Delta Star Rocket Plane

Excellent! Will be watching to see your progression.

Before fiberglassing the airframe, I put a tiny blob of plasticine clay in the two rail button Tnuts to keep epoxy out. After completing the airframe, I cut the FG skin off these spots.

Painted a big red triangle on the bottom to assist in visually determining orientation during flight.

Then fished out plasticine from rail button holes, put in a drop of epoxy to keep screws from rotating, and installed rail buttons.

Left just enough slack on screws to allow rail buttons to rotate freely for durability and minimal launch rail resistance.

Installed the CA hinges that came with kit, then added clear packing tape to further form elevon hinges.

Installed servos, linkages and horns. Temporarily installed receiver and battery.

Spent a fun couple hours playing with RC settings.

For RC setup:

As suggested in kit instructions have both dual rates and exponential set up.

Question: For delta wing elevons, what mix of elevator to aileron do fliers suggest?

Kit instructions call for each to be 50%, but some online references suggest more like elevator:aileron on the order of 4:1.

delta22 said:

Question: For delta wing elevons, what mix of elevator to aileron do fliers suggest?

Click to expand...

What transmitter did you end up getting? [Never mind, I see you went with the Hitec.]

For my Spektrum DX7, I didn't touch the default elevon mixing, I adjusted the travel on the aileron channel to get less roll sensitivity.

I use between 50% and 75% aileron and 100% elevator...I normally don't use exponential, however I'm pretty light on the sticks and run a lot of throw and don't have a problem tuning my thumbs to a sensitive control setting, if you are heavy handed then expo can help a lot. Maybe start with 50% aileron and have 75% on dual rate if you have it. I usually am more worried that I have enough elevator for post boost trim than for a sluggish roll rate.

Anyone else feel free to chime in with their experience.

Frank

delta22 said:

For RC setup:

As suggested in kit instructions have both dual rates and exponential set up.

Question: For delta wing elevons, what mix of elevator to aileron do fliers suggest?

Kit instructions call for each to be 50%, but some online references suggest more like elevator:aileron on the order of 4:1.

Click to expand...

Hi Boris,

I'll be interested in watching this fly.

I'm curious as to what effect the extra weight of fully sheeting the wing and fiberglassing will have on flight performance.

Back when I was into R/C airplanes, the ongoing debate in the club was whether to build light for "flyablity" or build strong for "survivablity".

It seemed when there was a hard crash, it didn't matter which way it was built.. The stronger and heavier plane just hit with more force and suffered similar damage as the lighter plane.

It was in normal every day flying that if built too light, it couldn't survive a hard landing without breaking something or if built too stong and heavy, performance suffered.

The extra balsa sheeting and fiberglass added about 7-8 oz. Stock delta Star is about 24 oz.

Stall speed is proportional to the square root of the weight. So glide speed will be about 20% faster than a stock build.

The thin shell of glass has greatly strengthened the airframe. It will not be immune from crashes, but will hold up much better in transport and handling on the ground.

As far as flying, I too am very eager to see this bird fly. I have flown a few slow RC planes and a computer sim. Had this kit for a couple years, flew it 1000 times in my imagination.

Will have a lot of motors ready for Saturday and fly very cautiously near the ground.

Plan to check trim, get a feel for control sensitivity and practice controlled landing maneuvers while I still have altitude for the first several flights.

Finalizing electronics and trim.

Went with:
50% dual rates
50% exponential at both rates
50% aileron
100% elevator

Thanks Frank and others for input.

Had a couple batteries to choose from. Ended up using a 6.4V LiFe 1300 mah battery as that provided lots of power and the perfect amount of nose weight. Had to replace connector.

Placed battery into nose of rocket and stuffed small pieces of foam rubber to lock it behind internal ribs.

Also pictured is mini wiring harness:
- connector top left connects to battery
- left screw switch is RC power
- right screw switch is power for RC solid state relay
- bottom left connector is receiver connection to relay
- middle bottom connector is power to receiver
- wires top right connect to ematches for 2nd and 3rd stage motors

Ground tested this twice and verified that this will fire two Rocketflite MF ematches.

Epoxying screw switches in place.

Yellow box encloses solid state relay:

https://servocity.com/html/electronic_pwm_switch__dual_.html

which fires one channel when unused rudder stick is pushed left and the other when pushed right.

Programmed transmitter to only activate these when dual rate switch is set for additional safety.

In second pic, ematch leads are seen top right and battery connection top left.

Third pic shows electronics secured in place with tie wraps.
- yellow box is two channel solid state relay
- small white box on right is a buzzer I added to one of the ematch channels in case glider is ever lost in tall grass
- black under all this is Hitec 6ch 2.4Ghz receiver

Glider as it will fly.

The two screw switches can be seen on the side in the middle.

With all electronics mounted glider weight is now 30.7 oz.

Looking forward to Saturday.

Boris, looks good, what motors are you going to use?

BTW, besides the dr switch, you can also use some expo on the rudder so that even if you bump it a bit it won't trigger the switch till you give full deflection. I used that for a bomb drop mechanism and it worked well to prevent glitches.

