Knief Racer - New Product & Build

[Wayne]

Starting work on a new toy:

Yeah, I'm bit of a sucker for orange planes. We will be adding these to the site once we get some flight time with these. I guess you could say they are a bit of a hit with the crew as half of them have already taken one home for their own. Always a good sign.

After playing with a bunch of numbers I'm going to outfit mine with a light weight setup. A DYS Fire 2600kv motor:

DYS Fire Motor

The FIRE series motors from DYS.Utilizing N54SH magnets and .1mm stator laminations, ISC Ball Bearings and 5mm hollow shaft, DYS has designed a motor that achieves smooth running and very respectable thrust numbers. More importantly, they fly really well.

alofthobbies.com

This is what I am looking at doing with it:

(I did not enter the aircraft weight for the calc above, so ignore the thrust to weight value.)

I might start of with the Emax Avon 2 bladed prop just to see what it does, they are an interesting prop, but not going to be as aggressive as the APC 6.5 pitch:

Avan Performance Propellers

Hmm,,, these look suspiciously like the excellent, most groovy, propellers from Racecraft; Oh yea,, thats because the Avans were designed by guru prop designer Sage Thayer who also designed for Racecraft as well as others. Sage designed the Avans to work

alofthobbies.com

Some KST X08 servos in the wings, and also for the elevator should do the trick.

I'm building up the glass version as this one had a little shipping damage to it. The guys all grabbed carbon versions, and the carbon does have a stiffer wing. I think the lighter weight of the glass version and the lightweight quad motor will be a good mix.

Wingspan is 1 meter. Looks like you could fit a 5S pack in there pretty easy, or do a custom 6S split back without much effort.

Hope to get some work in on it tonight.

 

[Wayne]

First some pics of the fuselage. She has lots of room for motor and battery: (battery shown is a 3S)

 

[Wayne]

Here is the gear I will be installing in this build.

And here is the hardware that comes with the kit:

You will see that I only use some of the above items in my build. I used the servo covers, motor mount and control horns. More on that later.

 

[Wayne]

I started with the motor mount. I needed to notch it with my dremel to allow my wires to pass. This is a result of me picking a somewhat odd motor for this plane. The blue tape marks the back of the firewall for me.

I would like to comment that I did not have to modify the outside diameter of the motor mount at all!! That has never happened before. It actually was a perfect fit from the factory!

Wires passing the motor mount.

After some test fitting:

Time to lock tight those motor screws - and be careful not to use too long a screw! You don't want your screw to go in and contact the motor windings. DYS supplies 3 different lengths, the shortest was perfect for this application.

I also added some bullet mounts to the motor wires.

Then I glued in the motor mount. I screwed up and ended up with a bit of down thrust on this one. Take your time and get it in right. I think zero degrees will work very nicely.

I just used a tiny drop or two of CA to lock the motor mount in place, and this is when I should have caught my down thrust issue... Then I used 5 minute epoxy. Yes, 5 minute. I like 5 minute here as it is a little more rubbery then the slower setting epoxy options. That and the motor mount presses in from inside the fuselage.

 

[Wayne]

OK - Onto the wing.

I used some fine file and cleaned up the saddle on the fuselage for a little better wing and tail fitting. Just sand down those flanges a bit in the wing area and you should have a very nice fit.

In the tail mount I cleaned up the flange on the lower surface, then sanded down the upper surface until the elevator would slip in nicely. I used a little blue masking tape to protect the paint on the elevator for this fitting. I ended up with a snug fit and a very square alignment without much effort. Sorry no pics..

Ok - Onto the wing servos. I only had X08N (no tabs) available for the build, so I did not use servo trays for the build. If I had some X08H, I would have used the supplied wood servo mounts. So first step is putting down some tape to protect the wing from damage.

It is interesting that the servo covers arrived already trimmed and fitting the pockets very nicely. Another nice little bonus.

