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-   -   Navaho Missile (http://www.Wattflyer.com/forums/showthread.php?t=73209)

JohnBoren 02-18-2014 06:02 AM

Navaho Missile
 
12 Attachment(s)
Just wanted to get a different opinion on what I am trying to do with this model, to see if Iím thinking correctly or not.

I designed and built this Navaho Missile that stands around 42Ē tall ready for take off, and yes it takes off under rocket power then the winged portion is powered by two small 27mm EDF units.

The model is for a National Scale Rocket Contest this summer. Instead of having the model glide back to the ground unguided, it will be RC controlled! To add realism in flight I thought I would add a couple of fan units to just help the model stay up an extra 15 seconds or so since this model doesnít have a lot of wing area.

So since the model will already be at altitude, about 400 feet up the fan units only have to provide thrust to keep the flight speed up so I can execute a couple of controlled turns and land back at the field. The model doesnít have to climb just have a controllable descent. Ready to fly back to the ground it should weigh about 16 oz.

Assuming I can get about 3 total ounces of thrust from both fans unit, should this be enough to extend my flight time?

The other issue that may make things a little harder on the fan unit is that the although I figure I have about .812 sq. inches on intake area for each fan unit, while the fan unit itself has about .742 sq. inches of swept fan area, the intake shape isnít optimized nor will there be any ducting.

One image shows the inside of the fuselage and the former where the two fan units will be mounted. As for exhaust exit area I've got tons, since the real Navaho used Ram Jets for power. I figured I would keep the duct exit diameter same as the fan shroud.

John Boren

CHELLIE 02-18-2014 06:31 AM

Neet project :ws: If You can fit 35mm EDF in there that should more than double your thrust, the flying wing has a nice flat lifting body on the bottom plus the wings, it should fly quite well, I would build a profile foam Chuck Glider model to get the cg correct and you might be able to take off with the rocket and edfs at the same time, elevons on the main wing should be all that you need, make them wide, 2 - 9 gram HXT servos should work well mounted flush in the fuselage, I Like it :D Take care and have fun, Chellie

with the 35mm edfs you will need to use a 20 amp esc each and at least a 2 cell 1000mah lipo 35C each. as they pull 20 amps WOT, you will also need to use a UBEC at least 3 amps so you dont go into a receiver brown out. edfs use a lot of Battery Juice

6 oz thrust each edf , OD. 37mm, total thrust 12 oz
http://www.hobbyking.com/hobbyking/s...Assembled.html

2.3 oz thrust each edf , OD. 29mm, total thrust 4.6 oz
http://www.hobbyking.com/hobbyking/s...assembled.html

dgjessing 02-18-2014 12:55 PM

Neat project indeed! I'm wondering if you wouldn't be better off just gliding down - would save a lot of weight (motors, escs (you need 2), battery). Still RC, but just a glider...

cyclops2 02-18-2014 01:21 PM

Definately a unpowered glider. Many ways to do the glide angle portion. A servo. Or a fully conceled small fishing weight on a simple servo pulley. The weight is right on the C O G point for takeoff. LONG servo arm to move the weight Foward or Backward to control decent angle in wind.

Rudder servo


Or use the 2 elevator flaps as elevons. Does both rudder & elevator controls with 2 servos.

Smallest RC gear will be more than enough to control glide.

Piece of cake. Enjoy the creating the RC controls.
What you need is probably in the indoor & micro section of this site.
Could possibly take everything from a micro sized RTF airplane. Cheaper & all the parts are sized with a battery & charger.

Enjoy.

cyclops2 02-18-2014 01:40 PM

EDIT
 
Large edit to control surfaces.

You can not have any loosenes in any pushrod holes or the hinges !!!
The maximum speeds may cause " Control surface flutter ".

That is why I offered the internal COG weight idea. You can also probably do turning with a servo that just has a weight on the end of a long servo arm. It would normally point straight to the rear on takeoff.

For glide turning it simply turns the weight left or right.

The use of internal solves all control surface problems. All the RC gear & servos with pullies & weights could be glued to a slide in & out inside motor tube. The sliding tube would allow you to use minimum weights to find the " sweet spot. Then tape the tube in for flight. & removal for charging.

Possibilities are endless.

Enjoy



Rocket motors ONLY !!!!! :)

Simple & light weight The sliding weight COULD be used to compensate for the loss of fuel weight. You have a fantastic project !! True design work.

Enjoy

JohnBoren 02-18-2014 02:48 PM

The model will have elevons for control. The torque tubes are already in the wings. I will use Micro Servos and a standard micro receiver for control. Total weight of radio is under and ounce. The fan units, ESC and battery add another 2.27 ounces. Airframe currently is 10.8 ounces, so by the time everything is installed and painted it's final weight should be around 16 ounces. My lack of a good air intake and area is why I didn't go with bigger fan units.

