DerJet F-35A 1/8 scale 100-120N
10-10-2016, 01:04 PM
#1
Thread Starter
DerJet F-35A 1/8 scale 100-120N
DerJet sent me this project back in 2015, for various reasons, unrelated to the kit its taken me till now to get it airborne. The first two flights took place two weekends ago and I had another two flights yesterday, each session has seen an improvement in the set up. The first flight showed the need to have 100% operation in the gear and doors, the F-35 reacts badly to gear hang-ups, look at the door angles from the front and you will see what I mean. The nose doors particularly cause some interesting yaw characteristics because they gape at the front.
Typically of this era of jet airframe its designed to be flown by a computer, we don't have that option yet, but the first two flights without the Powerbox iGyro showed its a nicer experience with the gyro active, first flight yesterday was with 20% gain in rate mode and second flight 25% in heading mode, I will continue to increase the gain, flight by flight and wind conditions. So far the heading mode is favourite, it deals with the balance change caused by the fuel tanks position (dictated by the gear position) the tanks are just forward of the balance point.
I've still not weighed my model (because you have little control over the final weight-so it is what it is!), but I went with a JetCat P-90Rxi turbine as I felt that if it needed more power it would be a simple task to swap to a P-140Rxi. Having had four flights I'd say the 105N of the P-90Rxi is perfect.
My model has JR 8911 servos on the flying elevators, JR 8411's on Ailerons and JR 3421NX on rudders,plus my standard JR 579 on nose steering.
Rx power is via a Powerbox Sensor switch with 2 x 2200 2s Li-Po packs right in the nose. The Turbine has a 5000 2s ECU pack also in the nose. The gear and doors require multiple electronic valves, I used 3 x JetTronic JD valves, 1 for the gear and 2 x gear doors (nose doors stay open gear down and main front doors are closed gear up or down. the leg doors are pulled shut by springs. I have a JetTronics M valve on the brakes.
I used two tanks for the gear/gear doors and one separate tank for brakes (so I can set pressure based on what was required to stop the wheels locking)
I considered several options on sequencing from a Jet Tronic sequencer, to Tx mixing or using the gear door function in my JR 28x tx. A rush to get it finished in time for one of our JMA jet meetings that have a full scale runway available, meant I set the F-35 up in my JR XG-14 and used mixes to control the nose doors. Initially I set a V mix to open and close the main doors, but realised guessing the time delay using servo slow was going to be difficult, so I have the aux switch channel the main doors are plugged into active and I can open and close the main doors when I chose.
The factory had originally designed the fins with a live hinge and a torque rod type linkage, all buried inside the fin. I spent sometime trying to reduce any give in the system, but was not surprised when Len who had one of the other early kits suffered rudder flutter on its first flight.The factory responded to the criticism amazingly quickly and redesigned the fins with conventional pin hinges and external linkages. My second flight also showed flutter (with no damage to the fins) and I was able to land. I flipped the servos over, slotted the fins for the servo arm and hysoled in glass horns, re used the linkages and ball links. The two flights yesterday showed no sign of flutter.
Right from the get go I knew the F-35 would struggle to rotate as the gear is 11" behind the balance point for model flying. The model sat level as supplied, so I had made up 1/2" (12mm) of packing between the retract bearers and units, this raised the nose a little. The first two flights were like this and the F-35 'leapt' into the air at high ground speeds. For yesterday I had added another 1/4" and although the rotation was less sudden it still jumps into the air. There is still a little space between the nose wheel and doors, so I will add another 1/8-3/16" before the next session. DerJet are monitoring this to include in the kit.
Because of the above I had drooped the ailerons 1/4" to try and increase lift, I expected a pitch down with the droop,but did not add any elevator compensation for the first flight. I realised that on rotation this probably helped pitch the nose back down after rotation, so I have left it like that and land clean (it slows up fine) Once I have the ground sit set, I'll experiment with this more.
Flights yesterday showed some good potential and overall its the reaction it gets that makes it a bit special-it looks mean!
So far I only know of one video pass filmed with an iPhone (can't work out how to upload that!) but will get video when I can.
There are various photos from numerous camera men from both weekends!
US interest to Eric Clapp, he's being kept up to date with details and hopefully his and Len's example will join that one in flight.
Dave
Typically of this era of jet airframe its designed to be flown by a computer, we don't have that option yet, but the first two flights without the Powerbox iGyro showed its a nicer experience with the gyro active, first flight yesterday was with 20% gain in rate mode and second flight 25% in heading mode, I will continue to increase the gain, flight by flight and wind conditions. So far the heading mode is favourite, it deals with the balance change caused by the fuel tanks position (dictated by the gear position) the tanks are just forward of the balance point.
