RC Jets Discuss RC jets in this forum plus rc turbines and ducted fan power systems

I'm building the TopRC F9F Cougar

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Old 07-16-2017, 05:30 AM
  #26  
rhklenke
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Oh, and BTW, the first Ziroli Panther to fly with a turbine was with a Funsonic turbine (no longer available) that produced 12 lbs of thrust...

Bob
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Old 07-16-2017, 07:54 AM
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Originally Posted by rhklenke View Post
Chris Gunner's son is flying an Extreme Jets Cougar (as stated above, basically the same airplane) on a Kingtech K45 engine - 9.9 lbs of thrust. It has a bit of a longer takeoff roll, but it flys *great* on that engine.

You do *NOT* need a 1-to-1 thrust to weight ratio in an aircraft to fly well - after all, the real Cougar had thrust equal to around 1/3 of its weight...

That being said, if you look at the specs of the newer 80N engines, namely the Bee 80 and Merlin VT 80, they are very close to the size and weight of the newer 60N engines like the K60. However, their fuel consumption is quite a bit higher. There are tradeoffs, but you don't *have* to have an 18 lbs thrust engine to fly this plane...

Bob
Pull up ,
I truly respect you on investigating the airframe needs. It will help many people out. That is what the forums are about. I occasionally do write ups as well. The need for more power is an arguable debate. In my perception, the less weight trade off versus more power, I tend to go on the lighter side . The extra engine weight also requires more fuel and that equals 5-7lbs more extra added weight. Is the airframe going to last longer while enduring higher stress levels ? IDK.
I remember flying 20lb models on 7-10lbs thrust and Yes I can be done and it works ! Longer take offs and staying on the power. This is for each to figure out on their own.

I did not know Mike was selling gear for it. I bought the Robarts because there was not any other options at that time. I have had their Warbirds and agree their stuff is Nice and fits perfectly. They designed it for that plane specific. Robarts is a retro fit setup. I will call Mike to order the TopRc gear set myself.

Did you plan to use air or servo operation for the body flaps? I was going to do servos.
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Old 07-16-2017, 10:17 AM
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Originally Posted by rhklenke View Post
Chris Gunner's son is flying an Extreme Jets Cougar (as stated above, basically the same airplane) on a Kingtech K45 engine - 9.9 lbs of thrust. It has a bit of a longer takeoff roll, but it flys *great* on that engine.

You do *NOT* need a 1-to-1 thrust to weight ratio in an aircraft to fly well - after all, the real Cougar had thrust equal to around 1/3 of its weight...

That being said, if you look at the specs of the newer 80N engines, namely the Bee 80 and Merlin VT 80, they are very close to the size and weight of the newer 60N engines like the K60. However, their fuel consumption is quite a bit higher. There are tradeoffs, but you don't *have* to have an 18 lbs thrust engine to fly this plane...

Bob
I appreciate your point of view.
I do have a couple points to make though. I try not to avoid speaking in absolutes, because it backfires. So, I never said you need 1:1 thrust ratio. And I never said you "have" to have 18lbs thrust to fly this plane. Even with an 80N engine, my ratio will be about 80% (not 1:1), which is a nice place to be especially launching on soft mat or grass. The surface condition can make a big difference. Perhaps I should have emphasized my biggest concern is the takeoff. It's all grass fields here. One in the air safely it will fly. But ya gotta get there, right?

Most of my comments were focused on the factory stating the plane's flying weight is 15lbs,which really can't happen. So if one is to make an informed decision on engine size, you need to start with an accurate flying weight, especially if the factory is willing to print one. If you feel comfortable flying a 21 or 22 lb jet off grass with 12lbs of thrust, go ahead. I'm betting most people wouldn't. When you buy any RC plane, the box usually has an engine choice range, like .60-.90 size, etc. Most people wisely shoot for the middle, or higher part of that range. So if you want to invest now $1000's in a plane and go the other direction, that's your choice. I'm betting most people wouldn't.

