EdwardB
Posts: 181
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Joined: 2/2/2002
Last Login: 7/26/2012
From: Lake Orion, MI, USA
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Phoon -- John answered a couple of your questions. I'll try to add a little.
1) Would the DA 50 R (inverted) fit within the Moth fiberglass cowl? The biggest concern is whether the width of the DA 50 R head is too large.
Answer: I didn't take mine apart, so these measurements aren't 100% exact, but reasonably right for inside the cowl:
5.75 inches from firewall to prop drive washer
5.25 inches from engine center line to inside of cowl bottom
3 - 3.5 inches wide at cowl location of cylinder head
Conclusion: All of these dimensions are less than the dimensions of the DA 50 R, minus the muffler. I personally don't see how it could fit.
2) The Laser 150 weighs 29.5 Oz, and the DA 50 R (with mounts) weighs 50 Oz, a difference of 20 .5 Oz or 1.28 Lbs. EdwardB, can you tell me fairly precisely how much lead weight you had to add to the nose of your Moth (with Laser 150 in place) to get proper CG, and whether it was close to 21 Oz?
Answer: I added over two pounds of lead to mine, so the weight difference is not an issue. Note that I added a scale tailwheel assembly (not light) and the Flair design, while very strong and sturdy, could be lightened in the back, in my opinion, without sacrificing anything. But mine flies great at 19-20 pounds (still inside the recommended weight) so I'm not worried about it, and won't change anything.
3) I gather that there are "engine bearers", wooden rails installed for the Laser 150 crank-case side lug mounts. The firewall is probably not adjustable for the Moth. The DA 50 R mounts flat against the firewall, and the wooden rails would have to be cut off flush to the Flair Moth firewall in my case. Can you envision a problem with DA 50 R length (above) of 6.7 inches (170 mm) for a "flush to the firewall" installation?
Answer: As John said, the engine beams could be cut off at the firewall, and a radial mount engine used without a problem. You can't remove the engine beams completely. Inside the fuse, they are also the main attachment point for the top wing cabane structure. But, the available length is still nearly an inch less than the DA needs. I don't see how you could move the firewall back that much. I wouldn't try it, anyway.
4) Recommended props are 22X12 or 24X8. Up here, a 22X16 or 24X10. EdwardB noted the “tip over” taxi issue during his maiden. Would a 22 or 24 inch prop exacerbate ground handling or ground clearance problems?
Answer: I measured 14 inches from the center of the prop shaft to the ground, with the tail up in flying position. So, ground clearance with a 22 or 24 inch prop should not be a problem. I don't think that large a prop would change anything regarding nosing over. While I mentioned this issue, don't forget this was on the first or second flight, and I'm not flying from the smoothest field. A change to higher rate elevator, and proper procedure on my part, and I'm expecting this to be a non issue. Certainly I don't consider this to be a design flaw, or anything to be overly concerned about. It's mostly self correction (me...).
5) Since gas runs hotter than glow, might have to enlarge vents in the cowl for cooling. Can you for-see any engine cooling issues with the Moth cowl?
Answer: The scale vents in the cowl are relatively small. I don't know if they would be enough to cool a gasser or not. I kind of doubt it, but that's an opinion without any real world testing. If they had to be bigger, it would certainly change the look of the cowl. As John said, this is a pretty small and narrow cowl. There isn't a lot there to cut out.
Conclusion (my opinions!): The DA 50 R is a nice engine, but I don't think a good fit for this size Tiger Moth. Yes the DA instructions say for a 14 - 16 pound airplane, but don't forget DA engines are mainly marketed for highly aerobatic, 3D style flying, where 2+ engine thrust to airplane weight ratio is common, and certainly not required for the Tiger Moth. Even at altitude, my opinion is that this is way too much engine for this particular model. I agree with John that the Laser 1.80 might be something to consider -- and focus on keeping the airplane at the lower weight range. With a little lightening in the back, 17-18 pounds should be achievable with the 1.80.
As much as I like the Tiger Moth, it may not be the best option for your situation, if you need that much extra power. A scale subject that used a radial engine (like a Sopwith Pup, a Nieuport, just to name a couple), rather than an in-line engine like the Tiger Moth, would have a big enough cowl area to go way oversize with the engine of your choice, with room to spare.
< Message edited by EdwardB -- 7/28/2005 8:03 AM >
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All Forums >> RC Airplanes >> Kit Building >> RE: 1/4th Scale Flair Tiger Moth Project 
RE: 1/4th Scale Flair Tiger Moth Project - 
..So i was hoping that one of you that built the flair kit could help me out with some pictures or instructions. 