I've still not weighed my model (because you have little control over the final weight-so it is what it is!), but I went with a JetCat P-90Rxi turbine as I felt that if it needed more power it would be a simple task to swap to a P-140Rxi. Having had four flights I'd say the 105N of the P-90Rxi is perfect.
My model has JR 8911 servos on the flying elevators, JR 8411's on Ailerons and JR 3421NX on rudders,plus my standard JR 579 on nose steering.
Rx power is via a Powerbox Sensor switch with 2 x 2200 2s Li-Po packs right in the nose. The Turbine has a 5000 2s ECU pack also in the nose. The gear and doors require multiple electronic valves, I used 3 x JetTronic JD valves, 1 for the gear and 2 x gear doors (nose doors stay open gear down and main front doors are closed gear up or down. the leg doors are pulled shut by springs. I have a JetTronics M valve on the brakes.
I used two tanks for the gear/gear doors and one separate tank for brakes (so I can set pressure based on what was required to stop the wheels locking)
I considered several options on sequencing from a Jet Tronic sequencer, to Tx mixing or using the gear door function in my JR 28x tx. A rush to get it finished in time for one of our JMA jet meetings that have a full scale runway available, meant I set the F-35 up in my JR XG-14 and used mixes to control the nose doors. Initially I set a V mix to open and close the main doors, but realised guessing the time delay using servo slow was going to be difficult, so I have the aux switch channel the main doors are plugged into active and I can open and close the main doors when I chose.
The factory had originally designed the fins with a live hinge and a torque rod type linkage, all buried inside the fin. I spent sometime trying to reduce any give in the system, but was not surprised when Len who had one of the other early kits suffered rudder flutter on its first flight.The factory responded to the criticism amazingly quickly and redesigned the fins with conventional pin hinges and external linkages. My second flight also showed flutter (with no damage to the fins) and I was able to land. I flipped the servos over, slotted the fins for the servo arm and hysoled in glass horns, re used the linkages and ball links. The two flights yesterday showed no sign of flutter.
Right from the get go I knew the F-35 would struggle to rotate as the gear is 11" behind the balance point for model flying. The model sat level as supplied, so I had made up 1/2" (12mm) of packing between the retract bearers and units, this raised the nose a little. The first two flights were like this and the F-35 'leapt' into the air at high ground speeds. For yesterday I had added another 1/4" and although the rotation was less sudden it still jumps into the air. There is still a little space between the nose wheel and doors, so I will add another 1/8-3/16" before the next session. DerJet are monitoring this to include in the kit.
Because of the above I had drooped the ailerons 1/4" to try and increase lift, I expected a pitch down with the droop,but did not add any elevator compensation for the first flight. I realised that on rotation this probably helped pitch the nose back down after rotation, so I have left it like that and land clean (it slows up fine) Once I have the ground sit set, I'll experiment with this more.
Flights yesterday showed some good potential and overall its the reaction it gets that makes it a bit special-it looks mean!
So far I only know of one video pass filmed with an iPhone (can't work out how to upload that!) but will get video when I can.
There are various photos from numerous camera men from both weekends!
US interest to Eric Clapp, he's being kept up to date with details and hopefully his and Len's example will join that one in flight.
Dave
10-11-2016, 02:42 AM
#2
Not sure if you have the option on your radio, but on mine (t18) you can dedicate a channel to be a 'timer' and then step-mix multiple other channels to it to operate the gear and gear door valves. Makes for the best sequencer you could ever want for.
This is what it looks like in action:
https://www.youtube.com/watch?v=UgKBsdB7NEI
can give you more details if you need them.
The only disadvantage is it does not provide low pressure failsafe obviously
This is what it looks like in action:
https://www.youtube.com/watch?v=UgKBsdB7NEI
can give you more details if you need them.
The only disadvantage is it does not provide low pressure failsafe obviously
10-11-2016, 04:51 AM
#3
Thread Starter
Maury
There are options like that on timing, but that still does not cover if the gear does not clear first time. After experimenting with pressure I think I'm there on this 95psi seems the sweet spot.
I don't believe in low pressure failsafe valves like Tams, there are times when its good and times bad...I prefer to just have gear that does not leak and in 16 years I'm pretty lucky ;-)
Dave
There are options like that on timing, but that still does not cover if the gear does not clear first time. After experimenting with pressure I think I'm there on this 95psi seems the sweet spot.
