plus spare fuel capacity. There doesn't seem to be a hugh margin, wouldn't reducing the fuel capacity work against me a little bit? What do you guys use as a rule of thumb on twins? I will be performing ground testing to help narrow this down, but any input is appreciated.
I'll look into splitting the center tank, I don't disagree with your logic regarding the two separate fuel systems.
Also, since we're on setup commentary. I see what you did with the air valves on the mains, which I'm considering as an option. I've also seen plenty of comments regarding hydraulic as well, but I'm wondering why no one is suggesting going electric. I've seen guys like Fenderbean build a nice install on a 1/7 Scale F15 using D&L's system, I like it. It's clean and looks reliable.
Is it cost, reliability or something else which is influencing folks not to suggest this, do you have an opinion by chance?
thanks in advance.
sc
Thanks for the advice, I appreciate the help. The three tanks (1x4.6 & 2x2.7 liters) equal to about 246 oz of total capacity, I'm basing this off of their online manual. I'll measure the capacity once I have the tanks in hand. Each of the 180s burn ~20oz p/minute at full throttle, at 246 oz of total capacity that's about a 6 minute burn time. I don't plan on flying at full throttle the entire flight but I would like a 6-10minute flight plus spare fuel capacity. There doesn't seem to be a hugh margin, wouldn't reducing the fuel capacity work against me a little bit? What do you guys use as a rule of thumb on twins? I will be performing ground testing to help narrow this down, but any input is appreciated.
I'll look into splitting the center tank, I don't disagree with your logic regarding the two separate fuel systems.
Also, since we're on setup commentary. I see what you did with the air valves on the mains, which I'm considering as an option. I've also seen plenty of comments regarding hydraulic as well, but I'm wondering why no one is suggesting going electric. I've seen guys like Fenderbean build a nice install on a 1/7 Scale F15 using D&L's system, I like it. It's clean and looks reliable.
Is it cost, reliability or something else which is influencing folks not to suggest this, do you have an opinion by chance?
thanks in advance.
sc
On the fuel...
I think 2 180s is to much engine with to high of fuel burn. Have you thought about trying to sell them for smaller engines like twin 120s or the new 160s would be the ideal engine. The reason why is because you will need allot more fuel for twin 180s and that's allot more weight in front of the CG. When I was doing my CG with all 3 tanks I filled them up to see how much it changed and its drastic. Aircraft is super nose heavy with that front tank fuel. I would say full its at least 7 lbs all in front of the CG.
I flew mine full of fuel this way and it did rotate and fly but it flies much better now with the front tank smaller. So I dont want to say what you have wont work because it will work but I highly recommend getting smaller engines that burn less fuel and reducing the front tank.
Also I dont think their online manual is correct. I think they used smaller tanks on the build in the manual. The center tank in the kit is HUGE!
#315
My Feedback: (18)
For the gear I didn't go electric for the cost also this gear needs to rotate unless you remove all the scale parts from the gear and for me that's not an option.
On the fuel...
I think 2 180s is to much engine with to high of fuel burn. Have you thought about trying to sell them for smaller engines like twin 120s or the new 160s would be the ideal engine. The reason why is because you will need allot more fuel for twin 180s and that's allot more weight in front of the CG. When I was doing my CG with all 3 tanks I filled them up to see how much it changed and its drastic. Aircraft is super nose heavy with that front tank fuel. I would say full its at least 7 lbs all in front of the CG.
I flew mine full of fuel this way and it did rotate and fly but it flies much better now with the front tank smaller. So I don't want to say what you have wont work because it will work but I highly recommend getting smaller engines that burn less fuel and reducing the front tank.
Also I dont think their online manual is correct. I think they used smaller tanks on the build in the manual. The center tank in the kit is HUGE!
On the fuel...
I think 2 180s is to much engine with to high of fuel burn. Have you thought about trying to sell them for smaller engines like twin 120s or the new 160s would be the ideal engine. The reason why is because you will need allot more fuel for twin 180s and that's allot more weight in front of the CG. When I was doing my CG with all 3 tanks I filled them up to see how much it changed and its drastic. Aircraft is super nose heavy with that front tank fuel. I would say full its at least 7 lbs all in front of the CG.
