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KMP F-7F Tigercat

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Old 01-31-2012, 02:15 PM
  #1951
BadLemon
 
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Default RE: KMP F-7F Tigercat

Does anybody know if the KMP kits where numbered? I just picked up a composite Tigercat this passed weekend I've looked it over and but couldn't find any numbers in the fuselage. Boy the fuselage is long!

Col Winter I heard you made a modification to strengthen the center support of the wing by cutting open the bottom and tying the wing tubes with a aluminum bar. Is the bar just installed into the tubes and epoxied in or did you do something different.

Lastly is anybody using the KMP struts only? I have a set of gen-3's, the retracts are junk but the struts don't look bad. I found I could easily adapt them to my Robart retracts pretty easily. I only have to make some small changes to the struts to make them reliable. See pic's
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Old 01-31-2012, 11:30 PM
  #1952
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Default RE: KMP F-7F Tigercat

Hi Badlemon. The center wing modification is in this forum. I show in detail how I constructed the modification. I don't remember which page but it is way back in the forum. If you can't find it let me know Col. Chuck Winter
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Old 02-01-2012, 06:09 PM
  #1953
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Default RE: KMP F-7F Tigercat

Got 5 more flights on mine at the Arizona Electric Festival. Fun twin to fly. Weighs in at 28 lbs.
Bob

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Old 02-07-2012, 04:28 PM
  #1954
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Default RE: KMP F-7F Tigercat

Bruff i just back ordered mine shiny one from TBM. they are using your plane on the web site and want to know if the plane comes with the yellow tips or did you add them?
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Old 02-11-2012, 12:05 AM
  #1955
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Default RE: KMP F-7F Tigercat

Bob,
Maybe this is not the place to address this, but I have a couple of questions about your tcat. I've been working on a similar one(actually an old cedar hobbies cat) for several yars, but I always have trouble trying to solve the electric problem of wire length from battery to ESC then to motor if I want to use one battery in the fuse. I could sure use some help on how to do this. I have eflite 110s at the moment, but am considering going up to 160s. If this is too involved maybe I sould start another thread. I am just very frustrated at the moment and want to get it in the air.
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Old 02-11-2012, 07:49 AM
  #1956
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Default RE: KMP F-7F Tigercat

Eagle,

Even though you didn't ask me ( ;-) ), I would offer my answer. I'm building the same airplane, and have faced this issue many times before. All of my planes are electric (24 of them...).
You will find a philosophical debate on whether you should extend the motor wires or battery wires. Some claim you should never extend the battery wires. Howeverthere is really no option here not to put the ESC next to the motors, which means you have to run some 2-3' wires between the battery and the ESC. The issue is that voltage ripple develops the longer the wires are. So you need to add capacitors to eliminate this ripple. Castle Creations has a capacitor pack for $25. I called them to ask, but they didn't know what to tell me in terms of what capacitors exactly, and why they have 3 capacitors instead of one larger. Their capacitors are 220uF/50V x4. However, if you know electronics, you will know that the wire length, the voltage, the current you are consuming, and even the wire gauge will all have an effect on the amount of ripple. I don't know if you are using a CC ESC, but if you doone of the parameters it logs is the input voltage ripple. You can try with short wires and see what kind of voltage ripple you have before you extend the wires.

My recommendation (and what I am doing myself, although I have not flow it yet) is to use a block of 4 capacitors (470uF/63V) in parallel, about half way between the ESC and the battery. I will also put a block like that right in front of the ESC itself. This means that I will have ~2000uF twice along each wire pairs. Why 4 capacitors (470uF each) instead, for example, a single 2200uF capacitor in each location? Better ESR.

So, you need a total of 16x 470uF/63V electrolytic capacitors. Make 4 capacitor blocks from them, each with 4 capacitors in parallel, and solder one block right before the ESC, and one in the middle of the wire length between the ESC and the battery.

One more thingthe thicker wire you use, the lower ripple you will have (less wire resistance/impedance). I am planning on using 10AWG wire. 8AWG would even be better, but don't use 12AWG or thinner.

