DD WITH qm and 7,4*8 prop at 26 + rpms
 

I HAVE TRIED A DIAMOND DUST WITH ONE OF THE FIRST 60 Lx ENgine, prepared by dubb jett.
This combo was a real break out at the field here in asuncion, paraguay.
The DD was in about 170 mph really amazing, the engine, the throlle response is excelente, the power is excelente, the launching with the APC 8.8* 9W is very powerfull. ALL the People were really affraid of seeing flying this Thunder bird. The engine is real screamer machine and fast.
Now I'm building a new DD, but with a QM 40 engine, and set on it a 60 lx carburator, just for
an instance and safe running, I mean To make sure and regulate a little bit the high speed, just
to have more control, but I know the engine will be working reach at below 20000 Rpms.

I' thinking to run this engine between 15000 rpms and 26.000 plus with these carburator, what do you think about it, Will it work???, I do not care most the transition but i Hope I not to have several engine stops when I throlle down.
IF i Make this true THis might be first diamond dust with qm I have never see one with qm.

RE: DD WITH qm and 7,4*8 prop at 26 + rpms
 

I suspect a carburator on a QM 40 will not work very well. It may give you some control but will cost you at top rpm. Maybe a mixture control would work better. Bob with Jett should chime in with the real answer :)

Even with the theroretical speed increasing I think you will not be much faster then with a 60LX. I don't think a DD can be made clean enough where thrust wont be a determining factor. That is just my opinion and it will be interesting to see how it works out. Keep us informed.

How did you measure the 170 mph or was it a guess?

RE: DD WITH qm and 7,4*8 prop at 26 + rpms
 

Thanks for writing.......

I am pleased to hear of your experiences with the 60LX engine. It is indeed a real powerhouse.

The QM engine is timed for high rpm. You must prop it using one of the APC 7.5x7.8 carbon props for best performance. It has to turn a minimum of 21,000 rpm on the ground to unload properly in the air. Do not select a prop that allows it to turn less than this. You will preferably want to have a ground peak rpm around 22,500 - and then back down from that about 800 rpm for launch. If you load it much beyond this, you will not see any decent performance. Propped as indicated, the engine will unload well over 25,000 rpm in the air.

You can install the carb on the engine. Dub has actually sold a few QM engines equipped with a carb in the past. The 60LX carb you have will work very well. It will result in about 500-600 rpm less than with the venturi, and will not unload quite as much in the air.

You will have some ability to throttle the engine, but do not expect any sustained idle capability.

Honestly, from reports from others that have tried something similar to this...... the Diamond Dust will fly better, and faster, with the 60XL and the bigger prop. Try one of the 8.8x9.25 props clipped to about 8.2" diameter

Be sure to email me some photos of you and the aircraft !

Bob

_____________________________

Bob Brassell
Jett Engineering - Engine Mfg Support Forum
[email protected] or [email protected]
RB-78

RE: DD WITH qm and 7,4*8 prop at 26 + rpms
 

Bob, time to report this faulty avatar ... html bug ? hahaha...

RE: DD WITH qm and 7,4*8 prop at 26 + rpms
 

nah... he copied and pasted my reply to him from the jett support forum

RE: DD WITH qm and 7,4*8 prop at 26 + rpms
 

Hi Bob,

What is the recommended prop (without cutting it down) for the Jett 60LX on the Diamond Dust. What RPMs should I expect on the ground?

RE: DD WITH qm and 7,4*8 prop at 26 + rpms
 

If you have the side exhaust, I would start with an 8.8x8.75 prop. Look for anything over 18K rpm. Most likey you will hit 19K.

I know the FIRE 60LX with the nitro pipe easily turns the 8.8x9 well over 19K rpm.

Try to stick with the D-1 racing props. They are just safer when you are running up near 20K rpm. The 8.8x9 is excellent ... also the 8.8x9.25 works nicely. If you try it, be sure the engine gets easily to 17,500 rpm (minimum) or better for launch. If not, you clip the tips a little - bring it down to 8.25 or 8.5 diameter - that will bring the rpm back above 18,000.