I flew mine full of fuel this way and it did rotate and fly but it flies much better now with the front tank smaller. So I don't want to say what you have wont work because it will work but I highly recommend getting smaller engines that burn less fuel and reducing the front tank.
Also I dont think their online manual is correct. I think they used smaller tanks on the build in the manual. The center tank in the kit is HUGE!
Gun,
The pilot animatronics and inlets look awesome, nice job man.
On the electric conversion it looks like they replace the air cylinders with a worm gear type of motor, I don't think you would lose the rotating function, I could be wrong though, I'll have to look at that in more detail. I'm still undecided and considering all options on the gear.
Regarding the fuel tanks and turbine. I'd like to say I simply went with more power and threw logic out of the window but I actually spent a lot of time trying to think it through and decide on something which made the most logical sense for me. Again, I could be wrong and have made horrible assumptions, I try and be a pragmatic as possible but when dealing with assumptions, it's difficult. Once I receive the model and components I'll be able to better test things and eliminate some of the assumptions and get to a final/final working design.
I'm certainly open to comments and ideas from you and the community, I'm the first to admit I get this stuff wrong all the time and have to rethink things as I go.
That said, let me share some of the points I tried to use as a basis for my decision, I'm putting this out there, and I'm soliciting for ideas and suggestions.
I won't cover the logic between single or twin turbines, that could be a whole other thread... I'll just cover why 180s in my twin setup.
1 - I noticed that the position of a single vs a twin is different. The single mounting position appears to be closer, but still slightly aft, to the CG of the model. The twin mounting position appears to be more aft than the single, perhaps 3-6 inches. Again, my assumption here is "looks further aft", I can't measure this until I have the model. This could potentially have a CG effect and in turn make the model less nose heavy in a twin design.
2 - Twins require two pipes vs one. What is the weight penalty between two pipes vs one bifurcated pipe is probably marginal, maybe the weight of two bells vs one, who knows. Again, I'm using probably, I'll have to weigh things to be sure. If there is a weight difference, it will be in the aft section of the plane, which may affect CG on a sliding scale.
3 - The conscious choice turbine manufacturers have made on recent turbines to standardize on a particular can design for multiple output turbines has to be considered. For example, if you take Jetcat's 90, 140 and 180 models, they are all based on a very similar can design. For sure the combustion chambers may be different, as I'm sure a number of internal components are, but the weight, size and shape difference is marginal. The differences internally ultimately effect the output and thus the burn rate of these turbines, but I could do that too. I could cap the high end RPM range by 10 or 20 or 30K and reduce the output to a range which works for my setup, and thus the burn rate too.
What are the effects of doing this on the turbine long term, or running it at mid-range to mid-high vs at high range, I don't know. I need to test this to know for sure. What I do know is that I would rather own a 180 vs a 90 if there is going to be size and weight parity between the two models. Especially if I am going to invest in two turbines of the same size, future proofing your investment and applicability makes sense to be considered.
I don't think companies like Jetcat did this by accident, I think they know this and I think they believe the consumer will lean on the side of power and spend more of their $ on the high end turbine, plus you could debate that it's less complex or expensive to have 3 motors based on the same can design. That is debatable as I've seen concepts get really complicated for vendors when they try and standardize things. But that is a topic for an other thread too, and my personal option...
4 - Market value, I did not want to buy two turbines of the same size unless I had the potential to reuse them or sell them at some point in time, this is obviously taking into consideration the biggest assumption of them all, one that everything goes well and I still have two working turbines a year from now. I certainly hope I do, but I wanted to buy two turbines which I knew there are several Jet models on the market as possible hosts for me to reuse and switch them around if needed. It sounds more fun that way. To add to that, if there are numerous models on the market in the 180 category, there should be more potential buyers as well for a second hand turbine if I decide to sell one one day.