I just flew my Interceptor at 24 oz rtf on a G-12, pretty slow boost, I'd think at 30 oz you might want something with a bit more push..

Frank

Primary motor: G64 or G80

The stiff, rigid airframe and strong elevon hinges should not have a problem with the estimated 165mph peak launch speed - straight up. This will allow me to use common, low cost G motors and standard rail setup.

If all goes well on the first few flights, 2nd/3rd stage: D11 or D12

At an HP launch would use E9 for 2/3 stage. Can't Saturday as total propellant mass would be too high.

2nd/3rd stage relay switch triggers at about 80% deflection, so sensitivity is perfect for this application. Set the lower dual rate that I would have set for liftoff to 0% for this channel for safety during launch prep at the pad. Confirmed that rudder stick will not trigger relay at all at this setting. Also confirmed that powering up, or loss of Tx signal also will not trigger ematches.

After main motor boost is done, flipping elevator dual rate enables rudder stick's ability to fire one ematch at 80% right and the other at 80% left. One side does double duty and also activates buzzer.

Boris, sounds good. A G-40 may be good as well, that got my X-15 at 37 ounces rtf up pretty well, but wasn't so fast that I couldn't steer it on the way up if needed. Hope you get some video.

Frank

delta22 said:

Primary motor: G64 or G80

The stiff, rigid airframe and strong elevon hinges should not have a problem with the estimated 165mph peak launch speed - straight up. This will allow me to use common, low cost G motors and standard rail setup.

If all goes well on the first few flights, 2nd/3rd stage: D11 or D12

At an HP launch would use E9 for 2/3 stage. Can't Saturday as total propellant mass would be too high.

2nd/3rd stage relay switch triggers at about 80% deflection, so sensitivity is perfect for this application. Set the lower dual rate that I would have set for liftoff to 0% for this channel for safety during launch prep at the pad. Confirmed that rudder stick will not trigger relay at all at this setting. Also confirmed that powering up, or loss of Tx signal also will not trigger ematches.

After main motor boost is done, flipping elevator dual rate enables rudder stick's ability to fire one ematch at 80% right and the other at 80% left. One side does double duty and also activates buzzer.

Click to expand...

This project is now officially named the Demon Star.

The Demon Star flew twice on Saturday, 1/14/12, at the CMASS Acton, MA launch.

Flight conditions were harsh, with temperatures in the twenties and wind in the teens.

Pic 1 - me with the rocket

Pic 2 - with Howard and Don setting up at the pad

Both flights went up on G64 power. Liftoff weight was 2.3 lbs and the first 200 ft or so was fast and straight.

As the rocket continued to about 400 ft, RC control was a wrestling match with the wind.

Both flights landed upside down. Due to fiberglass shell on airframe, damage was very slight.

Pictures thanks to Abel Grace.
pic 1 and 2 - first flight
pic 3 and 4 - second flight

Video thanks to Howard Greenblatt: https://youtu.be/N6goktp9Wuw

It was bone chilling cold.

Wind chill was about 0 F all day.

Only damage was slight scratches on the nose and a slight mashing of the top of the vertical stabilizers.

These turned out to be the landing surfaces for the first two flights.

Plan to repair these with epoxy and lay a strip of basswood or fiberglass on the top edge of the vertical stabilizers.

Boris, it looks very twitchy, maybe throws are too high and cg a bit far aft, it looks like you never were really able to get it trimmed and gliding in a known attitude...Just based on the video. Maybe a G-40 or G-33 would give a slower boost. Even in glide it looked like it was really twitchy, more in roll but also in pitch.

I'd say you were doing pretty well to get it to land inverted flat...

Is that what you felt?

Frank

Question concerning apparent RC problem:

Setup:
ground: Hitec Optic 6ch 2.4 Ghz transmitter

plane: Hitec 6ch 2.4 Ghz receiver
6.4V LiFe 1200 mAh battery
Hitec HS-82mg servos
screw switch

What worked: repeated ground tests
test at the field at 100+ ft
control throughout first flight and first 2/3 of second flight

Problem: For the last 20 seconds of the second flight there seemed to be a loss of RC control. During that time the plane did a helix spiral dive to the ground.

When I got to the plane the transmitter was in control of the elevons.

There is no visible damage to any part of the elevons, linkage, servos, battery, switch or wiring.

The receiver is set up to set elevons to a flat glide in one second if transmitter signal is lost.

It was as if the plane lost power for 20+ seconds.

I was not able to replicate the problem on the ground. All wiring is tie wrapped in place and no poking at the wiring or connectors was able to induce a loss of power. The screw switch is behaving well and all connectors are very snug.

> Any suggestions?

burkefj said:

Boris, it looks very twitchy, maybe throws are too high and cg a bit far aft, it looks like you never were really able to get it trimmed and gliding in a known attitude...Just based on the video. Maybe a G-40 or G-33 would give a slower boost. Even in glide it looked like it was really twitchy, more in roll but also in pitch.

