Bumpy Green Model Aerodrome: Speed 400 Prop Study

Gunther Propellor Replacement Study.
By Chinman ~ 30-04-2001

For owners and flyers of Pico-Jet, Pico-Jet Combat, Twin-Jet, Twin-Star, Star-Jet, Zagi Electric, Ripmax Mirage & Teddy Park Fly models etc.

All results gathered using Pico-Jet Combat & 35A BEC/ESC Speed 400 Motor.

Below is a chart of the various battery and prop combinations I have used and the results of the ''Kitchen Scale Thrust Testing'' ~ Don't let her indoors catch you doing this, especially with i/c models :o)

A reasonably accurate pair of kitchen scales. The Pico-Jet stood on it's nose on the scales with the lightest of steadying to stop if falling over. Scales set to zero and power applied~ Result: A rough guide to the actual thrust given by any battery/propeller combination relative to each other.

THIS IS NOT AN EXACT SCIENCE:
Do not take these results as Gospel, it is just a rough guide based on testing by someone with too much spare time. Although imperical, the data should be used for guidance only. Fly the combinations and decide for yourself which suits you, your plane and your flying style best.

	Standard Gunther: 5 x 4 Small and quiet, provides adequate thrust for a Pico-Jet or Combat. Also used successfully on a Speed 400 powered Zagi. Must be mounted with the writing on the white section facing backwards. Rubber Band model Bow Tie : 5 x ? Same diameter and from the tests, seems to have the same pitch as the Gunther but it is not printed anywhere (for 27p what do you expect) and it worked. I kept this on for weeks as a result enjoying many long flights with my newly aquired 9.6 1300 cells.

	Graupner CAM Speed: 5.5 x 4.3 A high perormance propeller I was loaned to try. It makes quite a lot of noise and was in the middle group of props for performance in tests. I have not flown with this prop but Choddys Twin-Jet did and it makes an improvement over Gunther types supplied. Windsor: 6 x 3.5 (similar to Master Airscrew) This prop falls into the highest rated pair, coming second only to the FK. Good thrust and reasonable noise. If I had found this prop before the FK I would probably still be using it.

	Kavan ~ FK: 6 x 4 The Yellow bendy prop, favoured by learners as it is almost impossible to break. Noisier than a Gunther but not by much. Great performance in the air. Very long flights with good climb, also make a great sound when held in a shallow dive. This prop gave the highest readings of all and is still in use now. Choddys Twin-Jet also flies a pair of these to very good effect. However it does protrude past the bottom of the Pico-Jets fuselage so touch-&-go's can be tricky. Thimble Drome: 5 x 3 This is a cut down 6 x 3 prop and fits the middle catagory for performance. A bargain from some 3 for a pound box at a show. Not sure if the COX .049 it was attached to will ever run again tho! Origianlly fitted to the Zagi 400 with limited success. This is the noisiest propeller of the whole lot and would probably annoy the hell out of the natives.

	Sanyo Cadnica 7 cell NiCad: 8.4v 500mAh The lightest pack at just 155g, this pack provides 3-4 minutes of reasonable flight. It is however the wrong shape to get far enough forward to correctly balance the Pico-Jet. Originally for a Zagi this battery is taken along only as a last flight pack.

	Ripmax 7 cell NiCad: 8.4v 500mAh This pack was used extensively in my Topic 400 prior to being conscripted into the Pico-Jet. Flight times of 6 minutes flat out and 8-10 with a little over half throttle (can we say throttle on an electric?) The pack is a little tall and has to be fitted laid at an angle inside the fuselage and goes just far enough forward to balance nicely. I still use one of these packs along with the Overlander packs.

	Sanyo Cadnica 8 cell NiCad: 9.6v 500mAh This battery gives lots of power for a very short time, and due to the low weight the climb is almost ballistic. It will sustain greater then 45deg climbs in the right conditions. Flight times are 2-3 minutes at full stick with 4-5 mins flying sensibly (if you can do such a thing with a Pico-Jet) Balance is ok as it is a slim pack and can fit quite far forward. Beware getting it wrong with this pack, very hard to keep the nose down if too far back.

	Overlander 8 cell Ni-mh: 9.6v 1300mAh The battery pack for Pico-Jets/Combats & similar. Although the voltage is the same as the Sanyo, the NiCad provides greater power for thrust but at a greatly reduced endurance. With the 1300 pack flights of over 10 minutes are not unusual and on a blowy day and some delicate elevon usage twenty minutes plus has been achieved with minimal power used every once in a while. I would recommend this pack to anyone who has a Pico-Jet or Combat, duration being my main selling point.


Battery Used:	Sanyo 8.4V 500mAh NiCad	Ripmax 8.4V 1100mAh NiCad	Sanyo 9.6V 500mAh NiCad	Overlander 9.6V 1300mAh Nimh
Weight:	155g	200g	175g	200g

Propeller/Thrust:
Gunther	200g	200g	250g	200g
Bow Tie	200g	200g	210g	200g
Thimble Drome	225g	225g	300g	250g
CAM Speed	225g	225g	300g	250g
Windsor	300g	300g	325g	275g
Yellow Bendy	310g	300g	350g	275g

Gunther Reversed: Now you know why it don't work	80g	80g	100g	90g

Also to be added are comparative results from a 480 powered Pico-Jet. Will try to get a tachometer at some point for more data. Flight speed will have to be determined for yourself with the combos, I don't know anyone with a Speed Radar Gun.

Tests so far on the Twin-Jet using 9.6v 2400mAh pack & dual Graupner 400 motors.
Preliminary testing yielded the following results

Gunther Props:	400g
CAM Speed Props:	500g
Yellow Bendy Props:	600+g

Flight performance notably improved with FK bendy props over Gunthers.

Again, This information should not to be taken as anything but a guide,
but using the same test scales and methods throughout I think the answers speak for themselves.

Send me your feedback or your own findings: Email Chinman

Enjoy!