mec

First of all I want to say “thank you” to Dustflyer. He helped me and gave all the information where to order, how to setup and tune the engine and plane. Again: thank you Mr. Dustflyer. I enjoy flying the DD. Whats the nitro for the engine, is the adrenalin for me.

Today i did some test runs (weather conditions 20° Celsius) with my Jett FIRE 50 engine with high rise header and tuned pipe (mounted on a Diamond Dust).
1. test run: with header shortened half an inch, APC 8.8x9.25 pylon prop, 15% nitro, OS Glow Plug #5: 17.700rpm.
2. test run: with 3 inch longer header: 14.500rpm.
3. test run: with 2 inch longer header: 15.500rpm.
4. test run: again same length as test run #1, but 50% nitro, 15%aerosaveoil: 18.700rpm (engine very hot however, glow plug gone).
5. test run: again 50% nitro, glow plug OS #8: 18.400rpm (engine very hot, glow plug gone again).
6. test run: again 50% nitro, APC 8x10 sport, GP Rossi #7: 18.500rpm.
7. test run: 30% nitro, 15% aerosaveoil, again APC 8x10 sport, GP Rossi #7: 18.100 rpm.
8. test run: same as above but APC 8.8x9.25 pylon prop: 18.300rpm.
9. test run: same as above but 15% nitro: 17.900rpm.
10. test run: same as above but APC 8x10 sport: 17.800rpm.
11. test run: same as above but 0% nitro: 17.600rpm.

my conclusions: high nitro fuel on this engine brings slightly more rpm, but the disadvantages predominate (all my planes consume 15%nitro, so I need to carry an extra bottle with me, shortened life of engine, gone glow plugs).
My setup for flights is test run 10: 15% nitro, APC 8x10 sport turning 17.800rpm.
For high speed flights an APC 8x11 or 8x12 would be worth a try (but where to buy?).

For the next days I hope to manage to put my GPS on the plane to do some speed measurements (last flight of the hot spot with PJ 130 engine showed a max of 380km/h on the display, however with an opened gear door, followed by an failure in the gear and a belly landing, but new thinner wings).

mec

jlong34016

My Feedback: (1)

I cut down 10x10,11x11,12x12 props to get the smaller diameter higher pitch.

mec

hi jlong34016,

11x11 and 12x12 props? what brands? where to buy?
thanx

mec

jlong34016

My Feedback: (1)

I use APC props from tower hobbies. www.towerhobbies.com

Dustflyer

My Feedback: (13)

Mec,

Just got back into town and saw your post. The pleasure is entirely mine, glad to be of any help.

Thanks for posting that info, you are getting some very impressive numbers. You will have a very fast Diamond Dust!

My Jett FIRE 50 is at Jett right now. I told them to do whatever they had to do to give my the fastest possible airplane with that engine and a MACS quiet pipe. Should be interesting to see what they come up with.

I'll keep you posted!

Cyclic Hardover

My Feedback: (3)

I have a Shrike .40 with a TT 46pro, 9/7 Apc and Ultrathrust Muffler turning 17,200 here at 5000ft. If i drop to the 8inch props, I would probably blow it apart.

mec

yesterday i did one test flight with the Garmin GPS on my DD to measure max speed of the plane:
weather was fine, 23°C, wind zero.
as seen in the pics the GPS unit was under the pipe, i little behind CG. therefore i counterbalanced with 2x3/4oz near the engine. launching was no problem. i did two fast passes and came in for landing. whole flight duration was 3min.

mec

front view

mec

fact one:
as can be seen in the pic the GPS showed 466km/h max speed.
fact two:
IMHO this must have been an error measurement! i have some experience in estimating groundspeed by doing these measurements from time to time with a lot of planes including trainers, aerobatic planes, hot spots and bandits. a hot spot is capable of doing 340km/h with a P 80 or similar engine, and reaching 400km/h with a P 120.
and the passes of my DD hadnt been as fast (however the much smaler DD appears faster as a big plane).
there are some explanations for this GPS errors:
three times the GPS failed: under a metalliy painted canopy, under a carbon fibre canopy and now under the metallic exhaust pipe. transporting the DD in my car with the GPS still mounted it flawless however. maybe the engine vibrations do no good? or the heat of the pipe?
one day i will make a second try.

funny thing:
after landing i found that one of the lead weights came off during flight. in the rear near one fin, the oracover film had a 4cm long crack. shacking the plane showed that the extra weight was captured within the fuselage between #1 and #2 rib. i didnt notice that during flight.