I'd say you were doing pretty well to get it to land inverted flat...

Is that what you felt?

Frank

Click to expand...

Yes, twitchy and totally hammered by the wind.

The fast S it did at the end of the burn happened before I touched the transmitter control stick.

Half the turning and rolling was driven by the wind and the other half was me responding.

The Delta star kit instructions specify a balance point, with no motor loaded, of 13.75" from the back of the rocket. For a 36.5" long rocket that = 22.75" from the front.

The Demon Star balanced out at 1/2" in front of that. The airframe is about 12 oz heavier than the kit and the motor mount 2" forward.

I figured I was being conservative and it would be slightly overstable as a rocket and nose heavy as a glider.

After the flights I checked to confirm that the fairly heavy battery (2.6 oz) in the nose had not shifted position back in the rocket as the glider felt unstable. The battery had not moved out of position and the balance point is still 1/2" in front of kit spec.

In addition to balance, would the flat surfaces on the front of the glider and thick airfoil of the wing also make it more vulnerable to the effects of the wind?

delta22 said:

In addition to balance, would the flat surfaces on the front of the glider and thick airfoil of the wing also make it more vulnerable to the effects of the wind?

Click to expand...

From the point of view of the plane in flight in a steady wind, there is no wind, just the ground inexplicably moving. If the model is moving through wind shear and turbulence it's a different story, but it's still governed by Cp and Cg. So short answer is no.

Boris, don't think the flat surfaces would make it more twitchy or sensitive to the wind, it would give more lifting surface forward, but that is part of their design so should be incorporated into their CG spec.

However I find it strange that they spec a CG with no motor, as the motor choice makes a big difference in the CG. I'd expect a CG with motor specified. It's hard to know if the CG is ok or not without knowing what motors they recommend. If you are using one of their recommended motors then using the no-motor CG should be ok.

You are running a straight 6.4v input with plenty of capacity even under a heavy flight load on the servos, a brownout seems unlikely, seems more likely that it lost power to the rx...I'm not familiar with the screw switches so I don't know if those might be an issue or not, I always just plug in my battery to the BEC or rx directly.

If you had just lost xmitter link it should have gone into the default trim setting...

I watched the mfg video again, and even their vid it seems a bit twitchy on boost.

I think you can tame down the throws quite a bit, use a slower boost, and as for loosing link or power, maybe try getting rid of the screw switch. The hitec receiver has an led to indicate if it looses link with the xmitter, was it flashing? You can do a test, turn off the xmitter and then back on and it should start blinking the number of times that happens...spektrums now do the same thing...won't help it from happening, but would help you debug if that was the issue.

Sorry I can't help more.

of course you know that batteries don't do well if they get cold(below 40F).

Thank you for the input gentlemen.

Rex R said:

of course you know that batteries don't do well if they get cold(below 40F).

Click to expand...

The battery has a lot of excess power capacity. However the servos were very active fighting a losing battle with the wind and this was at the end of the second flight. The servos were responding when I got to the rocket, but I was not activating them continuously as they were during flight.

As all mechanical and electrical parts seem to be in good working order, a cold battery temporarily browned out is distinct possibility.

I will try replicating this problem on the ground when temperatures are again in the twenties.

"When you eliminate the impossible, then whatever is left, no matter how improbable, must be the truth."

I would suggest recharging the pack after every flight. this would, ensure max run time, and let you know how much power an average flight needs. it has been a while...think I used to figure about 1 amp per servo.

delta22 said:

Thank you for the input gentlemen.

However the servos were very active fighting a losing battle with the wind and this was at the end of the second flight.

Click to expand...

With all respect I am not sure what you mean by servos "fighting the wind". Unless these are some sort of sub scale servos, any normal servo will not be blown back by the wind and unless there were tremendous gusts, once the rocket is gliding the wind really makes no difference to the control in the air, just to the ground speed.

Also, I am not sure how you land upside down so I take it the plane was out of control when it hit the ground? If so, my guess is that you have a control issue related to CG and/or probabaly too much throw, particularly in roll. These delta designs are sensitive in roll and they can fool you into thinking you have no control when they are gyrating on too much throw.

Talk to the designer and get him to tell you the CG range for boost and glide and then check it with whatever motor you are using, I agree with the others they should not spec a no motor CG. He is very responsive on email.

And no matter what you do, the boost stability versus low speed handling (and landing speed) will be a trade off with these rear motor designs.

I might suggest going to a low impulse motor to get the trims right and then move up the impulse curve.

Good luck!

Mr. Matt,

I was being somewhat creative with wording. You are quite right, these servos put the elevons wherever I point the control stick. I was fighting the loosing battle with the wind and continuously activating the servos during the flight in the process.

Did not intend to land upside down twice, control was very marginal throughout both flights.

Agree with the suggestions that CG needs to move forward.

Found a higher capacity LiFe battery that will:
> add more power reserve
> add nose weight
> fit in the nose

https://www.batteryspace.com/lifepo418650battery64v1350mahlong864wh4aratewithpcbandpolyswitch.aspx