My 2 cents, even though you didn't ask me...
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Old 02-11-2012, 08:33 PM
  #1957
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Default RE: KMP F-7F Tigercat

Thanks for the reply. It was basically an open question so I appreciate your response. My ESCs are castle so I went to their website and checked out the capacitor pack which seems to be just what I may need. I started with 2 4s lipos in each nacelle that were connected in series for a total of 29.6V feeding a phoenix HV85 esc and an eflite power 110 brushless motor. That was when I was working on using sierra giant scale air retracts that were made for me. As I progressed (slowly) I found that magnum RC has a conversion for the Sierras to electric retracts and so I sent them up the road to them. With no need for the air tank and the thought of lowering the battery weight and using one lipo for both motors I decided to put the battery in the fuse. This solved the problem of having batteries drawdown at different rates, but created the wiring problem. Your solution seems to be just what I need. Since I am not overly knowledgable about electrics (most of my planes are IC powered) the question now is do they need to be in a ventilated area or can they be in the wing. Castle says to put them close to the ESC. Do you think for the currect set up that I need to use 2 for each motor, or would one do it? Also since your are doing a similar project with similar weight (mine is about 28lb all up) will this setup provide enough power. What kind of wing loading are you expecting on yours?
this is definitely the heaviest project I have done and I just don't want to get to the end of the runway and struggle into the air only to stall and drop like a rock. Lots of work - no fun :-(
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Old 02-11-2012, 09:06 PM
  #1958
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Default RE: KMP F-7F Tigercat

Most likely if you were to put the batteries in the nacelle you would end up tail heavy. My setup is two E-flite power 160s, CC hv85 capacitors added by speed controller in the nacelles and 10s 2p thunder power 5000mah propower 30c batteries 17 cells right under the front of the canopy and one 3 cell pack behind the leading edge of the wing. I also have the sierra gear and it is well worth the money. I am interested in the electric conversion for the nose gear because I have had an issue with it not locking down with the scale door on the gear this set up is plenty of power and all up weight is 32 lbs.
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Old 02-12-2012, 07:13 AM
  #1959
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Default RE: KMP F-7F Tigercat

Guys,

My setup is two Tacon Bigfoot 160. They are very similar to the e-flite Power 160. Eagle, as far as the wing loadingit has nothing to do with the power, but everything to do with the weight. We will all have our planes with AUW of ~29-30lb, so we will all have the same wing loading (which will dictate the stall speed...). The battery/ESC/motor/prop combination is going to be critical. When I built my 16lb CMP P-40, I used the RIMFIRE 160. I used 10S (6S+4S) 5000mAh batteries, and a Master Airscrew 16x10x3 prop. The motor was heating up on the bench, and I didn't consider the reduced load during flight. So during flight, I found that I was consuming no more than 36A (~1300W!). No wonder the plane was flying slow... I had less than 100W/lb. I then increase the prop to 16x12x3, which was only slightly better. So I am now switching to a Zinger 18x12x3, and may actually go up to 12S.

For the F7F, which weighs almost twice as muchI need twice as much power. So, already have TWO 160 motors, planning to use two 18x12x3 props (I want to find props that can be counter rotating to each other, thus eliminating any prop torque and making this plane so much easier to fly, and especially to track the runway on takeoff...). I plan on using two 6S 8000mAh batteries (to get a total of 12S). I did buy the Hobbywing 120A HV OPTO, but not sure if I will use them eventually. I may buy a couple of CC 80HV. For the log, if nothing else...

Back to the capacitorsI know that CC recommends putting their capacitor pack right in front of the ESC, but speaking with themthey couldn't explain a lot of things which you need to consider. I would stick with my recommendation above (10AWG wires, make them as short as possible, two capacitor packs along each set of wires: one near the ESC and one in the middle). You cannot put them next to the battery, as the voltage ripple (which might "confuse" the ESC) develops along those lines, the FARTHER you get from the battery. High current (low AWG) wire will help. Short wires will help. Multiple capacitors will help.