John Boren

rcers 02-18-2014 03:08 PM

I think it is brilliant! The fans should help a fair bit - the tiny wing is, well, tiny but the fuse will account for a good deal of lift too. They might even be able to maintain - not sure about that.

I think they will provide enough to slow the descent pretty significantly.

Let us know - construction looks brilliant too!

Mike

JetPlaneFlyer 02-18-2014 04:38 PM

What a fantastic and unusual project, outstanding workmanship too.

Those little AEO fans tend to have very opimitic thrust ratings. By the time you mount them in a duct and in the real world you will most likely find they are well short of the cleimed thrust. Even so I'm sure you will meet your objective of a controlled descent, the fans should at least help to stretch the glide.

I dont suppose you have any plans drawn up?

JohnBoren 02-18-2014 05:35 PM

Well, that's two responses so far that say I'll get out of these fan units what I was hoping for. Any comments on my air intake shape and how this may or may not effect the air getting to the fans?



Quote:

I dont suppose you have any plans drawn up?

I designed the model in Auto Cad but don't have a kit type of plans drawn since I didn't need them. Not sure If I will make plans available in the future or not but I first need to see if this thing even flies.

John Boren

CHELLIE 02-18-2014 06:49 PM

Quote:

Originally Posted by JohnBoren (Post 940294)
The model will have elevons for control. The torque tubes are already in the wings. I will use Micro Servos and a standard micro receiver for control. Total weight of radio is under and ounce. The fan units, ESC and battery add another 2.27 ounces. Airframe currently is 10.8 ounces, so by the time everything is installed and painted it's final weight should be around 16 ounces. My lack of a good air intake and area is why I didn't go with bigger fan units.

John Boren

Hi, You can make some air inlet slots on the Front Bottom of the fuselage to let air in, the fuselage is hollow, so any inconspicuous place to make slots or holes at will help the intake of air to the EDFs.

the small 27mm edfs may help a little, but i think all they will do is just make a lot of noise and add weight, edfs are not very efficient at all, another idea would be to add some rocket motors to the flying wing and have the transmitter ignite the rocket motors, that will give you some more glide and it will look more realistic, use 2 igniter’s per rocket motor to be on the safe side.

JohnBoren 02-18-2014 07:25 PM

Quote:

air inlet slots on the Front Bottom of the fuselage
I would loose more points for adding these then I will be getting by having the ducted fans, since they judge scale outline in this event. Using rocket motors would only give me 1.5 seconds of Lots of thrust and I don't need that for landing.

Quote:

just make a lot of noise
I can live with that if that's all I get

Here's a link to the build thread.
http://www.rocketryforum.com/showthr...l-Build-Navaho


John Boren

CHELLIE 02-18-2014 07:42 PM

Quote:

Originally Posted by JohnBoren (Post 940317)
I would loose more points for adding these then I will be getting by having the ducted fans, since they judge scale outline in this event. Using rocket motors would only give me 1.5 seconds of Lots of thrust and I don't need that for landing.


I can live with that if that's all I get

Here's a link to the build thread.
http://www.rocketryforum.com/showthr...l-Build-Navaho


John Boren

Yea, Judging and Points, That Makes things Difficult :ws: Good Luck To You with the Project, Please post some Maiden Video, Take Care, Chellie

kyleservicetech 02-18-2014 09:07 PM

Quote:

Originally Posted by JohnBoren (Post 940276)
[FONT=Calibri]Just wanted to get a different opinion on what I am trying to do with this model, to see if Iím thinking correctly or not.

Back in the mid 1980's there was a rocket launched sailplane that several friends flew. Word of caution, these rockets accelerate extremely fast. And, that makes the controls very sensitive during the time the rocket motor is putting out thrust.

My friends found out really quickly to not touch the transmitter during the time the rocket running. Doing so resulted in a very quick loop back toward the ground!

cyclops2 02-18-2014 10:12 PM

Glider
 
Send me a P M when you decide & again on the final maiden.

Great project. :)

Rich

JohnBoren 02-18-2014 10:57 PM

Quote:

Word of caution, these rockets accelerate extremely fast
I am very familiar with flying rocket power airplanes. Been flying them since the mid 1980's. I cam currently the Head of the Estes R&D Department, so rockets are kind of my thing, plus I've been designing building and crashing RC airplanes of all size for over 30 years. I know just enough about everything to make me just dangerous enough.

John Boren

CHELLIE 02-18-2014 11:08 PM

Quote:

Originally Posted by JohnBoren (Post 940357)
I am very familiar with flying rocket power airplanes. Been flying them since the mid 1980's. I cam currently the Head of the Estes R&D Department, so rockets are kind of my thing, plus I've been designing building and crashing RC airplanes of all size for over 30 years. I know just enough about everything to make me just dangerous enough.

