39 replies to this topic

[Zinginex]

Hey everyone. Sorry I haven't replied. I've been away last week. Those two ideas for launching the gliders are really good and it was no problem for starting this thread . I didn't actually change the thread's name. One of the mods probably did. That must've been funny StevenRS. I will try some practical tests soon.

[pyromaniac303]

Sorry to bring up an old topic, I've just finished work on a small balsa glider with a 6mm ID end burner motor. The back of the plane, from around the centre of gravity to the tail has been brushed with a heavy coating of sodium silicate solution to hopefully fireproof it.

The motor retainer is a 3/8" ID tube, with a cap at one end to keep the motor securely fixed to the plane. At the moment this is attached to the plane with tape, although i plan to glue it if this flies well.

Motor specifications:
6mm ID, 2mm clay choke

fuel:
70:30 KNO3 : dextrose monohydrate, both finely ground, then also +20% willow meal powder to increase the burn rate.

Approx 1g of fuel fills the 1/4" x 2" motor casing, with 5mm extra clay rammed at the top end of the motor to seal it off.

The plane its self is from a BMFA kit, called a 'Nipper', originally designed to just be thrown, I thought it looked ideal for conversion to rocket power. The wing span is 30cm, with about 5 degrees dihedral to keep it stable. I chose not to add trim tabs for now, and see how it flies straight into wind.

Heres a photo:

Edited by pyromaniac303, 24 March 2008 - 05:28 PM.

[pyromaniac303]

Just tested it and it seems a bit underpowered and landed on the ground about 10s after firing, the burn time was good though, at least 20seconds. In the next test I'm going to reduce the oxidiser to fuel ratio of the KNO3:Dextrose mix, and add slightly more BP to speed up the burn rate and reduce the molten KNO3 formation around the nozzle.

I may also roll the casing with a bit of sodium silicate solition in the first few turns, as it was extremely weak and broke up during removal from the motor retainer.

[Zinginex]

Just tested it and it seems a bit underpowered and landed on the ground about 10s after firing, the burn time was good though, at least 20seconds. In the next test I'm going to reduce the oxidiser to fuel ratio of the KNO3:Dextrose mix, and add slightly more BP to speed up the burn rate and reduce the molten KNO3 formation around the nozzle.

I may also roll the casing with a bit of sodium silicate solition in the first few turns, as it was extremely weak and broke up during removal from the motor retainer.

Veery nice glider i would try one soon but I have a small garden lol
but that sounds very hopeful
Nice work

[pyromaniac303]

Here is an update on the rocket gliders...

I have just finished off 5 motors, as a drop in replacement for the Rapier motor system, and will test them tommorow night at the British Model Flying Association Nationals, free flight event.

Motor specs are as follows:

Length 65 mm
ID 7.5 mm
OD 14.2mm
Nozzle 2.2 mm
Nozzle clay depth 5mm
Fuel (low power) 60/40 KNO3/sucrose
Fuel (high power) as above with +5% fast willow meal powder

I built up 3 of the low power, one high power and one low to high power (changes half way through burn time).

Will see how it goes tommorow, and compare them to some of the commercial motors. On ground tests they seem to perform well, and the excessively thick walled tubes ensure the outside stays cool enough to touch even after a 20 second burn.

If the weather stays good, I may get my camera out and film a flight.

Edited by pyromaniac303, 23 August 2008 - 07:55 PM.

[icarus]

one problem with KNO3 and sugar rockets is they are very quick to absorb water i,m experimenting using wax instead of vaseline to moderate the burn speed ,it makes a superb solid pellet when pressed. the fuel doesnt absorb water as quickly, and a big bonus is a dense white smoke trail

[minalth]

Just in case you haven't done anything about it, if you just added the rocket on, it would be very nose heavy. If this is the case, it might account for the short flight/long burn time discrepancy.
I'm not trying to be patronising, I've just seen people miss very obvious things before
-Minalth

[pyromaniac303]

Oh thats one thing I forgot to mention, that was an early testing plane. The specifications of the new planes are 2ft wing span, approx 18" long, 4" wing width. The motor being mounted in line with the wing, along the centre of gravity.

Needless to say, they were hopelessly under powered in comparison to the commercial motors, and I am planning on experimenting with adding red iron oxide to increase the burn rate. If the red iron oxide proves successful I may completely abandon the additional meal powder, as this creates more of a spark hazard when hand launching.

I didn't have problems with moisture, as the completed motors were stored in a bag with dessicant packs immediately after I made them, then only removed minutes before they were used.

One thing I did pick up on the trade stands, I had a conversation about fireproofing agents for tubes. I was thinking along the lines of phenolic resin or other high temperature resistant products. I am going to try Aerokote from Deluxe materials, which gives a gloss finish, is chemical resistant and comes as a 2 part set (product and catalyst). Primarily it is used as a fuel proofer, but it seems to fit the description of what I was after. Whilst talking to the owner of the trade stand, he also showed me an instant card glue, which sets within a couple of seconds. Could be useful when rolling tubes using excessively thick card, to glue edges down.

[psiborg]

sorry, this is a bit off topic, but reading this thread reminded me of a tale from my uncle's childhood. He once built a model plane, of the balsa and tissue variety. Unfortunately, during construction, one of the wings became slightly warped, and the plane never flew straight. Eventually, he became fed up with the model, to such an extent that he placed one firecracker inside the fuselage, and one in the wing. My father was present on the day of this aircraft's last flight, and he recalls the spectacular sight of one firecracker removing the flimsy wing quite effectively, leaving the burning fuselage to spiral earthward, only to be destroyed by the second firecracker moments later.

[icarus]

flame proofing of tubes try sodium silicate solution also called waterglass It makes a strong sticky adhesive, its often put round hole in stinger spinning rockets . it will fire proof tissue for parachutes ,cases are rock hard and very flame resistant. Source is pottery suppliers ,Danger is tubes are brittle and would be shrapnel risk for salutes.bake tubes in oven 110C -120C