Micro GL - They Said It Couldn't Be Done . . .

[JohnT]

About 15 minutes of flying. It was flying so good. I did not even think about doing a dive test to check. CG.

I'll have to add that to my list of things to do next time. I fly it though. I was having such a good time just as was.

John

 

[Red]

About 15 minutes of flying. It was flying so good. I did not even think about doing a dive test to check. CG.

I'll have to add that to my list of things to do next time. I fly it though. I was having such a good time just as was.

John

Congrats on the first flight! Bluff Park is a great place to fly it.

Yeah, don’t bother with the dive test. That’s bad advice. The airfoil has a very strong positive pitching moment, which means the faster it goes, the more it wants to pitch up. This coupled with a little bit of incidence means it’s fairly speed stable. It’s designed this way to make it easy to fly and forgiving. Best thing to do is set the CG at the aft edge of the spar at the root. Fly it and trim for level flight, then look at the stab trim. You will want it level. If it’s not, adjust from there.

The dive test is the defacto standard for higher performance ships though, and is for sure the right way to test. However on light weight gas bags like this it’s nearly useless.

 

[Konrad]

About 15 minutes of flying. It was flying so good. I did not even think about doing a dive test to check. CG.

I'll have to add that to my list of things to do next time. I fly it though. I was having such a good time just as was.

John

That is key, having fun! I find that a properly set up plane results in a higher fun quotient. While it is true that the airfoil has a lot of camber I found that with the micro Sinbad I could get a lot more performance from a rather aft CG (reference the plan location). Note the oversized stabs. Each to his own. But do experiment to find what works best for you.

 

[Konrad]

Congrats on the first flight! Bluff Park is a great place to fly it.

Yeah, don’t bother with the dive test. That’s bad advice. The airfoil has a very strong positive pitching moment, which means the faster it goes, the more it wants to pitch up. This coupled with a little bit of incidence means it’s fairly speed stable. It’s designed this way to make it easy to fly and forgiving. Best thing to do is set the CG at the aft edge of the spar at the root. Fly it and trim for level flight, then look at the stab trim. You will want it level. If it’s not, adjust from there.

The dive test is the handling standard for higher performance ships though, and is for sure the right way to test. However on light weight gas bags like this it’s nearly useless.

Love this forum. Here we learn a bit about the design philosophy direct from the designer. This is great information for understanding why or how the ship might or might not be performing. Thank you Red for the insight.

For example I thought these micros had the CG placed so far forward to give the pilot and plane a chance to survive the maiden. Here the designer is saying the the plane is set up for a mono speed trim. Now that is fine. But I find this trim setting very difficult to fly as the plane never goes where I point her.

I look at how a ship performs and try to make changes to meet my expectation. The dive test is just a tool to try to find the tuck point. I use it trimming just about all my aircraft be them powered F3D, high cambered thermal duration gas bags, or fast F3F racers. Ok, maybe not with the Rogallo wing.

Here is a write up by Dr. Drela on what to look for in a dive test and how it effects the handling of the ship. Do spend some time on the Charles River RC site as there is a lot of great information on soaring by many learned contributors, dare I say legends!

https://charlesriverrc.org/articles/field-and-flying/center-of-gravity-location/

(Please note in the first sentence Dr. Drela’s comment about airfoils. )