Though interesting that the original F9F had a very low power/weight ratio, that says nothing about how this RC F9F will fly on a small engine. Most RC planes have much higher power/weight ratios for a reason. Airfoil reynolds numbers go awry as wings get smaller and smaller and finally approach RC plane sizes. I think it's because air molecules don't scale the same as wing area. Also, drag (surface area) and weight are not linear, but are some weird cube function. So OF COURSE the the original F9F's power/weight ratio was low. So are most full scale planes compared to their scale RC counterparts. Also, they had lousy engines back then. But unlike RC jets today, back then they didn't have any choice in the matter like we do. Oh, and they also had 5000 foot concrete runways.

The saying goes, "the longer your takeoff roll, the narrower the runway".

I still am impressed with TopRC's and Caiman's willingness to fix this. And I still personally would recommend an 80N engine for this plane. Sure, get the lightest one you can find. Another good choice would be the new K70 from Kingtech, which has 70n power in the same weight package as the K45/K60. But the final specs are not in, and it's not shipping yet.
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Old 07-16-2017, 10:30 AM
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I am VERY interested in the K70 as well for this plane when it becomes available. I fly off Asphalt 35x385. It has taken many many many years and lots of planes to get to where I hit it every time.
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Old 07-16-2017, 01:12 PM
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I'll chime in as I'm flying mine with a VT80.

It's more thrust than is needed. I also had to make major
mods to fit in a larger fuel tank. I have now cut down an xcalibur fuel tank to give me 2.4L as 1.7L was not enough.


The SM version will fly fine on a 60n engine. I am cruising around at half throttle most of the time with the VT80 and it goes just nicely. Full throttle is nice on the verticals but considering there is one flying on a K45 it shows that the airframe is fine on a lower thrust engine

I wouldn't stress about weight etc. It's a terrific flying airframe, stable and a delight to fly. (Well my SM version is)


Cheers

Jeremy
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Old 07-16-2017, 02:09 PM
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Originally Posted by Jeremy_D View Post
I'll chime in as I'm flying mine with a VT80.

It's more thrust than is needed. I also had to make major
mods to fit in a larger fuel tank. I have now cut down an xcalibur fuel tank to give me 2.4L as 1.7L was not enough.


The SM version will fly fine on a 60n engine. I am cruising around at half throttle most of the time with the VT80 and it goes just nicely. Full throttle is nice on the verticals but considering there is one flying on a K45 it shows that the airframe is fine on a lower thrust engine

I wouldn't stress about weight etc. It's a terrific flying airframe, stable and a delight to fly. (Well my SM version is)


Cheers

Jeremy
Very good information, Jeremy, thanks! I was considering a VT80 as well, but based on your experience, I think I'll wait for either the Merlin 70 or the K70, or go for a K60. I'll have to see what's available when I'm ready to buy my engine - probably around September...

Bob
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Old 07-16-2017, 02:54 PM
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Hi Bob, the biggest issue with the larger engine is the fuel tank. I'm not sure if you have seen my build pics but I wasn't happy with teh stock tank. The triangle shape of the tank and the way it was shaped to the bottom of the fuse made it impossible for the pickup to work effectively. To get it to travel up and down without hitting the back of the tank meant I had to sacrifice length of the pickup line meaning it would miss a bit of fuel (pic attached). I ended up removing the ducting to fit a new dubro tank (1.8L). This wasn't enough for the VT80 unless I wanted a 4 minute flight and I have since added the modified xcalibur tank which is 2.4L.

Even then because of the steering servo location it can only go so low into the fuse and can only be a certain length as it fouls the equipment tray former. (remember I am only speaking on behalf of the SM version, not sure what the top RC situation is)

If you are using a cockpit you are then also limited by height. If you are not using a cockpit you could get a higher tank in there with a larger capacity. If I was building this again, as it is a 'sport scale' airframe, I would just tint the canopy and lose the cockpit for a larger fuel tank.

Hope this helps.