John Boren

Thats Funny :D Me Too :ws: I have been into model rockets and Model planes for over 48 years, Thank my Father for getting me started at age 12 with a Cox PT-19, i flew rockets with my boys when they were small and I fly them with my Grand Kids now :ws: I use the cardboard tubes from econocote covering for the rocket body and balsa for the fins, Take care, Chellie

xmech2k 02-19-2014 01:35 AM

John, I'm afraid I can't help much with your project, but I just wanted to compliment your incredibly beautiful work on the model. I wish I had a fraction of your talent.

JohnBoren 02-19-2014 06:04 AM

5 Attachment(s)
Here's a question I know you guys can really help me out with. Since I've never had a twin electric before, at least not flying yet how do I hook up the speed controls to the receiver.

I have two brushless motors which means two speed controls. I am using only one battery to power both fan units. I will use a Y-harness for both speed control connectors to go into then this will go into the throttle channel of my reciever. I will also connect the single battery to both speed controls. Don't I have to remove a wire from one of the speed controls going to the reciever?

Attached are images of my other twin I designed about 9 years ago and finally built about three years ago. I'll need to set up the power system the same way as I am on the Navaho so you will be helping me out on two projects with your answer.



John Boren

xmech2k 02-19-2014 06:11 AM

Yes, if you're using getting rx power from the bec in the esc's, you'll have to remove the red wire (power from the bec) from one ESC. I guess there are issues if both are trying to supply power.

JetPlaneFlyer 02-19-2014 07:23 AM

Quote:

Originally Posted by JohnBoren (Post 940357)
I am very familiar with flying rocket power airplanes. Been flying them since the mid 1980's. I cam currently the Head of the Estes R&D Department, so rockets are kind of my thing, plus I've been designing building and crashing RC airplanes of all size for over 30 years. I know just enough about everything to make me just dangerous enough.

John Boren

John,

Did Estes ever consider developing a range of slow burning, low thrust long duration rockets, similar to what Dr Zigmund used to manufacture(and perhaps still does) in the Czech Republic?

I used to fly them a lot and if they were more readiliy available and perhaps available in higher rating better suited to RC use, they might be quite popular. They would be ideal for a project like your Navaho.

JetPlaneFlyer 02-19-2014 07:38 AM

Quote:

Originally Posted by xmech2k (Post 940400)
Yes, if you're using getting rx power from the bec in the esc's, you'll have to remove the red wire (power from the bec) from one ESC. I guess there are issues if both are trying to supply power.

If the ESC's have 'switching' type BEC's built in then yes, you need to disconnect the live (red) pin from the plug of one (not both) ESC's, otherwise the BEC's will interfere with each other.

On the other hand if the ESC's have linear BEC reculators then it's fine to leave both connected. As a general rule ESC's below 40A rated will usually be linear type. 40A and above switching is common, but there are many exceptions, so it's best to check and know for sure.

thepiper92 02-19-2014 08:38 AM

This is a very interesting build. I have looked into the idea of one esc running two motors and it is completely possible, as long as the motors are identical and they spin the same direction. I have an EDF that hasn't been flown, mainly due to the fact that I haven't really liked the fact that I need higher C batteries, and it is hard to fit batteries in the plane, but I actually connected the two EDF's in the plane to a single 80a car esc (I don't have a plane esc that big...yet). Both EDF's work fine when I ran it. With a design like this, with the EDF's only being used to take the missile down, it would certainly save a little bit of weight, plus take up less room.

http://www.youtube.com/watch?v=VhjqXcCncSk

fhhuber 02-19-2014 08:39 AM

Best bet is disconnect one ESC's red... or put diodes in both red wires to prevent backfeeding one BEC with the other.

***************

Attempts have been made to run 2 brushless with one ESC... you get one motor starting and the other just vibrating the prop more than half the time when you try to start the motors. If both start its fine. as long as the loads are even. But when the loads imbalance (yaw) you will have one motor trying to spin faster than the other and it can blow the timing and stop BOTH motors sometimes blowing the ESC.

Its just not reliable.

Works fine with brushed motors since they don't need timed power pulses.

thepiper92 02-19-2014 09:09 AM

Perhaps with this it will do fine though, as the edf's won't be used to flying around too much, but mainly landing, I would think anything to save weight would be good, but maybe not.

JetPlaneFlyer 02-19-2014 11:42 AM

It's a very bad idea to try to run two brushless motors from one ESC.. yes if both motors are identical it 'might work' most of tehe time, but then again it might very easily cause you to burn one motor and the ESC out.

Weight saving is not much because if you used one ESC it would have to have twice as high a current rating (and so close on twice the weight) compared to each of the twin ESC's..


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