Finallythose capacitors do NOT get warm. You can put them inside the wing without worrying.
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Old 02-12-2012, 07:30 AM
  #1960
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Default RE: KMP F-7F Tigercat

By the way, as far as retracts, I'm going to start with FIXED landing gear for the first few flights. The gear will be screwed and not glued to the plane, so I can "upgrade" to the retractable one later. Again, experience with the P-40, where I bent the nice (and expensive...) Sierra gear on it in the first 16lb landings... A combination of cheap HK struts (work very well), wheels, piano wire and I can fly. If I bend them on landing not a big deal. Later, when I feel my landings are getting better and smoother, I will switch to the retractable gear with less worry. I do have the original ESM air retracts, when I'm ready for them. I will have an air system, if only for one thing: brakes... Yes, I plan on putting brakes on this plane. Even though we have a paved 720' runway in our club this 30lb plane will come in heavy and fast for landing, and will "consume" that runway easily. I'm planning on the Robart brakes. Between the wheels, brakes, and proportional brake valve I'm looking at ~$200.
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Old 02-12-2012, 08:14 AM
  #1961
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Default RE: KMP F-7F Tigercat

Regarding ESC location, I believe the easiest solution is to locate the ESCs in the fuse near the batteries. I did that with my F7F and have no issues. No voltage spike issues so no capacitor worries. The only downside is having 3 wires running out to each nacelle instead of 2, so a little more weight. I mounted ESCs with heatsinks back-to-back, with a tiny 5v computer fan blowing cooling air between them. Very simple solution. FWIW I used the Hobbywing 100A HV ESC's, and have been quite impressed - very smooth & linear throttle response, and absolutely no dramas after quite a number of flights. I'm running about 2250W per side, and performance is fantastic.

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Old 02-12-2012, 08:15 AM
  #1962
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Default RE: KMP F-7F Tigercat

Duplicate post
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Old 02-12-2012, 03:47 PM
  #1963
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Default RE: KMP F-7F Tigercat

Mounting the ESC's in the fuse goes against the general train of thought but if it works who can argue (unless it stops working). I know that CC recommends putting the speed controller as close to the motor as possible. also if you run the motors counter rotating remember the prop nut will have to locked somehow or a reverse thread on the shaft and nut. I was considering it but could not find the right props. The tigercat flies great and I don’t think I would bother at this point changing it
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Old 02-12-2012, 04:35 PM
  #1964
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Default RE: KMP F-7F Tigercat

You know something? I completely forgot about the nuts... I may have to go with both props turning the same direction. Props would be cheaper, too... Thanks for that!!!
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Old 02-12-2012, 09:11 PM
  #1965
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Default RE: KMP F-7F Tigercat


Quote:
ORIGINAL: Ron McGrath

Mounting the ESC's in the fuse goes against the general train of thought but if it works who can argue (unless it stops working).
Over the years a number of ESC manufacturers have issued some fairly dire warnings about keeping the ESC to battery leads short. I recall Schulze was one of the first to explain the voltage ripple issue, and offer maximum permissable battery-to-ESC cable lengths. CC also take the issue seriously, with voltage ripple being a trackable data point in the ICE logging. On the motor side however, there doesn't seem to be much concern. The ESC already has to handle the inductance and resistance issues that the motor windings offer. Additional cable length will simply add to the inductance and resistance of those wires inside the motor. When one considers the inductance/resistance that a high-wind motor already offers, any cable length that we add (within reason, of course) should not have any significant impact.


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Old 02-12-2012, 10:18 PM
  #1966
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Default RE: KMP F-7F Tigercat

For my 100" Mossie, I toke the following options:
1. Scorpion 5525-225, CC ice2 HV80, 12s2p a123, 18*12 3-blade... twice
2. With one pack only, ESC ripple may interact...
3. Weight of the packs (4lbs each) is on the wheel... better structure when hard landing...
4. Very short wires... everything in a ctp tube... motor upfront, pack within, esc below...
5. Fast charge inplace with two iCharger 301B (15min)
6. Removable tail and wing tips for easy transport
7. All other functions in the fuse, except ailerons and half flap in the wing tips
8. Electric retract for main and tail
9. Jeti telemetry for main packs usage and speed
10. Emcotec SPS to cut main power (security and charging)
11. Dual a123 pair for rx power
12. All servos (except retract) are Hitec 645mg... radio Futaba FF9 with Jeti module.
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Old 02-13-2012, 02:05 AM
  #1967
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Default RE: KMP F-7F Tigercat