BruceDana

I doubt you will get much success with a "resource grade" GPS on your plane to measure top speed. The reason for this is that the sample rate you collect an instantaneous position at the receiver is probably too coarse (every second? every 5 seconds?). What is the sample interval of your unit? How straight can you fly between sample intervals?

You then have the problem that the instantaneous position calculated can be in error by as much a 30 meters +- or more (random in direction) in resource units. So the distance measured could possibly be 60 meters+- too long, or 60 meters+- too short between consecutive samples. Velocity is distance over time, and if distance is seriously in doubt, then so is velocity.

GPS works best in a static mode by taking lots of samples in a fixed spot, then averaging the instantaneous positions to find a more "accurate" position. Post processing with other receivers measuring the same satellites at the same time epochs is how surveyors get accurate (centemeter level) positions. In differential GPS (which is what your are doing), sometimes the positions may be corrected by using a fixed base receiver to determine positional errors errors, then applying the differential corrections of position to the rover unit (your plane) in the same time epoch. This may also be done in somewhat real-time through radio telemetry, and other sophisticated processing of the GPS signal itself and utilizing the properties of the different carrier signals. The real-time "survey grade" equipment that surveyors and photogrammetrists and the military use might work, but at a higher expense and payload.

Finally, you have the problem of antenna location. Your antenna must retain lock (by unabstructed line-of-site) on the satellites to work. If when turning (the plane's fuselage, wings, etc.), or by your muffler (as your picture depicts), or whatever obstructs line-of-sight between the antenna and the broadcasting satellite, you will loose satellite lock and no longer will have a useable signal from that SV. Given the speeds and manuevering you are flying, it is unlikely your receiver will re-acquire lost satellites. Also, the antenna design and location may prohibit good results, such as multipath signals reflecting off of the plane's surfaces to the antenna.

I don't know what equipment you are using precisely, but it looks like a hand-held unit of the "resource grade" type. If you can overcome some of the issues mentioned above, you might have a fighting chance using GPS for speed measurement. Be careful about validating results, as it is very unlikely you will be able to "black box" an inexpesive unit and get reliable results.

mec

hi bruce,

thanx for input.

i am no specialist in GPS devices nor in the method they use.

please visit http://www.garmin.com/products/emap/spec.html
there you find the specs for the Garmin emap answering some of your questions concerning update rate.

maybe you can give an additional comment after reading the infos.

why i am astonished:
this garmin device is used by some full size pilots to gave the infos they need.
i checked the function (especially speed measurements) several times: there had always been concordance to the speedometer in a car as it was in an airbus doing a trip to florida.

in a modelairplane we had some error messages however: under a metallic painted canopy, under carbon fibre canopy or under metal surface.


mec

BruceDana

Here is the pertinent information from your receiver's specs:

Acquisition Times:
Warm: approx. 15 seconds

This is the time it takes your receiver to re-acquire a usable signal to an SV if lock is broken. Note that this normally is under a steady state condition.

Update Rate: 1 second, continuous
This is how many times during a time interval the position is calculated and updated. I'm not sure what "continuous" means, but I can believe 1 second updates (how far does your plane travel in 1 second? - at 200 MPH that is 136 feet). One way to find out the true update rate is to connect your receiver to a computer and look at the signal (data) that is being logged. Your receiver says it is RS-232 compatable in NMEA format (which is text based) -> Interfaces: RS232 with NMEA 0183, RTCM 104 DGPS data format and proprietary GARMIN data formats

Accuracy:

Position: 15 meters (49 feet) RMS*
Velocity: 0.1 knot RMS steady state

Note the above position is Root Mean Squared accuracy (that means lots of measurements standing still, then averaged).

The velocity is, at first look, "better" (what you are after anyway), but the accuracy reported is in steady state mode (constant velocity in a uniform direction - something an R/C plane just does not do).

As you can see, the variables just don't fall in your favor for this application.

I have used GPS (top of the line stuff) in aircraft at work to locate the plane (camera) for photogrammetric work, and even using differential methods (fixed base station receivers on known control, the "rover" in the plane, radio differential corrections, etc.) and post processing including the careful placement of antennas on the full-scale plane (to avoid breaking lock, inteferance, and other "noise"), including the plane flighing a steady flightline, I still observe serious fluctuation in speed if just using the instantaneous positions reported by the receiver. Good results were only determined after post processing.

mec

thanx for clarification

mec