Re: Hints for Cat IV LPP flying

From: ykleetx <ykleetx_at_gmail.com>
Date: Wed, 24 Mar 2010 04:13:48 -0000

I want to give an update to my LPP preparations. I have experimented with partial motors equivalent to 2.5g and 3.0g of rubber and with a couple of different propellers.

For the 2.5g partial motor, I used 0.5g of 0.93" rubber (4 inches) and 2.0g dummy motor. This is an equivalent 1/5 motor. The best I could do was 30' peak altitude at 3:08.

For the 3.0g partial motor, I used the same 0.5g of 0.93" rubber and a 2.5g dummy motor, for an equivalent 1/6 motor. The best I could do was 27' peak altitude at 3:02 -- and consistently at 25'peak and 2:50.

Wound to about 500 turns, with 10 turns back off, launch torque 0.7 in-oz. Feels like a lot of torque.

The 3.0g partial motor result seems really good, so I tried a full 3.0g motor, which was 24" long. I was mainly interested to observe how such a long motor would wind and unwind. I noticed two immediate things. First, my tail hook did not give the rubber enough clearance; there was a lot of rubber bunched up everywhere but especially at the tail hook. I changed the tail hook to give 3/8" clearance. Second, the full 3.0g motor had noticeable power loss compared to the partial motor. Even the initial unwind was pretty weak. (I did not fly the plane with the 3.0g motor but observed the unwinding.)

I realized also that I "cheated" in the partial motor tests. Although I ballasted the dummy motor to 2.5g, it was only 6 in long and not long enough. Should have been around 7.5 in long for a 1/6 partial motor. The shorter dummy motor allowed my 0.5g partial motor to fly at around 3 in instead of the ~1.8in. When I lengthened the dummy motor to 7.5 in, there was more "bunching" of rubber, and I observed the corresponding loss of power. I have not finished testing with the new dummy motor -- my propeller was damaged -- but the initial results gave a best of 2:34 for the 1/6 motor.

So I did not have weight problems, unresolvable tangles, nor torque issues, but some kind of gremlins (as Bill put it) was present.

I welcome your suggestions to get back some of that 30s!

-Kang


> For motor weight probably the more the better until the gremlins start getting you. This will probably happen in the weight range you've already heard about. The gremlins are mainly associated with the motor length causing unresolvable tangles or the motor size causing launch torque issues or the extra flying weight causing structural problems like undesirable flexing. Lew Gitlow's book says that optimum for LPP is about 70% of model weight which is about 2.2 grams. I think you can go somewhat higher than this but I think 3 grams will probably be too much.
>
Received on Tue Mar 23 2010 - 21:15:53 CET