Jeremy
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Old 07-16-2017, 07:23 PM
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Originally Posted by TimD. View Post
Pull up ,
I truly respect you on investigating the airframe needs. It will help many people out. That is what the forums are about. I occasionally do write ups as well. The need for more power is an arguable debate. In my perception, the less weight trade off versus more power, I tend to go on the lighter side . The extra engine weight also requires more fuel and that equals 5-7lbs more extra added weight. Is the airframe going to last longer while enduring higher stress levels ? IDK.
I remember flying 20lb models on 7-10lbs thrust and Yes I can be done and it works ! Longer take offs and staying on the power. This is for each to figure out on their own.

I did not know Mike was selling gear for it. I bought the Robarts because there was not any other options at that time. I have had their Warbirds and agree their stuff is Nice and fits perfectly. They designed it for that plane specific. Robarts is a retro fit setup. I will call Mike to order the TopRc gear set myself

Did you plan to use air or servo operation for the body flaps? I was going to do servos.
The part numbers on many of the Robart components were labeled Caiman F9F Cougar, so they must be somewhat custom.

With the 80N engine, I did run some numbers based on my flying habits. The engine uses about 8.4oz fuel/minute at WOT. The tank is 64oz, so at average 75% throttle that gives me a 9 minute flight with a minute to get down. Most of the time my average is probably 60% throttle. Added margin. I've always modulated the throttle, even with propellers. Yes, I see guys who just burn up the sky the whole flight, but that completely omits a whole dimension of flying skill. So I didn't feel the need to enlarge the tank and thus add more weight. Here's a pic of the tank.

As for the flaps, I just used servos. I accidentally glued the control horns on a different distance from the hinge line, so to equalize the travel I had to customize the servo control arms.
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Old 07-18-2017, 05:04 AM
  #34  
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Waiting for the K80, so I'm tempting to dress up the bird a little.
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Old 07-21-2017, 05:39 AM
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This post illustrates the same thinking I had when choosing my engine size:
Post 142....
Ziroli F9F Panther - made in Serbia
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Old 07-21-2017, 05:47 AM
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The Kingtech K80 turbine has arrived in good time. Thanks Barry from Kingtech. Now to shove it in there. it's longer, so there will be some notching goin' on in the inlet ducting to allow the fuel line and maybe the wires to exit the engine without sharp bends. No big deal. I ran into a weird problem with the GSU also. It wouldn't power up with the plane's receiver/ECU power system switch. I'd have to unplug and replug it to get the display to come alive. I chased it down to the Fromeco Cricket voltage monitor, which has a capacitor array on it as brownout insurance. That causes the system to power up slower as those caps charge. The GSU won't power up with the slow rise time. I say "slow", meaning maybe 100msec or so. The GSU rejects that power up profile. So I have to switch it on twice, once to charge the caps, and again a couple seconds later to fire up the GSU too.
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Old 07-22-2017, 06:19 AM
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The Kingtech K80 is now installed. I used Hi Temp silicon to hold the FOD screen on. I don't know how advisable that is. But I don't even know what that oring that comes with it is supposed to do. Orings deteriorate quickly. I suppose it goes over the starter motor? But there are really no detents or grooves to hold the oring in place. Seems like an afterthought, but maybe I'm not doing it right. There is a big glue glue flange inside the bifurcated ducting right where the engine intake goes. I had to grind that down for about 1 1/2 inches of length to clear the larger dia engine. Otherwise, it seems like the engine went in easily. I did have to add a little extra onto the engine mounting rails as the scews were half off the wood. Typical mods needed for choices in hardware unknown to the original designers. This is ready for it's first run-up.
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Old 07-22-2017, 07:26 AM
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The O ring goes over the starter motor and holds the FOD guard on. It does an adequate job and I don't know anyone who has had problems with this method. The high-temp silicon probably won't cause any problems (other than getting goo on your engine), but its unnecessary...