5 - Final point, if in a year from now the model has been flying great and I'm really comfortable with it and I foolishly decide to take all the RPM caps off, I'd love to see how it flies at full power. ggggrrrrrrrrrrrrr
Anyway, I hope this isn't too long of a response, I felt the topic is deserving of some supporting details and I hope it may help some other fellas out there which may be wondering what to do as well. Again, I'm putting this out there and I'm open to opinions and advice.
Thank you again.
sc
Last edited by skunkwurk; 02-04-2016 at 06:11 AM.
#316
Thread Starter
My Feedback: (9)
Gunradd,
Try this link to acheive an animated pilot. you won't be disappointed.
http://www.churchillcreations.co.uk/animatronics.html
Regards,
Try this link to acheive an animated pilot. you won't be disappointed.
http://www.churchillcreations.co.uk/animatronics.html
Regards,
#317
My Feedback: (14)
Interesting discussion regarding the electric gear. Having fiddled with the F-15E gear a lot, I am certain you could use the electric conversion without worrying about the rotation mechanics .. they are separate .. the actuation from the cylinder is in a straight line. There would of course be some consideration on the maximum diameter and length of the drive motor in the space where the cylinder originally was.
It is encouraging that Kris has had success with his new two-valve air setup.
My own experience with electric gear has been mixed. With some of the smaller units there is a fine line between amping out when the gear retracts vs amping out due to air flow issues ... requiring a close eye on airspeed when retracting or extending gear. Perhaps on some of the larger units this is less of a problem.
If you do a simple "flat plate" calculation on the force of 100 mph air on the F-15E's tires, I get numbers in the 4-6 pound range .. so I am thinking it might be interesting to make measurements of the actual gear with a force gauge and see how much pressure the actuators can make out at the end of the leg where the wheel is.
At any rate, data is data and Kris' gear working is really good news!
Dave
It is encouraging that Kris has had success with his new two-valve air setup.
My own experience with electric gear has been mixed. With some of the smaller units there is a fine line between amping out when the gear retracts vs amping out due to air flow issues ... requiring a close eye on airspeed when retracting or extending gear. Perhaps on some of the larger units this is less of a problem.
If you do a simple "flat plate" calculation on the force of 100 mph air on the F-15E's tires, I get numbers in the 4-6 pound range .. so I am thinking it might be interesting to make measurements of the actual gear with a force gauge and see how much pressure the actuators can make out at the end of the leg where the wheel is.
At any rate, data is data and Kris' gear working is really good news!
Dave
#318
Thread Starter
My Feedback: (9)
Not only is it working but working well. On one of my dirty passes I got into the throttle and didn't pick the gear up as fast as I normally would and thought to myself no way the mains could have worked. After the turn flying down wind to my surprise all 3 legs where up. So clearly all the problems getting it up are volume issues. Give it more volume and it will work fine.
On the last few flights I had last weekend I didn't even worry about the gear anymore and did nothing special in flight just took off balls to the wall and hit the switch. Worked fine.
On the last few flights I had last weekend I didn't even worry about the gear anymore and did nothing special in flight just took off balls to the wall and hit the switch. Worked fine.
#319
Thread Starter
My Feedback: (9)
Found another poorly made part. The wheel bearings are junk and need to be replaced.
On my 16th flight the right main came apart just before rotation so I had to get off the throttle and let it run off the runway and it ripped both mains and mounts out. Bent the nose strut pin also... So back to repairs. Only have 3 weeks to get her ready for FLjets. Going to be tough.
Not sure where to get replacement bearings from. Ibremoved the other wheel and all the balls just fell out so that one was also about to let loose.
On my 16th flight the right main came apart just before rotation so I had to get off the throttle and let it run off the runway and it ripped both mains and mounts out. Bent the nose strut pin also... So back to repairs. Only have 3 weeks to get her ready for FLjets. Going to be tough.
Not sure where to get replacement bearings from. Ibremoved the other wheel and all the balls just fell out so that one was also about to let loose.
#322