I don't believe in low pressure failsafe valves like Tams, there are times when its good and times bad...I prefer to just have gear that does not leak and in 16 years I'm pretty lucky ;-)
Dave
10-11-2016, 05:00 AM
#4
Maury
There are options like that on timing, but that still does not cover if the gear does not clear first time. After experimenting with pressure I think I'm there on this 95psi seems the sweet spot.
I don't believe in low pressure failsafe valves like Tams, there are times when its good and times bad...I prefer to just have gear that does not leak and in 16 years I'm pretty lucky ;-)
Dave
There are options like that on timing, but that still does not cover if the gear does not clear first time. After experimenting with pressure I think I'm there on this 95psi seems the sweet spot.
I don't believe in low pressure failsafe valves like Tams, there are times when its good and times bad...I prefer to just have gear that does not leak and in 16 years I'm pretty lucky ;-)
Dave
Using the radio to do sequencing like this does away with some installed cost and weight, personally I think is the best way to do landing gear controls.
On the futaba you get to see a realtime graph for each mix, so you can graphically tell the exact point in the sequence where the gear clears the door and setup the door properly that way.
10-11-2016, 06:08 AM
#5
Thread Starter
The F-35 has twist and turn forward retracting main gear, for sure the speed of retraction will vary, so its important to have an base line of how long in the air with airflow and G the gear takes to go away.
At this time I am taking off, doing a dirty circuit, slowing into wind and putting the gear away, then the doors. Last time out it worked perfectly.
Dave
At this time I am taking off, doing a dirty circuit, slowing into wind and putting the gear away, then the doors. Last time out it worked perfectly.
Dave
10-11-2016, 11:10 PM
#8
Thread Starter
General feeling is models are getting too big. I know financially the manufactures like bigger models, but the average guy with average vehicle/workshop space, cannot have the huge models. The F-35 is not overly long, but it is 'chunky'
Its quite an undertaking for a small manufacturer like DerJet, they have done an amazing job getting this into production.
Dave
Its quite an undertaking for a small manufacturer like DerJet, they have done an amazing job getting this into production.
Dave
10-16-2016, 06:33 AM
#12
F35 slow mo take off
Heres a quick slow motion of the F35 taking off yesterday at the JMA event. Flown by Dave at Motors and Rotors.
Mark
https://youtu.be/shQnrr_3b-k
Mark
https://youtu.be/shQnrr_3b-k
10-16-2016, 08:50 AM
#14
Thread Starter
Thanks Marky. Idea behind this was to see load on the nose leg spring, I realised that it was quite soft and that the rear gear position at takeoff power was collapsing the nose oleo reducing the AOA before it started to rotate. I added a length of glow type silicon tube inside the spring to act as a bump stop. + 10 mm on uncompressed length.
Rotation was much better in on the three flights I did this weekend.
DW
Rotation was much better in on the three flights I did this weekend.
DW
10-16-2016, 01:21 PM
#16
10-17-2016, 05:52 AM
#17
Thread Starter
Mark also caught the landing on this flight...he's arty so it its in slow mo!
The wind was slightly in our faces all weekend.
https://www.youtube.com/watch?v=Fouu7-1NhcA
The wind was slightly in our faces all weekend.
https://www.youtube.com/watch?v=Fouu7-1NhcA
10-17-2016, 08:37 AM
#19
I had a rudder flutter away on my last flight\. Lucky for me the Deamon Cortex is dialed in so nicely that I did not notice until I landed. My buddies saw it fly away and got it for me.
I blame it on me. I CA the servo mount to the fin.....bad juju, they need to be hysoled in there. The F-35 has very sensitive rudders!
I blame it on me. I CA the servo mount to the fin.....bad juju, they need to be hysoled in there. The F-35 has very sensitive rudders!
10-17-2016, 10:45 AM
#20
Thread Starter
The orginal rudder set up from DerJet also allowed flutter as Len experienced on his first flight and I got on the second flight. The factory acted really quickly on a redesigned rudder setup and linkage. I'm working with them on that now.
My external linkages have been solid on the five flights since. I have a set of new fins to swap over.
My external linkages have been solid on the five flights since. I have a set of new fins to swap over.
01-14-2022, 12:17 PM
#23
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Thank you for your prompt reply. I have the instructions, but I thought there was another focal point that I had flown that would fit better.
so that the f-35 takes off better our runway is only 120 meters long.
so that the f-35 takes off better our runway is only 120 meters long.
01-14-2022, 12:32 PM
#24
Thread Starter
You need to pack the nose retract unit to gain a positive angle of attack on the ground, mine ended up with 25mm packing it will need just about all of the 120m for take off if it’s a hard runway.