I think that the engine mounting rails are spaced for a 120mm ducted fan and thus are too far apart for the smaller turbines that are suitable for this model.

Bob
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Old 07-22-2017, 08:25 AM
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Wow! I can't even imagine a 120N engine on this baby! Let those few be the guys to do the mods!
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Old 07-22-2017, 08:58 AM
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Originally Posted by Pull Up Now! View Post
Wow! I can't even imagine a 120N engine on this baby! Let those few be the guys to do the mods!
No, I'm not talking about a turbine engine, I'm talking about a 120mm EDF!

An example: https://www.turbines-rc.com/en/120mm...kv-motor-.html

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Old 07-22-2017, 10:59 AM
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Originally Posted by rhklenke View Post
No, I'm not talking about a turbine engine, I'm talking about a 120mm EDF!

An example: https://www.turbines-rc.com/en/120mm...kv-motor-.html

Bob
Oh, Duh on me Bob. All I saw was 120! I blanked out on the "ducted fan" part.
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Old 07-22-2017, 12:10 PM
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Originally Posted by Pull Up Now! View Post
The Kingtech K80 is now installed. I used Hi Temp silicon to hold the FOD screen on..
I have bought a few of these engines now and have been doing the exact same thing.
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Old 07-22-2017, 05:54 PM
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Originally Posted by TimD. View Post
I have bought a few of these engines now and have been doing the exact same thing.
I don't think there will be any goop in the engine. It's all cured.
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Old 09-23-2017, 11:47 AM
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Checking to see if you have had the chance to maiden it yet? If so tell us your opinions and adjustments.
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Old 09-24-2017, 12:33 AM
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I did maiden the .Cougar a few weeks ago. It flew really well. The ailerons were really sensitive, so I backed off the travel to less than what the book recommended, and added some expo also. Since the airframe and cg are now proven, I'm adding more rivets and scale details. It was a good decision to switch to the K80 turbine. The takeoff roll is within reason now, and the plane can handle the extra weight just fine. This ship is very slippery, so even with full barn door flaps it will blow right by you unless you come in low. Turn to final needs to be at less than 100 ft and be on top of the plane to prevent rolling inverted in the final turn. The flare and rollout are very smooth, but be prepared for the high alpha attitude in the flare. It looks scary but that's what it takes to slow it down, get it stalled, and to land on the mains. I really recommend this Top RC jet.
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Old 10-27-2017, 06:00 AM
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I have purchased the top rc cougar. I was looking at mini servos. Most are in the 50 Oz range. Is this enough for the elevators and speedbrake/ flaps? Also. Which mini servos have you used. Thanks!
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Old 10-27-2017, 07:02 AM
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Originally Posted by Saillfish View Post
I have purchased the top rc cougar. I was looking at mini servos. Most are in the 50 Oz range. Is this enough for the elevators and speedbrake/ flaps? Also. Which mini servos have you used. Thanks!
I'm building one as well. I'm using JR digital mini servos that have 50 oz-in. of torque at 4.8V on the elevators. That should be plenty of torque for the individual elevators. The split flaps are larger though, so I'm going to use a 70 oz-in, non-digital servo on those...

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Old 10-27-2017, 07:12 AM
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Bob, what servo has 70 Oz in a mini. My flap servo mounts have a piece of plywood glued over the hole that make it a mini size?
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Old 10-27-2017, 09:39 AM
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Originally Posted by Saillfish View Post
Bob, what servo has 70 Oz in a mini. My flap servo mounts have a piece of plywood glued over the hole that make it a mini size?
Actually, mine do as well, but I'm going to modify that to take a standard-size servo. I'll probably use something like a Futaba S3010 on the flaps.

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Old 10-27-2017, 12:23 PM
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Originally Posted by Saillfish View Post
Bob, what servo has 70 Oz in a mini. My flap servo mounts have a piece of plywood glued over the hole that make it a mini size?
MKS 747 range from 12kg to 15 kg so around 140oz to 200oz torque depends on what voltage you will used
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