I am working on a new WWI de Havilland DH-4 biplane and plan to use a DLE55 engine, mainly because it will fit in the long narrow cowl area.

Any thoughts on whether it will turn a 26" diameter prop with a 6" pitch at a reasonable RPN, sat 6000-6500 RPM?

This plane will onoly so fast anyway, even with 3 DLE55 engines! I do not need airspeed, just thrust.

26x8 might be pushing it for that engine but I don't have any facts to back that (I can only extrapolate from other props). I don't know of anyone running that large of diameter to tell you for sure. They are happier near 7000 RPM but you could run them at 6500. I run a Xoar 22x8 at 7400RPM on stock exhaust on 88" 17.5 pound aerobats and it's incredible power. 24x6 might be near 6900-7000. It's very possible that a 26x6 could turn in the range you stated but from my experience the engine is happier near 7k. For the type of flying you will do with that plane compared to my intense aerobatic flying, it might be just fine.

According to my trusty Thrust-HP program, a 26-6 prop at 6500 RPM should generate 55+ pounds of thrust (plenty) and 36 MPH (very scale speed)

Mr Pettit,

That certainly sounds like a fabulous plane, I hope you post many pictures of it for the rest of us to enjoy!

First, no 50cc engine is capable of turning a 26" prop anywhere near 5000 rpm, let alone 6500. At least it wouldn't be able to do it for long before blowing up. This is really 80cc territory. Some of the 80cc engines would fit that application very well, check out the ZDZ 80. As it is a bit longer than the DLE-55, the larger cylinder MAY fit in your cowl as well as the 55cc engine would.

Second, rather than use ThrustHP which notoriously overestimates both power and thrust. I recommend the spreadsheet developed by Pe Reivers here on RCU. Link here: http://mvvs.nl/prop-power-calculator.xls

Possibly an 80cc engine with a 26" high pitch prop on an all-out 3D plane I would agree with.

If the DLE55 can turn a 26- prop with a 6 inch pitch at 6000, it would provide enough power to fly.

According to Pe Reiver's spreadsheet, it would need 4.6 HP at 6000 RPM to turn this prop.

If the DLE55 can produce this many HP at 6000 RPM, it'll work.

The plane is being successfully flown with a 3W 55 and a 24-8 prop by the manufacturer and designer, Dave Lewis at Balsa USA.

If his 3W can spin a 24-8, the DLE55 could probably spin a 26-6.

DLE-55 is a very powerful engine, that's all I can say. My RPM numbers above are accurate. I used to only get 7000 tops on my ZDZ 50NG on the same prop (and tach). I get 400 more with the DLE-55. That's significant.

My DL-50 worked great with a 22x8 (6900-7100 rpm) and OK with a 23x8 prop (~6300 rpm), but would lug down with much more prop than that and overheat, and carburetion was less "accurate".

I REALLY doubt it will turn any 26" prop anywhere near 6000 rpm, but anything is possible. The 3W 55 is quite a bit stronger than a DLE-55 (flame suit on...), especially in its ability to turn a larger prop, so that engine may get away with it.

If the DL can swing a 24x8 at 6000, then you are correct it should be able to swing a 26x6 around ~6000. If you use the DLE in this way definitely get it enough cooling air flow (particularly keep the crank case cool to preserve the bearings) and don't skimp on the oil. Perhaps back off the timing a bit. Pick a prop with a very light load, such as a Dynathrust, Zinger, MA Scimitar (which would look somewhat scale), etc.

One more thing, is the thrust speed going to be fast enough to keep the plane in the air? I typically try for a thrust speed that is about 2.5 - 3 times faster than the stall speed. The thrust speed shows about 34 mph, which will certainly increase a bit in the air as the prop unloads. If the stall speed is expected to be in the low teens, then this should be about perfect for your plane. However if the stall speed is in the low 20's, there might not be enough excess "power" to get the plane out of a sticky situation. That said, the DH-4 will be so adept at "flying on its wings" that this may not be a problem in any way.

p.s. I have always enjoyed your articles in RC Report, they were always fair and honest and seemed less like an "advertisement" as many other reviews and articles can be.

Thanks for the kind words and useful information.

The DH-4 has 4100 square inches of wing and will weigh in the 35 pound range. That figures out to about 20 oz/sq ft. It should fly in a moderate breeze.

But I agree that extra power is always a nice thing to have in your pocket.

The reason I considered the DL engine (aqnd others) is the lack of width in the engine compartment. Any engine with a side mounted carb is out of the question.

Plus the cylinder will be pointed upwards due to the exit for the crankcase.

I have a month or so to finalize the engine choice anyway. I was just trying to do some homework first.

Thanks to all...

What about the RCGF 62, Dick? Kind of the same cylinder as the G62, but with a rear carb. Supposed to be stronger.

A G62 likes to spin up so I don't think it would help.


Dick

I put a 3 bladed CF 22x10 on a MT 57 and got 4800 rpm. Same prop on a 3W75 6400 rpm, that engine turns a 26x8 6400 rpm also. So I would think the DLE55 would turn a 26x6 about 5000 rpm. I flew my WildHare Ultimate with the 3 bladed prop with the MT57 turning 4800 rpm, it was very WWI scale like flight, great for your use, not so good for 3D. :^(

You might also want to look into http://www.xoarintl.com/props/model-...tar-light.html

When you increase the diameter of a prop the load increases on the engine in an exponential manner. The load farther from the center of the crank has much more leverage against the torque of the engine. When you keep the same diameter and just increase pitch the load will increase about the same for each step of increased pitch. When you increase diameter, each step in increased diameter loads at a higher rate, as an example, the first increase may cost 600 RPM, the second increase something like 1000 RPM, the third, 1500 RPM. The numbers are just examples to illistrate what I'm talking about. Not even sure where you could get a 26x6 propeller, Zinger makes a 26x8 that might load like a good prop at 26x6.

I agree with Jody, we saw aprox. 600 rpm drop on my friends DL50, going
from Vess 22b@7200 to 23B@6600 aprox., larger prop would just overheat
the engine and it would be out of the power range IMO.
From what I have observed the DL appears to have a higher rpm power
curve, wich is fine for low weight aerobatic planes.
I think higher compression engines with a higher low rpm torque curve, like
the 3W55 or ZDZ60 would turn the bigger props easier.

MY 2ct. Allen