Quick test fit of the servo:

And since this is a pretty tiny little plane I thought I would use Zbends for my linkages. I do this more and more on my fully molded airframes. They simply do not need adjustments if built right. In the background you can see the finished linkage:

Mark the length, put your other Zbend, trim and then double check. Fast and easy. I target the edge of the gap wiper on the flight surface. If all looks good, then mark where to cut into the aileron for the control horn:

I use a little diamond bit in my Dremel for this:

And I work in gradual passes double checking my depths as I go to avoid grinding through to the other side. I got it right on this one!

And after some test fitting of the hole we are ready for some glue:

Yeah, I bent one of the Zbends in the wrong direction.. Seems like I always screw this up..

Again I used 5 minute epoxy to set them in place.

 

[Wayne]

OK - Almost done. Time for the tail.

Do a little test fitting and make sure you have enough up and down travel. I sanded on the vertical fin to allow a little more up travel of the elevator. I wasn't sure it was going to be needed, but it was a lot easier to do now before the tail is glued on.

Before you go any further, I'm going to point out a little issue I ran into with my build. The elevator control horn was hitting the rear of the fuselage when down elevator was needed. It is a GREAT idea to trim this now while you have easy access!

So here is my simple elevator linkage setup. I used the supplied carbon pushrod and some wire I had in my collection, again just Zbends at the ends. In this photo I only have things pushed together, I put a slight curve on the wire ends where they go into the pushrods to create a friction fit. (In all honesty, I have not glued these connections yet, and the plane has flown. they offer enough bite to allow this, but I can fine tune the length if needed. Being a race plane, I will drop some glue in here soon.)

I like Zbends for a number of reasons, but one of the best things is that you can simply apply a drip of thin CA to the Zbend and let it cure, then simply break the connection free with some movement and the end result is a perfectly tight connection with no play.

After some debating of what I should do next, I opted to glue on the tail, and add the control horn after that. This worked out well, but I did all of my test fitting first.

Onto the gluing, I used some dots of CA to spot glue the elevator to the fuselage and then bolted the wing on and made sure everything was right and square. I put down some tape to avoid making my typical epoxy mess:

And then it was time to smear some epoxy, again I used 5 minute.

Then lifted the tape for a cleaner edge:

Yeah, I still had some mess.. Did I mention this was a quick build?

At this point I must have kicked into high gear as I failed to take any more photos. But I ground out a little hole for the elevator control horn just like I did for the ailerons and then slipped the servo and control horn assembly into the fuselage from the wing opening and glued the horn in place with a little 5 minute epoxy. Theis is about the time I noticed my little clearance issue with the horn and the back of the fuselage. My bad. Anyhow, pretty easy fix with the dremel. And the end result is something like this:

All three servos are glued in with a very small dab of 5 minute epoxy while the servos have all been programmed in the radio and are resting at their center positions. The elevator servo is placed towards the rear of the wing opening and is glued to the side of the fuselage.

 

[Wayne]

At this point the plane is basically done. I just taped on the servo covers and checked where my battery needed to go for my rough best guess at what the CG will be. (This is the first of these planes I have seen built.) I will report my CG findings once I get a few more flight on the plane. For maiden flights I used a simple 3S 1300 and I had this up against the back of the firewall. I just stuffed a paper towel in behind the battery to lock it into place. Needless to say you can use a much heavier motor should you like. LOL

I had rushed my setup and flew it for the first time when visiting another field for the first time. What could go wrong? We had been taking people of for their first flights (what a blast!) and after that I decided it was time for my own first flight. I rushed through the final setup of the plane, it all seemed close enough to be good. So we powered it up and tossed it out at about 1/2 throttle. Even on 3S this little motor screams. After getting thrown out at about a 30 degree up angle, the prop pulled her down towards the ground pretty quick.. Thanks downthrust! A little elevator correction and she flew out and I upped the throttle to 3/4 or so. She felt good!

I flew her around some and all seemed to be good so might as well go full throttle. No issues, she had good speed and didn't do anything bad. I was using a lot of aileron and a lot of elevator.. Oh yeah, I was on low rates. After a few more passes a a very slow roll I landed her for a little tuning. Brought her in low and slow and she touched down about 2 feet before my planned landing spot. Not bad. I kept very low throttle until just before touchdown for extra drag. Like all pylon planes, she likes a shallow and long landing pass.