100" Mossie? Where do I get one?????????? ARF?
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Old 02-13-2012, 02:23 AM
  #1968
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Default RE: KMP F-7F Tigercat

Here
http://www.mickreevesmodels.co.uk/~m...its/p4spit.htm
look at the bottom.
Not ARF but not bag of stick...
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Old 02-13-2012, 09:04 AM
  #1969
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Default RE: KMP F-7F Tigercat

I looked at that link. Some nice RAF workmanship there! I did notice the following, though (on the Mosquito):
"On 16 x 10 three blade props (right and left rotation). turning 6k9 rpm, 11 kg thrust. 34amps each motor. Ted cooks model the same. Both models have now flown with good performance"

This is the same problem I have with my P-40: it is under propped! You are only using 34A on each side. Weight is 24lb (the F7F will be heavier...), and at 12S (44V), you are getting 1500W on each side. I don't know about the motors you are using, but if they can take moreI would go with 18x12x3 props. You are probably getting very scale-like takeoffs. I felt the P-40 was just slow...
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Old 02-13-2012, 09:15 AM
  #1970
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Default RE: KMP F-7F Tigercat

@ysolomon
True, the config described on the site is probably too weak...
Look at mine...
A Scorpion goes up too nearly 2.5kW i.e. 77A under 32.4V (12s2p a123 under load) with 18"*12" 3-blade.
More than enough
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Old 02-13-2012, 09:50 AM
  #1971
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Default RE: KMP F-7F Tigercat

That's what I'm talking about!
What props are you using?
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Old 02-13-2012, 05:27 PM
  #1972
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Default RE: KMP F-7F Tigercat

Ron,
I like your set up, but I'm intrigued by the battery arraangement. I not real skilled in this area, so I thought it was always a good idea to use two of the same batteries in parallel. It sounds like you have one 10s and one 7s and 3s. Is that right or am I reading it incorrectly. If that will work it would solve some space issues. I really appreciate the info. Nobody around here is doing anything along these lines.
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Old 02-13-2012, 06:30 PM
  #1973
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Default RE: KMP F-7F Tigercat

The set up for the batteries is 10 s 2 p I have 2 5 cell packs 5+5=10(one set). And 2 3 cell and one 4 cell packs 3+3+4=10 cells(the other set) the hard part about this setup is how to connect the packs together in the confined space with keeping it as simple as possible. I have made some mistakes along the way and am happy with the configuration that I have now. Charging is a hole other issue! But I can now charge all 5 packs in under 15 minutes. If you count the 2 1350 mah packs for the rx I guess that's 7 packs in 15 min. My son and I will have 7 planes this season that will take a 10s 5000mah pack. And 2 of those will take 2 10s packs(the tigercat and a Stinson 108)
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Old 02-13-2012, 09:33 PM
  #1974
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Default RE: KMP F-7F Tigercat

@Ysolomon
Graupner Gsonic 18*12 3-blade
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Old 02-13-2012, 10:39 PM
  #1975
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Default RE: KMP F-7F Tigercat

ysolomon,
Thanks for the info on the capacitors. I like the method for solving the situation, so I've ordered 4 of them and some #10 wire. Now all I have to do is get 2 power 160s and decide what I need in the way of batteries and what will fit. I've got several 16 X 12 X 3 blades that I was going to use, but it looks like I need 18s. I had considered counter rotating props, but the thread problem and the fact that tcats have large vert stabs coupled with propportional throttles made me abandon the idea. I was also considering brakes, but when I contacted Frank Tiano about the landing distance required for his KMP tcat he replied he didn't think brakes were necessary as his landed with about a 70ft roll out.
I hope he was right since out field is only 400 ft.
Thanks for the retract idea for break in. I hadn't thought about the diffference in flight characteristics with a much heavier plane. I'll also be interested to see if the nose wheel door acts as a cunard when it it lowered. I really hope mine come back soon. I'm anxius to see what I have to do to accomodate them in their new configuration.
I guess I'll be getting some Graupner 18 x 12 3 blades as well. Lots to do.
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