Dynamic chambers?

Paul, Perhaps I have a tuned manifold rather than a dynamic chamber

then,

as I actually do not have a chamber.  The the 21" you cite above as

tuned

for 5000 rpm is in line with what I calculated for the time it took

pulse

generated by a closing port on one rotor to transverse the tube and

arrive

at the other rotor as its port was opening.   Now that is based on

the

assumption that the difference between ports is only 60Deg (or in

other

words the pulse does not miss a port in transit).

 So perhaps I should refrain from referring to my setup as a

"dynamic

chamber".  I would guess my my torque peaks in the 5000 rpm range

rather

than the 3000 rpm range based on the rpm increase from 5200 to 5800

on

cold

mornings

 I've got one of the 2nd generation NA manifolds with the dynamic

chamber

and the valve that switches between the long and short path (shown

in

your

second diagram), so I'll go measure the paths and see what length

they

are

and the correlation to the HP humps in the curve.

There is no question about the two humps in the torque curve and
interestingly it appears the short runner helps the HP at 6000 rpm

quite

bit. Looks like it increase the HP from 140 to 160 HP or by 14% -

pretty

significant.    So, I may have to get out the hacksaw and do some

trimming.

However, its always easier to cut off tubing length than add it on

{:>)

Ed


Dynamic chambers helps at 6000 RPM in comparison  to the old untuned

four

barrel carb set up.

So far we have no comparisons with a simple tuned manifold other than
the HP curve from the peripheral port Lemans engine. That engine
generated 120 HP per rotor or 240 HP at 6000 RPM for a two rotor
with a simple tuned runner length. I am working hard on the dyno and
I am making progress so we should have some numbers to add that data
and to what Al Geitzen has recently uploaded.

The fundamental characteristic of the single dynamic chamber is it

works

at only two RPMs. If it works at 6000 RPM it will work again at 12,000

RPM.

Extreme example. If it works at 3000 RPM it will work again at
6000 RPM but not as well as a simple tuned manifold IMHO.

Ideal for our use would be a Lemans type variable length set up
where we would have one length for take off RPMs and another for
top speed and a third for cruise RPM for best BSFC. Not all that
hard to do as we are only talking about a four or five inch
change in length. This will become more important as the 2.85:1
and 3.12:1 gear box and the higher max RPM  RX8 engine come into use.

I think Mazda has already found that out with the RX8 engine.
Basically the poor torque characteristics of the rotary engine
make it a better aircraft engine than a car engine.
IMHO Mazda will eventually address that issue with e
super charger to enhance the torque down low.

BTW Ed how far down your airstrip do the RPMs finally peak
if at all? What are the RPMs that you use to climb out
after you break ground?

Paul Lamar

It would be nice to try some different configuration on a dyno for
comparison.  My current sliding tube manifold was fabricated with the

idea

of trying different manifold lengths (can vary length by 2 1/2").  Its
currently set for the long position (21") but could be shortened to 18

1/2"

by simply opening a tube clamp and lowering the top part.  I had

envisioned

a high torque dc motor driving a screw to run the tubes in and out with

two position swithc "Take-Off" and "Cruise".  Had too many other

variables

early on to play with changing its length, but now might be the time to

do

so.

The RPM doesn't really peak until straight and level, max so far is 6100
rpm.  I climb out at 5400-5500 rpm until level off then it accelerates

to

6000 or so  unless I throttle back.  I think I may have some airflow
impediment at higher rpms.  The reason I say that is while I can hit
6000-6100 rpm in level flight at 3500 MSL, lowering the nose into a

slight

dive showing 200 mph IAS does not cause the engine to rev  higher as I

would

think it would with the prop/engine unloaded in the dive.

Ah, well, if we knew all the answers, it wouldn't be as fun {:>)

Ed

I have been thinking about it too. If you apply a point load on
telescopic tubing it tends to cock and jam. I am thinking about
a light weight integral annular hydraulic cylinder on each runner to
serves as  actuators. I'll draw something up.


Paul Lamar

Yes, the tubes can be adjusted by tapping on the plate welded to all four
(up or down), but had to keep the fit tight between outer and inner tubes to
stop air leaks and that does not lend itself to easily running them up and
down.  Be interested in your  drawing.

Finished the core molds today for my integrated plastic throttle body and
injectors mount.  Will pour the silicone rubber for the core inserts
tomorrow - first, time so this should be interesting.
Assuming the silicone cores turn out OK, I then will complete the mold for
the plastic reinforece resin and the we will see if this idea has any merit.

Ed Anderson


 
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