A little ground checking and I confirm my mid rates will be OK, no clearance issues. (I had not checked my outputs and total throws yet... A big no-no.) Ok - Lets toss her up into the air again. Launch was about the same, but now I had better elevator authority and a better roll rate. She is fun, and she is quick. I tried some low power stall turns to both sides and nothing, she just behaves. Basically did everything I asked of her and didn't try to bite me. I was very pleased. Before long it was time to land, and this landing is much better. I did use full elevator at one point, but again, I do not have a lot of travel, and the CG is not dialed in yet. She flared nice and set down easy. Very nice.

So now I need to dial things in a bit and figure out the CG and the throws I like for the plane. The kit quality and ease of build were very nice. My plane is a light weight example using a Quad motor and a fiberglass layup. They are also available in a carbon layup. We do have stock on these now, but they are not up on our site just yet as we do like to have the numbers ready for folks. We have some low quality video from the maiden flight we will see about adding here..

Once I have the throws and CG dialed in I can take her up with a 4S battery and really see what she can do. With the current 3S I would guess we only had 75mph of ground speed, but others there thought it was 100. I think with the 4S on this motor we will be around 100mph. Not super fast for this sort of plane, but not at all bad for the low cost power setup, and honestly for me, about what my eyes can handle for such a small plane. (Small planes always look a lot faster than they are.)

Thanks for following along.

 

[Diceman]

Awesome plane! I am itchin to get into these planes and I am sure Matt will as well. We like to race around with fast planes. Count me in for one. Orange of course.

 

[Wayne]

Any progress on yours?

 

[Doc J]

Wow! What a great building sequence, Wayne.

Outstanding.

Doc.

 

[Wayne]

Odd- I just ran my numbers for this motor again to confirm some things and I am not getting the same results from the calculator. I now show higher watts a lower speed. As far as I can tell all the parameters are the same. Odd.

 

[Wayne]

Been having a blast with my Knief Racer. This little 1 meter plane is a delight! She is FAST, clean and has no bad habits at all.

I started off with the Quad motor out front but this created an issue with the CG, just too light and had to get the battery all the way up in the nose. This powered the plane fine, but battery was limited to 3S way up in the nose like that, and honestly wanted a cleaner look.

This weekend switched over to an E-flight BL-15 we had kicking around, and with an APC 4.75 x 5.5 prop and a simple 3S battery she was ripping up the sky. Using the FrSky Neuron 60 amp ESC you get all kinds of great telemetry. Starting to like this little ESC alot. Here is the results of a full throttle static test in my kitchen while my wife was trying to sleep. LOL Battery is partially discharged. Amp load drops in flight. (at the field with a full battery we saw 72 or so amps on a quick static test pull, this is about 20 more amps than ecalc predicted.)

Take off is maybe 1/3 throttle. The plane flies super well. I'll have to measure the CG I am at as I have been eyeballing it to this point. I'll say we are currently slightly ahead of the wing bolts. No trim needed, but under full throttle she does climb as I did a crap job of mounting the motor mount. I was in a hurry on my build, I would have liked to have had no thrust angles on this plane, but looks like I ended up with some wonky angles, that is my mistake, not the planes. I think I have 2 degrees of up. I'll have to fix that before I put in a big motor. Maybe just shim it for now.

I added a couple of cooling holes for the motor and a couple in the rear of the plane. I don't know that they were needed as everything stays cool in flight, with the battery giving out a bit of heat. Voltage sag at full throttle is a thing with the 75C battery, but that keeps my 60 amp ESC in the happy range. Honestly I find myself flying this like a slope glider - When it slows down I blip the throttle to maybe 50%, and that gives me enough energy to glide around do big aerobatics at maybe 75 mph, and will glide pretty far up into vertical climbs, wing over and drop down for a speed pass and a quick roll. Maybe blip the throttle again and do a huge loop. Every now and then a full throttle pass for the bystanders. She is FUN!!

