I was just looking at the Sig Kadets on tower's website and noticed that the ARF kit can sustain an engine size of .40 to .53, yet the "assembly required" kit can only sustain an engine size of .29 to .40.

Why is that? What is the difference?

Mea Culpa Mea Culpa

4*60,
He was asking about Kadets, not LT-40s.

Are you sure the ARF and kit were the same wingspan? One a Kadet Sr. and one a Kadet Jr?

If the wingspan was the same, then 4* is probably right. Kit manufacturers have been increasing recommended engine sizes to keep up with OUR demand for more power on our planes.

An older kit would likely have lower engine recommendations than a newer one.
Dennis-

I think if you take a look the ARF has an 80'' wingspan and the kit a 78'' but the real difference will be in the overall weight , the kit says it will weigh in at about 6 LBS , and a careful builder can come in somewhere below that number ,

the ARF says 6 to 61/2 LBS this number is fixed without some kind of mods ,being done , so with the extra 2 inches in wing span and the added weight to get the same flying characteristics a little more engine might be required on the ARF.

Highlander

You'll definitely want to go with a .61 size engine on the Kadet Senior ARF. The plane may be light but it's a big and that extra power will come in handy in emergency or windy situations. There has been a couple of times that I was glad that I had the extra power to be able to pull out of bad situations. I usually fly at just less than half throttle in calm winds, but if it's windy you'll need more humph.

Also, you may find the ARF to be a little tail heavy and the larger engine will help to balance it out.

Yeah, the .61 is probably a good choice. I put one together for my wife and put a .47 in it and it could really use more. That big wing makes it fly like a sailboat.

Are you talking about the LT40 ARF or the Senior? I have an LT40 ARF, and am powering it with the Evolution .46 (not the trainer system, but the .46 engine by itself). I would put this engine up against anything else in its class.

The kit was made before anyone made .53 engines. The ARF has more up to date specs. Put what you want in it. It will handle it, within reason.

I was talking about the Sig Kadet Senior ARF Blue .40-.46,80" vs. the Sig Kadet Senior Kit .29-.40,78".

I just found it odd that the planes are very close in size and weight, yet had such a huge variance on engine size.