Hi, I'm not sure if any of the engine guys amogst you can help with something that has been puzzling me.... I have built an engine which uses the AMT Mercury(20lb thrust) wheels and naturally assumed I would get similar performance to this commercial engine. My engine has now completed some 2 hours flight testing, (around a dozen flights), with max power dialed down by 10krpm, so on paper for this rpm I would expect maybe somewhere around 15lb thrust max ? But the Super Reaper the engine is installed in has a t/o weight of around 23lb and goes straight up after rotation.... this just doesnt seem to add up.

Another guy flying a Jetcat P80 powered Super Reaper asked what my engine was because in his opinion it had better flight performance than his ????

Fuel efficiency seems good with only 1.5litres (around 40ozs) used in a 10 min flight, this may be because of the lower set max rpm.

I have downloaded the flight data from the Fadec ecu and the engine is definately only *****g out at 140krpm with max temps in the mid 600C area, this rules out over revving.

Any theories as to why this is happening ?

Rob.

What thrust is it putting out?

Hi

What don't you get a digital fish scale with some SS wire and hook it around UL mains.

This should give you an idea of your static thrust output.

If that doesn't appeal to you, use a digital scale cover the nose with foam and measure thrust that way.

Sounds like she has good power..........

Ian

I think its the tail cone design. Like a tune pipe. Question is your turbine wheel 66mm?

Not sure what the thrust is, I'll bolt the engine in the test rig and check it, but I would not be expecting more than 15lbs at this conservative rpm setting.

The turbine wheel is 65mm, the exhaust is modified AMT (demountable) but all the critical dimensions are the same. I have modified the diffuser system, not sure if that is producing more case pressure.

Another unusual trait the engine exhibits, similar to the TJT 3000, is the lack of noise, it really is very quiet in the air, just the exhaust efflux roar on higher throttle settings.

Rob.

Hi Rob,

Just out of intrest which NGV are you using?

jason

I think don't quote me , but your turbine wheel dimension is alot more than the standard 66mm. So more thrust for less RPM.
How do you modified the diffuser ????.

Hi Jason,
good to hear from you again, hope you got sorted with a longer thermocouple for your MW44 ?

The ngv is again a modified AMT item, the critical vane geometry is unchanged but whereas AMT bolt their shaft tube solidly to the ngv mine uses a TJT tube with a sliding interface and bearing carriers.

Turbine wheel is definately 65mm as you can see in the size comparison with the Wren 66mm wheel and the diffuser is only really modified to try and improve airflow to the front face of the combustion chamber due to a chamber/diffuser gap reduction.

Perhaps I should build a second engine with the parts I have to see if this first one was just a fluke

Rob.

So AMT ngv is bolted on to the the bearing housing. I like that setup better, Before assembling the case you can tell if your turbine wheel and the ngv is align properly sweet

I always wonder how AMT all in one case and cone work.

Looking at your caliper reading your turbine wheel 65.20 but your ngv 65.15 ??? . How many injectors your engine as ?.
I'm doing some experiment my self with a 32 lb engine. Its running ok with EGT of 480 max power.

Hummm...I know that some 66mm commercial engine are putting 25lbs trust. You have about 2 things to get more trust. Optimized diffusor or optimized combustion chamber.

You played with diffusor...That can be the answer..can you post a pic of you diffusor??

140K with 66mm engine seems to be quit high isnt it??? Since we run 54mm at 160000...

Not familiar with the AMT stuff, but the highest I have seen a 66mm turbine running is 127K....... so at running at 140K would produce a lot more thrust - all other things being equal.

I think he is using the 65mm wheel. But at max RPM 140k is very high for that size wheel. At some point there must be compressor or turbine wheel stall.

If you look at the throughput area of the AMT wheel you can see it is much less than the Wren 66, so although they are of a similar o/d the actual 'working' area is much reduced. The AMT wheel is designed/built from the outset for high rpm(150k+) the same as the 60mm Garrett compressor wheel up front. I burned many litres of fuel at max rpm before commiting the engine to an airframe.

The shaft and turbine wheel were machined/ground to within a couple of microns runout after a few heat cycles to allow the hot components to 'settle'. I then spent an evening concentrating on getting the rotor balance as good as my equipment would allow.

The turbine wheel/ngv tip clearance is just enough to avoid any 'rubbing', this I am told can lead to better fuel efficiency.

I thought the engine would sound similar in the air to an AMT but it's completely different, possibly due to the turned from solid alloy casing.

Next project engine will use the wheel on the right Shaft has just been turned ready for final grinding to size.

Rob.

Fantastic work.
Johnny

Hi Unknown, good to hear from a fellow engine builder, the caliper measures are for an unfinished wheel.

Can we see some pics of your 32lb engine ? What size is it ? Sounds like you've got plenty of scope for squeezing more power out of it, your egt is way too low.

Rob.

Thanks for the compliments Johnny, I have a lot of good friends that help me, so as with most successful things in life it's the culmination of a team effort.

This big titanium compressor wheel is slated for another big thrust project.

Also building a second 54 size engine to pair with my PST J600 for the Fokker 100 twin, this should be a load of fun to fly I reckon, not enough civil stuff around the shows if you ask me

Way too many projects and not enough time as always !!

Rob.

Hi Rob,

Yes I did get the longer thermo couple sorted thanks everything is fine now and just waiting for monday for the test flight.

I have a simjet 2300 which is rated at 27lb. I was unsure if this was right as they are normally about 23ish so I phoned Lars to ask him and he confirmed it was 27lb.

jason

Hi Jason, glad you got sorted, you'll have to let us know how the test flights go.

The Simjet sounds like a powerful beast, do you know if it uses the KKK 2038 compressor wheel as in the KJ 66 and Jetcat P80 ?

Rob.

not too sure what it is but its not the same as a p120 one but I know it is a wren 66.5 mm wheel and NGV.

jason

OK, there a few different wheels around that different manufacturers use, I more or less know most of them and what they can put out in terms of thrust.

Rob.

Hi ROBROW i will post some pictures of some of my engine. For compressor i'm using the lager wheel to the kkk 2038. I think its the GT 30 series not sure i will check my receipt.

That will be great, looking forward to seeing the pics.

Rob.

If possible, please post some pictures of the difference between your engine modifications and the original AMT setup. It would be interesting to compare to see where the actual performance increase is coming form, especially the diffuser/chamber, ngv/turbine wheel, shaft/tube carrier system, and case design.
Have you measured the actual/true thrust difference of the modified engine versus the stock AMT Mercury?
Thanks for posting your findings.

I'll post some pics when I next take the engine down to check thrust and see how the internals are fairing.

I aimed for as reliable a set-up as possible and after 100+ cycles the Fadec autostart ecu has not missed one start, light-up is instantanious every time. As a precaution max rpm was detuned by 10krpm and acceleration/deceleration times increased a little for flight assesment. I'll give it a few more hours flight time, then pending all still being OK mechanically I'll up the max rpm and shorten the accel/decel times and see what it is really capable of.

I'll also try to get a few more objective pilot opinions of the airborne performance in the meantime.

Parts build for the larger engine is now coming together, here's the shaft compared with an MW54 size ! Now I will just need something big to fly it in [>:]

Rob.

Robrow
Having some problem posting pictures from my DV camcorder. So PM me your Email and i will send it to you