I passed the plane off to 2 other pilots. That is how easy she is to fly. I was totally comfortable doing this. Pretty sure one of these pilots has only flown foam and or wood electrics. He had no issues. A lot of pylon planes are very twitchy, but not this one. For a tiny 1 meter plane she feels big and easy. But don't let her get beyond your sight limits, she is small and SKINNY.

We will have some very nice aluminum spinners in the near future and I'll finish her off with one. That should pick up the efficiency nicely. I really wish I could put a folding prop on here at this power level. (We are looking at getting some all carbon folding blades made for speed ships!)

This motor worked out really well, and for the price of FREE it is really hard to argue with. I'd say the speed was around 100 mph, maybe a bit more. Layout in the plane works well and the 3S 1800 75C battery is happy and the back of the battery is even with the wing bolts. So plenty of CG to support a heavier motor, and you can stuff a lot more battery into this plane. For now I really like the 3S setup on this motor. I'll stay with this for a while and dial in the CG and my throws, to get the most from the airframe. Later, I'll remotor to an HET on 4S as the BL-15 has too much KV for any more voltage, I think a 4S on it basically buys me 3 mph more. Funny thing is this would be a really fun plane even on 2S battery. She needs almost no power just to fly around and have a bunch of fun. I might give that a go just for fun. Something like a 2S 2600 and fly for half an hour or more. Our flight with the 1800 was something like 9 minutes.

Love this little plane!

Will talk to TJI about making up a glider fuselage for this wing. She would be a great slope ship! She carries energy really well.

 

[Konrad]

Glad to hear that the BL-15 is working out.

As to the problem of the emulation programs it is not uncommon for such errors at high rpm. This has to do with the problem with the simple modeling the prop and airflow. Any errors in modeling the prop grows as a function of rpm, as the ability of a prop to absorb power is a cubic function of RPM. This means that the values at high rpm, in the emulation programs should not be taken too literally.

I use these emulation programs as a comparative tool to test different configuration. Actual values are to be measured prior to flight.

If moving to a lower KV motors be aware that the higher resistance in the copper windings will result in more heat when moving over to the HET motors of close to the same weight.

All the best,
Konrad

 

[Wayne]

Yeah, when you are working towards top speeds over 100mph it seems the calcs can get complex very fast. But like you said, the calcs are very useful in comparing and helping with the basic setup and then experimenting from there. With the telemetry from this ESC I should be able to fine tune things nicely. I need to dig into the data it logged for the flights on Saturday. I'm a little too close to the limits of my ESC to be comfortable. OK - over the limits.

The lower KV will allow for higher voltage and a much wider prop selection. Between all of the APC, Quad and Speed Props, should be able to find something that will do the trick. Might have to have to come out to the field and give feedback. But with that said, I am super happy with the power now. I am serious about maybe just flying it on 2S.

I forget if I mentioned above, but I failed to fully kill the throttle on a couple of occasions. I had maybe 2 clicks of throttle. I only discovered this as my speed maintained well enough that I could not figure out why it was not bleeding down to the point I needed to give it more electrons. LOL So one or two clicks of throttle was probably giving me 50mph on the flat..? Might be interesting to see how long a flight I can get out of this 1800 pack. I'd guess it would fly a long longer than I could show self control not to blip the throttle. LOL I'd have to check, but I recall it was around a 1/4 amp draw at minimum throttle, that includes the draw for the servos and receiver.

 

[SC_Pilot]

I have a power set up from a 200mph funjet I built. 6cell 2650mah, 1900kv motor, 200amp Esc. It’s just too heavy to launch consistently due to a violent roll on take-off from the stubby wings, motor torque, and slow airspeed. The times I have been able to launch it, it hauls butt! 185mph I got.

Anyways, I‘ve been looking for a replacement airframe and was wondering what the diameter of that nose firewall plate was? If it’s 36mm in diameter or larger, I can fit that inrunner in there (36mm x 74mm). Also looks like there’s enough room in there for 2 3cells laid front to back...

~ Jacob

 

[Wayne]

Depending on the layout you could probably get an 8S battery in this plane. You would need the ESC right behind the motor, and 4 cells forward and 4 backward. I think we fit a 6S pack in there during testing..?

Anyhow, The nose ID is about 35mm. It opens up some, so maybe the 36mm could fit in there, but you may need to trim the nose back a little. It would be VERY tight. I'd be willing to bet this motor would give very impressive results:

Typhoon EDF 1W-40 28mm dia. 3300kv

High End Technologies (HET) offers the Typhoon line of inrunner brushless motors for EDF units or high speed pylon racers! These affordable, well made, efficient and powerful motors will be a fine powerplant for your latest project.For EDF jets/Pylon planes weighing up to 1600 grams...

alofthobbies.com

The motor can handle up to 140 amps for 15 seconds. With a 6S battery and a 4.75x5x5 blade she should be around 137 amps. For speed, I do not know, but should be substantial. Now fitting that motor and the big speed control will be a challenge. I would suggest creeping up on the setup and starting off with a smaller battery, and lower pitch prop once you jump to 6S. Same prop on 4S will draw around 75 amps.

Currently that is probably the most insane combo we can offer.

p.s. We have more speed props coming in from Germany. We have been going prop crazy lately. I think we will offer more top quality props for electrics than anyone else. We will be blowing out the quad props to make room for them all. I think we have over 500 top quality props now. APC, Aeronaut and Schulze. Will be getting into the exotics too. Lots of new spinners in the works too.

 

[SC_Pilot]

Depending on the layout you could probably get an 8S battery in this plane. You would need the ESC right behind the motor, and 4 cells forward and 4 backward. I think we fit a 6S pack in there during testing..?

Anyhow, The nose ID is about 35mm. It opens up some, so maybe the 36mm could fit in there, but you may need to trim the nose back a little. It would be VERY tight. I'd be willing to bet this motor would give very impressive results:

Typhoon EDF 1W-40 28mm dia. 3300kv

High End Technologies (HET) offers the Typhoon line of inrunner brushless motors for EDF units or high speed pylon racers! These affordable, well made, efficient and powerful motors will be a fine powerplant for your latest project.For EDF jets/Pylon planes weighing up to 1600 grams...

alofthobbies.com

The motor can handle up to 140 amps for 15 seconds. With a 6S battery and a 4.75x5x5 blade she should be around 137 amps. For speed, I do not know, but should be substantial. Now fitting that motor and the big speed control will be a challenge. I would suggest creeping up on the setup and starting off with a smaller battery, and lower pitch prop once you jump to 6S. Same prop on 4S will draw around 75 amps.

Currently that is probably the most insane combo we can offer.

p.s. We have more speed props coming in from Germany. We have been going prop crazy lately. I think we will offer more top quality props for electrics than anyone else. We will be blowing out the quad props to make room for them all. I think we have over 500 top quality props now. APC, Aeronaut and Schulze. Will be getting into the exotics too. Lots of new spinners in the works too.

Thank you for the measurements. I’ve been thumbing through different hot liners over the years and they all say 28mm diameter for motor req’s. This one looked to be bigger. I’ll have to check out the prop selection. I know I went through a lot of props trying to launch that funjet. I think I broke more number of props than I did on successfu flights. ?

 

[Wayne]

Yeah, I busted one on my last flight. The joys of a non folding prop and no landing gear.

 

[Konrad]

Hum, you guys are able to extent the life* of a prop by allowing it to fold? At these small scales I like the folding prop as it saves the fuselage (Firewall and maybe tail boom). As to the prop I've found that I need to replace the folder just as often as the fixed bladed prop when landing without an undercarriage.

* Ok, I can get about 50% more life as I'm often able to make up a set of prop blades from the undamaged blade from the two used sets.

 

[Wayne]

Yeah, I have only busted one prop, it was some cheap plastic thing from one of those bad hobby places overseas. It snapped the blade near the hub under power. Managed to land it after the motor and firewall ripped out of the plane!

I have been flying folding props for decades and that is the only folder I have killed. Ideally you are landing with low energy and the blades are folded back.

I'm not a thermal guy that does the spot landings for scores. I can see that taking a toll on blades!